pH mediated delamination of anionic clay-like nickel-zinc hydroxysalt in water through intercalation of zwitterionic p-aminobenzoate ions

p-aminobenzoate could be intercalated into the anionic clay, Ni3Zn2(OH)(8)(OAc)(2)center dot 2H(2)O at a high pH (similar to 10). When the pH was reduced to similar to 7 while washing colloidal dispersion due to delamination was observed. The development of partial positive charge on the amine end of the intercalated anion causes repulsion between the layers leading to delamination and colloidal dispersion of monolayers in water. The layers could be restacked from the colloid to form the parent solid either by increasing the pH or by evaporation.

Purification and properties of benzoate-4-hydroxylase from a soil pseudomonad

Benzoate-4-hydroxylase from a soil pseudomonad was isolated and purified about 50-fold. Polyacrylamide gel electrophoresis of this enzyme preparation showed one major band and one minor band. The approximate molecular weight of the enzyme was found to be 120,000. Benzoate-4-hydroxylase was most active around pH 7.2. The enzyme showed requirements for tetrahydropteridine as the cofactor and molecular oxygen as the electron acceptor. NADPH, NADH, dithiothreitol, β-mercaptoethanol, and ascorbic acid when added alone to the reaction mixture did not support the hydroxylation reaction to any significant extent. However, when these compounds were added together with tetrahydropteridine, they stimulated the hydroxylation. This stimulation is probably due to the reduction of the oxidized pteridine back to the reduced form. This enzyme was activated by Fe2+ and benzoate. It was observed that benzoate-4-hydroxylase could catalyze the oxidation of NADPH in the presence of benzoate,p-aminobenzoate, p-nitrobenzoate, p-chlorobenzoate, and p-methylbenzoate, with only benzoate showing maximum hydroxylation. Inhibition studies with substrate analogs and their kinetic analysis revealed that the carboxyl group is involved in binding the substrate to the enzyme at the active center. The enzyme catalyzed the conversion of 1 mol of benzoate to 1 mol of p-hydroxybenzoate with the consumption of slightly more than 1 mol of NADPH and oxygen.

Exfoliation of alpha-hydroxides of nickel and cobalt in water

p-Aminobenzoate ion intercalated alpha-hydroxides of nickel/cobalt were synthesized by precipitation using ammonia (pH = similar to 12). Aqueous colloidal suspension of alpha-hydroxide of nickel/cobalt was obtained on washing the precipitate as the pH was reduced to similar to 7. The development of partial positive charge on the amine end of the intercalated anion causes repulsion between the layers leading to exfoliation and colloidal suspension of monolayers in water. While theb layers could be restacked from the colloidal suspension in the presenceof other anions in the case of alpha-cobalt hydroxide, the exfoliation could not be reversed easily in the case of the nickel analog. (C) 2010 Elsevier Inc. All rights reserved.

A series of transition metal-azido extended complexes with various anionic and neutral co-ligands: synthesis, structure and their distinct magnetic behavior

The crystal structures and magnetic properties of five new transition metal-azido complexes with two anionic [pyrazine-2-carboxylate (pyzc) and p-aminobenzoate (paba)] and two neutral [pyrazine (pyz) and pyridine (py)] coligands are reported All five complexes were synthesized bysolvothermal methods The complex [Co-2(pyzc)(2)(N-3)(2)(H2O)(2)](n) (1) is 1D and exhibit canted antiferromagnetism, while the 3D complex [MnNa(pyzc)(N-3)(2)(H2O)(2)](n) (2) has a complicated structure and is weakly ferromagnetic in nature [Mn-2(paba)(2)(N-3)(2)(H2O)(2)](n) (3). is a 2D sheet and the Mn-II ions are found to be antiferromagnetically coupled The isostructural 2D complexes [Cu-3(pyz)(2)(N-3)(6)](n) (4) and [Cu-3(py)(2)(N-3)(6)](n) (5) resemble remarkably in their magnetic properties exhibiting moderately strong ferromagnetism. Density functional theory calculations (B3LYP functional) have been performed to provide a qualitative theoretical interpietation of the overall magnetic behavior shown by these complexes.

