title: Physico-chemical studies on the charge-transfer complex formed between sulfadoxine and pyrimethamine with chloranilic acid.
abstract: Thermodynamic studies on the charge-transfer complexes of sulfadoxine and pyrimethamine with chloranilic acid in non-aqueous 1,4-dioxan were investigated by spectrophotometric method. The absorption maxima for sulfadoxine and pyrimethamine were observed at 500 and 520 nm, respectively. We observed a bathochromic shift in the transitions of these complexes with respect to chloranilic acid, which absorb at 420 nm. The enthalpy of complexation was found to be -3.044 kJ/mole for pyrimethamine and -5.934 kJ/mole for sulfadoxine. Equilibrium constant values were generally high, that is 261.202 l/mole and 344.29 l/mole for pyrimethamine and sulfadoxine, respectively, at 303 K. Free energy values were negative, of the order of -14.420 kJ/mole for pyrimethamine and -15.384 kJ/mole for sulfadoxine, indicating that complex formations were exothermic. These data suggest that the complexes are very stable. Arguments are presented to support the application of charge-transfer interactions in the quantitative analysis of these drugs.
authors.affiliation: Department of Pharmaceutical Chemistry, Faculty of Pharmaceutical Sciences, University of Jos, P.M.B 2084, Jos, Nigeria. onahj@unijos.edu.ng
authors.forename: Johnson Ogoda
authors.initials: JO
authors.lastname: Onah
authors.forename: James Eromi
authors.initials: JE
authors.lastname: Odeiani
mesh_terms: D016227:Benzoquinones / Q000737:chemistry*; D011739:Pyrimethamine / Q000737:chemistry* / Q000302:isolation & purification; D012996:Solutions; D013056:Spectrophotometry, Ultraviolet; D013413:Sulfadoxine / Q000737:chemistry* / Q000302:isolation & purification; D013816:Thermodynamics
chemical_list: D016227:Benzoquinones; D012996:Solutions; D013413:Sulfadoxine; C014400:chloranilic acid; D011739:Pyrimethamine