Structural, magnetic and electrochemical investigation of novel binary Na2-x(Fe1-yMny)P2O7 (0 <= y <= 1) pyrophosphate compounds for rechargeable sodium-ion batteries

Pyrophosphate cathodes have been recently reported as a competent family of insertion compounds for sodium-ion batteries. In the current study, we have investigated the binary Na2 - x(Fe1 - yMny)P2O7 (0 <= y <= 1) pyrophosphate family, synthesized by the classical solid-state method. They form a continuous solid solution maintaining triclinic P-1 (#2) symmetry. The local structural coordination differs mainly by different degrees of Na site occupancy and preferential occupation of the Fe2 site by Mn. The structural and magnetic properties of these mixed-metal pyrophosphate phases have been studied. In each case, complete Fe3+/Fe2+ redox activity has been obtained centered at 3 V vs. Na. The Fe3+/Fe2+ redox process involves multiple steps between 2.5 and 3 V owing to Na-cation ordering during electrochemical cycling, which merge to form a broad single Fe3+/Fe2+ redox peak upon progressive Mn-doping. (C) 2014 Elsevier B.V. All rights reserved.

Na2.44Mn1.79(SO4)(3): a new member of the alluaudite family of insertion compounds for sodium ion batteries

Sodium-ion batteries have been extensively pursued as economic alternatives to lithium-ion batteries. Investigating the polyanion chemistry, alluaudite structured Na2Fe2II(SO4)(3) has been recently discovered as a 3.8 V positive electrode material (Barpanda et al., Nature Commun., 5: 4358, 2014). Registering the highest ever Fe-III/Fe-II redox potential (vs. Na/Na+) and formidable energy density, it has opened up a new polyanion family for sodium batteries. Exploring the alluaudite family, here we report isotypical Na2+2xMn2-xII(SO4)(3) (x = 0.22) as a novel high-voltage cathode material for the first time. Following low-temperature (ca. 350 degrees C) solid-state synthesis, the structure of this new alluaudite compound has been solved adopting a monoclinic framework (s.g. C2/c) showing antiferromagnetic ordering at 3.4 K. Synergising experimental and ab initio DFT investigation, Na2+2xMn2-xII(SO4)(3) has been found to be a potential high-voltage (ca. 4.4 V) cathode material for sodium batteries.

Studies of the polarographic and coulometric behaviour of aromatic nitro-compounds: I. Nitrobenzene in ethanol

A detailed polarographic (a.c. and d.c.) and coulometric investigation of nitrobenzene has been made at various pH values in the presence of different concentrations of ethanol. Below pH 4.7, two waves are apparent but above this pH, the second wave does not appear. Coulometric evidence indicates that the first and second waves correspond to the four-and two-electron processes, respectively. The coulometric method was not applicable in sodium hydroxide and sodium acetate solutions. When the diffusion coefficients (from the diaphragm cell) are used in the Ilkovic equation, no reliable conclusions can be reached for the number of electrons involved in the reduction process in alkaline solutions. The a.c. polarographic method gives evidence for the formation of species such as: C6H5NO2H22+, C6H5NO2− and C6H5NO22−. Analysis of d.c. polarographic data by Delahay's treatment of irreversible waves, indicates that the number of electrons involved in the rate-determining step is 2. In sodium hydroxide solutions, however, the first main wave is split indicating more than one rate-determining step. The results presented in this paper indicate that the first wave in the reduction of nitrobenzene is a four-electron process at all pH values. The second wave, which appears below pH 4.7, corresponds to a two-electron process irrespective of wave heights. The difference in the a.c. polarographic behaviour in acid and alkaline solutions has given evidence for the formation of species like C6H5NO2H2, C6H5NO2−, and C6H5NO22.

Colorimetric determination of 2,4-dinitrophenylamino groups by sodium borohydride reduction

When sodium borohydride is added to aqueous solutions of 2,4-dinitrophenylamino acids and related derivatives, an intense red color is formed. Measurement of the red color, with a 420 filter, permits the determination of such compounds in concentrations of 0.01 to 0.06 μmole per ml. with a precision to 2%. The reaction is highly specific-while 2,4-dinitroaniline will react to the test, o-, m-, and p-nitroanilines, 2,4-dinitrophenyl aryl or alkyl ethers, and 2,4-dinitrophenyl-imidazole and pyrrolidine derivatives will not. Heretofore aromatic nitro groups have been considered resistant to attack by sodium borohydride. The method, as developed, is applicable to the evaluation of the degree of substitution of protein amino groups by fluorodinitrobenzene.

