Article pubs.acs.org/Organometallics
New Luminescent Ag2Au2 Heteronuclear Alkynyl−Phosphine Complexes and Recognition of Homocysteine and Cysteine Yi Jiang,† Yong-Tao Wang,† Zheng-Gen Ma,† Zhi-Hong Li,† Qiao-Hua Wei,*,†,‡ and Guo-Nan Chen† †
Ministry of Education, Fujian Provincial Key Lab of Analysis and Detection for Food Safety, and Department of Chemistry, Fuzhou University, Fuzhou 3500108, People’s Republic of China ‡ Beijing Synchrotron Radiation Laboratory, Institute of High Energy Physics, The Chinese Academy of Sciences, Beijing 100039, People’s Republic of China S Supporting Information *
ABSTRACT: The four heteronuclear clusters [Ag2Au2(μ-dpppy)3(CCC6H4R-4)2](ClO4)2 (R = H (1) CH3 (2), COOCH3 (3), CHO (4)) were prepared by the self-assembly reaction between (AuCC6H4R-4)n (R = H, CH3, COOCH3, CHO) and [Ag2(μ-dpppy)3]2+ (dpppy = 2,6-bis(diphenylphosphino)pyridine) and characterized by elemental analyses, electrospray ionization mass spectrometry (ESI-MS), and 1H NMR and 31P{1H} NMR spectroscopy and by X-ray crystallography for 1, 3, and 4. It is revealed that the complexes exhibit bright blue (1−3) and green (4) luminescence in the solid state and in solution with the luminescent lifetimes in the microsecond range, indicating that the luminescence is most likely associated with a spinforbidden triplet parentage. Interestingly, only complex 4 displays distinctly mechanical grinding responsive emission switching. The recognition interactions of complex 4 containing aldehyde groups with homocysteine (Hcy) and cysteine (Cys) have been studied by UV−vis and emission titrations. A strong luminescence quench was found upon reaction of complex 4 only with Hcy or Cys, but not with other amino acids, proteins, and common anions, indicating a high specificity for recognition of Hcy and Cys.
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INTRODUCTION The heteronuclear complexes of group 11 metals have been an actively investigated topic since the last few decades, because of their interesting chemical reactivity, diversified structural topologies, and interesting luminescent properties,1−20 which are suitable for modern technological applications: for example, OLED displays,20 luminescent sensors,10a,b and bioimaging labels.11f Within this field, our group and others have reported the preparation of a number of heterometallic Au(I), Ag(I), and Cu(I) alkynyl−phosphine complexes using the self-assembly method, which exhibit intriguing photophysical properties associated with the metal−metal interactions.5−19 It is found that the structural topologies and physical properties of the resulting heterometallic alkynyl−phosphine complexes of group 11 metals depend on the metals, the alkynyl ligands, and, in particular, the type of diphosphine coligands. It should be noted that the number of reported Au(I)−Ag(I) alkynyl−phosphine complexes5−9 to date is still very limited, despite their attractive © 2013 American Chemical Society
luminescent properties. Furthermore, to the best of our knowledge, no coinage-metal alkynyl complexes that can be directly applied to probe the biomolecules have been reported to date, although there are a number of reports on the luminescent sensing of metal cations10a,b based on coinagemetal alkynyl complex probes. These have prompted us to further study on this chemistry and application to probe the biomolecules by searching for different structural topologies and modifying photophysical properties of these types of compounds via modification of the diphosphine coligands and the alkynyl ligands. Homocysteine (Hcy) and cysteine (Cys) are important amino acids containing a free thiol moiety in living systems, which play a critical role in a variety of cellular functions, such as detoxification and metabolism.21 Until now, the most widely Received: July 2, 2013 Published: August 20, 2013 4919
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Scheme 1. Synthetic Routes to Compounds 1−4 and the Recognition Mechanism of Complex 4 for Hcy and Cys
