RESUMO
The separation and purification of drugs and biological compounds, which are typically weak polyprotic acids, by HPLC is the subject of numerous literature reports. The development of separation methodologies depends on the acid dissociation constants, and the HPLC offers a valuable method for determining these constants, especially when the compounds are poorly soluble in water. This review presents general basic equations and shows how they are used for determining the pKa's. It also discusses the parameters affecting the pKa's and the methods of their measurement as presented in a representative number of research papers published in the last 20 years.
Assuntos
Ácidos/química , Cromatografia Líquida de Alta Pressão/métodosRESUMO
Macrophage cells treated with L-aspartyl-L-phenylalanine methyl ester (aspartame) produced leukotrienes and other arachidonic acid metabolites. Leukotriene C4, leukotriene B4, and 15-hydroxyeicosatetraenoic acid were the major metabolites detected. The aspartame-treated macrophage cell cultures produced three times as much arachidonic acid metabolites as did the untreated control cell cultures. Leukotriene C4 was produced in the largest amount by the aspartame-treated cells.
Assuntos
Aspartame/farmacologia , Leucotrienos/biossíntese , Macrófagos Peritoneais/efeitos dos fármacos , Macrófagos Peritoneais/metabolismo , Animais , Ácido Araquidônico/metabolismo , Radioisótopos de Carbono , Células Cultivadas , Cromatografia Líquida de Alta Pressão , Ácidos Hidroxieicosatetraenoicos/biossíntese , Leucotrieno B4/biossíntese , Leucotrieno C4/biossíntese , RatosRESUMO
A general equation relating the observed retention factor to the pH of the mobile phase, the dissociation constants, and the retention factors of the different ionic species has been derived. This equation is applicable to polyprotic weak acid and base dissociation events, that is, the secondary equilibria existing in the HPLC mobile phase. It is written as: [formula: see text] where the kr values are the retention factors of the dissociated species, and Ka(r), the product of the first r-dissociation constants, [formula: see text] is related to the pH of the mobile phase: x = 2.303.pH. The derived equation was used to calculate three dissociation constants of leukotriene E4. Also, a formula is established for calculating the range of pH values where an ionic species is most likely to be predominant in the mobile phase.
Assuntos
Ácidos/química , Álcalis/química , Cromatografia Líquida de Alta Pressão/métodos , Aminoácidos/química , Concentração de Íons de Hidrogênio , Leucotrieno E4/química , Modelos Químicos , ProbabilidadeRESUMO
Electrical potentials of cerebroside and lecithin bilayers in the presence of Na+, Ca2+, and Sr2+ were measured. Calculated membrane specific resistances were about 10(7) ohm cm2. Calculated transference numbers for Na+, Ca2+, and Sr2+ were between 0.5 and 0.6, and were higher in both membranes than in free solution. Thus membranes are slightly cation selective. Specific conductances and transference numbers were then used to calculate ionic flux of membranes. Sodium ions had a much greater ionic flux in both membranes than calcium and strontium ions. The results indicate that the electrical properties of cerebroside and lecithin bilayer membranes are compatible with the structures of those membranes.