Synthesis and Crystal Structure of a Dinuclear Cu(II) Complex Based on a Carboxyl-substituted 1H-1,2,3-Triazole and Its DNA Cleavage Activity①

LIU Wen-Qian ZHOU Shi-Lei FAN Ming-Zhu PAN Zhi-Quan CHEN Yun-Feng

(School of Chemistry and Environmental Engineering, Wuhan Institute of Technology, Wuhan 430073, China)

Synthesis and Crystal Structure of a Dinuclear Cu(II) Complex Based on a Carboxyl-substituted 1H-1,2,3-Triazole and Its DNA Cleavage Activity①

LIU Wen-Qian ZHOU Shi-Lei FAN Ming-Zhu PAN Zhi-Quan CHEN Yun-Feng②

(School of Chemistry and Environmental Engineering, Wuhan Institute of Technology, Wuhan 430073, China)

The novel dinuclear copper complex [Cu2(H2O)2(DMF)2(L)2] (1, H2L = 5-phenyl-2H-1,2,3-triazole-4-carboxylic acid, DMF = N,N-dimethyl-formamide) has been synthesized and characterized by X-ray single-crystal diffraction.The compound crystallizes in triclinic system, space group P1 with a = 9.591, b = 10.508, c = 15.515 ?, β = 75.11°, V = 1446.2 ?3, Z = 2, Mr= 683.62, Dc= 1.570 g/cm3, μ = 1.531 mm-1, F(000) = 700, the final R = 0.0404 and wR = 0.1130 for 5327 observed reflections with I > 2σ(I).In each unit of the complex, two Cu2+ions coordinated with two triazole ligands to form a dimeric [5,6,5] tricyclic structure.The central Cu atom is five-coordinated, and each copper atom shows a square pyramidal geometry.The crystal structure is stabilized by the inversion-related O–H··O hydrogen bond and C–H··O hydrogen bonding interactions to form a layer structure.Fluorescent spectra show an obvious quenching of fluorescence compared with free 1,2,3-triazole ligand.The results of agarose gel electrophoresis indicate that this complex can cleave the plasmid supercoiled DNA within shorter time in the 50-folds excess of ascorbate under physiological conditions, providing a new example in the research for artificial metal nucleic acid enzyme.

1,2,3-triazole, copper complex, crystal structure, fluorescent property, DNA cleavage activity;

1 INTRODUCTION

Design and syntheses of metal coordination complexes which can cleave DNA and RNA are the topics of modern bioinorganic chemistry[1].Many of these reagents have already provided useful footprinting reagents in vitro.However, the reagents which show indeed applications in intracellular were rare to date[2].There were some challenges to accomplish this goal, especially the toxic xenobiotics for normal cellular of metal complexes.Therefore, the choice of ligand and the coordination mode of complexes were the key factors for finding metal complexes as enzyme-like reagents.N-heterocycles are important ligands for transition metal chemistry, so far, some N-heterocycles, such as imidazoles, benzoimidazoles, pyrazoles, pyridines and 1,2,4-triazoles have been widely used as coordination ligand for transition metals[3].The 1,2,3-triazoles, which bear three successive nitrogen atoms, showunique properties by contrast with their isomeric 1,2,4-triazoles.The bioisosteres of amide show good thermal stability and resist the oxidative or reductive reagents.More importantly, the 1,2,3-triazoles show lower toxicity against the normal cell.Indeed, 1,2,3-triazoles and their derivatives have been widely used in many fields, especially in betalactamase inhibitors[4], bacteriostat[5], antineoplastic[6], anti-epileptic[7]and relieve pain[8].For the abundant coordination nitrogen atoms and high electron density of the 1,2,3-triazole ring together with their strong stability, they are also be used as ligands to form metal complexes, such as Cu, Zn, Co, Ni, Pd, etc[9-17].Some of them show intriguing structural features and unique properties.Carboxylatesubstituted 1,2,3-triazoles are good ligands for the syntheses of metal complexes.However, most of them are based on 1,2,3-triazole-4,5-dicarboxylic acid[18-22].Metal complexes based on unsymmetric carboxylate-substituted 1,2,3-triazoles ligands are rare so far.For example, there is no metal complex based on 5-phenyl-2H-1,2,3-triazole-4-carboxylic acid.There are three successive nitrogen atoms and a carboxyl group which can coordinate with different metal ions.Herein, we synthesize a dinuclear Cu(II)-ligand complex [Cu2(H2O)2(DMF)2(L)2].It is found that this complex can insert DNA grooves to cleave the DNA effectively.We proposed that the coordination environment and the special structure of this complex were the reasons for its high DNA-cleavage activity.At the same time, the controlled experiments also showed oxidative mechanism for its unique DNA-cleavage activity.

