Anionic Dinuclear Oxidovanadium(IV) Complexes with Azo

Article Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX

pubs.acs.org/IC

Anionic Dinuclear Oxidovanadium(IV) Complexes with Azo Functionalized Tridentate Ligands and μ‑Ethoxido Bridge Leading to an Unsymmetric Twisted Arrangement: Synthesis, X‑ray Structure, Magnetic Properties, and Cytotoxicity Satabdi Roy,†,∥ Michael Böhme,∇ Subhashree P. Dash,†,○ Monalisa Mohanty,† Axel Buchholz,∇ Winfried Plass,*,∇ Sudarshana Majumder,† Senthilguru Kulanthaivel,⊥ Indranil Banerjee,⊥ Hans Reuter,‡ Werner Kaminsky,§ and Rupam Dinda*,† †

Department of Chemistry and ⊥Department of Biotechnology and Medical Engineering, National Institute of Technology, Rourkela, 769008 Odisha, India ∥ Department of Chemistry, Indian Institute of Technology, Kanpur, 208016 Uttar Pradesh, India ∇ Institut für Anorganische und Analytische Chemie, Friedrich-Schiller-Universität Jena, Humboldtstr. 8, 07743 Jena, Germany ○ Department of Basic Sciences, Parala Maharaja Engineering College, Sitalapalli, Brahmapur, Odisha 761003, India ‡ Institute of Chemistry of New Materials, University of Osnabrück, Barbarastraße 6, 49069 Osnabrück, Germany § Department of Chemistry, University of Washington, Seattle, Washington 98195, United States S Supporting Information *

ABSTRACT: The synthesis of ethoxido-bridged dinuclear oxidovanadium(IV) complexes of the general formula (HNEt3)[(VOL1−3)2(μ-OEt)] (1−3) with the azo dyes 2-(2′-carboxy-5′-X-phenylazo)-4-methylphenol (H2L1, X = H; H2L2, X = NO2) and 2-(2′-carboxy-5′-Br-phenylazo)-2-naphthol (H2L3) as ligands is reported. The ligands differ in the substituents at the phenyl ring to probe their influence on the redox behavior, biological activity, and magnetochemistry of the complexes, for which the results are presented and discussed. All synthesized ligands and vanadium(IV) complexes have been characterized by various physicochemical techniques, namely, elemental analysis, electrospray ionization mass spectrometry, spectroscopic methods (UV/vis and IR), and cyclic voltammetry. X-ray crystallography of 1 and 3 revealed the presence of a twisted arrangement of the edged-shared bridging core unit. In agreement with the distorted nature of the twisted core, antiferromagnetic exchange interactions were observed between the vanadium(IV) centers of the dinuclear complexes with a superexchange mechanism operative. These results have been verified by DFT calculations. The complexes were also screened for their in vitro cytotoxicity against HeLa and HT-29 cancer cell lines. The results indicated that all the synthesized vanadium(IV) complexes (1−3) were cytotoxic in nature and were specific to a particular cell type. Complex 1 was found to be the most potent against HeLa cells (IC50 value 1.92 μM).

■

mellitus.8 Moreover, vanadium compounds are treated as an emerging class of agents that can show potent antitumor activity and are suited for the treatment of disease caused by parasites.9 Therefore, the development of new vanadium complexes with improved pharmacological activity is of current interest. In fact, oxidovanadium containing compounds have been reported to suppress growth of malignant cells and the dissemination of tumors by triggering apoptosis and limiting the proliferation of tumor cells.10 There are a number of reports that have demonstrated that complexation of a ligand fragment to vanadium(IV) ions remarkably improved its antitumor and

INTRODUCTION There is a contemporary interest in vanadium chemistry, which stems from the broad range of relevance and application of vanadium in biological as well as industrial processes.1 The knowledge of vanadium-based enzymes such as nitrogenases2 and especially haloperoxidases,3 with the latter having a strong structural link to certain phosphatases due to the chemical analogy between vanadate and phosphate,4 have been the source for a large number of model studies toward structural and functional properties.5 A strong interest also exists toward medicinal aspects of vanadium chemistry.6 This has been driven tremendously by the observation of insulin mimicking effects of vanadium(IV/V) complexes,7 which was even finalized in phase IIa clinical trials in humans for the treatment of type 2 diabetes © XXXX American Chemical Society

Received: January 5, 2018

A

DOI: 10.1021/acs.inorgchem.8b00035 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry antioxidant properties,11 as in case of flavonoids12 and in some substituted isoniazids.13 Despite promising results, a deeper understanding on their mode of action as well as selectivity toward their biological target, in order to reduce unbeneficial side effects, remains the main focus of current research toward medicinal vanadium chemistry.14 On the other hand, the coordination behavior of transition metals with azo (−NN−) ligands is of interest for their πacidity, versatile coordination modes and molecular structures, dye and pigmenting behavior, and redox, photophysical, catalytic, and biological properties.15 These properties are attributed to the low-lying π* orbitals of the azo functionality. Some notable examples of transition metal complexes based on azo-chelate ligands incorporate arylazooximes,16 arylazophenols,17 arylazopyridines,18 arylazoimidazoles,19 alkylthioazobenzenes,20 and sulfinylazobenzenes.21 However, rather limited attention has been focused on the synthesis of vanadium complexes with arylazo-based ligands.22 The 2-arylazophenol-based ligands used in this study lead to anionic dinuclear vanadium(IV) complexes, which to the best of our knowledge are the first structurally characterized examples possessing an unprecedented monoalkoxido bridging mode with the general formula [(VOL)2(μ-OEt)]−. Nevertheless, alkoxido-bridged dinuclear vanadium(IV) complexes are well-known but generally exhibit a bis-bridging mode in an edge-shared configuration with either a symmetric or mixed bridging ligand arrangement.23 As a general feature for the vast number of dinuclear oxidovanadium(IV) complexes, an antiferromagnetic coupling between the metal centers is observed.24 For edge-shared dinuclear vanadium(IV) complexes, this could be explained by a qualitative magnetostructural correlation, which is based on the classification of possible configurations for the orientation of the oxido groups at the two metal centers (see Scheme 1).25 Further support for this correlation has been provided by theoretical investigations on model complexes with [VO(μOR)2VO]2+ core.26 Assuming dihedral angles near to 180° between the two basal planes within the bridging moiety, three of these configurations (anti- and syn-orthogonal, as well as the syn-coplanar) are expected to show antiferromagnetic behavior, whereas only for the anti-coplanar and twisted configurations, ferromagnetic

coupling is predicted. For the subgroup of the orthogonal configurations, it was even possible to derive a quantitative magnetostructural correlation,27 due to the predominance of through space interaction between the magnetic orbitals leading to a direct overlay mechanism, which has been corroborated by theoretical findings.26 Remarkably, only very few examples are known with anti-coplanar and twisted configurations, all of which show ferromagnetic interactions, as predicted.25,28 In fact, in literature there is only one example with twisted configuration.25 It is noteworthy that there is one report for a syn-orthogonal dinuclear vanadium(IV) complex for which the magnetic behavior disagrees with the qualitative prediction based on the configurations given in Scheme 1, as it shows ferromagnetic interactions between the two vanadium(IV) centers.29 However, this can be attributed to a considerable deviation from coplanarity of the two basal coordination planes of the oxidovanadium(IV) moieties (111°), which clearly contradicts the assumed precondition of the qualitative magnetostructural correlation. Over the past years, we have been studying the chemistry of oxidovanadium complexes in N,O-donor environments,30 along with host−guest systems31 and some non-oxido vanadium(IV) complexes, which are very stable in solid state and solution.32 A current focus is placed on the synthesis of variable valence oxidovanadium complexes that mimic the coordination environment of the metal ions in enzymes as well as enhances the pharmacological activities.33 Herein, we report the syntheses of three diprotic tridentate ONO containing arylazo ligands coordinated to vanadium(IV) metal centers forming dinuclear complexes of the general formula (HNEt3)[(VOL)2(μ-OEt)]. The complexes have been characterized for their spectroscopic and redox properties as well as their magnetic behavior. In addition, the dinuclear vanadium(IV) complexes were probed for their antiproliferative activity against human cervical cancer (HeLa) and human colorectal adenocarcinoma (HT-29) cell lines.

■

EXPERIMENTAL SECTION

General Methods and Materials. Chemicals were purchased from commercial sources and used without further purification. VOSO4·5H2O and p-cresol were purchased from Loba Chemie. Anthranalic acid and its derivatives were purchased from SigmaAldrich. Reagent grade solvents were dried and distilled prior to use. Dulbecco’s modified Eagle medium (DMEM), Dulbecco’s phosphate buffered saline (DPBS), trypsin EDTA solution, fetal bovine serum (FBS), antibiotic−antimitotic solution, and MTT assay kit were purchased from Himedia, Mumbai, India. TRITC-phalloidin and DAPI were procured from Sigma-Aldrich, India. HeLa and HT-29 cell lines were procured from NCCS, Pune, India. Elemental analyses were performed on a Vario EL cube CHNS elemental analyzer. IR spectra were recorded on a PerkinElmer Spectrum RXI spectrophotometer. 1 H and 13C NMR spectra were recorded on a Bruker Ultrashield 400 MHz spectrometer using SiMe4 as an internal standard. Electronic spectra were recorded on a Lamda25, PerkinElmer spectrophotometer. ESI-MS were obtained on a SQ-300 MS instrument operating in both positive and negative ion ESI mode, employing complex concentration of 100 pmol/μL. The capillary exit voltage was 120 V, and the drying gas temperature was 300 °C. Electrochemical data were collected using a PAR electrochemical analyzer and a PC-controlled potentiostat/ galvanostat (PAR 273A) at 298 K in a dry nitrogen atmosphere. Cyclic voltammetry experiments were carried out with Pt working and auxiliary electrodes, Ag/AgCl as the reference electrode, and tetraethylammonium perchlorate (TEAP) as the supporting electrolyte. The starting potential used was 0.0 V.

Scheme 1. Arrangements of Dinuclear Vanadium(IV) Complexes with [VO(μ-OR)2VO]2+ Core

