Mj. Genet

Application of X-ray photoelectron spectroscopy to microorganisms

The use of X-ray photoelectron spectroscopy (XPS) for the analysis of microbial cell surfaces is described and discussed. This technique is well established in materials science; however, its application to biological samples calls for special considerations owing to the complexity of their chemical composition and because living cells are delicate samples needing careful handling. The results presented for various microorganisms demonstrate how data on the elemental composition can be upgraded into information on the functional groups by peak decomposition and how this can in turn be indicative of the molecular constituents present at the cell surface. The reproducibility of the analysis of microbial surfaces is shown to be currently better than 10% for major elements and functions; it is mainly determined by the variability of the biological material. The reliability of the results is examined with respect to the possibility of systematic errors and the influence of experimental conditions. The effects of washing of the cells, freeze drying, storage and manipulation for introduction into the spectrometer are checked. Sample degradation under the X-ray beam is examined. The influence of surface contamination and of uncertainties concerning sensitivity factors is discussed on the basis of biochemical standard compound analysis. Different sets of data show the dependence of surface composition on the nutrient availability (nature of the culture medium, yeast extract concentration, phosphate concentration), culture age and physiological state (vegetative cells, spores) and its relation to surface morphology. Relationships are observed between the surface electrical properties and the phosphate or nitrogen surface concentrations, depending on the type of microorganism. The chemical composition parameter (nitrogen, oxygen, carbon bound only to carbon and hydrogen) related to surface hydrophobicity depends on the type of microorganism. The surface composition is also found to be relevant to the behaviour of microbial cells with respect to interfaces (flotation, aggregation, adhesion to a solid support).

A Comparison Between the Elemental Surface Compositions and Electrokinetic Properties of Oral Streptococci With and Without Adsorbed Salivary Constituents

In order to characterize the functional cell surface, isoelectric points and elemental surface concentration, the ratios of nitrogen, oxygen and phosphorus to carbon of saliva-coated strains were determined by pH-dependent zeta potential measurements and X-ray photoelectron spectroscopy and compared with those of uncoated strains. The measurements of potential were carried out on completely hydrated cells, whereas the spectroscopy was on freeze-dried micro-organisms. The small increase in the nitrogen:carbon surface concentration ratio of saliva-coated streptococci in comparison to uncoated strains varied from 0.001 (Streptococcus mitis BA) to 0.029 (Streptococcus sanguis CH3) and was concurrent with an increase of the isoelectric point, ranging from 0.0 to 0.9. Increases in the oxygen:carbon ratio ranged from 0.006 (Strep. mitis BA) to 0.041 (Streptococcus mutans NS), whereas the phosphorus:carbon surface concentration ratio was unchanged after saliva treatment. Despite the fact that isoelectric and compositional measurements were made in different states of surface hydration, a decrease in the nitrogen:carbon ratio accompanied by an increase in oxygen:carbon ratio, was related to a decrease of the isoelectric point of the saliva-coated strains, and so analogous with previous observations for uncoated strains. Although there were changes in the physico-chemical properties of the strains upon saliva coating, all more or less kept their own surface identity despite adsorption of salivary constituents, possibly indicating some capacity to protect their own physico-chemical identity.

Ennoblement of stainless steel in the presence of glucose oxidase: Nature and role of interfacial processes

