Structural and electronic comparative analysis of aminopyridazines showing anti-GABA activity. Crystal structure of 2-(carboxy-3′-propyl)-3-amino-6-cyclohexylpyridazinium bromide.Ab initio Mulliken population analysis of the 6-phenyl-substituted analog compared to GABA

The crystal structure of 2-(carboxy-3-propyl)-3-amino-6-cyclohexylpyridazinium bromide has been determined by single-crystal X-ray diffraction techniques and refined by full-matrix least squares. The compound crystallized in the tri-clinic space groupP ¯1 witha=10.275(1),b=11.215(1),c=7.082(1) Å,=91.84(1),=102.21(1), =106.77(1)°, andZ=2. FinalR-factor is 0.045. The main structural results are very similar to the ones observed for the 6-phenyl analog. These two compounds are GABA-A antagonists.Ab initio molecular orbital calculations, with STO-3G and 4-31G basis sets, suggest that the exocyclic nitrogen accurately mimics the nitrogen atom of GABA.     

Do solid surface potential barriers retard convoy peak electrons?

Using a coaxial cylindric electron spectrometer and an electrostatic ion energy analyzer in tandem, a direct measurement of the difference of the energy of convoy peak electron and the electron equivalent ion energy of protons emerging from the downstream surface of C, Au and Al foils is performed in the proton energy range from 60 to 250 keV. This measurement is made possible using the accepted evidence that for a gas target these energies are equal. It is found that also for the beam foil convoy peak electrons, within an experimental average uncertainty of about ±0.1 eV, there is no difference between these energies. If one accepts that the origin of convoy electrons is from inside the solid, the conclusion is that no retardation by the solid surface potential barrier, which is of the order of a few eV, is observed. This is attributed to the strong electron-ion Coulomb interaction which almost completely overshadows the force exerted on the electron by the field of the surface barrier.     

Cooperative effects in phospholipid monolayers induced by a peptide from HIV-1 capsid protein

The study of interactions between biological molecules and model membranes is essential for the understanding of a number of physiological mechanisms involved in viral infections and dissemination. In this paper, the analysis of the interaction between a peptide from the p24 protein of Human Immunodeficiency Virus type 1 (HIV-1) and a phospholipid monolayer has pointed to a cooperative response in which very small amounts of peptide p24-1 (e.g. 0.05 mol%) can lead to measurable effects. Monolayer surface pressure and surface potential isotherms were affected for peptide concentrations as low as 0.05 mol%, with saturation at 0.5 mol%. The expansion effect from p24-1 is confirmed by changes in morphology of the monolayers using Brewster angle microscopy. Even though p24-1 is disordered in aqueous solutions, the interaction with dipalmitoyl phosphatidylcholine (DPPC) causes it to adopt an alpha-helix structure, as shown by circular dichroism (CD) data for multilamellar vesicles (MLV). The expansion of the phospholipid monolayer in a cooperative way may imply that p24-1 has potential antiviral activity, by participating in the cell rupture, with no need of specific receptors in the membrane.     

Structural stability and energetics of C,Si, and Ge microclusters: empirical many-body potential energy function calculation

The structural stability and energetics of carbon, silicon, and germanium microclusters containing 3?7 atoms have been investigated by using a recently developed empirical many-body potential energy function (PEF), which comprises two- and three-body atomic interactions. The PEF satisfies both bulk cohesive energy per atom and bulk stability exactly. It has been found that the most stable C_3?4 microclusters are linear withD _∞h symmetry but C_5?7 microclusters are planar withD _nh symmetry. Silicon and germanium microclusters show similar structural stability. TheX _n (X=Si, Ge;n=3?7) microclusters are found to be most stable in the following forms:X ₃ is triangular withD _3h symmetry,X ₄ is tetragonal withT _d symmetry,X ₅ is square pyramidal withD _4h symmetry,X ₆ is bipyramidal square withO _h symmetry, and finallyX ₇ is square pyramidal having two atoms underneath withD _2h symmetry.     

