RESUMO
Chitins and Chitosans with different degrees of deacetylation (DD¯) were analyzed for the first time by thermogravimetry coupled to infrared spectroscopy TG-FTIR in order to evaluate the effect of DD¯ on the thermal decomposition process. DD¯ values of chitins and chitosans were determined by 1H-NMR and structural difference were investigated by FTIR, SEM and XRD. Thermal stability of chitosan with 98, 87, 71% DD¯, chitins with 47 and 27% DD¯ and commercial α-chitin were evaluated. Thermal decomposition of chitosans occurs in two steps, while for chitins occurs predominantly in first stage under air atmosphere. Commercial chitin thermally decomposed at lower temperatures than highly deacetylated chitosan. A faster thermal degradation process was found for chitins, except for commercial sample. TG-FTIR of evolved gas evidenced a complex gaseous mixture mainly composed by ammonia, acetic acid, acetamide, water, monoxide and carbon dioxide in proportions that are deeply dependent on the DD¯.
RESUMO
Chitosans are versatile biopolymers recognized for their wide range of biological activities. However, the low solubility in neutral and basic solutions restricts the applications. Thus amphiphilic biopolymeric Schiff bases from chitosans, salicylaldehyde and glycidol were successfully synthesized and characterized using 1H-NMR, UV/Vis, FTIR, TG/DTG-DTA and tested for their antimicrobial activities against plant pathogenic microorganisms and human breast cancer cells (MCF-7). Overall, functionalization of chitosans with salicylaldehyde and glycidol with different molecular weight (Mw¯) was performed to improve the biological actives of chitosans. Thus the biological activity of the new amphiphilic compounds prepared in this work were evaluated regarding microorganisms with agricultural relevance and tumor cells. The biopolymeric amphiphilic Schiff bases showed significant effects against Pseudomonas syringae (IC50 < 5 µg mL-1) compared to the natural chitosans with medium Mw¯ (CHM 223 kDa) and low Mw¯ (CHL 64 kDa), which had IC50 values of 42 and 37 µg mL-1, respectively. In addition, they improved antitumor activity against tumor cells compared to the natural chitosan.