2 EXPERIMENTAL

2.1 Materials and general method

All chemicals were commercially available and used without further purification.Tris(hydroxymethyl) amino-methane (Tris), bromophenol blue, ethidium bromide (EB), agarose gel and pBR322 DNA were purchased from TOYOBO.CO.

The buffer solutions were prepared with doubledistilled water.TAE buffer: 60.5 g Tris-base, 14.3 mL acetic acid and 9.3 g EDTA in 250 mL water, pH = 8; Reaction solution: VDMF:VTB= 3:1; BSE solution: 0.25% bromophenol blue, 40% (w/v) sucrose, and kept at 4 ℃; EB solution: ethidium bromide 0.1 g in 100 mL water.

2.2 Synthesis of 5-phenyl-1H-1,2,3-triazole-4-carboxylic acid (L)

The synthetic routine was shown in Scheme.1.Iodobenzene (2.04 g, 10 mmol), PdCl2(PPh3)2(350 mg, 0.5 mmol), CuI (95.3 mg, 0.5 mmol), K2CO3(2.76 g, 20 mmol) and PPh3(157.4 mg, 0.6 mmol) were added to a pear-shaped Schlenk tube charged with a magnetic stirrer.The tube was evacuated and backfilled with argon and then degassed THF (80 mL) was introduced, followed by introducing ethyl propiolate (1.47 g, 15 mmol).The mixture was heated at 60 ℃ for 5 h, then poured into water and extracted with EtOAc.The organic layer was further washed with brine and dried with anhydrous Na2SO4.After filtration through a short column (silica gel), the eluent was concentrated under reduced pressure to give oil which was redissolved in DMSO (20 mL).Subsequently, NaN3(0.98 g, 15 mmol) was added into the solution, then heated at 100 ℃.The reaction was monitored by TLC.After the completion of the reaction, the mixture was poured into water and extracted with EtOAc.The organic layer was washed with brine and dried with anhydrous Na2SO4.After filtration, the solution was concentrated under reduced pressure, the crude product was dissolved in MeOH, and then NaOH (2.2 g, 55 mmol) was added.The solution was stirred at room temperature for 3 h, followed by adding HCl (2N).After that, the solution was concentrated under reduced pressure.The obtained solid was washed with cold water, then recrystallized with MeOH to give the 5-phenyl-2H-1,2,3-triazole-4-carboxylic acid (0.98 g, 52.06%).m.p: 200～202 ℃.IR (KBr, v·cm-1): 3240, 1728, 1685, 1615.

Scheme 1.Synthesis of 5-phenyl-2H-1,2,3-triazole-4-carboxylic acid

2.3 Synthesis of complex [Cu2(H2O)2(DMF)2(L)2] (1)

To a solution of 5-phenyl-2H-1,2,3-triazole-4-carboxylic acid (5 mg, 0.026 mol) in methanol (5 mL) was added Cu(OAc)2·H2O (15.6 mg, 0.078 mol) in one pot, then Et3N (5 mL) was added.The mixture was stirred at room temperature for 48 h.The obtained precipitate was filtered and washed with methanol twice to give a blue solid.This blue solid was dissolved with DMF, and the clear solution was kept in diethyl ether atmosphere at room temperature for 7 days, obtaining blue crystals of complex [Cu2(H2O)2(DMF)2(L)2] (17.5 mg, yield: 32.8%).Anal.Calcd.(%) for C24H28Cu2N8O8: C, 41.91; H, 4.30; N, 16.25.Found (%): C, 42.17; H, 4.13; N, 16.39.IR: ν(OH) 3242(s), ν(C=O) 1731(s), ν(C=N) 1645(s), 1589(w), 1408(w), 1259(w) cm-1.UV (DMF, 10-4M, λmax, 290 nm): 355 (s).