(m, 3H), 7.21 (d, J = 6.0 Hz, 2H), 7.67−7.61 (m, 10H), 7.42−7.36 (m, 18H), 7.24−7.19 (m, 24H), 7.10 (t, J = 6.0 Hz, 4H), 7.04 (t, J = 5.6 Hz, 6H), 6.97−6.93 (m, 6H), 6.82 (d, J = 6.0 Hz, 2H), 6.73 (d, J = 6.0 Hz, 4H). 31P{1H} NMR (202.3 MHz, CDCl3, ppm): δ 40.92 (s, AuPPyPAg), 14.30 (quadruplet of doublets, JAg−P = 575 Hz, JAg−P = 283 Hz, AgPPyPAu; 2JP−P = 30 Hz), 5.92 (quadruplet of doublets, JAg−P = 524 Hz, JAg−P = 251 Hz, AgPPyPAg; 2JP−P = 28 Hz). [Ag2Au2(μ-dpppy)3(CCC6H4CH3-4)2](PF6)2 (2). The same synthetic procedure as for 1 was employed by reaction of [Ag2(μdpppy)3](PF6)2 (110.8 mg, 0.06 mmol) with (AuCC6H4CH3-4)n (56.2 mg, 0.18 mmol). The resulting mixture was stirred for 6 h to give a greenish yellow solution, which was concentrated under reduced pressure. Slow diffusion of diethyl ether into its concentrated ethylene dichloride solutions gave greenish yellow crystals. Yield: 67.4 mg (45.5%). Anal. Calcd for C105H83N3F12P8Ag2Au2: C, 51.01, H, 3.38; N, 1.70. Found: C, 49.94; H, 3.47; N, 1.73. ESI-MS (m/z (%)): 1091.1 (100) [M]2+. IR (KBr; ν, cm−1): 2069 (w, CC), 840 (s, PF6−). 1H NMR (400.1 MHz, CDCl3, ppm): δ 8.04−7.98 (m, 3H), 7.70 (d, J = 6.0 Hz, 2H), 7.66−7.62 (m, 10H), 7.42−7.39 (m, 18H), 7.24−7.21 (m, 22H), 7.03 (t, J = 6.0 Hz, 6H), 6.97−6.93 (m, 10H), 6.91 (d, J = 6.0 Hz, 2H), 6.63 (d, J = 6.4 Hz, 4H), 2.29 (s, 6H). 31P{1H} NMR (202.3 MHz, CDCl3, ppm): δ 40.85 (s, AuPPyPAg), 14.07 (quadruplet of doublets, JAg−P = 558 Hz, JAg−P = 221 Hz, AgPPyPAu; 2JP−P = 28 Hz), 5.86 (quadruplet of doublets, JAg−P = 520 Hz, JAg−P = 257 Hz, AgPPyPAg; 2JP−P = 28 Hz), −144.63 (m, PF6). [Ag2Au2(μ-dpppy)3(CCC6H4COOCH3-4)2](ClO4)2 (3). This complex was prepared by the same procedure as for 1 except for the use of (AuCC6H4COOCH3-4)n instead of (AuCC6H5)n, and dichloromethane as the solvent instead of ethylene dichloride. Yield: 81.4 mg (55%). Anal. Calcd for C107H83N3P6Cl2Ag2Au2O12: C, 52.05; H, 3.39; N, 1.70. Found: C, 51.99; H, 3.54; N, 1.67. ESI-MS (m/z (%)): 2386 (100) {[Ag2Au2(μ-dpppy)3(CCC6H4COOCH3-4)2](ClO4) + H2O}+, 1626.6 [Ag2Au(dpppy)2(CCC6H4COOCH34)2]+, 1178.3 [Ag2Au(dpppy)(CCC6H4COOCH3-4)2]+. IR (KBr; ν, cm−1): 2081 (m, CC), 1715 (s, CO), 1278 (s, C−O), 1096 (s, ClO4−). 1H NMR (400.1 MHz, CDCl3, ppm): δ 8.08−8.05 (m, 3H), 7.99 (d, J = 8.4 Hz, 2H), 7.69 (d, J = 8.4 Hz, 6H), 7.56−7.52 (m, 22H), 7.42−7.36 (t, J = 16 Hz, 22H), 7.04 (t, J = 7.6 Hz, 8H), 6.99− 6.94 (m, 8H), 6.75 (d, J = 7.2 Hz, 2H), 6.59 (d, J = 8.0 Hz, 4H), 3.90 (s, 6H, CH3). 31P{1H} NMR (202.3 MHz, CDCl3, ppm): δ 40.69 (s, AuPPyPAg), 11.18 (d, JAg−P = 435 Hz, AgPPyPAu),6.68 (quadruplet of doublets, JAg−P = 657 Hz, JAg−P = 342 Hz, AgPPyPAg; 2JP−P = 30 Hz). [Ag2Au2(μ-dpppy)3(CCC6H4CHO-4)2](ClO4)2 (4). This complex was prepared by the same procedure as for 3 except for the use of (AuCC6H4CHO-4)n instead of (AuCCC6H4COOCH3-4)n. Yield: 76.6 mg (53%). Anal. Calcd for C105H79N3P6Cl2Ag2Au2O10: C, 52.35; H, 3.31; N, 1.74. Found: C, 51.96; H, 3.47; N, 1.74. ESI-MS (m/z
used method for determination of Hcy and Cys is based on electrochemistry or derivatization with chromophores or fluorophores in conjunction with HPLC or capillary electrophoresis separations or via immunoassays.22 In addition, some chromophores containing aldehyde groups have been designed in recent years as luminescent sensors for Hcy and Cys23,24 by reaction of aldehyde groups with Hcy and Cys. However, most of them are organic fluorophores suffering from undesirability such as low photostability, high background fluorescence, and small Stokes shift. In this contribution, we report on the synthesis of the four novel heteronuclear clusters [Ag2Au2(μ-dpppy)3(CCC6H4R4)2](ClO4)2 (R = H (1), CH3 (2), COOCH3 (3), CHO (4); dpppy = 2,6-bis(diphenylphosphino)pyridine), their structural characterization, and a detailed investigation of their photophysical characteristics together with the recognition of Hcy and Cys using complex 4 containing aldehyde groups by the formation of thiazinane or thiazolidine (Scheme 1).
