This is an open access article published under an ACS AuthorChoice License, which permits copying and redistribution of the article or any adaptations for non-commercial purposes.
Article Cite This: ACS Omega 2017, 2, 7803-7811
http://pubs.acs.org/journal/acsodf
Supramolecular Assembly of Uridine Monophosphate (UMP) and Thymidine Monophosphate (TMP) with a Dinuclear Copper(II) Receptor Md Mhahabubur Rhaman,† Douglas R. Powell,‡ and Md. Alamgir Hossain*,† †
Department of Chemistry and Biochemistry, Jackson State University, Jackson, Mississippi 39217, United States Department of Chemistry and Biochemistry, University of Oklahoma, Norman, Oklahoma 73019, United States
‡
S Supporting Information *
ABSTRACT: Understanding the intermolecular interactions between nucleotides and artificial receptors is crucial to understanding the role of nucleic acids in living systems. However, direct structural evidence showing precise interactions and bonding features of a nucleoside monophosphate (NMP) with a macrocycle-based synthetic molecule has not been provided so far. Herein, we present two novel crystal structures of uridine monophosphate (UMP) and thymidine monophosphate (TMP) complexes with a macrocycle-based dinuclear receptor. Structural characterization of these complexes reveals that the receptor recognizes UMP through coordinate−covalent interactions with phosphates and π−π stackings with nucleobases and TMP through coordinate−covalent interactions with phosphate groups. Furthermore, the receptor has been shown to effectively bind nucleoside monophosphates in the order of GMP > AMP > UMP > TMP > CMP in water at physiological pH, as investigated by an indicator displacement assay.
■
and salt bridges between the nucleotide and the protein.46 However, to the best of our knowledge, a crystallographically characterized NMP complex with a macrocycle-based synthetic receptor has not been reported yet. Most of the synthetic receptors for nucleotides are mainly based on the construction of recognition sites with positive charges from polyazamacrocycles that have been shown to be capable of binding nucleotides19−21,47−52 and of numerous catalytic activities, including hydrolase, phosphatase, and kinase activity.53−57 Their interactions, however, occur primarily through hydrogen bonding or electrostatic interactions between the charged groups and the phosphate moieties of nucleotides, which often depend on the pH of the solution. On the other hand, macrocycle-based dinuclear metal complexes are attractive hosts that have shown to bind nucleotides through Lewis acid/base (coordinate−covalent) interactions in water at physiological pH.58−64 Fabbrizzi and co-workers synthesized an expanded dinuclear cryptate that contains two copper(II) ions as binding sites to selectively recognize GMP with respect to other NMPs in MeOH/water solution.63 It was suggested that in addition to phosphate groups, enolate oxygen atoms of GMP formed bonds with the metal centers. Hydrazone-based dinuclear copper(II) complexes recently synthesized by
INTRODUCTION In recent years, there has been a growing interest in designing artificial receptors that recognize nucleotides as target substrates,1−27 with the goal to mimic their biological interactions with enzymes.25,28 Nucleotides are the fundamental building blocks of DNA and RNA, playing many critical roles in biology. For instance, adenosine triphosphate (ATP) is used in generating universal chemical energy for cellular functions, guanosine triphosphate (GTP) is involved in the synthesis of DNA and proteins, and uridine monophosphate (UMP) is the central building block in the synthesis of RNA.29,30 Although an abundance of information is available on solution binding studies and theoretical calculations predicting the binding modes of nucleotides,4−26 structural reports of nucleotide complexes with synthetic receptors are indeed limited.31−40 In 2008, Bianchi and co-workers reported the first structure of a nucleoside triphosphate complex with a synthetic receptor, showing hydrogen bonding and π−π stacking interactions between a thymidine 5′-triphosphate and a polyamine-based receptor.31 Several structures of nucleotides, nucleosides, or nucleobases as pure or mixed ligands with transition metal ions were also reported.32−40 In particular, the central role played by nucleoside monophosphates (NMPs) in many biological events makes them attractive targets for mimicking their biological interactions.41−46 For instance, as characterized by X-ray analysis, UMP was found within the cavity of a Bacillus subtilis orotidine 5′-monophosphate decarboxylase via hydrogen bonds © 2017 American Chemical Society
Received: September 3, 2017 Accepted: October 31, 2017 Published: November 10, 2017 7803
DOI: 10.1021/acsomega.7b01293 ACS Omega 2017, 2, 7803−7811
ACS Omega
Article
Dharmaraj and co-workers have been shown to bind DNA via an intercalative mode.64 Even though several transition metal complexes have been employed for nucleotide complexation, the design of artificial receptors that effectively recognize nucleotides in water at neutral pH still remains a challenge. Recently, we have been interested in simple and easily synthesizable macrocycle-based dinuclear complexes as probes for anion recognition, which are expected to be more flexible than their bicyclic analogues, thereby allowing them to interact with anions of variable shapes and sizes.65−68 As learned from nature,42−46 an ideal receptor for nucleotide binding should be designed on a multipoint recognition strategy to bind phosphate and aromatic base simultaneously. Herein, we describe a macrocyclic dinuclear copper(II) receptor 1 that possesses two metal centers and two aromatic groups, providing effective binding sites for multipoint recognition of NMPs (Chart 1). We have structurally
Figure 1. Crystal structure of [1·Br2]2+ (where 1 = [CuII2(L)]4+) (see Chart 1).
