Photodissociation Dynamics of Amino Acid Chromophores
Date Issued
2007
Date
2007
Author(s)
Hsu, Chien-Ming
DOI
zh-TW
Abstract
Although the absorption coefficients of aromatic amino acids in the ultraviolet region are very large, it has been shown that the fluorescence quantum yields are very small. Internal conversion to the electronic ground state was assumed to be the major non-radiative process. In the gas phase under collisionless conditions, molecules become highly vibrational excited in the electronic ground state after internal conversion. If the initial photon energy is larger than the chemical bond energy, bond cleavage eventually occurs. On the other hand, in the condensed phase molecules are quenched by surrounding solvent molecules and are stabilized. However, recent theoretical calculation predicts that H atom elimination from a repulsive electronic excited state is the major non-radiative process for aromatic amino acid chromophores. The dissociation from the repulsive state is too fast to be quenched even in the condensed phase. It becomes a potential problem for the photostability of amino acids upon UV irradiation. In this experiment, we focused on the photodissociation dynamics of amino acid chromophores. Dissociation occurs on the ground electric state or on a repulsive state after UV excitation was investigated by multimass ion imaging techniques. The results show that H atom elimination from the repulsive potential energy surface is important in small amino acid chromophores like 3-methylindole, but it is completely quenched in large amino acid chromophores like n-acetyl tryptophan ether ester and n-acetyl phenylalanine methyl ester. The only dissociation channel for this large chromophore is carbon-carbon cleavage.
Subjects
胺基酸
發色團
光分解
多質量離子影像儀
Amino Acid
Chromophores
PhotodissociationMulti-mass ions detection
Type
thesis
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