Dipeptide Complexes Of Palladium(II) And Platinum(II)

Author

Lewis Enos Nance, University of the Pacific

Date of Award

1972

Document Type

Dissertation

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Chemistry

First Advisor

Herschel Frye

First Committee Member

Paul H. Gross

Second Committee Member

Carl E. Wulfman

Third Committee Member

Richard P. Dodge

Fourth Committee Member

Charles A. Matuszak

Abstract

Due to recent interest in the role of heavy metals in enzymes. oxygen-carrying molecules. and anticarcinogenic compounds, the study of metal-protein bonding has assumed a new importance. Studies have been made utilizing platinum compounds as anticarcinogenic agents in several different types of cancerous activity. No study of the mechanism by which Pd(II) and Pt(II) compounds exhibit anticarcinogenic properties has been made to date.

The purpose of this research was to investigate the nature of bonding of Pd(II) and Pt(II) with various dipeptides, which were chosen in this study as a basic unit of protein-like material. These compounds have the advantage of having the bonding sites of larger peptides. An amino group, peptide-linkage carbonyl and amide group, and carboxyl group are available for bonding with metal ions to form complexes. The position of the donor atoms on dipeptides allow sterically for the formation of two five-membered rings in a complex when other conditions are suitable.

When PdBr₂ was refluxed in acetone with a dipeptide, PdBr₂ (XX)₂ (where XX is a dipeptide) resulted. Bonding of the dipeptide to Pd(II) was through the amino nitrogen atom. Analogous compounds were found to result when PtCl₂ was refluxed in acetone with a dipeptide.

K₂PdCl₄afforded a source of Pd(II) in which the dipeptide could function as a bidentate or tridentate ligand. At a pH near 13.0 the dipeptide was bound to Pd(II) through the amino and deprotonated nitrogen atoms. At a pH near 7.0 the carboxylate oxygen of the dipeptide was also bonded to Pd(II). Infrared measurement showed that the Amide I band of the dipeptide had shifted at least 50 c^-1 to lower energy upon coordination of the peptide nitogen to Pd(II). Electronic studies indicated that the λ (max) was at a minimum when the dipeptide was acting in a tridentate mode. There was a red shift when the hydroxide ion replaced the carboxylate group in the coordination sphere at pH values near 13.0. Nuclear magnetic resonance spectra indicated tridentate behavior of glycylvaline with Pd(II) at pD 7.11 but showed detachment of the carboxylate group from the coordination sphere at pD 13.06.

Infrared analysis showed that there was no reaction of Pt(Il) with the peptide linkage when K₂PtCl₄ was used at the Pt(II) source.

Zeise's salt was used as a third source of Pt(II). Infrared analysis, molecular weight determination, and elemental analysis indicated fission of the peptide bond and formation of compounds of the formula (C₂H₄PtClX)₂, where X is an amino acid residue from the dipeptide reacted with Zeise's salt. Both residues of each dipeptide, ValVal, ValLeu, and LeuVal, were incorporated in the product of Zeise's salt and the dipeptide. Infrared analysis indicated N-trans--O-trans of the donor atoms of the amino acid residues with respect to ethylene in the VaVal and LeuVal products, whereas ValLeu gave an N-trans--N-trans product.

Pages

111

Recommended Citation

Nance, Lewis Enos. (1972). Dipeptide Complexes Of Palladium(II) And Platinum(II). University of the Pacific, Dissertation. https://scholarlycommons.pacific.edu/uop_etds/3342