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Papers by harender singh bisht

European Polymer Journal, 2002

Copolymers of n-docosyl acrylate and acrylic acid were synthesized in tetrahydrofuran by conventi... more Copolymers of n-docosyl acrylate and acrylic acid were synthesized in tetrahydrofuran by conventional free radical polymerization using benzoyl peroxide as initiator. The increase in crystallinity of the copolymers with increasing C22 acrylate mole fraction was studied. It was found that even with very low mole fraction of C22 acrylate (0.14) in the polymer chain the copolymers shows significant crystallinity (crystallinity

Journal of Physical Chemistry B, 2004

The effect of incorporation of a central functionality (ether linkage/olefin double bond) in an n... more The effect of incorporation of a central functionality (ether linkage/olefin double bond) in an n-alkane chain on its conformation related properties has been studied using DSC, IR, and wide-angle X-ray scattering (WAXS) techniques. These investigations have also included the influence of alkyl chain length on phase transitions, conformational disorders and chain packing of thus obtained symmetrical alkenes and symmetrical alkyl ethers. The molecules studied involved four symmetrical ethers from 13-oxapentacosane (C 25 ) to 19oxaheptatriacontane (C 37 ) and three symmetrical alkenes from 15-triacontene (C 30 ) to 19-octatriacontene (C 38 ) having a constant chain length difference of four carbons among them. These compounds are analogues of n-alkanes that are known to exhibit a series of chain length-dependent premelt phase transitions. Symmetrical ethers exhibit a more pronounced effect on the depression of both melt and premelt transition temperatures than symmetrical alkenes. The enthalpy of the melt transition showed an increase in the case of symmetrical ethers but a decrease in the case of symmetrical alkenes as compared to the parent n-alkanes. However, the enthalpy of premelt transition has decreased for symmetrical ethers but is not altered significantly for symmetrical alkenes. IR absorption spectra of all symmetrical ethers and alkenes revealed the occurrence of almost all common conformational defects of n-alkanes at premelt and melt transition temperatures. The WAXS patterns indicate that the crystals of shorter chain (C 25 and C 29 ) symmetrical ethers may have a helical monoclinic crystal packing, whereas longer chain (C 33 and C 37 ) symmetrical ethers and all symmetrical alkenes have orthorhombic crystal packing at room temperature (ca. 23°C). The effect of chain length on conformational properties is more pronounced in symmetrical alkyl ethers than in symmetrical alkenes and n-alkanes.

European Polymer Journal, 2003

Octyl acrylate and styrene (OA-St) were copolymerized by conventional polymerization at 80°C and ... more Octyl acrylate and styrene (OA-St) were copolymerized by conventional polymerization at 80°C and atom transfer radical polymerizations at 130°C in different feed ratios (0.1-0.9 mole fraction of OA) using benzoyl peroxide and cuprous chloride/2,2 0 -bipyridine/1-phenyl ethyl chloride respectively. Two linear (Fineman-Ross, Kelen-T€ u ud€ o os) methods and a nonlinear least-squares method were employed for determination of monomer reactivity ratios (r OA ¼ 0:30 AE 0:02 and r St ¼ 0:69 AE 0:04). Integrated intensities of the three peaks observed in the 1 H NMR spectra of -OCH 2 group (3.2-4.2 ppm) were used to determine the mole fraction of 111, 112 or 211 and 212 triad sequences in the copolymers. In addition, the r OA value was used for theoretical determination of mole fraction of these triad sequences. Well-agreed theoretical and experimental values helped us in determining most probable mole fractions of the triad sequences of monomers.

Journal of Macromolecular Science-polymer Reviews, 2001

The synthesis of well-defined polymers with predetermined molecular weights, low polydispersities... more The synthesis of well-defined polymers with predetermined molecular weights, low polydispersities, precisely controlled end-group functionalities, and chain topologies is the ultimate target of preparative polymer chemistry. Such tailored macromolecules can be ...

Journal of Polymer Science Part A-polymer Chemistry, 2002

n-Dodecyl acrylate (DA) and dodecyl-4-vinyl benzoate (DVB) were copolymerized by conventional fre... more n-Dodecyl acrylate (DA) and dodecyl-4-vinyl benzoate (DVB) were copolymerized by conventional free-radical polymerization (CFRP); atom transfer radical polymerization (ATRP), and nitroxide-mediated living free-radical polymerization (NMLFRP) with benzoyl peroxide, 1-phenyl ethyl chloride/cuprous chloride/2,2′-bipyridine, and benzoyl peroxide/2,2,6,6-tetramethylpiperidinyl-1-oxy initiator systems, respectively. In CFRP and NMLFRP, toluene and xylene were used as solvents, whereas ATRP was performed in bulk. Mayo–Lewis, Kelen–Tüdös, and Fineman–Ross methods were used for the determination of the monomer reactivity ratios (r1 and r2). They all gave nearly the same values of r1 and r2. The reactivity ratios of the two monomers in CFRP, ATRP, and NMLFRP were 0.17 ≤ r1 ≤ 0.4 (DA) and 1.0 ≤ r2 ≤ 1.24 (DVB). The side-chain crystallinity of the copolymers decreased with an increasing DVB molar fraction. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1818–1830, 2002

