Synthesis And Characterization Of New Phenolate-bridged Binuclear Complexes With Different Para-substituents And Their Biological Activity In Cleavage Of DNA

With the rapid development of Molecular Biology, the researchers with different scientific background are provided with a good opportunity to enter the field. People can resolve some important different problems with all kinds of research methods and knowledge in their field. It is chemists' tribute that they can design and synthesize effective nucleic acid cleavage reagents with specific recognition ability and investigate their reaction mechanism, thus make it possible to search effective remedical reagents and structural probes by molecular design. In recent years, a great progress has been made in chemical mimic for the hydrolytic cleavage of phosphodiester bond by using bioinorganic methods. Among the metal complexes been found with the ability to cleavage nucleic acids in a hydrolytic mode, there are mononuclear metal complexes, as well as dinulear complexes, and the metal ions being transitional and lanthanide metal ions, but the reaction speeds are still smaller for several oerders than that of the natural enzymes. It should be a prosperous direction to mimic the hydrolytic cleavage of phosphodiester bond by taking the advantage of dinuclear and/or multinuclear metal complexes.To investigate the structure and activity of chemical nuclease, to find more effective chemical nuclease has been attracted great attention in recent years. Such a situation is benefited from the cognition of the importance that the active position of a number of natural enzymes in relation to nucleic acid usually has two or three cooperative metal ions, such as Zn(â…¡), Mg(â…¡), Ni(â…¡), etc. Meanwhile, research about using rare-earth ions and their complexes as artificial restriction enzymes has raised more and more interests and recognition, for they can cleave the phosphate diester bond in the hydrolytic path with higher efficiency. In this thesis, a series of ligands, R-HXTA (R-HXTA= 2,6-bis [bis-(carboxylatomethyl)aminomethyl]-4-R phenolate) were synthesized, where R is -CH₃, -Cl, -NO₂, -Br and -C(CH₃)₃, respectively, and hereby we signed them as L1, L2, L3, L4, L5. They can supply two same coordination environment arms for two metal ions. We have synthesized some new dinuclear metal complexes of these ligands and studied interaction and reaction mode between complexes and DNA. The content includes in the follows:1. We have synthesized ligands R-HXTA: HNa₄L1, HNa₄L2, HNa₄L3, HNa₄L4 and HNa₄L5(R=-CH₃, -Cl, -NO₂, -Br, -C(CH₃)₃).2. The new compounds of Zn₂L1, Zn₂L4, Ni₂L4 have been made and characterized by X-ray crystallography. It is worthy of mentioned that Zn₂L1 is formed linear polymer structure, constructed by Zn-O-Zn beridge and Zn(H₂O)₄ units.3. We have also synthesized other metal complexes Ce₂L2, Mg₂L3, Zn₂L3, Mg₂L4, Eu₂L4, Nd₂L4, and their structures are deduced with IR spectra and elemental analysis.4. Some metal complexes (Mg₂L3, Zn₂L3, Mg₂L4, Zn₂L4) were selected as the candidates for the study of bioactivity in the cleavage plasmid pBR322DNA by gel electrophoresis technique. The results showed that under 37℃, pH 7.20, the four complexes could cleave DNA effectively alone, transferring the DNA form ccc form into oc and linear forms. Furthermore, we studied the reaction mechanism of the four complexes and DNA by added radical scavengers (DMSO, glycerol and MeOH), and the result suggests that these complexes mediated cleavage reaction did not proceed via radical cleavage.5. By using UV spectra method and EB as a fluorescence probe, we studied the action modes of the complexes binding with DNA, and found the complexes possibly bind to DNA by the mode of interaction and electrostatic binding. The interaction of some lanthanide complexes with the DNA model compound BDNPP was also investigated with UV mothod. The experiments indicated that the complexes we have made are effective in the cleavage of P-O bond in BDNPP, and Nd₂L4 can accelerate the hydrolytic rate of BDNPP for 3000 folds, Ce₂L2 and Eu₂L4 can also accelerate the hydrolytic rate for 500 folds.To sum up, the metal complexes we synthesized can cleave DNA and hydrolysis DNA model compound effectively. They are hopeful candidates of chemical nuclease, but the further research is still needed.