A theoretical framework for the prediction of molecular transport in interacting biopolymer co-solute solutions

Abstract

A theoretical framework is presented that accounts for modifications to diffusive behaviour of a small molecule resulting from an interacting biopolymer in a liquid system. The equation makes use of the equilibrium association constant (K a ) to predict the fraction of bound ligand (θ), allowing for the weighted average diffusion of free and bound ligand to be calculated. θ is shown to be calculated effectively under all concentration regimes (ligand in excess, host in excess and equimolar) and it is demonstrated that even for relatively small K a values (weak interactions), there is still likely to be a non-negligible proportion of ligand bound to the host macromolecule. Modelling of the effective diffusion coefficient (D eff ) vs K a using the developed equation shows that, in a system with functional food/nutraceutical relevant molecular sizes for ligand and host (for example, 0.6 and 3.5 nm), the D eff values of the ligand can be reduced more than 5 fold with the presence of only a moderate ligand-host interaction (K a ∼2.5 x 103 M−1). The practical value of this approach is demonstrated by determining the fraction of bound ligand for an experimentally determined D eff . This work aims to demonstrate the importance of understanding the impact of molecular interactions in solutions for the design of novel delivery vehicles.</p