Non-Enzymatic Electroanalysis of Glucose on Electrodeposited Au-PEDOT Dendrites

Electrodeposition of Au on poly (3,4-ethylenedioxythiophene) (PEDOT) coated carbon paper electrode results in the formation of a stable 3-D urchin-like morphology. Au-PEDOT/C electrode exhibits higher surface area, greater catalytic activity, higher sensitivity and lower detection limit for glucose analysis in an alkaline medium than Au/C electrode. Au-PEDOT/C electrode exhibits a linear current response in glucose concentration ranging up to 10 mu M with sensitivity of 515 mu A cm(-2) mu M-1 (on the basis of geometric area) and a low detection limit of 0.03 mu M with signal to noise ratio of 3. Thus, the PEDOT under-layer improves the property of Au for glucose analysis. (c) 2013 The Electrochemical Society.

Mono- and Dialkyne Insertion Reactions of Cyclopalladated N,N `,N `'-Triarylguanidines kappa(2)(C,N)Pd(mu-Br)](2) and cis-/trans-kappa(2)(C,N)Pd(Lewis Base)Br]. Scaffolds for Enlarged, Rearranged, and Zwitterionic Palladacycles through Ring Contraction cum Amine-Imine Tautomerization

Insertion reactions of six-membered cyclopalladated N,N',N''-triarylguanidines, kappa(2)(C,N)Pd(mu-Br)](2) with various alkynes in CH2Cl2 under ambient conditions afforded diinserted eight-membered palladacycles, (kappa(2)(C,N):eta(2)(C=C)-PdBr] (1-11), in high yield (76-96%), while insertion reactions of six-membered cyclopalladated N,N',N''-triarylguanidines, kappa(2)(C,N)Pd(Lewis base)Br] (VI-XI), with various alkynes under the aforementioned conditions afforded monoinserted six-membered palladacycles, kappa(2)(C,N)-Pd(Lewis base)Br] (12-21), in high yield (81-91%) except for 14 (23%). The insertion reaction of VI with 2 equiv of dimethyl acetylenedicarboxylate (DMAD) and the insertion reaction of 12 with 1 equiv of DMAD in CH2Cl2 under ambient conditions resulted in the formation of a diinserted zwitterionic five-membered palladacycle, kappa(2)(C,C)Pd(2,6-lutidine)Br] (22), in 76% and 70% yields, respectively. Palladacycle 22 upon reaction with AgOTf in wet MeCN afforded the ionic palladacycle kappa(2)(C,C)Pd(2,6-lutidine)(H2O)]OTf] (23) in 78% yield. The ring size of the ``kappa(2)(C,N)Pd]'' unit in the structurally characterized diinserted palladacycles (1 center dot 2CH(2)Cl(2)center dot H2O, 2, 5, and 7), and monoinserted palladacycles (17, 18, and 20 center dot C7H8 H2O) is smaller than that anticipated for mono- and diinserted palladacycles, and this feature is mainly ascribed to the proclivity of III-XI to undergo ring contraction cum amine-imine tautomerization upon alkyne insertion. Palladacycle 22 represents the first diinserted product obtained in alkyne insertion reactions of kappa(2)(C,N)Pd(Lewis base)X] type palladarycles. The molecular structure of 22 center dot H2O determined by X-ray diffraction indicates that the positive charge on the guanidinium moiety is balanced by the negative charge on the palladium atom and thus represents the first structurally characterized zwitterionic palladacycle to be reported in alkyne insertion chemistry. Plausible mechanisms of formation of 12-21 and 22 have been outlined. The presence of more than one species in solution for some of the palladacycles in the series 1-7 and 12-21 was explained by invoking the C-N single-bond rotation of the CN3 unit of the guanidine moiety, while this process in conjunction with Pd-N(lutidine) bond rotation was invoked to explain the presence of four isomers of 15, as studied with the aid of variable-concentration H-1 NMR experiments carried out for 14 and 15.

