Basis set and correlation effects on computed proton affinities of some oxygen and nitrogen bases

Basis set expansion and correlation effects on the computed proton affinities of the oxygen and nitrogen bases CH₃OH, H₂CO, CO, CH₃NH₂, CH₂NH, and HCN have been evaluated. Basis set enhancements lead to systematic changes in computed proton affinities. These effects appear to be additive, and are greater for correlated proton affinities than for Hartree-Fock energies. Inclusion of correlation decreases proton affinities, with fourth-order Møller-Plesset energies bracketed by second and third order energies.     

Analysis of cell surface molecular distributions and cellular signaling by flow cytometry

Flow cytometry is a fast analysis and separation method for large cell populations, based on collection and processing of optical signals gained on a cell-by-cell basis. These optical signals are scattered light and fluorescence. Owing to its unique potential ofStatistical data analysis and sensitive monitoring of (micro)heterogeneities in large cell populations, flow cytometry—in combination with microscopic imaging techniques—is a powerful tool to study molecular details of cellular signal transduction processes as well. The method also has a widespread clinical application, mostly in analysis of lymphocyte subpopulations for diagnostic (or research) purposes in diseases related to the immune system. A special application of flow cytometry is the mapping of molecular interactions (proximity relationships between membrane proteins) at the cell surface, on a cell-by-cell basis. We developed two approaches to study such questions; both are based ondistance-dependent quenching of excited state fluorophores (donors) by fluorescent or dark (nitroxide radical) acceptors via Förstertype dipole-dipole resonance energy transfer (FRET) and long-range electron transfer (LRET) mechanisms, respectively. A critical evaluation of these methods using donor- or acceptor-conjugated monoclonal antibodies (or their Fab fragments) to select the appropriate cell surface receptor or antigen will be presented in comparison with other approaches for similar purposes. The applicability of FRET and LRET for two-dimensional antigen mapping as well as for detection of conformational changes in extracellular domains of membrane-bound proteins is discussed and illustrated by examples of several lymphoma cell lines. Another special application area of flow cytometry is the analysis of different aspects of cellular signal transduction, e.g., changes of intracellular ion (Ca²⁺, H⁺, Na⁺) concentrations, regulation of ion channel activities, or more complex physiological responses of cell to external stimuli via correlated fluorescence and scatter signal analysis, on a cell-by-cell basis. This way different signaling events such as changes in membrane permeability, membrane potential, cell size and shape, ion distribution, cell density, chromatin structure, etc., can be easily and quickly monitored over large cell populations with the advantage of revealing microheterogeneities in the cellular responses. Flow cytometry also offers the possibility to follow the kinetics of slow (minute- and hour-scale) biological processes in cell populations. These applications are illustrated by the example of complex flow cytometric analysis of signaling in extracellular ATP-triggered apoptosis (programmed cell death) of murine thymic lymphocytes.     

Basis set dependence of correlation corrections to protonation energies

The protonation energies of NH₃ and H₂O have been computed using a variety of basis sets. It is found that the effect of election correlation on these energies cannot reliably be determined without the use of large (triple-split and polarized) basis sets.     

New approach to the correlation spectrum near intermittency: A quantum mechanical analogy

The correlation spectrum of fully developed one-dimensional mappings is studied near and at a weakly intermittent situation. Using a suitable infinitematrix representation, the eigenvalue equation of the Frobenius-Perron operator is approximately reduced to the radial Schrödinger equation of the hydrogen atom. Corrections are calculated by quantum mechanical perturbation theory. Analytical expressions for the spectral properties and correlation functions are derived and checked numerically. Compared to our previous work, the accuracy of the present results is significantly higher owing to the controlled and systematic approximation scheme     

Hydrogen bonds between hydrogen halides and unsaturated hydrocarbons

Ab initio molecular orbital theory is used to study geometrics and energies of hydrogen-bonded complexes between hydrogen fluoride, hydrogen chloride (as proton donors) and acetylene, ethylene (as proton acceptors). Symmetrical T-shaped structures are found to be equilibrium structures for all four complexes. The strengths of the hydrogen bonds are found to be less than for conventional hydrogen bonds involving lone pairs of electrons.     