Exfoliation of copper hydroxysalt in water and the conversion of the exfoliated layers to cupric and cuprous oxide nanoparticles

P-aminobenzoate- intercalated copper hydroxysalt was prepared by coprecipitation at high pH (similar to 12). As the pH was reduced to similar to 7 on washing with water, the development of partial positive charge on the amine end of the intercalated anion caused repulsion between the layers leading to delamination and colloidal dispersion of monolayers of copper hydroxysalt in water. The dispersed copper hydroxysalt monolayers were used as precursors for the synthesis of copper(I)/(II) oxide nanoparticles at room temperature. While the hydroxysalt layers yielded spindle-shaped CuO particles when left to stand, they formed hollow spherical nanoparticles of Cu(2)O when treated with an alkaline solution of ascorbic acid.

Accommodating Unwelcome Guests in Inorganic Layered Hosts: Inclusion of Chloranil in a Layered Double Hydroxide

The host-guest chemistry of most inorganic layered solids is limited to ion-exchange reactions. The guest species are either cations or anions to compensate for the charge deficit, either positive or negative, of the inorganic layers. Here, we outline a strategy to include neutral molecules like ortho- and para-chloranil, that are known to be good acceptors in donor-acceptor or charge-transfer complexes, within the galleries of a layered solid. We have succeeded in including neutral ortho- and para-chloranil molecules within the galleries of an Mg-Al layered double hydroxide (LDH) by using charge-transfer interactions with preintercalated p-aminobenzoate ions as the driving force. The p-aminobenzoate ions are introduced in the Mg-Al LDH via ion exchange. The intercalated LDH can adsorb ortho- and para-chloranil from chloroform solutions by forming charge-transfer complexes with the p-aminobenzoate anions present in the galleries. We use X-ray diffraction, spectroscopy, and molecular dynamics simulations to establish the nature of interactions and arrangement of the charge-transfer complex within the galleries of the layered double hydroxide.

Charge-transfer-driven inclusion of neutral TCNQ molecules in the galleries of a layered double hydroxide: an experimental and computational study

The layered double hydroxides (LDH) or anionic clays are an important class of ion-exchange materials. They consist of positively charged brucite-like inorganic sheets with charge-compensating exchangeable anions in the interlamellar space. Here we show how neutral TCNQ (7,7,8,8-tetracyanoquinodimethane) molecules can be included within the galleries of an LDH. To do so, we exploit the fact that TCNQ is a good electron acceptor that forms donor acceptor complexes with a variety of donors. The electron donor aniline was intercalated into a Mg-Al LDH as p-aminobenzoate (AB) ions by a conventional ion-exchange reaction. We show here that neutral TCNQ molecules may be driven into the galleries of the layered solid by charge-transfer complex formation with the intercalated p-aminobenzoate anions. We use diffraction and spectroscopic measurements in combination with molecular dynamics simulations and quantum chemical calculations to establish the nature of interactions and arrangement of the charge-transfer complex within the galleries of the layered double hydroxide. Electrostatic interactions between the TCNQ molecules and the anchored AB ions, subsequent to charge transfer, are the driving force for the inclusion of TCNQ molecules in the galleries of the LDH.

Photoelectrochemical oxidation of p-nitrophenol on an expanded graphite-TiO2 electrode

In the quest for more efficient photoanodes in the photoelectrochemical oxidation processes for organic pollutant degradation and mineralisation in water treatment, we present the synthesis, characterisation and photoelectrochemical application of expanded graphite-TiO2 composite (EG-TiO2) prepared using the sol-gel method with organically modified silicate. The Brunauer-Emmett-Teller surface area analyser, ultraviolet-visible diffuse reflectance, scanning electron microscopy, energy dispersive spectroscopy, X-ray diffractometry, Raman spectrometry and X-ray photoelectron spectroscopy were employed for the characterisation of the composites. The applicability of the EG-TiO2 as photoanode material was investigated by the photoelectrochemical degradation of p-nitrophenol as a target pollutant in a 0.1 M Na2SO4 (pH 7) solution at a current density of 5 mA cm(-2). After optimising the TiO2 loading, initial p-nitrophenol concentration, pH and current density, a removal efficiency of 62% with an apparent kinetic rate constant of 10.4 x 10(-3) min(-1) was obtained for the photoelectrochemical process as compared to electrochemical oxidation and photolysis, where removal efficiencies of 6% and 24% were obtained respectively after 90 min. Furthermore, the EG-TiO2 electrode was able to withstand high current density due to its high stability. The EG-TiO2 electrode was also used to degrade 0.3 x 10(-4) M methylene blue and 0.1 x 10(-4) M Eosin Yellowish, leading to 94% and 47% removal efficiency within 120 reaction time. This confirms the suitability of the EG-TiO2 electrode to degrade other organic pollutants.