B


Article

Inorganic Chemistry Synthesis of Ligands (H2L1−3). The 2-(2′-carboxyphenylazo)phenol ligands were prepared by coupling substituted diazotized anthranilic acid with p-cresol (H2L1 and H2L2), or β-naphthol (H2L3).34 The resulting red compounds were filtered off, washed with ethanol, and dried over fused CaCl2. Elemental analyses, NMR (1H and 13C), and IR data of the ligands confirmed their structures. H2L1. Yield: 64%. Anal. Calcd for C14H12N2O3: C, 65.62; H, 4.72; N, 10.93. Found: C, 65.65; H, 4.73; N, 10.90. IR (KBr pellet, cm−1): 3542 ν(O−H) br; 1700 ν(CO); 1594 ν(NN); 1409 ν(C−O)phenolic. 1 H NMR (400 MHz, CDCl3, ppm): δ = 8.24−6.97 (m, 7H, aromatic), 2.36 (s, 3H, CH3). 13C NMR (100 MHz, CDCl3, ppm): δ = 168.82 (CO), 151.96−116.27 (12C, aromatic), 20.37 (−CH3). H2L2. Yield: 66%. Anal. Calcd for C14H11N3O5: C, 55.82; H, 3.68; N, 13.95. Found: C, 55.82; H, 3.66; N, 13.97. IR (KBr pellet, cm−1): 3510 ν(O−H) br; 1699 ν(CO); 1590 ν(NN); 1402 ν(C−O)phenolic. 1 H NMR (400 MHz, CDCl3, ppm): δ = 8.67−6.90 (m, 6H, aromatic), 2.39 (s, 3H, CH3). 13C NMR (100 MHz, CDCl3, ppm): δ = 166.39 (CO), 152.61−118.05 (12C, aromatic), 20.34 (−CH3). H2L3. Yield: 64%. Anal. Calcd for C17H11BrN2O3: C, 55.01; H, 2.99; N, 7.55. Found: C, 55.04; H, 3.01; N, 7.54. IR (KBr pellet, cm−1): 3337 ν(O−H) br; 1698 ν(CO); 1549 ν(NN); 1402 ν(C− O)phenolic. 1H NMR (400 MHz, CDCl3, ppm): δ = 11.8 (s, 1H, − COOH), 8.33−7.21 (m, 10H, aromatic). 13C NMR (100 MHz, CDCl3, ppm): δ = 169.12 (CO), 156.40−118.60 (16C, aromatic). Synthesis of (HNEt3)[(VOL1−3)2(μ-OEt)] (1−3). Triethylamine (100 mg, 1 mmol) was added to a hot ethanolic solution of H2L (1 mmol), followed by VOSO4·5H2O (253 mg, 1 mmol). After refluxing for 64 h, greenish black X-ray quality crystals of 1 and 3 were obtained directly from the reaction medium, suitable for X-ray measurements. However, for 2, crystals of X-ray quality could not be isolated, even by recrystallization attempts. (HNEt 3 )[(VOL 1 ) 2 (μ-OEt)] (1). Yield: 62%. Anal. Calcd for C36H41N5O9V2: C, 54.75; H, 5.23; N, 8.86. Found: C, 54.75; H, 5.21; N, 8.82. IR (KBr pellet, cm−1): 1664 ν(CO) s; 1493 ν(N N); 1373 ν(C−O)phenolic; 980, 966 ν(VO)s; 829 ν(V−O−V). ESIMS (CH3CN; positive ion mode): m/z 811.58 [M + Na]+; 827.59 [M + K]+. (HNEt 3 )[(VOL 2 ) 2 (μ-OEt)] (2). Yield: 57%. Anal. Calcd for C36H43N7O13V2: C, 48.93; H, 4.90; N, 11.10. Found: C, 49.05; H, 4.86; N, 11.15. IR (KBr pellet, cm−1): 1656 ν(CO) s; 1589 ν(N N); 1356 ν(C−O)phenolic; 985, 970 ν(VO)s; 831 ν(V−O−V). ESIMS (CH3CN; negative ion mode): m/z 781.48 [M − HNEt3]−. (HNEt 3 )[(VOL 3 ) 2 (μ-OEt)] (3). Yield: 66%. Anal. Calcd for C42H39Br2N5O9V2: C, 49.48; H, 3.85; N, 6.87. Found: C, 49.90; H, 3.87; N, 6.83. IR (KBr pellet, cm−1): 1677 ν(CO) s; 1502 ν(N N); 1349 ν(C−O)phenolic; 992, 973 ν(VO)s; 832 ν(V−O−V). ESIMS (CH3CN; positive ion mode): m/z 1019.60 [M]+. X-ray Crystallography. Complex 1. A suitable single crystal was selected using a polarizing microscope and mounted on a 50 μm MicroMesh MiTeGen Micromount using FROMBLIN Y perfluoropolyether (LVAC 16/6, Aldrich) before centering on a standard Bruker Kappa APEX II CCD-based 4-circle X-ray diffractometer using graphite monochromated Mo Kα radiation (λ = 0.71073 Å) of a fine focus molybdenum-target X-ray tube operating at 50 kV and 30 mA. The crystal was cooled to 100(2) K with a Kryoflex low temperature device. Initial unit cell parameters were obtained by least-squares refinement of the xyz centroids of strong reflections harvested from a series of 12 frames in each of three orthogonally related regions of the reciprocal space using the Evaluate routine of the APEX software suite.35 Final unit cell parameters were calculated at the end of intensity measurements from xyz centroids of 9664 well-centered reflections of the complete data set. Intensity data were collected via ω- and φ-scans in a range up to 2θ = 56° with scan widths of 0.5° and scan speeds of 3 s/frame at a crystal to detector distance of 40 mm. Collecting strategy was optimized by use of the Collect routine of the APEX software suite in order to reach an average data redundancy of 10 or better in about 24 h. Information about crystal mosaicity, as well as its scattering behavior at higher θ values was derived from prescans for unit cell determination. Integrated intensities were obtained with the Bruker SAINT36 software package using a narrow-frame algorithm

performing spatial corrections of frames, background subtractions, Lorentz and polarization corrections, profile fittings, and error analyses. Semiempirical absorption corrections based on equivalent reflections were made by use of the program SADABS.37 Details of the data collection parameters applied on the individual crystals are summarized in Table 1 with Rint = ∑|Fo2 − Fo2(mean)|/∑[Fo2] and

Table 1. Crystal Data and Refinement Details for 1 and 3 complex

1

3

formula M (g mol−1) cryst syst space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z dcalc (g cm−3) absorp coeff (mm−1) θ range for data collection (deg) F(000) cryst size (mm3) max/min transmittance 2θmax (deg) reflns collected unique reflns

C36H41N5O9V2 789.62 triclinic P1̅ 11.3507(7) 12.1801(8) 13.2000(8) 89.234(3) 89.231(3) 89.799(3) 1824.6(2) 2 1.437 0.573 2.87−28.00 820 0.13 × 0.24 × 0.29 0.9019/0.8648 28 168645 8784 [Rint = 0.0738] 0.0308, 0.0783 0.0362, 0.0814 1.047 0.447, −0.357

C42H39Br2N5O9V2 1019.48 triclinic P1̅ 11.0675(5) 12.2101(6) 16.9540(8) 93.516(2) 107.485(3) 95.750(2) 2164.12(18) 2 1.565 2.338 2.20−25.35 1028 0.50 × 0.30 × 0.20 0.9875/0.8953 30.5 16045 7824 [Rint = 0.0630]

R1[I > 2σ(I)], wR2 R1[all data], wR2 S[GOF] peak, hole (e·Å−3)

0.0590, 0.1207 0.1419, 0.1535 0.985 0.677, −0.653

Rsigma = ∑[σ(Fo2)]/∑[Fo2]. The centrosymmetric triclinic space group38 was determined from E-value statistics evaluated by the examine data routine of the APEX program suite and confirmed by successful refinement. Structure was solved by Direct Methods and subsequent difference Fourier syntheses of the program SHELXS39 and refined by full-matrix least-squares techniques on F2 with SHELXL.39 Atomic scattering factors were taken from International Tables for Crystallography.40 No extinction corrections were applied. Final agreement indices: R1 = ∑||Fo| − |Fc||/∑|Fo| and wR2 = [∑[w(Fo2 − Fc2)2]/∑(wFo2)2]]1/2. Weighting function used was w = 1/[σ2(Fo2) + (pP)2 + qP] with P = (Fo2 + 2Fc2)/3. GOF = [∑[w(Fo2 − Fc2)2]/(n − p)]1/2 where n is the number of reflections and p is the total number of parameters refined. All non-hydrogen atoms were refined with anisotropic displacement parameters; hydrogen atoms were refined with common isotropic displacement parameters for chemically related groups of hydrogen atoms. Although the hydrogen atoms could be localized in difference Fourier syntheses, those of the organic groups were refined in geometrically optimized positions riding on the corresponding carbon atoms with C−H distances of 0.98 Å (−CH3), 0.99 Å (−CH2−), 0.95 Å (CHarom), and 0.93 Å (R3N−H). Further details on the results of structure refinement are summarized in Table 1. Figures were drawn using DIAMOND41 and Mercury.42 In the ball and stick models, all atoms are drawn as thermal displacement ellipsoids at the 50% probability level with exception of the hydrogen atoms, which are shown as spheres of arbitrary radii. Hydrogen bridging bonds are drawn in red as dashed sticks. Complex 3. Suitable single crystals were chosen for X-ray diffraction studies. Crystallographic data and details of refinement are given in Table 1. Data was collected at 22 °C on a Nonius Kappa CCD FR590 single crystal X-ray diffractometer, Mo radiation. Data collection was C


Article

Inorganic Chemistry Scheme 2. Schematic Representation for the Synthesis of (HNEt3)[(VIVOL1−3)2(μ-OEt)] (1−3)

98.9% complete to 25° in θ. A total of 16045 partial and complete reflections were collected covering the indices h = −11 to 11, k = −23 to 21, and l = −20 to 23. Indexing and unit cell refinement indicated a triclinic P lattice. The space group was found to be P1̅ (No. 2). The data was integrated and scaled using hkl-SCALEPACK.41 This program applies a multiplicative correction factor (S) to the observed 2

by Yamaguchi.51 Within this theory, the coupling constant can be derived by eq 1.

J12 =

2(E BS − E HS) ⟨SHS2⟩ − ⟨SBS2⟩

(1)

Single-point calculations for the high-spin (HS) and brokensymmetry (BS) states have been performed with Becke’s threeparameter hybrid functional52 for the exchange part and the correlation functional of Lee−Yang−Parr,53 together denoted as B3LYP. Additional BS-DFT calculations were employed with the meta-GGA hybrid functional proposed by Tao, Perdew, Staroverov, and Scuseria (denoted as TPSSh).54 In all calculations the triple-ζ def2-TZVPP basis sets49 were used together with a tight self-consistent field (SCF) energy convergence criterion (10−8 au). Natural population analyses (NPA) have been performed with Turbomole based on the converged DFT/B3LYP/def2-TZVPP wave functions.55 Cytotoxicity Study. Anticancer properties of vanadium(IV) complexes (1−3) were tested against human colon cancer (HT-29) and cervical cancer (HeLa) cell lines in vitro by MTT assay. Cells cultured in DMEM media with 10% FBS in a humidified (95% humidity) CO2 incubator (5% CO2) at 37 °C were harvested by trypsinization and were seeded into a 96-well plate at a concentration of 1 × 104 cells/well. Tissue culture plate (TCP) was taken as control. After 12 h of initial seeding, the cancerous cells were subjected to treatment with the vanadium(IV) complexes (1−3) for a period of 48 h. For this purpose, five different concentrations (250, 100, 50, 10, and 5 μg/mL) of each compound prepared in complete DMEM media were used. As per the manufacturer’s instruction, MTT assay was performed after 48 h, using a MTT assay kit. The relative viability of the cells after treatment was reported in terms of cell viability index as per eq 2. All experiments were performed in quadruplets, and the data were expressed as mean ± SD. Single variance ANOVA under 95% confidence interval was used to evaluate the statistical significance of the data.

2

intensities (I) and has the following form: S = (e−2B(sin θ)/λ )/scale. S was calculated from the scale, and the B factor was determined for each frame and was then applied to I to give the corrected intensity (Icorr). The solution was achieved by direct methods (SHELXS, SIR9743) to produce a complete heavy atom phasing model that was consistent with the proposed structure. The structure was completed by difference Fourier synthesis with SHELXL97.44 Scattering factors were from Waasmair and Kirfel.45 Hydrogen atoms were placed in geometrically idealized positions and constrained to ride on their parent atoms with C−H distances in the range 0.95−1.00 Å. Isotropic thermal parameters Ueq were fixed such that they were 1.2Ueq of their parent atom Ueq for CH and 1.5Ueq of their parent atom Ueq in case of methyl groups. All non-hydrogen atoms were refined anisotropically by full-matrix least-squares. Magnetic Measurements. Magnetic susceptibility data were obtained from powdered samples in gelatin capsules at 1000 and 2000 Oe using a Quantum-Design MPMS-5 SQUID magnetometer equipped with a 5 T magnet in the range from 2 to 300 K. The data is corrected for the sample holder and the diamagnetic moment of the sample.46 Simulation of the data were performed using the MagProp package of DAVE (Data Analysis and Visualization Environment, www.ncnr.nist.gov/dave). For data calculation and graphics, OriginPro 8.5 (OriginLab, Northampton, MA) was used. Computational Details. The quantum chemical calculations were performed with the Turbomole package of programs (version 6.6).47 Geometries were taken from the crystallographic structures for which the position of the hydrogen atoms were energy optimized prior to single-point calculations. These optimizations were carried out using the gradient-corrected BP86 functional48 in combination with single-ζ def2-SVP basis sets 49 and the resolution of identity (RI) approximation.50 The magnetic exchange coupling constants were calculated within the model of a phenomenological Heisenberg− Dirac−van Vleck Hamiltonian HHDVV = −J12S1S2 utilizing the brokensymmetry (BS) approach with the spin projection procedure suggested

cell viability index =

absorbance of sample at 595 nm absorbance of control at 595 nm

(2)

From the absorbance−concentration plot, the compounds’ IC50 value was calculated by following the standard procedure.56 D


Article

Inorganic Chemistry Distribution of F-actin (cytoskeletal organization), shape of the nucleus, and its structural integrity were examined using fluorescence microscopy (Olympus). In brief, at the end of the treatment, cells were washed gently with PBS and were fixed with 4% paraformaldehyde for 15 min. Cells were then subjected to permeabilization (0.25% Triton X-100 in PBS, 10 min exposure). They were subsequently stained with DAPI and TRITC-phalloidin.57 The cells were treated with the compounds for 36 h at a concentration of 100 μg/mL, for this study.