2.4 X-ray data collection and refinement

A blue single crystal of the complex with dimensions of 0.12mm × 0.10mm × 0.10mm was mounted at 293(2) K by using a graphite-monochromated MoKα (λ = 0.71073 ?) radiation with an ω-φ scan mode (2.03<θ<25.50o).A total of 10552 reflections were collected and 5327 were independent with Rint= 0.0258, of which 5327 were observed with I > 2σ(I).Data reduction and cell refinement were performed by AMART and SAINT programs[23].All calculations were performed using SHELXTL-97 crystallographic software package[24].All nonhydrogen atoms were refined anisotropically and all hydrogen atoms except those of aqua molecule were determined with theoretical calculations and refined isotropically.The final R = 0.0404, wR = 0.1130 (w(Δρ)max= 0.542 and (Δρ)min= –0.590 e/?3.The selected bond lengths and bond angles are listed in Table 1.

Table 1.Selected Bond Lengths (?) and Bond Angles (°)

2.5 Physical measurements

IR spectra were recorded on a vector 22 FI-IR spectrophotometer using KBr disk.Elemental analyses were performed on a Perkin-Elmer 240 analyzer.UV-Vis spectra were recorded on an UV-2450 spectrophotometer.The liquid-state fluorescence emission/excitation spectra were recorded on a Hitachi F-7500 fluorescence spectrophotometer equipped with a continuous Xe-900 xenon lamp and a μF900 microsecond flash lamp.The Agarose gelelectrophoresis patterns were analyzed by UVPGDS-8000 gel imaging analysis system.

2.6 Experiment of agarose gel electrophoresis

Negative supercoiled pBR322 DNA (1 μL, 0.25 μg·μL-1) was treated with different concentration of complexes (3 μL) in Tris-HCl buffer (1 μL, 50 mmol·L-1Tris-HCl, 50 mmol·L-1NaCl, pH = 7.2).After mixing, the DNA solutions were incubated at room temperature for 1 h.The reactions were quenched by the addition of sterile solution (1 μL, 0.25% bromophenol blue and 40% w/v sucrose).The samples were then analyzed by electrophoresis for 45 min at 120 V on agarose gel in TAE buffer (40 mmol·L-1Tris-base, 40 mmol·L-1acetic acid and 1 mmol·L-1EDTA, pH = 7.4).The gel was stained with EB (1μg·μL-1) for 2 min after electrophoresis and then photographed.

3 RESULTS AND DISCUSSION

The symmetric unit of 1 contains two crystallographically unique complexes.Each complex includes two Cu2+ions, two water molecules, two DMF molecules and two 1,2,3-triazole ligands, as shown in Fig.1.The coordination configuration around each Cu(II) ion can be described as a square pyramid, in which the oxygen atom of DMF occupies the apical position, while two nitrogen atoms (from two triazoles) and two oxygen atoms (from carboxylate and H2O) are located on the base plane.Deviations of Cu(1) and Cu(2) atoms from the mean plane, formed by O(2), O(4), N(2) and N(3), as well as O(5), O(8), N(6) and N(7), are 0.099 and 0.120 ?, respectively.The coordination environments for these two Cu(II) ions are litter different for their bond distances and bond angles.The distances of Cu–O (H2O) are 1.981(4) and 1.995(3) ?, and those of Cu–O (COO–) are 1.960(3) and 1.955(3) ?, which show strong coordination, while the Cu–O (DMF) bonds are 2.413(3) and 2.380(3) ?, respectively, longer than Cu–O (H2O) and Cu–O (COO-).It reveals that the coordination of DMF is liable.By the way, although the central metal Cu(II) ions could form tetragonal bipyramidal structures, the potential steric repulsion maybe induces the formation of this pyramidal structure.Moreover, there are abundant hydrogen bonding interactions in the crystal structure, which play an important role in forming the 2D structure, as shown in Table 2.(a) H-bonding between the water and carboxylate O atom of H2L O(4)–H(4A)××O(2)#3 (d = 2.49(6) ?, q= 120(6)°); (b) H-bonding between the coordination water and N atoms from 1,2,3-tiazole O(4)–H(4B)××N(1) (d = 2.50(6) ?, q = 112(5)°); (c) H-bonding between the DMF and O atoms of carboxylate group C(10)–H(10)××O(6)#6 (d = 2.53 ?,q = 126.4°); (d) H-bonding between the water from one crystallographically unique complex and carboxylate O atom of another H2L molecule O(8)–H(8A)××O(1) (d = 2.259(14) ?, q = 170(6)°); (e) H-bonding between water and carboxylate O atom in the same molecule O(8)–H(8B)××O(5)#5 (d = 2.39(5) ?, q = 134(6)°); (f) H-bonding between the DMF from one crystallographically unique complex and O atom of the carboxylate group from another C(12)–H(12C)××O(6)#6 (d = 2.51 ?, q = 130.7°); (g) H-bonding between the methyl of DMF from the crystallographically unique complex and O atom of the carboxylate group from another C(22)–H(22)××O(1)#4 (d = 2.42 ?, q = 128.5°).With the contribution of these abundant hydrogen bonds, two complex molecules were connected to form a 3-D supramolecular network structure, as shown in Fig.2.