Phase Evolution in the AuCu/Sn System by Solid-State Reactive Diffusion

The interfacial reactions between several Au(Cu) alloys and pure Sn were studied experimentally at 200A degrees C. Amounts of Cu in the AuSn4 and AuSn2 phases were as low as 1 at.%. On the basis of these experimental results there is no continuous solid solution between (Au,Cu)Sn and (Cu,Au)(6)Sn-5. The copper content of (Au,Cu)Sn was determined to be approximately 7-8 at.%. Substantial amounts of Au were present in the (Cu,Au)(6)Sn-5 and (Cu,Au)(3)Sn phases. Two ternary compounds were formed, one with stoichiometry varying from (Au40.5Cu39)Sn-20.5 to (Au20.2Cu59.3)Sn-20.5 (ternary ``B''), the other with the composition Au34Cu33Sn33 (ternary ``C''). The measured phase boundary compositions of the product phases are plotted on the available Au-Cu-Sn isotherm and the phase equilibria are discussed. The complexity and average thickness of the diffusion zone decreases with increasing Cu content except for the Au(40 at.%Cu) couple.

Electron microscopy of Ag-(Ni-O) core-shell nanowires

This report provides information about an electrodeposition based two-step synthesis methodology for producing core-shell Ag-(Ni-O) nanowires and their detailed structural and compositional characterization using electron microscopy technique. Nanowires were produced by employing anodic alumina templates with a pore diameter of 200 nm. In the first step of the synthesis process, nanocrystalline Ni-O was electrodeposited in a controlled manner such that it heterogeneously nucleated and grew only on the template pore walls without filling the pores from bottom upwards. This alumina template with pore walls coated with Ni-O was then utilized as a template during the electrodeposition of Ag in the second step. Electrodeposited Ag filled the template pores to finally produce Ag-(Ni-O) core-shell nanowires with an overall diameter of 200 nm.

Local Structural and Environmental Factors Define the Efficiency of an RNA Pseudoknot Involved in Programmed Ribosomal Frameshift Process

In programmed -1 ribosomal frameshift, an RNA pseudoknot stalls the ribosome at specific sequence and restarts translation in a new reading frame. A precise understanding of structural characteristics of these pseudoknots and their PRF inducing ability has not been clear to date. To investigate this phenomenon, we have studied various structural aspects of a -1 PRF inducing RNA pseudoknot from BWYV using extensive molecular dynamics simulations. A set of functional and poorly functional forms, for which previous mutational data were available, were chosen for analysis. These structures differ from each other by either single base substitutions or base-pair replacements from the native structure. We have rationalized how certain mutations in RNA pseudoknot affect its function; e.g., a specific base substitution in loop 2 stabilizes the junction geometry by forming multiple noncanonical hydrogen bonds, leading to a highly rigid structure that could effectively resist ribosome-induced unfolding, thereby increasing efficiency. While, a CG to AU pair substitution in stem 1 leads to loss of noncanonical hydrogen bonds between stems and loop, resulting in a less stable structure and reduced PRF inducing ability, inversion of a pair in stem 2 alters specific base-pair geometry that might be required in ribosomal recognition of nucleobase groups, negatively affecting pseudoknot functioning. These observations illustrate that the ability of an RNA pseudoknot to induce -1 PRF with an optimal rate depends on several independent factors that contribute to either the local conformational variability or geometry

Exclusive Detection of Sub-Nanomolar Levels of Palladium(II) in Water: An Excellent Probe for Multiple Applications

A new colorimetric probe has been developed for the detection and estimation of Pd-II at sub-nanomolar concentrations. The probe consisted of rhodamine (signaling unit), which was linked with a bis-picolyl moiety (binding site) through a phenyl ring. Pd-II induced opening of the spirolactam ring of the probe with the generation of a prominent pink color. The excellent selectivity of the probe towards Pd-II over Pd-0 or Rh-II ensured its potential utility for the detection of residual palladium contamination in pharma-ceutical drugs and in Pd-catalyzed reactions. The probe showed a ``turn-on'' (bright yellow) fluorescence upon the addition of Pd-II, which made it suitable for the detection of Pd contaminants in mammalian cells.