coordinated with three macrocyclic nitrogens and one bromide in a square planar coordination environment. The two square planes remaining on the same side are approximately parallel with respect to each other, thus allowing the macrocycle to adopt a rigid boat-like structure. The Cu−Br distances are almost equal, with Cu−Br distances of 2.5705(17)−2.5582(17) Å. The bonded bromides are in equatorial positions, as opposed to the previously reported complex [CuII2(L)Br3(H2O)]+ in which one bromide coordinated to a copper ion in a square pyramidal geometry with an elongated Cu−Br bond (Cu−Br = 2.959(4)).65 The remaining two bromides (Br3 and Br4) are outside the cavity interacting with the secondary nitrogen atoms (N4 and N19) via NH···Br interactions. Thus, the receptor incorporates positive charges and planar hydrophobic groups as potential binding sites. UMP Complex of 1. The treatment of the receptor 1 with 2 equiv of Na2UMP in H2O/dimethyl sulfoxide (DMSO) (2:1, v/v) yielded suitable crystals for X-ray analysis. Structural analysis by single crystal X-ray diffraction reveals that the asymmetric unit of the complex contains two macrocycles, four CuII ions, and four UMP groups, providing two nearly identical UMP-bound units connected through phosphate groups (Figure 2a). The macrocycles are faced in opposite directions, whereas both UMP groups remain on the same side of each macrcocycle. Clearly, two coordinating bromides in [1·Br2]2+ (Figure 1) are exchanged with two UMP guests, forming the receptor−UMP complex. As shown in Figure 1b, two UMP units in their anionic forms are coordinated to the macrocyclic host through metal−ligand bonds, showing a folded conformation with aromatic spacers between the copper binding sites. The noteworthy feature of this structure is that each UMP binds to the receptor via two types of intermolecular interactions: (i) traditional metal−ligand (coordinate−covalent) interaction between CuII and phosphate and (ii) face-toface π−π stacking (centroid−centroid distances = 3.61−3.63 Å)69 between one aromatic ring of 1 and the uracil base (pyrimidine-2,4-dione) of UMP. The two aromatic rings are slightly shifted with respect to each other with a dihedral angle of 4.97 (1)°. Such an assembled complex of NMP with a synthetic receptor exhibiting multipoint recognition has not been structurally characterized before. The X-ray structure of the protein−DNA complex reported earlier showed similar types of interactions in which four positively charged groups on the protein (Arg 16, 21, 80 and Lys 46) exhibited strong electrostatic interactions with the DNA phosphates.70 Four aromatic residues (Tyr 26, 34, 41 and Phe 73) interacted via π−π stackings with each of the five nucleotide bases. In the complex [1·(UMP)2]2, each CuII is coordinated with three macrocyclic N atoms and two anionic O atoms in a
Chart 1. Chemical Structures of the Free Macrocycle L, Receptor 1 and Eosin Y (EY)
characterized two NMP complexes: one with UMP and the other with thymidine monophosphate (TMP), showing multipoint recognition with a dinuclear copper(II) receptor 1. The receptor and NMP alternatively assemble into a onedimensional chain through bonds between the phosphates and the metal ions.
■
RESULTS AND DISCUSSION Synthesis. The receptor 1 was synthesized from the reaction of L with 2 equiv of CuBr2 in H2O, as described previously.65 The molecule was characterized by single crystal X-ray diffraction analysis, confirming the formation of a dinuclear complex, as shown in Figure 1. Numerous attempts to obtain crystals of 1 with different nucleotides provided two X-ray quality crystals of UMP and TMP complexes that were grown from an aqueous solution of 1 containing 2 equiv of UMP and TMP, respectively. The isolated crystals were found to be stable at room temperature and characterized by single crystal X-ray diffraction analysis. Crystal Structure Analysis. Receptor 1. Structural analysis of the dinuclear copper complex (1) reveals that it crystallizes in the triclinic space group P1, with two CuII ions at both ends of the macrocycle, forming a dinuclear complex. As shown in Figure 2, the macrocycle is folded, where each CuII is 7804
DOI: 10.1021/acsomega.7b01293 ACS Omega 2017, 2, 7803−7811
ACS Omega
Article
Figure 2. Crystal structures of UMP complex with 1: (a) asymmetric unit of [1·(UMP)2]2, (b) single macrocyclic unit showing [1·(UMP)2] motif, and (c) assembled UMP complex showing a chain along the c axis. Hydrogen atoms and external solvent molecules are omitted for clarity.
thymine base. A similar steric effect of methyl groups was also predicted theoretically for the binding of thymine and uracil with a cholesterol-armed triazacyclononane.71 In crystals, each TMP serves as a linker of two macrocyclic units through phosphate and copper bonds. Notably, in both cases, the receptor and the NMP alternatively assemble into a onedimensional supramolecular polymer, forming a 1-D chain through bonds between phosphates and metal ions (Figures 2c and 3c). Fluorescence Binding Studies Based on IDA Mechanism. An indicator displacement assay that was first employed by Anslyn in anion binding chemistry72 was used to examine the binding ability of the receptor 1 (in the form of [Cu2LBr4]) for nucleoside monophosphates (NMPs) in solution. As shown in Figure 4, upon the increasing addition of 1 (2.0 × 10−4 M) to EY (eosin Y, 2.0 × 10−6 M) in water buffered with 20 mM HEPES at pH 7.4, the fluorescence intensity (I) gradually decreased possibly due to the Lewis acid−base interactions between the host and the negatively charged EY. The addition of 5 equiv of 1 to EY resulted in an almost complete quenching of the emission (fluorescent OFF). This phenomenon is attributed to the formation of a receptor−indicator complex (1· EY) that quenches the excited state of EY through an energytransfer process.66 The change in the fluorescence intensity (I/ I0) was analyzed by a nonlinear regression method, which gave
square pyramidal coordination environment. The distances of Cu···O bonds are 1.921(9) (Cu1···OIC) and 1.915(9) Å (Cu2···O1D), which are comparable to the corresponding distances reported for a copper complex with 5′-UMP (1.92(1) and 1.93(1) Å).32 Two uracil bases of the coordinated nucleotides in the complex are stacked with the aromatic rings of the receptor in a sandwich fashion (Figure 2c). Thus, this particular geometrical conformation of the receptor makes it ideal to recognize two UMPs, providing an example of a structurally characterized macrocycle-based nucleoside complex. TMP Complex of 1. We were also successful in growing Xray quality crystals of 1 with TMP from the treatment of 1 with 2 equiv of Na2TMP in water. As shown in Figure 3a, the structural aspects of this crystal are nearly similar to that of the UMP complex, containing two macrocycles, four CuII ions, and four TMP, whereas two nearly identical TMP-bound units are connected through phosphate groups of TMP in an asymmetric unit. Figure 3b shows the structural motif of a single macrocyclic unit as [1·(TMP)2], with two coordinating TMP groups on the same side of the folded macrocycle. However, as opposed to the 1-UMP complex exhibiting strong π−π interactions, there are no such interactions between the receptor’s rings and the thymine base (5-thethylpyrimidine2,4-dione) in the 1-TMP complex. This could be possibly due to the steric effect of the methyl group that is present on the 7805
DOI: 10.1021/acsomega.7b01293 ACS Omega 2017, 2, 7803−7811
ACS Omega
Article
Figure 3. Crystal structure of TMP complex of 1: (a) asymmetric unit of [1·(TMP)2]2, (b) single macrocyclic unit showing [1·(TMP)2] motif, and (c) assembled TMP complex showing a chain along the a axis. Hydrogen atoms and external solvent molecules are omitted for clarity.
