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Assessing competitive environmental catalytic reduction processes via NaBH4 is essential, as BH4− is both an energy carrier (as H2) and a reducing agent. A comprehensive catalytic study of the competition between the borohydride hydrolysis reaction (BHR, releasing H2) and 4-nitrophenol reduction via BH4− on M0- and M/M′ (alloy)-nanoparticle catalysts is reported. The results reveal an inverse correlation between the catalytic efficiency for BH4− hydrolysis and 4-nitrophenol reduction, indicating that catalysts performing well in one process exhibit lower activity in the other. Plausible catalytic mechanisms are discussed, focusing on the impact of reaction products such as 4-aminophenol and borate on the rate and yield of BH4− hydrolysis. The investigated catalysts were Ag0, Au0, Pt0, and Ag/Pt-alloy nanoparticles synthesized without any added stabilizer. Notably, the observed rate constants for the 4-nitrophenol reduction on Ag0, Ag-Pt (9:1), and Au0 are significantly higher than the corresponding rate constants for BH4− hydrolysis, suggesting that most reductions do not proceed through surface-adsorbed hydrogen atoms, as observed for Pt0 nanoparticles. This research emphasizes the conflicting nature of BH4− hydrolysis and reduction processes, provides insights for designing improved catalysts for competitive reactions, and sheds light on the catalyst properties required for each specific process. [ABSTRACT FROM AUTHOR]

Earth abundant transition metal oxides are low-cost promising catalysts for the oxygen evolution reaction (OER). Many transition metal oxides have shown higher OER activity than the noble metal oxides (RuO2 and IrO2). Many experimental and theoretical studies have been performed to understand the mechanism of OER. In this review article we have considered four earth abundant transition metal oxides, namely, titanium oxide (TiO2), manganese oxide/hydroxide (MnOx/MnOOH), cobalt oxide/hydroxide (CoOx/CoOOH), and nickel oxide/hydroxide (NiOx/NiOOH). The OER mechanism on three polymorphs of TiO2: TiO2 rutile (110), anatase (101), and brookite (210) are summarized. It is discussed that the surface peroxo O* intermediates formation required a smaller activation barrier compared to the dangling O* intermediates. Manganese-based oxide material CaMn4O5 is the active site of photosystem II where OER takes place in nature. The commonly known polymorphs of MnO2; α-(tetragonal), β-(tetragonal), and δ-(triclinic) are discussed for their OER activity. The electrochemical activity of electrochemically synthesized induced layer δ-MnO2 (EI-δ-MnO2) materials is discussed in comparison to precious metal oxides (Ir/RuOx). Hydrothermally synthesized α-MnO2 shows higher activity than δ-MnO2. The OER activity of different bulk oxide phases: (a) Mn3O4(001), (b) Mn2O3(110), and (c) MnO2(110) are comparatively discussed. Different crystalline phases of CoOOH and NiOOH are discussed considering different surfaces for the catalytic activity. In some cases, the effects of doping with other metals (e.g., doping of Fe to NiOOH) are discussed. [ABSTRACT FROM AUTHOR]

The kinetics of the reactions of H2 with rhodium and iridium nanoparticles (NPs), in aqueous suspensions, were studied by following their catalytic reduction of PW12O403−, POM. The reaction of H2 with the same size (∼2.5 nm) of two different nanoparticles was carried out to check how the nature of the nanoparticles affects the reaction kinetics. Herein we report the first kinetic measurement of H2 + Rh0 and Ir0 NPs in the absence of an electric field. A comparison of the apparent rate constants of the reactions Rh0-NPs and Ir0-NPs + H2 to the previously reported Pt0-NPs + H2 indicates that the rates decrease along the series k(Pt) > k(Rh) > k(Ir), though they are of the same order of magnitude. The adsorption of hydrogen and/or H atom can affect the structure of the M0-NPs. [ABSTRACT FROM AUTHOR]