Simultaneous Determination of Catecholamines in Presence of Uric Acid and Ascorbic Acid at a Highly Sensitive Electrochemically Activated Carbon Paste Electrode

A simple yet remarkable, electrochemically activated carbon paste electrode (EACPE) was prepared by successive potential cycling of carbon paste in a 0.1 M NaOH solution and was effectively used for the simultaneous determination of catecholamines such as dopamine (DA), epinephrine (E) and Norepinephrine (NE) in presence of uric acid (UA) and ascorbic acid (AA). Taking DA as the ideal catecholamine, the electrochemical behaviors of DA, UA and AA such as scan rate and pH variation was studied by cyclic voltammetry (CV) in phosphate buffer solution (PBS, pH 7.1). This electrochemical sensor exhibited strong electrocatalytic activity towards the oxidation of a mixture of catecholamines, UA and AA with apparent reduction of overpotentials. Crider optimum conditions, limit of detection (S/N = 3) of DA, E, NE, UA and AA was found to be 0.08, 0.08, 0.07, 0.1 and 6.0 mu M, respectively by differential pulse voltammetry (DPV). The analytical performance of this modified electrode as a biosensor was also demonstrated for the determination of DA, UA and AA in dopamine injection, human urine and vitamin C tablets, respectively, in presence of other interfering substances. (C) 2015 The Electrochemical Society. All-rights reserved.

Yielding of sensitive clays: micromechanical considerations

Test results reported on several natural sensitive soils show significant anisotropy of the yield curves, which are generally oriented along the coefficient of earth pressure at rest (K-0) axis. An attempt is made in this paper to explain the anisotropy in yielding from microstructural considerations. An elliptic pore, with particle domains aligned along the periphery of the pore, and with the major axis of the pore being oriented along the direction of the in situ major principal stress, is chosen as the unit of microstructure. An analysis of forces at the interdomain contacts around the ellipse is carried out with reference to experimentally determined yield stress conditions of one soil, and a yield criteria is defined. The analysis, with the proposed yield criteria, enables one to define the complete yield curve for any other soil from the results of only two tests (one constant eta compression test with eta close to eta(K?0), where eta is the stress ratio (= q/p) and eta(K?0) is the stress ratio corresponding to anisotropic K-0 compression, and another undrained shear test). Predicted yield curves are compared with experimental yield curves of several soils reported in the literature.

Remarkable Capacity Retention of Nanostructured Manganese Oxide upon Cycling as an Electrode Material for Supercapacitor

Electrochemical capacity retention of nearly X-ray amorphous nanostructured manganese oxide (nanoMnO2) synthesized by mixing directly KMnO4 with ethylene glycol under ambient conditions for supercapacitor studies is enhanced significantly. Although X-ray diffraction (XRD) pattern of nanoMnO2 shows poor crystallinity, it is found that by Mn K-edge X-ray absorption near edge structure (XANES) measurement that the nanoMnO2 obtained is locally arranged in a δ-MnO2-type layered structure composed of edge-shared network of MnO6 octahedra. Field emission scanning electron microscopy and XANES measurements show that nanoMnO2 contains nearly spherical shaped morphology with δ-MnO2 structure, and 1D nanorods of α-MnO2 type structure (powder XRD) in the annealed (600 °C) sample. Volumetric nitrogen adsorption−desorption isotherms, inductively coupled plasma analysis, and thermal analysis are carried out to obtain physicochemical properties such as surface area (230 m2 g−1), porosity of nanoMnO2 (secondary mesopores of diameter 14.5 nm), water content, composition, etc., which lead to the promising electrochemical properties as an electrode for supercapacitor. The nanoMnO2 shows a very high stability even after 1200 cycles with capacity retention of about 250 F g−1.

