(Benzylthio)- und (Arylthio)-substituierte Nitril-ylide: Thermische Erzeugung und Reaktionen

Thermal Generation and Reactions of (Benzylthio)-and (Arylthio)-Substituted Nitrile Ylides Thermolysis of 4-(benzylthio)- and 4-(arylthio)-1,3-oxazol-5(2H)-ones 6 , at 110–155° in the presence of dipolarophiles with activated C≡C, C?C, C?O, C?S, and N?N bonds, led to 5-membered cyclo-adducts and CO² (cf. Schemes 3, 5-7). Heating 6a and 6c in the presence of ethyl propiolate yielded ethyl quinoline-3-carboxylate ( 19 ) and ethyl pyridine-3-carboxylate( 22 ), respectively (cf. Scheme 8). These results are rationalized on the basis of the intermediate formation of thio-substituted nitrile ylides of type 7 (cf. Scheme 2), which undergo regioselective 1,3-dipolar cycloadditions with reactive dipolarophiles. In the absence of such a dipolarophile, the nitrile ylides isomerize via a [1,4]-H shift to give 2-aza-1,3-butadienes of type 20 . The latter are trapped in a Diels-Alder reaction with ethyl propiolate (cf. Scheme 8).     

Mise au point d'un calorimetre de reaction en milieu fluorhydrique - enthalpies de dissolution de kf dans les solutions aqueuses de HF

A calorimeter designed for studies of reactions in hydrofluoric acid has been constructed. Enthalpies of dissolution of KF in aqueous solutions of HF (from 1,05 N to 28,3 N) have been measured.     

Fractionation of basic nuclear proteins of human sperm by zinc chelate affinity chromatography

Immobilized metal affinity chromatography was investigated for the fractionation of basic nuclear proteins of human sperm. Human sperm nuclei essentially contain two classes of protamines: a protamine of type P1 (HPl), rich in cysteine but with only one histidine, and three protamines of type P2 (HP2, HP3, HP4), rich in cysteine and histidine (nine in protamine HP2), potential ligands for transition metal ions. The critical conditions for metal affinity chromatography were defined: choice of metal, protein material and buffer, type of elution and sample loading. Chromatography of nuclear proteins, without histones and with cysteine residues alkylated by iodoacetamide, was optimum on zinc Chelating Sepharose in a Tris-acetate buffer and elution with an increasing concentration gradient of imidazole. Under these conditions, the two classes of protamines were completely separated. The intermediate basic proteins were further purified by reversed-phase high-performance liquid chromatography. Heterogeneity of binding to zinc of protamine HP1 was demonstrated. The proposed method is simple and reproducible and the recovery of proteins is high. It may be applied to study the expression and function of P1 and P2 protamines, e.g., in the case of infertile men.     

Physicochemical characterization of cholesterol-beta cyclodextrin inclusion complexes

Study and characterization of molecular complexes between cholesterol and beta cyclodextrin has been done using X-ray diffraction, thermogravimetric analysis (TG), differential scanning calorimetry (DSC) and nuclear magnetic resonance spectroscopy (¹³C NMR). Whatever the value of the molar ratio cholesterol/βCD used during the preparation, the same compound is always obtained. Corresponding to a molar ratio 1/3 (cholesterol/βCD), this compound is a stable hydrate which, contrary toβCD, contains at room temperature a large amount of molecules of water. It can be dehydrated under low pressure but the thermal degradation occurs at 200°C (250°C forβCD). This implies that cholesterol is strongly bounded toβCD.     

Etude des enthalpies de dissolution A 298 K des fluorures alcalins dans les solutions aqueuses de HF

Enthalpies of solution of alkali fluorides in aqueous HF have been measured over a wide range of HF concentrations.     

Field desorption mass spectrometry of oligosaccharides in the presence of metallic salts

In the field desorption mass spectrometry of oligosaccharides, traces of contaminating salts in polar solvents decrease the detection sensitivity, and in some cases no ion could be detected in the molecular range. The present work shows that the addition of alkaline salts (NaI or KI) greatly increases the sensitivity, and cationized molecular ions are obtained. The influence of the molar ratio sugar/salt on the nature and relative intensity of the desorbed species has been studied on mixtures of α-D -trehalose and NaI. At the low salt ratio (100:1), high molecular weight clusters [X M + Na]⁺ are preferentially formed. At the high salt ratio (1:10), mixed clusters [M + NaI + Na]⁺, doubly charged ions [M + 2Na]²⁺ and monomeric cationized ions [M + Na]⁺ are observed along with salt clusters [NaI + Na]⁺ and [2NaI + Na]⁺. In the range of molar ratios sugar/salt of 10:1 to 1:1, the field desorption mass spectra exhibit a cationized ion [M + Na]⁺, which contributes more than 80% of Σ₁₀₀. This cationization technique has been applied to the field desorption mass spectrometry of several oligosaccharides. In all cases, the salt effect causes the replacement of the [M + H]⁺ ion by a [M + C]⁺ ion. (Note: the term [M + C]⁺ and similar ones mean an association between the whole molecule studied (M) and an alkaline cation [C]⁺ ([K)]⁺, [Na]⁺, [Li]⁺).) Thus, di, tri- and tetrasaccharides exhibit intense [M + Na]⁺ ions in the presence of NaI and only a few fragment peaks are observed in their field desorption mass spectra. This technique has been applied successfully to the detection of the hexasaccharide ajugose in a natural sample of pentasaccharide, and has also allowed the unambiguous determination of the composition of a mixture of partially methylated trehaloses. The salt effects are dicussed in terms of selective adsorption on the emitter, pre-existing soluble complexes sugar-salt, interactions between these species in the electric field and dissociative desorption of ionic complexes.