<p> The secondary kinetic isotope effects for the hydride transfer reactions from aliphatic alcohols to four carbocations (NAD⁺ models) in acetonitrile were determined. The results suggest that the hydride transfer takes place by tunneling and that the rehybridizations of both donor and acceptor carbons lag behind the H-tunneling. This is quite contrary to the observations in alcohol dehydrogenases where the importance of enzyme motions in catalysis is manifested.</p>

Thesis (Ph.D.)--Lehigh University, 2008.

Thesis (Ph. D.)--University of Illinois at Urbana-Champaign, 2008. / Source: Dissertation Abstracts International, Volume: 69-11, Section: B, page: 6812. Adviser: Jeffrey S. Moore. Includes bibliographical references. Available on microfilm from Pro Quest Information and Learning.

Thesis (Ph. D.)--Syracuse University, 2004. / "Publication number AAT 3132711."

All organic photovoltaics (OPVs) undergo four major processes to convert sunlight in electrical energy. The first process is the absorbance of sunlight. Due to the limit of available acceptor molecules, the burden of light absorbance weighs heavily on the donor material. This thesis focuses heavily on the development of dyes consisting of donor-acceptor dyads and triads for improved light harvesting in OPVs. Squaraine dyes show impressive light harvesting properties with absorbances in the UV to near IR region with extinction coefficients on the order of 105 M-1 cm-1. Unfortunately, improved light harvesting is not enough to insure optimized OPVs. Energy level tuning to increase VOC and insure efficient exciton dissociation is also required. Functionalizing squaraine dyes with electron donating or electron withdrawing groups allow for the systematic tuning of the HOMO energy levels. This tunability allows for the concurrent optimization of bandgap and VOC. Cyanine dyes have been explored for small molecule OPVs due to their impressive absorbance properties. The absorbance of ketocyanine dyes can be tuned by manipulating the strength of the acceptor moiety. Stronger acceptors are better able to stabilize the negative charge in the charge separated state of the dye. This stabilization allows for a greater contribution from the cyanine structure of the dye, thus red shifting the absorbance. Stronger acceptors also increase the communication between the two amine functionalities as demonstrated by cyclic voltammetry. Block copolymers show impressive morphological control through the tuning of the molecular weight of the blocks as well as the compatibility of the functional groups. This allows for the access of morphologies with small, well ordered, and continuous domains thought to be beneficial in the active layer of OPVs. Unfortunately, block copolymers often show inferior light harvesting compared to their conjugated polymer counterparts. Donor-acceptor systems are explored as sensitizers for block copolymer OPVs. Small molecules without twists or bends or acetylene linkers were found to be most effective for lowering the bandgap and aligning the energy levels.

A study of the adsorption of block copolymers with respect to such variables as adsorption rate, concentration, molecular weight, relative block sizes, architecture, adsorption solvent, and temperature was conducted for the adsorption block copolymers to silanol surfaces. Poly(styrene-b-isoprene) and poly(styrene-b-1,2-butadiene) with precise molecular weight and narrow polydispersity were synthesized by anionic polymerization techniques. These block copolymers were then specifically modified to incorporate an organic moiety (sticky foot) which would promote adsorption. Hydrosilylation to incorporate trimethoxysilanes into the diene block was unsuccessful due to low reaction yields and crosslinking. Hydroboration/oxidation to incorporate alcohols into the diene block was used to prepare polymers for adsorption studies due to the high reaction yields with no crosslinking. Adsorption studies examining the effects of molecular weight, number of adsorbing segments, time, concentration, polymer architecture, and adsorption solvent were conducted for the adsorption to aerosil 130. Adsorptions were analyzed by UV spectroscopy and thermal gravimetric analysis. Adsorption studies examining the effects of molecular weight, relative block sizes, and temperature were conducted for the adsorption to glass slides. Adsorptions were analyzed by water contact angle and X-ray photoelectron spectroscopy. The competitive polymer adsorptions between two different polymers adsorbing to aerosil 130 were studied. Simultaneous adsorptions for two polymers with respect to concentration were examined for three separate sets of polymers. The polymers were adsorbed to aerosil 130 and analyzed by gel permeation chromatography. Sequential competitive adsorptions for these same polymer sets were also conducted using the same substrate and analysis technique. The effect of surface affinity on polymer adsorption was examined by adsorbing one polymer sample to a series of different surfaces. Poly(chlorotrifluoroethylene) polymers with carboxylic acid, alcohol, amine, and ethyl ester surfaces as well as glass slide and aminated glass slide surfaces were prepared and used for adsorptions. These adsorptions were analyzed by X-ray photoelectron spectroscopy.

