Synthesis, characterization, thermal and spectroscopic studies and bioactivity of complexes of meloxicam with some bivalent transition metals

Complexes of meloxicam with Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) were prepared by aqueous precipitation. The compounds were characterized by means of X-ray powder diffractometry, infrared spectroscopy, theoretical calculation, elemental analysis (CNH), differential scanning calorimetry, simultaneous TG/DTG-DTA and evolved gas analysis (EGA). The results obtained from the TG/DTG-DTA curves and elemental analysis made it possible to establish the general formula of these compounds as [M(Hmel)2(H2O)2]nH2O, where M = Mn(II), Co(II), Ni(II); Cu(II) and Zn(II); Hmel = meloxicam and n = 2 (Mn, Co, Ni, Zn) and 1 (Cu). The simultaneous TG/DTG-DTA data provided previously unreported information about the thermal stability and thermal decomposition of these compounds in dynamic air and nitrogen atmospheres. The EGA showed the remarkable influence of the atmosphere in the thermal decomposition mechanism of these complexes, and it was also possible to identify the main gaseous products of thermal degradation. The lowest energy model structure of the Mn(II), Ni(II) and Zin(II) complexes has been proposed by using the density functional theory at the B3LYP/6-311++G(d) level of theory, and the theoretical spectra were calculated. The antibacterial activity of the compounds was also evaluated in relation to S. aureus by the diffusion method in agar, and the compounds showed little activity. The anti-inflammatory activity of the meloxicam–copper complex was also evaluated in vivo by the rat paw edema method. The compound showed no anti-inflammatory activity, which may have been due to loss of intrinsic activity or poor oral absorption caused by low solubility.