Quasielastic small-angle neutron scattering from heavy water solutions of cyclodextrins

TL;DR

This paper develops a comprehensive model for quasielastic neutron scattering in heavy water solutions of cyclodextrins, enabling detailed analysis of molecular dynamics and solute-solvent interactions.

Contribution

It extends static excluded volume theory to dynamic cases, providing simplified expressions for QENS spectra and insights into molecular diffusion and hydration shells.

Findings

The model accurately describes QESANS spectra of cyclodextrins in D2O.

It yields diffusion coefficients consistent with experimental data.

Potential to analyze solute-solvent interactions beyond the uniform fluid approximation.

Abstract

We present a model for quasielastic neutron scattering (QENS) by an aqueous solution of compact and inflexible molecules. This model accounts for time-dependent spatial pair correlations between the atoms of the same as well as of distinct molecules and includes all coherent and incoherent neutron scattering contributions. The extension of the static theory of the excluded volume effect [A. K. Soper, J. Phys.:Condens. Matter 9, 2399 (1997)] to the time-dependent (dynamic) case allows us to obtain simplified model expressions for QENS spectra in the low Q region in the uniform fluid approximation. The resulting expressions describe the quasielastic small-angle neutron scattering (QESANS) spectra of D2O solutions of native and methylated cyclodextrins well, yielding in particular translational and rotational diffusion coefficients of these compounds in aqueous solution. Finally, we discuss the full potential of the QESANS analysis (that is, beyond the uniform fluid approximation), in particular, the information on solute-solvent interactions (e.g., hydration shell properties) that such an analysis can provide, in principle.