Investigation of Sterol uptake by a new Beta-Cyclodextrin Porous Network

This report details the synthesis and analysis of new β-cyclodextrin (β-CD) networks: KβCD-MOF-1, KβCD-MOF-1-Chol and KβCD-MOF-2. Investigations of uptake of four sterols have also been conducted. The syntheses of the crystals were achieved by a vapour diffusion method at ambient temperature and pressure using mixtures of β-CD/potassium hydroxide in a ratio of 1:20, β-CD/potassium hydroxide/cholesterol in a ratio of 1:20:⅓ and β-CD/potassium benzoate in a ratio of 1:1, respectively. The analysis of crystals was performed using nuclear magnetic resonance (NMR) spectroscopy, X-ray diffraction (XRD) and optical and scanning electron microscopy. XRD showed KβCD-MOF-1 was made of accessible β-CD channels with each layer being perpendicular to the one above and the one below it. KβCD-MOF-1-Chol had a honeycomb like structure with cholesterol present in the β-CD channels. KβCD-MOF-2 was similar to a previously reported inclusion complex, although the crystallisation methods used were different.

Changes to crystal morphology of KβCD-MOF-1 and a control crystal were investigated using optical microscopy. The results of overnight soaking of these crystals using cholesterol dissolved in ethanol showed KβCD-MOF-1 crystal remained unchanged whilst the control crystal had nucleation occur on the edges.

Four types of sterols (Cholesterol, testosterone, beta-estradiol and deoxycholic acid) were used to investigate the uptake ratio of KβCD-MOF-1 and this was achieved using proton NMR analysis. The results showed that uptake of these sterols were successful. The NMR results also showed an inverse relation between numbers of polar groups in the sterol to the uptake by KβCD-MOF-1 network. The ratios of sterols:β-CD were observed to be 1:2, 1:4, 1:2 and 1:3 for cholesterol, testosterone, beta-estradiol and deoxycholic acid, respectively.

The encapsulations of UiO-66 crystals in to vesicles were investigated using fluorescence and electron microscopy. Although fluorescence microscopy provided some evidence of encapsulation however it was not confirmed by electron microscopy positively. Therefore the results remain inconclusive.