The fluorescence of the complex and ligand has been recorded in the DMF solution (10-4mmol·L-1) at room temperature.From Fig.3, the emission peaks have been observed at 352 nm (λex= 298) for H2L and 355 nm (λex= 290) for complex 1.The complex and ligand had different fluorescence intensity when tested in the same emission wavelength, and this difference could be attributed to the classic photoinduced electron transfer (PET) mechanism[25-28].When the triazole rings and the carboxylate group of the host formed a complex with the metal, the excited electron state of the1,2,3-triazole ring was then transferred to the LUMO of Cu2+, which induced the fluorescence quenching.

Fig.1.Binuclear structure of complex 1.Symmetry transformation for the compound: #1: –x, –y, –z+1; #2: –x+1, –y+2, –z

Fig.2.3-D structure of the complex

Fig.3.Fluorescence spectra of the complex and free ligand

Table 2.Hydrogen Bond Lengths (?) and Bond Angles (°)

Because each central copper(II) ion exhibits a square pyramidal structure, together with a liable coordinated DMF molecule, we proposed that this complex can form a flat structure by releasing the coordinated DMF molecules, which have the potential to insert DNA groove.So, the cleavage of supercoiled plasmid pBR322 DNA by the complex was studied in the presence of ascorbate and H2O2.As shown in Fig.4, with increasing the concentration of the complex, the amount of form I (supercoiled form) of DNA diminished obviously, whereas that of form III (linear form) increased.When the concentration of the complex was 150 μmmol·L-1, no fluorescent stripe could be seen, and we propose this form to be the smaller nicked DNA fragment.These results suggest that this complex indeed has DNA cleavage efficiency.At the same time, time dependence of the cleavage ability of DNA with the complex reveals that the cleavage of DNA increased with increasing the incubation time (Fig.5).The DNA cleavage activity is higher than the 1,10-phenanthroline-cuprous complex to some extent[29].Furthermore, the comparison experiments with typical scavengers also identify that this complex cleaves the DNA (Fig.6) via the general three steps procedure[30-32]: (1) complex binding with DNA, (2) the formation of reactive metal-oxo species (RMOS) because meta-dicopper structure favors RMOS in a synergic manner in the presence of O2, (3) the RMOS, which acts as a double strands DNA scissors, finally cleaved the supercoil DNA (form I) into linear DNA (form Ⅲ).The formation of cuprous complex is essential to the active oxygen to form a RMOS, so the ascorbate was needed to translate the Cu(Ⅱ) to Cu(I) in this reaction.

Fig.4.Agarose gel electrophoresis patterns for the cleavage of pBR322 DNA plasmid DNA by [Cu2(H2O)2(DMF)2(L1)2] in the presence of 50-fold excess of ascorbate and H2O2; Conditions: 0.25 μg.μL-1DNA 1 μL; 3 μL complex; 1 μL bromophenol-blue terminate agent; 50 fold ascorbate and H2O2; at room temperature for 60 min.Lane1: DNA control; Lane2-6: DNA and ascorbate and 25 μmol·L-1, 50 μmol·L-1, 100 μmol·L-1, 150 μmol·L-1or 200 μmol·L-1of the complex, respectively; Lane7-12: DNA and H2O2and 25 μmol·L-1, 50 μmol·L-1, 100 μmol·L-1, 150 μmol·L-1or 200 μmol·L-1of complex, respectively