The complex 1·EY was then investigated for its potential to bind several NMPs including UMP, GMP, AMP, TMP, and CMP in water at pH = 7.4. As depicted in Figure 5, the addition of UMP (2.0 × 10−3 M) to 1·EY (1/EY = 2:1, [EY]0 =2.0 × 10−6 M) led to a complete restoration of fluorescence intensity of EY. This observation suggests the formation of a receptor− UMP complex while the bound dye EY releases from 1·EY to the solution, as signaled by the fluorescence enhancement (fluorescent ON). Similar fluorescence enhancement was also observed on the addition of other analytes to 1·EY (Supporting Information). Analysis of the titration data from the fitting of I/ I0 with [anion]0/[1·EY]0 suggested the formation of a 1:1 complex. The calculated conditional constants (Kcon) for [1·EY + anion = 1·anion + EY], which are dependent on the experimental conditions, are listed in Table 1, showing the binding strength in the order of GMP > AMP > UMP > TMP > CMP. For comparison, we also investigated the binding interactions of 1·EY for ADP (as diphosphate), ATP (as triphosphate), and inorganic phosphate. The chemosensor showed a strong binding affinity (log Kcon) in the range from 5.12 (3) to 5.23 (3) toward GMP, UMP, and AMP, as compared to that of other anions included. However, no
Figure 4. Decrease of fluorescence intensity of EY upon the gradual addition of 1 in water at pH 7.4. λex = 470 nm, λem = 537 nm. The inset shows the titration plot of I/I0 against [1]0/[EY]0.
the best fit with a 1:1 binding model,73 yielding the association constant of 5.17 (in log K). 7806
DOI: 10.1021/acsomega.7b01293 ACS Omega 2017, 2, 7803−7811
ACS Omega
Article
Figure 5. Enhancement of fluorescence intensity of 1·EY upon the addition of UMP (a) and TMP (b) in water at pH 7.4. λex = 470 nm, λem = 537 nm. The insets show the titration plot of I/I0 against [NMP]0/[1·EY]0.
of the methyl group present on the thymine base (Figure 3a). However, the solution binding model is in contrast to that observed in the solid states for UMP or TMP, where suitable crystals of the NMP complexes were obtained under different conditions. Such discrepancy in anion binding modes in the solid state and solution was reported in the literature.74,75 It is important to note that at this pH, an NMP may be present as different species (e.g., diprotonated or monoprotonated); thus, this value may not account for the ionic state used for the titration or present in crystals. The results indicate that the ensemble 1·EY shows potential to act as a “fluorescent OFF− ON” probe for the fluorescence sensing of biologically relevant anions. A similar ensemble of [Ni2L(H2O)6]4+ with EY was previously reported that selectively binds biologically relevant oxalate anions, displaying the sharp color change in water at physiological pH.67
Table 1. Conditional Constants (Kcon) for Various Anions for the Equilibrium: 1·EY + Anion = 1·Anion + EY, As Measured by the Indicator Displacement Assay in Water at pH 7.4a anionb
log Kcon
GMP AMP UMP TMP CMP ADP ATP HPO42−
5.23(3) 5.18(2) 5.12(3) 4.78(3) 4.71(3) 5.00(2) 4.92(3) 4.10(2)
a
Error limit in Kcon was less that 15%, which was based on the standard deviation from the fit of experimental values. bGMP = guanosine monophosphate, AMP = adenosine monophosphate, UMP = uridine triphosphate, TMP = thymidine Monophosphate, CMP = cytidine monophosphate, ADP = adenosine diphosphate, and ATP = adenosine triphosphate.
■
CONCLUSIONS
We have shown that a dinuclear receptor possessing multipoint binding sites recognizes UMP via coordinate−covalent interactions for phosphates and hydrophobic π−π stackings for aromatic bases and TMP via coordinate−covalent interactions for phosphates, resulting in the formation of two rare examples of NMP complexes with a macrocycle-based artificial receptor. The structures clearly show the intermolecular bonding features between two discrete molecules, mimicking nucleotide−protein interactions, for example, in B. subtilis orotidine 5′-monophosphate decarboxylase,46 in ribonucleotide reductases of Salmonella typhimurium,42 and in single-stranded DNA with G5BP of bacteriophage fd.70 In addition, the receptor has been successfully employed in an indicator displacement approach72 for fluorescence sensing of nucleoside monophosphates in water at physiological pH. Understanding the interactions between nucleotides and synthetic receptors is a key step toward understanding the functions of nucleic acids in life. Taken together, these findings may be useful in developing highly sensitive molecular sensors for living cells19,20 and in drug design for biomedical applications.64,76,77
interactions were observed for nucleosides, such as adenosine, uridine, guanosine, cytidine, and thymidine, suggesting that the binding of NMP to 1·EY occurs primarily through the interactions of phosphate groups with 1·EY. Several dimetallic complexes have been previously reported by others with NMPs63 or nucleoside polyphosphate64 in solution. For example, Hamachi and co-workers reported a xanthene-based Zn(II) complex that was shown to strongly bind several polyphosphate derivatives in the range from (log Kcon) 5.69 to 6.23; however, it showed moderate affinity for cAMP (3.14) and no affinity for AMP or GMP.62 The observed binding trend, as listed in Table 1, roughly suggests that in addition to the metal−ligand interactions between the metal centers and the phosphate groups, the higher conjugated π-rings in nucleobases (e.g., GMP and AMP) contribute enhanced interactions possibly due to the π−π interactions between the nucleobases and the receptor’s aromatic groups. The appreciably higher binding strength of the ensemble 1·EY for UMP (log Kcon = 5.1) with respect to that for TMP (log Kcon = 4.8) is consistent with the crystal structure of [1·(UMP)2]2 exhibiting π−π interactions (Figure 2a), whereas such interactions are absent in [1·(TMP)2]2 due to the steric effect 7807
