Ultrafast Vibrational Dynamics Of Amide Bond Of Interfacial Proteins Investigated By Femtosecond Time-Resolved Sum Frequency Generation Vibrational Spectroscopy

The energy transfer of protein molecules on biological membrane is critical to the normal operation of biochemical reactions and physiological functions.Many important physiological and cellular processes depend on the ultrafast energy transfer process of proteins.For example,conformational transport and allosteric communication are directly related to energy transport along the protein backbone.Recently,our group has developed selective excitation of vibrational mode femtosecond Time-resolved Sum Frequency Generation Vibrational Spectroscopy(Tr-SFG),to investigate the effects of hydrogen bond on the ultrafast vibration kinetics of N-H of the interfacial a-helix and ?-sheet structures and the effects of hydrogen bond on both the vibrational energy transfer pathway and the transfer rate between the amide group N-H and C=O.Based on previous studies in our group,this dissertation presents the Tr-SFG results of the effects of various conditions on the vibrational dynamics of NH of the peptide and the coupling of NH/CO vibrations.The results show that in the presence of water molecules,the vibrational relaxation time of NH region decreases owing to the contribution from OH vibration relaxation.Under acidic conditions,the binding of protons to phospholipid heads increases the contribution of interfacial water,and also reduces the vibration relaxation time of NH region.In addition,different protein secondary structure will have direct impact on the hydrogen bond strength of the amide bond,which will further result in the difference in the vibrational relaxation time of NH.By comparing the NH vibration frequency and the vibration relaxation time,we found that the smaller the NH vibration frequency is,the smaller the vibration relaxation time will be.By selectively exciting the N-H vibration and then detecting the transient spectra of C=O,we found that the sequence of the a-helix peptide molecules has no significant effect on the coupling pathway and the coupling rate between N-H and C=O.The results in this dissertation will help us understand the ultrafast dynamics of protein and other hydrogen-bonded molecular biosystems.