Table 2. UV/Vis Spectral Data for 1−3 in DMSO complex 1 2 3

■

wavelength (nm) (εmax (M−1 cm−1)) 275 (11540) 258 (11580) 271 (11531)

376 (1560) 356 (1582) 358 (1500)

510 (7650) 509 (7600) 503 (7000)

866 (72) 828 (70) 869 (75)

band in the near IR range 869−828 nm is assigned to a d−d transition.59c Figure 1 shows the representative spectrum of 3. Mass spectra of 1−3 were recorded in acetonitrile solution in the ESI mode. The ESI-MS of complex 1 shows major peaks in the positive ion mode for [M + Na]+ and [M + K]+, at m/z 811.58 and 827.59, respectively. Complex 2 exhibits the major peak at m/z 781.48 [M − HNEt3]− in the negative ion mode, whereas the characteristic molecular ion peak, [M]+, is observed for complex 3 at m/z 1019.60. The Experimental Section summarizes the ESI-MS data. Figure S3 depicts the representative ESI-MS for complex 2, which could not be structurally characterized. Electrochemical Properties. The cyclic voltammetry (CV) of complexes 1 and 2 was examined in CH2Cl2 and that of 3 in DMF solution (0.1 M TEAP) at 100 mV s−1 scan rate, using a Ag/AgCl reference electrode, a Pt working electrode, and a Pt auxiliary electrode. Two oxidation and two reduction peaks are observed in the CVs of each complex (1− 3), which correspond to one electron transfer (Table 3). By comparing its current height with that of the standard ferrocene/ferrocenium couple under identical experimental conditions, the one-electron nature of this oxidation was verified. Figure 2 depicts the representative CV of 1. The anodic region of 1 shows one quasi-reversible and one irreversible single-electron wave at Ea1/2 0.46 V and Ea 1.09 V, respectively, which are assigned to the V(IV)/V(V) oxidation of the individual metal centers.61 Due to the reduction of each V(IV) center to V(III) at Ec1/2 −0.59 and −1.36 V, two quasireversible single-electron waves are observed in the cathodic region.62 In the anodic region, two irreversible single-electron oxidation waves at Ea 1.26 and 0.82 V and a quasi-reversible wave in the cathodic region at Ec1/2 −0.94 V were observed (see Figure 2), which are due to ligand oxidation and reduction processes, respectively. The corresponding cyclic voltammogram of the ligand H2L1 is shown in Figure S4, and it is observed that some of the redox peaks corresponding to the ligands are also present in the complexes with slight changes in their positions, which is due to change in the electronic environment upon coordination. The quasi-reversible nature of the redox processes was confirmed by comparing the cyclic voltammetry at different scan rates.63 X-ray Crystallography. Single crystal X-ray structure determinations revealed similar geometry and coordination environments for complexes 1 and 3. The ball and stick model of 1 and 3 with atom numbering schemes are depicted in Figures 3 and 4, respectively. The selected bond parameters are given in Table 4. The asymmetric unit of both structures comprises a dinuclear, monovalent anion, the charge of which is being balanced by a triethylammonium cation. The common feature of both anions is the presence of two VO groups linked via the oxygen atom O9 of an ethoxido ligand with bond angles of 104.04(4)° and 108.3(2)° for 1 and 3, respectively. Asymmetry of this bridge arises from the fact that the corresponding V−O bond lengths fall into two categories, a short one to V2 (1 1.977(1) Å; 3 1.961(4) Å) and a longer one to V1 (1 2.023(1) Å; 3 2.019(3) Å). In each case, the

RESULTS AND DISCUSSION Synthesis and Characterization. Three 2-(2′carboxyphenylazo)phenol ligands (H2L1−3) have been employed in the present study for the synthesis of ethoxidobridged dinuclear vanadium(IV) complexes. Scheme 2 summarizes the synthesis of the complexes. Reactions of the azo dyes with VOSO4·5H2O proceeded smoothly in refluxing ethanol and did not require dried solvents or inert atmosphere conditions. Complexes 1 and 3 were obtained directly from the reaction medium as greenish black color crystalline compounds in good yields. However, single crystals suitable for X-ray measurements could only be obtained for complexes 1 and 3. Elemental analysis confirmed the purity of the synthesized complexes. The solubility of all the three synthesized complexes in aprotic solvents, CH3CN, DMF, or DMSO, is very high, while complexes 1 and 2 are also partially soluble in protic solvents, EtOH, CH2Cl2, and CHCl3, and sparingly soluble in H2O. The complexes are stable in the solid and in the solution state for 24 h. The solution state stability was confirmed by time-dependent UV/vis (Figure S1), ESI-MS, and NMR spectroscopy. Further, by recording the electronic absorption of the complexes in the aqueous solution, the solution phase stability of the complexes for the biological assays was confirmed. Figure S2 depicts the representative spectrum of complex 1. The IR spectra of complexes 1−3 showed similar shift in wave numbers compared to those of their respective ligands. A band in the region of 3542−3337 cm−1 in the ligands is assigned to the stretching vibration of the aromatic O−H in the phenolic moiety. This band is not present in the corresponding metal complexes due to deprotonation upon coordination. Three bands are observed at ∼1699, ∼1578, and ∼1404 cm−1; these bands are attributed to the carboxylate (CO), azo (−NN), and C−O phenolic fragments, respectively, of the ligands.58 The observed band for the ν(CO) stretching vibration of the carboxylate group in the complexes at values of about 1666 cm−1 is characteristic for a monodentate bridging mode of the carboxylate group of the ligand in complexes 1− 3.58a The bands generally shift to lower frequency upon coordination to the metal center. The vanadium complexes show two additional strong and sharp bands for the ν(VO) stretching modes in the region between 992 and 966 cm−1,59 which are in agreement with two VO groups present in the complexes, while the presence of a bridging oxygen atom is indicated by a ν(V−O−V) stretching vibration at ∼831 cm−1 in all three complexes.60 Electronic absorption spectra of complexes 1−3 were recorded in DMSO (Table 2). In the wavelength range 510− 258 nm, three strong absorptions are observed for the complexes. The lower energy absorption in the visible range, λmax = 510−503 nm and the bands in the higher energy UV absorption region (376−258 nm), for the complexes are likely to be due to ligand centered transitions.22e The low intensity E


Article

Inorganic Chemistry

Figure 1. UV/vis spectra of 3 (3.2 × 10−4 M) in DMSO.

Table 3. Cyclic Voltammetric Results for 1−3 at 298 Ka complex

Ea1/2 (V)

Ea (V)

ΔEaP (mV)

Ec1/2 (V)

ΔEcP (mV)

1 2 3

0.46 0.42 0.45

1.09 1.05 1.07

236, 70 240, 71 232, 73

−0.59, −1.36 −0.56, −1.30 −0.60, −1.32

220, 420 222, 418 225, 417

for a trigonal-bipyramidal coordinated atom),64 a typical coordination geometry for vanadium(IV) centers.65 The V O distances to the apical oxygen atoms (1 1.594(1)/1.597(1), 3 1.589(4)/1.587(5) Å) are in the typically observed double bond range, whereas the bond lengths to the donor atoms of the organic ligand are single bonds with a clear variation in length. For the latter, the shortest bonds are observed for the aromatic oxygen donors with a moderate increase in length between the V2−O7 (1 1.922(1), 3 1.919(4) Å) and V1−O3 bond (1 1.945(1), 3 1.966(5) Å). In contrast, the V−O bonds to the carboxylato groups are of similar length for both vanadium centers at about 1.96 Å. The longest donor distances within the coordination sphere of the vanadium atoms are found for the V−N bonds of the azo groups at about 2.08 Å (see Table 4). Due to a weak bonding interaction with the carboxylato oxygen atom O5 of the neighboring metal fragment the coordination sphere of the V1 center is expanded to a distorted octahedral environment (V1−O5 for 1 2.344(1), 3 2.367(4) Å), as depicted in Figure 5. As a result an edge-shared bridging mode between the vanadium centers is observed leading to a four membered, butterfly-shaped ring with dihedral angles between the V1−O9−O5 and V2−O9−O5 planes of 34.3° and 31.1°, respectively. This is responsible for the nearly rectangular orientation of O4 and O8 (the two oxygen atoms in the apical position) of the VO groups when viewed along the V1···V2 axis (1 96.20(8)°, 3 85.5(2)°). The obtained bridging mode for complexes 1 and 3 can be assigned to a twisted arrangement based on the reported classification for dinuclear complexes with a [VO(μ-OR)2VO]2+ core (see Scheme 1).25 It should be noted that this is a very scarcely observed bridging mode for which only one other example has been reported in the literature.25 Although a similar weak interaction seems to be possible in case of V2 with respect to the phenolate oxygen donor O3 of the neighboring metal fragment, the V···O distance between both atoms is too long for relevant bonding interactions (1 2.808(1), 3 3.106(4) Å). In the solid state, the anions and cations are linked via a hydrogen bond between the carboxylate atom O2 as acceptor and HNEt3 as donor (Figures 5 and S5). The corresponding

1 and 2 in CH2Cl2 and 3 in DMF at a scan rate of 100 mV s−1. E1/2 = (Eap + Ecp)/2, where Eap and Ecp are anodic and cathodic peak potentials vs Ag/AgCl, respectively. ΔEP = Eap − Ecp.

a

Figure 2. Cyclic voltammogram of 1 (10−3 M) showing oxidation (V(IV) → V(V)) and reduction (V(IV) → V(III)) of each vanadium(IV) center.

coordination sphere of the vanadium atoms is completed by the donor atoms of the corresponding tridentate dianionic ligand (O1/O5 of carboxyl group, N1/N3 of azo group, and O3/O7 from phenoxido group) and a double bonded oxygen atom (O4/O8) resulting in a square-pyramidal [VO4N] coordination (1, τ(V1) = 0.15, τ(V2) = 0.25; 3, τ(V1) = 0.14, τ(V2) = 0.32; with τ = 0 for a square-pyramidal coordinated atom and τ = 1 F


Article

Inorganic Chemistry

Figure 3. Asymmetric unit in the crystal structure of 1 with the atom numbering scheme.

Table 4. Selected Geometric Parameters for (HNEt3)[(VIVOL1,3)2(μ-OEt)] (1 and 3) 1

3

Bond Lengths (Å) V1−O9/V2−O9 2.023(1)/1.977(1) V1−N1/V2−N3 2.096(1)/2.089(1) V1−O1/V2−O5 1.970(1)/1.959(1) V1−O3/V2−O7 1.945(1)/1.922(1) V1−O4/V2−O8 1.594(1)/1.597(1) V1−O5 2.344(1) Bond Angles (deg) V1−O5−V2/V1−O9−V2 93.82(4)/104.04(4) O1−V1−O3/O5−V2−O7 152.02(5)/140.12(5) O1−V1−O4/O5−V2−O8 103.87(5)/109.86(5) O1−V1−O9/O5−V2−O9 89.09(4)/79.41(4) O3−V1−O4/O7−V2−O8 104.09(5)/110.02(5) O3−V1−O9/O7−V2−O9 84.02(4)/90.49(4) O4−V1−O9/O8−V2−O9 102.13(5)/104.72(5) O1−V1−N1/O5−V2−N3 89.65(4)/86.27(5) O3−V1−N1/O7−V2−N3 88.37(5)/87.67(5) O4−V1−N1/O8−V2−N3 96.36(5)/99.08(5) O9−V1−N1/O9−V2−N3 161.22(5)/155.25(5) O1−V1−O5 77.50(4) O3−V1−O5 74.66(5) O4−V1−O5 171.93(5) O9−V1−O5 69.85(4) N1−V1−O5 91.59(4)

Figure 4. Asymmetric unit in the crystal structure of 3 with the atom numbering scheme.

donor−acceptor distances of 2.75 and 2.70 Å and angles of 174° and 164° at the hydrogen atom for complexes 1 and 3, respectively, are in good agreement with a hydrogen bond of medium strength.66 It is interesting to see, that these hydrogen bonded ion pairs interact with each other in a way that the cation moiety of one ion pair is sandwiched in the pocket of the anion of a neighboring ion pair. This is possible, since the anions possess a V-shaped conformation with the tridentate organic ligands forming both sides of the relevant opening, whereas the {VO(μ-OR)VO} moiety is located on the opposite side (Figure S6). Overall no other bonding between neighboring ion pairs other than van-der-Waals interactions is observed in complexes 1 and 3 (Figure S7). Magnetic Properties. The magnetic susceptibility data of 1 and 3 were measured in the temperature range from 2 to 300 K, and the corresponding data depicted in Figure 6. At room temperature, the χT values of 1 and 3 are virtually the same at about 0.7 emu K mol−1. This is slightly lower than the spin-only value for two independent S = 1/2 species (0.75 emu K mol−1 for g = 2), as expected for vanadium(IV) complexes with gvalues typically smaller than two. With decreasing temperature, the χT values decrease and reach low-temperature values consistent with an S = 0 ground state. This clearly indicates an antiferromagnetic coupling between the vanadium(IV) centers in the dinuclear complexes 1 and 3. The susceptibility data has

