Analysis of the thermal fluctuations in inclusion complexes of genistein with β-cyclodextrin derivatives

Elastic incoherent neutron scattering was employed to investigate the molecular mobility of inclusion complexes, formed by two beta-cyclodextrin (beta-CD) derivatives, namely (2-hydroxypropyl)-beta-cyclodextrin (HP-beta-CD) and methyl-beta-cyclodextrin (Me-beta-CD), with Genistein (Gen), a phytoestrogen having antioxidant and antic-arcinogenic activities, compared to the physical mixtures and single components. The results, collected in the 20-300 K temperature range, revealed a purely vibrational dynamics up to similar to 100 K, where a first anharmonic contribution, corresponding to the methyl rotational dynamics, was observed and represented by an Arrhenius trend. At higher temperatures, a second anharmonic process, also found to obey an Arrhenius-like behavior, occurred at T-d and was mainly ascribed to the relaxation of the H-bond network formed by host and guest molecules. Enthalpy and entropy changes associated to the activated anharmonic processes were obtained. The picoseconds timescale dynamics was finally connected to the thermal stability, suggesting HP-beta-CD as the most effective carrier for Gen.