Theoretical Study Of Excited State Hydrogen Bond Dynamics And Proton Transfer Mechanism For Biology Molecular

Hydrogen bonding is one of the most important weak interactions.Due to its important role in chemical and biological reactions,it is ubiquitous in nature and becomes the focus of the researches.In the complicated life systems,the molecular structure and the related functions are affected directly by the hydrogen bonding.For example,the hydrogen bond is strengthened in the excited state,which will help to accelerate the internal conversion rate between the electronic states of the hydrogen-bonding complexes and promote the occurrence of the excited proton transfer reaction.As one of the most important reactions in the biological field,the excited proton transfer reaction is used in designation and application of fluorescent probes and molecular field,moreover,in the development of the special drug molecules such as tumor and AIDs.Nowadays,how excited hydrogen bond kinetics and proton transfer processes affect the structure and related functions of biomolecular systems is still a concern for scientists,which is the focus of this paper.In this paper,the density functional theory(DFT)and the time-dependent density functional theory(DFT)are combined with the polarizable continuum model that uses the integral equation formalism variant(IEFPCM)to study the excited states hydrogen bond dynamics and proton transfer mechanism of small biological molecular systems.The following four specific biological small molecule systems are described in detail:(1)The number of water molecules involved in the excitation state proton transfer reaction in aqueous solution was studied by 2,6-Diazaindoles(2,6-DAI)of tryptophan analogues.It was first discovered that 2,6-DAI in aqueous solution can be formed with three or four water molecules to form a proton transfer reaction and determine the optimal reaction path,and found that the proton transfer reaction is a consistent process.(2)The excited states hydrogen bond dynamics behavior of natural product 3-hydroxyflavonoid derivative 4’-dimethylaminoflavonol(DMAF)molecule in high polar acetonitrile(ACN)solvent was studied.Upon photo-excitation,the DMAF molecule in the ACN solvent can adopt a twisted intramolecular charge-transfer state,and will further promote the excitation of the molecular proton transfer,in the previous experiments on the DMAF molecule under the ACN solvent to supplement the study.(3)we also studied the excited state intramolecular proton reaction of the 3-hydroxyflavonoid derivative 3,7-Dihydroxy-4-oxo-2-phenyl-4H-chromene-8-carbaldehyde(2a),and the reason that the single fluorescence was only measured by previous experiments.It has been demonstrated for the first time that there are three proton transfer structures of the 2a molecule in the first excited state,including two single proton transfer structures and one double proton transfer structure,and that the reason why single fluorescence occurs is reasonably explained.(4)Theoretical study of whether solvation has affected the excited state hydrogen bond dynamics and proton transfer process of the benzimidazole molecule derivative 2-(4′-amino-2′-hydroxyphenyl)-1H-imidazo-[4,5-c]pyridine(AHPIP-c).We have found that the excited intramolecular proton transfer process of AHPIP-c molecules increases with increasing polarity of the solvent.In short,our research content can not only prove that the selected quantitative calculation method has high efficiency and rationality,but also further from the theoretical point of view on the deficiency mechanism of the small biological molecule system in the previous experiments.