Scientific Article
previous document  unige:9978  next document
add to browser collection
Title

Microscopic Protonation Deprotonation Equilibria of the Antiinflammatory Agent Piroxicam

Authors
Takacsnovak, K.
Kokosi, J.
Podanyi, B.
Noszal, B.
Tsai, Ruey-Shiuan
Lisa, G.
Testa, Bernard
Published in Helvetica Chimica Acta. 1995, vol. 78, no. 3, p. 553-562
Abstract The microscopic ionization behavior of piroxicam was investigated using two different approaches, i.e., direct UV spectroscopy and an indirect analogue approach (deductive method). The best microscopic pK(a) values (PKa12 = 4.60, pK(a21) = 5.40, pK(a22) = 2.72, and pK(a11) = 1.92) were obtained by the deductive method using as pK(a22) the pK(a) of the enolic O-methylated piroxicam 2. The results show remarkable electrostatic effects in the protonation/deprotonation equilibria, a marked increase in the acidity of the enolic function (2.68 pK(a) units) being caused by the pyridinium group. The electronic structure of piroxicam was studied based on H-1-NMR chemical shifts at various ionization states, indicating an extended electron conjugation through the molecule. The partition measurements in octan-1-ol/H2O of zwitterionic compound 3 (the pyridyl N-methyl derivative of piroxicam (1)) suggest that the two opposite charges in zwitterionic piroxicam are indeed in a close intramolecular proximity
Full text
Citation
(ISO format)
TAKACSNOVAK, K. et al. Microscopic Protonation Deprotonation Equilibria of the Antiinflammatory Agent Piroxicam. In: Helvetica Chimica Acta, 1995, vol. 78, n° 3, p. 553-562. https://archive-ouverte.unige.ch/unige:9978

162 hits

0 download

Update

Deposited on : 2010-08-06

Export document
Format :
Citation style :