DOI: 10.1021/acsomega.7b01293 ACS Omega 2017, 2, 7803−7811
ACS Omega
■
Article
EXPERIMENTAL SECTION General. All reagents and solvents were purchased as reagent grades and were used without further purification. NMR spectra were recorded on a Varian Unity INOVA 500 FT-NMR. Chemical shifts for samples were measured in CDCl3 and calibrated with TMS as an internal reference. The elemental analysis was carried out using an ECS 4010 Analytical Platform (Costech Instrument). Fluorescence titration studies were performed using a Fluoromax-4 spectrofluorometer (HORIBA Scientific) in water at pH 7.4. The pH was adjusted by using 0.02 M HEPES purchased from Sigma-Aldrich Chemical Company. Experimental conditions were used as follows: λex = 470 nm, λem = 537 nm, dex = 2, and dem = 3 for eosin Y dye. Synthesis. L. The free macrocycle was synthesized following the procedure as described before.65 In a typical reaction, Nmethyl-2,2′-diaminodiethylamine (1.1719 g, 10.0 × 10−3 mol) in CH3OH (350 mL) and terephthalaldehyde (1.3413 g, 10.0 × 10−3 mol) in CH3OH (350 mL) were added slowly to a threeneck round-bottom flask containing 500 mL of CH3OH over 6 h under stirring at 0 °C. The reaction mixture was further stirred overnight at room temperature. The solvent was evaporated, and the imine thus obtained was reduced with NaBH4 (1.56 g) at room temperature for 8 h. The solvent was removed under reduced pressure, and the resulting reaction product was dispersed in water (100 mL). The macrocycle was extracted from the aqueous phase to organic phase by CH2Cl2 (3 × 100 mL). The organic portions were collected and dried by anhydrous MgSO4 (2 g). The solid was filtered off and the solvent was evaporated to dryness. The crude product was purified by column chromatography (neutral alumina, 2% CH3OH in CH2Cl2). Yield: 1.6342 g, (74%). 1H NMR (500 MHz, CDCl3, TMS): δ 7.19 (s, 8H, ArH), 3.75 (s, 8H, ArCH2), 2.78 (t, 8H, J = 5 Hz, NCH2CH2), 2.54 (t, 8H, J = 5 Hz, NCH2CH2), 2.16 (s, 6H, NCH3), 13C NMR (125 MHz, CDCl3): δ 138.92 (Ar-C), 128.00 (Ar-CH), 56.54 (ArCH2), 53.92 (NCH2CH2), 47.00 (NCH2CH2), 42.21 (NCH3). Anal. Calcd for C26H42N6: C, 71.19; H, 9.65; N, 19.16. Found: C, 71.27; H, 9.68; N, 19.22. [Cu2II(L)Br4]·H2O, 1. The free amine L (146 mg, 0.332 mmol) was mixed with 2 equiv of CuBr2 (148 mg, 0.662 mmol) in 5 mL of H2O. The solution was stirred at 60 °C for 1 h. After the solvent was evaporated under reduced pressure, the solid product was suspended in 2 mL of diethyl ether and collected by filtration. The blue microcrystals were dissolved in 2 mL of water−methanol mixture (1:1, v/v) and recrystallized by slow evaporation of the solution, providing air stable X-ray quality crystals after 3 days. Yield: 247 mg, 84%. Anal. Calcd for C26H44Br4Cu2N6O: C, 34.57; H, 4.91; N, 9.30. Found: C, 34.48; H, 4.94; N, 9.27. The compound was further characterized by X-ray diffraction analysis. [Cu2II(L)(UMP)2]2·2(C2H6OS)·24H2O. The metal complex (1) (88 mg, 0.1 mmol) was dissolved in 10 mL of water−DMSO (5:1, v/v) with 2 equiv of UMP (uridine 5′-momophosphate disodium) (74 mg, 0.2 mmol). After the solution was stirred for 20 min at room temperature, the mixture was kept for crystallization at room temperature, yielding X-ray quality crystals after one month. The compound was characterized by X-ray diffraction analysis. [Cu2II(L)(TMP)2]2·14H2O. The metal complex (1) (88 mg, 0.1 mmol) was dissolved in 10 mL of water−DMSO (5:1, v/v) with 2 equiv of TMP (thymidine 5′-momophosphate
disodium) (73 mg, 0.2 mmol). After the solution was stirred for 20 min at room temperature, the mixture was kept for crystallization at room temperature, yielding X-ray quality crystals after 1 month. The compound was characterized by Xray diffraction analysis. Fluorescence Binding Studies. Binding Constant of 1 for EY. The binding affinity of 1 for EY was determined from the titration of EY with 1 in water at pH 7.4. The pH of the solution was maintained using 20 mM HEPES in water. In this case, the quenching of fluorescence was observed due to the addition of 1 to EY. Initial concentrations of EY and 1 were 2.0 × 10−6 and 2.0 × 10−4 M, respectively. Each titration was performed by 20 measurements varying [1]0/[dye]0 = 0−20, and the conditional constant K was calculated by fitting the ratio of I/I0 (Φ = I/I0, where I0 = initial fluorescence intensity of EY, I = fluorescence intensity after the addition of 1) with a 1:1 association model73 using the equation (the error limit in K was less than 15%). ΔΦ = ([1]0 + [EY]0 + 1/K − ([1]0 + [EY]0 + 1/K )2) − 4[EY]0 [1]0 )1/2 ΔΦmax /2[EY]0
Binding Constant of 1·EY for NMP. The binding affinity of 1·EY for different NMPs was examined from the competition reaction, and binding constants were calculated from the titration of 1·EY with anions in water under the same experimental conditions described in the preceding section. Initial concentrations of 1·EY and an NMP were 2.0 × 10−6 and 2.0 × 10−3 M, respectively. In this case, EY was displaced from 1·EY by the addition of an NMP, resulting in an enhancement of the fluorescence intensity. Each titration was performed by 20 measurements varying the [anion]0/[1·EY]0 = 0−200, and the association constant K was calculated by fitting the ratio of I/I0 (Φ = I/I0, where I0 = initial fluorescence intensity of 1·EY, I = fluorescence intensity after the addition of an anion) with a 1:1 association model73 using the equation (the error limit in K was less than 15%). ΔΦ = ([A]0 + [1·EY]0 + 1/K
) 2
