Jean-Claude Fischer

Variability of dissolved Mn and Zn in the Seine estuary and chemical speciation of these metals in suspended matter

Abstract A general study of manganese and zinc in both dissolved and particulate forms in waters from the Seine river, its estuary and the Bay of Seine (in northern France) has been undertaken in order to investigate their fate and transport processes in riverine, estuarine and coastal environments. These samples have been analyzed using graphite-furnace atomic absorption spectroscopy (GFAAS), inductively coupled plasma-atomic emission spectroscopy (ICP-AES) and differential pulse anodic stripping voltammetry (DPASV). In this work, we have considered the different parameters (salinity, pH, temperature and total suspended matter) which may influence the metal distribution in the estuary, and have surveyed the evolution of these metals (with numerous soluble organic and inorganic ligands) in aqueous phases and their interaction with the various inorganic and organic solid fractions which compose the particles. The results show that dissolved Mn and Zn are mainly influenced by salinity. Furthermore, their variability is governed by temporal and spacial changes in tidal stress. Indeed, the distributions of dissolved Mn and Zn are linked to the internal properties of particles and the flow of sediments regulated by the tidally-induced perturbations in the estuary bed. Since the cause of these observations is in connection with the interactions between the liquid phase and the solids present, we have also undertaken the chemical speciation of Mn and Zn in the particles. The results obtained confirm the non-conservative behavior of these two metals. Owing to the paramagnetic properties of Mn, we have been able to analyze particles using electron spin resonance spectroscopy in order to gain further information about the nature of Mn compounds, their oxidation states and their combinations.

The biosynthesis of thiamine. Syntheses of [1,1,1,5-2H4]-1-deoxy-D-threo-2-pentulose and incorporation of this sugar in biosynthesis of thiazole by Escherichia coli cells

Non-growing, washed cells of Escherichia coli, depressed for the synthesis of thiamine, were incubated in the presence of [1,1,1,5-2H4]-1-deoxy-D-threo-2-pentulose (9) in a medium containing the pyrimidine moiety of thiamine, L-tyrosine, and glucose. The thiamine thus biosynthesized was extracted and cleaved to give 5-(2-hydroxyethyl)-4-methylthiazole (HET) which was examined as the trifluoroacetate derivative by electron-impact mass spectrometry. The distribution of the label in the fragments indicated that the pentulose (9) was a precursor of the C5-chain of HET without C–C bond cleavage. Several routes to 1-deoxypentuloses are described. Condensation of 2,4-O-benzylidene-D-[4-2H1]threose (23) with trideuteriomethylmagnesium iodide gave the protected 1-deoxypentitols (24) and (25). Brominolysis of the mixed dibutylstannylidenes then afforded [1,1,1,5-2H4]-3,5-O-benzylidene-1-deoxy-D-threo-2-pentulose (26), which was converted into the free sugar (9) by acidic hydrolysis. 1-Deoxy-D-erythro-2-pentulose was prepared in similar manner. Condensation of 2-([2H3]-methyl)-1,3-dithian with 2,3-O-isopropylidene-D-glyceraldehyde, followed by a C-3 epimerization step also led, after deprotection, to a mixture of [1,1,1-2H3]-1-deoxy-D-erythro- and [1,1,1-2H3]-1-deoxy-D-threo-2-pentulose, (5) and (6).

Speciation of dissolved and particulate manganese in the Seine river estuary

Abstract During four surveys covering various hydrodynamic conditions samples were collected in the Seine river estuary for the study of dissolved and particulate manganese. A new analytical method for direct determination of dissolved manganese was used in this study (atomic absorption spectrometry with Zeeman non-specific absorption correction). Generally, dissolved manganese versus salinity curves exhibits a peak concentration in the low salinity zone. Speciation studies of dissolved and particulate manganese have been performed in order to establish a model for manganese behaviour in the Seine estuary. Taking into consideration the solution composition as well as the values of stability constants of the complexes, dissolved manganese speciation has been calculated using an equilibrium Speciation program. Sequential extraction procedures (Tessiers scheme) have been applied to assess the manganese distribution in solid samples (sediment, suspended matter). Operational nature of empiricism inherent to these procedures has been partly eliminated by determining physicochemical form of Mn by electron spin resonance owing to the paramagnetic properties of manganese. This study has allowed us to show that manganese behaviour in the Seine estuary is strongly influenced, (i) in solid samples, by the presence of calcium carbonate which stabilise the Mn(II) form; (ii) in solution, by the increase of salinity, calcium, magnesium and suspended matter concentrations, by complexes formation and by diffusion from sediments to water.

