Synthesis And Bioactivity Of Silver Complexes With Bis-(Benzimidazole)-Thiapropane Ligands

Silver and the silver complexes have good bactericidal properties of antiviral, these properties has attracted widespread attention. Silver（I） has a very flexible coordination sphere, which enables it to adopt coordination numbers from 2 to 6, resulting in its coordination sphere ranging from linear to octahedral, respectively. As a typical heterocyclic ligand, benzimidazoles and their derivatives exhibit wideranging antiviral activities, photochemical and photophysical properties. Bis-（benzimidazole）-thiapropane ligands were choosen to react with unsaturated acid silver to get different complexes. Try to find ways to understand the different structures of silver complexes and properties of various aspects of the novel features.In this paper the V-shaped ligand 1,3-Bis（2-benzimidazyl）-2-thiapropane and its derivatives ligands were designed and synthesized. And on the basis of acid sodium, different kinds of unsaturated acid silver（Methacrylate acid silver, cinnamic acid silver, p-coumarate acid silver, o-coumarate acid silver, salicylic acid silver, crotonic acid silver） was designed. These different acid silver salts were reacted with the ligands and 4,4′-bipy, then got seven different complexes:[Ag（S²）（p-coumarate）]·2CH₃OH（1）[Ag（S³）（methacrylate）]（2）[Ag（S³）（cinnamate）]（3）[Ag（S³）2]（o-coumarate）·CH₃CN·2C₂H₅OH（4）[Ag（S³）（crotonate）]（5）[Ag（S⁴）（crotonate）]（6）{[Ag₄（μ-4,4′-bipy）3（μ-salicylate）2（salicylate）H₂O]2?2C₂H₅OH}n（7）X-ray single crystal diffraction analysis reveals that the structure of the complexes 1、2、3、 5、6 are similar. They are three-coordinated trigonal planar geometry. And the complexes 4 are four-coordinated distorted tetrahedral geometry. The complex 7 is a kind of inorganic polymer and forms trinuclear silver cluster.The polymeric unit consists two portions which are central symmetric. Each asymmetric group comprises four Ag（I） atoms, three 4,4′-bipy, three salicylate anions and one H2 O molecules. Each 4,4′-bipy adopts the μ2-bridging mode to link each silver atoms. The salicylate shows two kinds of coordination modes, in which one has μ2-bridging coordinated mode to link Ag1 and Ag3, Ag1 and Ag₄; other one has momodentate coordination mode linking Ag2. Ag1 display distorted square-based pyramidal geometry. The distortion of the square-based pyramidal geometry can be indicated by the calculated value of the τ5 parameter to describe the geometry of a five-coordinate metal system. The τ5 parameter is 0.11 for Ag1.The Ag2 is located in distorted plane triangle geometry of a three-coordinate metal system. Ag3 and Ag₄ both display distortion of the tetrahedral geometry.In iterms of the biological properties, the antioxidant activity of the compounds and the interaction between ligand and complexes with DNA has been studied. The hypochromism, Kb values, Ksv values were investigated. The results demonstrate that the complexes could bind to DNA by intercalation mode. And the abilities of binding to DNA of the complexes are stronger than the ligands.The antioxidant activities of the compounds were determined by fetion method and NBT illumination method. The abilitiy of scavenging free radicals was characterized by IC50. The IC50 of the complexes 1、4、6、7 were found to lower two orders of magnitude than standard antioxidants like vitamin C and mannitol. So the complexes possess potent hydroxyl radical scavenging activity. So it is better than standard antioxidants like vitamin C and mannitol. Furthermore, compared with SOD standard analog compounds, complexes 1、7 possess significant superoxide radical activity,so the complexes1、7 can be used as SOD mimic enzyme to scavenging superoxide anion free radicals.