## LSU Historical Dissertations and Theses

1987

Dissertation

#### Degree Name

Doctor of Philosophy (PhD)

Chemistry

#### Abstract

Theoretical explanations of the $\alpha$-helix to coil transition which employ rotational isomeric state calculations are reviewed. Recent advances in this field include the development of similar fundamentals for the intramolecular antiparallel $\beta$-sheet to coil transition. This dissertation adds to the current body of knowledge by outlining a formularization to calculate the mean square end-to-end distance, $\langle{\rm r}\sp2\rangle\sb{\rm o},$ of a homopolypeptide for the transition from random coil to intramolecular antiparallel $\beta$-sheet conformation. The formularization is translated into a computer program in the C language and values of $\langle{\rm r}\sp2\rangle\sb{\rm o}$ are calculated for a number of different statistical weights. These are analyzed parallel to other statistical parameters such as the fraction of residues in the $\beta$ sheet conformation, the average number of residues per sheet, the average number of strands per sheet, and the average number of residues per strand. Included are plots of $\surd\langle{\rm r}\sp2\rangle$ against the fraction of residues in a sheet, two experimentally obtainable parameters. Catechins and procyanidins, flavenoids synthesized by plants, are the monomers and dimers of the group of larger molecules known as tannins. Tannins are known to interact with proteins, rendering certain digestive enzymes inactive and casuing the precipitation of otherwise soluble proteins. Experimental research revolves around the effect of catechins and procyanidins on the conformational transitions mentioned above. The effect of catechins and procyanidins on the transition is studied by following the transition of a number of polypeptides in the presence and absence of catechins and procyanidins. The polypeptides vary by the degree of hydrophobic nature, and charge density in their side chains. The systems are also observed by fluorescence to determine the degree of interaction of catechins and procyanidins with the various side chains. Results of the experimental work support earlier proposals that the interaction of tannins and proteins is uniquely favored for the amino acid residue, proline. There may also be a slight effect on the $\beta$-sheet coil transition of poly (S-carboxymethyl cysteine). This is proposed to be due to a stabilization of the initial strand of the sheet by hydrogen bonding to the backbone.

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