A convenient method for the measurements of transverse relaxation rates in homonuclear scalar coupled spin systems.

A new solution-state NMR method is proposed to determine apparent transverse NMR relaxation rates in both weakly and strongly scalar coupled two-spin systems.

A combined spin trapping/EPR/mass spectrometry approach to study the formation of a cyclic peroxide by dienolic precursor autoxidation.

The spontaneous addition of air oxygen to a dienolic compound, yielding a cyclic peroxide, was followed by spin trapping (ST) combined with EPR spectroscopy and mass spectrometry (MS). Using two different nitrones, the ST/EPR study allowed the detection of the spin adduct of a radical intermediate, and the radical centre in the addend was identified after similar experiments performed with two different (13)C-labelled analogues of the substrate. The media were also submitted to electrospray ionisation, in both positive and negative modes, for structural characterisation of the spin adducts by tandem mass spectrometry.

Distinction and quantitation of sugar isomers in ternary mixtures using the kinetic method.

Quantitative isomeric analysis of fructose, galactose, and glucose was achieved using electrospray ionization and trimeric ion dissociation with data analysis by the kinetic method. Several L-amino acids and divalent metal cations were tested to select the best systems for isomeric distinction and quantitation of each monosaccharide. High discrimination could be achieved for most tested systems, and serine/Cu(2+) and aspartic acid/Mn(2+) were selected for quantitative analysis due to their ability to strongly distinguish the three analytes and to allow long-term reproducible measuring conditions.

Complex adsorption of short linear alkanes in the flexible metal-organic-framework MIL-53(Fe).

This investigation is based on a combination of experimental tools completed by a computational approach to deeply characterize the unusual adsorption behavior of the flexible MIL-53(Fe) in the presence of short linear alkanes. In contrast to the aluminum or chromium analogues we previously reported, the iron MIL-53 solid, which initially exhibits a closed structure in the dry state, shows more complex adsorption isotherms with multisteps occurring at pressures that depend on the nature of the alkane. This behavior has been attributed to the existence of four discrete pore openings during the whole adsorption process.

Solid state nuclear magnetic resonance as a tool to explore solvent-free MALDI samples.

Solid-state Nuclear magnetic resonance (NMR) was used here to explore structural characteristics of samples to be subjected to matrix-assisted laser desorption/ionization (MALDI) and prepared without the use of any solvent. The analytical systems scrutinized in NMR were mixtures of a 2,5-dihydroxybenzoic acid (2,5-DHB) matrix and caesium fluoride (CsF), used as the cationization agent in synthetic polymer MALDI mass analysis, at different molar ratios (1:1, 5:1, and 10:1). Complementary information could be obtained from 13C, 133Cs, and 19F NMR spectra.

Alternative spectrofluorimetric determination of short-chain volatile fatty acids in aqueous samples.

This paper presents a simple, rapid, and accurate method suitable for on-site measurement of short-chain volatile fatty acids (SCFA) in various environmental samples. This fluorimetric method involves a derivatization step of SCFA with N-(1-naphthyl)ethylenediamine (EDAN) and allows determination of acetic, butyric, propionic, valeric, lactic, succinic, and p-hydroxybenzoic acids in approximatively 10 min. To evaluate specificity and accuracy of the method, both laboratory-made waters and real samples ranging from wastewater plant and river to soils and composts have been tested.

A solid-state NMR study of lead and vanadium substitution into hydroxyapatite.

A systematic study on cationic and anionic substitution in hydroxyapatite structures was carried out, with the aim of understanding the impact of ion exchange on the crystalline structure and properties of these materials. Lead and vanadium were chosen for the exchange, due to their known effects on the redox and catalytic properties of hydroxypatites. Hydroxyapatites with variable Pb and V contents, Pb(x)Ca(10-x)(VO(4))(y)(PO(4))(6-y)(OH)(2) (x = 0, 2, 4, 6, 8 and 10 for y = 1; y = 0, 0.

Hückel-Lewis projection method: a "weights watcher" for mesomeric structures.

A new approach to extract the coefficients and weights of Lewis structures from the Hückel wave function is designed: Hückel-Lewis projection (HL-P). The weights are obtained by projection on overlapping Lewis structures. This straightforward alternative to ab initio approaches is detailed and used on typical cases, including acrolein, allyl radical, pyrrole-like systems, and imidazolylidene.