Enantiomers of sterically hindered n-aryl-4-pyridones: Chromatographic enrichment and thermal interconversion

N-Aryl-4-pyridones 1–6 were synthesized by condensation of the corresponding 4-pyrone with anilines. The enrichment of the enantiomers was achieved by liquid chromatography on triacctylcellulose, enantiomeric purities of(+)-1 and (+ )-2 being measured by ¹H-NMR in the presence of an optically active auxiliary. Barriers to partial rotation about the C-N bond in 1-4 were determined and compared with corresponding biphenyls.     

Structural dependence of electron transfer to non-covalent polar complexes

Electron attachment to polar molecules and their non-covalent complexes can lead to different kinds of anions which differ from their excess electron localization. Spectroscopic methods for studying anion structures are reviewed. In many cases, the neutral and anion structures are identical and can be deduced from the electron attachment properties. Examples are given for complexes containing polar solvents or building blocks of biomolecules (nucleobases, amino acid residues...).     

2-Cyano Δ3piperideine VII1 : the condensation of 2-cyano Δ3piperideine with sodium dimethylmalonate catalyzed by ZnCl2 or zero valent palladium and platinum complexes

ZnCl₂, Pd (PØ₃)₄ and Pt(PØ₃)₄ were found to be effective catalysts for the condensation of sodium dimethyl malonate with 2-cyano Δ³piperideine $\text{1}$ a–d.     

Development and validation of a high-performance liquid chromatographic method for the determination of clomazone residues in surface water

A method is described for the determination of clomazone residues in surface water by high-performance liquid chromatography with UV detection. The method involves solid-phase extraction with C18 extraction tubes. Clomazone was separated on a C18 column with a mobile phase of methanol-water (65:35, v/v) at pH 4.0 and a flow-rate of 1.0 ml/min. After optimization of the extraction and separation conditions, the method was validated. The method developed can be used for determination of clomazone in surface water, at the limit of 0.1 mcirog/l set by the European Union drinking water directive, with a 400-fold preconcentration.     

Competitive adsorption and desorption of a bi-solute mixture: effect of activated carbon type

This study aims to clarify the effects of carbon activation type and physical form on the extent of adsorption capacity and desorption capacity of a bi-solute mixture of phenol and 2-chlorophenol (2-CP). For this purpose, two different PACs; thermally activated Norit SA4 and chemically activated Norit CA1, and their granular countertypes with similar physical characteristics, thermally activated Norit PKDA and chemically activated Norit CAgran, were used. The thermally activated carbons were better adsorbers for phenol and 2-CP compared with chemically activated carbons, but adsorption was more reversible in the latter case. 2-CP was adsorbed preferentially by each type of activated carbon, but adsorption of phenol was strongly suppressed in the presence of 2-CP. The simplified ideal adsorbed solution (SIAS) model underestimated the 2-CP loadings and overestimated the phenol loadings. However, the improved and modified forms of the SIAS model could better predict the competitive adsorption. The type of carbon activation was decisive in the application of these models. For each activated carbon type, phenol was desorbed more readily in the bi-solute case, but desorption of 2-CP was less compared with single-solute. This was attributed to higher energies of 2-CP adsorption.     

Flow injection analysis : Part VI. The determination of phosphate and chloride in blood serum by dialysis and sample dilution

The rapid determination of chloride and inorganic phosphate in blood serum based on continuous flow spectrophotometry was adapted to Flow Injection Analysis by applying dialysis as well as differential dilution of the injected samples. In addition to the manual injection procedure, an automated microsampling unit was developed and used. By continuous dialysis, chloride could be determined reproducibly at a sampling rate of 125 samples per hour at sample volumes of 60 μl or less. A similar sampling rate and high precision were obtained for the determination of inorganic phosphate by using differential dilution.