Debasis Samanta

Micellization and clouding phenomenon of amphiphilic antidepressant drug amitriptyline hydrochloride: Effect of KCl

In the present study, we report the micellization and clouding behavior of an amphiphilic antidepressant drug viz., amitriptyline hydrochloride (AMT) at different fixed temperatures and KCl concentrations in aqueous solutions. The critical micelle concentration (cmc) of AMT, as measured by conductivity method, increases with increasing temperature and decreasing with KCl concentration. The thermodynamic parameters viz., standard Gibbs energy (ΔG(m)(0)), standard enthalpy (ΔH(m)(0)), and standard entropy (ΔS(m)(0)) of micellization of AMT are evaluated. The values clearly indicate more stability of the AMT solution in presence of KCl. Like surfactant, AMT also shows phase separation behavior. The cloud point (CP) of AMT in water decreases with increase in pH of the medium because of the deprotonation of the drug molecule. The CP values increase with increasing KCl concentration and AMT concentrations, clearly indicating the micellar growth at higher concentration. Furthermore, for better understanding of the behavior of drug molecule in water, we evaluated various thermodynamic parameters of the above drug molecule at CP.

The pH-sensitive polyampholyte nanogels: inclusion of carbon nanotubes for improved drug loading.

We report a simple and facile method to prepare a novel pH sensitive polyampholyte nanogel by copolymerizing vinylimidazole (VIM) with acrylic acid (AA) using functionalized single-walled carbon nanotubes (f-SWCNTs) (as reinforcing material) and cyanuric chloride via an intermolecular quaternization reaction. The polyampholyte nanogels have been characterized by various microscopic and spectroscopic methods. These studies reveal that incorporation of nanotubes in cross-linked copolymer of poly(vinylimidazole-co-acrylic acid) (PVI-co-AA) form polyampholyte nanogel with enhanced physical properties. The thermal experiments show that the introduction of f-SWCNTs into PVI-co-AA has significant impact on the thermal stability of nanogels. The rheological study showed that the nanogel is more viscoelastic than native gel. MTT assay indicates that the prepared polyampholyte gels possess biocompatibility and cell viability. The nanogel is also useful material to load water-soluble drug such as promethazine hydrochloride. The releasing profile of the drug from the nanogel clearly shows the pH-sensitive property of the material.

The reinforced hydrogel for drug loading: immobilization of single-walled carbon nanotubes in cross-linked polymers via multiple interactions

We report a facile method to prepare novel carbon nanotube (CNT)-based hydrogels in an aqueous environment. To maximize the bonding between nanotubes and polymers, we exploited several non-covalent interactions like ionic, π–π stacking, hydrophobic, H-bonding, etc. Importantly, the nano-hydrogels swell in both water and organic solvents. The materials showed improvements in various physicochemical properties. The new material is fairly biocompatible, as shown by MTT assay studies. It is also a useful material to load a water-soluble drug or micronutrient such as riboflavin (vitamin B2) or amitriptyline hydrochloride. The releasing study of the drug clearly showed pH responsive behaviour.

Nanoscale functionalization of surfaces by graft-through Sonogashira polymerization

Graft through Sonogashira polymerization was used to functionalize various surfaces with conjugate polymers in a dimension of less than 100 nm. Atomic force microscopy measurement revealed a dense surface coverage with several closely packed islands. UV-vis spectroscopy and cyclic voltammetry measurements suggested a moderate band gap, which is important for various applications in material science. A device was fabricated using polymer functionalized ITO and deposited aluminium as cathode to determine the current–voltage (I–V) characteristics and charge carrier mobility. Space charge limited current method indicated moderate charge carrier mobility while I–V characteristic data indicated a behaviour as semiconducting material.

Chromium-assisted immobilization of N-isopropylacrylamide-based methacrylic acid copolymers on collagen and leather surfaces: thermo-responsive behaviour

In the present paper, we report the non-covalent immobilization of pH and temperature responsive poly(N-isopropylacrylamide)-co-methacrylic acid on a protein collagen (type I) and a leather surface. The polymer has N-isopropylacrylamide (NIPAM) functionality that is responsible for the thermo-responsive characteristics and carboxylic acid/carboxylate functionality that facilitates the pH-responsive behaviour. We were able to tune the clouding behaviour of the polymer in water from 15 to 40 °C by changing the pH from 4.5 to 5.7. The binding of the polymer to a native collagen protein (type I) or leather is facilitated by the carboxylate groups that form coordination complexes with chromium(III). The polymer was successfully used in the retanning and coating of leather. The polymer-coated leather as well as the polymer-grafted collagen clearly show thermo-responsive characteristics.

A novel fuel cell membrane with high efficiency

A new class of polymer electrolyte membranes containing an azo based ionic diol (30, 40 and 50 mol%) was prepared for use in a fuel cell. Its proton conductivity, hydrolytic stability, water uptake capacity, swelling behaviour and ion-exchange capacity measurement data indicated its suitability for use as a proton exchange electrolyte membrane in fuel cells. For example, the membranes containing 30, 40 and 50 mol% of azo based ionic monomers exhibit fairly good proton conductivities of 0.073 S cm−1, 0.075 S cm−1 and 0.079 S cm−1, respectively at 30 °C. Moreover, the prepared membranes show a phase separated morphology and exhibit a high thermal stability up to 460 °C which are important parameters for successful fuel cell design. Two types of azo based sulfonated poly(arylene ether sulfone) (SPAES) such as the SPAES-30 and SPAES-50 membrane electrode assembly have been successfully fabricated and yielded a good fuel cell performance in the whole range of current density.

Microcapsules from diverse polyfunctional materials: synergistic interactions for a sharp response to pH changes

In the present article, we report the preparation of microcapsules from functionalized polymers, carbon nanotubes and silver nanoparticles, which are stabilized and interconnected by a cross-linking agent. These can be conveniently used to fine tune the release of important encapsulated materials like Vitamin B2 and anticancer drugs with very little variation of pH (e.g. pH 5.4 vs. pH 5.8) in the physiological range. It was observed that even though microcapsules can be formed with acid functionalized single walled carbon nanotubes (f-SWCNTs) or polymer–silver nanoparticle combinations, better stability and responsiveness were found with a polymer–silver nanoparticle–f-SWCNT combination. Optical microscopic studies (video and still pictures) showed that the microcapsules did not break even with an appreciable amount of disturbance by mechanical means (nitrogen gas flow) or the dropwise addition of acidified buffer/water, clearly indicating that the release phenomenon was happening through the gap produced by the nanomaterials rather than the breaking of the microcapsules. HRTEM and FESEM pictures showed those gaps and the composite natures of the different nanomaterials – clearly indicating that a possible synergistic effect is responsible for the superior stability and interlinking. ICP-OES analysis reveals the pH dependent release of the drugs and in vitro studies indicated that the prepared pH responsive microcapsules could be useful for pH-triggered targeted drug delivery applications.