Enhanced photocatalytic efficiency of AuPd nanoalloy decorated ZnO-reduced graphene oxide nanocomposites

Inhibition of electron-hole pair recombination is the most desirable solution for stimulating photocatalytic activity in semiconductor nanostructures. To implement this, herein we study the photocatalytic efficiency of elemental Au, Pd and bimetallic AuPd nanoalloy decorated pristine and reduced graphene oxide (RGO) hybridized ZnO nanorods for degrading rhodamine 6G (R6G) dye. Fabrication of Au, Pd and AuPd nanoalloy on pristine and RGO modified ZnO nanorods is simple and more importantly surfactant or polymer free. AuPd nanoalloyed ZnO-RGO nanocomposites exhibit higher photocatalytic activity for degrading dye than both Au and Pd hybridized ones, indicating the promising potential of bimetallic nanoalloys over elemental components. A non-monotonic dependence on the composite composition was found by analyzing photodegradation efficiency of a series of ZnO-RGO-AuPd hybrid nanostructures with different weight percentages of RGO. The hybrid nanostructure ZnO-RGO (5 wt%)-AuPd (1 wt%) exhibits highest photodegradation efficiency (similar to 100% degradation in 20 min) with an improvement in rate constant (k) by a factor of 10 compared to that of the ZnO-RGO nanocomposite. The enhancement of the photocatalytic activity is attributed to the better separation of photogenerated charge carriers in photocatalysts thereby suggesting possible usefulness in a broad range of applications, such as sensing, photocatalysis and solar energy conversion.

Analysis of Paschen Curves for air, N2 and SF6 Using the Townsend Breakdown Equation

It has been shown that it is possible to extend the validity of the Townsend breakdown criterion for evaluating the breakdown voltages in the complete pd range in which Paschen curves are available. Evaluation of the breakdown voltages for air (pd=0.0133 to 1400 kPa · cm), N2(pd=0.0313 to 1400 kPa · cm) and SF6 (pd=0.3000 to 1200 kPa · cm) has been done and in most cases the computed values are accurate to ±3% of the measured values. The computations show that it is also possible to estimate the secondary ionization coefficient ¿ in the pd ranges mentioned above.

EQCM Investigation of the Electrodeposition of MnO2 and Its Capacitance Behavior

Electro-oxidation of Mn2+ to MnO2 by cyclic voltammetry on gold in acidic (0.1 M H2SO4) and neutral (0.1 M Na2SO4) media was studied using electrochemical quartz-crystal microbalance (EQCM). The cyclic voltammetric behavior of Au is different in these electrolytes. From EQCM data of mass variation during cycling, the rate of electrodeposition of MnO2 is higher in the neutral medium than in the acidic medium. Specific capacitance of MnO2 deposited from the neutral medium is higher than that deposited from the acidic medium owing to different crystallographic structures.

Sonochemical synthesis of Ce1-xFexO2-delta (0 <= x <= 0.45) and Ce0.65Fe0.33Pd0.02O2-delta nanocrystallites: oxygen storage material, CO oxidation and water gas shift catalyst

