Thermal and biological properties of the Schiff base N,N′-bis(salicylidene)-1,2-phenylenediamine, a potential adjuvant to antibiotic therapy

• Physical and biological characterization of Schiff base salophen.
• Temperature dependence on Raman spectra of salophen.
• Phase transition from solid to liquid induced by thermal effects.
• A potential adjuvant to antibiotic therapy.

Schiff base N,N′-bis(salicylidene)-1,2-phenylenediamine, salophen, is a substance that presents synergism when combined with amikacin against Staphylococcus aureus and Escherichia coli. Measurements of temperature dependence of the Raman spectra of salophen combined with thermal analysis investigations are presented. The room temperature crystalline structure seems to be stable up to the temperature where the phase transition from solid to liquid (433–443 K) is observed. The Raman spectra in the temperature range 433–443 K were observed to be characterized by the loss of external vibrational modes, in accordance with thermal analysis curves. According to thermogravimetric analysis, salophen shows a weight loss variation in the temperature range 300–453 K corresponding to 5% loss in weight, which is attributed to dehydration and materials melting temperature. The enthalpy (ΔH) obtained from the integration of the differential scanning calorimetry peak at melting (Tm = 438 K) and decomposition temperature (Td = 484 K) is founded to be – 91 J/g and 239 J/g, respectively. Finally, it was carried out biological assays to evaluate the antibacterial potential of the salophen.