2.019(3)/1.961(4) 2.086(4)/2.050(6) 1.965(4)/1.957(4) 1.966(5)/1.919(4) 1.589(4)/1.587(5) 2.367(4) 96.0(2)/108.3(2) 154.0(2)/134.6(2) 101.8(2)/114.4(2) 91.6(2)/79.7(2) 104.1(2)/110.9(2) 86.1(2)/90.9(2) 99.9(2)/105.3(2) 88.7(2)/85.0(2) 86.2(2)/84.9(2) 97.1(2)/100.3(2) 162.6(2)/153.8(2) 78.5(1) 76.5(1) 169.2(2) 69.3(1) 93.7(2)

been simulated using the spin Hamiltonian Ĥ = −JS1̂ S2̂ for two interacting S = 1/2 ions. The best fit of the experimental data was obtained with the parameters g = 1.942 and J = −53.4 cm−1 and g = 1.939 and J = −52.4 cm−1 for complexes 1 and 3, respectively. The observed exchange coupling between the metal centers in complexes 1 and 3 is of moderate size and well within the reported range for dinuclear vanadium(IV) complexes.26,27 Although very few structures that show ferromagnetic coupling are known,25,28,29 the vast majority of the reported dinuclear vanadium(IV) complexes exhibit antiferromagnetic exchange interactions.24 A common feature for these complexes is the [VO(μ-OR)2VO]2+ core, which allows for a structural classification of the corresponding edge-shared bridging G


Article

Inorganic Chemistry

assigned to a twisted arrangement as depicted in Scheme 3. Based on the qualitative magnetostructural correlation Scheme 3. Representation for a Twisted Arrangement with Unsymmetric Bridging Corea

a

Broken line represents the flexibility in coordination number.

proposed for the twisted configuration, a ferromagnetic interaction between the vanadium centers should be expected due to an accidental orthogonality of their magnetic orbitals.25 However, this obviously disagrees with the experimental observations in the case of complexes 1 and 3. In fact, the relevant structural parameters clearly indicate the absence of such an accidental orthogonality of magnetic orbitals, as both the tilting angles between the VO groups (59.3° for 1 and 68.0° for 3) and the dihedral angles between the equatorial planes of the coordination polyhedra (O1−O3−O9−N1 and O5−O7−O9−N3 63.6° for 1 and 68.2° for 3) for both complexes significantly deviate from a rectangular arrangement. This is in contrast to the only other reported example with twisted configuration, for which such an accidental orthogonality (angles between VO groups = 83.5° and equatorial planes = 89.1°) and ferromagnetic exchange was observed.25 However, this is in agreement with DFT studies reported for model systems, which indicate the importance of the actual distortion and the ligand environment at the vanadium centers.26 As a result a superexchange mechanism through the bridging ethoxido oxygen donor can be expected to be operative leading to a moderate antiferromagnetic exchange interaction between the two vanadium(IV) centers in complexes 1 and 3. Moreover, this is in agreement with the large deviation from coplanarity observed for the two basal coordination planes of the oxidovanadium(IV) moieties, which contrasts the coplanarity presupposed for the qualitative magnetostructural correlation in Scheme 1. Computational Studies. To further elucidate the magnetic properties of the dinuclear complexes 1 and 3 calculations based on broken-symmetry density functional theory (BSDFT) were performed. The structural parameters used for these calculations were derived from the crystallographic data. In these calculations, two common density functionals (B3LYP and TPSSh) were employed, as they are known to reproduce properties of transition metal complexes.68 The energies of the high-spin (HS) and broken-symmetry (BS) states together with their corresponding spin expectation values ⟨S2⟩ and the exchange coupling constants J12 derived from eq 1 for complexes 1 and 3 are summarized in Table 5. For complex 1, the calculated coupling constant of about −55 cm−1 is virtually independent of the density functional used (B3LYP −55.1 cm−1; TPSSh −55.9 cm−1) and in excellent agreement with the experimental value of −53.4 cm−1. The situation is somewhat different for complex 3, for which the coupling constant derived from BS-DFT/B3LYP calculations was found to be −50.7 cm−1, whereas the calculations with the TPSSh functional gave a value of −41.5 cm−1. Although the B3LYP-based exchange coupling closely resembles the experimental value of −52.4 cm−1, the latter TPSSh-based value significantly underestimates the experimental coupling

Figure 5. Central part of the anion of 1 visualizing the weak interaction [broken line] of O5 with V1 and the hydrogen bond between O2 of the anion and the donor function of the triethylammonium ion [broken red line].

Figure 6. Representation of the temperature dependence of χT for 1 (top) and 3 (bottom). The solid red lines represent the simulated values with the best fit parameters given in the text.

modes with respect to the orientation of the VO groups leading to qualitative magnetostructural correlations (see Scheme 1).25 Although this classification was strictly proposed for dinuclear complexes with six-coordinate vanadium centers, it can basically also be applied for dinuclear complexes with five-coordinate metal centers in a square-pyramidal environment.67 Interestingly, for complexes 1 and 3, a mixed situation is observed, as one of the vanadium centers is six-coordinate (V1), whereas the other shows a square-pyramidal coordination (V2). The extended coordination sphere of V1 is due to an additional weak bonding interaction of the carboxylate oxygen donor O5 attached to V2 (1 2.344(1), 3 2.367(4) Å, cf. Figure 5). This leads to a four membered, butterfly-shaped ring as bridging core for complexes 1 and 3 with dihedral angles of about 33°. From a topological point of view, the bridging mode observed in complexes 1 and 3 (see Figure 5) can therefore be H


Article

Inorganic Chemistry

atoms are expected to play a role in the magnetic superexchange, however, with a dominance of the ethoxido oxygen donor atom (see Figures 7 and 8). Cytotoxicity Study. Analysis of the in vitro cytotoxicity study clearly showed that all the three compounds (1−3) are cytotoxic and can kill cancer cells effectively. The ligands and metal precursor showed significantly lower toxicity (IC50 values >100 μM) in both HeLa and HT-29 cancer cells, as compared to the divanadium(IV) arylazo complexes 1−3 (IC50 values 1.92−9.39 μM and 25.93−28.77 μM against HeLa and HT-29 cells (Table 6), respectively), indicating enhanced cytotoxicity upon complexation and the presence of the vanadium(IV) ion. A variation in potency was prominent at very low concentration of the compound (up to 10 μg/mL). At relatively higher concentration of about 50 μg/mL, such variation becomes insignificant, and there was 80% cell death with respect to the control for all treatment sets irrespective of the cell type. No further increase in cell death was observed with an increase in concentration above 50 μg/mL. Among the three complexes, 1 showed maximum cytotoxicity (IC50 value 1.92 μM) followed by 3 (IC50 value 6.57 μM) and 2 (IC50 value 9.39 μM) against HeLa cells. In the case of HT-29, although 3 showed highest cytotoxicity, the data was found statistically insignificant. Further analysis revealed that IC50 value of each compound was many fold less for HeLa cells in comparison to that of HT29 cells, which indicates the specificity of a compound toward a particular cell type (Table 6). The specificity of cytotoxic complexes toward particular cell line has also been reported earlier.70 It is already known that during the course of their action on the cell, many of the cytotoxic agents disrupt nuclear integrity and cytoskeletal structure.71 These include clinically active compounds like cisplatin72 (complexation of nucleic acids), doxorubicin73 (intercalation of nucleic acids), taxol74 (stabilization of microtubules), vinblastin75 (prevention of polymerization of microtubules), and other compounds like jasplakinolide76 (enhancement of polymerization of actin) and cytochalasin77 (prevention of polymerization of actin). Keeping this perspective in mind, cells after treatments were stained with fluorescence dyes specific for nucleus (stained with DAPI, blue colored) and F-actin (stained with TRITC-phalloidin, red colored) and investigated under a fluorescence microscope and imaged (Figure 9). Preliminary inspection confirmed that for all the treatment sets, cell nuclei remain intact, which ruled out the possibility of nuclear fragmentation. However, a critical analysis of the images revealed two very interesting points. In this study, we observed that under the exposure of the complexes (100

Table 5. Results of BS-DFT Calculations for 1 and 3 complex

density functional

J12 (cm−1)

1

B3LYP

−55.1

1

TPSSh

−55.9

3

B3LYP

−50.7

3

TPSSh

−41.5

state

energy (au)

⟨S2⟩

HS BS HS BS HS BS HS BS

−3942.24772 −3942.24784 −3943.67400 −3943.67412 −9317.71725 −9317.71736 −9319.34731 −9319.34740

2.02331 1.02091 2.02158 1.01824 2.02322 1.02054 2.02178 1.01831

constant. This result is somewhat unexpected, as the TPSSh density functional is reported to show promising performance in bioinorganic applications, including the prediction of the energy sequence of spin states.69 However, at least for the cases reported here, a preferable explanation is provided by the B3LYP functional for the energy splitting of the spin states, which might be due to the difference in the amount of exact Hartree−Fock exchange implemented in the B3LYP (20%) and TPSSh (10%) functional. Spin-density isosurfaces for the high-spin and brokensymmetry states of complexes 1 and 3 are depicted in Figures 7 and 8. Regarding the high-spin states of compounds 1 and 3, natural population analysis (NPA) based on DFT/B3LYP reveals (see Tables S1 and S2) that most of the spin density is, as expected, localized at both V(IV) centers in the [NO3] equatorial coordination plane (1, V1 1.0765, V2 1.0833; 3, V1 1.0699, V2 1.0754). As a result, a strong spin-polarization of the apical VO group oxygen atoms is apparent (1, O4 −0.1278, O8 −0.1283; 3, O4 −0.1306, O8 −0.1168; see also Figures 7 and 8). For the high-spin state in both compounds, a considerable spin density is observed at the bridging ethoxido oxygen donor O9 indicating a spin delocalization of the metal centers (1 0.0092; 3 0.0126). This is in agreement with an operative superexchange pathway through the ethoxido bridge. In case of complex 3 the higher spin density on donor atom O9 goes together with shorter V1−O9 and V2−O9 bonds as compared to compound 1 (see Table 4). Nevertheless, no significant difference in the experimentally obtained and calculated magnetic coupling constants of 1 and 3 is apparent. A weaker spin polarization of the carboxylate oxygen donor O5 (1 0.0079; 3 0.0055) can be attributed to the elongated V1−O5 bonds in 1 and 3, which are a direct consequence of the transeffect of the oxido ligand O4 at the corresponding VO group. As a result, in complexes 1 and 3 both bridging oxygen donor

Figure 7. Spin-density isosurfaces (0.003 au; turquoise = net α density; orange = net β density) for the high-spin (left) and broken-symmetry (right) states of 1 obtained with DFT/B3LYP. Hydrogen atoms are omitted for clarity. I


Article

Inorganic Chemistry

Figure 8. Spin-density isosurfaces (0.003 au; turquoise = net α density; orange = net β density) for the high-spin (left) and broken-symmetry (right) states of 3 obtained with DFT/B3LYP. Hydrogen atoms are omitted for clarity.