− ([A]0 + [1·EY]0 + 1/K ) − 4[1·EY]0 [A]0 )1/2 ΔΦmax /2[1·EY]0
X-ray Crystallography. The crystallographic data and details of data collection for the crystals (1, [1·(UMP)2]2 and [1·(TMP)2]2) are given in Tables S1−S3. Intensity data for 1 and [1·(UMP)2]2 were collected using a diffractometer with a Bruker APEX ccd area detector and graphite-monochromated Mo Kα radiation (λ = 0.71073 Å),78,79 whereas those for [1· (TMP)2]2, with a Rigaku diffractometer, with a Pilatus CMOS area detector and Cu Kα radiation (λ = 1.54178 Å),80 as described before. 81 The structures were refined by SHELXL2013 program.82 There were two macrocycles, four Cu(II) ions, and four UMP groups in the asymmetric unit of the cell for [1· (UMP)2]2. The asymmetric unit contains 24 water molecules and two DMSO molecules (not shown in figures for clarity). One of the two DMSO molecules was shown to be disordered. The occupancies of the T-labeled DMSO refined to 0.665(10) and 0.335(10) for the unprimed and primed atoms, respectively. Restraints on the positional parameters of the 7808
DOI: 10.1021/acsomega.7b01293 ACS Omega 2017, 2, 7803−7811
ACS Omega
Article
(9) Xu, Z.; Singh, N. J.; Lim, J.; Pan, J.; Kim, H. N.; Park, S.; Kim, K. S.; Yoon, J. Unique sandwich stacking of pyrene-adenine-pyrene for selective and ratiometric fluorescent sensing of atp at physiological pH. J. Am. Chem. Soc. 2009, 131, 15528−15533. (10) Arranz-Mascarós, P.; Bazzicalupi, C.; Bianchi, A.; Giorgi, C.; Godino-Salido, M. L.; Gutiérrez-Valero, M. D.; Lopez-Garzón, R.; Valtancoli, B. Binding and recognition of AMP, ADP, ATP and related inorganic phosphate anions by a tren-based ligand containing a pyrimidine functionality. New J. Chem. 2011, 35, 1883−1891. (11) Huang, F.; Hao, G.; Wu, F.; Feng, G. Fluorescence sensing of ADP over ATP and PPi in 100% aqueous solution. Analyst 2015, 140, 5873−5876. (12) Sahoo, J.; Arunachalam, R.; Subramanian, P. S.; Suresh, E.; Valkonen, A.; Rissanen, Kari.; Albrecht, M. Coordinatively Unsaturated Lanthanide (III) Helicates: Luminescence Sensors for Adenosine Monophosphate in Aqueous Media. Angew. Chem., Int. Ed. 2016, 55, 9625−9629. (13) Inclán, M.; Albelda, M. T.; Carbonell, E.; Blasco, S.; Bauzá, A.; Frontera, A.; García-España, E. Molecular Recognition of Nucleotides in Water by Scorpiand-Type Receptors Based on Nucleobase Discrimination. Chem. − Eur. J. 2014, 20, 3730−3741. (14) Rivera-Márquez, K. I.; Godoy-Alcántar, C.; Claudio-Catalán, M. Á .; Medrano, F. Adenine nucleotide recognition by spiramycin and some of its aromatic derivatives. J. Inclusion Phenom. Macrocyclic Chem. 2016, 86, 211−219. (15) Shi, L.; Hu, P.; Ren, Y.; Feng, G. An unexpected highly selective mononuclear zinc complex for adenosine diphosphate (ADP). Chem. Commun. 2013, 49, 11704−11706. (16) Kumar, A.; Pandey, R.; Kumar, A.; Gupta, R. K.; Dubey, M.; Mohammed, A.; Mobin, S. M.; Pandey, D. S. Self-assembled copper (II) metallacycles derived from asymmetric Schiff base ligands: efficient hosts for ADP/ATP in phosphate buffer. Dalton Trans. 2015, 44, 17152−17165. (17) Kataev, E. A.; Shumilova, T. A.; Fiedler, B.; Anacke, T.; Friedrich, J. Understanding stacking interactions between an aromatic ring and nucleobases in aqueous solution: experimental and theoretical study. J. Org. Chem. 2016, 81, 6505−6514. (18) Amabilino, D. B. Supramolecular sensing: Enzyme activity with a twist. Nat. Chem. 2015, 7, 275−277. (19) Zhou, Y.; Xu, Z.; Yoon, J. Fluorescent and colorimetric chemosensors for detection of nucleotides, FAD and NADH: highlighted research during 2004−2010. Chem. Soc. Rev. 2011, 40, 2222−2235. (20) Hargrove, A. E.; Nieto, S.; Zhang, T.; Sessler, J. L.; Anslyn, E. V. Artificial receptors for the recognition of phosphorylated molecules. Chem. Rev. 2011, 111, 6603−6782. (21) García-España, E.; Belda, R.; González, J.; Pitarch, J.; Bianchi, A. Receptors for Nucleotides. In Supramolecular Chemistry: From Molecules to Nanomaterials; Gale, P. A., Steed, J. W., Eds.; WileyVCH: Weinheim, 2012; Vol. 3, pp 1225−1257. (22) Aoki, S.; Honda, Y.; Kimura, E. The first selective and efficient transport of imide-containing nucleosides and nucleotides by lipophilic cyclen−zinc(II) complexes (cyclen = 1,4,7,10-tetraazacyclododecane). J. Am. Chem. Soc. 1998, 120, 10018−10026. (23) Aoki, S.; Kimura, E. Highly selective recognition of thymidine mono- and diphosphate nucleotides in aqueous solution by ditopic receptors Zinc(II)−bis(cyclen) complexes (cyclen = 1,4,7,10-tetraazacyclododecane). J. Am. Chem. Soc. 2000, 122, 4542−4548. (24) Aoki, S.; Kimura, E. Zinc−nucleic acid interaction. Chem. Rev. 2004, 104, 769−788. (25) Aoki, S.; Zulkefeli, M.; Shiro, M.; Kohsako, M.; Takeda, K.; Kimura, E. A Luminescence sensor of inositol 1,4,5-triphosphate and its model compound by ruthenium-templated assembly of a bis(Zn2+cyclen) complex having a 2,2′-bipyridyl linker (cyclen = 1,4,7,10tetraazacyclododecane). J. Am. Chem. Soc. 2005, 127, 9129−9139. (26) Kitamura, M.; Nishimoto, H.; Aoki, K.; Tsukamoto, M.; Aoki, S. Molecular recognition of inositol 1,4,5-trisphosphate and model compounds in aqueous solution by ditopic Zn2+ complexes containing chiral linkers. Inorg. Chem. 2010, 49, 5316−5327.
disordered DMSO, the positional parameters of hydrogens bonded to N and O atoms of the complex, and the displacement parameters of two water oxygens were required. In the case of [1·(TMP)2]2, there were also two macrocycles, four Cu(II) ions, and four TMP groups per asymmetric unit. Several waters were so disordered that they were best fit using the Squeeze program.83 Restraints on the positional parameters of the disordered atoms and the displacement parameters of all atoms were required. CCDC 1015181, 1019485, and 1536988.
