Studies On Rare Earth Metal Azamacycle Complex As Artificial Nuclease

At present,site-specific cleavage of DNA with high efficiency has attracted manyresearchers since artificial nucleases have potential application as novel restrictionenzymes and anticancer therapeutic agents. In the past few years, the studies of theinteraction between small organic molecules and nucleic acid have made great progress.Most reported cleavers are transition metal complexes, which break down DNA by redoxreaction.However,their pharmic use is hampered because of the free-radical generation andthe damage of bases and deoxyriboses during redox processes.In recent years,many research groups had obtained some satisfied results on the studyof the phosphate easters hydrolysis catalyzed by the artifical enzyme.Macrocyclic ligandcomplexes are involved in a number of fundamental biological systems has long beenrecognized.The synthesis of these compounds and further researches on their structure andproperty will help to reveal the rule of life and broad applications are prospected with thesecomplexes in the fields of chemistry,biology and medicine. Meanwhile, research aboutusing rare-earth ions and their complexes as artifical restriction enzymes has raised moreand more interests and recognition,as they are found to be effective in promotinghydrolysis of the phosphodiester linkage in DNA without damaging bases and ribose.In order to obtain highly catalytic system as artificial nuclease, in this thesis,thecatalytic kinetics and mechanisms were studied for the hydrolysis of nucleic acid and DNAmodel compound BNPP catalyzed by complexes made of Ce（Ⅲ） or La（Ⅲ） cation andthree kinds of tetraazamacycles ligands,respectively.The catalytic function was investigated for the hydrolysis of DNA model compoundBNPP by the rare earth metal complexes as artificial nucleases composed of Ce（Ⅲ） orLa（Ⅲ） cations in the presence of saturated azamacrocyclic （L₁）,unsaturatedazamacrocyclic （L₂） and unsaturated azamacrocyclic with carboxyl side arms（L₃） withUV-vis mothod. Furthmore,the catalytic mechanism was proposed by the spectral analysisand the kinetic results. The results suggested that the catalytic system show high catalyticactivity and stability at the appropriate acidity and temperature conditions,and the reactivespecies is the complex made of metal ions and ligand,and also found that the catalyticactivity of Ce（Ⅲ） azamacrocyclic complexes is higher than that of La（Ⅲ） azamacrocycliccomplexes under the same conditions.On the basis of the research for the mechanism of the hydrolysis of BNPP bylanthanide azamacycles complexes, the binding of the CeL₁,LaL₁,CeL₂and LaL₂metal azamacycles complexes to DNA has been studied by employing UV spectra method,fluorescenece and electrochemistry,and studies showed that the binding of the rare earthmetal azamacycles complexes with DNA occur through its phosphate groups whichconcurs with outside binding. Meanwhile,the cleavage activity of plasmid PMD-18t DNAby complexes was studied by gel electrophoresis technique.The results indicated that theLnL₁metal azamacycles complexes bound DNA the most strongely and cleave DNA themost effectively, while the catalytic function of LnL₂was less than that of LnL₁and alsoLnL₃almost showed no catalytic ability.Thus, the structure of the ligand played theimportant role in the DNA-binding affinity and DNA cleavage.To sum up,the rare earth metal azamacycles complexes which can cleave DNA andhydrolysis of DNA and its model compound effectively were highly catalytic system asartificial nuclease.It is worth explorating the design and synthesis of specific lanthanideazamacycles complexes as artificial nuclease for further catalytic activity and mechanisticstudy.