Acidos biliares e actividade biologica Alguns aspectos da relacao entre a estrutura quimica e as propriedades fisico-quimicas

Aiming to established a relationship between bile acids behaviour and their chemical structures and biological activities and since the knowledge of this relationship could make a very important contribution to the interpretation, on a molecular basis of some of their physiological functions, one carried out in this work different studies of bile acids in solution. Initially, the acidity constants of cholic, deoxycholic, chenodeoxycholic and dehydrocholic acids and their glycine conjugated in an aqueous solution whose ionic strength was adjusted to 0.15 mol dm"-"3 with Na CI were determined by potentiometric titration. These determinations were carried out either using bile acids or bile acids salts aqueous solutions at three different temperatures (10, 25 and 37 deg C), which also allowed the evaluation of the temperature effect on the pK_a. The glyco cholic acid acidity constants were also determined by nuclear magnetic resonance spectroscopy under the same experimental conditions. The cholic, chenodeoxycholic and ursodeoxycholic acids acidity constants were determined by potentiometric titration at 25 deg C in various methanol / water solutions of different co-solvent concentrations. The pK_a values in water were calculated by extrapolation for 0% methanol. Sodium cholate and glyco cholate critical micellar concentrations were determined from their pKa values at different bile salt concentration. These measurements were executed at 25 deg C with various ionic strengths (0.02, 0.05, 0.10, 0.15 and 0.20 mol dm"-"3 in Na CI) allowing the assessment of the ionic strength effect on the pKa as well as on the CMC of the bile acids..Available from Fundacao para a Ciencia e a Tecnologia, Servico de Informacao e Documentacao, Av. D. Carlos I, 126, 1249-074 Lisboa, Portugal / FCT - Fundação para o Ciência e a TecnologiaSIGLEPTPortuga