Aryl boronic acid-containing molecularly imprinted polymers (MIPs) for selective binding of cis-diol containing molecules

Abstract

Molecular recognition of saccharides in aqueous media at physiological pH is a prominent problem in bioorganic chemistry. Saccharides do show minor differences in the intrinsic geometrical orientation of their hydroxyl groups. However, in aqueous media, the competition between the saccharides’ hydroxyl groups and the hydroxyl groups of water is a major challenge. The aim of this study was to synthesise a polymer that could selectively adsorb specific saccharides from an aqueous environment. This thesis describes a covalently molecular imprinted method for the selective recognition of target saccharide molecules. The synthesised MIPs (molecularly imprinted polymers) were characterised using FT‒IR, TGA, DSC, XRD and SEM. The binding capacities of these MIPs were analysed using a combination of enzymatic and UPLC‒MS/MS methods. The prepared MIPs were also investigated as potential sorbents for use in solid‒phase extraction (SPE) columns, and the binding properties of these SPE columns were evaluated. Additionally, the composition of starch (a polysaccharide) from grapevine roots was explored via a GPC (gel permeation chromatography) method. This thesis reports, for the first time, that sucrose (a disaccharide) can form a two‒site binding complex with the functional monomer 4‒AAPBA (4‒(acrylamido)phenylboronic acid). The synthesised MIPs showed selective binding towards the target molecule, sucrose. It was also found that modification of the sucrose‒targeted MIP by addition of a co‒monomer, N‒(3‒ aminopropyl) acrylamide, could improve the binding capacity of the MIP. The MIP‒SPE columns displayed excellent binding of sucrose from a standard mixed sugar solution. Selective binding of sucrose was also observed when a sample of a commercial sports beverage (reported to contain sucrose, fructose and glucose) was passed through the MIP‒SPE column. Finally, the extension of this study to a polysaccharide such as starch was considered. In order to collect information on the biological presence and nature of starch, a preliminary study on grapevine roots was undertaken. Interestingly, this thesis reports that an external factor (the use of anti‒transpirant Vapour Gard (VG)) can affect both the total starch present and the relative ratio of the starch component (i.e. amylose/amylopectin). These results would have to be kept in mind when developing MIPs to target starch, as the application of the targeted MIP would alter only the total amount of starch.