Fig.5.Agarose gel electrophoresis patterns for the cleavage of pBR322 DNA plasmid DNA by [Cu2(H2O)2(DMF)2(L1)2] in the presence of 50-fold excess of ascorbate for different time; Conditions: 0.25 μg·μL-1DNA 1 μL; 3 μL complex (150 μmol·L-1); 1 μL bromophenol-blue terminate agent; 50 fold ascorbate; at room temperature; Lane1: DNA control Lane2-5: DNA, complex and ascorbate after 15, 30, 45 and 60 min, respectively

Fig.6.Agarose gel electrophoresis patterns for the cleavage of pBR322 DNA plasmid DNA by [Cu2(H2O)2(DMF)2(L1)2], and in the presence of DMSO, NaN3, KI and ascorbate, respectively; Conditions: 0.25 μg·μL-1DNA 1 μL; 3 μL complex; 1 μL bromophenol-blue terminate agent; 3 μL DMSO, NaN3, KI and ascorbate; at room temperature for 60 min; Lane1: DNA control; Lane2-6: DNA and complex, DNA, complex and DMSO (5 mmol·L-1), DNA, complex and NaN3(5 mmol·L-1), DNA ,complex and KI (5 mmol·L-1), DNA, complex and ascorbate (5 mmol·L-1), respectively

4 CONCLUSION

In summary, the 5-phenyl-2H-1,2,3-triazole-4-carboxylic acid ligand and its’ binuclear copper complex [Cu2(H2O)2(DMF)2(L1)2] 1 were synthesized, and its structure was characterized by single-crystal X-ray diffraction techniques.The central metal Cu(II) ions exhibit a square pyramidal geometry with a liable coordinated DMF.The fluorescence analysis reveals the quenching of the fluorescence properties.And this complex showed great cleavage activity towards pBR322 DNA in the presence of ascorbate.Within increasing the contractions and time, the supercoil DNA could be cleaved into linear DNA or even unrecognized fragments, and this potential flat dinuclear copper(II) structure may be the reason for interaction with DNA effectively.The mechanism of the complex DNA cleavage activity may prefer oxidative DNA cleavage, and further researches on its’ detail mechanism are underway.

REFERENCES

(1) Sigman, D.S.; Mazumder, A.; Perri, D.M.Chemical nuclease.Chem.Rev.1993, 93, 2295–2316.

(2) Yue, L.; Zhou, Y.Z.Chromium complexes with cleaving DNA activity.Prog.Chem.2009, 21, 2093–2099.

(3) Li, J.; Xiong, P.P.; Bu, H.Y.; Chen, S.P.Syntheses, structures, antifungal activities and DNA cleavage of transition metal coordination compounds with 4-(1H-1,2,4-triazol-1-ylmethyl).Acta Phys-Chim.Sin.2014, 30, 1354–1362.

(4) Kuzin, A.P.; Nukaga, M.; Nukaga, Y.; Hujer, A.; Bonomo, R.A.; Knox, J.R.Inhibition of the SHV-1 β-lactamase by sulfones: crystallographic observation of two reaction intermediates with tazobactam.Biochemistry 2001, 40, 1861–1866.

(5) Karanam, M.; Dev, S.; Choudhury, A, R.New polymorphs of fluconazole: results from cocrystallization experiments.Cryst.Growth Des.2012, 12, 240–252.

(6) Bratsos, I.; Urankar, D.; Zangrando, E.; Genova-Kalou, P.; K?smrlj, J.; Alessio, E.; Turel, I.1-(2-picolyl)-substituted 1,2,3-triazole as novel chelating ligand for the preparation of ruthenium complexes with potential anticancer activity.Dalton Trans.2011, 40, 5188–5199.

(7) Fisher, S.Z.; Aggarwal, M.; Kovalevsky, A, Y.; Silverman, D.N.; McKenna, R.Neutron diffraction of acetazolamide-bound human carbonic anhydrase II reveals atomic details of drug binding.J.Am.Chem.Soc.2012, 134, 14726?14729.

(8) Gall, M.; Kamdar, B.V.; Collins, R.J.Pharmacology of some metabolites of triazolam, alprazolam, and diazepam prepared by a simple, one-step oxidation of benzodiazepines.J.Med.Chem.1978, 21, 1290?1294.

