Studies On Aza-Crown Ether Metal Complexes With Functional Side Arms As Artificial Hydrolytic Nucleases

Studies on mimic nuclease could provide theoretical support for the design and application of new artificial nucleases in organisms,so it is a relatively active research field in biomimetic catalysis.Results showed that aza-crown ether metal complexes with special structures as artificial nucleases exhibit especial catalytic activity in the hydrolysis of DNA or model phosphate esters,so it is can be expected that this kind of metal complexes have significant potential application in some aspects including biological medicine,cell membrane transmission,biomimetic chemistry and mimic metalloenzymes in the future.In order to obtain highly effective and stable artificial nuclease,in this dissertation,new aza-crown ethers with four kinds of side arms and some their transition metal complexes and lanthanide complexes have been synthesized,and their catalytic functions for DNA hydrolytic cleavage have been studied,and some useful and important results and conclusions have been obtained.As for the synthesis of ligands and metal complexes,in this dissertation,four different aza-crown ethers derivatives(L1-L4)by introducing different side arms to the parent ligand(L=1,4,10,13-tetraoxa-7,16-diazacyclooctadecane)have been synthesized and their some corresponding transition metal complexes and lanthanide complexes(LaL,CeL,LaL1,CeL1,LaL2,CeL2,LaL3,CeL3,La L4,CeL4,CuL,ZnL,CuL1,ZnL1,CuL2,ZnL2,CuL3,ZnL3)have also been obtained,which will provide reference method on the further synthesis of aza-crown ether metal complexes with different functional side arms.As for the study of the catalytic functions of the metal complexes as artificial nuclease,in this dissertation,their catalytic behaviors for plasmid pUC19 DNA cleavage have been assessed by agarose gel electrophoresis.The effects of pH,reaction time and the complexes concentrations on the hydrolysis of DNA have been investigated.The effects of central metal ions and the side arms of the aza-crown ether metal complexes for DNA hydrolysis have been also investigated.Meanwhile,the mechanisms of DNA cleavage by using different metal complexes were also discussed and some important results and conclusions have been obtained:1).The catalytic activities of the metal complexes are associated with the characteristics of the ligand structures and central metal ions(such as Lewis acidity,the ionic radius,and so on),under the different catalytic conditions,the dominant factors affecting their catalytic functions are different.The results indicated that,when influenced by the dominant factors of the Lewis acidity of the central metal ions,the catalyticactivities follow the order: CeL>La L,CeL1>La L1,CuL1>ZnL1,CeL2>La L2;at the lower concentration,CeL3>La L3.When influenced by the dominant factors of the ionic radius of the metal ions,the catalytic activities follow the order: ZnL3>CuL3;at the lower concentration,ZnL>CuL.In the process of DNA hydrolysis,the higher complexes concentration may lead to the formation of unreactive μ-hydroxo dimmers,which will reduce the concentration of the active species and also the DNA cleavage efficiency.In this case,the catalytic activities follow the order: CuL>ZnL,CuL2>ZnL2,La L3>CeL3.2).Introducing specific functional side arms of the metal complexes are beneficial to enhance their catalytic activity.The experimental results indicated that,the catalytic activity follows the order: CeL1>LaL1>CeL>LaL,LaL3>CeL3>CeL>La L.This may be ascribed to the functional side arms of the ligands since they can not only improve the binding ability of the ligands to metal ions and then lead to the differences of the stability and catalytic activity of the metal complexes,but also enhance the bonding interaction between the complex and DNA molecule by the hydrogen bonding and then promote the formation and stability of the reaction intermediate.3).The pH of the catalytic system may change the structure of the complexes,and result in different catalytic activity.The complexes do not represent better catalytic activity at higher pH value.The results showed that the complexes with acetylamino side arms showed higher stability and catalytic ability under the slight alkaline condition while the complexes with hydroxyl(hydroxypropyl,hydroxyethyl,carboxyethyl)side arms exhibited higher stability and catalytic ability under the weak acidity condition.4).The applying several oxygen scavengers experimental results indicated that the DNA cleavage promoted by these transition metal complexes and lanthanide complexes take place by hydrolytic mechanisms.And based on the results,the tentative mechanisms of DNA cleavage catalyzed by these metal complexes have been proposed.But due to the limitation of the research time,the mechanisms just have been made the preliminary study,and the further research is needed to certify some relevant questions.5).The ultraviolet spectroscopy and fluorescent spectrometry have proved the formation of the metal complexes with carboxyethyl side arms LaL4 and CeL4.In addition,the gel electrophoresis assay indicated that the catalytic efficiency of LaL4 is higher than that of CeL4,but the reason needed to be further studied.The results also showed that the catalytic efficiency of complexes La L4 and CeL4 for DNA cleavage increases as the reaction time increases,but when the reaction time increases to 22 h,the DNA band appears dispersion trailing phenomenon,which may be due to the DNA been further cleaved tosmall fragment,the reason need to be further studied.