Quantitative SHINERS analysis of temporal changes in the passive layer at a gold electrode surface in a thiosulfate solution.

Shell-isolated gold nanoparticles (SHINs) were employed to record shell-isolated nanoparticle-enhanced Raman spectra (SHINERS) of a passive layer formed at a gold surface during gold leaching from thiosulfate solutions. The (3-aminopropyl)triethoxysilane (APTES) and a sodium silicate solution were used to coat gold nanoparticles with a protective silica layer. This protective silica layer prevented interactions between the thiosulfate electrolyte and the gold core of the SHINs when the SHINs-modified gold electrode was immersed into the thiosulfate lixiviant. The SHINERS spectra of the passive layer, formed from thiosulfate decomposition, contained bands indicative of hydrolyzed APTES. We have demonstrated how to exploit the presence of these APTES bands as an internal standard to compensate for fluctuations of the surface enhancement of the electric field of the photon. We have also developed a procedure that allows for removal of the interfering APTES bands from the SHINERS spectra. These methodological advancements have enabled us to identify the species forming the passive layer and to determine that the formation of elemental sulfur, cyclo-S8, and polymeric sulfur chains is responsible for inhibition of gold dissolution in oxygen rich thiosulfate solutions.

Direct visualization of the alamethicin pore formed in a planar phospholipid matrix.

We present direct visualization of pores formed by alamethicin (Alm) in a matrix of phospholipids using electrochemical scanning tunneling microscopy (EC-STM). High-resolution EC-STM images show individual peptide molecules forming channels. The channels are not dispersed randomly in the monolayer but agglomerate forming 2D nanocrystals with a hexagonal lattice in which the average channel-channel distance is 1.90 ± 0.1 nm. The STM images suggest that each Alm is shared between the two adjacent channels. Every channel consists of six Alm molecules. Three or four of these molecules have the hydrophilic group oriented toward the center of the channel allowing for water column formation inside the channel. The dimensions of the central pore in the images are consistent with the dimension of the water column in a model of hexameric pore proposed in the literature. The images obtained in this work validate the barrel-stave model of the pore formed in phospholipid membranes by amphiphatic peptides. They also provide direct evidence for cluster formation by such pores.

Plasma free amino acid kinetics in rainbow trout (Oncorhynchus mykiss) using a bolus injection of 15N-labeled amino acids.

To gain insight into the metabolic design of the amino acid carrier systems in fish, we injected a bolus of (15)N amino acids into the dorsal aorta in mature rainbow trout (Oncorhynchus mykiss). The plasma kinetic parameters including concentration, pool size, rate of disappearance (R(d)), half-life and turnover rate were determined for 15 amino acids. When corrected for metabolic rate, the R(d) values obtained for trout for most amino acids were largely comparable to human values, with the exception of glutamine (which was lower) and threonine (which was higher). R(d) values ranged from 0.9 µmol 100 g(-1) h(-1) (lysine) to 22.1 µmol 100 g(-1) h(-1) (threonine) with most values falling between 2 and 6 µmol 100 g(-1) h(-1). There was a significant correlation between R(d) and the molar proportion of amino acids in rainbow trout whole body protein hydrolysate. Other kinetic parameters did not correlate significantly with whole body amino acid composition. This indicates that an important design feature of the plasma-free amino acids system involves proportional delivery of amino acids to tissues for protein synthesis.