Surface Adsorption and Bulk Aggregation of Cyclodextrins by Computational Molecular Dynamics Simulations as a Function of Temperature: α-CD vs β-CD

Abstract

The structural simplicity of native cyclodextrins (CDs) contrasts with their complex behavior in the bulk of aqueous solutions, mainly when they are combined with other cosolutes. Many scientific and industrial applications based on these molecules are supported only by empirical information. The lack of fundamental knowledge, which would allow one to rationally optimize many of these applications, is notable mainly at the solution/air interface. Basic information on phenomena such as the spontaneous adsorption of native CDs or on the structure of CD aggregates in the bulk solution is really scarce. In order to fill these gaps, a detailed computational study on the adsorption and aggregation of α- and β-CDs as a function of temperature is presented here. Our simulations reproduce, at atomic resolution, the experimentally observed much higher ability of β-CD to aggregate compared to that of α-CD at 298 K, as well as their dependence on temperature. The adsorption of both individual CDs and small CD aggregates (up to 20 molecules) to the solution/air interface is found to be negligible. 0.8 μs long trajectories of single CD molecules in aqueous solution reveal that the main differences in the behavior of both CDs are their flexibility, higher for β-CD, and the occupancy of individual intramolecular hydrogen bonds that is significantly longer for the same cyclodextrin. The aggregation pattern of α- and β-CDs is followed at the hundreds of ns time scale, allowing both the spontaneous self-assembly of cyclodextrins and their redistribution along the aggregates to be observed. This is the first attempt to study the adsorption and aggregation of native cyclodextrins by atomistic molecular dynamics simulations.

A molecular dynamics study of conformations of beta-cyclodextrin and its eight derivatives in four different solvents

“…The distributions were fitted to a Gaussian model and the FWHM values were calculated using Table S2). The rmsd value of the native βCD in water is similar to the previous MD simulation using the same force field as us (Gromos53a6) 56 ;…”

Aggregation of Cyclodextrins: Fundamental Issues and Applications

“…Computational methods, including molecular dynamics (MD) simulations, have been increasingly recognized as a valuable tool for the interpretation of experimental data [34][35][36][37][38][39].…”

“…The aggregation of single CDs and CD-guest complexes, in water, has been described in a number of recent studies [2,3,13,31,37,40,41]. Despite the efforts for understanding the factors that govern inclusion/binding with guest molecules, the precise manner in which CD molecules aggregate and the cooperative effects underlying this phenomenon are much less studied and still far from consensual.…”

“…Computer simulations have been used to rationalize the experimental findings concerning recognition [77], inclusion [36,[77][78][79], and aggregation [34,35,37,39,80]. The cooperative binding of at least two CD monomers to a guest molecule has been considered the driving force responsible for self-assembly processes in the construction of CD-based nanoarchitectures [78].…”

“…Another study [37] focused on the spontaneous adsorption of native CDs and the respective aggregates and the related dependence on temperature. It was found that the adsorption of both individual CDs and small CD aggregates (ca.…”