Synthesis And DNA Photocleavage Of Ruthenium Polypyridine Complexes

Mimicking the activities of nucleases is increasingly becoming an attractive research area in molecular biology since artificial nucleases have their potential application as novel restricted anzymes and anticancer therapeutic agents.In the past decades,various ruthenium complexes have been reported as DNA photocleavage agents.Nevetheless,their activities are still limited.So,the development of synthetic agents to cleave DNA with high efficiency is a challenging work for the chemistry researchers.The complexes(1a,1b,1c) were synthesized with methyl viologen as electron acceptor covalently linked to the ruthenium tripyridyl photosensitizer via different length of flexible chains.After optimizing the synthetic route and method,the yield of products was enhanced evidently.By investigating the fluorescence spectra of the complexes,it can be found that the photoinduced intramolecular electron transfer in the ruthenium complexes dyads with methyl viologen covalently linked as electron acceptor were much more favorable than that of the intermolecular electron transfer,and the efficiency of the intramolecular electron transfer decreased with the increase of the length of the covalent chains,which can be deduced that the longer of the covalent chains between the methyl viologen and ruthenium tripyridyl complexes, the longer of the lifetime of electron separated state.The self-assemly of the complexes with CB8 orβ-CD offered a tool for the enhancement of the lifetime of the charge separated states.It was demonstrated that DNA can be oxidized by Ru³⁺ form of complexes by electrochemical and electrochemiluminescence spectra.Several methods such as Uv-vis,fluorescence spectra,fluorescence quenching and circular dichroism have been used to study the interaction between the complexes and calf thymus DNA.The binding affinity increased along with the length of chains.The complexes exhibited strong electrostatic interaction with DNA,while the viologen of the 1c was embedded into the groove of DNA.The results illustrated that the complexes 1c can effectively cleave the plasmid DNA strand under irradiation of visible light,and 1a,1b can not cleave the DNA effectively because of rapid back electron transfer.Through the investigation of the reactive oxygen species(ROS) inhibitors such as histidine,1,4-dithiothreitol(DTT),dimethylsulfoxide (DMSO),ethanol and sodium formate(HCOONa),it was proved that the DNA was cleaved with the mechanism of electron transfer.The self-assembly of complexes 1c with CB8 and β-CD can evidently inhibit the back electron transfer and enhance the efficiency of the DNA photocleavage.