The ennoblement of the free corrosion potential (E(corr)) of AISI 316L stainless steel which did not occur in synthetic fresh water (SFW), was observed after introduction of glucose oxidase (Gox) and glucose, or of hydrogen peroxide (H(2)O(2)). The composition of the surface was monitored using AFM and XPS, a detailed XPS analysis being based on the discrimination between oxygen of organic and inorganic nature proposed in a previous study. In H(2)O(2) medium, the main changes regarding the inorganic phase were the increase of the oxygen concentration in the passive film, the increase of the molar concentration ratio of oxidized species Fe(ox)/Cr(ox) and the growth of nanoparticles, presumably made of ferric oxide/hydroxide. In Gox medium, no significant changes were observed in both oxygen concentration and Fe(ox)/Cr(ox) ratio, but the density of colloidal particles decreased, indicating a dissolution of Fe oxide/hydroxide under the influence of gluconate. In contrast with H(2)O(2), in SFW and Gox the amount of organic compounds increased due to the accumulation of polysaccharides and proteins. The influence of glucose oxidase on the ennoblement of stainless steel is not due to indirect effects of H(2)O(2) through the change of surface composition. The E(corr) ennoblement seems to be directly due to the presence of H(2)O(2) and to the electrochemical behavior of H(2)O(2) and related oxygen species. This consideration is important for understanding and controlling microbial influenced corrosion.

Surface reduction of ruthenium compounds with long exposure to an X-ray beam in photoelectron spectroscopy

The reduction of Ru at the surface of commercial RuCl3 and RuO2 has been observed during XPS analysis. The experiments have been performed with either a non-monochromatized (Mg K-alpha) or a monochromatized (Al K-alpha) X-ray beam. Ruthenium reduction is enhanced by increasing the X-ray dose, but the residual pressure exerts only a weak influence. The initial composition of commercial ruthenium (III) chloride hydrate is a complex mixture of chloro or chlorohydroxo species rather than pure RuCl3. nH(2)O. RuCl3 is not suitable as a reference compound for ruthenium chloride compounds in XPS analysis, because it contains mainly Ru(IV) which is reduced under X-ray. A similar reduction occurs at the surface of RuO2 samples (by reduction of RuO3 layers), and on the adventitious carbon

ELEMENTAL SURFACE CONCENTRATION RATIOS AND SURFACE FREE-ENERGIES OF HUMAN-ENAMEL AFTER APPLICATION OF CHLORHEXIDINE AND ADSORPTION OF SALIVARY CONSTITUENTS

In vitro adsorption of chlorhexidine from a commercially available chlorhexidine-containing (0.12%) mouthrinse (Peridex) on both ground and polished and on saliva-coated enamel was studied by X-ray photoelectron spectroscopy and contact angle measurements. Furthermore, adsorption of salivary constituents was studied on chlorhexidine-treated enamel. Changes in the elemental surface composition obtained by X-ray photoelectron spectroscopy clearly demonstrated adsorption of chlorhexidine from the mouthrinse as indicated by increased N and C signals which were in all cases accompanied by a higher enamel surface free energy, estimated from the contact angle data. In addition, it was found that salivary constituents adsorb less to chlorhexidine-treated enamel than to ground and polished enamel and, moreover, that adsorbed salivary constituents were desorbed by chlorhexidine. In vivo, the effect of a 3-week use of chlorhexidine was compared with the use of a placebo and habitual oral hygiene of 10 volunteers by means of clinical contact angle measurements. Also in vivo adsorption of chlorhexidine yielded elevated surface free energies with respect to habitual oral hygiene or a placebo. Thus in vivo, the well-known favourable effects of the bactericidal properties of chlorhexidine completely overrule the unfavourable effects of high enamel surface free energies.

Characterisation of Al coordination at the outer surface of dealuminated mordenites by X-ray photoelectron spectroscopy

Abstract The chemical state of Al at the surface of dealuminated mordenites has been investigated by X-ray photoelectron spectroscopy. The Al 2p peaks can reasonably be decomposed into two components. The Al KLL Auger transition is more sensitive to the Al coordination, and three components can be separated in the corresponding peaks. The resulting modified Auger parameters have been established. The results are compared with those available in the literature. It appears that three types of Al are present at the surface of dealuminated mordenites, namely hexa-, tetra- and tricoordinated Al (Al VI, Al IV and Al III). From the decomposition of the Al KLL peaks, the surface Al VI/(Al + Si), Al IV/(Al + Si) and Al III/(Al + Si) ratios have been estimated.