Corosolic acid, a natural ursane-type 6-6-6-6-6 pentacyclic dihydroxy triterpenic acid, self-assembled in binary liquid mixtures yielding vesicles.

Plant metabolites being renewable in nature have tremendous significance for the development of a sustainable society. In this manuscript we show that, terpenoids having nanometric lengths, commonly having several functional groups and several centers of chirality, can be utilized as renewable Molecular Functional Nanos (MFNs). The terpenoids spontaneously self-assembled in liquids yielding different morphologies such as vesicles, tubes, flowers, petals and fibers of nano- to micro-meter dimensions and supramolecular gels. The self-assemblies were utilized for the entrapment and release of fluorophores including anticancer drug, pollutant capture, generation of hybrid materials and catalysis.

Maslinic acid, a naturally occurring dihydroxy triterpenoid having a 6-6-6-6-6 fused pentacyclic structure, is extractable from the fruits of olive (Olea europaea). As part of our ongoing investigations on the self-assembly of natural products, herein, we report the results of our detailed investigation on the self-assembly of maslinic acid in different liquids. The triterpenoid self-assembled in aqueous binary liquid mixtures yielding vesicles of nano to micrometer diameters. Detailed characterization of the self-assemblies was carried out by scanning electron microscopy, high-resolution transmission electron microscopy, atomic force microscopy, optical microscopy, Fourier-transform infrared spectroscopy, and low-angle X-ray diffraction studies. The vesicular self-assemblies were capable of entrapping fluorophores including the chemotherapeutic anticancer drug doxorubicin. Triton X-100-triggered release of the encapsulated drug was also demonstrated via rupture of vesicles.

Terpenoids are a large and structurally group of natural products containing multiple five carbon containing isoprene units. Previously we have reported that irrespective of their acyclic or alicyclic nature, all the triterpenoids containing 30C’s have nano-metric lengths. In the current studies, detailed computations have been carried out with 120 naturally occurring mono- (C10), sesqui- (C15), di- (C20), sester- (C25), sesqua- (C35) and tetra- (C40) terpenoids using Gaussian 09 software with Gauss view 07 and molecular mechanics calculation using Serena software. The heat of formation and the calculated molecular lengths obtained by the two methods were compared. Interestingly, monoterpenoid to tetraterpenoid all the terpenoids (except three monoterpenoid and one sesqui-terpenoid) have molecular lengths above one nanometer making them useful as nano-sized building blocks.