C. N. Murthy

Synthesis of Well-defined Amphiphilic Block Copolymers by Organotellurium-Mediated Living Radical Polymerization (TERP)

Low-molecular weight amphiphilic diblock copolymers, polystyrene-block-poly (2-vinylpyridine) (PS-b-P2VP), and (P2VP-b-PS) with different block ratios were synthesized for the first time via organotellurium-mediated living radical polymerization (TERP). For both the homo- and block copolymerizations, good agreement between the theoretical, and experimental molecular weights was found with nearly 100% yield in every case. The molecular weight distribution for all the samples ranged between 1.10 and 1.24, which is well below the theoretical lower limit of 1.50 for a conventional free radical polymerization. Furthermore, a very simple approach to producing highly dense arrays of titania nanoparticles (TiO2 ) is presented using a site-selective reaction of titanium tetraisopropoxide within the P2VP domains of micellar film of P2VP-b-PS in toluene through the sol-gel method.

Mössbauer studies of iron doped poly(methyl methacrylate) before and after ion beam modification

High-energy MeV ions from accelerators are known to produce drastic modifications in polymers. The typical effects include chain scissions, crosslinks, molecular emission and double bond formation. Poly(methyl methacrylate) was doped with Fe(III) and irradiated with 95 MeV O7+ ions.57Fe-Mössbauer studies were done on the doped samples before and after irradiation. Before irradiation, no Mössbauer absorption was observed. The irradiated samples showed a good Mössbauer absorption, which seems to indicate that there is a significant interaction between the metal ion and the polymer matrix. Two possibilities exist at these doses (∼ 22 × 1012 ions/cm): Fe(III) ions may be bridging the various polymer segments through crosslinking or amorphization of the sample leading to Fe-C bonding. Studies of FTIR, conductivity and glass transition temperatures on these samples support these observations.

Recent advances in carbon nanotube based electrochemical biosensors

There is an increasing need for rapid, low cost, reusable, reliable and sensitive detection systems for diagnosing infectious diseases, metabolic disorders, rapidly advancing cancers and detecting the presence of environmental pollutants. Most traditional methods are invasive, slow, expensive and laborious, requiring highly specialized instruments. Introduction of biosensors with nanomaterials as transducers of signals have helped in removing the disadvantages associated with traditional detectors. The properties of high mechanical strength, better electrical conductivity and ability to serve as efficient signal transducers make carbon nanotubes (CNTs) ideal material for biosensor applications among the gamut of nanomaterials. Further, CNTs with their high surface areas, easily functionalizable surfaces for receptor immobilization are gaining importance in the construction of biosensors. The expanding field of CNTs bridges the physical sciences with biology, as chemical methods are employed to develop novel tools and platforms for understanding biological systems, in disease diagnosis and treatment. This review presents recent advances in surface functionalization of CNTs necessary for immobilization of enzymes and antibodies for biosensor applications and the methodologies used for the detection of a number of chemical and biological species. The review ends with a speculation on future prospects for CNTs in biology and medicine.

SOLUBILITY CORRELATION OF [60]FULLERENE IN DIFFERENT SOLVENTS

The solubility of [60]fullerene in various solvents has been correlated to the molar volume ratio of [60]fullerene and the respective solvent. The solubility varies linearly with the molar volume for the alcohol series and the heteroatom containing solvents, though specific interactions of the charge transfer type seem to dominate in the case of aromatic hydrocarbons and the halogenated solvents. The symmetric nature of the [60]fullerene and its clustering behavior could be the reason for the solubility variations observed in the solvents where specific interactions are present. The aggregation behavior of [60]fullerene molecule studied by laser light scattering technique in the solvent mixture of toluene and N,N-dimethyl formamide confirms the cluster formation and its dependence on the volume ratio in the binary solvent mixture.

Metal Removal Studies by Composite Membrane of Polysulfone and Functionalized Single-Walled Carbon Nanotubes

Composite nanofiltration membranes were prepared by incorporating single-walled carbon nanotubes (SWNTs) into polysulfone polymer via the phase inversion method. Addition of SWCNTs resulted in the reduction of the pore size due to nanosize (0.7-1.3 nm) diameter of SWCNTs used. The increase in carbon nanotubes makes the surface of the membranes smoother, although the solvent and nonsolvent exchange process becomes slower due to increase in viscosity of the blend solution. The addition of SWCNTs improved the rejection of metal ions, the oxidized functionalized C/PS composite membranes gave 96.8% removal for Cr(VI), 87.6% for As(III), and 94.2% removal for Pb(II) which was just 30.3%, 28.5%, and 28.3%, respectively, with unblended virgin polysulfone membrane.

