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Elucidation of density profile of self-assembled sitosterol + oryzanol tubules with small-angle neutron scattering.

Faraday discussions (2012-12-14)
Arjen Bot, Elliot P Gilbert, Wim G Bouwman, Hassan Sawalha, Ruud den Adel, Vasil M Garamus, Paul Venema, Erik van der Linden, Eckhard Flöter
ABSTRACT

Small-angle neutron scattering (SANS) experiments have been performed on self-assembled tubules of sitosterol and oryzanol in triglyceride oils to investigate details of their structure. Alternative organic phases (deuterated and non-deuterated decane, limonene, castor oil and eugenol) were used to both vary the contrast with respect to the tubules and investigate the influence of solvent chemistry. The tubules were found to be composed of an inner and an outer shell containing the androsterol group of sitosterol or oryzanol and the ferulic acid moieties in the oryzanol molecule, respectively. While the inner shell has previously been detected in SAXS experiments, the outer shell was not discernible due to similar scattering length density with respect to the surrounding solvent for X-rays. By performing contrast variation SANS experiments, both for the solvent and structurant, a far more detailed description of the self-assembled system is obtainable. A model is introduced to fit the SANS data; we find that the dimensions of the inner shell agree quantitatively with the analysis performed in earlier SAXS data (radius of 39.4 +/- 5.6 angstroms for core and inner shell together, wall thickness of 15.1 +/- 5.5 angstroms). However, the newly revealed outer shell was found to be thinner than the inner shell (wall thickness 8.0 +/- 6.5 angstroms). The changes in the scattering patterns may be explained in terms of the contrast between the structurant and the organic phase and does not require any subtle indirect effects caused by the presence of water, other than water promoting the formation of sitosterol monohydrate in emulsions with aqueous phases with high water activity.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
(R)-(+)-Limonene, 97%
Supelco
(R)-(+)-Limonene, analytical standard
Sigma-Aldrich
Eugenol, ReagentPlus®, 99%
Sigma-Aldrich
Decane, anhydrous, ≥99%
Sigma-Aldrich
Decane, ReagentPlus®, ≥99%
Sigma-Aldrich
Castor oil
Sigma-Aldrich
Eugenol, natural, ≥98%, FG
Sigma-Aldrich
(S)-(−)-Limonene, 96%
Supelco
Decane, analytical standard
Sigma-Aldrich
Decane, ≥95%
Sigma-Aldrich
Dipentene, technical, for use as solvent (for the paint industry), mixture of various terpenes
Supelco
Eugenol, PESTANAL®, analytical standard
Sigma-Aldrich
Castor oil, tested according to Ph. Eur.
Sigma-Aldrich
Eugenol, ≥98%, FCC, FG
Sigma-Aldrich
(R)-(+)-Limonene, technical, ~90% (sum of enantiomers, GC)
Sigma-Aldrich
(S)-(−)-Limonene, ≥95%, FG
Sigma-Aldrich
Castor oil, meets testing specifications per USP
Supelco
Eugenol, Pharmaceutical Secondary Standard; Certified Reference Material
Supelco
(S)-(−)-Limonene, analytical standard
Supelco
Decane, analytical standard
Sigma-Aldrich
Dipentene, mixture of isomers