Thermal analyses as tools for proving the molecular imprinting with diosgenin and sclareol in acrylic copolymer matrices

Abstract

Thermogravimetric analysis (TG), derivative thermogravimetry (DTG), differential scanning calorimetry (DSC), dynamic mechanical thermal analysis, simultaneous differential thermogravimetry (SDT) coupled with mass spectrometry (MS), and pyrolysis coupled with gas chromatography/mass spectrometry (Py-GC/MS) were used to characterize molecularly imprinted polymers (MIPs) obtained with two anti-cancerous template molecules, diosgenin and sclareol, imprinted in acrylonitrile–acrylic acid copolymer matrices. First of all, TG analyses revealed a specific mass loss in the temperature range 220–300 °C characteristic to diosgenin-MIPs, while for the sclareol-MIPs, the specific interval was 100–240 °C. Further, the DSC analyses evidenced two major aspects: first, that the copolymer matrices have a single glass transition temperature (T g), which confirms the random statistic copolymer structure, an essential characteristic of a homogenous MIP matrix; secondly, both templates influence the T g values of the MIPs, fact that is an additional proof of molecular imprinting. The SDT results confirmed the TG and DSC results and, additionally, proved that the system with higher acrylic acid content generates stronger template–matrix interactions via hydrogen, van der Waals, and other non-covalent forces, fact that appears as an increased thermal stability on the TG curve and a higher maximum for template decomposition on the DTG curve. The MS results evidenced that a single mass fragment, 139 ± 1 m/z, characteristic for the class of steroid sapogenines of which diosgenin belongs, is enough to prove, qualitatively and quantitatively, the molecular imprinting and the template elution. As global conclusion, the applied thermal analyses proved to be exceptional tools for analyzing these molecularly imprinted polymers.