■
ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsomega.7b01293. NMR spectra and titrations spectra, Job plots, and the crystallographic data and details of data collection for the crystals (PDF) Crystallographic information files (CIF)
■
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Md. Alamgir Hossain: 0000-0003-4978-1664 Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS The National Science Foundation is acknowledged for a CAREER award (CHE-1056927) to M.A.H. This work was supported by National Institutes of Health (G12MD007581). The authors are grateful to the National Science Foundation (grant CHE-0130835) and the University of Oklahoma for funds to purchase the X-ray instrument and computers.
■
REFERENCES
(1) Dietrich, B.; Hosseini, M. W.; Lehn, J.-M.; Sessions, R. B. Synthesis and anion-binding properties of polyammonium macrocycles. J. Am. Chem. Soc. 1981, 103, 1282−1283. (2) Tabushi, I.; Kobuke, Y.; Imuta, J. Lipophilic diammonium cation having a rigid structure complementary to pyrophosphate dianions of nucleotides. Selective extraction and transport of nucleotides. J. Am. Chem. Soc. 1981, 103, 6152−6157. (3) Kimura, E.; Kodama, M.; Yatsunami, T. Macromonocyclic polyamines as biological polyanion complexons. 2. Ion-pair association with phosphate and nucleotides. J. Am. Chem. Soc. 1982, 104, 3182− 3187. (4) Hamilton, A. D.; Pant, N.; Muehldorf, A. Nucleotide base recognition: Ditopic binding of guanine to a macrocyclic receptor containing naphthyridine and naphthalene units. Pure Appl. Chem. 1988, 60, 533−538. (5) Kim, H. N.; Moon, J. H.; Kim, S. K.; Kwon, J. Y.; Jang, Y. J.; Lee, J. Y.; Yoon, J. Fluorescent sensing of triphosphate nucleotides via anthracene derivatives. J. Org. Chem. 2011, 76, 3805−3811. (6) Neelakandan, P. P.; Nandajan, P. C.; Subymol, B.; Ramaih, D. Study of cavity size and nature of bridging units on recognition of nucleotides by cyclophanes. Org. Biomol. Chem. 2011, 9, 1021−1029. (7) Schneider, H.-J.; Tianjun, L.; Lomadze, N. Molecular recognition in a supramolecular polymer system translated into mechanical motion. Angew. Chem., Int. Ed. 2003, 42, 3544−3546. (8) Belcher, W. J.; Fabre, M.; Farhan, T.; Steed, J. W. Pyridinium CH ··· anion and π-stacking interactions in modular tripodal anion binding hosts: ATP binding and solid-state chiral induction. Org. Biomol. Chem. 2006, 4, 781−786. 7809
DOI: 10.1021/acsomega.7b01293 ACS Omega 2017, 2, 7803−7811
ACS Omega
Article
(27) Mahon, C. S.; Fulton, D. A. Mimicking nature with synthetic macromolecules capable of recognition. Mimicking nature with synthetic macromolecules capable of recognition. Nat. Chem. 2014, 6, 665−672. (28) Dugas, H. Bioorganic Chemistry. In Bioorganic Chemistry of the Phosphate Groups and Polynucleotides, 3rd ed.; Springer: New York, 1996; pp 111−158. (29) Beijer, F. H.; Kooijman, H.; Spek, A. L.; Sijbesma, R. P.; Meijer, E. W. Self-complementarity achieved through quadruple hydrogen bonding. Angew. Chem., Int. Ed. 1998, 37, 75−78. (30) Lehn, J.-M. Toward complex matter: supramolecular chemistry and self-organization. Proc. Natl. Acad. Sci. U.S.A. 2002, 99, 4763− 4768. (31) Bazzicalupi, C.; Bencini, A.; Bianchi, A.; Faggi, E.; Giorgi, C.; Santarelli, S.; Valtancoli, B. Polyfunctional binding of thymidine 5′triphosphate with a synthetic polyammonium receptor containing aromatic groups. Crystal structure of the nucleotide−receptor adduct. J. Am. Chem. Soc. 2008, 130, 2440−2441. (32) Shiba, J. K.; Bau, R. Crystal and molecular structure of the monoclinic form of aqua (5′-cytidine monophosphato) cadmium (II)1.5-water. Inorg. Chem. 1978, 17, 3484−3488. (33) Orioli, P.; Cini, R.; Donati, D.; Mangani, S. Crystal and molecular structure of the ternary complex bis [(adenosine 5′triphosphato)(2, 2′-bipyridine) zinc(II)] tetrahydrate. J. Am. Chem. Soc. 1981, 103, 4446−4452. (34) Cini, R.; Pifferi, C. Supramolecular networks via hydrogen bonding and stacking interactions for adenosine 5′-diphosphate. Synthesis and crystal structure of diaqua(2,2′:6′,2″-terpyridine)copper(II) [adenosine 5′-diphosphato(3−)](2,2′:6′,2″-terpyridine)cuprate(II) adenosine 5′-diphosphate(1−) hexadecahydrate and density functional geometry optimization analysis of copper(II)- and zinc(II)-pyrophosphate complexes. J. Chem. Soc., Dalton Trans. 1999, 0, 699−710. (35) Kato, M.; Tanase, T. Tetranuclear copper (II) complex with glucose-1-phosphate and its phosphate ester exchange with ATP. Inorg. Chem. 2005, 44, 8−10. (36) Kato, M.; Sah, A. K.; Tanase, T.; Mikuriya, M. Transformation of a tetranuclear copper (II) complex bridged by sugar phosphates into nucleotide containing Cu4 aggregations. Eur J. Inorg. Chem. 2006, 2006, 2504−2513. (37) Huang, F.; Feng, G. Introducing ligand-based hydrogen bond donors to a receptor: both selectivity and binding affinity for anion recognition in water can be improved. J. Org. Chem. 2012, 77, 11405− 11408. (38) Zhou, P.; Yao, J.-F.; Sheng, C. -F; Li, H. A continuing tale of chirality: metal coordination extended axial chirality of 4, 4′-bipy to 1D infinite chain under cooperation of a nucleotide ligand. CrystEngComm 2013, 15, 8430−8436. (39) Smith, D. P.; Chen, H.; Ogo, S.; Elduque, A. I.; Eisenstein, M.; Olmstead, M. M.; Fish, R. H. Bioorganometallic Chemistry. 