K. P. Ravindranathan Kartha

A simple molecular framework obtained by cross-linking a hydrophobic chain with S,S- and R,R-tetritol by the copper-catalysed azide–alkyne cycloaddition reaction is found to serve as an excellent bioisostere for self-assembly. The hexadecyl-linked triazolyl tetritol composite spontaneously self-assembles in n-hepane and methanol to form hierarchical organogels. Microscopic analyses and X-ray diffraction studies demonstrate eventual formation of nanotubes through lamellar assembly of the amphiphiles. A rheological investigation shows solvent-dictated mechanical properties that obey power law behavior similar to other low molecular weight gelators (LMOGs). The gel network was then utilized for the entrapment of drugs e.g. ibuprofen and 5-fluorouracil, with tunable mechanical behaviour under applied stress. The differential release profiles of the drugs over a period of a few hours as a result of the relative spatio-temporal location in the supramolecular network can be utilized for topical formulations.

Diazepinium perchlorate-promoted acetylation of free as well as partially protected sugars, phenols, thiophenols, thiols, other alcohols and amines is described.

Non-forage crop residues like rice straw are among the most important and pertinent renewable biomass available for utilization for producing biofuels, specialty chemicals, aromatics etc. Recovery of cellulose from them and its processing for products are two key steps of value addition to these materials that are available in abundance. Of these, rice straw is perhaps the most recalcitrant of all. In this study, production of cellulose triacetate (CTA) from cellulose by three different (alternate) practical methods are reported. It has been demonstrated that cellulose in the form of microcrystalline cellulose (MCC), other celluloses commercially available from chemical suppliers, cotton linters, and rice straw as such (directly after powdering) are suitable as substrates for the reaction. The methods make use of either acetic acid, acetyl chloride or isopropenyl acetate (IPA) as the acetyl donor in the presence of methane sulfonic acid (a cheap and green reagent) as the acid catalyst. The conventional acetyl donor agent, acetic anhydride is also a suitable alternative reagent for the purpose. The post-reaction work-up procedure involves neutralization and filtration as the only two simple successive steps. The processes reported thus eliminate the need for using restricted/toxic chemicals (acetic anhydride and pyridine, respectively) and provide cellulose tri-O-acetate of high purity in excellent yields. Preparation of CTA directly from rice straw has been achieved in >70% yield, representing acetylation of the straw cellulose into its triacetate to an extent of 90%. With IPA as the acyl donor, acetone was a valuable and recoverable co-product. Although not demonstrated in this study, the residue from the acetylation reaction can be utilized for the recovery of value-added materials such as fine silica.

The antibacterial properties of twenty-eight novel ricinoleic acid glycosides synthesized by Koenigs–Knorr glycosylation are reported. Seven of them were found to show promising wide spectrum antibacterial activity against Gram positive bacteria of which two compounds, the mannopyranosyl- and the arabinofuranosyl derivatives, were proven effective against various non-clinical/clinical/NorA-overexpressed/resistant strains of Staphylococcus aureus as well as other Gram +ve bacteria such as Bacillus subtilis ATCC 6051 and Micrococcus luteus MTCC 2470. It was found that both the presence of the sugar and its structure are necessary and important for the compounds to be bioactive. The methyl ester protection of the carboxylic acid moiety of the ricinoleic acid unit was also found to be important for imparting good bioactivity to the molecule. Based on the membrane permeability and cell disintegration studies, these compounds are found to increase the bacterial cell membrane permeability, subsequently causing cell death.

Acyl transfer reactions of various carbohydrates, alcohols, phenols, thiols and thiophenols were achieved at room temperature in high yields and catalytic efficiency in the presence of methane sulfonic acid, a green organic acid, under solvent-free conditions over short time periods.