Excited electronic states and internal conversion in cyanocobalamin  

作　　者：Theodore E.Wiley Brenden C.Arruda Nicholas A.Miller Michael Lenard Roseanne J.Sension 

机构地区：[1]Department of Chemistry,University of Michigan

出　　处：《Chinese Chemical Letters》2015年第4期439-443,共5页中国化学快报（英文版）

基　　金：supported in part by NSF CHE-1150660

摘　　要：Cyanocobalamin （CNCbl） is a paradigm system for the study of excited electronic states and biological cofactors including the B12 vitamers, The photophysics of CNCbl has been thoroughly investigated using both ultrafast spectroscopy and time dependent density functional theory （TD-DFT）. Here we review the spectroscopic and theoretical investigations of CNCbl with emphasis on the nature of S1, the lowest excited electronic state, and extend the spectroscopic measurements to include the ultraviolet region of the spectrum. Ultrafast transient absorption measurements in the visible αβ band region and in the mid- infrared led to assignment of the S1 state to a ligand-to-metal charge transfer （LMCT） with lengthened axial bonds and a ~3 kcal/mol harrier for internal conversion to the ground state. The present measurements encompassing the y band region of the spectrum provide further support for the assignment of the S1 state. The experiments are in good agreement with the results of TD-DFT calculations which confirm the expected lengthening of the axial bonds in S1 and account for the observed barrier for internal conversion back to the ground state,Cyanocobalamin （CNCbl） is a paradigm system for the study of excited electronic states and biological cofactors including the B12 vitamers, The photophysics of CNCbl has been thoroughly investigated using both ultrafast spectroscopy and time dependent density functional theory （TD-DFT）. Here we review the spectroscopic and theoretical investigations of CNCbl with emphasis on the nature of S1, the lowest excited electronic state, and extend the spectroscopic measurements to include the ultraviolet region of the spectrum. Ultrafast transient absorption measurements in the visible αβ band region and in the mid- infrared led to assignment of the S1 state to a ligand-to-metal charge transfer （LMCT） with lengthened axial bonds and a ~3 kcal/mol harrier for internal conversion to the ground state. The present measurements encompassing the y band region of the spectrum provide further support for the assignment of the S1 state. The experiments are in good agreement with the results of TD-DFT calculations which confirm the expected lengthening of the axial bonds in S1 and account for the observed barrier for internal conversion back to the ground state,

关 键 词：CyanocobalaminExcited electronic statesUltrafast spectroscopyTime dependent density functional theoryLigand-to-metal charge transfer 

分 类 号：O629.4[理学—有机化学]