Viscosity of sodium carboxymethylcellulose in ethylene glycol–water mixed solvent media: Separation of the influences of polyion conformation and electrostatic interactions on the reduced viscosity

Precise measurements on the viscosities of the solutions of sodium carboxymethylcellulose in water and three ethylene glycol–water mixtures containing 10, 20, and 30 mass % of ethylene glycol have been reported at 35 °C. Isoionic dilutions were performed at total ionic strengths in the range of 0.0002–0.0008 eqv L^?1 using sodium chloride to obtain the intrinsic viscosities along with the Huggins constants. The influence of the medium and the ionic strength on the intrinsic viscosities have been interpreted from the points of view of the counterion condensation and expansion/contraction of the polyion chains in solution. The variations of Huggins constants, on the other hand, provided information on the intermolecular interactions in these solutions. A convenient method has been proposed to decompose the reduced viscosity of a polyelectrolyte solution into its conformational and electrostatic components. The electrostatic reduced viscosities obtained in the present study, purely from experimental considerations, quantitatively corroborates the conclusions derived from the Huggins constants. Using the Hess and Klein theoretical approach, an expression for the reduced viscosity due to the electrostatic interactions as a function of polyelectrolyte concentration could be obtained and the reported experimental electrostatic contributions could be nicely described with the help of this approach. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1196–1202, 2010     

Detection of flavonoids and assay for their antioxidant activity based on enlargement of gold nanoparticles

We report our findings that natural flavonoids such as quercetin, daizeol and puerarin can act as reductants for the enlargement of gold nanoparticles (Au-NPs). Consequently, the UV–vis spectra of a solution containing Au-NPs will be gradually changed, and the molecules of the natural herbs can be detected by making use of changes in the UV–visible spectra. Furthermore, we have prepared a self-assembled monolayer modified electrode by modifying cysteamine on a gold substrate electrode, which is further modified by some Au-NP seeds. When the modified electrode is immersed in a solution containing flavonoids and tetrachloroauric acid as a gold source for the growth of the Au-NP seeds, with the increase of the concentration of flavonoids, the Au-NP seeds on the surface of the modified electrode can be enlarged to varying degrees. As a result, the peak currents in the corresponding cyclic voltammograms are inversely decreased, and simultaneously the peak separation is increased. Therefore, an electrochemical method to detect flavonoids is also proposed. Compared with the optical detection method, the electrochemical method has an extraordinarily lower detection limit and a significantly extended detection range. Moreover, the optical and electrochemical experimental results can be also used to assay and compare the relative antioxidant activities of the flavonoids. Figure Enlargement of Au nanoparticles by flavonoids at cysteamine modified electrode     

Carbonylative Sonogashira annulation sequence: One-pot synthesis of 4-quinolone and 4H-chromen-4-one derivatives

Carbonylative Sonogashira annulation sequence for one pot synthesis of 4-quinolone and 4H-chromen-4-one has been developed in presence of Pd-NHC catalyst. Substituted 2-iodoaniline and 2-iodophenol independently underwent in the carbonylative Sonogashira annulation reaction with a variety of acetylenes to result in 4-quinolone and flavone derivatives respectively in good to excellent yield. Moreover, this protocol does not require toxic CO gas, high catalyst loading and any expensive salt/additive. Herein we, for the first time, are using Mo(CO)₆, as solid CO source for the one pot synthesis of flavone derivatives via carbonylative Sonogashira annulation reaction.     

Stereoselective synthesis of 3,4-di-substituted mercaptolactones via photoredox-catalyzed radical addition of thiophenols

A visible light mediated radical addition of thiophenols on 4-phenylbut-3-enoic acids to give diastereoselective synthesis of 3,4-disubstituted γ-lactones is reported. The reaction precludes the conventional prerequisite of conjugate addition. Furthermore, the lactones were successfully utilized in the synthesis of γ-ketoamides.     

Y(OTf)3 catalyzed substitution dependent oxidative C(sp)–C(sp) cleavage and regioselective dehydration of β-allyl-β-hydroxydithioesters: alternate route to α,β-unsaturated ketones and functionalized dienes

β-Allyl-β-hydroxydithioesters have been generated by the regioselective Grignard addition to the β-oxodithioesters. They have been successfully employed in selective C(sp³)–C(sp³) bond cleavage to construct α,β-unsaturated ketone residues by the treatment of an emerging catalyst yttrium(III)triflate for the first time. On the other hand, hetaryl substituted β-allyl-β-hydroxydithioesters led to the useful diene precursors through selective dehydration under the similar conditions.     

X-ray crystal structure of [VO(DPA)(H2O)2]·2H2O (DPA=Dipicolinate dianion)

The X-ray crystal structure of the trans-diaqua complex [VO(DPA)(H2O2)]·2H2O (1) (DPA=dipicolinate dianion) has been determined. Comparison with the known structure of [VO(DPA)(o-phen)]·3H2O (2), obtained from (1) by displacement of the two coordinated aqua molecules, shows that the coordination sphere around vanadium is reorganised during this reaction.     

