Self-assembly of betulinic acid, a renewable nano-sized 6-6-6-6-5 pentacyclic triterpenic acid studied in twenty two organic liquids and alcohol-water mixtures showed that it self-assembled in all the liquids studied affording strong gels in nineteen organic liquids and also in alcohol-water mixtures. Optical and electron microscopy and atomic force microscopy studies revealed fibrillar networks having fibers of nano- to micro-metre cross sections and micrometre lengths.

Studies on plant metabolites have gained renewed interest in recent years because these can serve as renewable chemicals for the development of a sustainable society. Among various plant secondary metabolites, terpenoids constitute the major component and triterpenoids are the 30C subset of it. In recent years, triterpenoids have drawn the attention of scientific community due to many of its potential and realized applications in medicine, drug delivery, thermochromic materials, pollutant capture, catalysis, liquid crystals, etc. In this personal review, we have discussed our computational results carried out on sixty representative naturally occurring triterpenoids demonstrating that all the triterpenoids are renewable functional nano-entities. Study of the self-assembly of several triterpenoids such as betulin, betulinic acid, oleanolic acid, glycyrrhetinic acid and arjunolic acid and their derivatives in different liquids have also been discussed. Moreover, the utilization of the resulting supramolecular architectures such as vesicles, spheres, flowers and fibrillar networks of nano- to micrometer dimensions and gels have also been discussed in the perspective of green, renewable and nanos.

Betulin, a naturally occurring 6-6-6-6-5 pentacyclic dihydroxy-triterpenoid, is extractable from the bark of white birch (Betula papyrifera). We report the first self-assembly properties of betulin in different liquids. The molecule spontaneously self-assembled in different media, yielding flower-like architectures of nano- to micrometers diameters via the formation of fibrillar networks. The self-assemblies have been characterized by optical microscopy, scanning electron microscopy, transmission electron microscopy, dynamic light scattering, FTIR, and X-ray diffraction studies. The porous microstructure of the self-assemblies has been utilized for the entrapment of fluorophore such as rhodamine-B and the anticancer drug doxorubicin. Moreover, the removal of toxic dyes such as rhodamine 6G, crystal violet, methylene blue, and cresol red has also been demonstrated.

Electronic Supplementary Information (ESI) available: Energy minimized structure and detailed characterizations of 1, additional SEM, AFM, OPM images of the self-assemblies 1 in different liquids, calculation of the thermodynamic parameters, X-ray diffractograms, FTIR, epifluorescence images and absorption and emission spectra of templated CdS, HRTEM and EDX spectrum of templated CdS nanoparticles. See

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Nine esters of a naturally occurring triterpenoid, arjunolic acid (from Terminalia arjuna), with alkyl chains have been synthesized, and their self-assembly has been studied in organic liquids. All of the esters examined were found to be excellent gelators. No birefringence was detected in optical micrographs of the transparent toluene gels with 5% (w/w) ethyl arjunolate or 5% (w/w) p-nitrobenzyl arjunolate as the gelator, but a spherulitic-type pattern was seen for a gel of 1.2% (w/w) p-nitrobenzyl arjunolate in 1/1 (w/w) chloroform/cyclohexane. Electron microscope images revealed self-assembled fibrillar network (SAFIN) structures with right-handed helical ribbons in some gels. With increasing concentration of the gelators, the gel-to-sol transition temperature (T(gel)) increased and then approached plateau values. Differential scanning thermograms demonstrated that the heats for transition from transparent gels to sols of ethyl arjunolate or p-nitrobenzyl ajunolate in toluene are very small. Powder X-ray diffractograms revealed that the molecular packing in the SAFIN of the 5% (w/w) ethyl aijunoate in the toluene gel was amorphous and similar to the diffractogram recorded for the neat gelator. Although the diffractogram of neat p-nitrobenzyl arjunolate consisted of broad peaks, suggesting disordered packing, the low-angle peaks of the corresponding toluene gel were much sharper; these results indicate more crystalline packing in the SAFIN than in the neat gelator. The kinetics and growth of the transformation of sols of p-nitrobenzyl arjunolate in 1/1 (w/w) chloroform/cyclohexane to their gels have been investigated at different incubation temperatures by circular dichroism spectroscopy. The data have been analyzed to probe the mechanism of SAFIN formation and the relationship between the molecular structures of the esters of arjunolic acid and their abilities to function as gelators of a wide variety of organic liquids.

Formation of vesicular gel and gel–gold nanoparticle hybrid material from arjunolic acid extractable from the saw-dust of Terminalia arjuna.

Ursolic acid, a naturally occurring 6-6-6-6-6 monohydroxy triterpenic acid, extractable from the leaves ofPlumeria rubra, spontaneously self-assemble in aqueous liquids yielding nanoarchitectures capable of entrapping guest molecules including anticancer drug.