Search results for "substrat"
showing 10 items of 1042 documents
Relationships between fatty acid monolayer structure on the subphase and on solid substrates
1991
Abstract Docosanoic acid monolayers with known molecular packings on the water surface have been deposited on thin polymer films and then investigated using transmission electron diffraction at normal and tilted incidence. The diffraction patterns from monolayers deposited under all conditions investigated could be indexed as arising from the same conformationally disordered centred rectangular packing with molecules standing perpendicular to the substrate, although with a spread of unit cell parameters within and between each deposition condition significantly greater than the experimental error. This packing has been seen in monolayers on the water surface, but only under conditions compl…
Assembly and Separation of Semiconductor Quantum Dot Dimers and Trimers
2011
Repeated precipitation of colloidal semiconductor quantum dots (QD) from a good solvent by adding a poor solvent leads to an increasing number of QD oligomers after redispersion in the good solvent. By using density gradient ultracentrifugation we have been able to separate QD monomer, dimer, and trimer fractions from higher oligomers in such solutions. In the corresponding fractions QD dimers and trimers have been enriched up to 90% and 64%, respectively. Besides directly coupled oligomers, QD dimers and trimers were also assembled by linkage with a rigid terrylene diimide dye (TDI) and separated again by ultracentrifugation. High-resolution transmission electron micrographs show that the …
Real-space observation of xenon adsorption and desorption kinetics on graphite (0001) by photoemission electron microscopy
2003
Abstract The growth and desorption of Xe monolayers on the basal plane of graphite has been investigated by real-space imaging using photoemission electron microscopy. Adsorption kinetics was studied at different substrate temperatures (39–65 K), corresponding to different growth modes. Coexisting phases showed up as different grey values in the image. Typical domain sizes of the 2D solid phases around 60 K are of the order of one to several μm. The domains exhibit an elongated shape with their long axis oriented preferentially parallel to step edges of the substrate. With increasing coverage the brightness of the domains increases, the 2D gas-phase regions shrink and finally disappear at h…
Carotenoid binding sites in LHCIIb
2000
The major light-harvesting complex of photosystem II can be reconstituted in vitro from its bacterially expressed apoprotein with chlorophylls a and b and neoxanthin, violaxanthin, lutein, or zeaxanthin as the only xanthophyll. Reconstitution of these one-carotenoid complexes requires low-stringency conditions during complex formation and isolation. Neoxanthin complexes (containing 30–50% of the all-trans isomer) disintegrate during electrophoresis, exhibit a largely reduced resistance against proteolytic attack; in addition, energy transfer from Chl b to Chl a is easily disrupted at elevated temperature. Complexes reconstituted in the presence of either zeaxanthin or lutein contain nearly …
Determination of major human cytochrome P450s activities in 96-well plates using liquid chromatography tandem mass spectrometry.
2007
At the early stage of drug discovery, thousands of new chemical entities (NCEs) may be screened before a single candidate can be identified for development. Evaluation of the effect of NCEs on human CYP450 enzyme activities is a key issue in pharmaceutical development as it may explain inter-subject variability, drug-drug interactions, non-linear pharmacokinetics and toxic effects. A liquid chromatography tandem mass spectrometry (HPLC-MS/MS) method has been developed for the fast and routine analysis of major human CYP450s enzyme activities (CYP1A2, CYP2A6, CYP2B6, CYP2C9, CYP2C19, CYP2D6, CYP2E1 and CYP3A4) in primary hepatocyte cell cultures. The high sensitivity and selectivity of mass …
Affinity chromatography with triazine dyes immobilized onto activated non-porous monodisperse silicas
1988
Abstract Non-porous monodisperse silicas with a particle diameter of 2.1 μm were modified with different silanes for immobilization of various triazine dyes including Procion Red HE3B, Procion Red MX5B, and Cibacron Blue F3GA. Lactate dehydrogenase and malate dehydrogenase from different species and aldehyde reductase from rat brain were purified by affinity elution using the substrate of the enzyme and NADH. With Cibacron F3GA the selectivity for NADH-dependent enzymes was higher than with the two Procion dyes. The utility of these immobilized triazine dye systems on non-porous silica supports for the rapid separation of Cohn Fraction III plasma proteins, including plasminogen, is also des…
Ion-exchange voltammetry at a surfactant-doped electrode: model of mass transfer kinetics to an anionic surface-charged electrode and its application…
2000
cited By 10; International audience; A theoretical model of mass transfer kinetics was developed for investigating the accumulation of cationic compounds at an anionic surfactant-doped screen-printed electrode. It was extended to an enzyme-generated cationic product for the indirect determination of alkaline phosphatase (AP). The model takes into account the analyte depletion, the kinetics of the ion-exchange reaction-diffusion and the kinetics of the enzymatic reaction. The relationship between the ion-exchange voltammetric anodic peak current and the enzyme incubation/accumulation time for a given concentration of AP was established and the validity of the theoretical model was verified e…
Screening of acetylcholinesterase inhibitors by CE after enzymatic reaction at capillary inlet.
2009
In this study the development of a procedure based on capillary electrophoresis after enzymatic reaction at capillary inlet methodology for the screening and in vitro evaluation of the biological activity of acetylcholinesterase (AChE) inhibitors is presented. The progress of the enzymatic reaction of the hydrolysis of acetylthiocholine at pH 8 in the presence of AChE and the inhibitor studied is determined by measuring at 230 nm the peak area of the reaction product thiocholine (TCh). In the method employed the capillary was first filled with 30 mM borate-phosphate buffer (pH 8.0) and subsequently, plugs of: (i) water, (ii) AChE solution, (iii) substrate solution with or without inhibitor,…
Secondary structure conformation of hydroperoxide lyase from green bell pepper, cloned in Yarrowia lipolytica, and its activity in selected media
2008
International audience; Circular dichroism (CD) spectroscopy of secondary structure conformation of the purified green bell pepper hydroperoxide lyase (HPL), cloned in the yeast Yarrowia lipolytica, was investigated. The CD spectra of HPL in iso-octane, obtained at 60 °C, in the presence of the reducing agent dithiothreitol showed dramatic increase in α-helix content. The enzyme conformation remained unchanged over a range of pH values of 5.0–7.0. Using 13-hydroperoxide of linoleic acid (13-HPOD) as substrate, the biocatalysis of HPL in organic solvent media, including chloroform, dichloromethane, hexane, iso-octane, octane and toluene, was investigated. The results indicated an increase in…
Core Histones Are Glutaminyl Substrates for Tissue Transglutaminase
1996
Chicken erythrocyte core histones are glutaminyl substrates in the transglutaminase (TGase) reaction with monodansylcadaverine (DNC) as donor amine. The modification is very fast when compared with that of many native substrates of TGase. Out of the 18 glutamines of the four histones, nine (namely glutamine 95 of H2B; glutamines 5, 19, and 125 of H3; glutamines 27 and 93 of H4; and glutamines 24, 104, and 112 of H2A) are the amine acceptors in free histones. The use of Gln112 of H2A requires a temperature-dependent partial unfolding of the histone, showing that structural determinants are decisive for the glutamine specificity. The structures of H2A and H2B do not appreciably change upon mo…