Understanding electron-transfer (ET) processes in proteins is of fundamental importance. In a series of photophysical studies of well-behaved peptide model systems, it has become evident that the ET through peptide spacers is greatly influenced by the separation between the acceptor (A) and the donor (D), the nature of the peptide backbone, the amino acid sequence, and the resulting flexibility of the peptide conjugates. In particular, it was suggested in the literature that the presence of H-bonding will increase the rate of ET, and there is experimental evidence, mostly in proteins, to suggest that H-bonding indeed increases the rate of ET.<p>My aim was to develop a potential-assisted deposition method for ferrocene peptide disulfides onto gold surfaces and investigate the electrochemical properties of these films. We made use of two classes of Fc-peptides: acylic ferrocenoyl (Fc)-peptide disulfides and cyclo-1,1-Fc-peptide disulfides, allowing the preparation of tightly packed films of cyclic and acylic Fc-peptides on gold surfaces within 30 minutes. This is a significant benefit compared to the conventional soaking method of self-assembly requiring several days for the assembly of well-packed films. Such films exhibited considerably improved stability. This electrodeposition method should find wide-spread applications for the formation of tightly-packed films from disulfides. Our studies allowed a direct comparison of the electron transfer kinetics of cyclic and acyclic Fc-peptide disulfide systems. Our results showed faster ET kinetics for films prepared from cyclic Fc-peptide conjugates compared to the acyclic systems, presumably as a result of the enhanced rigidity of the Fc-peptide conjugates on the surface and/or an increase of the number of conductive peptide wires to the surface. Following the idea of peptide dynamics as a major contributor to the observed electron transfer rate in peptides and peptide conjugates, variable temperature electrochemical studies of Fc-peptide films were performed. An estimation of the reorganization energy associated with ferrocene/ferrocenium (Fc/Fc+) redox process allowed us to probe the role of peptide dynamics. Three counter-ions were tested, exhibiting different strengths of association with the Fc+ group (BF4- < ClO4- < PF6-) and the reorganization energies were evaluated in each case. The highest reorganization energy was obtained for the weakly interacting anion BF4-. Weakly interacting anions also showed significant broadness in the redox peaks and emergence of the second oxidation peak which is attributed to phase separation of the ferrocene group. Ferrocene agglomeration was not observed for any of the cyclic Fc-peptide conjugates but occurred for some of the acyclic systems. In particular, for acyclic Val and Leu containing Fc-peptide conjugates agglomeration were observed and was presumably caused by lateral interactions between the hydrophobic side-groups of the peptides. Further experiments involving the interaction of Fc-peptide films with alkali metal ions gave additional evidence that electron transfer is influenced significantly by peptide dynamics.

Along with the rapid growth of the nanotechnology, nanoparticles (NPs) have found many applications in commercial products. However, there are only a few studies on the toxicity and the environmental effects of NPs in biological systems. <p>In the study described in this thesis, I have used water-soluble Au NPs that were synthesized using the Brust method and then modified by small molecules. I explored the interactions of these modified Au NPs with self-assembled monolayer films on gold surfaces.<p>Three types of self-assembled monolayer (SAM) modified gold surfaces were used in this study. The surfaces had SAMs that could be positively or negatively charged or carry no charge, or be able to engage in hydrogen bonding. <p>Cyclic voltammetry (CV) was used to characterize SAMs of disulfide-glycine conjugate, disulfide-aspartic conjugate, and 11-mercaptoundecanoic acid (MUA) on gold surface electrodes. The possible interactions of Au NPs with the disulfide-aminoacid conjugates and alkanethiol modified surfaces were evaluated by cyclic voltammetry and by electrochemical impedance spectroscopy (EIS). An apparent decline in current density observed in CV along with an electron transfer resistance increase in EIS measurements upon exposure of the films to the MUA-modified anionic Au NPs clearly indicate interactions of the NPs with the films. Likewise, upon exposure of the films to cationic NPs, electron transfer resistance decreases dramatically in EIS experiments. In addition, the current increase in CV measurements provided further evidences for the interactions. The interactions between modified Au NPs and the SAMs were investigated in more detail by infrared spectroscopy and by employing quartz crystal microbalance. These studies clearly showed that upon exposure of these SAM films to the water-soluble Au NPs, significant changes occur. As would be expected for the adsorption of the Au NPs onto the SAMs, the weight of the film increased due to the addition of the NPs on the surface. Moreover, there are significant increases in the carbonyl stretching vibration at 1735 cm-1 along with the appearance of the amide hydrogen stretching band, between 3160-3380 cm-1, which indicate the adsorption of Gly-CSA modified Au NPs onto the MUA film.

