Braja Gopal Bag

Templates, autocatalysis and molecular replication

The studies of self-replication in chemical viz. non-enzymatic model systems have gained significance in recent years for an improved understanding of the origin of life. This article briefly reviews the progress achieved, mainly during the past decade, from organic and bioorganic chemists point of view (1).

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

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.

Eugenol protects nicotine-induced superoxide mediated oxidative damage in murine peritoneal macrophages in vitro

The present work is aimed at evaluating the protective effect of eugenol against in vitro nicotine-induced toxicity in murine peritoneal macrophages, compared with N-acetylcysteine. Eugenol was isolated from Ocimum gratissimum and characterized by HPLC, FTIR, (1)H NMR. To establish most effective protective support, we used five different concentrations of eugenol (1, 5, 10, 15, and 20microg/ml) and N-acetylcysteine (0.25, 0.5, 1.0, 2.0, and 5.0microg/ml) against 10mM nicotine in mice peritoneal macrophages. A dose-dependent protective effect was observed with all doses of eugenol and N-acetylcysteine, as evidenced by decreased level of superoxide anion generation and malondialdehyde, and also increased level of reduced glutathione, and superoxide dismutase activity. Moreover, maximum protection was observed at the concentration of 15.0microg/ml eugenol (0.09nM) and 1.0microg/ml N-acetylcysteine (0.006nM). Further, eugenol (15.0microg/ml) and N-acetylcysteine (1.0microg/ml) were tested against nicotine (10mM) toxicity by analyzing the radical generation, lipid, protein, DNA damage, and endogenous antioxidant status. There was a significant increase in the level of radical generation, NADPH oxidase and myeloperoxidase activity, lipid, protein, DNA damage and oxidized glutathione level in nicotine-treated group, which were significantly reduced by eugenol and N-acetylcysteine supplementation. Antioxidant status was significantly depleted in the nicotine-treated group, which was effectively restored by eugenol and N-acetylcysteine supplementation. The protection by eugenol against nicotine toxicity was merely equal effective to that of N-acetylcysteine. These findings suggest the potential use and benefit of eugenol isolated from O. gratissimum as a modulator of nicotine-induced cellular damage and it may be used as an immunomodulatory drug against nicotine toxicity.

Acacia nilotica (Babool) leaf extract mediated size-controlled rapid synthesis of gold nanoparticles and study of its catalytic activity

The leaf extract of Acacia nilotica (Babool) is rich in different types of plant secondary metabolites such as flavanoids, tannins, triterpenoids, saponines, etc. We have demonstrated the use of the leaf extract for the synthesis of gold nanoparticles in water at room temperature under very mild conditions. The synthesis of the gold nanoparticles was complete in several minutes, and no extra stabilizing or capping agents were necessary. The size of the nanoparticles could be controlled by varying the concentration of the leaf extract. The gold nanoparticles were characterized by HRTEM, surface plasmon resonance spectroscopy, and X-ray diffraction studies. The synthesized gold nanoparticles have been used as an efficient catalyst for the reduction of 4-nitrophenol to 4-aminophenol in water at room temperature.

SYNTHESIS OF GOLD NANOPARTICLES USING RENEWABLE PUNICA GRANATUM JUICE AND STUDY OF ITS CATALYTIC ACTIVITY

Punica granatum juice, a delicious multivitamin drink of great medicinal significance, is rich in different types of phytochemicals, such as terpenoids, alkaloids, sterols, polyphenols, sugars, fatty acids, aromatic compounds, amino acids, tocopherols, etc. We have demonstrated the use of the juice for the synthesis of gold nanoparticles (AuNPs) at room temperature under very mild conditions. The synthesis of the AuNPs was complete in few minutes and no extra stabilizing or capping agents were necessary. The size of the nanoparticles could be controlled by varying the concentration of the fruit extract. The AuNPs were characterized by surface plasmon resonance spectroscopy, high resolution transmission electron microscopy, fourier transform infrared spectroscopy and X-ray diffraction studies. Catalytic activity of the synthesized colloidal AuNPs has also been demonstrated.

Self-assembly of a renewable nano-sized triterpenoid 18β-glycyrrhetinic acid

The nano-sized triterpenoid 18β-glycyrrhetinic acid extractable from Glycyrrhiza glabra self assembled in different liquids affording mostly nano to microsized spherical and flower like objects consisting of fibrillar networks yielding thermoreversible gels. The self-assemblies have been utilized for the templated growth of CdS nanoparticles.

Natural triterpenoids as renewable nanos

Plant metabolites are the most significant source of renewable chemical feedstocks for a sustainable future. Among various plant secondary metabolites, triterpenoids are a large and structurally diverse 30-carbons subset of the major component terpenoids. Whereas the acyclic triterpene squalene can exist in many different conformations, the cyclic triterpenoids are more rigidified and largely chiral. The tetra and pentacyclic triterpenoids are more abundant than other triterpenoids and molecules having ten chiral centers are common. We show that acyclic and mono-cyclic to fused pentacyclic triterpenes are all nano-sized molecules having varied rigid and flexible lengths. Monte-Carlo investigation of their conformational space revealed that the nanometric lengths are maintained even in the folded conformers rendering all the triterpenoids useful as renewablenanos.

Self-assembly of ketals of arjunolic acid into vesicles and fibers yielding gel-like dispersions.

Ten aliphatic and aromatic ketals of arjunolic acid, a renewable, nanosized triterpenic acid which is obtainable from Terminalia arjuna, have been synthesized upon condensation with aldehydes. Self-assembly properties of the ketals have been studied in a wide range of organic liquids. With the exception of the p-nitrobenzylidene derivative, low concentrations of the ketals self-assemble and form gel-like dispersions in many of the organic liquids examined. The morphologies of the assemblies, studied at different distance scales by optical, electron, and atomic-force microscopies, consisted of fibrillar networks and vesicles which were able to entrap 5(6)-carboxyfluorescein as a guest molecule. X-ray diffractograms indicate that the fibrillar objects are crystalline. A charge-transfer complex was formed from a 1:1 mixture of ketal derivatives with electron-donating and electron-accepting groups, and the 9-anthrylidene derivative in its fibrillar network dimerized upon irradiation. Results demonstrate that subtle changes in the ketal structures can lead to very different aggregation pathways.

A Terpenoid-based Gelator: The First Arjunolic Acid-derived Organogelator for Alcohols and Mixed Solvents

A derivative of arjunolic acid, a naturally occurring chiral triterpenoid, formed gels efficiently with a variety of organic solvents. Electron microscopy images revealed the morphology of the gels consisting of fibers and strands as well as ‘cabbage leaf’ type sheets of micrometer dimensions.

Arjunolic Acid in Molecular Recognition: First Synthesis and Cation Binding Studies of a novel Arjuna-18-crown-6

Arjunolic acid, a functionally rich chiral triterpenoid with a rigid pentacyclic backbone, has the potential to be used as a structural framework for the design of molecular receptors and supramolecular architectures. The design and synthesis of the first arjunolic acid-derived 18-crown-6 and its binding studies with metal and tert-butylammonium ions are reported.