27. Synthetic, X-ray crystallographic, and competitive binding studies in the reactions of nucleobases, nucleosides, and nucleotides with [Cp* Rh (H2O)3](OTf)2, as a function of pH, and the utilization of several Cp* Rh−DNA base complexes in host−guest chemistry. Organometallics 2014, 33, 2389−2404. (40) Lipscomb, W. N.; Strater, N. Recent advances in zinc enzymology. Chem. Rev. 1996, 96, 2375−2434. (41) Singleton, M. R.; Sawaya, M. R.; Ellenberger, T.; Wigley, D. B. Crystal structure of T7 gene 4 ring helicase indicates a mechanism for sequential hydrolysis of nucleotides. Cell 2000, 101, 589−600. (42) Uppsten, M.; Färnegardh, M.; Jordan, A.; Eliasson, R.; Eklund, H.; Uhlin, U. Structure of the large subunit of class ib ribonucleotide reductase from Salmonella typhimurium and its complexes with allosteric effectors. J. Mol. Biol. 2003, 330, 87−97. (43) Heinemann, U.; Saenger, W. Specific protein-nucleic acid recognition in ribonuclease T1−2′-guanylic acid complex: an X-ray study. Nature 1982, 299, 27−31. (44) Doan, T. T.; Kim, J.-K.; Ngo, H.-P.-T.; Tran, H.-T.; Cha, S.-S.; Chung, K. M.; Huynh, K.-H.; Ahn, Y.-J.; Kang, L.-W. Crystal structures
of d-alanine-d-alanine ligase from Xanthomonas oryzae pv. oryzae alone and in complex with nucleotides. Arch. Biochem. Biophys. 2014, 545, 92−99. (45) Costi, R.; Cuzzucoli, C. G.; Pescatori, L.; Messore, A.; Scipione, L.; Tortorella, S.; Amoroso, A.; Crespan, E.; Campiglia, P.; Maresca, B.; Novellino, E.; Gouge, J.; Delarue, M.; Maga, G.; di Santo, R.; et al. New nucleotide-competitive non-nucleoside inhibitors of terminal deoxynucleotidyl transferase: discovery, characterization, and crystal structure in complex with the target. J. Med. Chem. 2013, 56, 7431− 7441. (46) Appleby, T. C.; Kinsland, C.; Begley, T. P.; Ealick, S. E. The crystal structure and mechanism of orotidine 5′-monophosphate decarboxylase. Proc. Natl. Acad. Sci. U.S.A. 2000, 97, 2005−2010. (47) Bianchi, A.; Micheloni, M.; Paoletti, P. Supramolecular interaction between adenosine 5′-triphosphate (ATP) and polycharged tetraazamacrocycles. Thermodynamic and 31P NMR studies. Inorg. Chim. Acta 1998, 151, 269−272. (48) Hosseini, M. W.; Lehn, J. M. Binding of AMP, ADP, and ATP nucleotides by polyammonium macrocycles. Helv. Chim. Acta 1987, 70, 1312−1319. (49) Baudoin, O.; Gonnet, F.; Teulade-Fichou, M. P.; Vigneron, J. P.; Tabet, J. C.; Lehn, J. M. Molecular recognition of nucleotide pairs by a cyclo-bis-intercaland-type receptor molecule: A spectrophotometric and electrospray mass spectrometry study. Chem. − Eur. J. 1999, 5, 2762−2771. (50) Teulade-fichou, M. P.; Vigneron, J. P.; Lehn, J. M. Molecular recognition of nucleosides and nucleotides by a water-soluble cyclobis-intercaland receptor based on acridine subunits. Supramol. Chem. 1995, 5, 139−147. (51) Hosseini, M. W.; Lehn, J. M. Binding of AMP, ADP, and ATP nucleotides by polyammonium macrocycles. Helv. Chim. Acta 1987, 70, 1312−1319. (52) Dhaenens, M.; Lehn, J. M.; Vigneron, J. P. Molecular recognition of nucleosides, nucleotides and anionic planar substrates by a water-soluble bis-intercaland-type receptor molecule. J. Chem. Soc., Perkin Trans. 2 1993, 7, 1379−1381. (53) Hosseini, M. W.; Lehn, J. M.; Mertes, M. P. Efficient molecular Catalysis of ATP-hydrolysis by protonated macrocyclic polyamines. Helv. Chim. Acta 1983, 66, 2454−2466. (54) Hosseini, M. W.; Lehn, J. M. Supramolecular catalysis of adenosine triphosphate synthesis in aqueous solution mediated by a macrocyclic polyamine and divalent metal cations. J. Chem. Soc., Chem. Commun. 1991, 0, 451−453. (55) Hosseini, M. W.; Lehn, J. M.; Jones, K. C.; Plute, K. E.; Mertes, K. B.; Mertes, M. P. Supramolecular catalysis: polyammonium macrocycles as enzyme mimics for phosphoryl transfer in ATP hydrolysis. J. Am. Chem. Soc. 1989, 111, 6330−6365. (56) Bazzicalupi, C.; Bencini, A.; Berni, E.; Bianchi, A.; Fedi, V.; Fusi, V.; Giorgi, C.; Paoletti, P.; Valtancoli, B. Carboxy and diphosphate ester hydrolysis by a dizinc complex with a new alcohol-pendant macrocycle. Inorg. Chem. 1999, 38, 4115−4122. (57) Bazzicalupi, C.; Bencini, A.; Berni, E.; Bianchi, A.; Fornasari, P.; Giorgi, C.; Valtancoli, B. Insights into the activity of dinuclear Zn(II) complexes in phosphate ester hydrolysis. Inorg. Chem. 2004, 43, 6255− 6265. (58) Bencini, A.; Berni, E.; Bianchi, A.; Fedi, V.; Giorgi, C.; Paoletti, P.; Valtancoli, B. Carboxy and diphosphate ester hydrolysis promoted by dinuclear zinc(II) macrocyclic complexes. Role of Zn(II)-bound hydroxide as the nucleophilic function. Inorg. Chem. 1999, 38, 6323− 6325. (59) Wu, H.; He, C.; Lin, Z.; Liu, Y.; Duan, C. Metallohelical triangles for selective detection of adenosine triphosphate in aqueous media. Inorg. Chem. 2009, 48, 408−410. (60) Jose, D. A.; Mishra, S.; Ghosh, A.; Shrivastav, A.; Mishra, S. K.; Das, A. Colorimetric sensor for ATP in aqueous solution. Org. Lett. 2007, 9, 1979−1982. (61) Huang, X.; Lu, Y.; He, Y.; Chen, Z. A Metal−macrocycle complex as a fluorescent sensor for biological phosphate ions in aqueous solution. Eur. J. Org. Chem. 2010, 2010, 1921−1927. 7810
DOI: 10.1021/acsomega.7b01293 ACS Omega 2017, 2, 7803−7811
ACS Omega
Article
(82) Sheldrick, G. M. SHELXL; University of Gottingen, 2013. (83) Parsons, S.; Flack, H. D.; Wagner, T. Use of intensity quotients and differences in absolute structure refinement. Acta Crystallogr., Sect. B: Struct. Sci., Cryst. Eng. Mater. 2013, B69, 249−259.