The mechanism of reaction of DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) with ·CH 3 , CH 3 O 2 · and ·OH radicals were studied. The radicals were formed in situ radiolytically. The methyl radicals react orders of magnitude slower with DOTA and with MIII(DOTA)- than the hydroxyl radicals. The various final products were identified and mechanisms for their formation are proposed. CH 3 O 2 · radicals do not react, or react too slowly to be observed, with DOTA and with MIII(DOTA)- as long as the central cation is not oxidized by the peroxyl radical. The results imply that synthesis of the MIII(DOTA)-(MIII = radioisotope) complexes in a water-organic solvent (ethanol or 2-propanol or acetonitrile) mixture is not only kinetically desired but the so formed complex also decreases the radiolytic decomposition of DOTA. [Display omitted] • The mechanisms of the reactions of Hydroxyl, Methyl and Peroxyl radicals with DOTA are reported. • The implications to the synthesis of MIIIDOTA, (MIII = Radioactive isotope) are discussed. [ABSTRACT FROM AUTHOR]

The sodium borohydride, NaBH 4 , hydrolysis mechanism is studied via the H 2 O/D 2 O kinetic isotope effect (KIE). This reaction is of importance as NaBH 4 is considered as a hydrogen storage material. Nowadays, hydrogen is thought to be one of the most promising and efficient clean energy carriers. In order to control the rate of the hydrogen evolution reaction (HER), one has to understand the mechanism of its production. The H 2 O/D 2 O KIE of the reactions of NaBH 4 and NaBD 4 with water was studied in solutions containing a ratio of H 2 O/D 2 O = 1.00. The separation factor, α, of both reactions is α = 5.0 ± 1.0. The rate of the hydrolysis of BD 4 − in H 2 O is faster than that of BH 4 −. The results point out that the rate-determining step in all hydrolysis stages is the H–OH bond scission. [Display omitted] • The H/D kinetic isotope effect (KIE) in NaBH 4 hydrolysis is reported, α = 5.0 ± 1.0 • The rate-determining step in NaBH 4 hydrolysis is discussed. • The hydrolysis of BD 4 − in H 2 O is faster than that of BH 4 −. [ABSTRACT FROM AUTHOR]

Advanced oxidation technologies often use peroxymonosulfate in the presence of CoIIaq. It is commonly assumed that the reaction of Co(H2O)62+ with HSO5− yields CoIIIaq and SO4.−. DFT results point out that first CoII(SO5)(H2O)2 is formed. The homolysis of CoII(SO5)(H2O)2 to yield (H2O)CoII(SO5)OH.+SO4.−, is exothermic but has a large activation energy. However the cobalt is not oxidized in this reaction. CoII(SO5)(H2O)2 reacts with a second HSO5− to form CoII(SO5)2(H2O)2− that decomposes via disproportionation of the monoperoxysulfate ions without oxidation of the central cobalt ion. Surprisingly even in the presence of ligands, L, that stabilize CoIII, i. e., pyrophosphate; tri‐polyphosphate and ATP, the experimentally observed reaction mechanism involves the formation of LCoII‐OOSO3aq which then reacts with another HSO5− to form LCoII‐(OOSO32−)2. The latter complex decomposes via disproportionation of the monoperoxysulfate ligands followed by oxidation of the central cobalt cation. Alternatively, in the presence of excess CoIILaq, LCoII‐OOSO3aq reacts with CoIILaq to form 2CoIIILaq. These results point out that the mechanism of advanced oxidation processes initiated by a mixture of Co(H2O)62+ and HSO5− must be re‐considered. [ABSTRACT FROM AUTHOR]

Olefin metathesis, a powerful synthetic method with numerous practical applications, can be improved by developing heterogeneous catalysts that can be recycled. In this study, a single-stage process for the entrapment of ruthenium-based catalysts was developed by the sol–gel process. System effectiveness was quantified by measuring the conversion of the ring-closing metathesis reaction of the substrate diethyl diallylmalonate and the leakage of the catalysts from the matrix. The results indicate that the nature of the precursor affects pore size and catalyst activity. Moreover, matrices prepared with tetraethoxysilane at an alkaline pH exhibit a better reaction rate than in the homogenous system under certain reaction conditions. To the best of our knowledge, this is the first study to present a one-step process that is simpler and faster than the methods reported in the literature for catalyst entrapment by the sol–gel process under standard conditions. [ABSTRACT FROM AUTHOR]

The reactions of methyl radicals with MII-(ntp)(H2O)2 complexes were studied. The formation of an unstable intermediate (ntp)(H2O)MIII-CH3 is observed. This reaction is an equilibrium process, i.e. the MIII-C bond decomposes via homolysis. The (ntp)(H2O)MIII-CH3 complexes isomerize to a more stable form. The results compared to those obtained in analogous reactions of the MII-(nta)(H2O)2 complexes were shown to be similar with one exception – for the nta complexes no isomerization process is observed. [ABSTRACT FROM AUTHOR]

