Effect of pH on the micellar properties of amphiphilic drugs in aqueous solution

Abstract

The influence of pH on the micellar properties of several amphiphilic drugs under conditions of constant ionic strength has been investigated. No significant effect of pH on the critical micelle concentration or micellar size of chlorpromazine hydrochloride was noted over a pH range well below the pKa. The micellar properties of opipramol, thiopropazate, flupenthixol, clopenthixol, and trifluoperazine, which contain a piperazine moiety showed considerable pH dependence. The concentration dependence of the pKa in these micellar systems was taken into consideration in the selection of pH values representative of complete protonation of either one or both of the piperazine N atoms. A lower aggregation number and higher critical micelle concentration was observed at a low pH corresponding to complete protonation of both charge centres. Mepyramine maleate exhibited a non‐micellar mode of association at pH 5·5 which could be described by a stepwise association model in which association constants, KN, increased sequentially with aggregation number, N, according to the relationship, KN = K(N − 1)/N where K = 31·3 dm3 mol−1. No significant association could be detected at pH 2 when the pyridine ring N was fully protonated.

Self-Assembly Behavior of Colistin and Its Prodrug Colistin Methanesulfonate: Implications for Solution Stability and Solubilization

“…The slight deviation from linear scattering intensity vs. concentration for both colistin and CMS (Figure 2) is typical of charged compounds and has been observed in light scattering studies of other charged, micelle-forming drug molecules 26–28. The inflection points in the curves indicated a CMC for colistin at 1.5 mM and for CMS at 3.5 mM.…”

In vitro antibacterial activity of some antihistaminics belonging to different groups against multi-drug resistant clinical isolates

“…3B). The pH of the medium affects the surface activity and aggregation properties of the antihistaminics (9,37). At low pH values, protonation of tertiary amine groups occurs leading to elevated critical micelle concentrations (CMC) as well as lower aggregation number (n, the number of monomer molecules forming the micelle).…”

Study of the Additive Effect on the Cloud Point of Nortriptyline Hydrochloride Solutions

“…It has been established from earlier studies on these drugs that in water they form aggregates of approximately 8-10 monomers at a critical concentration, which can be detected by a discontinuity in the physical properties of the solution [3][4][5]. Drug self-association depends on structure and concentration of the drug, temperature, pH, ionic strength, and additive concentration [6][7][8][9]. These drugs also show clouding behavior.…”