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EXPERIMENTAL SECTION
Materials and Reagents. The reactions were carried out under a dry nitrogen atmosphere using Schlenk techniques. The solvents were purified and distilled by standard procedures prior to use. The ligand 2,6-bis(diphenylphosphino)pyridine (dpppy) was purchased from Lude Fine Chemical Industry Co., Ltd., People’s Republic of China. Phenylacetylene (HCCC6H5), 4-methylphenylacetylene (HC CC6H4CH3-4), 4-ethynylbenzaldehyde (HCCC6H4CHO-4), and 4-ethynylbenzoic acid methyl ester (HCCC6H4COOCH3-4) were obtained from Acros Organics. L-Cysteine (Cys) and homocysteine (Hcy) were purchased from Tianjin Chen Chemical Reagents Factory, People’s Republic of China. (AuCCC6H4-R-4)n (R = H, CH3, COOCH3, CHO)25 and [Ag2(μ-dpppy)2](ClO4)226a were prepared by literature procedures. [Ag2Au2(μ-dpppy)3(CCC6H5)2](ClO4)2 (1). To an ethylene dichloride (10 mL) solution of [Ag2(μ-dpppy)3](ClO4)2 (105.4 mg, 0.06 mmol) was added (AuCCC6H5)n (53.6 mg, 0.18 mmol). The resulting mixture was stirred for 6 h to give a pale yellow solution, which was concentrated under reduced pressure. Slow diffusion of diethyl ether vapor into its concentrated ethylene dichloride solution afforded pale yellow crystals. Yield: 74.8 mg (53%). Anal. Calcd for C103H79N3P6Cl2Ag2Au2O8·2CH2ClCH2Cl: C, 50.38; H, 3.44; N, 1.65. Found: C, 49.86; H, 3.30; N, 1.64. ESI-MS (m/z (%)): 1091.8 (100) [M + CH3OH]2+, 1507.5 [Ag2Au(dpppy)2(CCC6H5)2]+, 1063.1 [Ag2Au(dpppy)(CCC6H5)2]+. IR (KBr; ν, cm−1): 2081 (w, CC), 1096 (s, ClO4−). 1H NMR (400.1 MHz, CDCl3, ppm): δ 8.04−8.00 4920
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Figure 1. ORTEP views of (A) the complex cation of 1 with 30% thermal ellipsoids and (B) the structure with phenyl rings on the phosphorus atoms omitted for clarity. (%)): 2212.3 (100) [M − H]+, 1105.0 [Ag2Au2(dpppy)3(C CC6H4CHO-4)2]2+. IR (KBr; ν, cm−1): 2081 (m, CC), 1691 (s, CO), 1096 (s, ClO4−). 1H NMR (400.1 MHz, CDCl3, ppm): δ 10.02 (s, 2H, CHO), 8.24−8.11 (m, 5H), 7.84 (d, J = 8.0 Hz, 10H), 7.75−7.60 (m, 18H), 7.55−7.49 (m, 22H), 7.04 (t, J = 6.4 Hz, 8H), 7.00−6.95 (m, 8H), 6.75 (d, J = 8.4 Hz, 2H), 6.11 (d, J = 7.6 Hz, 4H). 31 1 P{ H} NMR (202.3 MHz, CD3CN, ppm): δ 41.07 (s, AuPPyPAg), 6.40 (quadruplet of doublets, JAg−P = 532 Hz, JAg−P = 271 Hz, AgPPyPAg; 2JP−P = 28 Hz). Crystal Structure Determination. A crystal of 1, 3, or 4 coated with epoxy resin was measured on a Mar CCD 165 nm diffractometer by the oscillation scan technique at 193 K using the Beijing Synchrotron Radiation Facility with a 3W1A beam (λ = 0.71073 Å). The cell refinement and data reduction were computed using HKL2000 software.27a Absorption correction was carried out on the basis of spherical harmonics expansion of the absorption surface using HKL2000 software. The structure was solved by direct methods or the heavy atoms were located from an E map. The remaining nonhydrogen atoms were determined from successive difference Fourier syntheses. All non-hydrogen atoms were refined anisotropically except those mentioned otherwise. The chlorine atoms on the ethylene dichloride solvent in crystal 1 were disordered, and therefore the hydrogen atoms on the solvent were not added. The program SQUEEZE in PLATON was applied to remove the disordered solvent moiety in crystal 1 and 3.27b The structure was refined on F2 by fullmatrix least-squares methods using the SHELXTL-97 program package.27c The crystallographic parameters and details for data collections and refinements of crystals 1, 3, and 4 are summarized in Table S1 in the Supporting Information. Full crystallographic data are also provided there as CIF files. Physical Measurements. Elemental analyses (C, H, and N) were carried out on an Elementar Vario MICRO automatic instrument, and positive-ion ESI-MS spectra were measured on a Thermo Finnigan DECAX-3000 LCQ mass spectrometer using dichloromethane/ methanol or acetonitrile/methanol as the mobile phase at the Fujian Institute of Research on the Structure of Matter, the Chinese Academy of Sciences. IR spectra were recorded on a Perkin-Elmer 2000 FT-IR spectrophotometer with KBr pellets. 1H NMR spectra with chemical shifts reported relative to tetramethylsilane were recorded on a Bruker AVANCE 400 MHz spectrometer at the Fujian Institute of Research on the Structure of Matter, the Chinese Academy of Sciences, and 31 1 P{ H} NMR spectra with chemical shifts relative to 85% H3PO4 external reference were recorded on a Bruker AVANCE 500 MHz spectrometer. UV−vis absorption spectra were measured on a PerkinElmer Lambda 750 UV−vis spectrometer. Steady-state emission and excitation spectra at room temperature were recorded on an Edinburgh Analytical Instruments FLS900 fluorescence spectrometer.
Emission lifetimes were determined on an Edinburgh Analytical Instruments FLS900 fluorescence spectrometer with a light-emitting diode lamp (405 nm) and analyzed by the use of a program for exponential fits. The luminescence quantum yield of the sample was determined according to
Φs = Φr (Br /Bs)(ns /nr)2 (Ds /Dr)
(1)
where the subscripts s and r refer to the sample and reference solutions, respectively, B = 1 − 10−AL, A is the absorbance at the excitation wavelength, L is the path length, n is the refractive index of the solvent, and D is the integrated emission intensity. A degassed aqueous solution of quinine sulfate (0.1 M H2SO4) (Φem = 0.58)28 was used as the reference.
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RESULTS AND DISCUSSION Synthesis and Characterization. The preparative methodology employed in compounds 1−4 is closely analogous to a well-established method leading to the families of heteronuclear Ag(I)−M(I) (M = Cu(I), Au(I)) clusters and involves treatment of the (AuCC6H4R-4)n polymeric acetylides with d10 metal diphosphine blocks.5,15,16 Depolymerization of (AuCC6H4R-4)n (R = H (1), CH3 (2), COOCH3 (3), CHO (4)) with [Ag2(μ-dpppy)3]2+ metal diphosphine blocks in ethylene dichloride (1 and 2) or dichloromethane (3 and 4) solutions gives a greenish yellow or pale yellow solution. The subsequent diffusion of diethyl ether into their concentrated solutions affords pale yellow or greenish yellow crystals in good yields. Compounds 1−4 were satisfactorily characterized by ESIMS, 1H NMR and 31P{1H} NMR spectroscopy, elemental analyses, and IR spectroscopy. The IR spectra of compounds 1−4 all display one weak ν(CC) stretching vibration in the range of 2070−2081 cm−1. In the 31P{1H} NMR spectra of compounds 1−3, the P donors bound to the gold(I) center display one singlet, whereas those bonded to silver(I) centers afford two quadruplets of doublets with different Ag−P couplings, which suggests that the six P donors in compounds 1−3 are not equivalent in solution. However, the 31P{1H} NMR spectra of compound 4 shows one singlet of the P donors bound to the gold(I) center and only one set of quadruplet of doublets of Ag−P couplings (Figure S1 in the Supporting Information), which may be due to the poor 4921
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Figure 2. ORTEP views of (A) the complex cation of 4 with 30% thermal ellipsoids and (B) the structure with the phenyl rings on the phosphorus atoms omitted for clarity.