Inverse relationship of the dehydrogenase and ADP-ribosylation activities in sodium-nitroprusside-treated glyceraldehyde-3-phosphate dehydrogenase is coincidental

Incubation of glyceraldehyde-3-phosphate dehydrogenase (GAPD) with sodium nitroprusside (SNP) decreased its activity in concentration- and time-dependent fashion in the presence of a thiol compounds, with DTT being more effective than GSH. Both forward and backward reactions were effected. Coinciding with this, HgCl2-sensitive labelling of the protein by [32P]NAD+ also increased, indicating the stimulation of ADP-ribosylation. Treatment with SNP of GAPD samples from rabbit muscle, sheep brain and yeast inactivated the dehydrogenase activity of the three, but only the mammalian proteins showed ADP-ribosylation activity. The SNP-modified protein of rabbit muscle GAPD, freed from the reagent by Sephadex filtration showed a concentration-dependent restoration of the dehydrogenase activity on preincubation with DTT and GSH. Such thiol-treated preparations also gave increased ADP-ribosylation activity with DTT, and to a lesser extent with GSH. The SNP-modified protein was unable to catalyze this activity with the native yeast enzyme and native and heat-inactivated muscle enzyme. It was possible to generate the ADP-ribosylation activity in muscle GAPD, by an NO-independent mechanism, on dialysis in Tris buffer under aerobic conditions , and on incubating with NADPH, but not NADH, in muscle and brain, but not yeast, enzymes. The results suggest that the inverse relationship of the dehydrogenase and ADP-ribosylation activities is coincidental but not correlated

Vasomodulatory effect of novel peroxovanadate compounds on rat aorta: Role of rho kinase and nitric oxide/cGMP pathway

The present study was undertaken to assess the role of reactive oxygen species (ROS) in rat aortic ring vasoreactivity and integrity by using various peroxovanadate (pV) compounds. All the pV compounds (1 nM-300 mu M) used in the present study exerted concentration-dependent contractions on endothelium intact rat aortic rings. All compounds with an exception of DPV-asparagine (DPV-asn) significantly altered vascular integrity as shown by diminished KCl responses. Phenylephrine (PE)-mediated contractions (3 nM-300 mu M) were unaltered in the presence of these compounds. Acetylcholine (Ach)-mediated relaxation in PE (1 mu M) pre-contracted rings was significantly reduced in presence of diperoxovanadate (DPV), poly (sodium styrene sulfonate-co-maleate)-pV (PSS-CoM-pV) and poly (sodium styrene 4-sulfonate)-pV (PSS-pV). However, no significant change in Ach-mediated responses was observed in the presence of poly (acrylate)-pV (PM-pV) and DPV-asn. DPV-asn was thus chosen to further elucidate mechanism involved in peroxide mediated modulation of vasoreactivity. DPV-asn (30 nM-300 mu M) exerted significantly more stable contractions, that was found to be catalase (100 U/ml) resistant in comparison with H(2)O(2) (30 nM-300 mu M) in endothelium intact aortic rings. These contractile responses were found to be dependent on extracellular Ca(2+) and were significantly inhibited in presence of ROS scavenger N-acetylcysteine (100 mu M). Intracellular calcium chelation by BAPTA-AM (10 mu M) had no significant effect on DPV-asn (30 nM-300 mu M) mediated contraction. Pretreatment of aortic rings by rho-kinase inhibitor Y-27632 (10 mu M) significantly inhibited DPV-asn-mediated vasoconstriction indicating role of voltage-dependent Ca(2+) influx and downstream activation of rho-kinase. The small initial relaxant effect obtained on addition of DPV-asn (30 nM-1 mu M) in PE (1 mu M) pre-contracted endothelium intact rings, was prevented in the presence of guanylate cyclase inhibitor, methylene blue (10 mu M) and/or nitric oxide synthase (NOS) inhibitor, L-NAME (100 mu M) suggesting involvement of nitric oxide and cGMP. DPV-asn, like H(2)O(2), exerted a response of vasoconstriction in normal arteries and vasodilation at low concentrations (30 nM-1 mu M) in PE-pre contracted rings with overlapping mechanisms. These findings suggest usefulness of DPV-asn having low toxicity, in exploring the peroxide-mediated effects on various vascular beds. The present study also convincingly demonstrates role of H(2)O(2) in the modulation of vasoreactivity by using stable peroxide DPV-asn and warrants future studies on peroxide mediated signaling from a newer perspective. (C) 2011 Published by Elsevier Ltd.

