title: [Determination of ionization constants of primaquine and study of its coordination ratio with vitamin C].
abstract: Primaquine (P) has long been used as an antimalarial drug. The following formulas are derived for determination of the ionization constants of PH3+3 by pH-titration method: Ka1 = [aH + (3 - a)Cp]/[(a - 2)Cp/aH - 1] Ka3 = [(1 - a)Cp aH - Kw]/(a Cp + Kw/aH) = (1/Ka2)[(2 - a)Cp a2H - Kw aH]/(Kw/aH + a Cp) + [(1 - a) Cp aH - Kw]/(Kw/aH + a Cp) in which Kw is the ionic product of water, a is the mole ratio of HClO4 to primaquine and Cp is the total concentration of primaquine. The ionization constants of primaquine in 50% (v/v) ethanol in water determined at 25 degrees C in the ionic strength range of 5 x 10(-3)-5 x 10(-2) mol/L are: Ka1 = (3.84 +/- 2.35) x 10(-2) (attributed to the secondary ammonium group of primaquine); Ka2 = (1.50 +/- 1.17) x 10(-8) (attributed to the tertiary ammonium group); Ka3 = (2.07 +/- 0.27) x 10(-10) (attributed to the primary ammonium group). The coordination ratio of primaquine to vitamin C in the above solvent is determined by continuous variation and mole ratio methods based on pH and conductance measurements to be 1:1, indicating that the coordination compound formed in the solution is mainly a 1:1 compound.
authors.affiliation: Department of Chemistry, School of Pharmacy, West China University of Medical Sciences, Chengdu.
authors.forename: X C
authors.initials: XC
authors.lastname: Yang
authors.forename: Y G
authors.initials: YG
authors.lastname: Li
authors.forename: Z F
authors.initials: ZF
authors.lastname: Xiao
authors.forename: H J
authors.initials: HJ
authors.lastname: Liu
authors.forename: P X
authors.initials: PX
authors.lastname: Liu
mesh_terms: D001205:Ascorbic Acid; D004338:Drug Combinations; D000431:Ethanol; D006863:Hydrogen-Ion Concentration; D011319:Primaquine; D012997:Solvents
chemical_list: D004338:Drug Combinations; D012997:Solvents; D000431:Ethanol; D011319:Primaquine; D001205:Ascorbic Acid