Table 1. Photophysical Data for Compounds 1−4 compd 1
2
3
4
medium crystalline CH2Cl2 MeCN MeCN/Tris−HCl crystalline CH2Cl2 CH3CN MeCN/Tris−HCl crystalline CH2Cl2 MeCN MeCN/Tris−HCl crystalline ground CH2Cl2 MeCN MeCN/Tris−HCl
λem/nm (τem/μs)a (298 K)
λabs/nm (ε/105 dm3 mol−1 cm−1)
230 (1.12), 268 (0.52), 336 (0.03) 204 (3.74), 268 (0.60), 352 (0.05) (pH 7.2, 1/1, v/v) 203 (1.98), 261 (0.57), 346 (0.10) 230 (1.10), 269 (0.51), 338 (0.03) 204 (3.03), 268 (0.53), 362 (0.03) (pH 7.2, 1/1, v/v) 205 (2.35), 261 (0.77), 357 (0.12) 230 (1.05), 269 (0.63), 306 (0.33), 343 (0.08) 204 (3.17), 269 (0.56), 286 (0.45), 302 (0.40), 342 (0.06) (pH 7.2, 1/1, v/v) 204 (2.33), 264 (0.76), 301 (0.46), 353 (0.18)
231 (1.25), 269 (0.67), 301 (0.43), 319 (0.41), 355 (0.08) 205 (4.52), 269 (0.55), 300 (0.49), 316 (0.51), 351 (0.09) (pH 7.2, 1/1, v/v) 204 (2.36), 272 (0.67), 314 (0.44), 361 (0.25)
472 467 468 459 481 472 473 468 486 474 472 473 516 512 494 493 497
(0.40) (0.20) (0.03) (0.01) (0.86) (0.12) (0.08) (0.01) (0.92), (1.11), (0.39), (0.03), (0.84), (0.94) (1.37), (0.40), (0.01),
λem/nm (77 K)
Φemb
467, 496 (sh) 0.017 0.006 0.042 480, 526 (sh) 0.020 0.014 0.044 533 508 508 520 696
(sh) (sh) (sh) (sh) (2.00)
527 (sh) 530 (sh) 529 (sh)
484, 533 (sh) 0.033 0.007 0.064 540, 578 (sh) 0.033 0.005 0.051
a The concentration of complexes 1−4 in different solutions is 100 μM, and reported values were averaged from at least three measurements with a relative standard deviation of ∼10%. bMeasured using a degassed aqueous solution of quinine sulfate (0.1 M H2SO4) (Φem= 0.58) as the standard.28
Au···Au contact of 2.8825(8)−3.0186(7) Å and a Ag···Au contact of 2.8290(10)−2.9831(7) Å, which are in the range typical for heterometallic Au(I)−Ag(I) alkynyl−phosphine compounds.5−9 These distances are shorter than the sum of Au(I) and M(I) van der Waals radii (3.40 Å for Au(I)−Au(I) and Au(I)−Ag(I)), implicating the presence of significant metallophilic interactions.5−9 The [Ag2(μ-dpppy)]2+ plane is almost perpendicular to two [Ag(μ-dpppy)Au]2+ planes with dihedral angles of 81.6−97.3°, and the dihedral angles between two [Ag(μ-dpppy)Au]2+ planes are 127.5 and 138.5° in complexes 1 and 3, respectively, but only 34.1° in complex 4. The alkynyl ligands adopt an asymmetric μ2-η1 bonding mode in complexes 1 and 3 but a μ2-η1:η2 bonding mode in complex 4 to join the gold(I) atom in the middle of the [Ag2Au(μdpppy)3]3+ block and one silver(I) atom, in which the Au−C lengths (1.975(5)−2.001(5) Å) are always much shorter than the Ag−C lengths (2.364(4)−2.671(3) Å) found in other
solubility that cause the other Ag−P coupling signal to be missing. Crystal Structures. The structures of compounds 1, 3, and 4 were determined by X-ray crystallography. Selected bonding parameters are presented in Table S2 (Supporting Information). The perspective views of the coordination cations of complexes 1, 4, and 3 are depicted in Figures 1 and 2 and Figure S2 in the Supporting Information, respectively. As shown in Figures 1 and 2 and Figure S2, the basic skeletons of 1, 3, and 4 consist of two silver(I) centers and two gold(I) centers, which are bridged by three dpppy ligands and two alkynyl ligands. Three dpppy ligands all adopt a bidentate bridging mode, only with six phosphorus atoms bound to two silver(I) atoms and one gold(I) atom to form one [Ag2Au(μdpppy)3]3+ block consisting of one [Ag2(μ-dpppy)3]3+ block and two [Ag(μ-dpppy)Au]2+ blocks. The other gold(I) center lies in the middle of the [Ag2Au(μ-dpppy)3]3+ block with a 4922
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heterometallic Au(I)−Ag(I) alkynyl−phosphine compounds.5−9 The two gold(I) atoms, adopting acetylide and P donors, respectively, are both in a linear coordination (C− Au(1)−C = 169.06(16)−174.99(16)°, P−Au(2)−P = 161.04(4)−170.72(4)°, respectively), whereas the silver(I) centers display a distorted-trigonal-planar environment with CP2 donors (C−Ag−P = 103.84(11)−126.88(11)°, P−Ag−P = 119.14(3)−132.39(4)°, respectively). Photophysical Properties. The photophysical data of complexes 1−4 are summarized in Table 1. The UV−vis spectra of complexes 1−4 are characterized by two high-energy bands at ca. 204−230 nm with a shoulder at 250−290 nm and a low-energy band at ca. 300−375 nm, which are typical for ligand-centered [π → π*] (diphosphine dpppy)27 and [π → π*] (CCC6H4R-4) transitions,5−20 respectively. Complexes 1−3 exhibit bright blue luminescence, and complex 4 displays green luminescence in the solid state and in solution at 298 K with excitation at λexc >300 nm. The solidstate lifetime at 298 K is in the microsecond domain, revealing that the emission is most likely associated with a spin-forbidden triplet parentage. The luminescence quantum yield and lifetimes of all four complexes depend on the solvent. It is clear from Figure 3 and Table 1 that the luminescence quantum
Figure 4. Emission spectra of complexes 1 and 2 in the solid state at 298 K.
