A systematic study on the interactions between carnosic acid and ethylpyrrolidine methacrylate–methyl methacrylate copolymer in supercritical media

In the present work, a systematic study on the interactions between carnosic acid (potent natural antioxidant from rosemary) and ethylpyrrolidine methacrylate–methyl methacrylate (EPyM/MMA) copolymer (synthesized in our laboratory) has been performed using different spectroscopic and thermogravimetric techniques. By comparing data obtained for the reference sample (carnosic acid + copolymer) with data of carnosic acid and copolymer alone, a polar interaction could be observed between the carboxylic acid group of carnosic acid with the tertiary amine of the EPyM/MMA copolymer, thus suggesting a charge-transfer complex of the carnosic acid molecules with the pyrrolidine nitrogen (conclusion supported by NMR, FT-IR and TGA data). In order to evaluate the possibility of using, in the near future, the copolymer as a selective stationary phase for preparative-SFC (supercritical fluid chromatography), the work has been completed by studying the remaining interactions, in the reference sample, once treated under several supercritical conditions. After the supercritical treatment (using CO2 at different pressures and temperatures), depressurization takes place in the extraction cell and the samples remaining were characterized by 1H NMR, TGA and FT-IR. From the results obtained, it can be inferred that interactions remain after supercritical treatment, thus allowing the design of selective polymers to be used in the purification of carnosic acid.