Imidazole-Based Monomer as Functional Unit for the Specific Detection of Paraxanthine in Aqueous Environments

Abstract

In the context of personalized medicine, the paraxanthine-to-caffeine ratio is an accepted standard for the optimization of the dose-response effect of many pharmaceuticals in individual patients. There is a strong drive towards the development of cheaper and portable devices for the detection of biomarkers, including paraxanthine and caffeine, which requires materials with high binding efficiency and specificity. We designed a recognition unit specific for paraxanthine which can discriminate molecules with small structural differences and can be used to increase the sensitivity of sensors. A number of functional units were screened by nuclear magnetic resonance for their ability to form specific binding interactions with paraxanthine in water and negligible interactions with its structural analogue caffeine. Imidazole was identified as the unit showing the most promising results and its two polymerizable derivatives were evaluated by isothermal titration calorimetry to identify the best monomer. The data suggested that 4-vinylimidazole was the most promising unit forming specific and strong binding interaction with paraxanthine. The calorimetry experiments allowed also the determination of the thermodynamic parameters of all interactions and the association constant values. Optimization of polymerization protocols in water, achieving high monomer conversions and chemical yields, demonstrate the suitability of the selected functional monomer for polymer preparations, targeting the detection of paraxanthine in aqueous environments.