The compositions, in terms of Au, Ag, Cu, and Hg, of about 1200 placer and lode gold grains from the Fraser River drainage were determined by microprobe analysis. The lode samples are from the Bralorne and Cariboo Gold Quartz mines. Seventeen placer samples are from the Cariboo district and the Bridge River, Fraser River and their tributaries. Bralorne gold and many placer grains contain Hg which ranges up to 6%. Evidence is presented to show that this Hg is primary. Placer gold grains also contain Cu, ranging up to 31%, but high-Cu gold has little Ag or Hg. The compositional data were used to define populations on Hg-Cu-Fineness plots for each sample location. A comparison of the populations shows that placers located near lodes reflect these sources but that simple downstream transport of the gold cannot explain the populations found far from known sources. In order to explain the population found in downstream placers it is necessary to postulate contributions from undiscovered lodes, fossil placers, or other unknown sources. Many placer grains from the Fraser River have rims that are nearly pure gold. The rimming is thought to have taken place in an "intermediate collector" (fossil placer?) by leaching of Ag. Rimmed gold is not found in the Bridge River. From the data on the composition of the gold one is able to divide the Fraser River drainage into two metallogenic provinces: a Cu-Hg-rich province that includes the Bridge River drainage and a Cu-Hg-poor province typified by the Cariboo region. The data from the lode deposits suggest that the deposits can not only be uniquely characterized but that it may be possible to distinguish zoning within the lodes. In addition, it appears that much of the Cu- and Hg-rich gold is associated with ultrabasic rocks and major faults. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

The mechanism of organothiol (OT) binding to gold has remained controversial for decades. There are three mechanisms proposed for OT binding to gold surfaces. The first is the radical pathway in which the sulfur-bound hydrogen atoms (RS-H) are released as hydrogen atoms which eventually converted into hydrogen gas. Second is the deprotonation pathway in which the sulfur-bound hydrogen atoms leave as protons. Third is direct adsorption in which the RS-H bonds remain intact on the gold surface. This study demonstrates a combined pH and surface enhanced Raman spectroscopic study of organothiol binding to citrate- and borohydride-reduced gold nanoparticles (AuNPs) in polar (water), moderately polar (dichloromethane), and nonpolar (toluene,hexane) solvents. Thiol deprotonation provides a unified pathway for OT binding to AuNPs regardless of solvent polarity of the ligand binding solutions. This work should contribute to resolve the long-standing debate on the fate of the sulfur-bound hydrogen of organothiols self-assembled on gold.

Proteins and organothiols are known for their high binding affinity to noble metal surface including gold nanoparticles (AuNPs). Numerous reports have been dedicated to AuNP interaction with protein or organothiol alone. Competitive protein and organothiol (OT) interaction is, however, mostly an unexplored area. The research reported here focused on developing a fundamental understanding of sequential and simultaneous protein and organothiol interaction with AuNPs in which protein and OT are added either simultaneously or sequentially into the colloidal AuNP solutions. In studies of OT interactions with bovine serum albumin (BSA) stabilized AuNPs, we found that the protein coating layer is highly porous and permeable for small molecules such as mercaptobenzimidazole (MBI), cysteine (Cys), homocysteine (Hcy), and glutathione (GSH). Based on the amounts of MBI adsorbed and the kinetics of MBI adsorption onto BSA stabilized AuNPs, we were able to get an insight into protein conformational changes on the AuNPs. The competitive and sequential studies of protein and OT interactions with AuNPs involving eight model organothiols showed that the protein and OT cosorption onto AuNPs is a kinetically controlled process. The AuNP stability against ligandsorption-induced AuNP aggregation differed significantly among the AuNP/OT and AuNP/BSA/OT mixtures where the AuNP stability order increased from (AuNP/OT)/BSA to AuNP/(BSA/OT), and finally (AuNP/BSA)/OT samples (the two components inside the parenthesis are mixed first followed by the addition of the third component). The studies on the role of cysteine in protein-AuNP interactions found that the cysteine has no significant effect on the kinetics of protein adsorption onto AuNPs. However the stability of the protein-AuNP complex against the organothiolsorption induced AuNP aggregation increased as the number of cysteine residues increased from zero to two. Besides providing new insights on protein interaction with AuNPs, this research is important for AuNP biological/biomedical applications because AuNPs in biofuids encounter a mixture of proteins and OTs in addition to other molecular species.