Nanocrystalline Ce1-xFexO2-delta (0 <= x <= 0.45) and Ce0.65Fe0.33Pd0.02O2-delta of similar to 4 nm sizes were synthesized by a sonochemical method using diethyletriamine (DETA) as a complexing agent. Compounds were characterized by powder X-ray diffraction (XRD), X-ray photo-electron spectroscopy (XPS) and transmission electron microscopy (TEM). Ce1-xFexO2-delta (0 <= x <= 0.45) and Ce0.65Fe0.33Pd0.02O2-delta crystallize in fluorite structure where Fe is in +3, Ce is in +4 and Pd is in +2 oxidation state. Due to substitution of smaller Fe3+ ion in CeO2, lattice oxygen is activated and 33% Fe substituted CeO2 i.e. Ce0.67Fe0.33O1.835 reversibly releases 0.31O] up to 600 degrees C which is higher or comparable to the oxygen storage capacity of CeO2-ZrO2 based solid solutions (Catal. Today 2002, 74, 225-234). Due to interaction of redox potentials of Pd2+/0(0.89 V) and Fe3+/2+ (0.77 V) with Ce4+/3+ (1.61 V), Pd ion accelerates the electron transfer from Fe2+ to Ce4+ in Ce0.65Fe0.33Pd0.02O1.815, making it a high oxygen storage material as well as a highly active catalyst for CO oxidation and water gas shift reaction. The activation energy for CO oxidation with Ce0.65Fe0.33Pd0.02O1.815 is found to be as low as 38 kJ mol(-1). Ce0.67Fe0.33O1.835 and Ce0.65Fe0.33Pd0.02O1.815 have also shown high activity for the water gas shift reaction. CO conversion to CO2 is 100% H-2 specific with these catalysts and conversion rate was found to be as high 27.2 mu moles g(-1) s(-1) and the activation energy was found to be 46.4 kJ mol(-1) for Ce0.65Fe0.33Pd0.02O1.815.

Synthesis and photocatalytic properties of AgLi1/3Ru2/3]O-2: A new delafossite oxide

A new delafossite oxide, AgLi1/3Ru2/3]O-2, synthesized by ion-exchanging interlayer-Li+ with Ag+ in layered Li2RuO3, is reported. The transformation of layered Li2RuO3 (monoclinic, space group C2/c) to AgLi1/3Ru2/3]O-2 possessing a delafossite structure (space group R (3) over barm) has been established with powder X-ray diffraction. The successful conversion of LiLi1/3Ru2/3]O-2 to AgLi1/3Ru2/3]O-2 is further confirmed by EDAX analysis. The diffuse reflectance spectrum of AgLi1/3Ru2/3]O-2 shows broad absorption in the UV-visible region suggesting its use as a photocatalyst. The photocatalytic activity of AgLi1/3Ru2/3]O-2 has been investigated by degrading various dyes. It showed significant photocatalytic activity for dye degradation both under UV and solar radiation. (C) 2010 Elsevier B.V. All rights reserved.

Ce0.98Pd0.02O2-delta: Recyclable, ligand free palladium(II) catalyst for Heck reaction

Palladium substituted in cerium dioxide in the form of a solid solution, Ce-0.98 Pd-0.02 O-1.98 is a new heterogeneous catalyst which exhibits high activity and 100% trans-selectivity for the Heck reactions of aryl bromides including heteroaryls with olefins. The catalytic reactions work without any ligand. Nano-crystalline Ce-0.98 Pd-0.02 O-1.98 is prepared by solution combustion method and Pd is in +2 state. The catalyst can be separated, recovered and reused without significant loss in activity.

Electrochemical, phosphate hydrolysis, DNA binding and DNA cleavage properties of new polyaza macrobicyclic dinickel(II) complexes