<p> In this work the redox properties of cytochrome c nitrite reductase (CcNiR), a decaheme homodimer that was isolated from <i>S. oneidensis,</i> were determined in the presence and absence of the strong-field ligands cyanide and nitrite. Four hemes per CcNiR protomer are hexa-coordinate with tightly bound axial histidines, while the fifth (active site) has one tightly bound lysine and a distal site that can be open, or contain exogenous ligands such as the substrate nitrite. Controlled potential electrolysis in combination with UV/visible absorption (UV-vis) and electron paramagnetic resonance (EPR) spectroscopies allowed for assignment of all heme midpoint potentials under each set of conditions. The studies show that the active-site heme is the first to be reduced under all conditions. The midpoint redox potential of that heme shifts approximately 70mV to the positive upon binding a strong field ligand such as nitrite or cyanide. When controlled potential electrolysis was carried out in the presence of nitrite, a concerted two electron reduction was observed by UV-vis, and a {Fe(NO)}⁷ reduced product was revealed in EPR. In addition, an asymmetry in ligand binding between active sites was revealed. This information is relevant for the interpretation of planned and ongoing mechanistic studies of CcNiR. </p><p> Over-expression, partial purification and characterization of another <i> S. oneidensis</i> multiheme enzyme, known as octaheme tetrathionate reductase (OTR), is also described herein. Though of unknown cellular function, OTR was previously reported to have tetrathionate reductase activity, in addition to nitrite and hydroxylamine reductase activities. The new results indicate that the expression of OTR has no effect on tetrathionate or nitrite reductase activities in the whole cell lysate, and only hydroxylamine reductase activity was substantially elevated in the overexpressing bacteria. OTR was stable in buffered solutions, but substantial activity loss during all attempts at column chromatography was a major obstacle to the complete purification. OTR also proved quite hydrophobic, so possible membrane association should be considered in future attempts to purify this protein. </p><p> Finally, this dissertation also reports attempts to improve <i> S. oneidensis'</i> ability to express foreign proteins. Though ideally suited to expressing c-hemes, it proved difficult to express carboxy his-tagged proteins in <i>S. oneidensis</i> because of persistent tag degradation. Attempts to knock out lon protease, a cytoplasmic carboxypeptidase, as well as the result of redirecting ccNiR from the SecA to the possibly more protected signal particle recognition (SRP) secretion pathway, are described. </p><p> Iron heme cofactors are single-electron transport moieties that play a crucial role in respiration. While oxygen is the electron acceptor of choice in aerobic atmospheres, microorganisms that live in anaerobic environments utilize other molecules with similarly high reduction potentials. <i> S. oneidensis</i> can utilize numerous terminal electron acceptors, including nitrite, dimethylsulfoxide and even uranium, thanks to a particularly rich array of multi c-heme respiratory proteins. Understanding of how the midpoint potentials and heme arrangements within the proteins influence these exotic respiratory processes is of interest in the fields of bioremediation and fuel development.</p>

This thesis presents the development and redesign of a commercial electrochemical quartz crystal microbalance with dissipation (E–QCM–D). This was used to study factors affecting the efficiency of the four electron reduction catalysed by the fuel cell enzyme bilirubin oxidase from Myrothecium verrucaria immobilised on thiol modified gold surfaces. Within this thesis, the E–QCM–D was used to show that application of a constant potential to bilirubin oxidase adsorbed to thiol-modified gold surfaces causes activity loss that can be attributed to a change in structural arrangement. Varying the load by potential cycling distorts the enzyme by inducing rapid mass loss and denaturation. Attaching the enzyme covalently reduces the mass loss caused by potential cycling but does not mitigate activity loss. Covalent attachment also changes the orientation of the surface bound enzyme as verified by the position of the catalytic wave (related to the overpotential for catalysis) and reactive labelling followed by mass spectrometry analysis. The E–QCM–D was used to show how electrostatic interactions affect enzyme conformation where high pH causes a reduction in both mass loading at the electrode and a reduction in activity. At pH lower than the enzyme isoelectric point, there is a build up of multilayers in a clustered adsorption. When enzyme adsorbs to hydrophobic surfaces there is a rapid denaturation which completely inactivates the enzyme. Changing the surface chemistry from carboxyl groups to hydroxyl and acetamido groups shows that catalysis is shifted to more negative potentials as a result of an enzyme misorientation. Further to this, increasing the chain length of the thiol modifier indicates that an increased distance between surface and enzyme reduces activity, enzyme loading and results in a conformational rearrangement that permits electron transfer over longer distances.