Theoretical Investigation On Mechanisms Of Nucleic Acid Bases Interact With Molecule Ions

In this paper, interactions between nucleic acid bases and molecule ions were selected as models to investigate systematically, for the purpose of discussing the proton transfer processes and mechanisms. The research work can be divided into three pieces: first, water molecules play a significant role in the tautomeric process of nucleic acid bases, studies revealed that a water molecule might influence the stability of different tautomeric forms of nucleic acid bases through hydrogen bonding interactions, meanwhile, water-assisted proton transfer will greatly increase the populations of the rare tautomers by lowering the activation energy barrier of the intramolecular proton transfer; second, the methyl effect on the interaction between nucleic acid bases and amino acids have been investigated for a series of N- and C-methylated structures, which are generated, respectively, by interactions between the most stable nucleic acid base uracil and the most stable amino acid glycine in the gas phase; third, the inherent mechanisms of proton transfer in four different single electron involved nucleic acid base pair such as electron assists proton transfer or electron couples proton transfer or the other inherent mechanisms will be discussed in details, the driving forces of proton transfer turns out to be a key factor and in dire need of interpretation for many biological processes.Study for the"catalysed effect of water molecules and of charge on intramolecular proton transfer of uracil"indicates that point mutations induced by uracil deformation can be got deeper insight into. Toward the target, the activation energies of the intramolecular proton transfer (tautomeric process) as well as the catalysis effects of water molecules and of charges attached are investaged using density functional theory calculations by means of the B3LYP exchange and correlation functions. Results reveal that water molecules hold stronger catalysis effect on the proton transfer in these negative charged uracil hydrates than in the neutral counterparts. The optimal number of water molecules needed to catalyze the proton transfer is determined as two in the neutral hydrated systems, whereas is three in the negative charged systems. Positive charge attachment, however, hinders the intramolecualr proton transfer of uracil, and the charge and the proton of uracil will transfer to the water clusters if water molecules are attached. Analysis reveals that it is the acceptance process of the last proton to determine the impossibility of proton transfer and result in the failure of tautomeric processes. Detailed structural parameters and energies changes are discussed for above different processes.Study for the"methyl effect on the interaction of nucleic acid bases and amino acids" indicates that in the neutral complexes, only double proton transfer process between neutral species can occur. The activation energy can be teeny reduced by a single methyl substitute, which being a pindling influence on the charge distribution. In the anionic complexes, methyl effect on the dipole moment is far greater than that in the neutral complexes. Barrier free proton transfer can be induced by a negative charge, and it is still a barrier free proton transfer process with a methyl substitute. In the cationic complexes, not only single proton transfer but also barrier free proton transfer can occur in the processes, accompanying with structures change influenced by the methyl. The mechanism of driving force of single proton transfer of anionic complexes is different from cationic complexes, which discussed in details in this article. Additionally, switches effect under the influence of methyl have been investigated adequately, expecting that the findings could be the starting point for the quest for more effective and specific drugs-packer, in another word, leading to new insights in the treatment of human diseases at biological molecules level rather than by exerting cytotoxic drug effects.Study for the"mechanisms of proton transfer in four different single electrons involved guanine-cytosine base pair"indicates that there is an excess electron assists proton transfer in anionic guanine-cytosine radical, only a proton exothermic with a small energetic barrier transfers. It becomes endothermic with a little enhanced energetic barrier in cationic guanine-cytosine radical, a process of the hole assists proton to transfer, followed with proton transfers. The zero-point correction dependent reaction mechanism for zinc ion and guanine-cytosine complexes is also that the hole assists proton to transfer, but in especial instance there is the electrostatic power assists proton to transfer reversely. In addition, all copper ion and guanine-cytosine complexes are spontaneous with more stable proton transferred structures compared to their reactants, and the driving force is the powerful copper ion due to both electrostatic and oxidative effects.