Lumi I --> Lumi II: the last detergent independent process in rhodopsin photoexcitationt

Time-resolved absorbance difference spectra were collected at delays from 1 to 128 micros after photolysis of membrane and detergent suspensions of rhodopsin at 20 degrees C. Fitting both sets of data with two exponential decays plus a constant showed a similar fast process (lifetime 11 micros in membrane, 12 micros in 5% dodecyl maltoside) with a small but similar spectral change. This demonstrates that the Lumi I - Lumi II process, previously characterized in detergent suspensions, has similar properties in membrane without significant effect of detergent. The slower exponential process detected in the data is quite different in membrane compared to detergent solubilized samples, showing that the pronounced effect of detergent on the later rhodopsin photointermediates begins fairly abruptly near 20 micros. Besides affecting the late processes, the data collected here shows that detergent induces a small blue shift in the 1 micros difference spectrum (the Lumi I minus rhodopsin difference spectrum). The blue shift is similar to one induced by chloride ion in the E181Q rhodopsin mutant and may indicate that the ionization state of Glu181 in rhodopsin is affected by detergent.     

Ellipsometry of silica nanoparticulate Langmuir-Blodgett films for the verification of the validity of effective medium approximations

The validity of various effective medium approximations (EMAs) (Bruggeman, Maxwell-Garnett) was studied for nanostructured systems, where the scale of inhomogeneities is comparable to the wavelength. Langmuir-Blodgett (LB) layers of St?ber silica nanospheres of diameters between 40 and 129 nm are excellent model structures for the experimental verification of the validity of the EMA methods in spectroscopic ellipsometry (SE) evaluation. Nanostructured mono- and multilayered silica films were investigated by SE and reflectance spectroscopy. The effective refractive index and film thickness were determined from the results of multiparameter fitting of SE spectra in the 300-759 nm wavelength region. The distribution of the effective refractive index in the particulate films was calculated assuming an ideal close-packed arrangement of particles. The average deviation from such a structure was deduced from the corrected model by introducing a "fill factor". In the EMA approximation, the spherical shape of the silica particle determines the optical behavior, rather than the "depth distribution" of silica or porosity. Therefore, the shape of particles has a dominant effect on the optical properties of nanoparticulate LB films.     

Development of a capillary electrophoretic method for the analysis of low-molecular-weight amines from metal working fluid aerosols and ambient air

A method for the determination of low-molecular-weight amines from indoor and ambient air was developed using a concentration device followed by CE coupled with indirect spectrophotometric and mass spectrometric detection that enables a reliable, rapid-response and easy-to-operate method. In indirect detection method, the selected amines were separated from interfering metal ions and amino alcohols present in the samples with an imidazole-based buffer with ethanol and EDTA as modifier. By replacing imidazole with ammonium, the final buffer was applicable for MS detection for the analytes with m/z higher than 50. A novel monolithic polymer material based on poly(methacrylate-acrylate) copolymer was developed for sampling short-chain amines from the gaseous phase. The selected analysis conditions were applied to quantify the selected short-chain amines with detection limits for the whole procedure determined between 1 and 2 microg/filter when 40 L air was sampled with 1 L/min velocity. Improved linearity and precision were obtained when the raw, time-scaled electropherogram data were transformed into mobility-scale applied for the determination of the performance characteristics of the methods. The applicability of the process of data transformation into the mobility scale was demonstrated by studying the matrix effect of water-miscible metal working fluid (stable water-oil emulsion) and of ambient air as real samples. CE-indirect UV and CE-MS, combined with the possibility of rapid air sampling, can be useful for the estimation of short-term exposure of the selected biogenic amines.     

Structural effects of lipophilic methotrexate conjugates on model phospholipid biomembranes

Lipophilic conjugates of the antitumor drug methotrexate (MTX) with lipoamino acids (LAAs) have been previously described as a tool to enhance MTX passive entrance into cells, overcoming a form of transport resistance which makes tumour cells insensitive to the antimetabolite. A knowledge of the mechanisms of interaction of such lipophilic derivatives with cell membranes could be useful for planning further lipophilic MTX derivatives with an optimal antitumour activity. To this aim, a calorimetric study was undertaken using a biomembrane model made from synthetic 1,2-dipalmitoyl-glycero-3-phosphocholine (DPPC) multilamellar liposomes. The effects of MTX and conjugates on the phase transition of liposomes were investigated using differential scanning calorimetry.

The interaction of pure MTX with the liposomes was limited to the outer part of the phospholipid bilayers, due to the polar nature of the drug. Conversely, its lipophilic conjugates showed a hydrophobic kind of interaction, perturbing the packing order of DPPC bilayers. In particular, a reduction of the enthalpy of transition from the gel to the liquid crystal phase of DPPC membranes was observed. Such an effect was related to the structure and mole fraction of the conjugates in the liposomes.

The antitumour activity of MTX conjugates was evaluated against cultures of a CCRF–CEM human leukemic T-cell line and a related MTX resistant sub-line. The in vitro cell growth inhibitory activity was higher for bis(tetradecyl) conjugates than for both the other shorter- and longer-chain derivatives. The biological effectiveness of the various MTX derivatives correlated very well with the thermotropic effects observed on the phase transition of DPPC biomembranes.     

Quasilinear Molecule par Excellence,SrCl2: Structure from High‐Temperature Gas‐Phase Electron Diffraction and Quantum‐Chemical Calculations—Computed Structures of SrCl2×Argon Complexes.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.     

Improvement of thermal stability of EPDM by radiation cross-linking for space applications

Journal of Thermal Analysis and Calorimetry - The investigation of radiation effects on ethylene–propylene–diene terpolymer (EPDM) loaded with trifunctional monomer (trimethylolpropane...     

Repeated random insertion into a priority queue

The average cost of inserting n elements into an initially empty heap is analyzed, under the assumption that the n! orders in which the n elements can be inserted are equally likely. It is proved that this average, expressed in number of exchanges per insertion, is bounded by a constant about 1.7645.     

Book Reviews

Structural Chemistry -     

Book Review

Structural Chemistry -     

Molecular structure and ring distortions of p-dichlorobenzene as determined by electron diffraction

The molecular structure of p-dichlorobenzene in the vapour phase has been studied by electron diffraction. Least-squares refinement of a model with D_2h symmetry has led to the accurate determination of the small deviations of the benzene ring from D_6h symmetry caused by the chlorine substituents. The most appreciable effect is an increase from 120° to 121.6 ± 0.2° of the internal angle at the ipso carbon, associated with a shortening of the distance between the two ipso atoms. A less pronounced effect is a shortening of the C-C bonds that originate from the ipso carbons as compared to the central C-C bonds (r_g = 139.0 ± 0.3 pm vs. 139.5 ± 0.4 pm). Other bond distances are r_g (C-Cl) - 173.0 ± 0.4 pm and r_g (C-H) = 109.4 ± 1.0 pm. The observed ring distortions are in agreement with those obtained by low-temperature X-ray crystallography on three different crystal phases of p-dichlorobenzene. They are also consistent with those obtained for chloro-benzene by gas-phase electron diffraction and by NMR spectroscopy in a nematic solvent. The r_s structure of chlorobenzene obtained in a recent study by micro-wave spectroscopy is shown to need revision, as far as the ipso region of the ring is concerned.