Diffusions of β-cyclodextrins in mucus studied by 19F diffusion NMR

beta-Cyclodextrin (beta-CD) based materials have been widely used as drug carriers for pharmaceutical applications. To understand the diffusion of beta-CDs in mucus is important for selecting beta-CD based drug carriers for applications targeting mucosal absorption because the surfaces of many biological membranes are covered with a highly viscous aqueous mucus layer which forms relatively effective diffusion barriers for drugs. In this study, F-19 self-diffusion NMR technique has been applied to study the self-diffusions of beta-CDs in mucus. The F-19 NMR signals arose from 1-fluoroadamantane molecules entrapped in the cavities of beta-CDs. The diffusive abilities of different beta-CDs in mucus were assessed through analyzing the diffusion coefficients using the presented kinetic model, and Ogston's and Renkin's diffusion models for hydrogel systems. The kinetic results show that 2-hydroxypropyl-beta-CD and 2-Carboxyethyl-beta-CD have the smallest binding affinities to bovine submaxillary mucin and human nasal mucin among five tested beta-CDs. The mesh sizes of the bovine submaxillary mucus at different concentrations and that of the human nasal mucus were evaluated using the diffusion models. We hope that this F-19 diffusion method will be useful to study the diffusion of beta-CD based materials in other biological systems.