Simultaneous determination of sub-mg/1 levels of sulphur and chlorine in liquid hydrocarbons by a coupled combustion—ion chromatography technique

A method for elemental analysis that employs a novel coupled combustion—ion chromatography (C---IC) apparatus is described in detail. The samples are combusted and the products collected in a dilute peroxide solution. This solution is loaded onto a concentrator column which is then introduced into the injection position of a suppressed conductivity anion chromatography system. The method is rapid, reliable, free from interferences and has the capacity for simultaneous determination of sulphur and chlorine in organic liquids at concentrations down to 0.03 mg/1. Provided that the capacity of the concentrator column is not exceeded, the recovery for organic standards of both chlorine and sulphur in a variety of organic solvents is greater than 93%, irrespective of the solvent and the sample volume and concentration. Repeatability is only slightly worse than that observed for conventional direct IC analysis of aqueous solutions. At concentrations of 0.4 mg/1 C1 and 0.5 mg/1 S, the % standard deviations (n = 10) were found to be 2.9 and 3.5% respectively. The results obtained with the C---IC analyser for both standards and petroleum-based samples are in good agreement with those obtained by microcoulometry.     

Mode-coupling theory for multiple-time correlation functions of tagged particle densities and dynamical filters designed for glassy systems

The theoretical framework for higher-order correlation functions involving multiple times and multiple points in a classical, many-body system developed by Van Zon and Schofield [Phys. Rev. E 2002, 65, 011106] is extended here to include tagged particle densities. Such densities have found an intriguing application as proposed measures of dynamical heterogeneities in structural glasses. The theoretical formalism is based upon projection operator techniques which are used to isolate the slow time evolution of dynamical variables by expanding the slowly evolving component of arbitrary variables in an infinite basis composed of the products of slow variables of the system. The resulting formally exact mode-coupling expressions for multiple-point and multiple-time correlation functions are made tractable by applying the so-called N-ordering method. This theory is used to derive for moderate densities the leading mode coupling expressions for indicators of relaxation type and domain relaxation, which use dynamical filters that lead to multiple-time correlations of a tagged particle density. The mode coupling expressions for higher order correlation functions are also successfully tested against simulations of a hard sphere fluid at relatively low density.     

Cation–π Interactions Contribute to Substrate Recognition in γ‐Butyrobetaine Hydroxylase Catalysis

γ‐Butyrobetaine hydroxylase (BBOX) is a non‐heme Fe^II‐ and 2‐oxoglutarate‐dependent oxygenase that catalyzes the stereoselective hydroxylation of an unactivated C?H bond of γ‐butyrobetaine (γBB) in the final step of carnitine biosynthesis. BBOX contains an aromatic cage for the recognition of the positively charged trimethylammonium group of the γBB substrate. Enzyme binding and kinetic analyses on substrate analogues with P and As substituting for N in the trimethylammonium group show that the analogues are good BBOX substrates, which follow the efficiency trend N⁺>P⁺>As⁺. The results reveal that an uncharged carbon analogue of γBB is not a BBOX substrate, thus highlighting the importance of the energetically favorable cation–π interactions in productive substrate recognition.     

Electronic effects induced by single hydrogen atoms on the Ge(001) surface

The properties of an isolated dangling bond formed by the chemisorption of a single hydrogen atom on a dimer of the Ge(001) surface are investigated by first-principles density functional theory (DFT) calculations, and scanning tunneling microscopy (STM) measurements. Two stable atomic configurations of the Ge-Ge-H hemihydride with respect to the neighboring bare Ge-Ge dimers are predicted by DFT. For both configurations, the unpaired electron of the HGe(001) system is found to be delocalized over the surface, rendering the isolated dangling bond of the hemihydride unoccupied. However, local surface charge accumulation, such as may occur during STM imaging, leads to the localization of two electrons onto the hemihydride dangling bond. The calculated surface densities of states for one of the charged Ge-Ge-H hemihydride configurations are found to be in good agreement with atomic-resolution STM measurements on n-type Ge(001). Comparison with a Si-Si-H hemihydride of the Si(001) surface shows similarities in structural properties, but substantial differences in electronic properties.     

Substrate-independent approach for polymer brush growth by surface atom transfer radical polymerization

A simple method for growing polymer brushes by atom transfer radical polymerization (ATRP) off solid surfaces has been devised. This entails pulsed plasmachemical deposition of a halogen-containing initiator layer, followed by either organic or aqueous phase controlled surface polymerization. The wide-scale applicability of this approach is exemplified by functionalizing flat substrates, microbeads, and nonwoven textiles.     

Functionalization of solid surfaces with thermoresponsive protein-resistant films

Pulsed plasma polymerization of N-isopropylacrylamide leads to the deposition of thermoresponsive films. The reversible (switching) behavior of these poly(N-isopropylacrylamide) surfaces has been exemplified by screening the adsorption of fibrinogen and fluorescein isothiocyanate labeled bovine serum albumin proteins by surface plasmon resonance (SPR) and fluorescence microscopy at low and elevated temperatures.     

Poly(N-acryloylsarcosine methyl ester) protein-resistant surfaces

A new class of protein-resistant film based on N-substituted glycine derivatives is described. Pulsed plasma deposited poly(N-acryloylsarcosine methyl ester) coatings are shown to be resistant toward the adsorption of fibrinogen and lysozyme. Deposition and UV irradiation of the polymer through a masked grid are found to be effective ways for generating negative and positive image protein arrays, respectively, onto a range of different substrate materials.     

Synthesis of deuterium labelled L- and D-glutamate semialdehydes and their evaluation as substrates for carboxymethylproline synthase (CarB)--implications for carbapenem biosynthesis

Carboxymethylproline synthase was shown to condense L-glutamate semialdehyde with malonyl-coenzyme A to produce (2S,5S)-carboxymethylproline, while incubation of D-glutamate semialdehyde results only in uncoupled turnover of malonyl-CoA.     

Ein Beitrag zum Einfluß des Stoffüberganges auf eine erzwungene Konvektion an einer fluiden Phasengrenze

The interfacial-dynamic behaviour of a fluid two-phase-system with mass transfer was investigated under influence of forced convection in the manner of flat jets directed to the interface. The tangential velocities were measured at a characteristic point near to the interface air/water or in the interface itself using a Laser-Doppler-Velocimeter in dependence on the velocities of jets into two phases in both cases with and without transfer of acetone. The variations of velocities due to the interfacial effects are only detectable at small velocities of the jets. They are discussed by model conceptions and compared with the results of a theoretical research of heat transfer in a fluid two-phase-system (Interfacial-dynamic surface renewal model).