Interactions in the model system alpha-cyclodextrin-glycerol - Experimental and theoretical study

The association between alpha-cyclodextrin and glycerol has been studied using experimental and theoretical methods. The experimental technique used was microcalorimetric stepwise titration at 288.15, 298.15 and 313.15 K. The formation of a 1:1 complex between alpha-cyclodextrin and glycerol, in aqueous solutions, is indicated. There was no temperature dependence of the observed parameters. The thermodynamic parameters were K = 1.34 +/- 0.07, Delta H degrees = (-3.1 +/- 0.1) kJ mol(-1), Delta G degrees = (-0.7 +/- 0.1) kJ mol(-1) and Delta S degrees = (-8 +/- 4) J K-1 mol(-1) (Gibbs energy and entropy values calculated for 298.15 K). Molecular dynamics simulations have also been carried out. The average structures, obtained from 100 ps of dynamics, are compared with the solvated 'empty' alpha-cyclodextrin average structure. The dynamics calculations show that there is a structurally and energetically favourable association between the molecules, which is in good agreement with the experimental findings.