Theoretical Study On The Excited-state Intramolecular Proton Transfer Mechanism Of Biologically Active Substance

Proton transfer plays an important role in many life processes.The hydrogen bond enables life body to be set up,as the construction of biomolecular.Excited-state intramolecular proton transfer is closely related to the life processes such as energy change,enzymatic catalysis,the identification and interaction between receptor and reactive intermediate of substrate,DNA recombination,genes mutations,and variation of the organisms.Therefore,the study of excited-state intramolecular proton transfer could provide explains to the phenomena of life.There are many kinds of active substances in the organisms,which have special physiological activities,take on important physiological functions and have a variety of biological effects on the organisms.The chromone,which belongs to the biological active substances,which have the properties of the anti-bacterial,anti-allergic,anti-convulsive,relieving asthma,reducing sugar-blood,fatness-blood,and resisting cancer cell.Some of the chromone derivatives,could occur the intramolecular proton transfer in excited state,thanks to the hydrogen bond strengthening.Derivatives of 3-hydroxychromone is one of the representatives of chromone family.Discussing the mechanisms in depth has profound significance for the investigation of the properties of biological active substances.In this paper,we have investigated the excited-state intramolecular proton transfer mechanism of biological active substances using theoretical calculation.By calculating the molecular structure,absorption spectrum,fluorescent spectrum,frontier molecular orbitals,charge distribution,and potential energy surface in the ground state and excited state,we could describe the mechanism of exited-state proton transfer in detail.In this paper,the excited-state intramolecular proton transfer mechanism of2-?quinolin-2-yl?-3-hydroxychromine?Q3HC?in 1,2-dichlorethane solvent have been investigated via the density functional theoretical?DFT?and the time-dependent density functional theory?TDDFT?method.At the level of B3LYP/TZVP,we have optimized three configurations Q3HC-A,Q3HC-B and Q3HC-C,respectively.The calculated absorption and fluorescence spectra of Q3HC-A,Q3HC-B and Q3HC-C are agreement with the experimental data.It is found that the Q3HC-B and Q3HC-A can be mutual conversion in the S₀ and S₁states.Moreover,the hydrogen bond is strengthened in the S₁ state.Meanwhile,we also have constructed the potential energy curves of S₀ and S₁ states,and further discussed the mechanisms of excited-state proton transfer of Q3HC-A,Q3HC-B and Q3HC-C.At the same time,we have confirmed the difficulty degree in the occurrence of the reaction.The studies have shown that the excited-state proton transfer of Q3HC-C occurs more easily than that of Q3HC-A and Q3HC-B.Combination with reduced density gradient function?RDG?,the hydrogen bond O-H???N of Q3HC-C is strongest,compared with Q3HC-A and Q3HC-B,And it also can provide the real evidence that the excited-state proton transfer of Q3HC-C is more favorable than that of Q3HC-A and Q3HC-B.