Ionization Potential And Electron Affinity Between The Dna Bases And The Peptide Chain And The Potential And Hydrogen Bonding Interactions Of Theoretical Research

DNA occupies a central role in the development and functioning of living organisms for its functions of storing and transfer of genetic information.However,it is notable that all the performances of the functions must depend on the interactions with proteins.Among so-called protein-nucleic acid interactions,The H-bonding interactions between protein and nucleic acid have been found to be a vital actor in the process of repairing oxidative damage to DNA. Besides,Multiple HBs between an amino acid side chain and bases are expected to alter in different ways the electronic properties of nucleic acid bases,which act an important role in understanding DNA and RNA damages.And the formation of anions and cations at various sites within nucleotide strands is suspected to be the initial step of the high-energy radiation damage to DNA and RNA.Thus a correct determination of the ionization potentials(IP) and the electron affinities(EA) of the nucleotide bases is of great importance to the study of DNA and RNA radiation damage.It is due to the facts above that we endeavor in our present work to make an investigation on the ionization potentials(IP) and electron affinities(EA) of cytosine-formamide complexes.Besides,cytosine and formamide have been adopted as a model for the study of the H-bonding interactions between DNA and proteins.The whole paper is made up of six parts.The first chapter includes a brief introduction of development of quantum chemistry theory and an elucidation of the matter that intrigues our interests and the value of our investication.The second chapter referring to ionization potentials(IP) and electron affinities(EA) and HBs is something about the contents we seriously investigate in the system.The third part related to calculation methods which used in the present paper have been succinctly introduced.In brief,the first three chapters are the basis and background of our studies,which offer us useful and reliable quantum methods.Based upon the mentioned work,The chapter 4 sets off with the probation of how the electronic properties of nucleic acid bases change and,sequentially,what effects these chances will make on the mutation of DNA.The geometric and energetic changes of cytosine monomer and cytosine-formamide complexes have been investigated using B3LYP methold,and ionization potentials(IP) and electron affinities(EA) of the system have also been calculated.Both the detachment and attachment of one electron have an impact on the structures of the complexes. The former merely has influence on the intermolecular geometries while the later on both the intermolecular and intramolecular geometries.Furthermore,we found the H-bonding interactions between cytosine and formamide would facilitate adiabatical electron detachment and attachment but have different effects on vertical electron detachment and attachment.In chapter 5,we add one to four formamide molecules to form cytosine-formamide complexes,because of the complexities involved with interactions of DNA and its surrounding environment as well as the large number of atoms involved in the molecular system,so the ionization potentials(IP) and electron affinities(EA) of the system have also been calculated using B3LYP methold.As far as energies is concerned,the system become unstable during the process of electron detachment as well as electron attachment,and the cations is more unstable than the anions.This chapter is the further study of the chapter 4.In the last part,we increase the number of formamide molecules on the basis of work of chapter five to eventually form a locked chain around cytosine.The structures of hydrogen-bonded complexes C-F_n(n=2-7) of cytosine with formamide molecules have been fully optimized at B3LYP/6-31G(d) basis set level.The most interesting geometrical change of cytosine upon the complex is the shortening of bond C4-N7 resulting from the strengthening of the conjugation between theπsystem of the cytosine ring and the lone pair of the nitrogen atom. The significant elongation of C1-O8 bond is up to 1.292(?).Therefore,this bond may be considered as a single C-O~- bond rather than a double bond.As is mentioned above,we concluded that the impact on the properties of bases made by the H-bonding interactions should not to be ignored,which will make a further influence upon the functions on DNA in living organisms.We hope the present work would provide other investigators in the same field with valuable references.