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Self-Assembled Networks of Ribbons in Molecular Hydrogels of Cationic Deoxycholic Acid Analogues

Terech, Pierre and Sangeetha, Neralagatta M and Deme, Bruno and Maitra, Uday (2005) Self-Assembled Networks of Ribbons in Molecular Hydrogels of Cationic Deoxycholic Acid Analogues. In: Journal of Physical Chemistry B, 109 (25). pp. 12270-12276.

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Official URL: http://pubs.acs.org/doi/abs/10.1021/jp050666l

Abstract

Aqueous gels derived from three cationic 24-nor 3,12-dihydroxy cholane (DC) derivatives with N-methyl-2-pyrrolidinone (NMP), N-methylmorpholine (NMM), and 1,4-diazabicyclo[2.2.2]octane (DABCO) at the side chain positions have been exhaustively characterized by small-angle neutron-scattering experiments. Although the molecular structures differ slightly by the heterocycle grafted to the steroid core, the derived gels exhibit a range of structural behaviors at the nanoscale that depart from those observed with simple deoxycholate systems. The NMM-DC aggregates are ribbons with a bimolecular thickness of t = 37 A and an anisotropy of the section b/a 0.1. DABCO \approx DC exhibits a remarkable transition from ribbons (t = 29.5 A, b/a = 0.18) to thicker cylindrical fibers (R \approx 59 A), involving four original ribbons, upon a concentration increase. The NMP-DC system forms thick cylindrical fibers (R \approx 68 A) with steroid molecules organized in a specific morphology. Bilayered or interdigited structures are formed and favored by the presence of multiple polar interaction centers in the DC molecules. Secondary aggregation mechanisms are invoked in the formation of bundles having a lower cross-sectional anisotropic symmetry and exhibiting Bragg peaks corresponding to molecular length periodicities. The relations between the structural information and the rheological properties are discussed.

Item Type: Journal Article
Additional Information: Copyright of this article belongs to American Chemical Society.
Department/Centre: Division of Chemical Sciences > Organic Chemistry
Date Deposited: 22 Aug 2005
Last Modified: 07 Feb 2012 08:44
URI: http://eprints.iisc.ernet.in/id/eprint/3407

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