noteworthy that complexes 3 and 4 containing electrondeficient 4-ethynylbenzoic acid methyl ester and 4-ethynylbenzaldehyde, respectively, show an emission centered at 472−515 nm with a shoulder at 508−533 nm with a single-exponential emission decay lifetime of 0.39−1.37 μs. Obviously, the emission energies of complexes 3 and 4 are considerably redshifted in comparison to complexes 1 and 2, and the luminescence lifetimes of complexes 3 and 4 are also much longer than those of complexes 1 and 2. On the basis of these observations together with the corresponding literature,1,15a it is likely that this emission originates from a metal perturbed intraligand transition, including the alkynyl ligands (4ethynylbenzoic acid methyl ester and 4-ethynylbenzaldehyde) and the dpppy ligand, since the emission energy is close to those in the free alkynyl ligand and in complexes [Ag2(μdpppy)3]2+ and [Au2(μ-dpppy)3]2+.26 Upon irradiation in the solid state with excitation light λexc >300 nm at 298 K, crystals of complex 4 exhibit bright green luminescence with an emission maximum at 516 nm (lifetime 0.84 μs) together with a lower energy emission band at 696 nm (lifetime 2.00 μs). Interestingly, when crystals of complex 4 were mechanically ground at 298 K, the lower energy emission at 696 nm gradually disappeared, whereas that at 516 nm was slightly blue-shifted to 514 nm, as depicted in Figure 5. Furthermore, the crystalline arrangement and the emission of crystals of complex 4 could be perfectly reverted when the ground powder sample was crystallized in dichloromethane solution. A similar mechanical grinding responsive emission
Figure 3. Emission spectra of 100 μM complex 4 in CH2Cl2 (black line), MeCN (red line), and MeCN/Tris-HCl (pH 7.2, 1/1, v/v) buffer solution (blue line) at 298 K with the different quantum yields.
yield of all four complexes in the different solvents follows the order MeCN/Tris−HCl (pH 7.2, 1/1, v/v) > CH2Cl2 > MeCN, whereas the luminescence lifetimes follow the order CH2Cl2 > MeCN > MeCN/Tris−HCl (pH 7.2, 1/1, v/v). The higher luminescence quantum yield in MeCN/Tris−HCl (pH 7.2, 1/1, v/v) should be due to aggregation-induced emission (AIE) as reported by the other groups,29 since complexes 1−4 are soluble in MeCN and insoluble in Tris−HCl buffer solution. When the emission bands of 1 and 2 are compared in the solid state (shown in Figure 4) or in fluid solution, a slight red shift in energy is observed on going from the phenylacetylide complex 1 to the 4-methylphenylacetylide counterpart 2, which is consistent with the better electron-donating ability of the CCC6H4CH3-4 ligand. Therefore, the emissive states of 1 and 2 are likely derived from a 3LMMCT (CCC6H4R-4 → Ag2Au2) transition, mixed with a metal cluster centered (d → s) excited state modified by metal−metal interactions in view of the short Au−Au and Au−Ag contacts observed, which also agree with the proposed emission origin in other heteronuclear Au−Ag alkynyl complexes described in the literature.5−9 It is
Figure 5. Emission spectra of crystalline complex 4 (black) and a mechanically ground sample (red) at 298 K. 4923
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switching was also found in the Ag(I)−Cu(I) complex [Ag16Cu9(μ-dpepp)3(CCC6H4But-4)20]5+.16a On the basis of the corresponding literature,16a,30 the significant emission spectral changes are probably relevant to molecular twisting, unordered packing, or lattice energy loss induced by mechanical stimuli. Recognition of Hcy and Cys. Selective reaction of the aldehyde moiety with β- and γ-aminoalkanethiol groups to form thiazolidines has been extensively applied in Hcy and Cys detection.23,24 In the present study, we first report that the Au(I)−Ag(I) heteronuclear alkynyl complex 4 with an aldehyde group has a similar ability to recognize Hcy and Cys. a. Electronic Absorption Spectroscopy. Upon addition of Hcy or Cys to the MeCN/Tris−HCl (pH 7.2, 1/1, v/v) buffer solution of 10 μM complex 4, UV−vis spectral changes of complex 4 were observed. As shown in Figure 6 and Figure S3
Figure 7. (A) Emission spectra changes of 10 μM 4 in the MeCN/ Tris−HCl (pH 7.2, 1/1, v/v) buffer solution with different concentrations of Hcy from 1 to 11: 0, 2.0, 4.0, 6.0, 8.0, 10.0, 12.0, 14.0, 16.0, 18.0, 20.0 μM. (B) Plot of (I0 − I)/I0 vs the logarithm of the Hcy concentration. I0 and I are the area integrations of the emission intensity of 4 without and with Hcy, respectively.
