Rhodium and silicon system: II. Rhodium silicide formation

Detailed characterizations of rhodium/silicon films prepared by co-deposition using magnetron sputtering have been carried out on silicon substrates at room temperature up to 900 degrees C. The properties of the films were investigated using XPS/UPS, XRD, SIMS, SEM and AFM techniques. It should be emphasized that XPS/UPS measurements are carried out without breaking the vacuum to avoid any contamination of the film. Up to 500 degrees C an interdiffusion between the oxidized silicon wafer and the deposited Rh/Si film occurred leading to hole formation in the entire film at 900 degrees C. Diffraction patterns for the compounds Rh(2)Si, Rh(5)Si(3), RhSi and Rh(3)Si(4) were measured. Upon annealing the covalent character is increased and for the samples forming the compound RhSi the valence band structure is markedly changed. Depth profiling (XPS and SIMS) reveals a stable composition in the bulk of the film. For these measurements the silicon-rich alloy in the interfacial layer is probably an effect of sputtering, by implanting the Rh atoms into the silicon substrate. A previously reported negative shift for the compound Rh(5)Si(3) could be connected to the sample preparation, as sputtering of the surface is reducing the silicon content and inducing a glassy state. For the first phase Rh(2)Si formed on the rhodium-rich side the shift in binding energy is unclear, for all the other compounds encountered in this work a positive shift relative to pure rhodium was found.

Optical characterization of alignment and effective refractive index in carbon nanotube films

We have characterized the thickness and effective refractive index of carbon nanotube forests by fitting reflectance measurements in the visible and near infrared ranges. The measurements were performed with polarized light. An effective medium layer consisting of a mixture of graphite and air was used to simulate the nanotube film. The proposed model accurately described the behaviour of the reflected s-polarized component (Rs), which allowed for the precise determination of the thickness and porosity of the films, in very good agreement with SEM measurements of film thickness. The p-polarized component (Rp), on the other hand, could not be described in terms of the developed model. In badly aligned samples, where there is a mixture of Rs and Rp behaviour, the model fails to fit the Rs component as well. This effect can therefore be taken as an indirect indication of lack of alignment in the samples.

Differentiation of infection structures of the powdery mildew fungusUncinula necatorand adhesion to the host cuticle

Development and adhesion of infection structures of the grapevine powdery mildew fungus, Uncinula necator (Schw.) Burr., were investigated during the early stages of leaf colonization. Light microscopy showed that primary appressoria occurred 3.5 h post inoculation (p.i.) and that hyphae on the leaf surface, indicative of successful host colonization, appeared 14 h p.i. Low temperature scanning electron microscopy revealed deposits of extracellular material at the contact zone of fungal structures and plant cuticle, suggesting firm attachment of the pathogen. To investigate whether or not esterase or cutinase activity is involved in establishing the fungus on the host cuticle, histochemical assays and inhibitor studies were performed. Results indicated that esterase activity was associated with conidia and infection structures. A single fungal extracellular protein was identified as a cutinase by its ability to hydrolyze3H-cutin. Probing Southern blots of genomic DNA of U. necator, Magnaporthe grisea, and Fusarium solani f.sp. pisi with the cutinase gene of F. solani f.sp. pisi suggested that the cutinase gene of U. necator shares only limited sequence similarities with the cutinase genes of the other fungi investigated. Adhesion assays showed that the presence of esterase-cutinase inhibitors on the cuticle did not significantly affect adhesion. The role of the enzyme in fungal adhesion is discussed.Key words: grapevine powdery mildew, Vitis vinifera, cutinase, extracellular matrix, cryofixation, low temperature scanning electron microscopy.

Evaluation of the interface between one-bottle bonding agents and dentin by cryopreparation and low-temperature scanning electron microscopy (LTSEM). A pilot study on perfused dentinal samples

OBJECTIVES

Dentin bonding samples are generally observed in the high vacuum chamber of an electron microscope only after completion of the bonding procedure fixation, dehydration and drying of the specimens. The purpose of this study was to observe the effect of each step in the application of various one-bottle dentin bonding agents (DBA) using cryopreparation followed by low-temperature scanning electron microscopy (LTSEM).

METHODS

Prime&Bond 2.1 (P&B 2.1), Coltène Experimental (Exp.) and Syntac Single Component (Syntac SC) were applied onto perfused dentin of extracted, human third permanent molar teeth. After acid-etching, rinsing and drying, and following the application of the respective resins, the teeth were fractured at random and plunge-frozen in liquid nitrogen before examination under LTSEM. As this method preserves the state of the treated surface at the moment when it is frozen, each step of the application of the DBA can be observed as if it were a 'real-time' procedure.

