Properties and Structure of Aqueous Solutions of Hydroxypropyl‐beta‐Cyclodextrin

Abstract

Molecules of hydroxypropyl‐beta‐cyclodextrin (HPBCD) in aqueous solution interact with each other via hydrogen bonds. Especially for concentrations beyond 50% (w/w), a strong increase in viscosity and a considerable decrease of freezable water can be determined. The addition of substances which are able to break the water structure (urea, KSCN) reduces these effects remarkably. The formation of inclusion compounds with urea could not be detected. Endothermic phase transformations confirm the presence of liquid crystalline structures at low temperatures. These liquid crystalline structures are not detectable at room temperatures, but the freeze fracture technique shows micelle‐like associates of a size of about 20 nm. Studies on the complexation of phenolphthalein as well as surface tension measurements of HPBCD solutions indicate that a minimum concentration of HPBC is necessary for the association phenomena.

Aggregation of Cyclodextrins: Fundamental Issues and Applications

“…A similar observation was found for γ-CD (10% m/v) solutions [45], at physiological pH. In both works, the self-aggregation of CD monomers is justified by intermolecular H-bonding interactions promoted by the hydrophilic rims [44,45].…”

“…These authors have also pointed out that such aggregates are acting as "structure making" [43] by tightening water-water hydrogen bonding. Ten years later, Häusler and Müller-Goymann [44] have observed that at concentrations above 50% (w/w), hydroxypropyl (HP)-β-CD self-aggregates, leading to an increase in the solution viscosity. They also found that the addition of chaotropic solutes (e.g., urea and NaCl) tends to decrease the viscosity of solutions as a consequence of CD disaggregation.…”

Porous materials via nanocasting procedures: innovative materials and learning about soft-matter organization

“…It is known from the literature 85 that these 'barrels' have an exterior which is covered by OH-groups while the interior cavity is quite hydrophopic, characterized by CH 2 groups. Due to the difficulties involved in the direct investigation (as already mentioned previously) the true solution structure of cyclodextrins in solution was still a matter of discussion 86,87 despite their high technical relevance.…”

Investigation on γ-cyclodextrin nanotube induced by -diphenylbenzidine molecule

“…In order to apply the DLS technique to the investigation on cyclodextrin nanotubes, it is necessary to ascertain the self-aggregation phenomenon of cyclodextrin itself. Actually, the existing state of cyclodextrin in pure water still remains controvertible to some extent [27,28]. Recently, the self-aggregation of cyclodextrins and inclusion complexes between cyclodextrins and guest molecules has been investigated through DLS [29][30][31][32].…”