Saturation transfer difference (STD) NMR has emerged as one of the most popular ligand-based NMR techniques for the study of protein−ligand interactions. The success of this technique is a consequence of its robustness and the fact that it is focused on the signals of the ligand, without any need of processing NMR information about the receptor and only using small quantities of nonlabeled macromolecule. Moreover, the attractiveness of this experiment is also extendable to the classroom. In the context of a practical NMR class, this experiment is ideal to illustrate some fundamental NMR concepts, such as the nuclear Overhauser effect and relaxation in a multidisciplinary context, bridging chemistry and biochemistry with a taste of medicinal chemistry. We use the readily available human serum albumin (HSA), 6-d,l-methyl-tryptophan (6-CH3-Trp), and 7- d,l-methyl-tryptophan (7-CH3-Trp) to introduce the STD-NMR experiment and to illustrate its applicability for ligand screening, mapping of binding moieties, and determination of the dissociation constant, in a context that can be explored or adapted to the student’s course level and topic (chemistry or biochemistry). We also cover the most important theoretical aspects of the STD experiment, calling attention to some of its limitations and drawbacks without a complex theoretical approach.

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THEDES, so called therapeutic deep eutectic solvents are here defined as a mixture of two components, which at a particular molar composition become liquid at room temperature and in which one of them is an active pharmaceutical ingredient (API). In this work, THEDES based on menthol complexed with three different APIs, ibuprofen (ibu), BA (BA) and phenylacetic acid (PA), were prepared. The interactions between the components that constitute the THEDES were studied by NMR, confirming that the eutectic system is formed by H-bonds between menthol and the API. The mobility of the THEDES components was studied by PFGSE NMR spectroscopy. It was determined that the self-diffusion of the species followed the same behavior as observed previously for ionic liquids, in which the components migrate via jumping between voids in the suprastructure created by punctual thermal fluctuations. The solubility and permeability of the systems in an isotonic solution was evaluated and a comparison with the pure APIs was established through diffusion and permeability studies carried out in a Franz cell. The solubility of the APIs when in the THEDES system can be improved up to 12 fold, namely for the system containing ibu. Furthermore, for this system the permeability was calculated to be 14×10cm/s representing a 3 fold increase in comparison with the pure API. With the exception of the systems containing PA an increase in the solubility, coupled with an increase in permeability was observed. In this work, we hence demonstrate the efficiency of THEDES as a new formulation for the enhancement of the bioavailability of APIs by changing the physical state of the molecules from a solid dosage to a liquid system.