Structure determination of gas-phase niobium and tantalum carbide nanocrystals via infrared spectroscopy

Niobium and tantalum carbide clusters have been isolated in the gas phase and irradiated with intense tunable infrared (IR) light. Stable neutral clusters are selectively ionized and subsequently detected in a mass spectrometer. By tuning the IR frequency, infrared multiphoton absorption spectra are obtained for a whole range of clusters. These mass-selective IR spectra lead to insights into the structures of small niobium and tantalum carbide clusters and nanocrystals.     

Diffuse-reflectance spectroscopy from 500 to 1060 nm by correction for inhomogeneously distributed absorbers

Diffuse-reflectance spectroscopy for measurement of the absorption and scattering coefficients of biological tissue produces reliable results for wavelengths from 650 to 1050 nm. Implicitly, this approach assumes homogeneously distributed absorbers. A correction factor is introduced for inhomogeneous distribution of blood concentrated in discrete cylindrical vessels. This factor extends the applicability of diffusion theory to lower wavelengths. We present measurements of in vivo optical properties in the wavelength range 500-1060 nm.     

Speciation of arsenic in coarse and fine urban aerosols using sequential extraction combined with liquid chromatography and atomic fluorescence detection

An analytical procedure for speciation of As in urban aerosol samples was developed. The aerosols were collected by sequential filtration through membrane filters. Part of each filter was investigated by INAA for the total amount of As. Another part of the filters was treated by a sequential extraction procedure to differentiate between water-extractable, phosphate-extractable and refractory chemical forms. Water-extractable forms were further differentiated into anionic As species by HPLC-HGAFS. Extractability of As into water exhibited a clear dependency on the aerosol size fraction (12% in coarse fraction and 50% in fine fraction). Dependency of the phosphate extractable As on the aerosol size fraction seems not to be significant (10-15% in both size fractions). The remaining amount, i.e., about 78% of the coarse As and about 40% of the fine As was considered to be refractory or environmentally immobile As. Water-extractable As forms could only be attributed to arsenate.     

Amperometric biosensor based on D-aminoacid oxidase for the R-perindopril assay

A new amperometric biosensor based on D-aminoacid oxidase is described for the assay of R-perindopril. R-perindopril can be determined in the 400-20 nmol/L concentration range; the detection limit is 10 nmol/L. The selectivity was checked with S-perindopril, D- and L-proline, and polyvinylpyrrolidone. The main interfering species was D-proline. An automated system for the assay of R-perindopril based on the concept of flow injection with an amperometric biosensor (based on D-aminoacid oxidase) as detector is also described. The system is suitable for the on-line monitoring of R-perindopril at a sampling rate of 72 samples/h, in the linear range: 100 nmol/L -20 nmol/L with an RSD better than 0.09% (n = 10).     

Catalysis of the addition of benzenethiol to 2-cyclohexen-1-ones by uranyl-salophen complexes: a catalytic metallocleft with high substrate specificity

The base induced addition of benzenethiol to 2-cyclohexen-1-one and its 4,4-, 5,5- and 6,6-dimethyl derivatives is catalysed by a salophen-uranyl based metallocleft 2 in chloroform solution with high turnover efficiency and low product inhibition. Analysis of rate data coupled with equilibrium measurements for complexation of the catalyst with the enone reactants and addition products shows that the catalytic mechanism involves the three main steps typical of single-substrate enzymatic processes, namely substrate binding and recognition, transformation of the bound substrate, and release of the reaction product. Unlike the reference salophen-uranyl 1, catalyst 2 is endowed with a structured binding site responsible for a high degree of substrate specificity among the investigated enones, due to recognition of their shape and size.     

Optimization of capillary electrophoretic separation of several inhibitors of the angiotensin-converting enzyme

Capillary electrophoretic separation of eight inhibitors of the angiotensin-converting enzyme, viz., enalapril, lisinopril, quinapril, fosinopril, perindopril, ramipril, benazepril and cilazapril, was investigated with respect to the following parameters: pH of the running buffer, organic modifiers and surfactants. The most critical parameter is the pH of the running buffer. The addition of sodium dodecyl sulfate had a negative influence on the peak symmetry, and selectivity was not improved. The separation of the eight compounds can be performed by means of two phosphate buffers (each 100 mM) at pH 7.0 and pH 6.25, respectively. This combination is necessary for the selective identification of structurally related substances because of their similar pKa values.     

Combinatorial Chemistry for Ligand Development in Catalysis: Synthesis and Catalysis Screening of Peptidosulfonamide Tweezers on the Solid Phase

On the basis of a pyrrolidine tweezer 1, a library of peptidosulfonamide tweezers (15a-e, 16a-e) was synthesized on the solid phase. This library was screened in a simultaneous substrate screening procedure for the ability to enantioselectively catalyze the Ti(O-i-Pr)(4)-mediated addition of diethylzinc to aldehydes. One of the best solid-phase tweezer catalyst (i.e., 16d, giving an ee of 32% in solid-phase catalysis) was resynthesized in solution (compounds 20 and 21). The now homogeneous solution-phase catalysis showed even better enantioselectivity (i.e., up to 66%).     

Effects of UV irradiation on skin and nonskin-associated herpes simplex virus infections in rats

Herpes simplex virus (HSV) normally causes vescular lesions on mucocutaneous surfaces but can also cause encephalitis. The virus can reactivate from the latent state in neurons to form recrudescent lesions. One common stimulus for reactivation is exposure to sunlight. In the present study, the effects of irradiating rats with suberythemal ultraviolet (UV) before or after infecting them epidermally with HSV was investigated. Preexposure to UV impaired HSV-specific cellular immune responses, as indicated by delayed type hypersensitivity (DTH) and in vitro lymphoproliferation assays. However, the number and severity of the skin lesions were not altered. In contrast, exposure after infection did not affect cellular immunity but resulted in a large increase in the severity and number of lesions. In a second series of experiments, the effects of preirradiating with UV on HSV infection was examined using a route of inoculation which was not skin-associated, namely intranasal, allowing direct non-invasive access to the nervous system. It was found that suppressed DTH resulted, together with an increase in the incidence and severity of neurological symptoms and an increased viral load in the brain. Therefore, unlike the situation in the skin, irradiation of rats before intranasal inoculation led to a suppressed immune response to HSV which correlated with increased viral load and symptoms. These results indicate that the effects of UV may be dependent on whether the animal is exposed before or after the infection, and whether the infection is skin-associated or systemic.     

Gas chromatography/sniffing port analysis of aroma compounds released under mouth conditions

The release of aroma compounds from rehydrated French beans in an artificial mouth system and in the mouths of 12 assessors was studied by gas chromatography combined with flame ionisation detection and sniffing port detection. In an artificial mouth system, volatile compounds were isolated under mouth conditions, such as temperature, salivation, and mastication. No significant differences were determined between the aroma release from the beans in the artificial mouth and release in the mouths of assessors. However, both the real and artificial mouth systems differed significantly from a purge-and-trap and a dynamic headspace system in aroma release. In order to study aroma release over time, volatile compounds were isolated from rehydrated French beans for 1, 1.5, 3 and 12 min in the artificial mouth system and analysed by gas chromatography/sniffing port analysis. 2-Methylpropanal, 2-/3-methylbutanal, hexanal, 2-methyl-2-butenal, 1-octen-3-one, and dimethyl trisulphide possessed detectable odours when isolated from the French beans in the artificial mouth for all time periods. The odour active compounds 2-/3-methylbutanal and hexanal were shown to be released at a constant rate. Different sampling times resulted in identical selections of aroma compounds, while mutual proportions were retained.