Understanding long range electron transfer (ET) in proteins is of fundamental interest to elucidate the complex nature of many biological processes. The mechanistic discussion is highly debated in the literature and the factors that control this process are still not clear. Because of the structural complexity and dynamic nature, it is very difficult to correctly evaluate long range ET in proteins. The study of simple model peptides having specific secondary structures is useful for a systematic and accurate evaluation. The polypeptide matrix in the photosynthetic reaction centre is rich in helices and this particular structural motif is believed to play an important role in ET in nature. In this thesis, ET study through some synthetic α-helical model peptides is described. The model peptides studied herein contain the redox-active ferrocene at one end and the thiol-functionalised Cys residue at the other. Films of these peptides were formed on the surface of gold electrodes via the Au-S bond, and by employing cyclic voltammetry, the rate of ET between the pendant ferrocene and the gold electrode through the peptide spacer has been evaluated. My study indicates that ET in α-helical peptides is a function of molecular dynamics and occurs via a tunnelling mechanism. These findings are significant and expected to offer new directions in the highly controversial discussion on ET in proteins.<p>This thesis also describes investigations in two important areas of applications of the α-helices. The first is photocurrent generation upon laser excitation of light-harvesting chromophore-functionalised peptides which mimics the natural photosynthetic centre. This important area of research can promote development of nano-scaled photovoltaic devices. Surprisingly, following the conventional experimental protocols, a photocurrent was observed in the absence of a chromophore and even by the irradiation of a bare gold electrode with laser light. It is suggested that an important consequence of laser irradiation has been overlooked in several publications and the so-called photocurrent phenomenon may be a consequence of laser heating. <p>Peptide-protected nanoparticles is another area of research receiving significant attention these days due to its potential relevance in biomedical applications. However, peptides are highly flexible and their structure can change depending on the nature of the environment. Since the reactivity of a peptide is related to its secondary structure, any conformational change could seriously alter the overall activity of the peptide-protected nanoparticles. In this thesis, the structural investigation of an α-helical peptide was carried out and it was found that the radius of curvature of nanoparticles has a profound effect on the structure of the adsorbate peptides and thereby, may affect the overall activity of the peptide-protected nanoparticles.

Crevice corrosion is a form of galvanic corrosion that occurs when a metal is exposed to different environments. This occurs when the oxygen within the crevice gets depleted, thus acting as the anodic site for metal dissolution reaction. The anodic site thus encourages the migration of Cl- ions into the crevice leading to the development of an aggressive local solution. The acidic conditions present in the crevice reaches a critical crevice solution composition and results in the loss of stability of the passive film which further leads to a rapid breakdown of these films on the metal thus indicating the onset of active corrosion.<p> In this research, it is hypothesized that the onset of crevice corrosion can be detected by measuring the galvanic coupling current between electrodes in a crevice and an external metal surface composed of the same material as the electrodes. To prove this hypothesis an engineered crevice was designed to measure IR controlled crevice currents along the crevice length of AISI 304 stainless steel immersed in a 0.5 M solution and a 1 M NaCl solution. Varying crevice openings were used to determine the effect of crevice gap (G) on the initiation of crevice corrosion and the position of the accelerated attack within the crevice.<p> Multiplexed corrosion potential measurement and galvanic corrosion measurement techniques were used to measure the change in the open circuit potential (OCP) and the galvanic current for the four channels along the crevice length of the galvanic couple. The results obtained from the MGC test for the 100 µm crevice width immersed in 0.5 M NaCl solution showed good results with high anodic current at approximately 1 cm from the crevice mouth. This finding was in close agreement with the peak pH value observed at the position closest to the crevice mouth in the work of Alavi and Cottis (1987) and the model prediction of Kennell et al. 2009. However, for test samples with crevice width ≥ 200 µm, there was no initiation of crevice corrosion and the results obtained were discarded. The Linear polarization resistance scan and Potentiodynamic polarization scan carried out along the crevice to measure the polarization resistance, Rp , and to obtain the region of passivity along an AISI 304 SS crevice did not yield good results. Low corrosion rate in the range of 0.06 mm/yr was calculated for the AISI 304 stainless steel crevice.