In this study, WO 3 (trioxide tungsten) was investigated as a catalyst for water reduction by NaBH 4 in basic conditions, which are not typical for NaBH 4 reduction processes. The results indicate that the structure of the WO 3 phase strongly affects the catalytic process. The uncalcinated WO 3, ncWO 3 , which contains primarily tungstite with traces of hydro-tungstite is the only WO 3 form that acts as an effective catalyst. A cubic WO 3 is formed or exposed during the reduction process. Hydrogen production increases during reaction cycles; an interesting and important result. Plausible mechanisms of the catalytic process observed are outlined. The results have far-reaching effects that should be further investigated in other systems, such as the phase structures acting as a catalyst for treating toxic organic compounds. [Display omitted] • WO 3 is a catalyst for HER in alkaline solutions (pH 8–11). • NaBH 4 plays an important role in WO 3 -driven HER in basic conditions. • Orthorhombic tungstite and monoclinic hydrotungstite catalyze water reduction. • Dehydrated, cubic WO 3 is formed, or is exposed, from the ncWO 3 during the process. • Calcined WO 3 is less effective than ncWO 3 as a catalyst for HER in basic conditions. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Synthesis of ED3A-Silica gel based resin. • Characterization by solid state NMR, CS analyzer, BET, ICP-OES. • pH based preconcentration of Uranium and Cerium. • Adsorption optimum at pH 5.2, desorption below pH 2.0. • Capacity of 150 micromol/g with a surface area of 330.5 m2/g. Abstract Ethylene-di-amine-tri-acetate was covalently bound to a Silica-gel matrix (ED3A-SG). The resin thus obtained was examined as a possible Ion Exchange Resin for pre-concentration of actinides and lanthanides. ED3A-SG was prepared by reacting Sodium N-(tri-methoxy-silyl-propyl)-ethylene-di-amine-tri-acetate (ED3A-Silane coupler) with silica-gel. The porosity of the system was measured using BET analysis. The capacity of the resin was measured by two techniques: a. Determination of the carbon content of the Resin using Carbon Sulfur Analyzer (CS Analyzer). b. Saturating the Resin with nickel ions and determining their amount by inductively coupled plasma optical emission spectrometer (ICP-OES). The behavior of the ED3A-SG resin as function of pH was measured by determining the recovery value of cations solutions buffered at different pH values. The molecular structure of the resin was examined by 13C NMR and 29Si NMR. [ABSTRACT FROM AUTHOR]

Graphical abstract Gold and silver nanoparticle catalyzed reductive dehalogenation of halo acetic acids are investigated both experimentally and theoretically. Highlights • Gold and Silver nanoparticle entrapped in silica matrices have been synthesized. • Reductive dehalogenation of halo acetic acids proceeds via different mechanisms. • Reduction depends on the nature of nanoparticle and the rate of addition of NaBH 4. • DFT calculation and isotopic labeling experiments support the mechanism. Abstract This study investigated the reductive de-halogenations of toxic Br 3 CCO 2 −, Br 2 CHCO 2 −, BrCH 2 CO 2 −, CH 3 CHBrCO 2 −, CH 2 BrCH 2 CO 2 −, CH 2 BrCHBrCO 2 −, Cl 3 CCO 2 −, Cl 2 CHCO 2 - and ClCH 2 CO 2 − by sodium borohydride catalyzed by sol-gel silica entrapped Au0 and Ag0 nanoparticles. The results indicate that the mechanism of reduction of Br 3 CCO 2 − differs from that of Cl 3 CCO 2 −. Calculated by DFT, the source of this difference lies in the larger bond strength of C Cl compared to that of C Br and the weaker M0 C bond strength in Au0-CBr 2 CO 2 − compared to those of Au0-CCl 2 CO 2 − and Au0-CH 2 CO 2 −. Furthermore, the de-halogenation mechanisms catalyzed by Ag0-NPs differ from those catalyzed by Au0-NPs. The latter observation is attributed to the different Ag C and Au C bond strengths and to the different over-potentials for H 2 release of these M0-NPs. In addition, product composition depends on the rate of BH 4 − addition. Proton labeling experiments prove that nearly all the hydrogen atoms in the products originated from the water solvent and not from the BH 4 −. The detailed mechanistic conclusions that can be drawn from these results differ considerably from those commonly accepted for de-halogenation processes. [ABSTRACT FROM AUTHOR]

