Infrared dichroism measurements on the alkyl chain packing of an ionic detergent intercalated between silicate layers

 Microcrystals of the metal silicate hydrate ilerite orient macroscopically on the surface of a ATR-crystals and thus, are accessible for infrared linear dichroism measurements. We present first results which indicate that the alkyl chain packing and the orientation of the polar group of dodecyltrimethylammoniumbromide (DTAB) intercalated between silicate layers can be determined in terms of infrared order parameters. The properties of DTAB can be modulated by the relative humidity of the surrounding atmosphere and by temperature. Upon heating DTAB undergoes a phase transition from a paraffin-like solid to a fluid phase. The former is characterized by the orthorhombic perpendicular packing of the frozen alkyl chains with tilted long axes. The interactions between the ionic groups of the surfactant and that of the host matrix stabilize the lamellar arrangement of DTAB in the crystalline and in the fluid phases. Received: 14 January 1998 Accepted: 27 July 1998     

Extraction of proteins from plant tissues for two-dimensional electrophoresis analysis

To increase the number of proteins detectable by two-dimensional electrophoresis (2-DE) in plants, we present a new procedure for extracting total proteins from plant tissue. This method avoids any loss of proteins in the course of sample preparation and results in two different fractions, one comprising mainly the cytoplasmatic proteins, the other one containing predominantly structure bond proteins. 2-DE patterns obtained from these two fractions show that the total number of different protein spots detected exceeds the degree of resolution commonly reported for plant proteins threefold.     

Identification of mouse brain proteins after two-dimensional electrophoresis and electroblotting by microsequence analysis and amino acid composition analysis

Two-dimensional electrophoretic separation and immobilization of proteins onto inert membranes for subsequent amino acid sequence and amino acid composition analysis is described as a rapid procedure for the identification or characterization of proteins from complex mixtures. This method avoids the drawbacks of classical purification and isolation methods which involve time-consuming operations with low resolution and, often, insufficient yields. Excellent overall yields of minor amounts (in the low microgram range) using this method allow for sequence determination of yet inaccessible proteins. Solubilized cell proteins of mouse brain were separated by high resolution two-dimensional electrophoresis and electroblotted onto a siliconized glass fiber membrane. The immobilized proteins were stained with Coomassie Brilliant Blue R-250, and twelve proteins spots were then submitted to both Edman degradation and amino acid analysis. Proteins were identified by comparison of the experimentally determined amino acid composition with a dataset derived from the Protein Identification Resource (PIR) protein sequence database. Eight out of twelve proteins tested were identified by amino acid analysis and confirmed by N-terminal sequence determination.     

Analysis of mouse beta-haptoglobin chain by lectin affinoblotting detection

Two different human mammary carcinoma cell lines were xenotransplanted into nude mice. Serum samples were obtained prior to and after transplantation and investigated by two-dimensional electrophoresis (2-DE). By comparison of these silver-stained patterns additional protein spots were detected resulting either from proteins secreted or shed by the tumor itself or from mouse proteins induced by the tumor or the transplantation procedure. One group of spots detectable in post-transplantation serum as well as in control serum after mock-transplantation but not in pretransplantation serum was microsequenced and identified as mouse beta-haptoglobin. The carbohydrate structures of beta-haptoglobin were characterized by two different immunochemical glycoprotein staining procedures to detect differential terminal glycan modifications.     

Tautomerism in monothio-β-diketones studied by PMR and quantum chemical calculations

It is shown by proton NMR and quantum chemical PCILO calculations that monothio-β-ketones

in solution exist as different isomers depending on substituents, solvent and temperature. In solvents with low dielectric constants the hydrogen-bridged cis enol form predominates, and is in fast equilibrium (in the NMR scale) with nonchelated trans enol forms down to ?100°C at least. Transition enthalpies are of the order of 7–15 kJ mol^?1. In compounds with R₂ = Me the rotation of the Me -CS group around the neighbouring C-C- bond can be detected and the thermodynamic and kinetic parameters estimated. The reason for the slowing down of this rotation, inferred from the line broadening in NMR, is probably the stabilization of a trans isomer by interaction between the protons of the methyl group and the lone pairs of the oxygen atom. There are no indications for the presence of chelated and non-chelated enethiol isomers from the PMR studies and quantum chemical calculations performed.     

