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Characterization of the Interaction of Photo-Generated Cob(I)inamide with Carbon Dioxide in Anaerobic Aqueous Solution

Jawdat, BenMaan I. (2010)
Honors Thesis (36 pages)
Committee Chair / Thesis Adviser: Warncke, Kurt
Committee Members: Huynh, B H Vincent ; MacBeth, Cora
Research Fields: Energy; Physics, General; Chemistry, Biochemistry
Keywords: cobalamin; cobinamide; EutB; solar energy; artificial photosynthesis; compressed photosynthesis; CO2 reduction; cob(I)inamide; 5'-deazariboflavin; photoreduction;
Program: College Honors Program, Physics
Permanent url: http://pid.emory.edu/ark:/25593/7tb3b

Abstract

Abstract Characterization of the Interaction of Photo-Generated Cob(I)inamide with Carbon Dioxide in Anaerobic Aqueous Solution By BenMaan I. Jawdat One of the greatest challenges facing today's scientists is the creation of a viable renewable energy system to meet the demands of a growing population. The use of solar energy is currently a research focus. The long-term goal of this project is to develop a light-driven catalytic module in a re-engineered protein, that will be used for conversion of carbon dioxide (CO2) to a stable fuel in aqueous solution. The selected protein is the EutB protein from ethanolamine ammonia-lyase, which contains the native, cobalt-containing cobalamin cofactor. In this project, the reactivity of the free cobinamide (modified cobalamin) molecule with CO2 is studied in buffered aqueous solution, outside of the protein environment. Static and time-resolved ultraviolet (UV)/visible spectroscopy is used to characterize the cobinamide in the absence and presence of CO2. The fully-reduced cob(I)inamide, was generated by photoreduction of methylcob(III)inamide with 5'-deazariboflavin/EDTA in anaerobic, buffered (pH=6.0) solution. The subsequent cob(I)inamide decay reaction was measured by the loss of absorbance at 387 nm, with and without CO2 in solution. An assay was developed, in which the photolysis of methylcobalamin, and the subsequent reaction of the cob(II)alamin photoproduct with oxygen (O2) to form AquoCbl, was used to quantify the oxygen content in the samples. The careful control of pH and exclusion of oxygen led to dramatic improvement in the reproducibilty of the cob(I)inamide reaction measurements, relative to previous attemps. Decay of cob(I)inamide in the absence of CO2 (τ=9.0 min) was assigned to a proton reduction reaction. Increased time constants for decay of cob(I)inamide (up to τ=13.5 min) were observed in the presence of CO2. We propose that the effect is caused by the interaction of CO2 with cob(I)inamide.

Table of Contents

Table of Contents -- -- Chapter -- -- Page -- -- I. -- -- Introduction -- -- 1 -- -- II. -- -- Experimental Procedures -- -- 5 -- -- - Absorption Spectroscopy -- -- 5 -- -- - Photolysis Studies -- -- 5 -- -- - Preparation of MeCbi Samples -- -- 6 -- -- - Fitting of the Cob(I)inamide Decay Kinetics -- -- 8 -- -- III. -- -- Results -- - Absorption Spectra of Different Cobalamin and Cobinamide Redox States -- - Assay for the Determination of Oxygen Concentration in the Samples -- - Reaction of Cob(I)inamide in Aqueous Solution at pH 6.0 -- - Reaction of Cob(I)inamide with CO2 in Aqueous Solution at pH 6.0 -- -- 9 -- 9 -- 11 -- 14 -- 15 -- -- IV. -- -- Discussion -- -- 20 -- -- - Establishment of Reliability and Reproducibility in Cobalamin/ Cobinamide - CO2 Reactivity Measurements -- -- 20 -- -- - Dihydrogen Formation -- -- 21 -- -- - CO2 Binding Interaction with Cob(I)inamide -- -- 22 -- -- - Future Experiments and Outlook -- -- 23 -- -- V. -- -- References -- -- 25 --

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