On the basis of the aforesaid fact, we hypothesize that this set of compounds may possess similar properties. Commonly used chemotherapeutic drugs like cisplatin, cyclophosphamide, tamoxifen, and 5-fluorouridine have shown comparable antiproliferative efficacy under similar conditions, against HeLa and HT-29 cells (Table 6).79 The μ-ethoxido dinuclear arylazovanadium(IV) complexes (1−3) have shown improved in vitro cytotoxicity results as compared to our earlier cytotoxicity reports on vanadium33 and molybdenum hydrazone80 and copper thiosemicarbazone complexes81 (IC50 10−40 μM) against HeLa cells. The IC50 values of 1−3 are either lower than or comparable to photocytotoxic oxidovanadium(IV) complexes of polypyridyl ligands82 (IC50 3.9−16.2 μM) and curcuminoids83 (IC50 2.4− 10.9 μM). The antiproliferative efficacy of 1−3 was also better than or comparable to other vanadium complexes (>47 μM against HT-29 for [VO(sal-L-tryp)(acetylethTSC)]·C2H5OH,

Table 6. Antiproliferative Effect of Complexes 1−3 against HeLa and HT-29 Cells after 48 h Exposure IC50 (μM) complex

HeLa cells

HT-29 cells

1 2 3 cisplatin cyclophosphamide tamoxifen 5-fluorouridine

1.92 ± 0.26 9.39 ± 0.95 6.57 ± 0.55 70 21.5 9.3 0.3

28.77 ± 2.27 27.28 ± 1.91 25.93 ± 1.71 12.2 1689 8.82 2.85

μg/mL for 36 h) although individual cells were able to maintain their cytoskeletal integrity, both HeLa and HT-29 cells failed to form a colony. Such variation was more profound in the cells treated with 1 and 3. So far, there are a number of cytotoxic compounds reported that effectively inhibit colony formation.78

Figure 9. Cytotoxicity of 1−3 against HeLa (A1) and HT-29 cells (A2) after 48 h exposure. The data were stated as mean ± SD. The experiments were performed in quadruplets. Morphology of HeLa (B1) and HT-29 (B2) cells treated with complexes (1−3) for 36 h. The cells were visualized under fluorescent microscope after staining with DAPI (blue color, nucleus) and TRITC phalloidin (red color, F-actin). J


Article

Inorganic Chemistry

free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

[VO(sal-L-tryp)(Me-ATSC)], and [VO(salL-tryp)(N-ethhymethohcarbthio)]·H2O).84

■

CONCLUSIONS Three dinuclear oxidovanadium(IV) complexes with the general formula (HNEt3)[(VIVOL1−3)2(μ-OEt)] (1−3) with diprotic tridendate 2-arylazophenol ligands are reported, where the resulting negative charge of the complex fragment is balanced by a triethylammonium cation. Compounds 1 and 3 were crystallographically characterized. Based on their structure, their central edge-shared core can be classified as a twisted arrangement, which is unsymmetrically bridged with a μ-ethoxido and a carboxylate group of one of the tridentate ligand fragments. These complexes are the first examples with this type of ligand and to the best of our knowledge add the second report on dinuclear vanadium(IV) complexes with a twisted core configuration. In the structures, the cation is found to be hydrogen bridged to the one coordinated O atom of the carboxylate group, which does not take part in the bridging core unit. Based on variable temperature magnetic susceptibility measurements an unexpected antiferromagnetic coupling of moderate size between the two vanadium(IV) centers was found to be operative, based on the earlier reported qualitative magnetostructural correlation, which is related to the arrangement of the core configuration. This is due to the distorted nature of the twisted bridging core preventing the presence of an accidental orthogonality of the VO groups and, therefore, allowing for a superexchange pathway leading to antiferromagnetic coupling. As for the only other reported complex with twisted arrangement, the required accidental orthogonality is indeed observed, which consequently leads to a ferromagnetic exchange, the complexes reported here clearly show that in the absence of strict symmetry rules distortion can easily lead to a variation in magnetic behavior. However, these findings are in good agreement with theoretical results obtained for complexes 1 and 3. Time dependent UV/vis spectroscopy studies in DMSO revealed the presence of d−d transition bands even after 24 h, thus proving the stability of the complexes in the solution state. Cytotoxicity studies against human cancer cell lines HeLa and HT-29 confirmed the antiproliferative effect of the complexes and their specificity over particular cell types. Even though all the complexes were found to be cytotoxic, 1 was most potent among them.

■

■

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (R. Dinda). *E-mail: [email protected] (W. Plass). ORCID

Michael Böhme: 0000-0003-2097-4657 Winfried Plass: 0000-0003-3473-9682 Rupam Dinda: 0000-0001-9452-7791 Author Contributions

The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS The authors thank the reviewers for their comments and suggestions, which were helpful in preparing the revised version of the manuscript. R.D. thanks Prof. S. K. Chattopadhyay for discussion and electrochemical study. R.D. thanks DBT, Govt. of India [Grant No. 6241 P112/RGCB/PMD/DBT/RPDA/ 2015] and Council of Scientific and Industrial Research, New Delhi [Grant No. 01(2735)/13/EMR-II] for funding this research.

■

REFERENCES

(1) (a) Crans, D. C.; Smee, J. J.; Gaidamauskas, E.; Yang, L. Q. The Chemistry and Biochemistry of Vanadium and the Biological Activities Exerted by Vanadium Compounds. Chem. Rev. 2004, 104, 849−902. (b) Costa Pessoa, J.; Garribba, E.; Santos, M. F. A.; Santos-Silva, T. Vanadium and proteins: Uptake, transport, structure, activity and function. Coord. Chem. Rev. 2015, 301−302, 49−86. (c) Rehder, D. Implications of vanadium in technical applications and pharmaceutical issues. Inorg. Chim. Acta 2017, 455, 378−389. (2) (a) Eady, R. R. Structure−Function Relationships of Alternative Nitrogenases. Chem. Rev. 1996, 96, 3013−3030. (b) Hu, Y.; Lee, C. C.; Ribbe, M. W. Vanadium nitrogenase: a two-hit wonder? Dalton Trans. 2012, 41, 1118−1127. (3) (a) Wever, R.; Hemrika, W. In Handbook of Metalloproteins; Messerschmidt, A., Hubert, R., Poulos, T., Wieghardt, K., Eds.; John Wiley & Sons, Ltd: Chichester, 2001; Vol. 2, pp 1417−1428. (b) Leblanc, C.; Vilter, H.; Fournier, J. B.; Delage, L.; Potin, P.; Rebuffet, E.; Michel, G.; Solari, P. L.; Feiters, M. C.; Czjzek, M. Vanadium haloperoxidases: From the discovery 30 years ago to X-ray crystallographic and V K-edge absorption spectroscopic studies. Coord. Chem. Rev. 2015, 301−302, 134−146. (4) Plass, W. Phosphate and vanadate in biological systems: Chemical relatives or more? Angew. Chem., Int. Ed. 1999, 38, 909−912. (5) (a) Wischang, D.; Brücher, O.; Hartung, J. Bromoperoxidases and functional enzyme mimics as catalysts for oxidative brominationA sustainable synthetic approach. Coord. Chem. Rev. 2011, 255, 2204− 2217. (b) Plass, W. Chiral and supramolecular model complexes for vanadium haloperoxidases: Host-guest systems and hydrogen bonding relays for vanadate species. Coord. Chem. Rev. 2011, 255, 2378−2387. (c) Conte, V.; Coletti, A.; Floris, B.; Licini, G.; Zonta, C. Mechanistic aspects of vanadium catalysed oxidations with peroxides. Coord. Chem. Rev. 2011, 255, 2165−2177. (d) Plass, W. Vanadium haloperoxidases as supramolecular hosts: Synthetic and computational models. Pure Appl. Chem. 2009, 81, 1229−1239. (e) Sutradhar, M.; Martins, L. M. D. R. S.; Guedes da Silva, M. F. C.; Pombeiro, A. J. L. Vanadium

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.8b00035. Time dependent UV/vis spectra of 1 in DMSO and aqueous solution, ESI-MS of 2 in CH3CN, cyclic voltammogram of H2L1, space-filling model of the hydrogen bonded ion-pairs found in the crystal structure of 1, space-filling model representing the anion−cation interaction between two neighboring ion pairs in 1, packing of ion pairs in the crystal structure of 1, selected total densities derived from natural population analysis for 1 and 3, and selected spin densities derived from natural population analysis for 1 and 3 (PDF) Accession Codes

CCDC 1406078 and 1408476 contain the supplementary crystallographic data for this paper. These data can be obtained K


Article

Inorganic Chemistry complexes: Recent progress in oxidation catalysis. Coord. Chem. Rev. 2015, 301−302, 200−239. (f) Plass, W. Supramolecular interactions of vanadate species: vanadium(V) complexes with N-salicylidenehydrazides as versatile models. Coord. Chem. Rev. 2003, 237, 205−212. (g) Schwendt, P.; Tatiersky, J.; Krivosudský, L.; Šimuneková, M. Peroxido complexes of vanadium. Coord. Chem. Rev. 2016, 318, 135− 157. (6) (a) Mjos, K. D.; Orvig, C. Metallodrugs in Medicinal Inorganic Chemistry. Chem. Rev. 2014, 114, 4540−4563. (b) Rehder, D. The potentiality of vanadium in medicinal applications. Future Med. Chem. 2012, 4, 1823−1837. (7) Heyliger, C. E.; Tahiliani, A. G.; McNeill, J. H. Effect of vanadate on elevated blood glucose and depessed cardiac performance of diabetic rats. Science 1985, 227, 1474−1477. (8) (a) Scior, T.; Guevara-Garcia, J.; Do, Q.-T.; Bernard, P.; Laufer, S. Why Antidiabetic Vanadium Complexes are Not in the Pipeline of “Big Pharma” Drug Research? A Critical Review. Curr. Med. Chem. 2016, 23, 2874−2891. (b) Thompson, K. H.; Lichter, J.; LeBel, C.; Scaife, M. C.; McNeill, J. H.; Orvig, C. Vanadium treatment of type 2 diabetes: A view to the future. J. Inorg. Biochem. 2009, 103, 554−558. (9) (a) Kioseoglou, E.; Petanidis, S.; Gabriel, C.; Salifoglou, A. The chemistry and biology of vanadium compounds in cancer therapeutics. Coord. Chem. Rev. 2015, 301−302, 87−105. (b) Gambino, D. Potentiality of vanadium compounds as anti-parasitic agents. Coord. Chem. Rev. 2011, 255, 2193−2203. (10) (a) Hazari, P. P.; Pandey, A. K.; Chaturvedi, S.; Tiwari, A. K.; Chandna, S.; Dwarakanath, B. S.; Mishra, A. K. Synthesis of oxovanadium(IV) Schiff base complexes derived from C-substituted diamines and pyridoxal-5-phosphate as antitumor agents. Chem. Biol. Drug Des. 2012, 79, 223−234. (b) Kowalski, S.; Hac, S.; Wyrzykowski, D.; Zauszkiewicz-Pawlak, A.; Inkielewicz-Stepniak, I. Selective cytotoxicity of vanadium complexes on human pancreatic ductal adenocarcinoma cell line by inducing necroptosis, apoptosis and mitotic catastrophe process. Oncotarget 2017, 8, 60324−60341. (c) Narla, R. K.; Dong, Y. H.; D’Cruz, O. J.; Navara, C.; Uckun, F. M. Bis(4,7-dimethyl-1,10-phenanthroline) sulfatooxovanadium(IV) as a novel apoptosis-inducing anticancer agent. Clin. Cancer Res. 2000, 6, 1546−1556. (d) Benitez, J.; Guggeri, L.; Tomaz, I.; Arrambide, G.; Navarro, M.; Costa Pessoa, J.; Garat, B.; Gambino, D. Design of vanadium mixed-ligand complexes as potential anti-protozoa agents. J. Inorg. Biochem. 2009, 103, 609−616. (11) (a) Sasmal, P. K.; Saha, S.; Majumdar, R.; Dighe, R. R.; Chakravarty, A. R. Photocytotoxic oxovanadium(IV) complexes showing light-induced DNA and protein cleavage activity. Inorg. Chem. 2010, 49, 849−859. (b) Naso, L.; Ferrer, E. G.; Lezama, L.; Rojo, T.; Etcheverry, S. B.; Williams, P. Role of oxidative stress in the antitumoral action of a new vanadyl(IV) complex with the flavonoid chrysin in two osteoblast cell lines: relationship with the radical scavenger activity. JBIC, J. Biol. Inorg. Chem. 2010, 15, 889−902. (c) Naso, L. G.; Valcarcel, M.; Roura-Ferrer, M.; Kortazar, D.; Salado, C.; Lezama, L.; Rojo, T.; Gonzalez-Baro, A. C.; Williams, P. A.; Ferrer, E. G. Promising antioxidant and anticancer (human breast cancer) oxidovanadium(IV) complex of chlorogenic acid. Synthesis, characterization and spectroscopic examination on the transport mechanism with bovine serum albumin. J. Inorg. Biochem. 2014, 135, 86−99. (12) Naso, L.; Valcarcel, M.; Villace, P.; Roura-Ferrer, M.; Salado, C.; Ferrer, E. G.; Williams, P. A. M. Specific antitumor activities of natural and oxovanadium(iv) complexed flavonoids in human breast cancer cells. New J. Chem. 2014, 38, 2414−2421. (13) Liao, X.; Lu, J.; Ying, P.; Zhao, P.; Bai, Y.; Li, W.; Liu, M. DNA binding, antitumor activities, and hydroxyl radical scavenging properties of novel oxovanadium(IV) complexes with substituted isoniazid. JBIC, J. Biol. Inorg. Chem. 2013, 18, 975−984. (14) Pessoa, J. C.; Etcheverry, S.; Gambino, D. Vanadium compounds in medicine. Coord. Chem. Rev. 2015, 301−302, 24−48. (15) (a) Kawata, S.; Kawata, Y. Three-dimensional optical data storage using photochromic materials. Chem. Rev. 2000, 100, 1777− 1788. (b) Nejati, K.; Rezvani, Z.; Seyedahmadian, M. The synthesis, characterization, thermal and optical properties of copper, nickel, and

