Analysis of malts by capillary electrophoresis

A range of malts, as well as their high- and low-molecular-mass fractions, has been examined by capillary electrophoresis in phosphate buffer, pH 2.5, and in carbonate buffer, pH 9.5, and the results have been compared with those for roasted barley and for caramels. The malts fall into two categories: (i) the lightly roasted malts, where the high-molecular-mass coloured fraction is negatively charged at pH 9.5 and positively charged at pH 2.5; and (ii) the highly roasted malts (and the roasted barley), where the high-molecular-mass fraction migrates close to the electro-osmotic flow at both pH 9.5 and 2.5, implying that it carries little or no charge. The former category shows migration patterns similar to Class III caramels, whereas the latter migrates differently from Class I, III and IV caramels as well as from the former. Capillary electrophoresis therefore has considerable potential for differentiating between malts and between malts and caramels and roasted barley. (C) 2002 Society of Chemical Industry.

Application of static charge transfer within an ionic-liquid force field and its effect on structure and dynamics

The effects of linear scaling of the atomic charges of a reference potential on the structure, dynamics, and energetics of the ionic liquid 1,3-dimethylimidazolium chloride are investigated. Diffusion coefficients that span over four orders of magnitude are observed between the original model and a scaled model in which the ionic charges are +/- 0.5 e. While the three-dimensional structure of the liquid is less affected, the partial radial distribution functions change markedly-with the positive result that for ionic charges of +/- 0.7 e, an excellent agreement is observed with ab initio molecular dynamics data. Cohesive energy densities calculated from these partial-charge models are also in better agreement with those calculated from the ab initio data. We postulate that ionic-liquid models in which the ionic charges are assumed to be +/- 1 e overestimate the intermolecular attractions between ions, which results in overstructuring, slow dynamics, and increased cohesive energy densities. The use of scaled-charge sets may be of benefit in the simulation of these systems-especially when looking at properties beyond liquid structure-thus providing on alternative to computationally expensive polarisable force fields.

Measurements of absolute, single charge-exchange cross sections of H+, He+ and He2+ with H2O and CO2

Absolute measurements have been made of single-electron charge-exchange cross sections of H+, He+, and He2+ in H2O and CO2 in the energy range 0.3-7.5 keV amu(-1). Collisions of this type occur in the interaction of solar wind ions with cometary gases and have been observed by the Giotto spacecraft using the Ion Mass Spectrometer/High Energy Range Spectrometer (IMS/HERS) during a close encounter with comet Halley in 1986. Increases in the He+ ion density, and in the He2+ to H+ density ratio were reported by Shelley et al, and Fuselier et al. and were explained by charge exchange. However, the lack of reliable cross sections for this process made interpretation of the data difficult. New cross sections are presented and discussed in relation to the Giotto observations.