Part 1: Excited electronic state decomposition of energetic molecules. Part 2: Conformation specific reactivity of radical cation intermediates of bioactive molecules.

摘要

Energetic materials have a wide variety of industrial, civil, and military applications. They include a number of organic compounds such as RDX (1,3,5-trinitroheahydro-s-triazine), HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine), DAAF (3,3'-diamino-4,4'-azoxyfurazan), DAATO3.5 (3,3'-azobis(6-amino-1,2,4,5-tetrazine)-mixed N-oxides), etc. These materials release huge chemical energy during their decomposition. The decomposition of energetic materials is initiated with a shock or compression wave or a spark. Such events in solids generate molecules in the excited electronic states. Hence, in order to maximize release of the stored chemical energy in the most efficient and useful manner and to design new energetic materials, the unimolecular decomposition mechanisms and dynamics from excited electronic states should be understood for these systems. This thesis describes understanding about unimolecular decomposition of energetic materials from their excited electronic states. A few fundamental questions at molecular level dealing with electronic excitation of energetic materials are addressed here: (a) what happens immediately after electronic excitation of energetic molecules?; (b) how is excess energy partitioned among product molecules following electronic excitation?; (b) what are the mechanism and dynamics of molecular decomposition?; (d) does nonadiabatic chemistry (a process that spans multiple electronic potential energy surfaces) through conical intersection (crossing of different potential energy surfaces) dominate system behavior?;Part 2 of this thesis discusses about conformation specific reactivity of radical cation intermediates of biomolecules. The radical cation intermediates are generated by means of removal of an electron from the parent biomolecules due to the effect of ionizing radiation, oxidative stress, and metal cofactors, which finally causes extensive damage to amino acids, peptides, and living body. Therefore, a detailed conformation specific characterization of the reactivity and stability of radical cationic bioactive species is highly desirable.;In this effort, first, conformation specific radical cation intermediate chemistry of alpha-substituted (amino, hydroxy, and keto) bioactive carboxylic acids is discussed. Finally, folding specific reactivity of small peptide analogues is addressed. The reactivity of radical cation carboxylic acids and peptide analogue molecule is investigated on the basis of mass spectrometry, infrared-vacuum ultraviolet (IR-VUV) photoionization spectroscopy, and high-level correlated ab initio calculations. Their reactivity is found to be highly conformation specific and is governed by their initial charge distribution following ionization. In the present work, the radical cations of lactic acid, pyruvic acid, glycine, valine, and a peptide analogue CH 3CO-Gly-NH2 are studied to probe their stability and conformation specific reactivity following single photon, vertical ionization at 10.5 eV. For lactic acid, glycine, and valine, the localization site of the hole following sudden removal of an electron depends on their specific intramolecular hydrogen bonding network. Folding/turn specific dissociation of radical cationic peptide analogue CH3CO-Gly-NH2 is also predicted. Thus, the present study reveals that the specific conformations of biomolecules govern their radical cationic reactivity. (Abstract shortened by UMI.)