Thermodynamics of Nicotinic Acid Interactions with Some Saccharides

摘要

The interactions of nicotinic acid with α-D-glucose and maltose, and with α-, β-, hydroxypropyl-α- and hydroxypropyl-β-cyclodextrins were studied by using solution calorimetry at T = 298.15 K and pH = 3.4. The thermodynamic parameters (log10 K, Δ G∘c, Δ H∘c and Δ S∘c) were calculated for the systems in which complex formation was observed. Systems with weak interparticle interactions lacking complex formation were characterized by enthalpic virial coefficients calculated on the basis of the McMillan–Mayer theory. It was found that the complexation affinity of α-cyclodextrin to nicotinic acid is stronger in comparison to β-cyclodextrin and the mono- and disaccharides. The influence of different factors, such as the availability of the macrocyclic hydrophobic cavity, the relationship of the sizes of guest molecule to the host cavity, the presence of bulky hydroxypropyl substitutes and their structure, and the solvation of guest molecules on the stability of complexes and their thermodynamic parameters of interaction is discussed.