RESULTS

Acid-etching the dentin resulted in the removal of the smear layer for all materials tested. Those one-bottle DBAs which recommend the application of two consecutive resin layers (P&B 2.1 and Syntac SC) showed incomplete saturation of the dentinal surface after application of the first layer. With Syntac SC the incomplete saturation was more pronounced than with P&B 2.1. The use of Exp. resulted in a much more homogeneous coverage of the dentin despite only one layer of resin having been applied.

CONCLUSION

It is concluded that cryo-preparation followed by LTSEM appears to be a method which allows each stage of the application of DBA to be evaluated.

Trichorhinophalangeal syndrome type III

Trichorhinophalangeal syndrome (TRPS) type III is a newly defined clinical entity. This symptom complex is inherited as an autosomal dominant trait and clinically characterized by growth retardation, craniofacial abnormalities, severe brachydactyly and sparse hair. In addition, absence of mental retardation and cartilaginous exostoses are required for the diagnosis of TRPS III. To further delineate this newly recognized entity, we report on a patient from a Turkish family segregating TRPS III in 7 family members. The patient had a very short stature (147 cm, < 3rd standard deviation), a thin upper lip and a prominent lower lip, a pear-shaped nose, stubby fingers and toes with cone-shaped epiphyses and sparse scalp hair. Scanning electron microscopy findings and results of energy-dispersive X-ray microanalysis are presented in such a patient for the first time.

Oxidation of midazolam and triazolam by human liver cytochrome P450IIIA4

The metabolism of midazolam and triazolam to their 1'-hydroxy and 4-hydroxy metabolites was studied in microsomes of 15 human livers. The formation of both metabolites was inhibited by more than 90% by an antiserum directed against a pregnenolone 16 alpha-carbonitrile-inducible cytochrome P450 (P450PCN1) of rat liver. Moreover, midazolam hydroxylase activity was immunoprecipitated from solubilized human microsomes with polyclonal antibodies against rat P450PCN1 and the closely related human isozyme P450NF. A close correlation was observed between the amount of protein detected in immunoblots with these antibodies and the midazolam or triazolam hydrxylase activity. The formation of both metabolites of midazolam was inhibited by triacetyloleandomycin, a known inhibitor of cytochromes P450 of the IIIA family. Direct evidence that P450IIIA4 catalyzes the metabolism of midazolam was provided through the use of cDNA-directed expression. Monkey COS cells transfected with human P450PCN1 cDNA were able to catalyze both the 1'- and the 4-hydroxylation of midazolam. We conclude that the metabolism of midazolam and triazolam in human liver is predominantly mediated by cytochrome P450IIIA4. Two of 15 human livers expressed a second immunoreactive microsomal protein of higher apparent Mr and were more active in midazolam 1'-hydroxylation. Our data also provide evidence that the marked interindividual variation in the response to these widely used benzodiazepine drugs is due to variable hepatic metabolism.

High-performance liquid chromatographic assays for bufuralol 1'-hydroxylase, debrisoquine 4-hydroxylase, and dextromethorphan O-demethylase in microsomes and purified cytochrome P-450 isozymes of human liver

Bufuralol, debrisoquine, and dextromethorphan are three prototype substrates of the common genetic deficiency of oxidative drug metabolism in man known as debrisoquine/sparteine-type polymorphism. We describe assays for the in vitro metabolism of (+)- and (-)-bufuralol, debrisoquine, and dextromethorphan in human liver microsomes and reconstituted purified cytochrome P-450 isozymes. These assays combine nonextractive sample preparation by precipitation of protein with perchloric acid with reversed-phase inorganic ion-pair HPLC and fluorescence detection. The minimal detectable levels of the major metabolites formed are 1'-hydroxybufuralol, 0.1 ng/ml; 4-hydroxydebrisoquine, 0.8 ng/ml; and dextrorphan, 0.1 ng/ml. Formation of these metabolites is linear for at least 45 min and between 1 and 100 micrograms of microsomal protein. Comparative kinetic analysis of the three monooxygenase reactions in human liver microsomes revealed an apparent biphasicity of (+)- and (-)-bufuralol 1'-hydroxylation and dextromethorphan O-demethylation but monophasic formation of 4-hydroxydebrisoquine in the substrate concentration range (less than 1 mM) studied. These data, in combination with those obtained by purified human cytochrome P-450 isozymes indicate the involvement of the same enzyme in the metabolism of all three substrates investigated. However, additional and distinct activities contribute to the metabolism of (+)- and (-)-bufuralol and dextromethorphan.