Being a drug, piroxicam has been studied in various heterogeneous media, such as cyclodextrins (CD), reversed
micelles, and human serum albumin (HSA) protein. For aqueous CD solutions, it has been shown that neutral species of 1 form a 1:1 complex through the benzothiazine part of the molecule. The ESIPT emission is allowed, and it is attributed to the hydrophobicity of the CD cavity. This leads to increased inclusion of intramolecularly hydrogen-bonded enol tautomer 1a by converting the anionic form into an encapsulated neutral one.The spectroscopic behavior of 1 in reverse micelles
is similar to the one observed in -CD. The equilibrium between neutral and anionic forms has been found very sensitive to water content and pH of the environment. At pH = 4, the neutral form of the drug is preferentially located in the interfacial region between hydrophobic and hydrophilic domains, whereas at pH = 7, the anionic species is prevalent and is deeper inside the water core of the reversed micelle.These findings reflect the sensitivity of the drug to traces of water in both protic and aprotic solvents.