Patrice Rubini

Quantitative carbon-13 and proton nuclear magnetic resonance spectroscopy of crude oil and petroleum products. I. Some rules for obtaining a set of reliable structural parameters

Abstract Optimum experimental conditions for a quantitative n.m.r. analysis of oil products are given together with the expected degree of repeatibility and accuracy. Conclusions are drawn regarding the possibility of using characteristic shift ranges to recognize structural features of chemical importance. In this respect aromatic carbons may be subdivided into four categories: protonated, methyl-and alkyl-substituted, and condensed (polyaromatic and benzonaphthenic carbons). A method is suggested to estimate approximately the aliphatic and naphthenic saturated carbons.

Speciation and structural aspects of interactions of Al(III) with small biomolecules

Abstract Complexes formed with low molecular mass biomolecules are the ‘dynamic or mobile units’ of Al(III), which may be involved in the absorption and transport processes of this toxic element in organisms. This paper reviews the interactions of Al(III), from speciation and structural aspects, with biologically relevant endogenous and exogenous small biomolecules such as inorganic ligands (hydroxide, fluoride, (oligo)phosphates and silicic acid), amino acids, phosphorylated amino acids, oligopeptides, biophosphates including nucleotides, phosphonates, hydroxamates, and aromatic and aliphatic hydroxycarboxylates. The importance of time in biospeciation is demonstrated on the examples of binary and ternary systems involving Al(III) and citric acid. Examples are also given for the implications of the speciation of Al(III) with such small biomolecules in biology.

Quantitative carbon-13 and proton nuclear magnetic resonance spectroscopy of crude oil and petroleum products. 2. Average structure parameters of representative samples

Abstract The n.m.r. methods described previously are tested upon a synthetic base oil made up of a mixture of alkylbenzenes, and are then applied to five heavy ends derived from the same Arabian Light crude oil. The computed structure parameters show a regular increase of the aromaticity factor and of the aromatic and naphthenic condensation degree from the middle distillate (gas oil) to the heavy residues (vacuum residue and asphalt).

Aluminium polyphosphate complexes in the mycorrhizal basidiomycete Laccaria bicolor: A 27Al-nuclear magnetic resonance study

The techniques of 27Al- and 31P-nuclear magnetic resonance (NMR) spectroscopy were used to investigate the interactions of aluminium with intracellular ligands within the mycelium of the ectomycorrhizal basidiomycete Laccaria bicolor (Maire) Orton (S238). The vegetative mycelium was grown on medium containing 0.5 mM AlCl3 for 0.5 to 3 d. The 27Al-NMR spectra showed that aluminium was rapidly taken up and accumulated into polyphosphate complexes in the vacuole. Comparison with Al-polyphosphate complexes obtained in vitro on model systems indicated that Al forms at least three mixed-solvation complexes with Pi and polyphosphates, that there is more than one complex present under any set of conditions, and that the equilibrium between these complexes shifts dramatically with Al concentration in the medium. The high phosphate concentrations in the growth medium favoured the accumulation of the Al-polyphosphate complexes. When mycelium containing Al-polyphosphate complexes was transferred to Al-free nutrient solution for 9 d, the Alpolyphosphate complexes were not remobilized. The sequestration of Al in the polyphosphate complexes could therefore make a significant contribution to the protection of mycorrhizal plants against aluminium toxicity.

Hypaphorine accumulation in hyphae of the ectomycorrhizal fungus, Pisolithus tinctorius

Tryptophan betaine or hypaphorine, is the major indolic compound detectable in free-living hyphae of the ectomycorrhizal fungus, Pisolithus tinctorius. Hypaphorine could not be detected in five other ectomycorrhizal species.

Complexes of praseodymium(III) with d-gluconic acid

Abstract The complexation of the praseodymium(III) ion with d -gluconic acid was studied by potentiometry, UV–Vis spectrophotometry, circular dichroism (CD) experiments and 1H and 13C NMR. In order to determine the coordination sites, the study of the complexation with d -galactonic and d -gulonic acids was also achieved. It was found that six different complexes are formed in solution from pH 2 to 11.5. The formation constants were determined. For four species among the six, d -gluconic acid binds the cation with deprotonated hydroxylic group(s) in addition to the carboxylate group. On the basis of the spectroscopic results, the structures of the complexes are discussed.

