Prediction of self-assembly of adenosine analogues in solution: a computational approach validated by isothermal titration calorimetry.

The recent discovery of the role of adenosine-analogues as neuroprotectants and cognitive enhancers has sparked interest in these molecules as new therapeutic drugs. Understanding the behavior of these molecules in solution and predicting their ability to self-assemble will accelerate new discoveries. We propose a computational approach based on density functional theory, a polarizable continuum solvation description of the aqueous environment, and an efficient search procedure to probe the potential energy surface, to determine the structure and thermodynamic stability of molecular clusters of adenosine analogues in solution, using caffeine as a model. The method was validated as a tool for the prediction of the impact of small structural variations on self-assembly using paraxanthine. The computational results were supported by isothermal titration calorimetry experiments. The thermodynamic parameters enabled the quantification of the actual percentage of dimer present in solution as a function of concentration. The data suggest that both caffeine and paraxanthine are present at concentrations comparable to the ones found in biological samples.

Bare carbon electrodes as simple and efficient sensors for the quantification of caffeine in commercial beverages.

Food quality control is a mandatory task in the food industry and relies on the availability of simple, cost-effective and stable sensing platforms. In the present work, the applicability of bare glassy carbon electrodes for routine analysis of food samples was evaluated as a valid alternative to chromatographic techniques, using caffeine as test analyte. A number of experimental parameters were optimized and a differential pulse voltammetry was applied for quantification experiments. The detection limit was found to be 2 × 10-5 M (3σ criterion) and repeatability was evaluated by the relative standard deviation of 4.5%. The influence of sugars, and compounds structurally related to caffeine on the current response of caffeine was evaluated and found to have no significant influence on the electrode performance. The suitability of bare carbon electrodes for routine analysis was successfully demonstrated by quantifying caffeine content in seven commercially available drinks and the results were validated using a standard ultra-high performance liquid chromatography method. This work demonstrates that bare glassy carbon electrodes are a simple, reliable and cost-effective platform for rapid analysis of targets such as caffeine in commercial products and they represent therefore a competitive alternative to the existing analytical methodologies for routine food analysis.

Rapid sucrose monitoring in green coffee samples using multienzymatic biosensor.

Amperometric biosensor utilizing FAD-dependent glucose dehydrogenase (FAD-GDH) for a specific sucrose monitoring in green coffee is described. FAD-GDH was co-immobilized with invertase and mutarotase on a thin-layer gold planar electrode using chitosan. The biosensor showed a wide linearity (from 10 to 1200 µM), low detection limit (8.4 µM), fast response time (50 s), and appeared to be O2 independent. In addition the biosensors exhibited a good operational (3 days) and storage (1 year) stability. Finally, the results achieved from the biosensor measurements of sucrose in 17 samples of green coffee (Coffea arabica, C. canephora and C. liberica) were compared with those obtained by the standard HPLC method. The good correlation among results of real samples, satisfactory analytical performance and simple use of the presented biosensor make it suitable for application in coffee industry.