(62) Ojida, A.; Takashima, I.; Kohira, T.; Nonaka, H.; Hamachi, I. Turn-on fluorescence sensing of nucleoside polyphosphates using a xanthene-based Zn(II) complex chemosensor. J. Am. Chem. Soc. 2008, 130, 12095−12101. (63) Amendola, V.; Bergamaschi, G.; Buttafava, A.; Fabbrizzi, L.; Monzani, E. Recognition and sensing of nucleoside monophosphates by a dicopper(II) cryptate. J. Am. Chem. Soc. 2010, 132, 147−156. (64) Alagesan, M.; Bhuvanesh, N. S.; Dharmaraj, N. Binuclear copper complexes: synthesis, X-ray structure and interaction study with nucleotide/protein by in vitro biochemical and electrochemical analysis. Eur. J. Med. Chem. 2014, 78, 281−293. (65) Mendy, J. S.; Saeed, M. A.; Fronczek, F. R.; Powell, D. R.; Hossain, M. A. Anion recognition and sensing by a new macrocyclic dinuclear copper (II) complex: A selective receptor for iodide. Inorg. Chem. 2010, 49, 7223−7225. (66) Saeed, M. A.; Powell, D. R.; Hossain, M. A. Fluorescent detection of phosphate anion by a highly selective chemosensor in water. Tetrahedron Lett. 2010, 51, 4904−4907. (67) Rhaman, M. M.; Fronczek, F. R.; Powell, D.; Hossain, M. A. Colourimetric and fluorescent detection of oxalate in water by a new macrocycle-based dinuclear nickel complex: A remarkable red shift of fluorescence band. Dalton Trans. 2014, 43, 4618−4621. (68) Rhaman, M. M.; Alamgir, A.; Wong, B. M.; Powell, D. R.; Hossain, M. A. A highly efficient dinuclear Cu(II) chemosensor for colorimetric and fluorescent detection of cyanide in water. RSC Adv. 2014, 4, 54263−54267. (69) Janiak, C. A critical account on π−π stacking in metal complexes with aromatic nitrogen-containing ligands. J. Chem. Soc., Dalton Trans. 2000, 0, 3885−3896. (70) Brayer, G. D.; McPherson, A. Mechanism of DNA binding to the gene 5 protein of bacteriophage fd. Biochemistry 1984, 23, 340− 349. (71) Mori, T.; Okamoto, K.; Endo, H.; Hill, J. P.; Shinoda, S.; Matsukura, M.; Tsukube, H.; Suzuki, Y.; Kanekiyo, Y.; Ariga, K. Mechanical tuning of molecular recognition to discriminate the singlemethyl-group difference between thymine and uracil. J. Am. Chem. Soc. 2010, 132, 12868−12870. (72) Metzger, A.; Anslyn, E. V. A chemosensor for citrate in beverages. Angew. Chem., Int. Ed. 1998, 37, 649−652. (73) Schneider, H. J.; Kramer, R.; Simova, S.; Schneider, U. Solvent and salt effects on binding constants of organic substrates in macrocyclic host compounds. A general equation measuring hydrophobic binding contributions. J. Am. Chem. Soc. 1988, 110, 6442− 6448. (74) Hossain, M. A.; Llinares, J. M.; Powell, D.; Bowman-James, K. Multiple hydrogen bond stabilization of a sandwich complex of sulfate between two macrocyclic tetraamides. Inorg. Chem. 2001, 40, 2936− 2937. (75) Pramanik, A.; Thompson, B.; Hayes, T.; Tucker, K.; Powell, D. R.; Bonnesen, P. V.; Ellis, E. D.; Lee, K. S.; Yu, H.; Hossain, M. A. Seven-coordinate anion complex with a tren-based urea: Binding discrepancy of hydrogen sulfate in solid and solution states. Org. Biomol. Chem. 2011, 9, 4444−4447. (76) Keene, F. R.; Smith, J. A.; Collins, J. G. Metal complexes as structure-selective binding agents for nucleic acids. Coord. Chem. Rev. 2009, 253, 2021−2035. (77) Jungwirth, U.; Kowol, C. R.; Keppler, B. K.; Hartinger, C. G.; Berger, W.; Heffeter, P. Anticancer activity of metal complexes: involvement of redox processes. Antioxid. Redox Signaling 2011, 15, 1085−1127. (78) Data Collection: SMART Software Reference Manual; BrukerAXS: 5465 E. Cheryl Parkway, Madison, WI, 1998. (79) Sheldrick, G. M. A Short History of SHELX. Acta Crystallogr., Sect. A: Found. Crystallogr. 2008, 64, 112−122. (80) Otwinowski, Z.; Minor, W.; Majewski, W. HKL-3000, 2003. (81) Ahmed, L.; Rhaman, M. M.; Mendy, J. S.; Wang, J.; Fronczek, F. R.; Powell, D. R.; Jerzy Leszczynski, J.; Hossain, M. A. Experimental and theoretical studies on halide binding with a p-xylyl-based azamacrocycle. J. Phys. Chem. A 2015, 119, 383−394. 7811
DOI: 10.1021/acsomega.7b01293 ACS Omega 2017, 2, 7803−7811