Carbohydrate and amino acid metabolism in Tuber borchii mycelium during glucose utilization: a 13C NMR study

The metabolism of [1-13C]glucose in the vegetative mycelium of the ectomycorrhizal ascomycete Tuber borchii was studied in order to characterize the biochemical pathways for the assimilation of glucose and amino acid biosynthesis. The pathways were characterized using nuclear magnetic resonance spectroscopy in conjunction with [1-13C]glucose labeling. The enzymes of mannitol cycle and ammonium assimilation were also evaluated. The majority of the 13C label was incorporated into mannitol and this polyol was formed via a direct route from absorbed glucose. Amino acid biosynthesis was also an important sink of assimilated carbon and 13C was mainly incorporated into alanine and glutamate. From this intramolecular 13C enrichment, it is concluded that pyruvate, arising from [1-13C]glucose catabolism, was used by alanine aminotransferase, pyruvate dehydrogenase and pyruvate carboxylase before entering the Krebs cycle. The transfer of 13C-labeled mycelium on [12C]glucose showed that mannitol, alanine, and glutamate carbon were used to synthesize glutamine and arginine that likely play a storage role.

Aluminium speciation studies in biological fluids. Part 8. A quantitative investigation of Al(III)–amino acid complex equilibria and assessment of their potential implications for aluminium metabolism and toxicity

Abstract Aluminium bioavailability has raised much interest in the last two decades because of both the acute toxicity of high doses of the metal in some therapies and the chronic toxicity of dietary intakes in respect of senile dementias. In particular, a number of common dietary acids has recently been shown to play a part in this context. Essential amino acids, which are naturally released by digestion of vegetal and animal proteins, are also present as such in a large majority of industrial foods and drinks. They may, therefore, also interact with aluminium metabolism, especially in the gastrointestinal tract where they can reach quite appreciable levels. The objective of this work was to assess the extent of such potential interactions quantitatively. Aluminium complex formation equilibria of a series of essential amino acids involving glycine (used as a reference for all glycine-like amino acids), serine, threonine and histidine, were investigated under physiological conditions of ionic strength and temperature through glass electrode potentiometry and NMR. The only significant complex identified with the four ligands is M 2 LH −2 . Simulations based on corresponding formation constants indicate that no particular risk is to be expected from these amino acids in normal conditions of alimentation and aluminium-based therapy.

Complexes of aluminium(III) with glucose-6-phosphate in aqueous solutions.

The interaction of aluminium(III) with glucose-6-phosphate (GP: LH2) in aqueous solutions has been studied from pH 1 to pH 8, by pH-potentiometry and multinuclear (31P, 27Al, 13C) NMR spectroscopy. Various mononuclear species (MLH2, MLH, ML, ML2H, ML2 and MLH(-3)) and dinuclear complexes M2L2H-n (n=1-4) are formed in the system. NMR clearly indicates that GP is already bound to Al(III) at pH 1. The potentiometric speciation results are confirmed and completed by spectroscopic experiments. Many peaks are observed in the 31P NMR spectra suggesting the formation of isomeric species. An attempt to assign the signals to the corresponding complexes is made, allowing a discussion about their structure. Interestingly enough no metal ion-induced deprotonation and coordination of the alcoholic-OH functions have been observed.

Potentiometric and spectroscopic studies on the dimethyltin(IV) complexes of 2-hydroxyhippuric acid.

Equilibrium and spectroscopic (1H, 13C NMR and 119Sn Mössbauer) studies in aqueous solution are reported for dimethyltin(IV) complexes of 2-hydroxyhippuric acid (Sal-Gly). Below pH 4, oxygen-coordinated complexes MLH and ML are formed. In the pH range 5-8.5, the species MLH(-1), predominates at any metal-to-ligand ratio. The ligand exchange of this species is slow on the NMR time scale, which allows its structural characterization by NMR spectroscopy: the coordination polyhedron around the tin atom is distorted trigonal bipyramidal, with tridentate [O-,N-,COO-] coordination of Sal-Gly, involving two equatorial methyl groups. The NMR results reveal that the main cause of the distortion of the polyhedron is the large CH3-Sn-CH3 angle of 136+/-4 degrees. The presented results supplement the data available on the dimethyltin(IV)-promoted amide deprotonation of peptides, and provide further arguments for the fundamental role of the carboxylate as an anchoring group in this process.