Real-time monitoring of the heat of transfer of a homologous series of m-alkoxy phenols from isotonic aqueous solution to bacterial cells

Abstract

O calor de dissolução de uma série homóloga de m-alcoxifenóis numa solução isotônica osmoticamente estável e no mesmo meio contendo em suspensão células de Escherichia coli foi obtido à 298 K usando um calorímetro de batelada diferencial de condução de calor. As curvas calorimétricas mostram uma dissolução inicial rápida do soluto, seguida por um processo exotérmico. A partir dos calores de solução, o calor de transferência (Q trs ) destes compostos da solução aquosa para as células, foi calculado. Q trs é exotérmico e aumenta com a hidrofobicidade dos compostos, devido às conseqüências biológicas do processo de interação com a fase lipídica.Heats of dissolution of a homologous series of m-alkoxy phenols in an osmotically stable isotonic solution and in the same media containing a suspension of Escherichia coli cells were obtained by a differential heat conduction batch calorimeter at 298 K. The calorimetric curves show an initial rapid endothermic dissolution of the solute, followed by an exothermic process. From the heats of solution, the heat of transfer (Q trs ) of these compounds from the aqueous solution to the cells was calculated. The heat of transfer is exothermic and increases with the hydrophobicity of the compounds due to the biological consequences of the interaction process with the lipidic phase.Keywords: lipidic phase transfer, biological calorimetry, m-alkoxy phenols, Escherichia coli IntroductionThe importance of thermodynamic data for the characterization of drug action was emphasized in recent papers. [1][2][3][4] There is much interest in the relationship between biological response, BR, and drug structure, and the parameter most frequently used to study this relationship is the partition coefficient K D . 5 Values of K D for a wide range of structures have been determined, 5 but usually at only one temperature. In a very few instances, more detailed thermodynamic data are available to describe the transfer of a molecule from aqueous to non-aqueous solvents.Selection of the appropriate non-aqueous solvent to represent the properties of a biological system is, however, a serious problem. 1-Octanol is the most commonly used solvent for a wide variety of systems. The successful use of 1-octanol/water partition coefficients has been ascribed to its hydrophobic and hydrophilic properties 6 and to its solvating and associating properties. 7 However the matter is still open to investigation and no definite choice of an appropriate solvent can be made until the solution thermodynamics of such systems are known in much greater detail than it is at present. Kinkel et al. 8 discussed the use of the van't Hoff isochore to deduce values of enthalpy change which is inappropriate when the solvent pair used for the partition studies has (i) high mutual solubility and (ii) molecular states which are temperature sensitive. They suggest that the 1-octanol/water system suffers such limitations. Beezer and co-workers 9,10 have shown that the van't Hoff determined enthalpies of transfer of resorcinol monoethers ...