emission intensity of 4 in the absence and presence of Hcy, and R is the regression coefficient. Similarly, the quenched ratio of the area integrations of the emission intensity of 4 showed a good linearity in the concentrations of 0−10 and 10−20 μM for Cys, shown in Figure S4 in the Supporting Information. The strong luminescence quench of 4 was in contrast to those found in other metal complexes containing aldehyde groups upon addition of Hcy or Cys.24 To confirm the recognition mechanism of complex 4 for Hcy and Cys, the emission intensity changes of complexes 1−3 were investigated upon addition of Hcy or Cys to the MeCN/Tris− HCl (pH 7.2, 1/1, v/v) buffer solution of 10 μM complexes 1− 3, shown in Figure S5 in the Supporting Information. It was found on addition of Hcy or Cys to the MeCN/Tris−HCl (pH 7.2, 1/1, v/v) buffer solution of 10 μM complexes 1−3, the emission intensities of complexes 1−3 were almost not changed, which indicated that the aldehyde group with Hcy or Cys to form thiazinane or thiazolidine was a key role in the selective recognition of Hcy and Cys. To further confirm the reaction of complex 4 with Hcy, 1H NMR spectroscopy of complex 4 and Hcy in CD3CN/D2O (10/1) was also carried out. Upon addition of Hcy to the CD3CN/D2O (10/1) solution of complex 4, the signal corresponding to CHO was weakened, and a new signal corresponding to NCHS appeared at 5.94 ppm, as shown in Figure S6 in the Supporting Information. The results further demonstrated that Hcy could reaction with the aldehyde group of complex 4. c. Selective Optical Response of 4 to Various Amino Acids, Proteins, and Common Anions. The selectivity of complex 4 to other elementary amino acids, proteins, and common anions was investigated by photoluminescent spectroscopy. Upon the addition of a 100-fold excess of amino acids such as L-alanine (Ala), L-asparagine (Asp), L-glutamine (Glu), L-glycine (Gly), Lhistidine (His), L-lysine (Lys), L-methionine (Met), L-phenylalanine (Phe), L-proline (Pro), L-serine (Ser), L-tryptophan (Try), and L-tyrosine (Tyr), proteins such as α-fetoprotein (AFP) and human serum albumin (HSA), and other common anions such as K+, Na+, Mg2+, Ca2+, and Zn2+ to the MeCN/ Tris−HCl (pH 7.2, 1/1, v/v) buffer solution of 10 μM complex 4, no obvious changes or a very small luminescence decrease was measured in the emission spectra (Figure 8), which
Figure 6. Changes in UV−vis absorption spectra of 10 μM 4 in the MeCN/Tris−HCl (pH 7.2, 1/1, v/v) buffer solution with various amounts of Hcy (0−25 μM).
(Supporting Information), a slight increase of the absorption band at 250−290 nm and a slight decrease of the band at 300− 375 nm with a slight red shift of 5−10 nm produce a perfectly clean isosbestic point at ca. 286 nm upon addition of Hcy or Cys. These results suggested that the formation of thiazinane in the aldehyde groups of complex 4 would reduce the electronwithdrawing effect of the alkynyl ligand and result in the large changes in the UV−vis absorption spectra with a red shift of the ligand-centered [π → π*] (CCC6H4R-4) transition band. b. Photoluminescence Properties. The recognition ability of the new complex 4 for Cys and Hcy was also investigated by emission spectrophotometric studies. Figure 7 shows the emission intensity changes of 10 μM 4 in the MeCN/Tris− HCl (pH 7.2, 1/1, v/v) buffer solution with different concentrations of Hcy. The emission intensity of 4 was decreased rapidly with increasing Hcy concentration from 0 to 10 μM and then was decreased slowly upon further increasing the Hcy concentration to 20 μM, indicating that the reaction rate between complex 4 and Hcy is dependent on the concentration of Hcy. The quenched ratio of the area integrations of the emission intensity ((I0 − I)/I0) was linear with the logarithm of the Hcy concentration (CHcy) in the ranges 0−10 and 10−20 μM, and the regression equation was (I0 − I)/I0 = −0.01043 + 0.63714 log(CHcy × 106), R2 = 0.9974 (CHcy in the range of 0−10 μM) and (I0 − I)/I0 = 0.27673 + 0.33810 log(CHcy × 106), R2 = 0.9824 (CHcy in the range of 10− 20 μM), respectively. I0 and I are the area integrations of the 4924
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A) of the Fujian Provincial Department of Education, People’s Republic of China (Grant JA12021), and Fuzhou University (Grant XRC-0723).
indicated that complex 4 had a high specificity for recognition of Hcy and Cys.
