Abstract: The requirements for quality food products have been increased in recent years and the interest in the quality and purity of spirits, wines and fruit juices has grown in this connection as well. In the early 90 s the EU adopted the 2H-NMR method for wine analysis as an official method (EEC 2676/90), in order to tackle the problem of over-chapitalization of wines in Europe. A deuterium natural abundance quantitative NMR method (SNIF-NMR) was developed as an efficient and powerful tool capable of characterizing the chemical origins of organic molecules and distinguishing their biological and geographical origin. Usually this type of measurements are performed with dedicated NMR equipments and computerized programs elaborated, commercialized and maintained by Eurofins Scientific (France).
Abstract: The major protein component from aleurone cells of barley (Hordeum vulgare L.), PACB, is related to 7S globulins present in other cereals and to the vicilin-type 7S globulins of legumes and cotton seed. It contains 4 subunits of about 20, 25, 40 and 50 kDa molecular weights. The N-terminal sequence of 16 amino acids (over 260 atoms) in the protein was previously determined, and our aim is the prediction of its secondary structure. The empirical Chou-Fasman method was applied in an improved version as well as the empirical DSC method (discrimination of protein secondary structure class) with quite similar results. A molecular dynamics simulation was also performed, using the FF99SB forcefield within AMBER version 9.0. Solvation effects were incorporated using the Born model. The results are compared and a 3D model is proposed.
Abstract: The inclusion of vanillin by β-cyclodextrin was investigated by 1H NMR. The continuous variation technique was used to evidence the formation of soluble 1:1 complex in aqueous solution. The association constant of vanillin with β-cyclodextrin has been obtained at 298 K by fitting the experimental chemical shifts differences, Δδobs = δfree - δobs of the observed guest and host protons, with a non-linear regression method. Besides the effective association constant, the fitting procedure allows a precise determination of all chemical shift parameters characterizing the pure complex. They can by used for an analysis of the geometry of the molecular complex in solution.
Abstract: A self-association of vanillin have been studied by 1H NMR spectroscopy using the analysis of proton chemical shifts changes in aqueous solution as a function of concentration. The experimental results have been analysed using indefinite non-cooperative and cooperative models of molecular self-association, enabling the determination of equilibrium constants, parameters of cooperativity and the limiting values of vanillin proton chemical shifts in the complex. It was found that the dimer formation creates energetically favourable conditions for subsequent molecular association.
Abstract: The interaction between indomethacin and human serum albumin (HSA) was investigated by fluorescence quenching technique and UV-vis absorption spectroscopy. The results of fluorescence titration revealed that indomethacin, strongly quench the intrinsic fluorescence of HSA by static quenching and nonradiative energy transfer. The binding site number n and the apparent binding constant KA, were calculated using linear and nonlinear fit to the experimental data. The distance r between donor (HSA) and acceptor (indomethacin) was obtained according to fluorescence resonance energy transfer (FRET). The study suggests that the donor and the acceptor are bound at different locations but within the quenching distance.
Abstract: Novel extended tetrahedral forms of CO2 have been synthesized recently under high-pressure conditions. We perform ab initio density functional theory calculations to investigate whether doping with Si can extend the stability range of such tetrahedral forms of CO2 to ambient pressure. Calculations are performed with a simple cubic cell containing eight formula units in a β-cristobalite-like structure. Though we find that all the SixC1−xO2 structures considered by us are thermodynamically unstable with respect to decomposition into the end members at ambient pressures, the energy differences are small, suggesting that it might be possible for such phases to exist in metastable forms. At higher pressures, the heat of formation is found to be negative. The bonding between C and O atoms is more covalent than that between Si and O atoms. We also find indications that some C atoms may prefer three-fold coordination at low pressure.
Abstract: Ab initio density functional calculations were performed on the CH2 pale yellow stable tautomer of 2-(2',4'-dinitrobenzyl)pyridine and on his photoinduced dark blue NH tautomer. We used B3LYP hybrid functional with 6-31G(d), 6-31G** and 6-31++G** basis sets. Good agreement is found between the calculated and experimental structures and vibrational spectra. The discrepancies are associated with the fact that the experimental values are obtained from a crystal, the theoretical ones being calculated in the gas phase.
Abstract: We report a reversible liquid-solid transition upon heating of a simple solution composed of a-cyclodextrine (alphaCD), water, and 4-methylpyridine. These solutions are homogeneous and transparent at ambient temperature and solidify when heated to temperatures between 45° and 75°. Quasielastic and elastic neutron scattering show that molecular motions are slowed down in the solid and that crystalline order is established. The solution "freezes on heating." This process is fully reversible, on cooling the solid melts. A rearrangement of hydrogen bonds is postulated to be responsible for the observed phenomenon.
Abstract: The experimental data on 235U enrichment by isotopic exchange 235U/238U in U4+ - UO22+ system on cation exchange resin C-100 (produced by Purolite) and in the system U4+-[UO2Clx]2-x, on anion exchange resin Dowex-1 (Sigma) are presented. In both cases a thermostated glass lumn was utilised. Cation exchange resin was passed in R-Ti3+ form, then the column was feeded with 0.047M UO2Cl2 solution. According to the isotopic exchange between U4+ fixed on resin and UO22+ from solution 235U is enriched in the solution phase at the front of U band, and 238U in the resin phase at the rear of uranium band. The uranium solution which has passed through the column was fractioned, by means of an automatic sample colector, in 100 small fractions. For each sample fraction uranium content, and uranium isotopic ratio 235U/238U were determined. In the case of Dowex-1 the resin was converted in R-Cl form with 5M HCl solution, then 0.1 M UO2Cl2 solution in 5M HCl was feeded in the column, and on the resin were fixed the following complex anions: [UO2Cl3]-, [UO2Cl4]2-. When all resin was passed in R-U(IV) form, the column was feeded with 0.1 M TiCl3 solution in 5 M HCl. According to the isotopic exchange between [UO2Clx]2-x fixed on resin and U4+ from solution 235U will be enriched in the resin phase, at the rear edge of uranium band. The effluent from the bottom of the column was collected in small fractions on which uranium content and isotopic ratio 235U/238U were determined. All isotopic analysis were performed on SMIT-1 thermoionization mass spectrometer. In both cases presented here, 235U enrichments were experimentally determined. Temperature increase with 10°C had not a significant effect on 235U enrichment in U4+-UO22+ exchange system on cation exchange resin C-100. The 235U enrichment was diminished when feed flow rate of the column with Dowex-1 increased two times. The eluent volume, corresponding to the uranium 235U maximum enrichment was 1428 mL on cation exchange resin, and 692 mL on anion exchange resin.
