Some micellar properties of long-chain acylcarnitines

Samuel H Yalkowsky, George Zografi

Research output: Contribution to journalArticle

41 Scopus citations

Abstract

The acid dissociation constants of long-chain esters of carnitine (β-hydroxy-γ-trimethylammonium-butyrate) above the critical micelle concentration were determined potentiometrically at several concentrations of added KCl. As the degree of protonation β increases the apparent pK values decrease owing to the increased positive charge on the micelle. The difference in pK between the neutral (zwitterionic) micelle and the value at any given β was used to determine the surface potential of the micelle Ψ at that degree of protonation. At each degree of protonation the measured surface potential was related to the surface charge density σ with the aid of the calculations of Loeb, Wiersema, and Overbeek for a spherical impenetrable particle. The surface potentials and surface charge densities of lauryl-, myristyl-, and palmitylcarnitine are nearly identical at a given degree of protonation and ionic strength, and, as expected, increasing the ionic strength produces a decrease in the surface potential. From the partial molal volume of each surfactant in the micelle and the calculated surface charge density it was possible to calculate the aggregation number n of the micelle. Good agreement was found between the calculated values of n and values obtained from light-scattering experiments at several ionic strengths and degrees of protonation.

Original languageEnglish (US)
Pages (from-to)525-533
Number of pages9
JournalJournal of Colloid and Interface Science
Volume34
Issue number4
DOIs
Publication statusPublished - 1970
Externally publishedYes

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ASJC Scopus subject areas

  • Colloid and Surface Chemistry
  • Physical and Theoretical Chemistry
  • Surfaces and Interfaces

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