Patra Ashis K, Nethaji Munirathinam, Chakravarty Akhil R
Department of Inorganic and Physical Chemistry, Indian Institute of Science, Sir C.V. Raman Avenue, Bangalore 560012, India.
J Inorg Biochem. 2007 Feb;101(2):233-44. doi: 10.1016/j.jinorgbio.2006.09.018. Epub 2006 Sep 28.
Ternary S-methyl-L-cysteine (SMe-l-cys) copper(II) complexes Cu(SMe-L-cys)(B)(H(2)O) (1-4), where the heterocyclic base B is 2,2'-bipyridine (bpy, 1), 1,10-phenanthroline (phen, 2), dipyridoquinoxaline (dpq, 3) and dipyridophenazine (dppz, 4), and X is ClO(4)(-) (1-3) or NO(3)(-) (4), are prepared and their DNA binding and cleavage properties studied. Complexes 2 and 4 are structurally characterized by X-ray crystallography. Both the crystal structures show distorted square-pyramidal (4+1) CuN(3)O(2) coordination geometry of the complexes in which the N,O-donor S-methyl-L-cysteine and N,N-donor heterocyclic base bind at the basal plane with a water molecule as the axial ligand. In addition, the dppz structure shows the presence of a 1D-chain formed due to covalent linkage of the carboxylate oxygen atom belonging to another molecule at the elongated axial site. The crystal structures show chemically significant non-covalent interactions like hydrogen bonding involving the axial aqua ligand and pi-pi interactions between dppz ligands. The complexes display a d-d band in the range of 605-654 nm in aqueous dimethylformamide (DMF) solution (9:1 v/v). The redox active complexes show quasireversible cyclic voltammetric response near 0.1 V in DMF assignable to the Cu(II)/Cu(I) couple. The complexes show good binding affinity to calf thymus (CT) DNA giving the order: 4 (dppz)>3 (dpq)>2 (phen)>>1 (bpy). The intrinsic binding constants, obtained from UV-visible spectroscopic studies, are 1.3x10(4) and 2.15 x 10(4) M(-1) for 3 and 4, respectively. Control DNA cleavage experiments using pUC19 supercoiled (SC) DNA and minor groove binder distamycin suggest major groove binding propensity for the dppz complex, while the phen and dpq complexes bind at the minor groove of DNA. Complexes 2-4 show DNA cleavage activity in dark in the presence of a reducing agent 3-mercaptopropionic acid (MPA) via a mechanistic pathway involving formation of hydroxyl radical as the reactive species. The complexes also show efficient photo-induced DNA cleavage activity on irradiation with a monochromatic UV light of 365 nm in absence of any external reagent. The cleavage efficiency follows the order: 3>4>2. The complexes exhibit significant DNA cleavage activity on irradiation with visible light of 633 nm. Control experiments show inhibition of cleavage in presence of singlet oxygen quenchers like sodium azide, histidine and enhancement of cleavage in D(2)O, suggesting formation of singlet oxygen as a reactive species in a type-II process. The photosensitizing effect of the thiomethyl group of the amino acid is evidenced from the observation of significant DNA photocleavage activity of the phen complex 2 as the phen ligand itself is not a photosensitizer.
三元S-甲基-L-半胱氨酸（SMe-L-cys）铜（II）配合物Cu（SMe-L-cys）（B）（H₂O）（1 - 4）已被制备出来，其中杂环碱B为2,2'-联吡啶（bpy，1）、1,10-菲咯啉（phen，2）、二吡啶并喹喔啉（dpq，3）和二吡啶并菲嗪（dppz，4），且X为ClO₄⁻（1 - 3）或NO₃⁻（4），并对其DNA结合和切割性质进行了研究。配合物2和4通过X射线晶体学进行了结构表征。两种晶体结构均显示配合物具有扭曲的四方锥（4 + 1）CuN₃O₂配位几何构型，其中N、O供体的S-甲基-L-半胱氨酸和N、N供体的杂环碱在基面结合，水分子作为轴向配体。此外，dppz结构显示在伸长的轴向位置由于属于另一个分子的羧酸根氧原子的共价连接而形成了一维链。晶体结构显示出具有化学意义的非共价相互作用，如涉及轴向水合配体的氢键以及dppz配体之间的π-π相互作用。这些配合物在二甲基甲酰胺（DMF）水溶液（9:1 v/v）中在605 - 654 nm范围内显示出d - d带。氧化还原活性配合物在DMF中在0.1 V附近显示出准可逆循环伏安响应，归因于Cu（II）/Cu（I）电对。这些配合物对小牛胸腺（CT）DNA表现出良好的结合亲和力，顺序为：4（dppz）>3（dpq）>2（phen）>>1（bpy）。通过紫外可见光谱研究获得的固有结合常数，对于3和4分别为1.3×10⁴和2.15×10⁴ M⁻¹。使用pUC19超螺旋（SC）DNA和小沟结合剂地霉素进行的对照DNA切割实验表明，dppz配合物倾向于大沟结合，而phen和dpq配合物则结合在DNA的小沟处。配合物2 - 4在还原剂3-巯基丙酸（MPA）存在下于黑暗中通过涉及形成羟基自由基作为活性物种的机制途径显示出DNA切割活性。这些配合物在没有任何外部试剂的情况下用365 nm单色紫外光照射时也显示出有效的光诱导DNA切割活性。切割效率顺序为：3>4>2。这些配合物在633 nm可见光照射下表现出显著的DNA切割活性。对照实验表明，在存在叠氮化钠、组氨酸等单线态氧猝灭剂时切割受到抑制，而在D₂O中切割增强，表明在II型过程中形成单线态氧作为活性物种。从phen配合物2具有显著的DNA光切割活性这一观察结果可以证明氨基酸的硫甲基基团的光敏化作用，因为phen配体本身不是光敏剂。
