Small-angle neutron scattering studies on water soluble complexes of poly(ethylene glycol)-based cationic random copolymer and SDS

The interaction of cationic random copolymers of methoxy poly(ethylene glycol) monomethacrylate and (3-(methacryloylamino)propyl) trimethylammonium chloride with oppositely charged surfactant, sodium dodecyl sulphate, and the influence of surfactant association on the polymer conformation have been investigated by small-angle neutron scattering. SANS data showed a positive indication of the formation of RCPSDS complexes. Even though the complete structure of the polyion complexes could not be ascertained, the results obtained give us the information on the local structure in these polymer-surfactant systems. The data were analysed using the log-normal distribution of the polydispersed spherical aggregate model for the local structure in these complexes. For all the systems the median radius and the polydispersity were found to be in the range of 20 ± 2 Å and 0.6 ± 0.05, respectively

Observation of Nd3+ visible line emission in ZnO : Nd3+ prepared by a controlled reaction in the solid state

Visible emission from ZnO is usually broadband and realizing line emission from rare earth f-f transitions in ZnO at room temperature has proven to be difficult. A controlled solid-state reaction process with different standing times to synthesize rare earth doped (Nd3+) zinc oxide (ZnO) has shown that sharp and intense line emission in the orange region (595 nm) could be realized under blue excitation, where both excitation and emission transitions occur between Nd3+ levels situated intragap in ZnO. In addition, host-to-Nd3+ energy transfer is also observed under band-to-band excitation. Incidentally, undoped ZnO synthesized by an identical process exhibits a broad green emission. Detailed characterization of the ZnO : Nd3+ powder by x-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, x-ray photoelectron spectroscopy, photoluminescence spectroscopy and time-resolved decay indicates a hexagonal phase with the presence of Nd3+ in the ZnO lattice, forming spherical particles (similar to 200 nm) having a sharp visible emission with decay time in the microsecond range (9.60 mu s)

Probing high temperature ferromagnetism and its paramagnetic phase change due to Eu3+ incorporation in ZnO nanophosphors

Ferromagnetic oxide semiconductors exhibiting efficient luminescent properties together with robust ferromagnetism above room temperature form an exclusive class of spintronic materials endowed with both charge and spin degrees of freedom. Herein, we report on the occurrence of high temperature ferromagnetism (>600 K) in zinc oxide nanophosphors attributed to the presence of defects in the host lattice and wherein incorporation of rare earth ions contributed to a gradual reduction in the ferromagnetic character and steady transformation to paramagnetic behavior. Although undoped ZnO nanophosphors exhibit a high coercive field and saturation magnetization along with a prominent green emission (536 nm) attributed to the presence of oxygen vacancies V-o, Eu3+ doping results in a decrease in green emission along with coercivity as well as magnetization efficient line emission in the orange red region (618-622 nm) pointing to a definite correlation between the V-o and ferromagnetism. The temperature dependence of the magnetization shows stable ferromagnetism with Curie temperature above 600 K for undoped ZnO and a ferromagnetic to paramagnetic transition with an increase in Eu3+ concentration that has been explained through an F+ center exchange mechanism

Water-soluble complexes from random copolymer and oppositely charged surfactant. 2. complexes of poly(ethylene glycol)-based cationic random copolymer and bile salts

The complexes formed between the positively charged random copolymers (RCPs) of methoxy-poly(ethylene glycol) monomethacrylate (MePEGMA) and (3-(methacryloylamino)propyl)trimethylammonium chloride (MAPTAC) with oppositely charged biosurfactants (bile salts) were studied using turbidimetric titration, steady-state fluorescence, dynamic light scattering, and electron microscopy. Studies showed that the complexes of the RCPs of MAPTAC and MePEGMA with less than 68 mol % of PEG content precipitate in water, whereas the complexes of the copolymer with 89 and 94 mol % of PEG content do not precipitate in the entire range of composition of the mixture including stoichiometric compositions when the electroneutral complexes are formed. The complexes with true hydrophobic domains, which are a prerequisite characteristic to serve as a carrier, can be obtained at much lower concentration than the critical micelle concentration of the corresponding surfactant. For a particular surfactant, hydrophobic domains are obtained at lower Z_-/+ for the random copolymer with lower PEG content. The hydrodynamic radii of these complexes vary over a range of 20−35 nm. Overall results reveal that these complexes are qualitatively similar to the polyion complex micelles or block ionomer complexes obtained from the block copolymers and oppositely charged surfactants. As the surfactants used in this study are biocompatible, we hope that these soluble particles will be promising vectors in the field of drug delivery

Viable Method for the Synthesis of Biphasic TiO₂ Nanocrystals with Tunable Phase Composition and Enabled Visible-Light Photocatalytic Performance

Here we demonstrate a facile method to synthesize high-surface-area TiO₂ nanoparticles in aqueous-ethanol system with tunable brookite/rutile and brookite/anatase ratio possessing high surface area that exhibits enhanced photoactivity. Titanium tetrachloride (TiCl₄) is used as the metal precursor of choice and the tuning of phase compositions are achieved by varying the water:ethanol ratio, used as mixed solvent system. The synthesized samples were characterized in detail using X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), BET nitrogen sorption measurements, and UV–vis diffuse reflectance spectroscopy (UV-DRS). The photocatalytic activity of biphasic TiO₂ nanocrystals was evaluated by following the degradation kinetics of rhodamine-B dye in aqueous solution and under visible light. Mixed-phase TiO₂ nanostructures composing 83% brookite and 17% of rutile exhibited superior photoactivity when compared to Degussa P25 and phase-pure anatase nanocrystals. The exceptional photocatalytic activity of the synthesized nanostructures can be elucidated on the account of their large surface area and biphasic composition. On the basis of the detailed investigation reported herein, we conclude that tuning the ethanol volume in the mixed-solvent reaction system holds the key to tailor and control the final TiO₂ phase obtained