The nature of H‐atoms adsorbed on M0‐nanoparticles is of major importance in many catalyzed reduction processes. Using isotope labeling, we determined that hydrogen evolution from transient {(M0‐NP)‐Hn}n− proceeds mainly via the Heyrovsky mechanism when n is large (i.e., the hydrogens behave as hydrides) but mainly via the Tafel mechanism when n is small (i.e., the hydrogens behave as atoms). Additionally, the relative contributions of the two mechanisms differ considerably for M=Au and Ag. The results are analogous to those recently reported for the M0‐NP‐catalyzed de‐halogenation processes. [ABSTRACT FROM AUTHOR]

The nature of H‐atoms adsorbed on M0‐nanoparticles is of major importance in many catalyzed reduction processes. Using isotope labeling, we determined that hydrogen evolution from transient {(M0‐NP)‐Hn}n− proceeds mainly via the Heyrovsky mechanism when n is large (i.e., the hydrogens behave as hydrides) but mainly via the Tafel mechanism when n is small (i.e., the hydrogens behave as atoms). Additionally, the relative contributions of the two mechanisms differ considerably for M=Au and Ag. The results are analogous to those recently reported for the M0‐NP‐catalyzed de‐halogenation processes. The nature of H‐atoms adsorbed on metal nanoparticles (NPs) is of major importance in many catalyzed reduction processes. The H‐atoms of the transient {(M0‐NP)‐Hn}n− behave mainly as hydrides when n is large (the Heyrovsky mechanism), and as atoms when n is small (the Tafel mechanism). The relative contributions of the two mechanisms differ considerably for Au and Ag‐NPs. [ABSTRACT FROM AUTHOR]

Halo-organic acids in aqueous solutions are widespread pollutants. An enormous number of technologies have been proposed for their elimination. In this context, reducing electron exchange columns seem to be an optimal solution for their degradation, as they do not introduce any new chemical into the solution to be purified. The electron exchange columns used in this study consist of entrapped polyoxometalates (POMs) in silica sol-gel matrices that were used as the reducing medium for the reductive de-halogenation of Br3CCO2−, Cl3CCO2−, BrCH2CO2− and ClCH2CO2−. The same matrices were also applied as catalysts for the reduction of the investigated halo-acetates by BH4−. Surprisingly, the results indicate that the mechanisms of de-halogenation of Br3CCO2−, Cl3CCO2−, BrCH2CO2− and ClCH2CO2− differ from each other. [ABSTRACT FROM AUTHOR]

During an effort to synthesize the trans-III-copper(II) complex with 1,4,8,11-tetramethyl-pyro-phosphonate-1,4,8,11-tetra-aza-cyclo-tetradecane, using only perchlorate salts, it was noted that the perchlorate is reduced to chloride. Analysis of the reactions leading to this surprising result points out that Cu(H2O)42+ catalyzes the reduction of perchlorate by H2 and by CH2O. These reactions are slow at room temperature and ambient pressures. A plausible mechanism, supported by DFT calculations, is proposed pointing out that the role of CuH+ under mild conditions cannot be ignored. [ABSTRACT FROM AUTHOR]

The dehalogenation reaction mechanism of CH 3 X (X = Br, Cl) on Ag(111) and Au(111) surfaces is explored computationally. It is found that the CH 3 X species are stronger adsorbed on Au(111) surface than on Ag(111) surface due to the increased charge transfer between the adsorbent and the surface. The dehalogenation on Au(111) and Ag(111) surface is slow due to large activation energy barriers. In presence of water, the release of CH 4 is plausible. CH 4 is also released when pre-adsorbed ⁎H atoms are on the Ag(111) and Au(111) surfaces. The calculations indicate that the presence of co-adsorbents, mainly charged co-adsorbates, affects the reaction kinetics of CH 3 X dehalogenation as their adsorption is accompanied by charge transfer, thus altering the electronic charge of the surface. It is proposed that the kinetics of the dehalogenation of CH 3 X depends considerably on the charge on the metallic surface. Ag(111) is found to be a more promising catalyst for the dehalogenation of CH 3 X than Au(111). [Display omitted] • Methyl halides are stronger adsorbed on Au(111) than on Ag0-NPs • On M(111) surface the methyl halide (CH 3 X) dehalogenation is slow due to the large activation energy barriers. • Co-adsorbates play an important role in heterogeneous catalysis. • Charged Co-adsorbates enhance dehalogenation by reducing the activation energy barriers. • Ag(111) surface is found to be a more promising catalyst for the dehalogenation of CH 3 X than Au(111) surface. [ABSTRACT FROM AUTHOR]