Journal of Polymer Science Part A-polymer Chemistry, 2003

Langmuir, 2007

This article describes the stability and reversibility of ultrathin films of N-isopropylacrylamid... more This article describes the stability and reversibility of ultrathin films of N-isopropylacrylamide (NIPA)-vinylimidazole (VI)-poly(ethylene glycol) (PEG) graft terpolymer adsorbed at the solid-liquid interface upon temperature cycling from below to above its phase transition temperature. The coil-to-globule and globule-to-coil phase transitions were captured by in situ fluid tapping atomic force microscopy (AFM). The film thickness of 1 nm was determined by AFM, X-ray photoelectron spectroscopy, and X-ray reflectivity. The concentration required to reach full coverage was found to be higher when adsorption occurred below the phase transition temperature. From 23 to 42°C, the adsorbed NIPA terpolymer film was observed to be molecularly smooth, corresponding to the close-packed structure of flexible polymer coils. Particles containing between one and a few globules appeared abruptly at the interface at 42-43°C, the same temperature as the solution phase transition temperature, which was determined by dynamic light scattering. The size of the particles did not change with temperature, whereas the number of particles increased with increasing temperature up to 60°C. The particles correspond to the collapsed and associated state of the globules. The film morphological changes were found to be reversible upon temperature cycling. Subtle differences were observed between dip-coated and spin-coated films that are consistent with a higher degree of molecular freedom for spin-coated films. The study contributes to the fundamental understanding and applications of smart ultrathin films and coatings. Figure 7. Variation in the number of particles per unit area as a function of temperature for dip-coated and spin-coated films.

Expert Opinion on Drug Delivery, 2005

Macromolecular and colloidal systems used for the systemic delivery of drugs and genes promise to... more Macromolecular and colloidal systems used for the systemic delivery of drugs and genes promise to improve the way we treat and prevent numerous diseases. New generations of drug and gene delivery systems (DGDS) are being designed to enhance further efficiency by using a range of endogenous and external stimuli. This review focuses on three qualitatively distinct ways a stimulus can improve the efficiency of DGDS; namely, by selectively triggering release of the therapeutic agent from the DGDS, by modulating physical properties of DGDS and by favourably altering physiological properties of tissues to enhance DGDS transport. Recent developments in these areas are discussed to illustrate the potential of stimulus-controlled DGDS in the development of new generations of therapeutics.

Biomacromolecules, 2006

End-functionalized poly(N-isopropylacrylamide) (PNIPA) was synthesized by living free radical pol... more End-functionalized poly(N-isopropylacrylamide) (PNIPA) was synthesized by living free radical polymerization and conventional free radical polymerization and was used to prepare graft copolymers with poly(ethylenimine) (PEI). The copolymers exhibited lower critical solution temperature (LCST) behavior between 30 and 32°C and formed complexes with plasmid DNA. The LCST of the copolymers in the DNA complexes increased slightly to ∼34-35°C. Cytotoxicity of the copolymers was evaluated by measuring lactate dehydrogenase (LDH) release from cells. The copolymers exhibited temperature-dependent toxicity, with higher levels of LDH release observed at temperatures above the LCST. Cellular uptake and transfection activity of the DNA complexes with the PEIg-PNIPA copolymers were lower than those of the control PEI/DNA complexes at temperature below the LCST but increased to the PEI/DNA levels at temperatures above the LCST.

Journal of Controlled Release, 2005

Use of bioactive cationic peptides as gene carriers is limited by instability of their DNA comple... more Use of bioactive cationic peptides as gene carriers is limited by instability of their DNA complexes in vivo and by the loss of their biological activity due to undesired interactions of their bioactive parts with the DNA. To overcome the two major limitations, biodegradable high-molecular-weight form of TAT peptide (POLYTAT) sensitive to cellular redox-potential gradients was synthesized in this study by oxidative polycondensation. Physicochemical and transfection properties of DNA polyplexes based on POLYTAT were investigated and compared with polyplexes based on TAT polymer prepared by in situ template-assisted polymerization. Physicochemical properties of TAT-based polyplexes were affected by the molecular weight and method of polymerization of the TAT peptide. All TAT-based DNA polyplexes exhibited reduced cytotoxicity when compared with control polyethylenimine (PEI) polyplexes. Polyplexes based on both high-molecular-weight TAT polypeptides exhibited increased transfection efficiency compared to control TAT peptide but lower than that of PEI polyplexes. The evidence shows that transfection activity of TAT-based polyplexes is strongly dependent on the presence of chloroquine and therefore suggests that TAT polyplexes are internalized by an endocytosis. Overall, high-molecular-weight reducible polycations based on bioactive peptides has the potential as versatile carriers of nucleic acids that display low cytotoxicity and can prove to be especially beneficial in cases that require surface presentation of membrane-active or cell-specific targeting peptides.