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(1) (a) Yam, V. W.-W. Acc. Chem. Res. 2002, 35, 555. (b) Wong, K. M.-C.; Yam, V. W.-W. Acc. Chem. Res. 2011, 44, 424. (2) (a) Long, N. J.; Williams, C. K. Angew. Chem., Int. Ed. 2003, 42, 2586. (b) Buschbeck, R.; Low, P. J.; Lang, H. Coord. Chem. Rev. 2011, 255, 241. (3) Chen, Z.-N.; Zhao, N.; Fan, Y.; Ni, J. Coord. Chem. Rev. 2009, 253, 1. (4) (a) Jia, J.-H.; Wang, Q.-M. J. Am. Chem. Soc. 2009, 131, 16634. (b) Manbeck, G. F.; Brennessel, W. W.; Stockland, J.; Robert, A.; Eisenberg, R. J. Am. Chem. Soc. 2010, 132, 12307. (c) Wang, Q.-M.; Lee, Y.-A.; Crespo, O.; Deaton, J.; Tang, C.; Gysling, H. J.; Gimeno, M. C.; Larraz, C.; Villacampa, M. D.; Laguna, A.; Eisenberg, R. J. Am. Chem. Soc. 2004, 126, 9488. (5) (a) Wei, Q.-H.; Zhang, L.-Y.; Yin, G.-Q.; Shi, L.-X.; Chen, Z.-N. J. Am. Chem. Soc. 2004, 126, 9940. (b) Wei, Q.-H.; Zhang, L.-Y.; Yin, G.Q.; Shi, L.-X.; Chen, Z.-N. Organometallics 2005, 24, 3818. (c) Wei, Q.-H.; Yin, G.-Q.; Zhang, L.-Y.; Chen, Z.-N. Organometallics 2006, 25, 4941. (6) (a) Koshevoy, I. O.; Karttunen, A. J.; Kritchenkou, I. S.; Krupenya, D. V.; Selivanov, S. I.; Melnikov, A. S.; Tunik, S. P.; Haukka, M.; Pakkanen, T. A. Inorg. Chem. 2013, 52, 3663. (b) Koshevoy, I. O.; Lin, C.-L.; Karttunen, A. J.; Jänis, J.; Haukka, M.; Tunik, S. P.; Chou, P.-T.; Pakkanen, T. A. Inorg. Chem. 2011, 50, 2395. (c) Koshevoy, I. O.; Lin, Y.-C.; Chen, Y.-C.; Karttunen, A. J.; Haukka, M.; Chou, P.-T.; Tunik, S. P.; Pakkanen, T. A. Chem. Commun. 2010, 46, 1440. (d) Koshevoy, I. O.; Karttunen, A. J.; Shakirova, J. R.; Melnikov, A. S.; Haukka, M.; Tunik, S. P.; Pakkanen, T. A. Angew. Chem., Int. Ed. 2010, 49, 8864−8866. (7) Blanco, M. C.; Cámara, J.; Gimeno, M. C.; Jones, P. G.; Laguna, A.; López-de- Luzuriaga, J. M.; Olmos, M. E.; Villacampa, M. D. Organometallics 2012, 31, 2597−2605. (8) Vicente, J.; Chicote, M.-T.; Alvarez-Falcón, M. M.; Jones, P. G. Organometallics 2005, 24, 4666. (9) Schuster, O.; Monkowius, U.; Schmidbaur, H.; Ray, R. S.; Krüger, S.; Rösch, N. Organometallics 2006, 25, 1004. (10) (a) He, X. M.; Zhu, N. Y.; Yam, V. W.-W. Dalton Trans. 2011, 40, 9703. (b) He, X. M.; Yam, V. W.-W. Coord. Chem. Rev. 2011, 255, 2111. (c) Yip, S.-K.; Chan, C.-L.; Lam, W. H.; Cheung, K.-K.; Yam, V. W.-W. Photochem. Photobiol. Sci. 2007, 6, 365. (11) (a) Koshevoy, I. O.; Koskinen, L.; Haukka, M.; Tunik, S. P.; Serdobintsev, P. Y.; Melnikov, A. S.; Pakkanen, T. A. Angew. Chem., Int. Ed. 2008, 47, 3942. (b) Koshevoy, I. O.; Chang, Y.-C.; Karttunen, A. J.; Haukka, M.; Pakkanen, T.; Chou, P.-T. J. Am. Chem. Soc. 2012, 134, 6564. (c) Koshevoy, I. O.; Chang, Y.-C.; Karttunen, A. J.; Shakirova, J. R.; Jänis, J.; Haukka, M.; Pakkanen, T.; Chou, P.-T. Chem. Eur. J. 2013, 19, 5104. (d) Shakirova, J. R.; Grachova, E. V.; Gurzhiy, V. V.; Koshevoy, I. O.; Melnikov, A. S.; Sizova, O. V.; Tunik, S. P.; Laguna, A. Dalton Trans. 2012, 41, 2941. (e) Koshevoy, I. O.; Lin, Y.-C.; Karttunen, A. J.; Chou, P.-T.; Vainiotalo, P.; Tunik, S. P.; Haukka, M.; Pakkanen, T. A. Inorg. Chem. 2009, 48, 2094. (f) Koshevoy, I. O.; Lin, Y.-C.; Chen, Y.-C.; Karttunen, A. J.; Haukka, M.; Chou, P.-T.; Tunik, S. P.; Pakkanen, T. A. Chem. Commun. 2010, 46, 1440. (12) Lang, H.; Koc̈her, S.; Back, S.; Rheinwald, G.; van Koten, G. Organometallics 2001, 20, 1968.. (13) de la Riva, H.; Nieuwhuyzen, M.; Fierro, C. M.; Raithby, P. R.; Male, L.; Lagunas, M. C. Inorg. Chem. 2006, 45, 1418. (14) Bruce, M. I.; Hall, B. C.; Skelton, B. W.; Smith, M. E.; White, A. H. Dalton Trans. 2002, 995. (15) (a) Wei, Q.-H.; Yin, G.-Q.; Zhang, L.-Y.; Shi, L.-X.; Mao, Z.-W.; Chen, Z.-N. Inorg. Chem. 2004, 43, 3484. (b) Wei, Q.-H.; Yin, G.-Q.; Zhang, L.-Y.; Chen, Z.-N. Inorg. Chem. 2006, 45, 10371.
Figure 8. Emission intensity changes of complex 10 μM 4 in the MeCN/Tris−HCl (pH 7.2, 1/1, v/v) buffer solution upon the addition of 100 equiv of amino acids, proteins, and common anions and 2 equiv of Hcy and Cys.
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CONCLUSIONS This paper has described the synthesis, characterization, and photophysical properties of the four luminescent heteronuclear alkynyl clusters [Ag2Au2(μ-dpppy)3(CCC6H4R-4)2](ClO4)2 (R = H (1), CH3 (2), COOCH3 (3), CHO (4)). It is revealed that the utilization of the tridentate dpppy ligand provides an opportunity for the systematic variation of the structural topologies of the desired heteronuclear Ag(I)−Au(I) alkynyl− phosphine complexes, which show novel photophysical properties. The recognition interactions of complex 4 containing aldehyde groups with homocysteine (Hcy) and cysteine (Cys) resulted in a strong luminescence quench. The method for the recognition of Hcy and Cys is selective and sensitive without the interference of other amino acids, proteins, and common anions. This work provided a new strategy for the design of other heteronuclear alkynyl cluster based luminescence probes for selective recognition of Hcy or Cys and could be expected to extend the applications of heteronuclear alkynyl clusters in various biological sensing applications.