vanadyl complexes derived from azo dyes. Dyes Pigm. 2009, 83, 304− 311. (c) Bianchi, A.; Delgado-Pinar, E.; García-España, E.; Giorgi, C.; Pina, F. Highlights of metal ion-based photochemical switches. Coord. Chem. Rev. 2014, 260, 156−215. (d) Kaim, W. Complexes with 2,2′azobispyridine and related ‘S-frame’ bridging ligands containing the azo function. Coord. Chem. Rev. 2001, 219, 463−488. (e) Pourrieux, G.; Fagalde, F.; Romero, I.; Fontrodona, X.; Parella, T.; Katz, N. E. Electron-, proton-, and photon-induced spectroscopic changes in chromophore-quencher tricarbonyl(2,2′-bipyridine)rhenium(I) complexes with 4,4′-azobis(pyridine). Inorg. Chem. 2010, 49, 4084−4091. (f) Sanyal, A.; Banerjee, P.; Lee, G.-H.; Peng, S.-M.; Hung, C.-H.; Goswami, S. Unusual Reduction of Ammonium Heptamolybdate to Novel Molybdenum(IV)-Stabilized Azo Anion Radical Complexes. Inorg. Chem. 2004, 43, 7456−7462. (g) Aljamali, N. M. Review in Azo Compounds and its Biological Activity. Biochem. Anal. Biochem. 2015, 4, 169. (16) Pal, C. K.; Chattopadhyay, S.; Sinha, C.; Chakravorty, A. A Bis(azo−imine)palladium(II) System with 10 Ligand π Electrons. Synthesis, Structure, Serial Redox, and Relationship to Bis(azooximates) and Other Species. Inorg. Chem. 1996, 35, 2442−2447. (17) Acharyya, R.; Peng, S.-M.; Lee, G.-H.; Bhattacharya, S. An Unprecedented Oxidative Migration of a Methyl Group from 2-(2′,6′Dimethylphenylazo)-4-methylphenol Mediated by Ruthenium and Osmium. Inorg. Chem. 2003, 42, 7378−7380. (18) Kar, S.; Pradhan, B.; Sinha, R. K.; Kundu, T.; Kodgire, P.; Rao, K. K.; Puranik, V. G.; Lahiri, G. K. Synthesis, structure, redox, NLO and DNA interaction aspects of [{(L′−‴)2RuII)3(m3-L)]3+ and [(L′)2RuII(NC5H4S−)]+ [L3‑ = 1,3,5-triazine-2,4,6-trithiolato, L′−‴ = arylazopyridine]. Dalton Trans. 2004, 1752−1760. (19) Misra, T. K.; Das, D.; Sinha, C.; Ghosh; Pal, C. K. Chemistry of Azoimidazoles: Synthesis, Spectral Characterization, Electrochemical Studies, and X-ray Crystal Structures of Isomeric Dichloro Bis[1-alkyl2-(arylazo)imidazole] Complexes of Ruthenium(II). Inorg. Chem. 1998, 37, 1672−1678. (20) Pal, C. K.; Chattopadhyay, S.; Sinha, C.; Chakravorty, A. Synthesis and structure of a thioazobenzene oxygen insertion into the Pd-C bond by m-chloroperbenzoic acid. J. Organomet. Chem. 1992, 439, 91−99. (21) Sinha, C.; Bandyopadhyay, D.; Chakravorty, A. Aromatic Hydroxylation via Cyclometalation. Metaloxylation of Palladated 2(Alkylsulfinyl)azobenzenes. Inorg. Chem. 1988, 27, 1173−1178. (22) (a) Sanna, D.; Varnagy, K.; Lihi, N.; Micera, G.; Garribba, E. Formation of New Non-oxido Vanadium(IV) Species in Aqueous Solution and in the Solid State by Tridentate (O, N, O) Ligands and Rationalization of Their EPR Behavior. Inorg. Chem. 2013, 52, 8202− 8213. (b) Chakravarty, J.; Dutta, S.; Chakravorty, A. A VO3+ Complex Incorporating Aromatic Carboxylate Binding: Synthesis, Structure and Metal Redox. J. Chem. Soc., Chem. Commun. 1993, 1091−1092. (c) Chakravarty, J.; Dutta, S.; Chakravorty, A. Valence delocalisation in a triad of binuclear [L(O)VIVOVV(O)L]− species electrogenerated from structurally characterised divanadium(V) analogues (L = tridentate ONO ligand). J. Chem. Soc., Dalton Trans. 1993, 2857− 2858. (d) Chakravarty, J.; Dutta, S.; Chandra, S. K.; Basu, P.; Chakravorty, A. Chemistry of Variable-Valence VOz+ (z = 2, 3) Complexes: Synthesis, Structure, and Metal Redox of New VVO(ONO)(ON) and VIVO(ONO)(NN) Families. Inorg. Chem. 1993, 32, 4249−4255. (e) Dutta, S.; Basu, P.; Chakravorty, A. Chemistry of Mononuclear and Binuclear Oxidic VV, VVVV, and VVVIV Azophenolates. Inorg. Chem. 1993, 32, 5343−5348. (23) (a) Ahmed, M. A. K.; Fjellvag, H.; Kjekshus, A.; Klewe, B. New Oxovanadium(IV) Complexes with Mixed Ligands - Synthesis, Thermal Stability, and Crystal Structure of (VO)2(acac)2(m-OEt)2 and (VO)2(thd)2(m-OEt)2. Z. Anorg. Allg. Chem. 2004, 630, 2311− 2318. (b) Carrano, C. J.; Nunn, C. M.; Quan, R.; Bonadies, J. A.; Pecoraro, V. L. Monomeric and dimeric vanadium(IV) and -(V) complexes of N-(hydroxyalkyl)salicylideneamines: structures, magnetochemistry and reactivity. Inorg. Chem. 1990, 29, 944−951. (c) Castro, S. L.; Cass, M. E.; Hollander, F. J.; Bartley, S. L. The OxoVanadium(IV) Dimer of 3-Hydroxy-3-methylglutarate: X-ray Crystal L


Article

Inorganic Chemistry

Falvello, L. R.; Mak, T. C. W. Alkali metal (Na+ and K+)-mediated supramolecular assembly of oxovanadium(V) complexes: Synthesis and structural characterization. Polyhedron 2010, 29, 248−253. (e) Nica, S.; Buchholz, A.; Rudolph, M.; Schweitzer, A.; Wächtler, M.; Breitzke, H.; Buntkowsky, G.; Plass, W. Mixed-Ligand Oxidovanadium(V) Complexes with N′-Salicylidenehydrazides: Synthesis, Structure, and 51V Solid-State MAS NMR Investigation. Eur. J. Inorg. Chem. 2008, 2008, 2350−2359. (f) Nica, S.; Pohlmann, A.; Plass, W. Vanadium(V) oxoperoxo complexes with side chain substituted N-salicylidenehydrazides: Modeling supramolecular interactions in vanadium haloperoxidases. Eur. J. Inorg. Chem. 2005, 2005, 2032−2036. (g) Dash, S. P.; Roy, S.; Mohanty, M.; Carvalho, M. F. N. N.; Kuznetsov, M. L.; Pessoa, J. C.; Kumar, A.; Patil, Y. P.; Crochet, A.; Dinda, R. Versatile Reactivity and Theoretical Evaluation of Monoand Dinuclear Oxidovanadium(V) Compounds of Aroylazines: Electrogeneration of Mixed-Valence Divanadium(IV,V) Complexes. Inorg. Chem. 2016, 55, 8407−8421. (31) (a) Lippold, I.; Görls, H.; Plass, W. New Aspects for Modeling Supramolecular Interactions in Vanadium Haloperoxidases: b-Cyclodextrin Inclusion Compounds of cis-Dioxovanadium(V) Complexes. Eur. J. Inorg. Chem. 2007, 2007, 1487−1491. (b) Lippold, I.; Vlay, K.; Görls, H.; Plass, W. Cyclodextrin inclusion compounds of vanadium complexes: Structural characterization and catalytic sulfoxidation. J. Inorg. Biochem. 2009, 103, 480−486. (32) (a) Dash, S. P.; Majumder, S.; Banerjee, A.; Carvalho, M. F. N. N.; Adao, P.; Pessoa, J. C.; Brzezinski, K.; Garribba, E.; Reuter, H.; Dinda, R. Chemistry of Monomeric and Dinuclear Non-Oxido Vanadium(IV) and Oxidovanadium(V) Aroylazine Complexes: Exploring Solution Behavior. Inorg. Chem. 2016, 55, 1165−1182. (b) Dash, S. P.; Pasayat, S.; Bhakat, S.; Roy, S.; Dinda, R.; Tiekink, E. R. T.; Mukhopadhyay, S.; Bhutia, S. K.; Hardikar, M. R.; Joshi, B. N.; Patil, Y. P.; Nethaji, M. Highly Stable Hexacoordinated Nonoxidovanadium(IV) Complexes of Sterically Constrained Ligands: Syntheses, Structure, and Study of Antiproliferative and Insulin Mimetic Activity. Inorg. Chem. 2013, 52, 14096−14107. (33) (a) Dash, S. P.; Panda, A. K.; Dhaka, S.; Pasayat, S.; Biswas, A.; Maurya, M. R.; Majhi, P. K.; Crochet, A.; Dinda, R. A study of DNA/ BSA interaction and catalytic potential of oxidovanadium(V) complexes with ONO donor ligands. Dalton Trans. 2016, 45, 18292−18307. (b) Nica, S.; Rudolph, M.; Lippold, I.; Buchholz, A.; Görls, H.; Plass, W. Vanadium(V) complex with Schiff-base ligand containing a flexible amino side chain: Synthesis, structure and reactivity. J. Inorg. Biochem. 2015, 147, 193−203. (c) Dash, S. P.; Panda, A. K.; Pasayat, S.; Dinda, R.; Biswas, A.; Tiekink, E. R. T.; Patil, Y. P.; Nethaji, M.; Kaminsky, W.; Mukhopadhyay, S.; Bhutia, S. K. Syntheses and structural investigation of some alkali metal ionmediated LVVO2− (L2‑ = tridentate ONO ligands) species: DNA binding, photoinduced DNA cleavage and cytotoxic activities. Dalton Trans. 2014, 43, 10139−10156. (d) Dash, S. P.; Panda, A. K.; Pasayat, S.; Dinda, R.; Biswas, A.; Tiekink, E. R. T.; Mukhopadhyay, S.; Bhutia, S. K.; Kaminsky, W.; Sinn, E. Oxidovanadium(V) complexes of aroylhydrazones incorporating heterocycles: synthesis, characterization and study of DNA binding, photoinduced DNA cleavage and cytotoxic activities. RSC Adv. 2015, 5, 51852−51867. (e) Dash, S. P.; Panda, A. K.; Pasayat, S.; Majumder, S.; Biswas, A.; Kaminsky, W.; Mukhopadhyay, S.; Bhutia, S. K.; Dinda, R. Evaluation of the cell cytotoxicity and DNA/BSA binding and cleavage activity of some dioxidovanadium(V) complexes containing aroylhydrazones. J. Inorg. Biochem. 2015, 144, 1−12. (34) Baksi, S.; Acharyya, R.; Dutta, S.; Blake, A. J.; Drew, M. G. B.; Bhattacharya, S. Interaction of 2-(arylazo)phenols with rhodium. Usual coordination vs. C−H and C−C activation. J. Organomet. Chem. 2007, 692, 1025−1032. (35) APEX 2 − Suit of Crystallographic Software; Bruker AXS Inc.: Madison, Wisconsin, USA, 2008. (36) SAINT; Bruker AXS Inc.: Madison, Wisconsin, USA, 2008. (37) SADABS; Bruker AXS Inc.: Madison, Wisconsin, USA, 2008. (38) Hahn, T. Space-Group Symmetry, 4th ed.; Kluwer Academic Publishers: Dordrecht, 1996; Vol. A.

