Resumen

RAMA RAJU, B; SANTHEE DEVI, K V; PADMAJA, N  y  NAGESWARA RAO, G. PROTONATION EQUILIBRIA OF L-DOPA AND 1,10 PHENONTHROLINE IN PROPYLENE GLYCOL-WATER MIXTURES. J. Chil. Chem. Soc. [online]. 2011, vol.56, n.4, pp. 842-847. ISSN 0717-9707.  doi: 10.4067/S0717-97072011000400004.

Protonation equilibria of L-Dopa and 1,10 phenonthroline have been studied in varying concentrations (0-60% v/v) of propylene glycol-water mixtures maintaining an ionic strength of 0.16 mol dm^-3 at 303 K using pH metric method. The protonation constants have been calculated with the computer program MINIQUAD75 and the best fit models are arrived at based on statistical grounds employing crystallographic R factor, χ² , skewness and kurtosis. Dopa has three dissociable protons and one amino group which associate with proton. It exists as LH₄⁺ at low pH and gets deprotonated with the formation of LH₃, LH₂^- and LH^2- successively with increase in pH. Phen forms LH₂²⁺ at low pH and gets deprotonated with the formation of LH⁺ and L with increase in pH. Secondary formation functions confirm the existence of 3 and 2 protonation equilibria for dopa and phen, respectively. The linear increase of log values of protonation constants of Dopa with decreasing dielectric constant of PG-water mixtures indicates the dominance of electrostatic forces in the protonation-deprotonation equilibria. Phen exhibits non-linear trend indicating the dominance of non-electrostatic forces.

Palabras clave : Protonation equilibria; propylene glycol; L-Dopa; 1,10-Phenanthroline.