Optical and electronic properties of polyaniline sulfonic acid-ribonucleic acid-gold nanobiocomposites

Finely fibrillar polyaniline sulfonic acid (PSA)/ribonucleic acid (RNA) hybrids are developed by wrapping PSA with RNA from a mixture of aqueous PSA (P) and RNA (R) solutions of different compositions. FTIR spectra suggest H-bonding and π-π interactions in the hybrids and dedoping of self doped PSA during hybrid formation. UV-vis spectra exhibit a blue shift of the π-band to polaron band transition of PSA from 870 to 581 nm due to dedoping. The PR hybrids show enhanced PL-properties when excited at 540 nm relative to PSA which also exhibits rectification behavior in current (I)-voltage (V) curves. Gold nanoparticles (Au NPs) grown on these PR hybrids by the reduction of Au(3+) by PSA show different morphologies with varying composition. FTIR spectra of the nanobiocomposites indicate that Au NPs are stabilized by the co-ordination of the nitrogen atoms of -N=Q=N- bonds of PSA (Q = quinonoid ring). The intensity of the Au plasmon band gradually decreases with time but the PL-intensities of the PAu/PRAu nanocomposites increase with time. The PL-intensity of the nanocomposites is higher than that of PSA and PR hybrids. The DC-conductivity of the PR hybrids increases by an order of magnitude on addition of Au NPs. I-V curves of the nanobiocomposites show negative differential resistance (NDR) in PSA rich systems with a stable NDR ratio of 7 in the PRAu21 and PRAu11 hybrids. Possible reasons from the accumulation of charges on the Au NPs and its stabilization through the π-clouds of RNA bases are discussed. The PRAu11 system also exhibits rectification properties with a rectification ratio of 14.     

Effects of dip coating parameters on the morphology and transport properties of cellulose acetate–ceramic composite membranes

This work presents the fabrication of cellulose acetate (CA)–ceramic composite membranes using dip coating technique. Ceramic supports used in this work were prepared from kaolin with an average pore size of 560 nm and total porosity of 33%. The dip coating parameters studied experimentally were the concentration of CA solution (varying from 2 wt% to 8 wt%) in acetone and dipping time (varying from 30 s to 150 s). The fabricated composite membranes were characterized using scanning electron microscope, gas permeation, pure water flux and ultrafiltration (UF) experiments using bovine serum albumin (BSA). It was observed that the membrane prepared with 2 wt% and 4 wt% CA were suitable for microfiltration applications and those with 6 wt% and 8 wt% were for ultrafiltration applications. Theoretical investigation was conducted to know the macroporous and mesoporous structure of the prepared membranes using Knudsen and viscous permeability analysis of air. A resistance in series model was applied to identify different resistances responsible for the flux decline. Phenomenological models were proposed to illustrate the dependency of hydraulic resistance of membrane on the structural parameters such as average pore size, effective porosity as well as dip coating parameters like dipping time and concentration of CA. It was found that, the growth rate of CA film on the ceramic support followed exponential growth law with respect to dipping time. The total hydraulic resistance of the membrane was evaluated to be inversely proportional to the ratio of pore sizes of top layer and ceramic support. The resistance due to the CA film was found to be depended to the order of 1.73 with respect to concentration of CA. An increase in the concentration of CA was found to be more effective than dipping time to reduce the membrane pore size.     

Mechanistic studies on the oxidation of glyoxylic and pyruvic acids by a {Mn3O4}4+ core in aqueous media

In aqueous media, the Mn^IV trimer [Mn^IV₃(μ‐O)₄(phen)₄(H₂O)₂]⁴⁺ ( 1 , phen = 1,10‐phenanthroline) equilibrates with its deprotonated from [Mn₃(μ‐O)₄(phen)₄(H₂O)(OH)]³⁺ ( 2 ). Among the several synthetic multinuclear oxo‐ and/or carboxylato‐bridged manganese complexes known to date containing metal‐bound water, to the best of our knowledge, 1 is one of the rare examples that deprotonates ( 1 ? 2 + H⁺; pK_a = 4.00 (±0.15) at 25.0°C, I = 1.0 mol dm^?3, maintained with NaNO₃) at physiological pH. In aqueous media (pH 2–4), 1 oxidizes both glyoxylic and pyruvic acids to formic and acetic acid, respectively, along with the formation of CO₂, the end manganese state being Mn^II. Kinetic studies suggest that the species 1 , its deprotonated form 2 , the reducing acids (HA), and their conjugate bases (A^?) all take part in the reaction. The oxidant 1 is found to be more reactive than its conjugate base 2 , and HA reacts faster than A^? in reducing 1 or 2 . The gem‐diol form of the α‐oxo acids (especially for glyoxylic acid) is the possible reducing species. The Mn^IV₃ to Mn^II transition in the present observation proceeds through the intermediate generation of the spectrally characterized mixed‐valent Mn^IIIMn^IV dimer that quickly collapses to Mn^II. The observed rates of glyoxylic or pyruvic acid oxidation do not depend on the variation of 1,10‐phenanthroline content of the solution, indicating the absence of any phen‐releasing preequilibrium of the title complex in solution. The reactions rates were found to be lowered in media enriched with D₂O in comparison to that in H₂O and a rate‐limiting one electron one proton (1e, 1H⁺) electroprotic mechanism is proposed. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 323–335, 2010