A Facile and Green Approach for the Controlled Synthesis of Porous SnO₂ Nanospheres: Application as an Efficient Photocatalyst and an Excellent Gas Sensing Material

A facile and elegant methodology invoking the principles of Green Chemistry for the synthesis of porous tin dioxide nanospheres has been described. The low-temperature (∼50 °C) synthesis of SnO₂ nanoparticles and their self-assembly into organized, uniform, and monodispersed porous nanospheres with high surface area is facilitated by controlling the concentration of glucose, which acts as a stabilizing as well as structure-directing agent. A systematic control on the stannate to glucose molar concentration ratio determines the exact conditions to obtain monodispersed nanospheres, preferentially over random aggregation. Detailed characterization of the structure, morphology, and chemical composition reveals that the synthesized material, 50 nm SnO₂ porous nanospheres possess BET surface area of about 160 m²/g. Each porous nanosphere consists of a few hundred nanoparticles ∼2–3 nm in diameter with tetragonal cassiterite crystal structure. The SnO₂ nanospheres exhibit elevated photocatalytic activity toward methyl orange with good recyclability. Because of the high activity and stability of this photocatalyst, the material is ideal for applications in environmental remediation. Moreover, SnO₂ nanospheres display excellent gas sensing capabilities toward hydrogen. Surface modification of the nanospheres with Pd transforms this sensing material into a highly sensitive and selective room-temperature hydrogen sensor

Water-soluble nanoparticles from random copolymer and oppositely charged surfactant, 3

Summary: In this report, we investigate the nanoparticle formation between random copolymers (RCPs) of methoxy-poly(ethylene glycol) monomethacrylate (MePEGMA) and (3-(methacryloylamino)propyl)trimethylammonium chloride (MAPTAC) and oppositely charged natural surfactants, sodium oleate and sodium laurate, using turbidimetric titration, steady-state fluorescence, dynamic light scattering, and electron microscopy. Though sodium oleate and sodium laurate are sparingly soluble in water, the nanoparticle complexes formed between the RCPs and these surfactants are soluble in the entire range of compositions studied here, including the stoichiometric electronetural complexes. The spherical nature of these nanoparticle complexes is revealed by electron microscopic (EM) analysis. Dynamic light scattering (DLS) showed that the average diameters of the nanoparticles are in the range 50 to 150 nm, which is supported by EM analysis. Pyrene fluorescence experiments suggested that these soluble nanoparticles have hydrophobic cores, which may solubilize hydrophobic drug molecules. The polarity index (I₁/I₃) obtained from the pyrene fluorescence spectra and the conductometric measurements showed that the critical concentration of fatty acid salts needed to obtain nanoparticles are in the order of 10⁻⁴M. Further, the complexation of such poorly water-soluble amphiphilic surfactants with polymers offers a useful method for the immobilization of hydrophobic compounds towards water-soluble drug carrier formulations

Complexes of Poly(ethylene glycol)-based cationic random copolymer and calf thymus DNA: a complete biophysical characterization

Complete biophysical characterization of complexes (polyplexes) of cationic polymers and DNA is needed to understand the mechanism underlying nonviral therapeutic gene transfer. In this article, we propose a new series of synthesized random cationic polymers (RCPs) from methoxy poly(ethylene glycol) monomethacrylate (MePEGMA) and (3-(methacryloylamino)propyl)trimethylammonium chloride with different mole ratios (32:68, 11:89, and 6:94) which could be used as a model system to address and answer the basic questions relating to the mechanism of the interaction of calf thymus DNA (CT-DNA) and cationic polymers. The solubility of the complexes of CT-DNA and RCP was followed by turbidity measurements. It has been observed that complexes of RCP with 68 mol % MePEGMA precipitate near the charge neutralization point, whereas complexes of the other two polymers are water-soluble and stable at all compositions. Dnase 1 digestion experiments show that DNA is inaccessible when it forms complexes with RCP. Ethidium bromide exclusion and gel electrophoretic mobility show that both polymers are capable of binding with CT-DNA. Atomic force microscopy images in conjunction with light scattering experiments showed that the complexes are spherical in nature and 75−100 nm in diameter. Circular dichroism spectroscopy studies indicated that the secondary structure of DNA in the complexes is not perturbed due to the presence of poly(ethylene glycol) segments in the polymer. Furthermore, we used a combination of spectroscopic and calorimetric techniques to determine complete thermodynamic profiles accompanying the helix−coil transition of CT-DNA in the complexes. UV and differential scanning calorimetry melting experiments revealed that DNA in the complexes is more stable than in the free state and the extent of stability depends on the polymer composition. Isothermal titration calorimetry experiments showed that the binding of these RCPs to CT-DNA is associated with small exothermic enthalpy changes. A complete thermodynamic profile showed that the RCP/DNA complex formation is entropically favorable. Much broader opportunities to vary the architecture of the polymers studied here make these systems promising in addressing various basic and practical problems in gene delivery systems