Putrescine-Sensitive (Artifactual) and Insensitive (Biosynthetic) S-Adenosyl-L-Methionine Decarboxylase Activities of Lathyrus sativus Seedlings

The crude extracts of 3-day-old etiolated seedlings of Lathyrus sativus contained two S-adenosyl-L-methionine decarboxylase activities. The artifactual putrescine-dependent activity was due to the H2O2 generated by diamine oxidase (EC 1.4.3.6) of this plant system and was inhibited by catalase. This observation was confirmed by using an electrophoretically and immunologically homogeneous preparation of L. sativus diamine oxidase. In the presence of putrescine, diamine oxidase, in addition to S-adenosylmethionine, decarboxylated L-lysine, L-arginine, L-ornithine, L-methionine and L-glutamic acid to varying degrees. The decarboxylation was not metal-ion dependent. The biosynthetic S-adenosylmethionine decarboxylase (EC 4.1.1.21) was detected after removing diamine oxidase specifically from the crude extracts by employing an immunoaffinity column. This Mg2+ -dependent decarboxylase was not stimulated by putrescine or inhibited by catalase. The enzyme activity was inhibited by semicarbazide, 4-bromo-3-hydroxybenzoylamine dihydrogen phosphate and methylglyoxal-bis (guanylhydrazone). It was largely localized in the shoots of the etiolated seedlings and was purified 40-fold by employing a p-hydroxymercuribenzoate/AH-Sepharose affinity column, which also separated the decarboxylase activity from spermidine synthase.

Kinetics of hydrogen evolution on a stainless steel electrode

The kinetic parameters for the hydrogen evolution reaction on a stainless steel substrate have been obtained from a study of the steady-state polarization curves as well as the galvanostatic transients. The high Tafel slope obtained in the steady-state polarization measurements was ascribed to the presence of an oxide film present on the surface of the stainless steel electrode.

Carbon nanotube reinforced supramolecular gels with electrically conducting, viscoelastic and near-infrared sensitive properties

Pristine and long-chain functionalized single-walled carbon nanotubes (SWNTs) were incorporated successfully in supramolecular organogels formed by an all-trans tri(p-phenylenevinylene) bis-aldoxime to give rise to new nanocomposites with interesting mechanical, thermal and electrical properties. Variable-temperature UV-vis and fluorescence spectra reveal both pristine and functionalized SWNTs promote aggregation of the gelator molecules and result in quenching of the UV-vis and fluorescence intensity. Electron microscopy and confocal microscopy show the existence of a densely packed and directionally aligned fibrous network in the resulting nanocomposites. Differential scanning calorimetry (DSC) of the composites shows that incorporation of SWNTs increases the gel formation temperature. The DSC of the xerogels of 1-SWNT composites indicates formation of different thermotropic mesophases which is also evident from polarized optical microscopy. The reinforced aggregation of the gelators on SWNT doping was reflected in the mechanical properties of the composites. Rheology of the composites demonstrates the formation of a rigid and viscoelastic solid-like assembly on SWNT incorporation. The composites from gel-SWNTs were found to be semiconducting in nature and showed enhanced electrical conductivity compared to that of the native organogel. Upon irradiation with a near IR laser at 1064 nm for 5 min it was possible to selectively induce a gel-to-sol phase transition of the nanocomposites, while irradiation for even 30 min of the native organogel under identical conditions did not cause any gel-to-sol conversion.

Electrochemical reduction of Cu(II)-EDTA complex at dropping mercury electrode. An impedance approach

The study of electrochemical reduction of Cu(II)-EDTA system by phase sensitive a.c. impedance method at dropping mercury electrode reveals several interesting features. The complex plane polarograms exhibit loop like shape in contrast to the classical zinc ion reduction where crest like shape is found. Again, the relative placement of peaks of in-phase and quadrature components, and the relative placement of portions before and after the peaks of complex plane polarograms are different from that of zinc ion reduction. The complex plane plots suggest that electrochemical reduction of Cu-EDTA is charge transfer controlled.