Colloquium
Department of Physics, NCU
Specific Peptide-Bond Dissociation of Some Peptide Model Molecules
Prof. Chen-Lin Liu (劉振霖)
National Synchrotron Radiation Research Center
Date 2022.04.26 (Tue)
Place S4-625
Time 14:00-16:00
Abstract :
The core-excited peptide model, N-methylformamide, and its isotopically substituted molecules were used to resolve the channel of specific dissociation by using soft X-ray from synchrotron radiation. The branching ratio of the products varying with excitation energy are observed from experiments. High branching ratios of some products were specifically following exciting the molecule at some specific energies, which could be defined as specific dissociation. The variation of the branching ratios with photon energy of each product from three isotopically substituted molecules were measured. From the branching ratios of the products with varied ratios of mass to charge, the variation of the branching ratio with photon energy of each dissociation channel was resolved. It was revealed that the peptide bond was efficiently broken after resonant core excitation to the first π* orbital, but the obvious specific reaction mechanism that is dominant involves only the dissociation channel with breaking the peptide bond and eliminating two hydrogen atoms to form CNH2+; the accompanying branching ratio increased as much as 80 %. On exciting a 1s electron from carbon or oxygen coupled with some vibrational excitation, breaking a C=O bond is also slightly enhanced as an element specific dissociation. Furthermore, the isotope substituted molecules were used to calculate the branching ratio at each excitation energy for each dissociation channel even though they look the same products. It turns out that the specific dissociation channels were observed at specific excitation energies especially exciting the nitrogen core electrons.