Speciation study of the anti-inflammatory drug tenoxicam (Htenox) with Cu(II): X-ray crystal structure of [Cu(tenox) 2(py) 2]·EtOH

Abstract

A speciation study was carried out in aqueous solution of the anti-inflammatory drug tenoxicam (Htenox), under quasi-physiological conditions (temperature of 37 °C and ionic strength 0.15 M NaCl) in order to determine the acidity constants from spectrophotometric studies, the p K a values found being p K 1=1.143±0.008 and p K 2=4.970±0.004. Subsequently, the spectrophotometrical speciation of the different complexes of Cu(II) with the drug was performed under the same conditions of temperature and ionic strength, observing the formation of Cu(Htenox) 2 2+ with log β 212=20.05±0.01, Cu(tenox) 2 with log β 012=13.6±0.1, Cu(Htenox) 2+ with log β 111=10.52±0.08, as well as Cu(tenox) + with log β 011=7.0±0.2, all of them in solution, and solid species Cu(tenox) 2(s) with an estimated value of log β 012(s)≈18.7. The crystalline structure of the complex [Cu(tenox) 2(py) 2]·EtOH, was also determined, and it was observed that tenoxicam employs the oxygen of the amide group and the pyridyl nitrogen to bond to the cation.