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Kinetic analysis of the aggregation of complexes formed by columnar types of α- and γ-cyclodextrins (α-CDcol and γ-CDcol) and poly(alkylene glycols) is performed by the dynamic light scattering method. For comparison, analogous studies were conducted for systems containing initial α- and γ-cyclodextrins (α-CD and γ-CD). Upon the aggregation of systems containing α-CD, the number of nuclei with critical sizes slowly increases at the initial part of kinetic curve throughout the solution bulk; when some limiting concentration and sizes of formed aggregates are achieved, the system is transformed into the gel-like state. The aggregation of γ-CDcol-poly(ethylene glycol) system proceeds into two stages. At the first fast stage, aggregates are formed by particles representing single-strand inclusion complexes composed of one γ-CDcol molecule and two units of ethylene oxide. At the second, much slower stage, aggregates are formed by two-strand complexes composed of one γ-CDcol molecule and four units of ethylene oxide. It follows from the comparison of aggregative properties of γ-CDcol-poly(ethylene glycol) and γ-CDcol-poly(propylene glycol) systems that the rate of aggregation is much higher in the second case.

A new method for the synthesis of associates of cyclodextrins (CDs) of the columnar type consisting of the precipitation of CDs from aqueous solutions into acetone at lowered temperatures is developed. It is shown that columnar structures exist in both a crystalline state and in aqueous solutions. Hydrodynamic radii and molecular masses of noncovalent columnar structures (NCSs) in aqueous solutions are determined by the dynamic and static light scattering methods. The degree of association of noncovalent columnar polymers is ∼40. It is revealed the NCS associates based on β-CD are stable and their hydrodynamic radius Rh is equal to 100 ± 10 nm. The kinetics of interactions of initial β-CD and NCS with poly(propylene oxide) (PPO) is studied. The pattern of kinetic curves of Rh growth upon interaction between NCS and PPO indicates that the aggregation of the particles of polymer inclusion complex proceeds in the regime of reaction-limited cluster-cluster aggregation. Kinetic curves describing the interaction processes between β-cyclodextrin and PPO are characterized by the presence of induction period t0. At t > t0, Rh ∞ t0.56 which is typical for the diffusion-limited cluster-cluster aggregation. Schemes of the formation of polymer inclusion complexes between initial β-CD or NCS and poly(propylene oxide) are proposed. Comparison of kinetic data on the complexation of β-CD in solution in the form of associates of two types with PPO demonstrates that columnar forms of associates are reactive species acting as macroreceptors.

A simple procedure is proposed for the detection of association of cyclodextrins (CDs) and their derivatives in aqueous solutions by analyzing the curves of titration of these substances with dyes. Dissociation constants of cyclodextrin-dye complexes and concentrations of sites involved in the complexation are determined by the nonlinear regression analysis. The processes of CD association were characterized using deviations of the function of CD saturation with ligands from a simple scheme CD + ligand ⇆ complex. Two association mechanisms were disclosed: cooperative association (for α-CD and dihydroxypropyl-β-CD) and step association (for β-CD, dimethyl-β-CD, hydroxypropyl-β-CD, and γ-CD). In the case of stepwise-associating compounds, association constants for head groups of cyclodextrins are found to vary from 3 × 103 to 8 × 103 M−1. The titration data on CD association are confirmed by studying solutions of the above compounds using dynamic light scattering.