Parshuram G. Shukla

Enhancing the reusability of endoglucanase-gold nanoparticle bioconjugates by tethering to polyurethane microspheres

The synthesis of polyurethane microsphere‐gold nanoparticle “core‐shell” structures and their use in the immobilization of the enzyme endoglucanase are described. Assembly of gold nanoparticles on the surface of polymer microspheres occurs through interaction of the nitrogens in the polymer with the nanoparticles, thereby precluding the need for modifying the polymer microspheres to enable such nanoparticle binding. Endoglucanse could thereafter be bound to the gold nanoparticles decorating the polyurethane microspheres, leading to a highly stable biocatalyst with excellent reuse characteristics. The immobilized enzyme retains its biocatalytic activity and exhibits improved thermal stability relative to free enzyme in solution. The high surface area of the host gold nanoparticles renders the immobilized enzyme “quasi free”, while at the same time retaining advantages of immobilization such as ease of reuse, enhanced temporal and thermal stability, etc.

Preparation of Polyurethane Microspheres via Dispersion Polycondensation Using Poly(1,4-isoprene)-block-poly(ethylene oxide) as Steric Stabilizer

A novel dispersion polymerization of a diisocyanate and a diol for the preparation of spherical polyurethane particles is reported. An amphiphilic block copolymer, namely, poly(1,4-isoprene)-block-poly(ethylene oxide) was used as a steric stabilizer. Monodisperse spherical particles were obtained in the size range from 0.2 to 2.0 μm. The polyurethane particle formation was dependent on the concentration of the steric stabilizer, the block segment molecular weight and the nature of dispersion medium. The polyurethane particles were stabilized by a mechanism involving physical adsorption of the steric stabilizer on the surface of the growing particle.

Preparation and characterization of microcapsules containing industrially important reactive water-soluble polyamine

Polyurea microcapsules containing water-soluble reactive polyamine, namely, polyaziridine (A33), were prepared by interfacial polymerization technique in non-aqueous medium, wherein (i) A33 was encapsulated for the first time as a neat amine without forming its salt or adduct and (ii) microcapsules formed were without any deleterious effect on A33. A systematic study was conducted by preparing microcapsules with different polyurea wall architectures. Fourier transform infrared (FTIR) and proton nuclear magnetic resonance (1H NMR) spectroscopic analysis of extracted A33 from microcapsules do not show any structural changes during microencapsulation. A titration method was developed to analyze the amount of encapsulated A33 quantitatively. Polyurea microcapsules obtained from reaction of ethylene diamine (E) and isophorone diisocyanate (I) monomers have shown better properties such as encapsulation efficiency and extent of agglomeration. Significant reduction in the size was observed when microcapsules of EI wall material were prepared by homogenizing the initial emulsion of A33 in paraffin oil. The process described in this paper for the preparation of microcapsules is cost-effective and industrially viable, which can find applications in agrochemicals, coatings, self-healing composites, etc.

Structure of carbofuran in crosslinked starch matrix by 13C n.m.r.: correlation of release and swelling kinetics with the dynamic behaviour of polymer chains

Abstract A solid state 13C cross-polarization/magic angle spinning n.m.r. study was carried out to elucidate the structure of carbofuran inside starch crosslinked by urea formaldehyde. It was confirmed that carbofuran is physically entrapped in the matrix. Linewidth measurements showed the maximum degree of crosslinking occurs for a urea to starch ratio of 0.6 (w/w). The observed trends in relaxation times showed that release and swelling phenomena are partly governed by the relaxation mechanism. This conclusion is similar to that obtained from in vitro release kinetics of carbofuran from crosslinked starch matrix.