T-1101

The role of the average pore diameter (APD) of 1.7μm Atlantis^TM Premier BEH^TM Particles derivatized with a zwitterionic group (propylsulfobetaine) on the efficiency of their 2.1 × 50 mm hydrophilic interaction liquid chromatography (HILIC) packed columns is investigated experimentally. Van Deemter plots for toluene (neutral, hydrophobic), cytosine (neutral, polar), tosylate (negatively charged), bretylium and atenolol (positively charged) were measured on three HILIC columns packed with BEH Z-HILIC Particles having APDs of 95 Å, 130 Å, and 300 Å. The intraparticle diffusivities of the analytes across these three BEH Z-HILIC Particles were measured by the peak parking method. The experimental data reveal that the slope of the C-branch of the van Deemter plots can be reduced by factors of about 15 for toluene, 2.5 for cytosine, 6 for atenolol, 5 for tosylate, and 14 for bretylium with increasing the APD from 95 Å to 300 Å. This observation is explained by: (1) the reduced amount of the highly viscous water diffuse layer and subsequent increase of the amount of acetonitrile-rich eluent in the mesopores, (2) the localized electrostatic adsorption of the retained analytes onto the zwitterion-bonded BEH Particles, and (3) depletion/excess of the analytes into the water diffuse layer. A general model of intraparticle diffusivity was then proposed to account for the impact of the APD of Z-HILIC Particles on the solid-to-liquid mass transfer resistance of small molecules. The model highlights the relevance of the thickness of the water diffuse layer, the access of the bulk eluent into the mesopore, the localized electrostatic adsorption, and the partitioning constant of the retained analyte between the bulk eluent and the water diffuse layer.

This work presents a simple computational methodol. to determine new theor. mol. descriptor scales convenient for use in QSPR correlations and the anal. of solvation-related properties.On the basis of low-cost quantum chem. computations using DFT/COSMO approach, in particular that implemented in the ADF/COSMO-RS module of the Amsterdam Modeling Studio program package, optimized geometry and local screening charge d. of a considered mol. are obtained and related to the proposed descriptors through an a priori simple reasoning.Values of four mol. descriptors, namely volume V^*_COSMO, hydrogen bond/Lewis acidity α_COSMO and basicity β_COSMO, and charge asymmetry of the nonpolar region of the mol. δ_COSMO have been calculated and are presented for sets of 128 non-ionic organic mols. and 47 ions composing ionic liquidsRelation of the proposed scales to some others that are widely known or presented recently in the literature has been examinedAlthough the present methodol. is completely independent of any exptl. data, the theor. descriptor scales proposed here have been found to correlate linearly quite well with the resp. empirical scales (mostly R² > 0.8, and for some R² > 0.9).For non-ionic organics, just the direct proportionality provided adequate fits of the well-established prominent scales such as those of Abraham, Klamt, Kamlet-Taft, Catalan, Gutmann, and Laurence and showed only a few statistically justifiable outliers.For ions composing ILs, the linear fits of seven acidity or basicity scales presented previously with those proposed in this work were of similar quality.Examining the observed outliers, several descriptor values reported in the literature were identified as being in error.Good performance of the new descriptor scales has been demonstrated by employing them for LSER fitting of various solvation-related thermodn. and kinetic properties such as standard vaporization enthalpy, standard hydration enthalpy, air-water partition coefficient, air-IL partition coefficient, and solvent effects on the activation Gibbs energy or rate constant of SN1 and SNAr reactions.The quality of these correlations appears to be comparable to that of the correlations currently available for these properties, regardless of the role, solute or solvent, the involved mols. played.