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ASSOCIATED CONTENT
S Supporting Information *
A table giving crystallographic parameters and the details for data collection and refinement of compounds 1, 3, and 4, CIF files giving the X-ray crystallographic data for the structure determination of compounds 1, 3, and 4 and Figures S1−S6. This material is available free of charge via the Internet at http://pubs.acs.org.
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REFERENCES
AUTHOR INFORMATION
Corresponding Author
*E-mail for Q.-H.W.:
[email protected]. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This study was financially supported by the National Basic Research Program of China (Grant 2010CB732403), the National Science Foundation for Fostering Talents in Basic Research of China (No. J1103303), Key Science Project (type 4925
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(16) (a) Chen, Z.-H.; Zhang, L.-Y.; Chen, Z.-N. Organometallics 2012, 31, 256. (b) Xie, Z.-L.; Wei, Q.-H.; Zhang, L.-Y.; Chen, Z.-N. Inorg. Chem. Commun. 2007, 10, 1206. (17) Connell, T. U.; Sandanayake, S.; Khairallah, G. N.; White, J. M.; O’Hair, R. A. J.; Donnelly, P. S.; Williams, S. J. Dalton Trans. 2013, 42, 4903. (18) Koshevoy, I. O.; Karttunen, A. J.; Lin, Y.-C.; Lin, C.-C.; Chou, P.-T; Tunik, S. P.; Haukka, M.; Pakkanen, T. A. Dalton Trans. 2010, 39, 2395. (19) Abu-Salaha, O. M.; Hussain, M. S.; Schlemper, E. O. Chem. Commun. 1988, 212. (20) Evans, R. C.; Douglas, P.; Winscom, C. J. Coord. Chem. Rev. 2006, 250, 2093. (21) Wood, Z. A.; Schröder, E.; Harris, J. R.; Poole, L. B. Trends Biochem. Sci. 2003, 28, 32. (22) Nekrassova, O.; Lawrence, N. S.; Compton, R. G. Talanta 2003, 60, 1085. (23) (a) Rusin, O.; Luce, N. N. S.; Agbaria, R. A.; Escobedo, J. O.; Jiang, S.; Warner, I. M.; Dawan, F. B.; Lian, K.; Strongin, R. M. J. Am. Chem. Soc. 2004, 126, 438. (b) Wang, W. H.; Rusin, O.; Xu, X. Y.; Kim, K. K.; Escobedo, J. O.; Fakayode, S. O.; Fletcher, K. A.; Lowry, M.; Schowalter, C. M.; Lawrence, C. M.; Fronczek, F. R.; Warner, I. M.; Strongin, R. M. J. Am. Chem. Soc. 2005, 127, 15949. (24) (a) Chen, H. L.; Zhao, Q.; Wu, Y. B.; Li, F. Y.; Yang, H.; Yi, T.; Huang, C. H. Inorg. Chem. 2007, 46, 11075. (b) Li, M. J.; Zhan, C. Q.; Nie, M. J.; Chen, G. N.; Chen, X. J. Inorg. Biochem. 2011, 105, 420. (25) Coates, G. E.; Parkin, C. J. Chem. Soc. 1962, 3220. (26) (a) Kuang, S. M.; Zhang, L. M.; Zhang, Z. Z.; Wu, B. M.; Mak, T. C. W. Inorg. Chim. Acta 1999, 284, 278. (b) Shieh, S.-J.; Li, D.; Peng, S.-M.; Che, C.-M. J. Chem. Soc., Dalton Trans. 1993, 195. (27) (a) Evans, P. R. Proceedings of the CCP4 Study Weekend. Recent Advances in Phasing; Wilson, K. S., Davies, G., Ashton, A. W., Bailey, S., Eds.; Daresbury Laboratory: Warrington, U.K., 1997. (b) Spek, A. L. J. Appl. Crystallogr. 2003, 36, 7. (c) Sheldrick, G. M. SHELXL-97, Program for the Refinement of Crystal Structures; University of Göttingen, Göttingen, Germany, 1997. (28) Demas, J. N.; Crosby, G. A. J. Phys. Chem. 1971, 75, 991. (29) (a) Yu, G.; Yin, S. W.; Liu, Y. Q.; Chen, J. S.; Xu, X. J.; Sun, X. B.; Ma, D. G.; Zhan, X. W.; Peng, Q.; Shuai, Z. G.; Tang, B. Z.; Zhu, D. B.; Fang, W. H.; Luo, Y. J. Am. Chem. Soc. 2005, 127, 6335. (b) Wu, H. Z.; Yang, T. S.; Zhao, Q.; Zhou, J.; Li, C. Y.; Li, F. Y. Dalton Trans. 2011, 40, 1969. (c) Jiang, Y. H.; Wang, Y. C.; Hua, J. L.; Tang, J.; Li, B.; Qian, S. X.; Tian, H. Chem. Commun. 2010, 46, 4689. (30) (a) Lee, Y.-A.; Eisenberg, R. J. Am. Chem. Soc. 2003, 125, 7778. (b) Kuchison, A. M.; Wolf, M. O.; Patrick, B. O. Chem. Commun. 2009, 7387. (c) Laguna, A.; Lasanta, T.; López-de-Luzuriaga, J. M.; Monge, M.; Naumov, P.; Olmos, M. E. J. Am. Chem. Soc. 2010, 132, 456. (d) Osawa, M.; Kawata, I.; Igawa, S.; Hoshino, M.; Fukunaga, T.; Hashizume, D. Chem. Eur. J. 2010, 16, 12114. (e) Tsukuda, T.; Kawase, M.; Dairiki, A.; Matsumoto, K.; Tsubomura, T. Chem. Commun. 2010, 46, 1905.
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