RESUMO
The self-assembly of non-ionic amphiphiles with a hydroxylated oxanorbornane head-group was controlled using amino acid units as spacers between hydrophilic and lipophilic domains to get spherical supramolecular aggregates. The ability of these systems to harbour therapeutic agents like ibuprofen, and their drug-release profiles were evaluated. Apart from directing the assembly, the intervening amino acid unit was found to help in drug entrapment as well. The presence of cholesterol improved their drug-loading ability, and an encapsulation efficiency of up to 66% was shown by the formulation containing the phenylalanine residue as the spacer (NC1c). There was no burst release, and 45% drug release was observed at the end of 24 h in this case (cf. soyaphosphatidylcholine based formulation = 49%). The results from SEM, Cryo-TEM, PXRD and confocal microscopic studies with some insights into molecular packing in this class of aggregates are also included.
RESUMO
Achiral amphiphiles with hydroxylated oxanorbornane headgroups showed specific morphological characteristics and hierarchical preferences depending upon the nature of lipophilic units. Detailed scanning electron microscopic (SEM) studies showed that twisted ribbonlike aggregates are characteristic of monoalkoxyaryl lipids with hydrocarbon chain length in the range C10-C13; these systems also had a preference toward lamellar arrangement. Asymmetric packing of these lipids is a unique occurrence and shows that the presence of molecular chirality is not an absolute requirement for curvature effects in their supramolecular assemblies. Aryl units in these systems were found to be important for the observed morphological preferences, which became evident from comparative studies involving simple long chain esters without this moiety. Single-crystal X-ray diffraction analysis of one of the lipids from the latter group gave finer details of strong and weak secondary interactions, which operate during their assembly process. Introduction of more than one alkyl chain on the aromatic ring caused a notable shift in the packing propensity toward columnar arrangement. Most of these cone-shaped molecules were found to give doughnut-shaped aggregates from acetone solution through the intermediary of fibrous structures, which was confirmed through SEM, transmission electron microscopic, and atomic force microscopic studies.