Ethanol and halothane differently modulate HLA class I and class II oligomerization. A new look at the mode of action of anesthetic agents through fluorescence spectroscopy

The field of research considering the working mechanism of anesthetic agents is a complex one and the site or sites of action of general anesthetics are yet to be elucidated. Through the years, on the molecular level, the discussion has shifted from the lipid theories to the more specific interaction with the proteins responsible for the signal transduction. While this approach led to several models, they offer, at best, partial explanations for the observed phenomena. Anesthetic agents interact with many systems, of which the neuronal is best studied, leaving interaction with the immune defense system relatively unexplored. In this study we focus on the interaction of ethanol and halothane with the co-localization on the membrane of HLA I and II molecules. We show that ethanol tends to randomize the distribution of HLA I and II molecules, while halothane increases the clustering of HLA I proteins. The notion that anesthetics modulate cell function by disrupting clustering and thereby promoting a random distribution is a novel approach that may explain the general involvement of many systems during exposition to anesthetic drugs. In this study we show the disturbance of co-localization of molecules that may form a functional network. The relevance of this finding depends on the importance of these networks for extracellular and intracellular processes.     

Radiotracer analysis of the physico-chemical state of trace elements in aqueous solutions III. Lead

The physico-chemical state of trace lead in aqueous nitrate solutions (I=0.01) was studied using equilibrium calculation, free-liquid electrophoresis, dialysis and centrifugation methods and^{210, 212}Pb. It has been found that lead is present exclusively as nonhydrolyzed cations in solutions of pH 2–3.5. Colloidal or larger particulate forms of lead exist in solutions of lower acidity (pH>4). They are of pseudocolloidal nature, i.e. they are formed by adsorption of lead on solid impurities in the studied solutions. The pseudocolloids are negatively charged at pH>5 and reversible at pH 4–7. Reversibility of the adsorption of lead on impurities decreases at pH>7. Experiments have indicated that a significant hydrolysis of bivalent lead takes place already at pH>4. Anionic hydroxo-complexes of lead predominate in alkaline solutions of pH>12.     

Factors affecting interaction of radiocesium with freshwater solids

The paper aims at the analysis of principal factors affecting the interaction of radiocesium with freshwater solids, important for the migration of radiocesium in rivers. Uptake and release of radiocesium by bottom sediment and suspended solids from a small stream were studied as a function of contact time during the uptake and releases, of concentration of the solid phases and of temperature, using laboratory model experiments. Kinetics of the uptake were found to be singificantly affected by temperature and concentration of the solid phase. The kinetics and the concentration effect can be quantitatively described using kinetic model of two parallel or consecutive reactions. Kinetic parameters for the model were determined. Distribution coefficient K_d is independent of sediment concentration in the range of 20–70 mg·dm^?3 but passes through a maximum at higher concentration values. Release of radiocesium adsorbed on the freshwater solids was found to be quite rapid and a simple kinetics of the release from freshwater solids was observed. The amount released decreased with increasing contact time of radiocesium with solid phase. Quantitative evaluation of the release revealed partial irreversibility of radiocesium uptake on the solids studied. Results obtained are compared with literature data and conclusions are drawn on the importance of the factors studied for modeling of radiocesium migration in rivers.     

Lifetime simulation and thermal characterization of PVC cable insulation materials

Thermal behavior of commercial PVC cable insulation both before and after extraction of plasticizers, fillers and other agents were tested by TG/DTG and DSC during heating in the range 20-800°C in air. The ultrasound enhanced hexane extraction and dissolution in THF with subsequent precipitation of PVC were used to prepare 'extracted' and 'precipitated' samples. The total mass loss measured for the 'non-treated', 'extracted' and 'precipitated' PVC samples was 71.6, 66.6 and 97%, respectively. In the temperature range 200-340°C the release of dioctylphthalate, HCl and CO₂was observed by simultaneous TG/FTIR. From TG results measured at different heating rates (1.5, 5, 10, 15 K min^-1) in the range 200-340°C the non-isothermal kinetics of the PVC samples degradation was determined. Activation energy values of the thermal degradation processes calculated by ASTM E 698 method, for 'non-treated', 'extracted' and 'precipitated' PVC samples were 174.6±17 kJ min^-1, 192.8±19 kJ min^-1, 217.1±20 kJ min^-1, respectively. These kinetic parameters were used for the lifetime simulation of the materials.