Kausar, Nighat (2008) Experimental spectroscopic and theoretical studies of amino acid derivatives. PhD thesis, University of Greenwich.

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Abstract

Experimental vibrational/electronic circular dichroism spectroscopic and theoretical studies of amino acid derivatives, i.e. N-acetyl-L-Asp, N-acetyl-L-Glu, and di-amino acid peptide/derivatives, i.e. L-Asp-L-Glu, a-N-acetyl-L-Asp-L-Glu, and ß-N-acetyl-L-Asp-L-Glu are reported.

The calculated structures for N-acetyl-L-Asp and N-acetyl-L-Glu differ. The conformation of the trans amide moiety changes with the carbon chain length of the side chain of the amino acid derivatives. In the computed structures of N-acetyl-L-Asp and N-acetyl-L-Glu all backbone atoms are in-plane, except the side chain group; with respect to C2-C3 they both possess a staggered conformation. In addition both the N-acetyl and the side chain carboxylic acid groups are present in the anti-periplanar (i.e. anti- or trans-conformation). The amide I band occurs in the IR and Raman spectra of N-acetyl-L-Asp as a strong band at 1646 cm-1. In the case of N-acetyl-L-Glu it occurs as a weak, broad band at 1690 cm-1 in the solid state Raman spectrum; in the solution state Raman spectrum the amide I band is blue shifted, and presented at 1728 cm-1. The two different wavenumbers for C=O stretching vibrations, for both molecules, indicate that the two carboxylic acid groups are in different environments. According to DFT band assignments, the amide I bands are predicted at 1679 1682 cm-1 for N-acetyl-L-Asp and N-acetyl-L-Glu, respectively.

A band due to the trans amide II mode is found at ˜1545 cm-1 for N-acetyl-L-Asp in the IR spectrum and for N-acetyl-L-Glu at ˜1575 cm-1 in both solid state IR and Raman spectra. The amide II mode is not observed in the solid or solution state Raman spectra of N-acetyl-L-Asp. In the solution state Raman spectrum of N-acetyl-L-Glu, the amide II mode is blue shifted and occurs at 1647 cm-1. The calculated wavenumber value for the amide II mode is ˜1482 cm-1 for both amino acid derivatives. The amide III mode for N-acetyl-L-Asp is found at 1229 cm-1 in both solid state IR and Raman spectra. In the solution state Raman spectrum, this is found as a very weak band at 1238 cm-1. This mode is not observed in the solid state IR and solution Raman spectra of N-acetyl-L-Glu, but it appears at 1233 cm-1 in the solid state Raman spectrum. According to DFT calculations, the amide III mode is predicted at ˜1210 cm-1 for both acetyl derivatives.

The calculated vibrational spectra of L-Asp-L-Glu show a good fit with the experimentally recorded vibrational spectra. For example, the predicted and observed wavenumbers for amide I and amide II modes are similar i.e. observed values for amide I mode are at 1676 and 1692 cm-1 for solid state IR/Raman and solution state Raman spectra, respectively, and the predicted value is 1693 cm-1.

Item Type:	Thesis (PhD)
Additional Information:	uk.bl.ethos.491204
Uncontrolled Keywords:	spectroscopy, amino acids,
Subjects:	R Medicine > RS Pharmacy and materia medica
Faculty / School / Research Centre / Research Group:	Faculty of Engineering & Science > School of Science (SCI)
Last Modified:	17 Oct 2016 09:11
URI:	http://gala.gre.ac.uk/id/eprint/6207

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