Surface modification of citrate-reduced gold nanoparticles with 2-mercaptosuccinic acid (MSA) was carried out in the aqueous phase. This provides a way to obtain carboxylic acid functionalized gold nanoparticles with diameter above 10 nm. The influence of the protecting MSA layer on the behavior of the modified gold nanoparticles in comparison with that of the traditional citrate-reduced gold colloid was evaluated by HCl titration, cyanide etching, and seeded growth tests. The modified gold nanoparticles show an improved stability against pH changes and cyanide etching. They do show further growth, which appears to be more homogeneous than for the unmodified particles.

To gain more insight into protein structure-function relationships that govern ectopic biomineralization processes in kidney stone formation, we have studied the ability of urinary proteins (Tamm-Horsfall protein, osteopontin (OPN), prothrombin fragment 1 (PTF1), bikunin, lysozyme, albumin, fetuin-A), and model compounds (a bikunin fragment, recombinant-, milk-, bone osteopontin, poly-L-aspartic acid (poly asp), poly-L-glutamic acid (poly glu)) in modulating precipitation reactions of kidney stone-related calcium oxalate mono- and dihydrates (COM, COD). Combining scanning confocal microscopy and fluorescence imaging, we determined the crystal faces of COM with which these polypeptides interact; using scanning electron microscopy, we characterized their effects on crystal habits and precipitated volumes. Our findings demonstrate that polypeptide adsorption to COM crystals is dictated first by the polypeptide's affinity for the crystal followed by its preference for a crystal face: basic and relatively hydrophobic macromolecules show no adsorption, while acidic and more hydrophilic polypeptides adsorb either nonspecifically to all faces of COM or preferentially to {100}/{121} edges and {100} faces. However, investigating calcium oxalates grown in the presence of these polypeptides showed that some acidic proteins that adsorb to crystals do not affect crystallization, even if present in excess of physiological concentrations. These proteins (albumin, bikunin, PTF1, recombinant OPN) have estimated total hydrophilicities from 200 to 850 kJ/mol and net negative charges from -9 to -35, perhaps representing a "window" in which proteins adsorb and coat urinary crystals (support of excretion) without affecting crystallization. Strongest effects on crystallization were observed for polypeptides that are either highly hydrophilic (>950 kJ/mol) and highly carboxylated (poly asp, poly glu), or else highly hydrophilic and highly phosphorylated (native OPN isoforms), suggesting that highly hydrophilic proteins strongly affect precipitation processes in the urinary tract. Therefore, the level of hydrophilicity and net charge is a critical factor in the ability of polypeptides to affect crystallization and to regulate biomineralization processes.

Self-assembled monolayers (SAMs) of 4-biphenylthiol (BT) and 4,4'-biphenyldithiol (BDT) formed on polycrystalline silver substrates were characterized by surface plasmon resonance spectroscopy (SPR), reflection absorption infrared spectroscopy (RAIRS), and X-ray photoelectron spectroscopy (XPS). The RAIRS measurements reveal that the molecules in a BT-SAM are oriented perpendicular to the surface whereas the adsorption of BDT results in the formation of multilayers due to the oxidative coupling of the terminal thiol groups forming disulfide-bridged species. The process of multilayer formation was monitored by SPR and RAIRS indicating that BDT initially forms a monolayer which exhibits a structure similar to the one found for BT and that disorder is introduced by the rapid oxidation of the exposed thiol groups resulting in the formation of a multilayer. The addition of tri-n-butylphosphine to the self-assembly solution of 4,4'-biphenyldithiol prevents the formation of multilayers and allows the generation of well-ordered monolayers of the dithiol in which the molecules adopt a standing-up orientation as observed for 4-biphenylthiol. The existence of free thiol groups at the surface of the dithiol SAM was proven by quantitative XPS measurements.