A new cocrystal of Norfloxacin, a poorly soluble fluoroquinolone antibiotic, has been synthetized by a solvent-mediated transformation experiment in toluene, using resorcinol as a coformer. The new cocrystal exists in both anhydrous and monohydrate forms with the same (1:1) Norfloxacin/resorcinol stoichiometry. The solubility of Norfloxacin and the hydrated cocrystal were determined by the shake-flask method. While Norfloxacin has a solubility of 0.32 ± 0.02 mg/mL, the cocrystal has a solubility of 2.64 ± 0.39 mg/mL, approximately 10-fold higher. The dissolution rate was tested at four biorelevant pH levels of the gastrointestinal tract: 2.0, 4.0, 5.5, and 7.4. In a first set of comparative tests, the dissolution rate of Norfloxacin and the cocrystal was determined separately at each pH value. Both solid forms showed the highest dissolution rate at pH 2.0, where Norfloxacin is totally protonated. Then, the dissolution rate decreases as pH increases. In a second set of experiments, the dissolution of the cocrystal was evaluated by a unique dissolution test, in which the pH dynamically changed from 2.0 to 7.4, stepping 30 min at each of the four biorelevant pH values. Results were quite different in this case, since dissolution at pH 2 affects the behavior of Norfloxacin at the rest of the pH values.

The problem-based learning (PBL) methodology has been applied in a set of chemistry courses at the University of Barcelona to determine the main factors that are relevant to a satisfactory application of this educational approach in different contexts (from undergraduate to master subjects). The exceptional situation resulting from the COVID-19 pandemic has also forced us to adapt this methodology from the traditional face-to-face modality to an online version. Thus, the resulting comparative study has allowed us to identify the main aspects of each subject, student background, and modality used, which are relevant to a satisfactory application of PBL. In general, the application of the PBL methodology using Moodle and BBCollaborate as live teaching platforms has a positive impact on student learning and satisfaction. Interestingly, although the face-to-face implementation is preferred to the online modality, students evaluate positively the application of online PBL with respect to the traditional online teaching. Thus, the intrinsic characteristics of PBL, which enhance the learning motivation with suitable problems to be solved in groups, makes this required collaborative work a key point to facilitate student learning.