High-Yielding One-Step Conversion of D-Glucose and D-Galactose to the Corresponding α and β Methyl-D-glucofuranosides and Galactofuranosides

Abstract D-Glucose and D-Galactose are transformed to the corresponding α and β -Methyl D-Glucofuranosides in good yields using methanol and Ferric chloride as catalyst.

Thioglycosides as Potential Glycosyl Donors in Electrochemical Glycosylation Reactions. Part 2: Their Reactivity Toward Sugar Alcohols.

Abstract Constant potential electrolysis of the glycosyl donors p-methylphenyl 2,3,4,6-tetra-O-benzyl-1-thio-β-D-glucopyranoside (1) and p-methylphenyl 3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-1-thio-β-D-glucopyranoside (4) in dry acetonitrile in the presence of various primary and secondary sugar alcohols, performed in an undivided cell, gave β-linked disaccharide derivatives selectively in good yields. Oxidative coupling of p-methoxyphenyl 2,3,4-tri-O-benzyl-1-thio-β-L-fucopyranoside (2 1) with p-methoxybenzyl 4,6-O-benzylidene-2-deoxy-2-phthalimido-β-D-glucopyranoside (16) gave selectively the α-linked disaccharide 22 in good yield.

Determination des constantes de dissociation ionique du chlorure de nitrosyle et de N2O4 dans le sulfolane

Determination of the ionic dissociation constants of nitrosyl chloride and dinitrogen tetroxide in sulpholane. A silver chloride—silver electrode is used to study electrochemical systems involving nitrosyl chloride and dinitrogen tetroxide in sulpholane: Ag↓ + NOCl ⇌ AgCl↓ + NO+ + e- and Ag↓ + NOCl + NO-3 ⇌ AgCl↓ + N2O4 + e- The dissociation constants of these two NO+ donors determined in this way are: K(NOCl) = 10-11.8 mol l-1 and K(N2O4) = 10-7.2 mol l-1. A titration of N2O4 solutions alone or in the presence of nitric acid is described. This titration is possible in mixtures which contain up to 90% (w/w) nitric acid.

Crystal and molecular structure of a carbohydrate-derived oxetan-3-one. Definitive evidence for a novel participation of a pyranose ring oxygen atom

The crystal and molecular structure of (1S)-5,7-anhydro-8-deoxy-1,2 :3,4-di-O-isopropylidene-1-O-methyl-D-glycero-D-galacto-octos-6-ulose has been determined by X-ray analysis. It crystallizes in the tetragonal P41(P43) space group, with a=b= 10.239(5), c= 16.369(7)A, Z= 4. The structure was solved by direct methods and refined to an R value of 5.3%. The octose chain is bent in such a way as to keep C-2, -3, -4, and -5 in the same plane. The formation of this compound during the methanolysis of 7,8-dideoxy-7-diazo-1,2 :3,4-di-O-isopropylidene-α-D-galacto-octos-6-ulopyranose(3) by participation of the pyranose ring oxygen atom is discussed in the light of current ideas on diazo-ketone substitution.

Preparative synthesis of 1-deoxy-D-erythro-2-pentulose and some of its derivatives

Methyl 4,6-O-benzylidene-2-deoxy-α-D-erythro-hexopyranosid-3-ulose (1) was converted, by means of lithium hydroxide in a two-phase system, into 3,5-O-benzylidene-1-deoxy-keto-D-erythro-2-pentulose (2) in 55% yield. Compound 2 was further characterized as its (2,4-dinitrophenyl)hydrazone 3, its 4-acetate 4, and the 4-benzoate 5. The configurational assignment for the corresponding pentitol derivatives (6 and 8) of 2 was achieved by 1Hmr analysis of the cyclic carbonates 11 (from 6) and 13 (from 8) and confirmed by comparing the physical constants of the 1-deoxypentitols having the D-ribo (12) and D-arabino (14) configurations with literature data. Hydrolysis of 2 with mild acid afforded the title ketose (9) as a syrup that gave a crystalline (2,4-dinitrophenyl)hydrazone (10), and an acyclic triacetate (15) as an oil. A mechanism for the chain degradation of compound 1 to give 2 is proposed.