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Dissertation/Thesis Abstract

Homogeneous Catalysis of Hydrolysis of Phosphate Esters by Schiff Base Complexes
by Okeke, Ugochukwu C., Ph.D., Howard University, 2017, 157; 10279666
Abstract (Summary)

Metalloenzymes catalyze hydrolytic reactions of various functional groups such as nitriles, amides (proteases) and phosphate esters (phosphatases). A large number of these enzymes contain one or more metal ions at their active centers. There has been much interest in the synthesis and study of such enzyme models for the purpose of detoxification of herbicides and insecticides which are phosphate esters. Phosphate esters are found in the hydrophilic head of phospholipids and the nucleoside units in DNA and RNA are bridged by phosphate esters. The active sites of enzymes are modeled by metal complexes that catalyze the hydrolysis of phosphate esters. Cells possess highly evolved enzymatic mechanisms to make and break various bonds in high rate reactions, which are otherwise extremely slow reactions at physiological pH. In this work some Zn(II), Cu(II), and Ni(II) complexes have been synthesized, structurally characterized, and studied for their catalytic properties. In addition, a series of Mn(III) complexes with varied functional groups were studied to determine the features of the complexes that enhance the rates for the catalysis of hydrolysis of phosphate ester bonds.

Transition metal complexes of the ligands, 1,3 (2-pyridyliminomethyl)phenylenediamine] (PIMPD), 1,3 (2-pyridyliminomethyl)phenylenediamine (SalPea), of N1,N2-bis(pyridin-2-ylmethyl)ethane-1,2-diamine (PcaEN), and 2,6-bis((E)-((2-(1H-imidazol-4-yl)ethyl)imino)methyl)-4-( tert-butyl)phenol (T-Imol) have been synthesized and studied for their catalytic properties in the hydrolysis of phosphate esters. The rates of hydrolysis were investigated at various pH, temperatures, complex and substrate concentration ratios, metal ion comparisons and by monitoring the progress of the hydrolysis of the substrates bis(p-nitrophenylphosphate) and p-nitrophenylphosphate by measurement of the absorbance at 400 nm as a function of time. This paper is a report of the rates of catalysis by these complexes of chelating ligands with nitrogen donors in the hydrolysis of phosphate esters.

Indexing (document details)
Advisor: Gultneh, Yilma
Commitee: Anderson, Alan, Gultneh, Yilma, Morris, Vernon, Stockwell, William, Talanova, Galina
School: Howard University
Department: Chemistry
School Location: United States -- District of Columbia
Source: DAI-B 78/12(E), Dissertation Abstracts International
Subjects: Chemistry, Analytical chemistry, Inorganic chemistry
Keywords: Catalysis, Hydrolysis, Inorganic complexes, Metalloenzymes, Phosphate esters
Publication Number: 10279666
ISBN: 978-0-355-07875-6
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