Efficient syntheses of benzothiazepines as antagonists for the mitochondrial sodium-calcium exchanger: Potential therapeutics for type II diabetes

Type II diabetes mellitus is a chronic metabolic disorder that can lead to serious cardiovascular, renal, neurologic, and retinal complications. While several drugs are currently prescribed to treat type II diabetes, their efficacy is limited by mechanism-related side effects (weight gain, hypoglycemia, gastrointestinal distress), inadequate efficacy for use as monotherapy, and the development of tolerance to the agents. Consequently, combination therapies are frequently employed to effectively regulate blood glucose levels. We have focused on the mitochondrial sodium-calcium exchanger (mNCE) as a novel target for diabetes drug discovery. We have proposed that inhibition of the mNCE can be used to regulate calcium flux across the mitochondrial membrane, thereby enhancing mitochondrial oxidative metabolism, which in turn enhances glucose-stimulated insulin secretion (GSIS) in the pancreatic beta-cell. In this paper, we report the facile synthesis of benzothiazepines and derivatives by S-alkylation using 2-aminobenzhydrols. The syntheses of other bicyclic analogues based on benzothiazepine, benzothiazecine, benzodiazecine, and benzodiazepine templates are also described. These compounds have been evaluated for their inhibition of mNCE activity, and the results from the structure-activity relationship (SAR) studies are discussed.

Electrochemical oxidation of boron containing compounds on titanium carbide and its implications to direct fuel cells

Electrochemical oxidation of sodium borohydride (NaBH(4)) and ammonia borane (NH(3)BH(3)) (AB) have been studied on titanium carbide electrode. The oxidation is followed by using cyclic voltammetry, chronoamperometry and polarization measurements. A fuel cell with TiC as anode and 40 wt% Pt/C as cathode is constructed and the polarization behaviour is studied with NaBH(4) as anodic fuel and hydrogen peroxide as catholyte. A maximum power density of 65 mW cm(-2) at a load current density of 83 mA cm(-2) is obtained at 343 K in the case of borhydride-based fuel cell and a value of 85 mW cm(-2) at 105 mA cm(-2) is obtained in the case of AB-based fuel cell at 353 K. (C) 2011 Elsevier Ltd. All rights reserved.

t-Na-2(VO)P2O7: A 3.8 V Pyrophosphate Insertion Material for Sodium-Ion Batteries

Pyrophosphate oxyanionic framework compounds offer a great platform to investigate new battery materials. In our continuing effort to explore pyrophosphate cathodes for sodium-ion batteries, we report, for the first time, the synthesis and use of tetragonal Na-2(VO)P2O7 as a potential sodium-ion insertion material. This material can be easily prepared by using a conventional solid-state route at a relatively low temperature of 400 degrees C. Stabilizing as a tetragonal structure with an open framework, the material offers pathways for Na+ diffusion. The as-synthesized material, with no further cathode optimization, yields a reversible capacity (Q) approaching 80 mAh g(-1) (Q(Theoretical) = 93.4 mAh g(-1)) involving a one electron V5+/V4+ redox potential located at 3.8 V (vs. Na/Na+). Furthermore, the material exhibits decent rate kinetics and reversibility. Combining green synthesis and moderate electrochemical properties, t-Na-2(VO)P2O7 is reported as a new addition to the growing family of pyrophosphate cathodes for sodium-ion batteries.

A Mild Protocol for the Regioselective Ring Opening of Doubly Activated Cyclopropanes by Using Selenolates Generated in Situ: Synthesis of Functionalized Organoselenium Compounds

A variety of functionalized organoselenium compounds were synthesized from doubly activated cyclopropanes and diselenides in the presence of sodium borohydride. A range of substituents were stable under these reaction conditions. Additionally, we extended the scope of the method by reducing nitro groups in the products to give the corresponding selenium-containing unnatural amino acids.

