Thermal characterization of antimicrobial peptide stigmurin employing thermal analytical techniques

Stigmurin is a peptide with amidated C-terminus (FFSLIPSLVGGLISAFK-NH 2 ) identified in the transcriptome of the scorpion Tityus stigmurus that has shown antimicrobial action against methicillin-resistant pathogens and low antihemolytic activity, and recently proved to be efficient in controlling sepsis. Despite its pharmacological potential, there is no report about thermal studies for the characterization of the amorphous solid. The objective of this work is to characterize stigmurin using thermoanalytical techniques in the solid state in an inert and oxidative atmosphere. Stigmurin presents glass transition temperature at 149 °C. The results of TG–FTIR and pyrolysis suggest that the pathways for decomposition include homolytic breakdown of the side chains of amino acid residues. Decomposition possibly begins at the N-terminus, with formation of the aromatic compounds, amines, nitriles, alcohols, and ethers among others followed by defragmentation reactions (mainly decarboxylation and deamination) and intramolecular condensation reactions. It generates compounds similar to 2,5-diketopiperazine or DKP, and releases water and low molecular mass products (CO 2 , NH 3 , CO, HCNO). The decomposition of stigmurin is an endothermic process where the product of decomposition is originated in the liquid state according to DSC-photovisual images. Stigmurin is more stable in nitrogen atmosphere than synthetic air. This approach provides important information about the thermal decomposition of stigmurin, a molecule endowed with potent antimicrobial activity, supplying relevant parameters (temperature, degradation products, etc.) for technological strategies focusing on quality control and development studies of preformulation involving stigmurin and synthetic peptides in general.