Solvent Relaxation of Prodan and Patman: A Useful Tool for the Determination of Polarity and Rigidity Changes in Membranes

The time dependence of the solvent relaxation behavior of two polarity-sensitive dyes called Prodan and Patman has been investigated in detail in artificial membrane systems of different compositions. The works provides a comparison of the solvent relaxation behavior of the mentioned dyes, using steady-state and time-resolved fluorescence methods, and exemplifies their complementary use for membrane studies.     

Analysis of flame retardants and elements of concern in printed wiring boards with respect to origin and year of construction

Thirty-one populated printed wiring boards, covering a range of 30 years of construction, and originating from various electronic devices, were investigated using different analytical procedures. Noble, precious and rare metals, as well as environmentally relevant elements were identified by EDXRF, and lead and the flame retardant (FR) indicator bromine were localised by means of microbeam EDXRF. A GC/MS procedure was developed to identify and quantify FR substances. Several sample preparation techniques were applied, optimised and compared. The method of first choice was ultrasonic extraction because it provided the best compromise between effort, cost and quality of the analytical results. Altogether, a wide variety of elements of concern, and halogenated and phosphate-based FRs were found in the investigated boards. Their occurrence is partially related to the origin and/or year of construction.

Nitrite impurities are responsible for the reaction observed between vitamin B12 and nitric oxide in acidic aqueous solution

The reaction between aquacobalamin, Cbl(H2O), and NO was studied at low pH. As previously reported, the final product of the reaction is the same as that obtained in the reaction of NO and reduced Cbl(H2O), viz. Cbl(NO-). Nevertheless, this reductive nitrosylation is preceded by a faster reaction (accompanied by small absorbance changes) that depends on the HNO2 concentration but not on the NO concentration. Kinetic and UV-vis spectroscopic data show that Cbl(NO2-) is generated during this reaction. Spectroscopic data show that the dimethylbenzimidazole group trans to the NO2- ligand is protonated and partially dechelated at pH 1, by which a reaction with NO is induced. DFT calculations were performed to compare the ability of NO and NO2- to bind to cobalamin and their influence on the stability of the dimethylbenzimidazole group. The reductive nitrosylation reaction shows a quadratic dependence on the HNO2 concentration and an inverse dependence on the NO concentration. It also strongly depends on pH and is no longer observed at pH > 4. On the basis of earlier work performed on a series of Co(III) porphyrins, a mechanism is proposed that can quantitatively account for the HNO2 and NO dependencies. The reductive nitrosylation reaction is practically dominated by a back reaction, i.e., the reaction between Cbl(NO-) and HNO2, which accounts for the strange NO and HNO2 concentration dependencies observed.     

Redox reactions of a Ru(III)-edta complex with thioamino acids. Kinetic and mechanistic studies

The kinetics of reduction of [Ru(III)(edta)pz]? (edta?? = ethylenediaminetetraacetate; pz = pyrazine) by thioamino acids (RSH = cysteine, glutathione) resulting in the formation of a red [Ru(II)(edta)pz]2? species (λ(max) = 462 nm) has been studied spectrophotometrically using both conventional mixing and stopped-flow techniques. The time course of the reaction was followed as a function of [RSH], pH, temperature and pressure. Alkali metal ions were found to have a positive influence (K(+) > Na(+) > Li(+)) on the reaction rate. Kinetic data and activation parameters are interpreted in terms of a mechanism involving outer-sphere electron transfer between the reaction partners. A detailed reaction mechanism in agreement with the spectral and kinetic data is presented.     

Does natural weathering change the stable isotope composition (²H, ¹³C, ¹⁵N, ¹⁸O and ³⁴S) of cattle hair?

Stable isotope analysis of hair has found applications in many fields of science because it provides a temporally resolved, fairly stable isotopic archive of mammalian individuals. We investigated whether this hair archive is modified by natural weathering while attached to a living animal. We analyzed the tail switch hairs of one suckler cow, sampled seven times over a period of four annual summer pasture-winter stall feeding cycles. We compared relative isotope ratios (δ2H, δ13C, δ1?N, δ1?O and δ3?S) of sections of hair that grew simultaneously but were exposed to natural weathering conditions over different periods of time. Natural wear caused a loss of mass of approx. 0.13% day?1, with no apparent effect of environmental conditions. Changes in δ2H, δ13C, δ1?N and δ1?O were below the detection limit, indicating that hair is a reliable archive for the isotopes of these elements. In contrast, δ3?S values increased during the grazing period by about 1‰, with exposure to UV radiation appearing to have a major influence on this result. The δ3?S values decreased during the subsequent stall period, probably due to abrasion. Seasonal variation in δ3?S may indicate alternating environments that differ in their weathering conditions.