XPS study of the effect of the conditions of peptide chemisorption to gold and silver coated polymer surfaces

Silver deposition on titanium surface by electrochemical anodizing process reduces bacterial adhesion of Streptococcus sanguinis and Lactobacillus salivarius

OBJECTIVES

The aim of this study was to determine the antibacterial properties of silver-doped titanium surfaces prepared with a novel electrochemical anodizing process.

MATERIAL AND METHODS

Titanium samples were anodized with a pulsed process in a solution of silver nitrate and sodium thiosulphate at room temperature with stirring. Samples were processed with different electrolyte concentrations and treatment cycles to improve silver deposition. Physicochemical properties were determined by X-ray photoelectron spectroscopy, contact angle measurements, white-light interferometry, and scanning electron microscopy. Cellular cytotoxicity in human fibroblasts was studied with lactate dehydrogenase assays. The in vitro effect of treated surfaces on two oral bacteria strains (Streptococcus sanguinis and Lactobacillus salivarius) was studied with viable bacterial adhesion measurements and growth curve assays. Nonparametric statistical Kruskal-Wallis and Mann-Whitney U-tests were used for multiple and paired comparisons, respectively. Post hoc Spearman's correlation tests were calculated to check the dependence between bacteria adhesion and surface properties.

RESULTS

X-ray photoelectron spectroscopy results confirmed the presence of silver on treated samples and showed that treatments with higher silver nitrate concentration and more cycles increased the silver deposition on titanium surface. No negative effects in fibroblast cell viability were detected and a significant reduction on bacterial adhesion in vitro was achieved in silver-treated samples compared with control titanium.

CONCLUSIONS

Silver deposition on titanium with a novel electrochemical anodizing process produced surfaces with significant antibacterial properties in vitro without negative effects on cell viability.

Probing chiral interfaces by infrared spectroscopic methods

Biological homochirality on earth and its tremendous consequences for pharmaceutical science and technology has led to an ever increasing interest in the selective production, the resolution and the detection of enantiomers of a chiral compound. Chiral surfaces and interfaces that can distinguish between enantiomers play a key role in this respect as enantioselective catalysts as well as for separation purposes. Despite the impressive progress in these areas in the last decade, molecular-level understanding of the interactions that are at the origin of enantiodiscrimination are lagging behind due to the lack of powerful experimental techniques to spot these interactions selectively with high sensitivity. In this article, techniques based on infrared spectroscopy are highlighted that are able to selectively target the chiral properties of interfaces. In particular, these methods are the combination of Attenuated Total Reflection InfraRed (ATR-IR) with Modulation Excitation Spectroscopy (MES) to probe enantiodiscriminating interactions at chiral solid-liquid interfaces and Vibrational Circular Dichroism (VCD), which is used to probe the structure of chirally-modified metal nanoparticles. The former technique aims at suppressing signals arising from non-selective interactions, which may completely hide the signals of interest due to enantiodiscriminating interactions. Recently, this method was successfully applied to investigate enantiodiscrimination at self-assembled monolayers of chiral thiols on gold surfaces. The nanometer size analogues of the latter--gold nanoparticles protected by a monolayer of a chiral thiol--are amenable to VCD spectroscopy. It is shown that this technique yields detailed structural information on the adsorption mode and the conformation of the adsorbed thiol. This may also turn out to be useful to clarify how chirality can be bestowed onto the metal core itself and the nature of the chirality of the latter, which is manifested in the metal-based circular dichroism activity of these nanoparticles.

Microbial adhesion to zirconium alloys

We present data and analyses concerning the adhesion of clinically relevant Staphylococcus aureus, Staphylococcus epidermidis, and Pseudomonas aeruginosa (bacteria) and Candida albicans (yeast) to Zircaloy-2 (Zry-2) and Zircadyne-705 (Zr705) surfaces. These zirconium-based materials are similar to those now being used in total hip and knee replacements. Here we study clinical strains of microbes under shaken and stationary exposure conditions, and their ability to adhere to Zr surfaces having different oxide thicknesses. We use X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), viable counts, endotoxin assays, and statistical analysis methods, and demonstrate a predictive model for microbial adhesion based on XPS data.

L-glutathione chemisorption on gold and acid/base induced structural changes: a PM-IRRAS and time-resolved in situ ATR-IR spectroscopic study

Adsorption of the tripeptide L-glutathione (gamma-glu-cys-gly) on gold surfaces was investigated by polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) and attenuated total reflection (ATR) infrared spectroscopy. PM-IRRAS was used to study ex situ the adsorbate layer prepared from aqueous solutions at different pH, whereas ATR-IR was applied to study in situ adsorption from ethanol in the presence and absence of acid and base. ATR-IR was furthermore combined with modulation spectroscopy in order to investigate the reversible changes within the adsorbate layer induced by acid and base stimuli, respectively. The molecule is firmly anchored on the gold surface via the thiol group of the cys part. However, the ATR-IR spectra in ethanol indicate a further interaction with the gold surface via the carboxylic acid group of the gly part of the molecule, which deprotonates upon adsorption. Hydrochloric acid readily protonates the two acid groups of the adsorbed molecule. During subsequent ethanol flow the acid groups deprotonate again, a process which proceeds in two distinct steps: a fast step associated with the deprotonation of the acid in the glu part of the molecule and a considerably slower step associated with deprotonation of the acid in the gly moiety. The latter process is assisted by the interaction of the corresponding acid group with the surface. The spectra furthermore indicate a rearrangement of the hydrogen bonding network within the adsorbate layer upon deprotonation. Depending on the protonation state during adsorption of l-glutathione, the response toward identical protonation-deprotonation stimuli is significantly different. This is explained by the ionic state-dependent shape of the molecule, as supported by density functional theory calculations. The different shapes of the individual molecules during layer formation thus influence the structure of the adsorbate layer.