The ruthenium dinuclear complexes with end-caping of pyridinedicarboxylate complexes of terpyridine (2,2':6',2'-terpyridine) and (tBu)3-terpyridine (4,4¡¦,4¡¦¡¦-tri-tert-butyl-2,2¡¦:6¡¦,2¡¦¡¦-terpyridine) bridging with carbon-rich alkynyl group are reported. These novel complexes are characterized by NMR, MALDI-MS, FT-IR, UV, and electrochemistry. In comparison with the system of tpy-Ru-tpy-(¡Ý)n-tpy-Ru-tpy, we found some interesting characteristics in the studies of electronic spectra and electrochemical measurements. Furthermore, one reversible and one irreversible electrochemical redox waves in positive wave were observed (E1/2 at 0.59 and 1.15 V (irrev.) for the complex with ethynyl spacer and E1/2 at 0.62 and 1.10 V (irrev.) for the complex with butynyl spacer), indicating a strong electronic interaction between two Ru metal centers. However, in the tpy-Ru-tpy-(¡Ý)n-tpy-Ru-tpy system, only one electrochemical redox wave at ~1.3 V was found. From the electronic and electrochemical analysis , the electronic interaction between two metal centers decreases as the number of alkynyl group increases.

Electrochemical Mechanical Polishing (ECMP) has become increasingly important due to the continuous decrease of the device size in integrated circuit (IC) fabrication. Tantalum (Ta) is a promising material as a substitute for copper in ICs. This dissertation studies the tribology and electrochemistry of Ta ECMP. The present research uses experimental combined analysis approaches. A specially designed experimental setup assembling a tribometer and a potentiostat was used to carry out Ta ECMP. The friction force and electrochemical reactions were measured simultaneously. Using this setup, we found the factors which affected the frictional behaviors of Ta during ECMP. The technique of single frequency electrochemical impedance spectroscopy (EIS) was employed to investigate the material removal mechanisms in Ta ECMP. The results presented the competing mechanisms of removal and formation of a surface oxide layer of Ta. In order to further the investigation in a nanoscale, the atomic force microscope (AFM) was used to measure the material removal rate. The Preston equation for the Ta ECMP was established. A new methodology was developed to study the oxidation state and process of Ta during ECMP. Through comparing the material removal rate measured by using the AFM and the calculated one via the Faraday’s law, the distribution of the Ta suboxides and pentoxide, as well as the oxidation process, was revealed. The oxidation process was strongly dependent of the applied anodic potential, thickness of the oxide layer, mechanical forces, and surface orientation. A polymer environmental cell was designed and produced. Using this cell and AFM, it was found that the material removal in the nanometer scale was a function of the surface orientations. This research is beneficial for optimization of the Ta ECMP process. This dissertation includes six chapters. After Introduction and Motivation and Objectives, the material, setup, and testing conditions are discussed in Chapter III. Chapter IV discusses the tribology and material removal mechanisms in Ta ECMP, while Chapter V the oxidation of Ta during ECMP, followed by Conclusions and Future Work.

We described the synthesis of multilayer organic thin films prepared by sequential vapor-phase coupling of monomers. The reactions were carried out at room temperature and atmospheric pressure. Films prepared using up to six sequential coupling reactions are reported. Homobifunctionalized monomers, such as hexamethylenediamine, react primarily via a single endgroup rather than cross coupling to the reactive surface via both reactive groups. We synthesized bifunctionalized polyamidoamine (PAMAM) dendrimers having both quaternary ammonium groups and primary amines on their periphery were prepared. The high positive charge on the surface of these dendrimers prevents agglomeration, and the unquanternized amine groups provide a reactive handle for immobilizing the dendrimer-encapsulated nanoparticles onto surfaces. We prepared highly monodisperse, 1-2 nm diameter Au nanoparticles using bifunctionalized PAMAM dendrimers as templates. The synthesis is carried out in water, takes less than 30 min, and requires no subsequent purification. The high monodispersity is a function of the template synthesis, which avoids size variations arising from random nucleation and growth phenomena, and the use of magic number equivalent ratios of AuCl4-/dendrimer. We investigated the electrochemical properties of Au, Pd and PdAu monolayer-protected clusters (MPCs), prepared by dendrimer-templating and subsequent extraction, are described. Purification of the extracted Au, Pd and PdAu nanoparticles was not required to obtain well-defined differential pulse voltammetry peaks arising from quantized double-layer charging. The calculated sizes of the nanoparticles were essentially identical to those determined from the electrochemical data. The capacitance of the particles was independent of the composition of core metal.

The preparations of multinuclear supramolecules assembled from ethynylferrocene(s) redox-active subunit end-capping with [(£b5-C5H5)(dppe)Ru] metal centers are described. Electrochemical measurements indicate that ferrocenyl-ethynyl spacers appear to be promising spacers which can ensure fast and quantitative transfer of information between two Ru2+ metal centers.

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references. Available also in a digital version from Dissertation Abstracts.

Thesis (Ph. D.)--University of Texas at Austin, 2001. / Vita. Includes bibliographical references. Available also from UMI/Dissertation Abstracts International.