Structure and dynamics of a sponge phase in the methyl δ-aminolevulinate/monoolein/water/propylene glycol system

Johanna Bender*, Patrik Jarvoll, Magnus Nydén, Sven Engström

*Corresponding author for this work

Research output: Contribution to journalArticle

18 Citations (Scopus)

Abstract

The structural effect caused by the addition of up to 16% (w/w) of the hydrochloride salt of δ-aminolevulinic acid (ALA, HOOC-CH2-CH2-CO-CH2-NH2•HCl) or its methyl ester (m-ALA) to the sponge phase formed of monoolein/water/propylene glycol was investigated by means of crossed polarizers, small angle X-ray diffraction (SAXD) and nuclear magnetic resonance diffusometry (NMRD). Inspection with crossed polarizers revealed that additions of 4-16% (w/w) m-ALA transformed the isotropic bicontinuous sponge phase partly (4-10%) or completely (13 and 16%) into an anisotropic lamellar phase, indicating that m-ALA has a flattening effect on the bilayer curvature. The addition of 16% (w/w) ALA did not show any effect on the sponge phase. By addition of water to the anisotropic m-ALA samples, isotropic liquids were re-formed. The SAXD data for the isotropic liquids showed a diffuse Bragg peak and the NMRD self-diffusion coefficients for the drug (m-ALA) and the components of the original sponge phase (monoolein, water and propylene glycol) were shown to be essentially constant for 0-16% (w/w) added m-ALA. These results confirmed the hypothesis that the re-formed isotropic phases were indeed sponge phases. Water, for example, showed a diffusion coefficient of 3.1 - 3.9 × 10-10 m2 s-1 in the sponge phase, compared to 5.3 - 5.7 × 10-10 m2 s-1 in relevant water/propylene glycol solutions or 2.3 × 10-9 m2 s-1 in pure water. The reduction can be explained as a consequence of the microstructure (congruent monoolein bilayer) of the sponge phase and of the viscosity effect caused by propylene glycol and m-ALA.

Original languageEnglish
Pages (from-to)577-584
Number of pages8
JournalJournal of Colloid and Interface Science
Volume317
Issue number2
DOIs
Publication statusPublished - 15 Jan 2008
Externally publishedYes

Keywords

  • Sponge phase
  • Self-diffusion
  • NMRD
  • SAXD
  • m-ALA
  • ALA
  • Monoolein
  • Propylene glycol

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