Characterisation of Gas-Chromatographic Poly(Siloxane) Stationary Phases by Theoretical Molecular Descriptors and Prediction of McReynolds Constants.

Retention in gas-liquid chromatography is mainly governed by the extent of intermolecular interactions between the solute and the stationary phase. While molecular descriptors of computational origin are commonly used to encode the effect of the solute structure in quantitative structure-retention relationship (QSRR) approaches, characterisation of stationary phases is historically based on empirical scales, the McReynolds system of phase constants being one of the most popular. In this work, poly(siloxane) stationary phases, which occupy a dominant position in modern gas-liquid chromatography, were characterised by theoretical molecular descriptors. With this aim, the first five McReynolds constants of 29 columns were modelled by multilinear regression (MLR) coupled with genetic algorithm (GA) variable selection applied to the molecular descriptors provided by software Dragon. The generalisation ability of the established GA-MLR models, evaluated by both external prediction and repeated calibration/evaluation splitting, was better than that reported in analogous studies regarding nonpolymeric (molecular) stationary phases. Principal component analysis on the significant molecular descriptors allowed to classify the poly(siloxanes) according to their chemical composition and partitioning properties. Development of QSRR-based models combining molecular descriptors of both solutes and stationary phases, which will be applied to transfer retention data among different columns, is in progress.

Physicochemical properties of fluorescent probes: experimental and computational determination of the overlapping pKa values of carboxyfluorescein.

The overlapping pKa values of carboxyfluorescein have been measured by applying a UV-vis spectroscopic method that uses absorbance diagrams and chemometric analysis. Quantum chemical calculations have also been performed in order to analyze the experimental data.

Electrochemical, pulsed-field-gradient spin-echo NMR spectroscopic, and ESR spectroscopic study of the diffusivity of molecular probes inside gel-type cross-linked polymers.

The permeability of five gel-type synthetic resins, obtained by polymerization of 1-vinylpyrrolidin-2-one cross-linked with N,N'-methylenebisacrylamide (1, 2, 3, 4, and 5 wt %) and swollen by N,N-dimethylformamide (DMF), has been analyzed. The diffusion of 2,2,6,6-tetramethyl-4-oxo-1-piperidinyloxyl (TEMPONE) was studied by ultramicroelectrode voltammetry. Similar measurements were performed for solutions of non-cross-linked poly(vinylpyrrolidone) in DMF. To provide information on the rotational mobility of TEMPONE and the translational mobility of DMF, electron spin resonance (ESR) spectroscopic and pulsed-field-gradient spin-echo nuclear magnetic resonance (PGSE-NMR) spectroscopic experiments, respectively, were carried out. Comparative analysis of the results obtained by electrochemical, ESR spectroscopic, and PGSE-NMR spectroscopic measurements showed that diffusivity inside the polymer framework is significantly affected by the extent of cross-linking, the size of the diffusing probe, and the presence of electrolytes.

Nanomorphology of polymer frameworks and their role as templates for generating size-controlled metal nanoclusters.

The microporous (gel-type) functional resin co-poly-N,N-dimethylacrylamide (DMAA) (88 % mol)/methacrylic acid (MAA) (8 % mol)/N,N'-methylenebisacrylamide (MBAA) (4 % mol) (MPIF(H)) is employed as the hosting framework for the production of resin-supported Pd(0) nanoclusters. The obtained composite MPIF(-)Na(+)/Pd(0) is prepared upon reducing, in ethanol, MPIF(-)Pd(2+) (0.5), obtained upon previous homogeneous dispersion of "Pd(2+)" inside the resin particles (XRMA control) through ion-exchange. Metal nanoclusters appear to be size-controlled (2.0+/-0.2 nm) and are seen to reasonably fit the predominant resin "nanopores" diameter, determined in ethanol (3.2 nm) by means of inverse steric exclusion chromatography (ISEC).