Elena Alvira

Molecular modelling study of β-cyclodextrin inclusion complexes

Abstract The interaction energy between β-CD and some different molecules is determined using a simple pairwise-additive Lennard-Jones potential and the ‘rigid molecule approximation’ of the molecular mechanics approach. A comparative study of the potential energy experienced by the molecules allows us to examine the influence of size, structure and composition of the guest molecule in inclusion complex formation. The decisive factors determining the interaction potential are composition for small guest molecules and shape for large ones.

Molecular modelling study for chiral separation of equol enantiomers by β-cyclodextrin

Abstract The intermolecular forces responsible for complexation of equol, a chiral molecule, with β-cyclodextrin are determined using a molecular modelling study. The differential interactions between each enantiomer and the chiral host give rise to different configurations for the corresponding inclusion complexes which give rise to enantiodifferentiation. The van der Waals term is the main contributor to the total potential; however, the electrostatic term influences the enantioselectivity significantly since it establishes a difference between the most stable position of R- and S-equol and hence between their energies. A statistical analysis of the minimized energies is carried out to determine that R-equol is more retained than S-equol.

A model for the interaction between β-cyclodextrin and some acrylic esters

Abstract The interaction between β-cyclodextrin and some acrylic esters is determined on the basis of semi-empirical potentials including Lennard-Jones, electrostatic and hydrogen bond contributions. The interaction energy is calculated using the ‘rigid molecule approximation’ of the molecular mechanics approach. A study of the potential energy experienced by the acrylic esters inside and beside the cavity allows us to determine the evolution (position and orientation) of molecules until they form inclusion complexes. There is a correlation between the increase in interaction energy and the hydrophobicity of the alkyl group in the esters, in agreement with experimental findings.

Diels-Alder reactions in β-cyclodextrin cavities. A molecular modelling study

Abstract The catalytic effect of the β-cyclodextrin on a series of Diels-Alder reactions is explained by means of a molecular model including the calculated transition structures, their interaction with the cyclodextrin and the solvation energies of the reagents. The anomalous behaviour of the diethyl maleate is also expalined on the basis of this model.

Capacity of small molecules to form β-cyclodextrin inclusion complexes

The mobility of atoms and cyclic or spherical guest molecules inside and around β-cyclodextrin (β-CD) is analysed, along with the influence of temperature on inclusion complex formation, by means of a molecular dynamics simulation at constant temperature. The intermolecular energy is modelled by a Lennard-Jones potential and a continuum description of the cavity walls. The potential energy parameter σ principally determines the mobility of the guest inside the cavity in the CD, the preferred position and the probability of forming an inclusion complex, while the parameter ϵ is responsible for the guest staying inside or exiting from the cavity after the inclusion time. The probability of entering increases with the temperature of the process.

Physisorption in cyclodextrin cavities: an analytical model

Abstract We have studied the interaction energy between α-, β- and γ-cyclodextrin with guest molecules of different sizes, using a simple pairwise-additive Lennard-Jones potential and a continuum description of the cavity walls, assuming two types of geometries for the latter: cylindrical and conical. This simple interaction potential allows us to establish the parameter σ of the guest molecule which forms the most stable inclusion complex with each cyclodextrin, as well as the maximum size of the guest molecule above which inclusion complexes cannot be formed.

Stereochemical features of the physisorption of linear molecules in β-cyclodextrin

The aim of the present work is to analyse the dependence of the interaction energy between β-cyclodextrin and linear guest molecules on the atomic distribution of the latter. The intermolecular energy is modelled by a Lennard-Jones potential, where the molecular composition is represented by two different pairs of parameters (σ1, ϵ1; σ2, ϵ2), and a continuum description of the guest and cavity walls. The shape of the interaction potential does not depend on the symmetry of the molecular configuration, but it is related to the position of the larger atoms in the linear guest. For the differences in the interaction energy between isomers to be appreciable, the molecule must be longer than 8 Å and there must be a sudden change rather than multiple variations in the atomic size.