Direct Potentiometric Study of Cationic and Nonionic Surfactants in Disinfectants and Personal Care Products by New Surfactant Sensor Based on 1,3-Dihexadecyl−1H-benzo[d]imidazol−3-ium

A novel, simple, low-cost, and user-friendly potentiometric surfactant sensor based on the new 1,3-dihexadecyl−1H-benzo[d]imidazol−3-ium-tetraphenylborate (DHBI–TPB) ion-pair for the detection of cationic surfactants in personal care products and disinfectants is presented here. The new cationic surfactant DHBI-Br was successfully synthesized and characterized by nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR) spectrometry, liquid chromatography–mass spectrometry (LC–MS) and elemental analysis and was further employed for DHBI–TPB ion-pair preparation. The sensor gave excellent response characteristics for CTAB, CPC and Hyamine with a Nernstian slope (57.1 to 59.1 mV/decade) whereas the lowest limit of detection (LOD) value was measured for CTAB (0.3 × 10⁻⁶ M). The sensor exhibited a fast dynamic response to dodecyl sulfate (DDS) and TPB. High sensor performances stayed intact regardless of the employment of inorganic and organic cations and in a broad pH range (2−11). Titration of cationic and etoxylated (EO)-nonionic surfactant (NSs) (in Ba²⁺) mixtures with TPB revealed the first inflexion point for a cationic surfactant and the second for an EO-nonionic surfactant. The increased concentration of EO-nonionic surfactants and the number of EO groups had a negative influence on titration curves and signal change. The sensor was successfully applied for the quantification of technical-grade cationic surfactants and in 12 personal care products and disinfectants. The results showed good agreement with the measurements obtained by a commercial surfactant sensor and by a two-phase titration. A good recovery for the standard addition method (98–102%) was observed.     

Gene expression profiling using advanced mass spectrometric approaches

In the era of systems biology, computational and high-throughput experimental biological approaches are increasingly being combined to provide global snapshots of entire genomes and proteomes under tissue- and disease-specific conditions. The aim is to identify proteins changing in concentration and/or post-translational state and/or location, and develop a better molecular level understanding of the operation of biological systems. Here we describe an approach for comparative proteomics that builds upon the combination of high-performance nano-scale separations with the high-mass measurement accuracy, mass-resolving power and sensitivity of Fourier transform ion cyclotron resonance mass spectrometry to provide broad dynamic range, comprehensive and quantitative proteome measurements.     

Pulsradiolytische Untersuchungen der Reaktion des e aq − mit halogenierten aromatischen Verbindungen

Kinetic pulse radiolysis experiments (1 s pulse duration) on the reaction of e _aq ^– with halogenated aromatic compounds (fluoro-, chloro-, bromobenzene, benzylchloride and phenethylchloride were carried out in order to check the existence and to investigate the fate of an electron adduct. The measured absorption spectra, being identical with those previously observed for the phenyl and benzyl radical, and thepH dependence of the formation of the H-adducts, indicating no protonation of an intermediateRX ^–, can be explained simply by quantitative elimination of the halide. No evidence for the existence of an electron adduct as an intermediate could be obtained under the applied experimental conditions.

     

Charging of silver bromide aqueous interface: Evaluation of enthalpy and entropy of interfacial reactions from surface potential data

Dependence of surface potential (electrostatic potential at the inner Helmholtz plane, Ψ(0)) at the silver bromide aqueous electrolyte interface was measured as a function of the activities of Br(-) and Ag(+) by using a single crystal silver bromide electrode (SCr-AgBr). Absolute values of surface potentials were obtained from electrode potentials of SCr-AgBr and isoelectric points. Measurements were performed at different temperatures in the range from 10 to 50°C. Corresponding equilibrium constants of interfacial reactions were obtained using the surface complexation model and interpreted via the van't Hoff equation. As a result of the interpretation for the binding of bromide ions leading to a negative surface charge, the thermodynamic parameters obtained were Δ(n)H(°)=-33kJmol(-1) and Δ(n)S(°)=-31Jmol(-1)K(-1); and for the binding of silver ions leading to a positive surface charge, Δ(p)H(°)=-72kJmol(-1) and Δ(p)S(°)=-196Jmol(-1)K(-1). Association of counterions (CI) with oppositely charged surface sites partially compensates the surface charge. Assuming approximately the same affinities for anions (NO(3)(-)) and cations (K(+)) thermodynamic parameters for their binding were obtained as Δ(CI)H(°)≈7kJmol(-1) and Δ(CI)S(°)≈105Jmol(-1)K(-1).     

