Chandrakant Mukesh

Dissolution of α-chitin in deep eutectic solvents

Deep eutectic solvents (DESs) consisting of mixtures of choline halide (chloride/bromide)–urea, choline chloride–thiourea, chlorocholine chloride–urea and betaine hydrochloride–urea were demonstrated to be effective solvent systems for α-chitin. The dissolution of the biopolymer in the DESs was carried out by conventional heating, heating under microwave irradiation and heating assisted by ultrasonication under an inert atmosphere. Microwave and ultrasonication helped to reduce the time and temperature required for dissolution. Maximum dissolution of the biopolymer (9% w/w) was observed in the DES consisting of choline chloride–thiourea. The absence of insoluble particles in the solutions was confirmed by optical light microscope. No remarkable degradation of chitin during the dissolution process was observed upon investigations using FT-IR, XRD, 1H NMR, TGA, viscometry and rheology.

Rapid dissolution of DNA in a novel bio-based ionic liquid with long-term structural and chemical stability: successful recycling of the ionic liquid for reuse in the process

DNA from salmon testes was solubilised in two bio-based ionic liquids up to 3.5% w/w in 6 h. No structural degradation of the molecule was observed for the sample solubilised in choline-indole-3-acetate (chol-IAA). However, the molecule was found to be denatured in choline-indole-3-butyrate (chol-IBA). The structural and chemical stability of the DNA molecules after six months of storage in the former was established. Further recyclability of the ionic liquid with very high yield (90-95%) for consecutive reuse in the redissolution of DNA was demonstrated.

Choline chloride-thiourea, a deep eutectic solvent for the production of chitin nanofibers.

Deep eutectic solvents (DESs) consisting of the mixtures of choline halide (chloride/bromide)-urea and choline chloride-thiourea were used as solvents to prepare α-chitin nanofibers (CNFs). CNFs of diameter 20-30 nm could be obtained using the DESs comprising of the mixture of choline chloride and thiourea (CCT 1:2); however, NFs could not be obtained using the DESs having urea (CCU 1:2) as hydrogen bond donor. The physicochemical properties of thus obtained NFs were compared with those obtained using a couple of imidazolium based ionic liquids namely, 1-butyl-3-methylimidazolium hydrogen sulphate [(Bmim)HSO4] and 1-methylimidazolium hydrogen sulphate [(Hmim)HSO4] as well as choline based bio-ILs namely, choline hydrogen sulphate [(Chol)HSO4] and choline acrylate. The CNFs obtained using the DES as a solvent were used to prepare calcium alginate bio-nanocomposite gel beads having enhanced elasticity in comparison to Ca-alginate beads. The bio-nanocomposite gel beads thus obtained were used to study slow release of 5-fluorouracil, an anticancer drug.

Preparation of tamarind gum based soft ion gels having thixotropic properties

Tamarind gum was used to prepare ion gels using both synthetic ionic liquids (ILs) namely 1-butyl-3-methylimidazolium chloride and 1-butyl-3-methylimidazolium bromide and bio-based ionic liquids (Bio-ILs) namely choline acrylate, choline caproate and choline caprylate by heating cooling process. The gels were found to have good thermal stability and exhibited thixotropic behaviour. Upon relaxation after applied breaking strain, the recovery of gel structures after ten consecutive cycles was observed. The hydrogel of the gum prepared using ethanol aqueous solution had much inferior quality in terms of viscosity, viscoelasticity, thermal stability and thixotropicity when compared with the ion gels. The ion gels also showed very good adherence to human finger muscles and skin. The ion gels thus prepared may find application in electrochemistry, sensors, actuators and the gels prepared with Bio-ILs could even be useful in biomedical applications.

Self-healing guar gum and guar gum-multiwalled carbon nanotubes nanocomposite gels prepared in an ionic liquid

Guar gum is a galactomannan extracted from the seed of the leguminous shrub Cyamopsis tetragonoloba. It was found to form a soft viscoelastic gel in 1-butyl-3-methylimidazolium chloride, an ionic liquid at an optimized concentration of 10%w/v. A nanocomposite gel of the gum with enhanced strength could be prepared with 0.2%w/v of multiwalled carbon nanotubes (MWCNTs) in the ionic liquid. When the gels thus prepared were subjected to surface fractures or bisected completely, they found to self-heal at room temperature without any external interventions. The self-healing process could be repeated several times. These viscoelastic gel systems showed thixotropic nature and recovery of the storage modulus with time for several cycles was observed upon rheological investigations. The interaction took place between ionic liquid, guar gum and MWCNT was studied by SEM, TEM, FT-IR, powder XRD and rheometry. The results suggested that, upon standing at room temperature development of electrostatic interactions and the van der Waals interactions among the ionic liquid molecules facilitated the formation of reversible noncovalent bonds and eventually activated the self-healing in the gel systems through appropriate chain entanglements.

Solvent responsive healing of guar gum and guar gum–multiwalled carbon nanotube nanocomposite gels prepared in an ionic liquid

Guar gum, a galactomannan extracted from the seed of the leguminous shrub Cyamopsis tetragonoloba was found to form a soft elastic gel in 1-butyl-3-methylimidazolium chloride (10% w/v). A nanocomposite gel of the gum with higher strength was prepared in the presence of multiwalled carbon nanotubes (MWCNT). The gels showed healing ability in the presence of three polar aprotic solvents namely acetone, dimethyl sulfoxide and dimethylformamide. However, they did not heal in the presence of acetonitrile. The interactions taking place between the ionic liquid, guar gum and MWCNT were studied by SEM, TEM, FT-IR, powder XRD and rheological property measurements. It was concluded that the electrostatic interactions and the van der Waals interactions among the ionic liquid molecules facilitated the formation of reversible noncovalent bonds and eventually activated the healing in the gel systems through appropriate polymer entanglements. Further, the interactions with the solvents induced favourable polymeric chain mobility required for the healing.

Studies on the effect of bio-ionic liquid structures on the spontaneous reduction and dispersion stability of graphene oxide in aqueous media

Treatment of graphene oxide (GO) at elevated temperature with four choline based bio-ionic liquids (Bio-ILs) having counter anions with different nucleophilicity, namely, choline bicarbonate (chol-HCO3), choline hydroxide (chol-OH), choline formate (chol-HCOO) and choline caproate (chol-C5H11COO) resulted in the formation of partially reduced GO (prGO). The prGO formed in the presence of chol-HCOO and chol-C5H11COO had long term dispersion stability in water (>1 year). The results showed that ILs having strong nucleophiles were able to reduce GO to a higher extent with short term dispersion stability of the prGO, while the ILs with weaker nucleophiles gave the formation of prGO with long term dispersion stability in water.

Stimuli responsive ion gels based on polysaccharides and other polymers prepared using ionic liquids and deep eutectic solvents

Ion gels and self-healing gels prepared using ionic liquids (ILs) and deep eutectic solvents (DESs) have been largely investigated in the past years due to their remarkable applications in different research areas. Herewith we provide an overview on the ILs and DESs used for the preparation of ion gels, highlight the preparation and physicochemical characteristics of stimuli responsive gel materials based on co-polymers and biopolymers, with special emphasis on polysaccharides and discuss their applications. Overall, this review summarizes the fundamentals and advances in ion gels with switchable properties prepared using ILs or DESs, as well as their potential applications in electrochemistry, in sensing devices and as drug delivery vehicles.