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Cell adhesion and growth are central issues in the otherwise promising method of endothelialization of materials for improving blood compatibility. To improve cell adhesion to biomaterial surfaces, surface modification with cell adhesion peptides is often used. In particular, arginine-glycine-aspartic acid (RGD), long recognized as a peptide sequence that plays and important role in cell adhesion, has been covalently attached to surfaces to enhance cell adhesion. In this work, the effect of the orientation of the cell adhesion peptide immobilized on the surface was studied through using gold surfaces, which can be readily modified with thiols and sulfur-containing groups. Peptide orientation was controlled by the placement of the cysteine (C) at either the C- or N-terminus, Two cell adhesion peptides, the non-specific RGD and more endothelial cell specific REDV (arginine-glutamic acid-aspartic acid-valine), were studied for their effect on the surface chemical and biological properties, including effects on the interactions with the endothelial cell line ECV304. Vitronectin adsorption to the modified surfaces was specifically examined as a possible reason for differences noted. The results suggest that peptide orientation plays an important role in the interactions of cells and proteins to the modified surfaces. Peptides with the cysteine at the N-terminus showed increased adhesion of endothelial cells from the ECV304 line, with the greatest adhesion noted consistently on the CREDV-modified surfaces. Differences in surface chemistry as evaluated by x-ray photoelectron spectroscopy were also found higher levels of bonded peptide when the thiol-containing cysteine was in the N-terminal position. These results suggest that the secondary structure of the peptide can be used to enhance or to limit its reaction with the surface. Furthermore, while cell adhesion was noted during culture in the absence of serum, significant increases in the numbers of adherent cells were noted on all surfaces when the cells were grown in the presence of serum. Immunoblotting and culture with antibodies demonstrated that this increase in the adhesion of the cells is likely mediated primarily by the cell adhesion peptide vitronectin. / Thesis / Master of Engineering (ME)

Gold, as a chemically inert metal, does not form a stable oxide, but has strong specific interactions with sulfur functions. It has been found that thiols or disulfides can chemisorb to gold under mild conditions (room temperature), and form densely packed monolayers on the gold surface due to the high density of binding sites (gold atoms). Thus, it is possible to form closely packed and stable monolayers of thiolates containing desirable bioactive moieties. Thiol-gold chemistry may therefore be considered as a potentially important tool in the surface modification of materials for biomedical applications. In order to develop surfaces with antithrombogenic properties, a number of thrombin inhibitors (heparin, hirudin and PPACK) have been bonded or immobilized to the material surfaces. In the present study, a series of short peptides, cys-pro-arg (CPR), cys-phe-pro-arg (CFPR) and cys-(D)-phe-pro-arg (C[D]FPR), analogues of PR and FPR respectively, were chosen as potential thrombin inhibitors to attach to gold-coated polyurethane surfaces via the cysteine residue. Their inhibitory activity against thrombin was verified by a chromogenic substrate assay. C(D)FPR, showed a relatively high level of inhibition activity. The surfaces were characterized by water contact angle, XPS, AFM, SEM, ellipsometry, and infrared reflection-absorption spectroscopy, and the adsorption of thrombin from buffer and modified plasma was investigated. It was found that the peptide modified gold surfaces adsorbed significantly more thrombin than the unmodified control surfaces. The C(D)FPR-modified gold surface showed the highest thrombin adsorption both from buffer and plasma. This results is in accord with previous studies showing that the D form of phenylalananine in the FPR peptide creates a favourable site geometry for binding to thrombin. The activity of thrombin adsorbed on these peptide modified gold surfaces was also investigated using a chromogenic substrate assay. Inhibition of adsorbed thrombin was demonstrated, and the C(D)FPR surface showed the strongest inhibitory activity. The presence of thrombin on the peptide surfaces following exposure to modified plasma was verified by elution of proteins and identification of thrombin in the eluate. Probing of the eluates with antibodies to 25 plasma proteins showed that the peptide surfaces are relatively non-adsorptive, suggesting they have some degree of selectivity for thrombin binding. / Thesis / Master of Engineering (ME)