Iron(II), (Fe(H2O)62+, (FeII) participates in many reactions of natural and biological importance. It is critically important to understand the rates and the mechanism of FeII oxidation by dissolved molecular oxygen, O2, under environmental conditions containing bicarbonate (HCO3−), which exists up to millimolar concentrations. In the absence and presence of HCO3−, the formation of reactive oxygen species (O2⋅−, H2O2, and HO⋅) in FeII oxidation by O2 has been suggested. In contrast, our study demonstrates for the first time the rapid generation of carbonate radical anions (CO3⋅−) in the oxidation of FeII by O2 in the presence of bicarbonate, HCO3−. The rate of the formation of CO3⋅− may be expressed as d[CO3⋅−]/dt=[FeII[[O2][HCO3−]2. The formation of reactive species was investigated using 1H nuclear magnetic resonance (1H NMR) and gas chromatographic techniques. The study presented herein provides new insights into the reaction mechanism of FeII oxidation by O2 in the presence of bicarbonate and highlights the importance of considering the formation of CO3⋅− in the geochemical cycling of iron and carbon. [ABSTRACT FROM AUTHOR]

Iron(II), (Fe(H2O)62+, (FeII) participates in many reactions of natural and biological importance. It is critically important to understand the rates and the mechanism of FeII oxidation by dissolved molecular oxygen, O2, under environmental conditions containing bicarbonate (HCO3−), which exists up to millimolar concentrations. In the absence and presence of HCO3−, the formation of reactive oxygen species (O2⋅−, H2O2, and HO⋅) in FeII oxidation by O2 has been suggested. In contrast, our study demonstrates for the first time the rapid generation of carbonate radical anions (CO3⋅−) in the oxidation of FeII by O2 in the presence of bicarbonate, HCO3−. The rate of the formation of CO3⋅− may be expressed as d[CO3⋅−]/dt=[FeII[[O2][HCO3−]2. The formation of reactive species was investigated using 1H nuclear magnetic resonance (1H NMR) and gas chromatographic techniques. The study presented herein provides new insights into the reaction mechanism of FeII oxidation by O2 in the presence of bicarbonate and highlights the importance of considering the formation of CO3⋅− in the geochemical cycling of iron and carbon. [ABSTRACT FROM AUTHOR]

The CuI/IIATP react with methyl radicals to form methane and methanol, where CuIATP reacts with •CH 3 in a process that is surprisingly slow. The low-rate constant of this process is attributed to the significant rearrangement of the chelating ligand required for the transient's formation. These results were corroborated by DFT calculations of the relevant compounds. The M06-2×/6–311 + g(d,p) optimized structure of the of the [H 3 C-CuIII-ATP]2− intermediate, demonstrating the carbon-metal σ bond between the copper ion and the methyl radical. [Display omitted] • The reactions of Cu(II/I)ATP complexes with CH 3 radicals are surprisingly slow. • The slow rate constants are attributed to the rigidity of the chelating ligand. • The reaction rates are independent of the CH 3 radical steady state concentration. [ABSTRACT FROM AUTHOR]

The measurement of the hydroxyl radical scavenging properties of a compound is not indicative on its antioxidant properties in vivo. To get such information one has to elucidate the mechanism of its reaction with typical secondary radicals, mainly typical RO2. radicals and to some degree with R. radicals. Elucidation of the mechanisms of reaction is essential before a conclusion regarding the antioxidant properties can be derived. One should remember that in vivo even vitamins C and E might act as pro-oxidants. [ABSTRACT FROM AUTHOR]

