Steric Effect in Threshold Photoionization Dissociations of Serine Conformers.pdfVIP

Steric Effect in Threshold Photoionization Dissociations of Serine Conformers** † † † ‡ ‡ ‡ Shan Xi Tian, * Jinlong Yang, Hai-Bei Li, Yang Pan, Taichang Zhang, and Liusi Sheng † Hefei National Laboratory for Physical Sciences at Microscale, Department of Chemical Physics, University of Science and Technology of China, Hefei, Anhui 230026, China ‡ National Laboratory of Synchrotron Radiation, University of Science and Technology of China, Hefei, Anhui 230029, China * Corresponding author. E-mail: sxtian@ustc.edu.cn. ** Electronic supplementary information (ESI) available. Abstract Steric effect in the threshold dissociative ionizations of serine conformers [CH OH-C H(NH )-C OOH] is revealed by high-level ab initio calculations combined with 2 α 2 β our newly developed infrared laser desorption / tunable VUV photoionization mass spectrometry. We find that near the ionization thresholds the C ―C and C ―C bonds are α β α selectively broken for the respective cationic conformers, yielding the different fragments. Novel dynamic processes, proton transfer and reorientation between the predissociative fragments, are involved in the threshold photoionization dissociations. ARTWORK 1 The knowledge of the formation, stabilities, and rearrangments of radical-cationic amino acids (RCAAs) is of great importance in chemistry and biology, e.g., disease development1,2 and protein sequentiation.3 It is a serious fact that the active RCAA