Structure, Solid State Magnetism, and Solution Spectroscopy. Inorg. Chem. 1995, 34, 466−472. (d) Dean, N. S.; Bond, M. R.; O'Connor, C. J.; Carrano, C. J. Structure and magnetism of dibridged vanadium(IV) hydrotris(pyrazolyl)borate dimers. Inorg. Chem. 1996, 35, 7643−7648. (e) del Rio, D.; Galindo, A.; Vicente, R.; Mealli, C.; Ienco, A.; Masi, D. Synthesis, molecular structure and properties of oxo-vanadium(IV) complexes containing the oxydiacetate ligand. Dalton Trans. 2003, 1813−1820. (f) Dutton, J. C.; Murray, K. S.; Tiekink, E. R. T. Magnetism of Oxovanadium(IV) Complexes of Binucleating Ligands. Oxidation to and Structure of a Mononuclear Oxovanadium(V) Complex of N,N′(pentan-3-ol)bis(salicylaldimine). Inorg. Chim. Acta 1989, 166, 5−8. (g) Musiani, M. M.; Milani, F.; Graziani, R.; Vidali, M.; Casellato, U.; Vigato, P. A. Synthesis and Catalytic Activity of Alkoxyoxovanadium(IV) Diketonates, Crystal and Molecular Structure of Bis-[Methoxyoxovanadium(IV) Acetylacetonate]. Inorg. Chim. Acta 1982, 61, 115−120. (h) Noshiranzadeh, N.; Emami, M.; Bikas, R.; Sanchiz, J.; Otręba, M.; Aleshkevych, P.; Lis, T. Synthesis, characterization and magnetic properties of a dinuclear oxidovanadium(IV) complex: Magneto-structural DFT studies on the effects of out-of-plane −OCH3 angle. Polyhedron 2017, 122, 194−202. (i) Sun, Y.; Melchior, M.; Summers, D. A.; Thompson, R. C.; Rettig, S. J.; Orvig, C. [(m-OCH3)VO(ma)]2, a Strongly Antiferromagnetic Oxovanadium(IV) Dimer. Inorg. Chem. 1998, 37, 3119−3121. (j) Yue, H.; Zhang, D.; Shi, Z.; Feng, S. Dinuclear oxovanadium(IV) compounds from designed amino acid derivatives. Inorg. Chim. Acta 2007, 360, 2681−2685. (24) (a) Garribba, E.; Micera, G.; Lodyga-Chruscinska, E.; Sanna, D. Oxovanadium(IV) Complexes with Pyrazinecarboxylic Acids:The Coordinating Properties of Ligands with the (Naromatic, COO−) Donor Set. Eur. J. Inorg. Chem. 2006, 2006, 2690−2700. (b) Syamal, A. Spin-spin coupling in oxovanadium(VI) complexes. Coord. Chem. Rev. 1975, 16, 309−339. (25) Plass, W. Magneto-Structural Correlations in Dinuclear d1-d1 Complexes: Structure and Magnetochemistry of Two Ferromagnetically Coupled Vanadium(IV) Dimers. Angew. Chem., Int. Ed. Engl. 1996, 35, 627−631. (26) Rodríguez-Fortea, A.; Alemany, P.; Alvarez, S.; Ruiz, E. A Theoretical Study of the Exchange Coupling in Hydroxo- and AlkoxoBridged Dinuclear Oxovanadium(IV) Compounds. Eur. J. Inorg. Chem. 2004, 2004, 143−153. (27) Plass, W. Oxovanadium(IV) Complexes with Multidentate Amine Alcohol Ligands: Magneto-structural Correlations for the {VO(μ-OR)2VO} Core. Z. Anorg. Allg. Chem. 1997, 623, 1290−1298. (28) (a) Tsaramyrsi, M.; Kaliva, M.; Salifoglou, A.; Raptopoulou, C. P.; Terzis, A.; Tangoulis, V.; Giapintzakis, J. Vanadium(IV)−Citrate Complex Interconversions in Aqueous Solutions. A pH-Dependent Synthetic, Structural, Spectroscopic, and Magnetic Study. Inorg. Chem. 2001, 40, 5772−5779. (b) Velayutham, M.; Varghese, B.; Subramanian, S. Magneto−Structural Correlation Studies of A Ferromagnetically Coupled Dinuclear Vanadium(IV) Complex. Single-Crystal EPR Study. Inorg. Chem. 1998, 37, 1336−1340. (29) Tsai, Y.-F.; Huang, G.-S.; Yang, C.-I.; Tsai, H.-L.; Liu, Y.-H.; Kuo, T.-S.; Hsu, H.-F. Dinuclear oxovanadium(IV) thiolate complexes with ferromagnetically coupled interaction between vanadium centers. Inorg. Chem. 2007, 46, 10467−10469. (30) (a) Pasayat, S.; Böhme, M.; Dhaka, S.; Dash, S. P.; Majumder, S.; Maurya, M. R.; Plass, W.; Kaminsky, W.; Dinda, R. Synthesis, Theoretical Study and Catalytic Application of Oxidometal (Mo or V) Complexes: Unexpected Coordination Due to Ligand Rearrangement through Metal-Mediated C−C Bond Formation. Eur. J. Inorg. Chem. 2016, 2016, 1604−1618. (b) Mohammadnezhad, G.; Böhme, M.; Geibig, D.; Burkhardt, A.; Goerls, H.; Plass, W. Chiral vanadium(V) complexes with 2-aminoglucose Schiff-base ligands and their solution configurations: synthesis, structures, and DFT calculations. Dalton Trans. 2013, 42, 11812−11823. (c) Dash, S. P.; Pasayat, S.; Saswati; Dash, H. R.; Das, S.; Butcher, R. J.; Dinda, R. Oxovanadium(V) complexes incorporating tridentate aroylhydrazoneoximes: Synthesis, characterizations and antibacterial activity. Polyhedron 2012, 31, 524− 529. (d) Dinda, R.; Majhi, P. K.; Sengupta, P.; Pasayat, S.; Ghosh, S.; M


Article

Inorganic Chemistry (39) Sheldrick, G. M. A short history of SHELX. Acta Crystallogr., Sect. A: Found. Crystallogr. 2008, 64, 112−122. (40) Wilson, A. J. C. International Tables for Crystallography; Kluwer, Academic Publishers: Dordrecht, 1992; Vol. C. (41) Brandenburg, K. Diamond − Crystal and Molecular Visualization; Crystal Impact: Bonn, Germany, 2006. (42) Macrae, C. F.; Bruno, I. J.; Chisholm, J. A.; Edgington, P. R.; McCabe, P.; Pidcock, E.; Rodriguez-Monge, L.; Taylor, R.; van de Streek, J.; Wood, P. A. Mercury CSD 2.0 - new features for the visualization and investigation of crystal structures. J. Appl. Crystallogr. 2008, 41, 466−470. (43) (a) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L.; Giacovazzo, C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna, R. SIR97: a new tool for crystal structure determination and refinement. J. Appl. Crystallogr. 1999, 32, 115−119. (b) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A. Completion and refinement of crystal structures with SIR92. J. Appl. Crystallogr. 1993, 26, 343−350. (44) (a) Sheldrick, G. M. SHELXL-97: Program for the Refinement of Crystal Structures; University of Göttingen: Göttingen, Germany, 1997. (b) Mackay, S.; Edwards, C.; Henderson, A.; Gilmore, C.; Stewart, N.; Shankland, K.; Donald, A. MaXus: A Computer Program for the Solution of Crystal Structures from Diffraction Data; University of Glasgow: Scotland, 1997. (45) Waasmaier, D.; Kirfel, A. New analytical scattering-factor functions for free atoms and ions. Acta Crystallogr., Sect. A: Found. Crystallogr. 1995, 51, 416−431. (46) Spielberg, E. T.; Gilb, A.; Plaul, D.; Geibig, D.; Hornig, D.; Schuch, D.; Buchholz, A.; Ardavan, A.; Plass, W. A spin-frustrated trinuclear copper complex based on triaminoguanidine with an energetically well-separated degenerate ground state. Inorg. Chem. 2015, 54, 3432−3438. (47) (a) Turbomole 6.6; A development of University of Karlsruhe and Forschungszentrum Karlsruhe GmbH, 1989−2007; Turbomole GmbH, 2014; available from http://www.turbomole.com. (b) Ahlrichs, R.; Bär, M.; Häser, M.; Horn, H.; Kölmel, C. Electronic structure calculations on workstation computers: The program system TURBOMOLE. Chem. Phys. Lett. 1989, 162, 165−169. (48) (a) Perdew, J. P. Density-functional approximation for the correlation energy of the inhomogeneous electron gas. Phys. Rev. B: Condens. Matter Mater. Phys. 1986, 33, 8822−8824. (b) Becke, A. D. Density-functional exchange-energy approximation with correct asymptotic behavior. Phys. Rev. A: At., Mol., Opt. Phys. 1988, 38, 3098−3100. (49) (a) Schäfer, A.; Horn, H.; Ahlrichs, R. Fully optimized contracted Gaussian basis sets for atoms Li to Kr. J. Chem. Phys. 1992, 97, 2571−2577. (b) Weigend, F.; Häser, M.; Patzelt, H.; Ahlrichs, R. RI-MP2: optimized auxiliary basis sets and demonstration of efficiency. Chem. Phys. Lett. 1998, 294, 143−152. (c) Weigend, F.; Ahlrichs, R. Balanced basis sets of split valence, triple zeta valence and quadruple zeta valence quality for H to Rn: Design and assessment of accuracy. Phys. Chem. Chem. Phys. 2005, 7, 3297−3305. (50) (a) Baerends, E. J.; Ellis, D. E.; Ros, P. Self-consistent molecular Hartree-Fock-Slater calculations I. The computational procedure. Chem. Phys. 1973, 2, 41−51. (b) Whitten, J. L. Coulombic potential energy integrals and approximations. J. Chem. Phys. 1973, 58, 4496− 4501. (c) Dunlap, B. I.; Connolly, J. W. D.; Sabin, J. R. On some approximations in applications of Xa theory. J. Chem. Phys. 1979, 71, 3396−3402. (d) Van Alsenoy, C. Ab initio calculations on large molecules: The multiplicative integral approximation. J. Comput. Chem. 1988, 9, 620−626. (51) Yamaguchi, K.; Tsunekawa, T.; Toyoda, Y.; Fueno, T. Ab initio molecular orbital calculations of effective exchange integrals between transition metal ions. Chem. Phys. Lett. 1988, 143, 371−376. (52) Becke, A. D. Density-functional thermochemistry. III. The role of exact exchange. J. Chem. Phys. 1993, 98, 5648−5652. (53) Lee, C.; Yang, W.; Parr, R. G. Development of the Colle-Salvetti correlation-energy formula into a functional of the electron density. Phys. Rev. B: Condens. Matter Mater. Phys. 1988, 37, 785−789.

(54) Tao, J. M.; Perdew, J. P.; Staroverov, V. N.; Scuseria, G. E. Climbing the density functional ladder: Nonempirical meta-generalized gradient approximation designed for molecules and solids. Phys. Rev. Lett. 2003, 91, 146401. (55) Reed, A. E.; Weinstock, R. B.; Weinhold, F. Natural population analysis. J. Chem. Phys. 1985, 83, 735−746. (56) Serpe, L.; Catalano, M. G.; Cavalli, R.; Ugazio, E.; Bosco, O.; Canaparo, R.; Muntoni, E.; Frairia, R.; Gasco, M. R.; Eandi, M.; Zara, G. P. Cytotoxicity of anticancer drugs incorporated nanoparticles on HT-29 colorectal cancer in solid lipid cell line. Eur. J. Pharm. Biopharm. 2004, 58, 673−680. (57) Wang, X.; Tanaka, M.; Krstin, S.; Peixoto, H. S.; Moura, C. C. d. M.; Wink, M. Cytoskeletal interference - A new mode of action for the anticancer drugs camptothecin and topotecan. Eur. J. Pharmacol. 2016, 789, 265−274. (58) (a) Zeleňaḱ , V.; Vargová, Z.; Györyová, K. Correlation of infrared spectra of zinc(II) carboxylates with their structures. Spectrochim. Acta, Part A 2007, 66, 262−272. (b) Halder, S.; Drew, M. G. B.; Bhattacharya, S. Palladium and platinum complexes of 2-(2′carboxyphenylazo)-4-methylphenol: Synthesis, structure and spectral properties. J. Chem. Sci. 2008, 120, 441−446. (59) (a) Selbin, J. Oxovanadium(IV) Complexes. Coord. Chem. Rev. 1966, 1, 293−314. (b) Hamilton, D. E. Reinvestigation VanadiumOxygen Stretch in the IR Spectrum of Bis[N-(4-chlorophenyl)salicylideneaminato]oxovanadium (IV). Inorg. Chem. 1991, 30, 1670− 1671. (c) Copeland, E. P.; Kahwa, I. A.; Mague, J. T.; McPherson, G. L. Novel mixed-valence vanadium(IV/V) molecule exhibiting unusual electron delocalization over the [V2O3]3+ core. J. Chem. Soc., Dalton Trans. 1997, 2849−2852. (d) Bhattacharyya, S.; Mukhopadhyay, S.; Samanta, S.; Weakley, T. J. R.; Chaudhury, M. Synthesis, Characterization, and Reactivity of Mononuclear O,N-Chelated Vanadium(IV) and -(III) Complexes of Methyl 2-Aminocyclopent-1-ene-1-dithiocarboxylate Based Ligand: Reporting an Example of Conformational Isomerism in the Solid State. Inorg. Chem. 2002, 41, 2433−2440. (e) Melchior, M.; Thompson, K. H.; Jong, J. M.; Rettig, S. J.; Shuter, E.; Yuen, V. G.; Zhou, Y.; McNeill, J. H.; Orvig, C. Vanadium Complexes as Insulin Mimetic Agents: Coordination Chemistry and in Vivo Studies of Oxovanadium(IV) and Dioxovanadate(V) Complexes Formed from Naturally Occurring Chelating Oxazolinate, Thiazolinate, or Picolinate Units. Inorg. Chem. 1999, 38, 2288−2293. (f) Dinda, R.; Sengupta, P.; Ghosh, S.; Mak, T. C. W. Valence delocalization in a mixed-oxidation divanadium (IV, V) complex electrogenerated from its structurally characterized divanadium (V) analogue with a tridentate (ONO) ligand. Inorg. Chem. 2002, 41, 1684−1688. (g) Dinda, R.; Sengupta, P.; Sutradhar, M.; Mak, T. C. W.; Ghosh, S. Solution study of a structurally characterized monoalkoxo-bound monooxo-vanadium(V) complex: Spontaneous generation of the corresponding oxobridged divanadium(V,V) complex and its electroreduction to a mixed-valence species in solution. Inorg. Chem. 2008, 47, 5634−5640. (60) Li, Y. T.; Yan, C. W.; Guo, B. R.; Liao, D. Z. Synthesis, characterization and magnetic properties of novel m-isophthalato oxovanadium(IV) binuclear complexes. Polyhedron 1997, 16, 4379− 4384. (61) (a) Chatterjee, P. B.; Bhattacharya, S.; Audhya, A.; Choi, K.-Y.; Endo, A.; Chaudhury, M. Coordination Asymmetry in Divanadium(V) Compounds Containing a V2O3 Core: Synthesis, Characterization, and Redox Properties. Inorg. Chem. 2008, 47, 4891−4902. (b) Plass, W. Oxovanadium(IV) and -(V) complexes with aminoalcohol ligands: Synthesis, structure, electrochemical, and magnetic properties. Eur. J. Inorg. Chem. 1998, 1998, 799−805. (62) Smith, K. I.; Borer, L. L.; Olmstead, M. M. Vanadium(IV) and Vanadium(V) Complexes of Salicyladimine Ligands. Inorg. Chem. 2003, 42, 7410−7415. (63) Aristov, N.; Habekost, A. Cyclic Voltammetry - A Versatile Electrochemical Method Investigating Electron Transfer Processes. World J. Chem. Educ. 2015, 3, 115−119. (64) Addison, A. W.; Rao, T. N.; Reedijk, J.; van Rijn, J.; Verschoor, G. C. Synthesis, structure, and spectroscopic properties of copper(II) N