Nanoscale degradation of polypyrrole films under oxidative stress: An atomic force microscopy study and review

Atomic force microscopy (AFM) is employed to monitor the surface morphology of polypyrrole (PPy) films grown on vitreous carbon substrates during the catalytic reduction of Cr(VI) to Cr(III). The morphology of freshly-prepared films depends on substrate characteristics. Upon reaction, uniform nodules of aggregated PPy clusters appear. No significant differences in surface morphology are found between its oxidized and reduced forms. Loss of catalytic activity after 8-9 oxidation/reduction cycles of exposure to the chromate solution (oxidation) and electrochemical recharging of the film at negative potentials (reduction) correlates well with the observed polymer film dissolution/detachment from the carbon substrate. Formation of well-defined circular features (PPy rings) at different stages leads to a model for the film degradation process that includes formation of Cl₂ gas inside the polymer matrix. In the final stages, the bulk of the film typically fractures and detaches from the electrode. A catalytically inactive, ultrathin PPy layer remains on the substrate even after prolonged exposure to the target solution. A review of techniques for the study of PPy aging/degradation is given.     

Structure and dynamics of an unfolded protein examined by molecular dynamics simulation

The accurate characterization of the structure and dynamics of proteins in disordered states is a difficult problem at the frontier of structural biology whose solution promises to further our understanding of protein folding and intrinsically disordered proteins. Molecular dynamics (MD) simulations have added considerably to our understanding of folded proteins, but the accuracy with which the force fields used in such simulations can describe disordered proteins is unclear. In this work, using a modern force field, we performed a 200 μs unrestrained MD simulation of the acid-unfolded state of an experimentally well-characterized protein, ACBP, to explore the extent to which state-of-the-art simulation can describe the structural and dynamical features of a disordered protein. By comparing the simulation results with the results of NMR experiments, we demonstrate that the simulation successfully captures important aspects of both the local and global structure. Our simulation was ~2 orders of magnitude longer than those in previous studies of unfolded proteins, a length sufficient to observe repeated formation and breaking of helical structure, which we found to occur on a multimicrosecond time scale. We observed one structural feature that formed but did not break during the simulation, highlighting the difficulty in sampling disordered states. Overall, however, our simulation results are in reasonable agreement with the experimental data, demonstrating that MD simulations can already be useful in describing disordered proteins. Finally, our direct calculation of certain NMR observables from the simulation provides new insight into the general relationship between structural features of disordered proteins and experimental NMR relaxation properties.     

The semantics of knowledge attributions

The basic idea of conversational contextualism is that knowledge attributions are context sensitive in that a given knowledge attribution may be true if made in one context but false if made in another, owing to differences in the attributors’ conversational contexts. Moreover, the context sensitivity involved is traced back to the context sensitivity of the word “know,” which, in turn, is commonly modelled on the case either of genuine indexicals such as “I” or “here” or of comparative adjectives such as “tall” or “rich.” But contextualism faces various problems. I argue that in order to solve these problems we need to look for another account of the context sensitivity involved in knowledge attributions and I sketch an alternative proposal.     

Hydrolysis and retro‐aldol cleavage of ethyl threo‐2‐(1‐adamantyl)‐3‐hydroxybutyrate: competing reactions

The hydrolysis of ethyl threo‐2‐(1‐adamantyl)‐3‐hydroxybutyrate ( 1 ) and the parent ester ethyl 3‐hydroxybutyrate ( 4 ) has been studied experimentally and computationally. In the hydrolysis of threo‐ester 1 with 2 M NaOH, predominantly retro‐aldol product was observed, whereas the hydrolyzed product was present in a minor amount. When the reaction is carried out under the same conditions with the parent ester ethyl 3‐hydroxybutyrate ( 4 ), hydrolyzed product is exclusively observed. The competitive pathways, namely hydrolysis and the retro‐aldol reaction for 1 and 4 were investigated using DFT calculations in the both gas and solvent phase. The calculated results in the solvent phase at B3LYP/6–31 + G* level revealed that the formation of retro‐aldol products is kinetically preferred over the hydrolysis of threo‐ester 1 in the presence of a base. However, the parent ester 4 showed that the retro‐aldol process is less favored than the hydrolysis process under similar conditions. The steric effect imposed by the bulky adamantyl group to enhance the activation barriers for the hydrolysis of the ethyl threo‐2‐(1‐adamantyl)‐3‐hydroxybutyrate ( 1 ) was further supported by the calculations performed with tert‐butyl group at the α‐carbon atom of ethyl 3‐hydroxybutyrate ( 7 ). Copyright © 2010 John Wiley & Sons, Ltd.     

基于窄带多区域水平集方法的遥感图像分割

由于遥感图像存在边缘混叠等问题,经典的C-V模型会产生大量的冗余轮廓,而且无法分割多个同质区域的目标.为此,提出了基于C-V模型的窄带多区域水平集图像分割方法,采用N-1个水平集函数将图像分割成N(N＞1)个区域,每个水平集函数表达一个区域.该方法一方面通过建立独立多区域水平集模型可以消除多余的轮廓,避免分割区域的重叠...