Giant Heat Release and Time-Dependent Thermal Expansion of Nb-Ti-D

Glasslike anomalies of low-temperature thermal properties were observed for the polycrystalline Nb₃₇Ti₆₃ alloy and Nb₃₇Ti₆₃ doped with deuterium. A giant heat release effect was found in (Nb-Ti)₉₂D₈ corresponding to a spectral density of two level systems of 7.8·10⁴⁵ J^–1 m^–3. After rapid cooling of the sample a length relaxation with a quadratic dependence on the starting temperature was detected obeying a logarithmic time dependence. The results fit to the standard tunneling model assuming a temperature and time independent Grüneisen parameter. A constant Grüneisen parameter is compatible with a constant deformation potential but requires /V to depend on /₀. For both systems the thermal expansion coefficient exhibits a linear temperature term in the superconducting state dominating below 1 K.     

The bradykinin B2 receptor couples less efficiently than the angiotensin AT1 receptor to the G protein Gq in transiently transfected COS-7 cells

The purpose of this study was to compare the efficiency of two different Gq protein-coupled receptors (AT1 receptor for angiotensin II and B2 receptor for bradykinin) to activate phospholipase C (PLC). When the receptors were expressed at a similar level of 0.5 pmol/mg of protein, inositol trisphosphate (IP) accumulation elicited by AT1 receptor was four times higher than that elicited by B2 receptor. Genistein and pertussis toxin did not modify AT1 receptor- or B2 receptor-induced IP accumulation. These results indicate that in COS-7 cells, the two receptors activate PLC beta through G proteins of the Gq family. AT1 or B2 receptors were co-expressed with the alpha subunit of either Gq or G11. Both alpha subunits potentiated to the same extent AT1 receptor-induced IP accumulation. alpha 11 was also as efficient as alpha q to potentiate B2 receptor-induced response. Interestingly, however, the potentiating effect of alpha q and alpha 11 was more important (by 5-fold) on AT1 receptor-mediated response than on B2 receptor-mediated response. These results demonstrate that the extent of activation of PLC beta by different Gq-coupled receptors depends on the level of expression of these receptors and on their coupling efficiency. These are important parameters that determine the relative contribution of specific hormones to different biological processes.     

Toxicokinetic model describing bioconcentration and biotransformation of diazinon in Daphnia magna

A toxicokinetic model for Daphnia magna , which simulates the internal concentration of the insecticide diazinon, its detoxification product 2-isopropyl-6-methyl-4-pyrimidinol, and its active metabolite diazoxon, is presented. During in vivo exposure to diazinon with and without inhibition of cytochrome P450 by piperonyl butoxide, the parent compound as well as its metabolites were quantified with high-performance liquid chromatography-tandem mass spectrometry (LC-MS/MS) in extracts of D. magna . Rate constants of all relevant toxicokinetic steps were obtained by modeling the time course of the internal concentrations with a multicomponent first-order kinetics model. When cytochrome P450 was inhibited, the kinetic bioconcentration factor (BCF) of diazinon increased from 17.8 to 51.0 mL·g(ww)(-1). This clearly indicates that diazinon is biotransformed to a high degree by cytochrome P450 in D. magna . The dominant elimination step of diazinon was shown to be its oxidative dearylation to pyrimidinol (62% of total elimination) with a corresponding rate constant of 0.16 h(-1). In contrast, oxidative activation to diazoxon with a rate constant of 0.02 h(-1) amounted to only 8% of the total elimination. During exposure to diazinon, the active metabolite diazoxon could be detected only in very low concentrations (approximately 0.5% of the parent compound), presumably due to a very fast reaction with the target site acetylcholinesterase. During the exposure experiments (no feeding of daphnids), an exponential decline of the lipid content in D. magna with a first-order rate constant of 0.013 h(-1) was observed. For short exposure times (≤ 24 h), this had only a minor influence on the determined TK parameters. Such a TK model containing detailed biotransformation processes is an important tool for estimation of the toxic potential of chemicals, particularly, when active metabolites are formed inside an organism.     

A quantitative study of factors that influence the substantivity of fragrance chemicals on laundered and dried fabrics

Model investigations of physicochemical aspects of the substantivity of fragrance raw materials on laundered fabrics were performed. The overall process was divided into two consecutive steps, laundry and dryout, which were characterized by affinity and tenacity, respectively. The affinities of fifteen fragrance raw materials to cotton and polyacrylonitrile were measured in standard fabric softener and detergent solutions. Affinities correlated with the corresponding partition coefficient, P(o/w). To study the impact of parameters independent of the chemical structure of the fragrance molecules, 1-[³H]-3-methyl-5-phenylpentanol (phenylhexanol) was selected, and aqueous solutions of defined anionic, nonionic and cationic surfactants were used as model detergent and fabric softener media. A sequence of experiments, based on the fractional factorial design, was planted for quantifying the relative contribution on substantivity of a number of variables: the concentration of the fragrance chemical, the type and concentration of the surfactants, the type and weight of the fabrics (cotton or polyacrylonitrile) and the washing temperature in the case of cotton. The affinity that characterizes the washing process depends mainly on the type of fabric and the type of surfactant and, to a lesser extent, on the surfactant concentration and the temperature. Anionic and nonionic surfactants, the main components of detergent powders, behave similarly, whereas the combination of cationic surfactant with cotton markedly enhances the affinity. For phenylhexanol, the tenacity after dryout is largely controlled by the type of fabric. The role of fiber swelling is discussed. The substantivity, which represents the global effect of laundering and dryout, shows the same trend as the affinity. The complexity of the physicochemical phenomena involved is highlighted by the importance of the interactions between the main contributing factors.