Studies on Protein–[60]Fullerene Interactions: The Lysozyme–[60]Fullerene Model System

Abstract A lysozyme–[60]fullerene adduct was synthesized and isolated for the first time. This adduct was water‐soluble and showed strong interaction between lysozyme and [60]fullerene and was characterized by UV‐VIS and fluorescence energy transfer technique. Keeping possible biomedical applications of [60]fullerene in view, the protein–[60]fullerene interactions were studied taking lysozyme as a model protein.

Cyclodextrin encapsulated monometallic and inverted core–shell bimetallic nanoparticles as efficient free radical scavengers

An effective method for the synthesis of monometallic and inverted core–shell bimetallic nanoparticles of silver and gold using four different cyclodextrins (α-CD, β-CD, γ-CD or HP β-CD) in aqueous alkaline medium at room temperature, stable for several months and having radical scavenging activity is reported. UV-visible absorbance spectra showed surface plasmon absorption maxima at 407 and 528 nm, for silver and gold respectively. The inverted core–shell bimetallic nanoparticles showed absorption maxima between the peaks corresponding to pure silver and pure gold nanoparticles & changed linearly with increasing concentration of shell metal precursor in the bimetallic nanoparticles. TEM showed the presence of uniform spherical particles in the range of 12–14 nm size and incase of bimetallic nanoparticles shows the inverted core–shell nanostructures in the range of 15–17 nm. All the encapsulated nanoparticles showed radical scavenging behavior as observed from the rapid quenching of the DPPH light absorption.

Aqueous Solubilization of [60]Fullerene by Selectively Modified β-Cyclodextrin

A selectively modified β-cyclodextrin has been covalently attached to [60]fullerene via a cycloaddition reaction. First, a diazido functionalized β-cyclodextrin was synthesized that was found to have higher aqueous solubility than the parent β-cyclodextrin. The azide functionalitys reactivity towards [60]fullerene was efficiently used to attach the diazido functionalized cyclodextrin to [60]fullerene to get a highly water-soluble product. Analysis of this product showed that the [60]fullerene was both covalently linked to cyclodextrin as well as formed an inclusion complex resulting in a head-tail type nanostructure in aqueous media. These observations were confirmed from UV-Vis, FTIR, NMR and thermogravimetric analysis. This covalent linkage between cyclodextrin and fullerene allows [60]fullerene to be solubilized in both polar and nonpolar media, which is useful for radical scavenging and DNA-cleaving applications in biomedical research.

Synthesis and characterization of hydrogels from template polymerization of acrylic acid on to modified chitosan

A novel hydrogel based on chitosan was prepared by graft copolymerization of acrylic acid on diamino derivative of chitosan, i.e., 6-amino-6-deoxy-chitosan (6a6dC). This diamino chitosan was grafted with acrylic acid in an aqueous solution in contrast to acetic acid in the conventional method. Hydrogen peroxide/l-ascorbic acid redox system was found to be an efficient initiator system for grafting reaction in an aqueous system at room temperature. The synthesized hydrogel, 6a6dC-g-PAA, was characterized by Fourier transform infrared, thermogravimetric analyses and Scanning electron microscopy (SEM). Thermal studies showed that it is more stable than chitosan and 6-amino-6-deoxy-chitosan. This 6a6dC-g-PAA, also showed an appreciable water absorbing capacity which was attributed to the very porous surface as observed from SEM analysis.

Cyclodextrin-based low molecular weight polymers as encapsulates for nonpolar drug molecules

Low molecular weight water-soluble polymers containing maltose and cyclodextrin (CD) in the main chain were synthesized and used for slow release of a water-soluble drug. These low molecular weight polymers were synthesized from CDs (β-, γ-, and HP-β-CD) and maltose using the differential reactivity of a triazine linker through a single pot polycondensation reaction under controlled conditions. The low molecular weight polymers were characterized by 1H-NMR, FT-IR spectroscopy, XRD analysis, TGA, ESI-mass, and aqueous solubility determination; and were confirmed to be linear. In addition, the inclusion complex formation of Efavirenz (an anti-HIV drug) with the CD–maltose polymer was confirmed from FT-IR and UV–Vis spectroscopy. Comparison of the stability of drug-inclusion complexes of different CD–maltose polymers with that of the parent CDs using the phase solubility studies indicated that the polymers were better at inclusion of the drug. The release performances of Efavirenz with the polymers were investigated through conventional dissolution studies with similar results. The results are explained based on the expansion of the nonpolar cavity due to functionalization of the parent CD.