Pursuit of Sustainable Iron-Based Sodium Battery Cathodes: Two Case Studies

Rechargeable batteries have been the torchbearer electrochemical energy storage devices empowering small-scale electronic gadgets to large-scale grid storage. Complementing the lithium-ion technology, sodium-ion batteries have emerged as viable economic alternatives in applications unrestricted by volume/weight. What is the best performance limit for new-age Na-ion batteries? This mission has unravelled suites of oxides and polyanionic positive insertion (cathode) compounds in the quest to realize high energy density. Economically and ecologically, iron-based cathodes are ideal for mass-scale dissemination of sodium batteries. This Perspective captures the progress of Fe-containing earth-abundant sodium battery cathodes with two best examples: (i) an oxide system delivering the highest capacity (similar to 200 mA h/g) and (ii) a polyanionic system showing the highest redox potential (3.8 V). Both develop very high energy density with commercial promise for large-scale applications. Here, the structural and electrochemical properties of these two cathodes are compared and contrasted to describe two alternate strategies to achieve the same goal, i.e., improved energy density in Fe-based sodium battery cathodes.

Na2M2(SO4)(3) (M = Fe, Mn, Co and Ni): towards high-voltage sodium battery applications

Sodium-ion-based batteries have evolved as excellent alternatives to their lithium-ion-based counterparts due to the abundance, uniform geographical distribution and low price of Na resources. In the pursuit of sodium chemistry, recently the alluaudite framework Na2M2(SO4)(3) has been unveiled as a high-voltage sodium insertion system. In this context, the framework of density functional theory has been applied to systematically investigate the crystal structure evolution, density of states and charge transfer with sodium ions insertion, and the corresponding average redox potential, for Na2M2(SO4)(3) (M = Fe, Mn, Co and Ni). It is shown that full removal of sodium atoms from the Fe-based device is not a favorable process due to the 8% volume shrinkage. The imaginary frequencies obtained in the phonon dispersion also reflect this instability and the possible phase transition. This high volume change has not been observed in the cases of the Co- and Ni-based compounds. This is because the redox reaction assumes a different mechanism for each of the compounds investigated. For the polyanion with Fe, the removal of sodium ions induces a charge reorganization at the Fe centers. For the Mn case, the redox process induces a charge reorganization of the Mn centers with a small participation of the oxygen atoms. The Co and Ni compounds present a distinct trend with the redox reaction occurring with a strong participation of the oxygen sublattice, resulting in a very small volume change upon desodiation. Moreover, the average deintercalation potential for each of the compounds has been computed. The implications of our findings have been discussed both from the scientific perspective and in terms of technological aspects.

Elastic Properties Of Sodium Borovanadate Glasses

The elastic properties of sodium borovanadate glasses have been studied over a wide range of composition using ultrasonic measurements. It is found that variation of different elastic moduli is very similar in any given series of composition. The bulk and shear moduli show a monotonic variation with the covalent bond energy densities calculated from the proposed structural model for these glasses. The bulk moduli also vary as a negative power function of the mean atomic volume. The Debye temperature varies linearly with the glass transition temperature. The implications of the observed behavior have been discussed.

Spontaneous generation of optical activity in urea inclusion compounds vis-a-vis current theories

A novel test of recent theories of the origin of optical activity has been designed based on the inclusion of certain alkyl 2-methylhexanoates into urea channels.

A Synthetic Model for the Inhibition of Glutathione Peroxidase by Antiarthritic Gold Compounds

In this paper, inhibition of the glutathione peroxidase activity of two synthetic organoselenium compounds, bis[2-(N,N-dimethylamino)benzyl]diselenide (5) and bis[2-(N,N-dimethylamino)benzyl]selenide (9), by gold(I) thioglucose (1), chloro(triethylphosphine)gold(I), chloro(trimethylphosphine)gold(I), and chloro(triphenylphosphine)gold(I) is described. The inhibition is found to be competitive with respect to a peroxide (H2O2) substrate and noncompetitive with respect to a thiol (PhSH) cosubstrate. The diselenide 5 reacts with PhSH to produce the corresponding selenol (6), which upon treatment with 1 equiv of gold(I) chlorides produces the corresponding gold selenolate complexes 11−13. However, the addition of 1 equiv of selenol 6 to complexes 11−13 leads to the formation of bis-selenolate complex 14 by ligand displacement reactions involving the elimination of phosphine ligands. The phosphine ligands eliminated from these reactions are further converted to the corresponding phosphine oxides (R3PO) and selenides (R3PSe). In addition to the replacement of the phosphine ligand by selenol 6, an interchange between two different phosphine ligands is also observed. For example, the reaction of complex 11 having a trimethylphosphine ligand with triphenylphosphine produces complex 13 by phosphine interchange reactions via the formation of intermediates 15 and 16. The reactivity of selenol 6 toward gold(I) phosphines is found to be similar to that of selenocysteine.