g-factor of magnesium particles of diameter between 10 and 30 Å

ESR measurements of Mg particles smaller than about 40 Å show evidence for a quantum size effect on the g-value. The large g-shift of our bulk Mg has allowed us to follow the evolution of the g-factor as a function of particle size. The theoretical model of Myles and Buttet, which predicts a gradual change from the bulk g-value to the free electron g-value when the size decreases is in qualitative agreement with the experimental data.     

Chiral discrimination of dansyl-amino-acid enantiomers on teicoplanin phase: sucrose-perchlorate anion dependence

The chiral recognition mechanism for a series of d,l-dansyl-amino-acids (test solutes) on a teicoplanin stationary phase was investigated in reversed phase liquid chromatography (RPLC). The effect of both a surface tension modifier (sucrose) and a chaotropic agent (perchlorate anion) on the enantiomeric separation was studied by varying their concentration, c, in the mobile phase. The thermodynamic data supported the fact that the sucrose molecule acted only on the hydrophobic part of the interaction teicoplanin/dansyl-amino-acid and not on the specific chiral part. It was demonstrated that the enhancement of the separation factor observed as the perchlorate salt concentration increased in the mobile phase was enthalpically controlled owing to stereoselective bonding interactions. Such behavior was used to optimize the chromatographic conditions for separation of dansyl-amino-acids on teicoplanin.     

Solid-Phase Extraction and LC with Fluorescence Detection for Analysis of PAHs in Rainwater

The efficiency of extraction of polycyclic aromatic hydrocarbons (PAHs) from rainwater by solid-phase extraction (SPE) with three different types of cartridge, and analysis by high-performance liquid chromatography with fluorescence detection, are discussed in this paper. Three cartridges were investigated but only one was suitable. After equilibration in a desiccator for 65–80 h or in ambient air for 90–100 h the SPE cartridges were activated with 5 mL dichloromethane then 5 mL 2-propanol. The volume of sample passed through the cartridges was 50 mL; after loading of the sample the cartridges were dried under vacuum for approximately 20 min by application of a pressure of 15 mbar to the SPE manifold. The PAHs were eluted with 5 mL dichloromethane–hexane, 50:50 (v/v). The flow rate used for conditioning, sample loading, and elution was 2.5 mL min⁻¹, achieved by application of a pressure of 6 mbar. For analysis of PAHs in rainwater, recovery was between 67 and 99%, the relative standard deviation varied between 2 and 5%, and the detection limits of the method were less than 16.9 ng L⁻¹ for several PAHs. These optimum conditions were used for analysis of rainwater collected between June 2002 and May 2003 at two sites in Alsace (eastern France) and 17 PAHs were quantitatively determined. Concentrations varied between 1.6 and 968.1 ng L⁻¹.     

On the origin of the thermostabilization of proteins induced by sodium phosphate

The B1 domain of protein L shows a linear rise in thermostability with increasing concentrations of sodium phosphate. Equal behavior is observed for a set of mutant proteins where surface lysines are mutated to noncharged residues, but the mutant's thermostabilities show different sensitivities to phosphate, encoded in the varying slopes observed (mi). The melting temperature in the absence of the cosolute also correlates linearly with mi. The stabilizing effect of the phosphate ion reaches a saturation point, which has been experimentally determined for protein L (1610 mM phosphate). These results indicate that the phosphate-induced stabilization is an inherent property of the protein, encoded in the amino acid sequence. Changes in stability upon mutation are attributed to a redistribution of the overall network of solvated surface charges. Stabilization by phosphate is understood in terms of interactions with the protein surface, reducing the unfavorable contacts between like charges, maximizing the number of accessible conformations of the surface-charged side chains, and optimizing solvation.     

Role of the Na+ ion on phenol derivatives/hydroxypropyl-beta-cyclodextrin complex formation on porous graphitic carbon phase

The reversed-phase liquid chromatography retention of phenol derivatives was investigated over a concentration range of sodium chloride (0-10(-2) M) and hydroxypropyl-beta-cyclodextrin (HP-beta-CD) (0-35x10(-3) M) using a porous graphitic carbon (PGC) stationary phase and a methanol/water mixture (50:50 (v/v)) as the mobile phase. A theoretical treatment was developed to investigate the effect of the sodium chloride and hydroxypropyl-beta-cyclodextrin on the equilibrium between the solutes with the PGC surface and the aqueous medium, respectively. The thermodynamic parameter variations were calculated using van't Hoff plots. It was expected that the sodium ion acted on the solute-PGC association process by modifying the surface tension of both the bulk solvent and the PGC surface. The phenol derivative/HP-beta-cyclodextrin complexation was shown to be entropically controlled for all the solutes except for the one which contained the -NO2 group in its structure, i.e. the nitro phenol derivative. A comparison of the compensation temperature of the solute-PGC association process when sodium chloride and HP-beta-CD concentration changed in the mobile phase led to the conclusion that these two modifiers acted via a variation in the hydrophobic effect.