Fractionnement et analyse des complexes organo-mineraux de sols bruns et de chernozems

Résumé Les auteurs définissent plusieurs formes de matières organiques et procèdent à leur inventaire dans des sols bruns et des chernozems. Ils effectuent un premier fractionnement par tamisage destiné à quantifier la matière végétale figurée et à séparer les complexes organo-minéraux. Ils procèdent ensuite sur ces derniers, à des extractions chimiques en vue de déterminer les complexes organométalliques et les complexes organo-argilliques. Les résultats démontrent que les sols bruns étudiés sont formés d'agrégats de consistance très lâche, caractérisés par un fort taux de complexes organométalliques à base d'acides fulviques à turn-over très rapide. Ces propriétés contrastent beaucoup avec celles des chernozems qui sont constitués d'agrégats très compacts renfermant un fort taux d'acides humiques très polycondensés, liés à un taux élevé de complexes organo-argilliques, ces deux types de produits apparaissant très résistants aux dégradations microbiennes.     

Marqueurs Á spin construits directement sur le squelette carboné de sucres

Treatment of aldehydo-sugars with 2,3-bis(hydroxyamino)-2,3-dimethylbutane gave the corresponding 1,3-dihydroxyimidazolidines. Oxidation of these compounds gave, successively, unstable, free radicals having a 3-hydroxyimidazolidine 1-oxyl structure, then stable, free radicals having a 2-glycosyl-2-imidazoline 3-oxide 1-oxyl structure, which were reduced to stable 2-glycosyl-2-imidazoline 1-oxyl compounds. The orientation of the two last-named series of compounds around the σ bond between carbohydrate and heterocyclic residues that bears the radical centre is indicated by the value of the hyperfine coupling aH of the carbohydrate proton nearest to the nitrogenous heterocyclic residue. The study of numerous compounds of both series shows that the value of the hyperfine coupling depends greatly on the structure of the carbohydrate residue. A general explanation based on the preponderance of eclipsed forms and on the primary influence of steric hindrance due to the substituents of the carbohydrate residue is proposed. This study also gives some indirect information on the conformation of diamagnetic compounds that show little sterical difference, and about which ¹H-n.m.r. spectroscopy does not provide useful information.     

Diurnal variations of plasma testosterone in men

Plasma testosterone (T) levels were assayed by a Competitive Protein Binding (CPB) technique in a group of 31 healthy males. In 22 subjects a single blood sample was taken between 8:00 and 9:00 A.M. and the mean T concentration was 6.84 ± 2.11 ng/ml. In the other 9 normal men, blood samples were taken every 4 hours. The existence of temporal variations for testosterone was confirmed by finding the highest mean plasma levels at 4:00 A.M. (9.28 ± 1.17 ng/ml) and lowest mean levels at 8:00 P.M. (2.66 ± 0.52 ng/ml).     

Michael Heidelberger as a Carbohydrate Chemist

The deoxyaldaric acids corresponding in structure to the 3-deoxy-2-C-(hydroxymethyl)aldonic (isosaccharinic) acids have been identified as products of treatment of various carbohydrates with alkali and oxygen-alkali. The structures of the acids were determined from the mass spectra of their Me₃Si derivatives on the basis of previously known, specific fragmentation reactions. The g.l.c.-m.s. technique was used, and g.l.c. retention data are given. The identified species are 2-deoxy-3-C-(hydroxymethyl)tetraric, 3-deoxy-2-C-hydroxymethyl-erythro-pentaric, 3-deoxy-2-C-hydroxymethyl-threo-pentaric, 2-methyltartronic, 2-(2-hydroxyethyl)tartronic, and 2-(2,3-dihydroxypropyl)tartronic acids. Their formation from 4-O-substituted uronic and ulosonic acids is briefly discussed.     

Contrasting patterns of morphological variation with dietary preferences in Micropogonias furnieri: insights from stable‐isotope and digestive‐trait analyses

The dietary preferences of populations of whitemouth croaker Micropogonias furnieri, which commonly inhabit estuarine and oceanic environments of the south‐western Atlantic Ocean, were investigated using stable‐isotope analysis and digestive traits, and compared with previous genetic and morphometric surveys of this species. Isotopic and C:N‐derived data suggested that individuals from coastal lagoons are the most differentiated from the remaining localities surveyed. In contrast, the analysis of the digestive traits did not show the same differentiation pattern. The overall correlation between isotopic, molecular and morphological variations suggests that genetic and phenotypic differences among populations are accompanied by differential resource use, supporting the idea that selective forces could be playing an important role in population differentiation.     

Potassium and veratrine-stimulated l-[3H]cysteine sulfinate and l-[3H]glutamate release from rat brain slices

The release of l-[³H]cysteine sulfinic acid, l-[³H]glutamatic acid and [³H]GABA from preloaded slices of various rat brain regions in response to either 30 mM K⁺ or veratrin was investigated. All these aminoacids were released by both depolarizing agents, which did not produce any changes in the spontaneous efflux of [³H]lysine. The K⁺ stimulated cysteine sulfinate release from superfused slices was found partly Ca²⁺-dependent in the subiculum, and mainly Ca²⁺-independent in the hippocampus whereas the K⁺-elicited glutamate release was partly Ca²⁺-dependent in both regions. The veratrine-induced release of both cysteine sulfinate and glutamate was blocked by verapamil in a dose-dependent way, although a small verapamil concentration independent release remained. The release pattern of both amino acids was heterogeneous, but roughly correlated among brain regions, except in the subiculum and hypothalamus.These findings demonstrate the releasability of both substances from various brain regions and suggest that those releases occur from different pools, being probably mainly of neuronal origin. They give further evidence that cysteine sulfinate as well as glutamate may serve a neurotransmitter role in the CNS.