A critical approach to the thermodynamic characterization of inclusion complexes: multiple-temperature isothermal titration calorimetric studies of native cyclodextrins with sodium dodecyl sulfate.

Inclusion complexes based on native cyclodextrins are basic building blocks for the design of a new generation of promising materials. The design process can be optimized by maximizing the population of the desired chemical species. This is greatly facilitated by an accurate characterization of the thermodynamic parameters for their formation. A critically assessed literature review of equilibrium constants for cyclodextrin:sodium dodecyl sulfate (CD:SDS) complexes is reported. We performed multiple-temperature isothermal titration calorimetric (283-323 K) measurements for these systems, leading to the first reported heat capacity changes of binding. Data were analyzed using two thermodynamic models by homemade programs that also provide the distribution of chemical species as a function of the experimental variables. Assisted by earlier molecular dynamic simulations, a microscopic-level discussion of the contributions to the thermodynamic parameters is given. On the basis of our results, a number of recommendations to obtain reliable association parameters for CD-based inclusion complexes are listed.