Keywords

Dihydrogen production, femo co, nafy femo co, cdse nanoparticles, nifen protein, molybdate reduction

Abstract

Humankind’s tremendous industrial and technological progress over the last two centuries has been driven by the natural abundance and availability of fossil fuels. As those reserves deplete, the prudent course of action would be to develop other readily available fuel sources. Some research efforts using biomolecules involve the hydrogenases and nitrogenases with the goal of evolving dihydrogen. At the nitrogenase active site, the iron-molybdenum cofactor (FeMo-co) catalyzes the reduction of dinitrogen and protons to form ammonia and dihydrogen. Toward the goal of producing dihydrogen passively as an alternative fuel, a novel advanced material has been developed. CdSe nanoparticles complexed with FeMo-co, in both aqueous and organic solvent systems showed complex formation. When the system was interrogated by EPR spectroscopy, evidence of electron transfer was observed. The CdSeMSA●NafY●FeMo-co system when illuminated with visible light evolved dihydrogen consistently in four different experimental sets under the same reaction conditions. NifEN protein plays an important role in the biosynthesis of FeMo-co in addition to the involvement of NifU, NifS, NifB, NifX, NifH and NafY. After NifB synthesizes a FeMo-co precursor, 6-Fe NifB-co, NifEN further incorporates additional Fe, S, Mo, and (R)-homocitrate to complete the synthesis of FeMo-co. Molybdenum is provided to NifEN as its oxoanion, Mo(VI)O4 2- ; however, in FeMo-co molybdenum is in the oxidation state of Mo(IV). EPR spectroscopic investigation of NifEN turnover samples showed a signal at g = 2.00 that was dependent on molybdate concentration. Power and temperature profiles gave evidence that the g iv = 2.00 EPR signal was distinct from the Fe-S clusters in NifEN. The species observed at g = 2.00 was assigned to the reduction of Mo(VI) to Mo(V). How to utilize the effectiveness of FeMo-co and complex it to photoactive materials for the purpose of evolving dihyrogen upon illumination, thus providing a sustainable alternative energy source is one subject of this dissertation. A related subject is to gain an understanding of the biosynthetic pathway of FeMo-co by investigation of NifEN turnover experiments. This understanding should contribute towards the development of improved catalysts for meeting future energy demands.

Notes

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Graduation Date

2012

Semester

Summer

Advisor

Igarashi, Robert

Degree

Doctor of Philosophy (Ph.D.)

College

College of Sciences

Department

Chemistry

Degree Program

Chemistry

Format

application/pdf

Identifier

CFE0004623

URL

http://purl.fcla.edu/fcla/etd/CFE0004623

Language

English

Release Date

February 2013

Length of Campus-only Access

None

Access Status

Doctoral Dissertation (Open Access)

Subjects

Dissertations, Academic -- Sciences, Sciences -- Dissertations, Academic

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Chemistry Commons

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