Reduction of nitrobenzene with NaBH4 using zero-valent iron nanoparticles (ZVI-NPs) and NiCl2∙6H2O incorporated in organically modified hybrid silica matrices as ZVI@ORMOSIL and Ni(II)@ORMOSIL catalysts is proposed as a remediation strategy. Ni(II)@ORMOSIL is prepared by ion-exchanging H+ of the ORMOSIL matrix with NiII. Ni(II)@ORMOSIL is a pre-catalyst that undergoes reduction by NaBH4 by an in-situ reaction and promotes nitrobenzene reduction by the unconsumed NaBH4, leading to sparing use of the catalyst. Ni(II)@ORMOSIL undergoes color change from green to black in this process, returning to a green hue after washing and drying. Nitrobenzene reductions were examined in aqueous acetonitrile solvent mixtures, and the reduction cascade produced the reaction end-products with catalytic implications. Plausible mechanisms of ZVI@ORMOSIL and Ni(II)@ORMOSIL catalyzed reductions of nitrobenzene are discussed. This work is the first to report M(II)@ORMOSIL pre-catalysts for in-situ reduction of nitrobenzene, and expands the scope of the ORMOSIL series of catalysts for the reduction of polluting compounds. This approach enables the development of catalysts that use very low concentrations of transition metal cations. [ABSTRACT FROM AUTHOR]

Abstract: Usually, investigations of erythrocyte aggregation at rest are focused on effects of the strength of erythrocyte–erythrocyte attractive interactions and the volume fraction of the cells, whereas the role of prior flow velocity has not been thoroughly investigated. The aim of this study is to fill this gap. The main conclusions extracted from time records of the complex admittance of blood are as follows: (1) Dispersion of blood in a prior flow into discrete aggregates increases the mesh size of network, which, as has been recently shown, is formed in the quiescent blood. (2) If the energy of the flow field is sufficient to prevent the formation of face-to-side intercellular links, so that the dispersed phase consists of linear rouleaux, changes in the mesh size correlate positively with the length of rouleaux. (3) At slower prior flow velocities, the cells are combined into branched aggregates. As the degree of branching increases, the effect becomes less important. (4) The effects of the length of linear rouleaux and the degree of branching of ramified aggregates on the mesh size are qualitatively similar for suspensions with different aggregating media. (5) Erythrocytes suspended in strongly aggregating media form at low flow conditions a network-like structure. In this case, unlike high and moderate prior flow regimes, the mesh size of RBC network at rest is less than that formed after the stoppage of completely dispersed blood. [ABSTRACT FROM AUTHOR]

Abstract: The rate constant of the electron self-exchange reaction, which proceeds via the outer sphere mechanism, k 11, of a redox couple, reflects the basic tendency of the reaction to participate in redox processes. Often k 11 is derived from the rate constant of a redox reaction, k 12, by applying the Marcus cross relation: k 12 =(k 11 k 22 K 12 f 12)1/2 W 12. This derivation is based on the assumption that the products of the cross reaction are formed in their ground states. However, the k11 values obtained by this method for several redox systems, e.g. for [Co(NH3)6]3+/2+, Cu2+/+(aq) and Eu3+/2+(aq), depend strongly on the redox reaction studied for its derivation. It is proposed that these discrepancies are due to the formation, in some of these reactions, of products in vibrationally excited states and/or as isomers of the final products. Thus, the lowest value of k 11 obtained experimentally is either correct or an upper limit for the correct value if correct k 22 are used. [Copyright &y& Elsevier]

Presents a study which investigated the reaction of .NO with organometallic complexes with cobalt- and nickel-carbon...bonds. Research methodology; Statistical data; Statistical data analysis; Results of this study.

Sonochemical formation of Pt0 nanoparticles in formic acid media involves the reduction of PtVI by carboxyl radicals (.CO2H/CO2.−). [ABSTRACT FROM AUTHOR]

• The radicals R = CH 3 or CH 2 OH, react with the complex CuII(ntp)(H 2 O). • The kinetics of formation of (ntp)CuIII-R fit pseudo first order rate laws. • The decomposition of (ntp)CuIII-CH 3 at pH > 7 involves homolysis of the CuIII-C bond. • At pH < 6 (ntp)CuIII-R decomposes via inter-molecular e- transfer to CuII species. The reactions of the radicals R, R = CH 3 or CH 2 OH, with the complex CuII(ntp)(H 2 O) were studied. The kinetics of formation of the transient complexes (ntp)CuIII-R fit pseudo first order rate laws. The mechanism of decomposition of the transient complex (ntp)CuIII-CH 3 at pH ≥ 7 involves homolysis of the CuIII-C bond. However, at pH < 6 the decomposition mechanisms of the transient complexes (ntp)CuIII-R involve inter-molecular electron transfer to CuII(ntp)(H 2 O) and slow intra-molecular electron transfer. [ABSTRACT FROM AUTHOR]