A new class of macrobicyclic dinickel(II) complexes Ni2L1,2 B](ClO4)(4) (1-6), where L-1,L-2 are polyaza macrobicyclic binucleating ligands, and B is a N,N-donor heterocyclic base (viz. 2,2'-bipyridine (bipy) and 1,10-phenanthroline (phen)) are synthesized and characterized. The redox, catalytic, DNA binding and DNA cleavage properties were studied. They exhibit two irreversible waves in the cathodic region around E-pc = -0.95 V and E-pa = -0.85 V vs. Ag/Ag+ in CH3CN-0.1 M TBAP, respectively. The first order rate constants for the hydrolysis of 4-nitrophenylphosphate to 4-nitrophenolate by the dinickel(II) complexes 1-6 are in the range from 3.36 x 10(-5) to 10.83 x 10(-5) Ms-1. The complexes 3 and 6 show good binding propensity to calf thymus DNA giving binding constant values (K-b) in the range from 3.08 x 10(5) to 5.37 x 10(5) M-1. The binding site sizes and viscosity data suggest the DNA intercalative and/or groove binding nature of the complexes. The complexes display significant hydrolytic cleavage of supercoiled pBR322DNA at pH 7.2 and 37 degrees C. The hydrolytic cleavage of DNA by the complexes is supported by the evidence from free radical quenching and T4 ligase ligation. The pseudo Michaelis-Menten kinetic parameters k(cat) = 5.44 x 10(-2) h(-1) and K-M = 6.23 x 10(-3) M for complex 3 were obtained. Complex 3 also shows an enormous enhancement of the cleavage rate, of 1.5 x 10(6), in comparison to the uncatalysed hydrolysis rate (k = 3.6 x 10(-8) h(-1)) of ds-DNA.

Activation of Lattice Oxygen of TiO2 by Pd2+ Ion: Correlation of Low-Temperature CO and Hydrocarbon Oxidation with Structure of Ti1-xPdxO2-x (x=0.01-0.03)

Lattice oxygen of TiO2 is activated by the substitution of Pd ion in its lattice. Ti1-xPdxO2-x (x = 0.01-0.03) have been synthesized by solution combustion method crystallizing in anatase TiO2 structure. Pd is in +2 oxidation state and Ti is in +4 oxidation state in the catalyst. Pd is more ionic in TiO2 lattice compared to Pd in PdO. Oxygen storage capacity defined by ``amount of oxygen that is used reversibly to oxidize CO'' is as high as 5100 mu mol/g of Ti0.97Pd0.03O1.97. Oxygen is extracted by CO to CO2 in absence of feed oxygen even at room temperature which is more than 20 times compared to pure TiO2. Rate of CO oxidation is 2.75 mu mol g(-1) s(-1) at 60 degrees C over Ti0.97Pd0.03O1.97 and C2H2 gets oxidized to CO2 and H2O at room temperature. Catalyst is not poisoned on long time operation of the reactor. Such high catalytic activity is due to activated lattice oxygen created by the substitution of Pd ion as seen from first-principles density functional theory (DFT) calculations with 96 atom supercells of Ti32O64, Ti31Pd1O63, Ti30Pd2O62, and Ti29Pd3O61. The compounds crystallize in anatase TiO2 structure with Pd2+ ion in nearly square planar geometry and TiO6 octahedra are distorted by the creation of weakly bound oxygens. Structural analysis of Ti31Pd1O63 which is close to 3% Pd ion substituted TiO2 shows that oxygens associated with both Ti and Pd ions in the lattice show bond valence sum of 1.87, a low value characteristic of weak oxygen in the lattice compared to oxygens with valence 2 and above in the same lattice. Exact positions of activated oxygens have been identified in the lattice from DFT calculations.

Gold nanoparticles anchored reduced graphene oxide as catalyst for oxygen electrode of rechargeable Li-O-2 cells

Gold nanoparticles decorated reduced graphene oxide (Au-RGO) catalyst for O-2 electrode is prepared by in situ reduction of Au3+ ions and graphene oxide dispersed in water. The Au nanoparticles are uniformly distributed on the two-dimensional RGO layers. Li-O-2 cells assembled in a non-aqueous electrolyte using Au-RGO catalyst exhibit an initial discharge capacity as high as 5.89 mA h cm-(2) (5230 mA h g(-1))at a current density of 0.1 mA cm(-2). The voltage gap between the charge and discharge curves is less for Li-O-2(Au-RGO) cell in comparison with Li-O-2(RGO) cell. The Li-O-2(Au-RGO) cells are cycled over about 120 charge-discharge cycles. The results suggest that Au-RGO is a promising catalyst for rechargeable Li-O-2 cells.