Size Matters! On the Way to Ionic Liquid Systems without Ion Pairing

Several, partly new, ionic liquids (ILs) containing imidazolium and ammonium cations as well as the medium‐sized [NTf₂]^? (0.230 nm³; Tf=CF₃SO₃^?) and the large [Al(hfip)₄]^? (0.581 nm³; hfip=OC(H)(CF₃)₂) anions were synthesized and characterized. Their temperature‐dependent viscosities and conductivities between 25 and 80 °C showed typical Vogel–Fulcher–Tammann (VFT) behavior. Ion‐specific self‐diffusion constants were measured at room temperature by pulsed‐gradient stimulated‐echo (PGSTE) NMR experiments. In general, self‐diffusion constants of both cations and anions in [Al(hfip)₄]^?‐based ILs were higher than in [NTf₂]^?‐based ILs. Ionicities were calculated from self‐diffusion constants and measured bulk conductivities, and showed that [Al(hfip)₄]^?‐based ILs yield higher ionicities than their [NTf₂]^? analogues, the former of which reach values of virtually 100 % in some cases.From these observations it was concluded that [Al(hfip)₄]^?‐based ILs come close to systems without any interactions, and this hypothesis is underlined with a Hirshfeld analysis. Additionally, a robust, modified Marcus theory quantitatively accounted for the differences between the two anions and yielded a minimum of the activation energy for ion movement at an anion diameter of slightly greater than 1 nm, which fits almost perfectly the size of [Al(hfip)₄]^?. Shallow Coulomb potential wells are responsible for the high mobility of ILs with such anions.     

Mode competition effects in CW dye lasers

The output characteristics of a rhodamine 6G jet stream cw dye laser equipped with a mirror grating combination for mode selection, have been studied experimentally. The tuning range proved to be considerably narrower than that to be expected from the gain profile under the (erroneous) assumption of independently oscillating modes. Actually, the reduction of the tuning range is a consequence of mode competition, as pointed out in a previous theoretical paper. Moreover, the intensity of the selected mode has been found to be independent of the wavelength. All experimental findings are in a good agreement with the results of a theoretical analysis.     

N.m.r. studies of the keto–enol tautomerism of acylthioacetamides

Acetylthioacetamides exist as different keto and enol isomers in chloroform solutions. The keto form with intramolecular hydrogen bonding between the NH and the carbonyl group is the dominant keto isomer. On the other hand the enol forms with intramolecular hydrogen bonding between the OH and the thioketo group are the dominant enol isomers in the temperature range 60°C to ?60°C. The thermodynamic data of the keto-enol equilibria were obtained by measuring the intensities of appropriate high resolution proton signals as a function of temperature. At low temperatures all lines characteristic of the enol forms are doubled in the N-phenyl-substituted derivatives because the rotation of the NH? C₆H₅ group around the C? N bond becomes slow and the chemical shifts characteristic of the E and Z isomers are different. We estimated approximate thermodynamic data of the E/Z equilibrium in some of the compounds. The changes of the line shape as well as the chemical shifts as a function of temperature indicate the presence of various additional exchange processes. In order to obtain further information we performed curve fittings of the chemical shifts of one acetylthioacetanilide and of a series of monothio-β-diketones (studied in another paper) assuming a fast two site exchange process. On the basis of the results obtained a reaction scheme for N-substituted acylthioacetanilides in solution is proposed.     

Fluorescence tomography with simulated data based on the equation of radiative transfer

The quantification of a nonuniform quantum yield or fluorophore absorption distribution is of major interest in molecular imaging of biological tissue. We introduce what is believed to be the first fluorescence image reconstruction algorithm based on the equation of radiative transfer that recovers the spatial distribution of light-emitting fluorophores inside a highly scattering medium from measurements made on the surface of the medium. We obtain images of either the quantum yield or the fluorophore absorption.