Showing papers by "Francesc Mas published in 1998"

Use of activity coefficients for bound and free sites to describe metal–macromolecule complexation

Abstract: A thermodynamic formalism to describe the small molecule–macromolecule complexation equilibrium, based on the concept of free and occupied sites (formal species) is presented. The formalism is particularly useful in systems with a large number of species and allows for the inclusion of either transport phenomena or adsorption on the boundary of the system. The homogeneous and independent complexation behaviour is denoted ideal complexation. All other behaviours of complexation are treated as deviations from such an ideal system by means of their activity coefficients, this allows the definition of a thermodynamical equilibrium constant, K, for any complexation process, written in terms of formal species. Irrespective of the model of complexation considered in the system, the concentration equilibrium relationship for formal species tends to K when the concentration of the small molecule tends to vanish (limit of ligand excess). The experimental recording of activity coefficients is straightforward and there is no need for numerical derivatives of experimental data. The analysis of the activity coefficients vs. the free metal concentration plots allows an easy and general characterization of the complexation process. Two particular cases of non-ideal complexation (interactions between bound sites and the presence of chelates) are selected to illustrate the general characteristics of the activity coefficients, and to relate them to the affinity spectrum. Expressions for the first two moments of the affinity distribution in terms of the characteristics of the activity coefficients are given.

Application of Maximum Entropy Formalism in the Determination of the Affinity Spectrum in Macromolecular Complexation

Abstract: Binding of small molecules to heterogeneous ligands and/ or adsorption on heterogeneous surfaces with a multiplicity of specific binding sites is of great importance in many fields, ranging from the analysis of interactions between receptors and ligands in biochemistry to environmental sciences. This paper presents the application of the Maximum Entropy (MaxEnt) formalism to the calculation of the Langmuirian affinity distribution function or affinity spectrum, describing the interactions between small molecules and a surface or a macromolecule. Discrete, continuous, and mixed affinity distribution functions are successfully reproduced using a very reduced number of simulated data of coverage versus free complexing agent concentration and without any a priori assumption on the number of kinds of sites. MaxEnt is also applied to experimental data previously reported in the literature. Finally, the advantages and drawbacks of applying MaxEnt formalism to the spectral analysis of coverage data are discussed.