Spectrophotometric study of time stability and acid-base characteristics of chelerythrine and dihydrochelerythrine

Time stability, acid-base and UV-VIS spectral properties of dihydrochelerythrine (DHCHE) were studied spectrophotometrically in water:methanol and water:ethanol media. DHCHE is stable in strongly acid milieu (pH < 3) and at the higher amounts (60% v/v) alcohol. Acid-base characteristics and UV-VIS spectral properties of chelerythrine (CHE) were studied in aqueous solutions in the presence of different concentrations of HCl, HNO 3 , H 2 SO 4 , H 3 PO 4 and their mixtures. Remarkable shifts of formation parts of absorbance-pH ( A-pH ) curves to the alkaline medium were observed depending on the type and concentration of inert electrolyte (most remarkable for HNO 3 and HCl). The corresponding equilibrium constants pK R+ of the transition reaction between charged iminium Q + and uncharged QOH (pseudo-base, 6-hydroxy-dihydro derivative) forms of chelerythine were calculated using a numerical interpretation of A-pH curves by a SQUAD-G computer program which ranged from 8.51–9.31. The highest changes of Δp K R+ (0.75 and 0.53) were observed for H 3 PO 4 and H 2 SO 4 , respectively. The priority effect of ionic species and ionic strength was confirmed in the presence of additions of NaCl and KCl. The strength of interaction of CHE with biomacromolecular compounds ( i.e. , peptides, proteins, nucleic acids etc. ) may be affected because of the observed influence of both cation and anion of the inert electrolyte on acid-base behavior.