(9) Hu, M.C.; Wang, Y.; Zhai, Q.G.; Li, S.Y.; Jiang, Y.C.; Zhang, Y.Synthesis, crystal structures, and photoluminescent properties of the Cu(I)/X/α,ω-bis(benzotraizole)alkane hybrid family (X = Cl, Br, I, and CN).Inorg.Chem.2009, 48, 1449–1468.

(10) Huang, S.; Clark, R.J.; Zhu, L.Highly sensitive fluorescent probes for zinc ion based on triazolyl-containing tetradentate coordinate motifs.Org.Lett.2007, 9, 4999–5002.

(11) Schweinfurth, D.; Demeshko, S.; Khusniyarov, M.M.; Dechert, S.; Gurram, V.; Buchmeiser, M.R.; Meyer, F.; Sarkar, B.Capped-tetrahedrally coordinated Fe(II) and Co(II) complexes using a ''click''-derived tripodal ligand: geometric and electronic structures.Inorg.Chem.2012, 51, 7592?7597.

(12) Schweinfurth, D.; Krzystek, J.; Schapiro, I.; Demeshko, S.; Klein, J.; Telser, J.; Ozarowski, A.; Su, C.Y.; Meyer, F.; Atanasov, M.; Neese, F.; Sarkar, B.Electronic structures of octahedral Ni(II) complexes with "click" derived triazole ligands: a combined structural, magnetometric,spectroscopic, and theoretical study.Inorg.Chem.2013, 52, 6880?6892.

(13) Kilpin, K.J.; Gavey, E.L.; McAdam, C.J.; Anderson, C.B.; Lind, S.J.; Keep, C.C.; Gordon, K.C.; Crowley, J.D.Palladium(II) complexes of readily functionalized bidentate 2-pyridyl-1,2,3-triazole ''click'' ligands: a synthetic, structural, spectroscopic, and computational study.Inorg.Chem.2011, 50, 6334–6346.

(14) Zhou, X.H.A dinuclear Ni(Ⅱ) complex [Ni2(Htda)2(H2O)6]·4H2O: synthesis, crystal structure and properties.Chem.J.Chin.Uni.2010, 26, 801–806.

(15) Urankar, D.; Pinter, B.; Pevec, A.; Proft, F.D.; Turel, I.; Kosmrlj, J.Click-triazole N2 coordination to transition-metal ions is assisted by a pendant pyridine substituent.Inorg.Chem.2010, 49, 4820–4829.

(16) Yue, Y.F.; Wang, B.W.; Gao, E.Q.; Fang, C.J.; He, C.; Yan, C.H.A novel three-dimensional heterometallic compound: templated assembly of the unprecedented planar ‘‘Na∈[Cu4]’’ metalloporphyrin-like subunits.Chem.Commun.2007, 2034–2036.

(17) Li, Y.J.; Huffman, J.C.; Flood, A.H.Can terdentate 2,6-bis(1,2,3-triazol-4-yl)pyridines form stable coordination compounds? Chem.Commun.2007, 2692–2694.

(18) (a) Zhang, W.X.; Xue, W.; Lin, J.B.; Zheng, Y.Z.; Chen, X.M.3D geometrically frustrated magnets assembled by transition metal ion and 1,2,3-triazole-4,5-dicarboxylate as triangular nodes.CrystEngComm.2008, 10, 1770–1776.(b) Zhang, W.X.; Xue, W.; Chen, X.M.Flexible mixed-spin Kagomé coordinationpolymers with reversible magnetism triggered by dehydration and rehydration.Inorg.Chem.2011, 50, 309–316.(c) Zhang, W.X.; Xue, W.; Zheng, Y.Z.; Chen, X.M.Two spin-competing manganese(II) coordination polymers exhibiting unusual multi-step magnetization jumps.Chem.Commun.2009, 3804–3806.

(19) (a) Yuan, G.; Shao, K.Z.; Wang, X.L.; Lan, Y.Q.; Du, D.Y.; Zhong, M.S.A series of novel chiral lanthanide coordination polymers with channels constructed from 16Ln-based cage-like building units.CrystEngComm.2010, 12, 1147–1152.(b) Yuan, G.; Shao, K.Z.; Du, D.Y.; Wang, X.L.; Zhong, M.S.Syntheses, structures, and photoluminescence of d10coordination architectures: from 1D to 3D complexes based on mixed ligands.Solid State Sciences 2011, 13, 1083–1091.