Article

Inorganic Chemistry compounds containing nitrogen-sulphur donor ligands; the crystal and molecular structure of aqua[1,7-bis(N-methylbenzimidazol-2′-yl)-2,6dithiaheptane]copper(II) perchlorate. J. Chem. Soc., Dalton Trans. 1984, 1349−1356. (65) (a) Tarlton, M. L.; Anderson, A. E.; Weberski, M. P., Jr.; RiartFerrer, X.; Nelson, B. M.; McLauchlan, C. C. Synthesis, characterization, and electrochemical properties of m-oxalate bridged vanadium(III) and (IV) dimers incorporating the Kläui ligand, (CpPORCo (R = Me, Et). Inorg. Chim. Acta 2014, 420, 159−165. (b) Kanmani Raja, K.; Lekha, L.; Hariharan, R.; Easwaramoorthy, D.; Rajagopal, G. Synthesis, structural, spectral, electrochemical and catalytic properties of VO (IV) complexes containing N, O donors. J. Mol. Struct. 2014, 1075, 227− 233. (c) Sartzi, H.; Stoumpos, C. C.; Giouli, M.; Verginadis, I. I.; Karkabounas, S. C.; Cunha-Silva, L.; Escuer, A.; Perlepes, S. P. The ″periodic table″ of di-2-pyridyl ketone: vanadium complexes. Dalton Trans. 2012, 41, 11984−11988. (d) Hanninen, M. M.; Peuronen, A.; Damlin, P.; Tyystjarvi, V.; Kivela, H.; Lehtonen, A. Vanadium complexes with multidentate amine bisphenols. Dalton Trans. 2014, 43, 14022−14028. (66) (a) Plass, W.; Yozgatli, H. P. Synthesis, reactivity, and structural characterization of dioxovanadium(V) complexes with tridentate Schiff base ligand: Vanadium complexes in supramolecular networks. Z. Anorg. Allg. Chem. 2003, 629, 65−70. (b) Buchholz, A.; Nica, S.; Debel, R.; Fenn, A.; Breitzke, H.; Buntkowsky, G.; Plass, W. Vanadium complexes with side chain functionalized N-salicylidene hydrazides: Hydrogen-bonding relays as structural directive for supramolecular interactions. Inorg. Chim. Acta 2014, 420, 166−176. (67) Plass, W. Competing Magnetic Exchange Interactions in Tetranuclear d1 Systems: Synthesis, Structure, and Magnetochemistry of a Neutral Vanadium(IV) Complex with a {(VO)4(m3-OR)2(m2OR)4}2+ Core. Inorg. Chem. 1997, 36, 2200−2205. (68) Cramer, C. J.; Truhlar, D. G. Density functional theory for transition metals and transition metal chemistry. Phys. Chem. Chem. Phys. 2009, 11, 10757−10816. (69) Jensen, K. P. Bioinorganic Chemistry Modeled with the TPSSh Density Functional. Inorg. Chem. 2008, 47, 10357−10365. (70) Majumder, S.; Pasayat, S.; Panda, A. K.; Dash, S. P.; Roy, S.; Biswas, A.; Varma, M. E.; Joshi, B. N.; Garribba, E.; Kausar, C.; Patra, S. K.; Kaminsky, W.; Crochet, A.; Dinda, R. Monomeric and Dimeric Oxidomolybdenum(V and VI) Complexes, Cytotoxicity, and DNA Interaction Studies: Molybdenum Assisted CN Bond Cleavage of Salophen Ligands. Inorg. Chem. 2017, 56, 11190−11210. (71) (a) El-Awady, R. A.; Semreen, M. H.; Saber-Ayad, M. M.; Cyprian, F.; Menon, V.; Al-Tel, T. H. Modulation of DNA damage response and induction of apoptosis mediates synergism between doxorubicin and a new imidazopyridine derivative in breast and lung cancer cells. DNA Repair 2016, 37, 1−11. (b) Jordan, M. A.; Wilson, L. Microtubules and actin filaments: dynamic targets for cancer chemotherapy. Curr. Opin. Cell Biol. 1998, 10, 123−130. (72) Siddik, Z. H. Cisplatin: mode of cytotoxic action and molecular basis of resistance. Oncogene 2003, 22, 7265−7279. (73) Temperini, C.; Messori, L.; Orioli, P.; Bugno, C. D.; Animati, F.; Ughetto, G. The crystal structure of the complex between a disaccharide anthracycline and the DNA hexamer d(CGATCG) reveals two different binding sites involving two DNA duplexes. Nucleic Acids Res. 2003, 31, 1464−1469. (74) Wani, M. C.; Taylor, H. L.; Wall, M. E.; Coggon, P.; McPhail, A. T. Plant antitumor agents. VI. Isolation and structure of taxol, a novel antileukemic and antitumor agent from Taxus brevifolia. J. Am. Chem. Soc. 1971, 93, 2325−2327. (75) Jordan, M. A.; Wilson, L. Microtubules as a target for anticancer drugs. Nat. Rev. Cancer 2004, 4, 253−265. (76) Sasse, F.; Kunze, B.; Gronewold, T. M. A.; Reichenbach, H. The chondramides: Cytostatic agents from myxobacteria acting on the actin cytoskeleton. J. Natl. Cancer Inst. 1998, 90, 1559−1563. (77) Cooper, J. A. Effects of Cytoshalasin and Phalloidin on Actin. J. Cell Biol. 1987, 105, 1473−1478. (78) (a) Lee, E. A.; Keutmann, M. K.; Dowling, M. L.; Harris, E.; Chan, G.; Kao, G. D. Inactivation of the mitotic checkpoint as a

determinant of the efficacy of microtubule-targeted drugs in killing human cancer cells. Mol. Cancer Ther. 2004, 3, 661−669. (b) Nair, H. K.; Rao, K. V. K.; Aalinkeel, R.; Mahajan, S.; Chawda, R.; Schwartz, S. A. Inhibition ofPprostate Cancer Cell Colony Formation by the Flavonoid Quercetin Correlates with Modulation of Specific Regulatory Genes. Clin. Diagn. Lab. Immunol. 2004, 11, 63−69. (c) Stehn, J. R.; Haass, N. K.; Bonello, T.; Desouza, M.; Kottyan, G.; Treutlein, H.; Zeng, J.; Nascimento, P. R. B. B.; Sequeira, V. B.; Butler, T. L.; Allanson, M.; Fath, T.; Hill, T. A.; McCluskey, A.; Schevzov, G.; Palmer, S. J.; Hardeman, E. C.; Winlaw, D.; Reeve, V. E.; Dixon, I.; Weninger, W.; Cripe, T. P.; Gunning, P. W. A Novel Class of Anticancer Compounds Targets the Actin Cytoskeleton in Tumor Cells. Cancer Res. 2013, 73, 5169−5182. (79) (a) Reytman, L.; Braitbard, O.; Tshuva, E. Y. Highly cytotoxic vanadium(V) complexes of salan ligands; insights on the role of hydrolysis. Dalton Trans. 2012, 41, 5241−5247. (b) Lewis, A. D.; Forrester, L. M.; Hayes, J. D.; Wareing, C. J.; Carmichael, J.; Harris, A. L.; Mooghen, M.; Wolf, C. R. Glutathione S-transferase isoenzymes in human tumors and tumor derived cell-lines. Br. J. Cancer 1989, 60, 327−331. (c) Takara, K.; Sakaeda, T.; Yagami, T.; Kobayashi, H.; Ohmoto, N.; Horinouchi, M.; Nishiguchi, K.; Okumura, K. Cytotoxic effects of 27 anticancer drugs in HeLa and MDR1-overexpressing derivative cell lines. Biol. Pharm. Bull. 2002, 25, 771−778. (d) Petinari, L.; Kohn, L. K.; de Carvalho, J. E.; Genari, S. C. Cytotoxicity of tamoxifen in normal and tumoral cell lines and its ability to induce cellular transformation in vitro. Cell Biol. Int. 2004, 28, 531−539. (80) Pasayat, S.; Dash, S. P.; Majumder, S.; Dinda, R.; Sinn, E.; Stoeckli-Evans, H.; Mukhopadhyay, S.; Bhutia, S. K.; Mitra, P. Synthesis, structure, characterization and study of antiproliferative activity of dimeric and tetrameric oxidomolybdenum(VI) complexes of N,N′-disalicyloylhydrazine. Polyhedron 2014, 80, 198−205. (81) Saswati; Chakraborty, A.; Dash, S. P.; Panda, A. K.; Acharyya, R.; Biswas, A.; Mukhopadhyay, S.; Bhutia, S. K.; Crochet, A.; Patil, Y. P.; Nethaji, M.; Dinda, R. Synthesis, X-ray structure and in vitro cytotoxicity studies of Cu(I/II) complexes of thiosemicarbazone: special emphasis on their interactions with DNA. Dalton Trans. 2015, 44, 6140−6157. (82) Banerjee, S.; Hussain, A.; Prasad, P.; Khan, I.; Banik, B.; Kondaiah, P.; Chakravarty, A. R. Photocytotoxic Oxidovanadium(IV) Complexes of Polypyridyl Ligands Showing DNA-Cleavage Activity in Near-IR Light. Eur. J. Inorg. Chem. 2012, 2012, 3899−3908. (83) Balaji, B.; Balakrishnan, B.; Perumalla, S.; Karande, A. A.; Chakravarty, A. R. Photoactivated cytotoxicity of ferrocenyl-terpyridine oxovanadium(IV) complexes of curcuminoids. Eur. J. Med. Chem. 2014, 85, 458−467. (84) Lewis, N. A.; Liu, F.; Seymour, L.; Magnusen, A.; Erves, T. R.; Arca, J. F.; Beckford, F. A.; Venkatraman, R.; Gonzalez-Sarrias, A.; Fronczek, F. R.; VanDerveer, D. G.; Seeram, N. P.; Liu, A.; Jarrett, W. L.; Holder, A. A. Synthesis, Characterisation, and Preliminary In Vitro Studies of Vanadium(IV) Complexes with a Schiff Base and Thiosemicarbazones as Mixed Ligands. Eur. J. Inorg. Chem. 2012, 2012, 664−677.

O


Anionic Dinuclear Oxidovanadium(IV) Complexes with Azo

Recommend Documents