Effects of medium and chemical modification on thermal characteristics of Β-lactoglobulin

The thermal properties of gif" alt="Bgr" align="BASELINE" BORDER="0">-lactoglobulin (gif" alt="Bgr" align="BASELINE" BORDER="0">-LG) were studied by differential scanning calorimetry (DSC) under different medium conditions.pH, neutral salts, protein perturbants, and polyols all affected the DSC characteristics of gif" alt="Bgr" align="BASELINE" BORDER="0">-LG. Acylation with fatty acids also changed the thermal properties, particularly peak width at half-height. The results suggest that the structural stability of gif" alt="Bgr" align="BASELINE" BORDER="0">-LG is controlled by non-covalent forces, particularly electrostatic and hydrophobic interactions. Disulfide bonds did not contribute to the thermal response of gif" alt="Bgr" align="BASELINE" BORDER="0">-LG. Fatty N-acyl-amino acids caused marked increases in thermal stability and decreases in denaturation enthalpy, and additional peaks were observed in the presence of some palmitoyl derivatives.Contribution No. 2310, Centre for Food and Animal Research.We thank D. Raymond for her excellent technical assistance.     

Ab initio SCF investigation of the intramolecular hydrogen bonding in δ-aminopentanoic acid

The potential energy surface of the neutral form ofgif" alt="delta" align="BASELINE" BORDER="0">-aminopentanoic acid was investigated by means of ab initio 4-31G SCF calculations. Four symmetry unique local minima are stabilized by an intramolecular O-H gif" alt="ctdot" align="MIDDLE" BORDER="0"> NH₂ hydrogen bond. The geometries, energies, and wave numbers of these conformers are reported. The hydrogen bond is discussed with respect to all reactions of these conformers and in comparison with the homologues glycine,gif" alt="Bgr" align="BASELINE" BORDER="0">-alanine, andgif" alt="gamma" align="MIDDLE" BORDER="0">-aminobutyric acid and also with the bimolecular adducts between formic acid, acetic acid, and propionic acid, on the one hand, and ammonia, methylamine, and ethylamine, on the other hand.     

Optimisation of Supercritical Carbon Dioxide Systems for Complexation of Naproxen : Beta-Cyclodextrin

Supercritical carbon dioxide (scCO₂)offers several attractive scenarios for thepharmaceutical processing as an alternativeto aqueous and organic solvents. In thiswork naproxen, a widely used non steroidalanti-inflammatory drug with analgesic andanti-inflammatory properties, was chosenas a model drug. Its complexation with cyclodextrinsimproves the rate and extent of dissolutionof the drug, increase its rate of absorption and mayreduce the unpleasant side-effects of the drug.The interest in using this supercritical technologyled us to develop an experimental unit for the useof supercritical CO₂ as a processing medium forthe complexation of naproxen with beta cyclodextrin (CD).     

Comments on the electronic properties of cyclopropane,cyclobutane, and cyclohexane

Spectral quantities of cyclopropane, cyclobutane, cyclohexane, and of several derivatives, have been calculated by a semiempirical all-valence electron SCF-CI MO method. In cyclopropane, HOMO is practically localized in the carbon-frame, and LVMO is purely so. In cyclobutane, these two MO's are based on C-H bonds, while cyclohexane holds an intermediate position. Despite the overall similarity-experimental and computed-of the spectra of these molecules, assignments are non-parallel. Like cyclopropane, cyclobutane can extend conjugation, but to a diminished degree; cyclohexane behaves in this respect like an acyclic alkane. An interpretation of this gradation, in terms of the nature of high-lying MO's, is proposed.     

Theoretical studies on the conformation of saccharides

Conformations of 2-methoxytetrahydropyran as a model for the six-membered ring in aldopyranosides have been calculated by the PCILO method using the algorithm of the conjugated gradient to optimize the geometry. The calculated geometry of the fourteen basic forms of 2-methoxytetrahydropyran was found to be in agreement with the available data obtained by X-ray diffraction of pyranosides. The results indicate differences in the geometry of 2-methoxytetrahydropyran resulting from the change of the axial vs. equatorial position of the methoxyl group. These changes are particularly meaningful in the values of bond angles and they are in agreement with the anomeric and exoanomeric effects. The experimentally found differences in the energies of an axial (⁴ C ₁) and equatorial (¹ C ₄) conformer, gif" alt="Delta" align="BASELINE" BORDER="0">G = 2.9–3.7 kJ/mol, and the dipole moment, gif" alt="mgr" align="MIDDLE" BORDER="0"> = 1.20 ± 0.05 D (1D = 3.33 10^–30mAs) agree well with the calculated values gif" alt="Delta" align="BASELINE" BORDER="0">E = 3.18 kJ/mol and " alt="mgr" align="MIDDLE" BORDER="0">> = 1.18 D which, in turn, suggest that the axial conformer is preferred over the equatorial one by a ratio a:e = 78:22.     

An efficient ab initio gradient program

An ab initio Hartree-Fock gradient program is described. It is characterized by (1) efficiency of the gradient evaluation, and (2) capability of handling higher angular momentum (d andf) basis functions. The latter are constructed from shifted Cartesian Gaussian p-type primitives. A satisfactory solution is presented for the problems connected with the neglect of small integrals in a gradient program. Methods for increasing the efficiency of the SCF procedure are discussed.     

COMPOSITION OF THE ESSENTIAL OIL OF Haplophyllum myrtifolium

The chemical composition of the essential oil ofHaplophyllum myrtifoliumBoiss., endemic to Turkey, was examined by GC/MS. Ninety-seven compounds were characterized with linalool (12.8%), gif" alt="beta" align="MIDDLE" BORDER="0">-caryophyllene (10.3 %), and methyleugenol (5.9 %) as the main constituents.     

Methyl trifluoropyruvate in the Pictet-Spengler reaction

Condensation of methyl trifluoropyruvate with 2-(3,4-dimethoxyphenyl)ethylamine, tryptamine, and (D, L)-tryptophan yielded 1-methoxycarbonyl-1-trifluoromethyl-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline, 1-methoxycarbonyl-1-trifluoromethyl-1,2,3,4-tetrahydro-9H-pyrido[3,4-b]indole, and Z-1-methoxycarbonyl-1-trifluoromethyl-3-carboxy-1,2,3,4-tetrahydro-9H-pyrido[3,4-b]indole, respectively. The Z configuration of the latter was determined by x-ray structural analysis.A. N. Nesmayanov Institute of Organoelemental Compounds, Russian Academy of Sciences, 117813 Moscow, Russia. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 8, pp. 1831–1836, August, 1992.