(20) Shi, W.; Chen, X.Y.; Xu, N.; Song, H.B.; Zhao, B.; Cheng, P.; Liao, D.Z.; Yan, S.P.Synthesis, crystal structures, and magnetic properties of 2D manganese(II) and 1D gadolinium(III) coordination polymers with 1H-1,2,3-triazole-4,5-dicarboxylic acid.Eur.J.Inorg.Chem.2006, 4931–4937.

(21) Wang, S.; Zhao, T.T.; Li, G.H.; Wojtas, L.; Huo, Q.S.; Eddaoudi, M.; Liu, Y.L.From metal-organic squares to porous zeolite-like supramolecular assemblies.J.Am.Chem.Soc.2010, 132, 18039–18041.

(22) Net, G.; Bayón, J.C.; Esteban, P.; Rasmussen, P.G.; Alvarez-Larena, A.; Piniella, dinuclear rhodium(I) and iridium(I) dicarboxytriazolate complexes and their oxidation products.Crystal structures of [NBu4][Rh2(Dcbt)(CO)4]·0.4CH2C12and [NBu4][Rh2(Dcbt)(CO)2(PPh3)2].Inorg.Chem.1993, 32, 5313–5321.

(23) SMART and SAINT.Area Detector Control and Integration Software.Siemens analytical X-ray systems, Inc., Madison, WI 1996.

(24) Sheldrick, G.M.SHELXTL V5.1.Software Reference Manual.AXS Bruker, Inc., Madison, Wisconsin, USA 1997.

(25) Xu, J.T.; Jung, K.; Boyer, C.Oxygen tolerance study of photoinduced electron transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization mediated by Ru(bpy)3Cl2.Macromolecules 2014, 47, 4217?4229.

(26) Jonas, M.; Blechert, S.; Steckhan, E.Photochemically induced electron transfer (PET) catalyzed radical cyclization: a practical method for inducing structural changes in peptides by formation of cyclic amino acid derivatives.J.Org.Chem.2001, 66, 6896–6904.

(27) Ashokkumar, P.; Ramakrishnan, V.T.; Ramamurthy, P.Photoinduced electron transfer (PET) based Zn2+fluorescent probe: transformation of turn-on sensors into ratiometric ones with dual emission in acetonitrile.J.Phys.Chem.A 2011, 115, 14292–14299.

(28) Fabbrizzi, L.; Licchelli, M.; Pallavicini, P.; Taglietti, A.A zinc(II)-driven intramolecular photoinduced electron transfer.Inorg.Chem.1996, 35, 1733–1736.

(29) Thederahn, T.B.; Kuwabara, M.D.; Larsen, T.A.; Sigman, D.S.Nuclease activity of 1,10-phenanthroline-copper: kinetic mechanism.J.Am.Chem.Soc.1989, 111, 4941–4946.

(30) Humphreys, K.J.; Karlin, K.D.; Rokita, S.E.Efficient and specific strand scission of DNA by a dinuclear copper complex: comparative reactivity of complexes with linked tris(2-pyridylmethyl)amine moieties.J.Am.Chem.Soc.2002, 124, 6009–6019.

(31) Dhar, S.; Senapati, D.; Das, P.K.; Chattopadhyay, P.; Nethaji, M.; Chakravarty, A.R.Ternary copper complexes for photocleavage of DNA by red light: direct evidence for sulfur-to-copper charge transfer and d-d band involvement.J.Am.Chem.Soc.2003, 125, 12118–12124.

(32) Sun, H.; Yang, W.Q.; He, W.J.; Guo, Z.J.Oxidative DNA cleavage mediated by copper complexes.Chem.J.Chin.Uni.2011, 32, 437–450.

13 January 2015; accepted 25 March 2015 (CCDC 1042995)

① This work was supported by the National Natural Science Foundation of China (No.21002076) and Wuhan Youth Chenguang Program of Science and Technology (No.201271031374)

② Corresponding author.Chen Yun-Feng.E-mail: chyfch@hotmail.com

10.14102/j.cnki.0254-5861.2011-0634