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The kinetics and metabolism of L-alpha-glycerylphosphoryl-choline (alpha-GPC) were investigated in male and female rats after i.v. (10 mg/kg) and oral doses (100-300 mg/kg). alpha-GPC was labelled with [14C]-glycerol ([14G]-GPC) or [14C]-choline ([14C]-GPC). Different kinetic and metabolic profiles were observed after i.v. and oral administration. It is assumed that alpha-GPC is hydrolyzed by phosphodiesterases in the gut mucosa. The different labelled metabolites have different kinetic properties of absorption, distribution and clearance, leading to different blood concentration-time curves of total radioactivity. Both labelled compounds gave a wide distribution of radioactivity, particularly concentrated in the liver, kidney, lung and spleen compared to blood. Brain concentrations of [14C]-GPC were comparable to ([14G]-GPC) or lower than ([14C]-GPC) total blood radioactivity. The metabolite profile in the perfused brain showed a small amount of choline and two unknown metabolites, probably the same as in blood. In addition, choline was incorporated into brain phospholipids in increasing amounts within 24 h of dosing. In all cases renal and fecal excretion of radioactivity was low and comparable for [14G]-GPC and [14C]-GPC. Mostly the administered radioactivity was exhaled as 14CO2, this degradation being faster and more pronounced for the glycerol-labelled metabolites than for the choline-labelled metabolites for both routes of administration. In all cases the results were the same for male and female rats.

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The reduction of hexavalent chromium, Cr(VI), by hydrogen peroxide in both buffered and non-buffered aqueous solutions was investigated as a function of concentration, pH, ionic strength, effect of radical scavengers, temperature and pressure. The rate of the reaction between Cr(VI) and hydrogen peroxide exhibited a strong dependence on the pH of the reaction mixture, viz. a decrease in reaction rate with increasing pH from 1.0 to 7.0. For a 2.5 x 10 -4 mol·dm -3 Cr(VI) solution, a H 2 O 2 concentration of at least 10 times the initial Cr(VI) concentration was required for complete reduction in this pH range. Neither the ionic strength of the reaction mixture, nor the presence of a radical scavenger had an effect on the rate of the ratedetermining step. From the temperature dependence of the reaction the activation enthalpy (∆H ≠ ) was calculated to be 10.4 ± 0.5 kJ·mol -1 and the activation entropy (∆S ≠ ) to be -186 ± 3 J K -1 ·mol -1 for the rate-determining step. The volume of activation (∆V ≠ ) was found to be -6.1 ± 0.5 cm 3 ·mol -1 from the pressure dependence of the reaction rate. The empirical data could be fitted to: k obs = k[H + ][H 2 O 2 ]/(K a + [H + ]), with k = (48.4 ± 1.4) x 10 3 dm 3 ·mol -1 ·s -1 and K a the acid dissociation constant of H 2 CrO 4 . A reaction mechanism in which a Cr(VI)/H 2 O 2 adduct is formed in the rate determining step, is proposed. The theoretical rate law that can be derived from this mechanism is in agreement with the empirical rate law.

The self-metathesis reaction of 1-octene with several well-known Grubbs-type precatalysts and the new Z-selective Grubbs precatalyst were studied with molecular modeling. The obtained Gibbs-free energy values for all the steps during the productive metathesis of 1-octene were compared to the values obtained for some low catalytic activity precatalysts. Determining how the Gibbs-free energy values of highly active precatalysts compare to that of low catalytic activity precatalysts gave a deeper insight into the mechanism. The questionable correlation of the theoretically observed trends with those obtained experimentally does point to the need to be very cautious when making assumptions from theoretical results without a sufficiently large dataset.