Self-Assembly of Esters of Arjunolic Acid into Fibrous Networks and the Properties of their Organogels

Abstract

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.

Synthesis of Fan-Shaped C 3 Molecule with Three Glycyrrhetinic Acid Units and Self-Assembly Properties

“…The self-assembly behavior of 7 was studied in different mixed solvents. The primary results showed that 7 could form weak organogel in THF-methanol (V∶ V＝3∶1) with the MGC of 2.3 g/100 cm 3 (MGC, minimum gelator concentration at which gelation was observed to restrict the flow of the medium 28 ) and the T gel ＝36 ℃ (T gel , the required temperature for the organogel to collapse, was determined by the dropping ball method at MGC 33 ) (Figure 2a). To gain visual insight into the aggregation mode of this weak gel, scanning electron microscopy (SEM) was used to investigate the gel structure (Figure 2b).…”

“…[16][17][18][19][20][21] Despite of chiral rigid skeleton, relative low-toxicity and biocompatibility, there is few reports about triterpenoids as the scaffolds in supramolecular and recognition chemistry. [22][23][24][25][26][27][28] To continue our previous work 23,24,29,30 a new kind fan-shaped C 3 molecule with three GA units ( Figure 1) was synthesized and the self-assembly properties were studied.…”

Synthesis of Macroheterocyclic Compounds with a Furan Bridge Possessing Structural Fragments of 1,2,3-Triazoles and Natural Diterpenoids

“…[5] With similar structural properties as the biogenic homologue of steroids, triterpenoids (18β-glycyrrhetinic acid, oleanolic acid) have also started to emerge in recognition and assembly systems, thus attracting more and more attention from organic and material scientists. [6][7][8] Among the synthesized macrocyclic steroidal dimers the compounds with good inverse recognition properties, [9] as well as cytotoxic hormone receptor modulating activities [10] were obtained. Glycyrrhetinic acidtweezer receptors with excellent selectivity and affinity for Hg 2+ ion, [11] and stable cyclic dimer based on oleanolic acid with remarkable binding ability to F -ion [7] were reported.…”

“…The solvent was evaporated, the residue was subjected to chromatography on silica gel (eluent chloroform-methanol, 100:2) to isolate 0.394 g (53 %) of compound 17 and 0.220 g (30 %) of dimeric compound 18. (1S,4aR,5S,8aR) (6). 1-azido-2-(2-azidoethoxy)ethane 5 (0.17 g, 1.07 mmol) was added to a mixture of compound 11 (0.50 g, 1.07 mmol) in dichloromethane (107 mL) and solutions of CuSO 4 •5H 2 O (0.11 g, 0.43 mmol) in H 2 O (0.5 mL) and sodium ascorbate (0.21 g, 1.07 mmol) in H 2 O (0.5 mL) with stirring.…”

Influence of Functionalization Degree on the Rheological Properties of Isocyanate-Functionalized Chitin- and Chitosan-Based Chemical Oleogels for Lubricant Applications

“…Organogels are generating great interest and expectation in a wide spectrum of applications such as medical and pharmaceutical [1][2][3][4], development of new materials with specific optical and mechanical properties [5][6][7], matrixes for food systems [8,9], art conservation [10,11], etc. The term organogel refers to a variety of soft materials, from viscoelastic liquid-like to solid-like, comprised of an organic liquid and some molecules, i.e., organogelators, which are able to produce self-assembling and structure the organic medium [12].…”