Iqbal, Azhar (2010) Towards understanding the photochemistry of tyrosine. PhD thesis, University of Warwick.

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Abstract

The H-atom detachment driven through the 1πσ* states of biological
chromophores containing an X-H bond (where X = N or O) upon UV absorption is
ubiquitous in nature. Understanding the role of this dissociative state in the
chromophores and their respective amino acids following UV excitation would
enable a step change towards establishing a better understanding of the mechanisms
of photostability of larger peptides in the gas-phase. The work presented in this thesis
focuses on the H-atom elimination of phenol and indole, the chromophores of the
amino acids tyrosine and tryptophan, respectively. The H-atom elimination has also
been carried out in tyrosine and its sub-units p-ethylphenol and tyramine upon
excitation at 200 nm. In all these systems the O-H bond fission on the phenol ring
results in a range of H-atoms kinetic energy release.
Using a combination of femtosecond pump-probe spectroscopy, time-offlight
mass spectroscopy (TOF-MS) and velocity map ion imaging (VMI) reveals
that H-atom elimination in all these systems occurs on an ultrafast timescale (~200
fs) for both fast and slow H-atoms. This casts considerable doubt over the previously
assigned statistical origin of the slow H-atoms and suggests direct pathways to their
formation. The H-atom kinetic energy spectrum in tyrosine also implies that H-atom
elimination is occurring through the same coordinate i.e. O-H bond as exhibited by
it’s phenol chromophore, thus confirming the active participation of the 1πσ* states
from the chromophore of the amino acid to the amino acid itself. These findings are
of great importance enabling one to compare these results with existing calculations
on the chromophores which often model the system in an isolated environment.
These results also provide ground work for more complex calculation to be carried
out, in particular on the amino acids and the di/tri peptides.

Item Type:	Thesis or Dissertation (PhD)
Subjects:	Q Science > QD Chemistry
Library of Congress Subject Headings (LCSH):	Hydrogen, Phenol, Indole, Tyrosine, Tryptophan, Ultraviolet radiation, Photochemistry
Official Date:	June 2010
Dates:	Date Event June 2010 Submitted
Institution:	University of Warwick
Theses Department:	Department of Chemistry
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Stavros, Vasilios
Extent:	218 leaves : ill., charts
Language:	eng
URI:	http://wrap.warwick.ac.uk/id/eprint/3735

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