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Experimental spectroscopic and theoretical studies of amino acid derivatives

Experimental spectroscopic and theoretical studies of amino acid derivatives

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 / Department / Research Group: Faculty of Engineering & Science > Department of Pharmaceutical, Chemical & Environmental Sciences
Last Modified: 17 Oct 2016 09:11
Selected for GREAT 2016: None
Selected for GREAT 2017: None
Selected for GREAT 2018: None
URI: http://gala.gre.ac.uk/id/eprint/6207

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