The efficient reductive dechlorination, as remediation of dichloroacetamide and monochloroacetamide, toxic and abundant pollutants, using sodium borohydride catalyzed by zero valent iron nanoparticles (ZVI-NPs), entrapped in organically modified hybrid silica matrices prepared via the sol-gel route, ZVI@ORMOSIL, is demonstrated. The results indicate that the extent of the dechlorination reaction depends on the nature of the substrate and on the reaction medium. By varying the amount of catalyst or reductant in the reaction it was possible to obtain conditions for full dechlorination of these pollutants to nontoxic acetamide and acetic acid. A plausible mechanism of the catalytic process is discussed. The present work expands the scope of ZVI-NP catalyzed reduction of polluting compounds, first reports the catalytic parameters of chloroacetamide reduction, and offers additional insight into the heterogeneous catalyst structure of M0@ORMOSIL sol-gel. The ZVI@ORMOSIL catalyst is ferromagnetic and hence can be recycled easily. [ABSTRACT FROM AUTHOR]

Zero-valent iron-nanoparticles (ZVI-NPs) entrapped in silica matrices through a sol-gel procedure are investigated as redox catalysts with BH 4 − (NaBH 4) as the reducing agent. The results indicated that the matrix functions as an efficient and multifunctional catalyst for the reduction of halo-acetic acids (HAAs), [BrO 3 −] and 4-nitrophenol pollutants present in the contaminated water. The present study revealed that the reduction mechanism depends on the nature of the substrate, M0 used and the rate of the reductant addition (batch mode reactor system). The novelty of the present work is double-fold: First, in pointing out that the mechanism of the catalytic de-halogenation reaction depends on the nature of M0-NPs used as a catalyst, probably due to the different over-potential for the HER reaction on each M0-NPs and second, the development of a cost-effective remediation alternative compared to the analogous Au0-NPs or Ag0-NPs catalysts reported in the literature. Unlabelled Image • ZVI Nps entrapped in sol-gel matrices is an effective catalyst for variety of redox processes. • ZVI NPs can replace Ag0 and Au0 Nps as catalysts in de-halogenation processes. • The reduction products obtained depend on the nature of the metal in the M0-NPs used. [ABSTRACT FROM AUTHOR]

Silica supported silver nanoparticles, SiO2‐Ag0‐NPs, catalyze the hydrolysis of BH4−. A comparison of the isotopic composition of the hydrogen formed in the hydrolysis of BD4− points out that the contribution of hydrides, the Heyrovsky mechanism, rather than that of hydrogen atoms, the Tafel mechanism, to the hydrogen evolution is considerably larger for the SiO2‐Ag0‐NPs catalyzed process than for the Ag0‐NPs catalyzed process. This indicates some electron transfer from the SiO2 to the silver that increases the negative charge on the Ag0‐NPs. [ABSTRACT FROM AUTHOR]

Review: 53 refs. [ABSTRACT FROM AUTHOR]

Review: 171 refs. [ABSTRACT FROM AUTHOR]

The kinetics of the reaction of Cu II (GGG), Cu II (GGGGG) and Cu II (GGGGS), where G = glycine and S = sarcosine, with 4-nitrophenyl-acetate were measured. The results point out that at pH 9.0 hydroxide is an axial, or equatorial ligand to a significant amount of these complexes. The source of the different mechanisms of reaction of the analogous nickel complexes is attributed to the axial water ligand of the copper complexes. The biological implications of axial hydroxide binding to copper peptides is discussed. [ABSTRACT FROM AUTHOR]

DFTcalculations concerning the plausible mechanism of Fenton-like reactionscatalyzed by Fe(II) and Co(II) cations in the presence of carboxylateligands suggest that hydroxyl radicals are not formed in these reactions.This conclusion suggests that the commonly accepted mechanisms ofFenton-like reactions induced oxidative stress and advanced oxidationprocesses have to be reconsidered. [ABSTRACT FROM AUTHOR]

Photocatalytic hydrogen production is proposed as a sustainable energy source. Simultaneous reduction and oxidation of water is a complex multistep reaction with high overpotential. Photocatalytic processes involving semiconductors transfer electrons from the valence band to the conduction band. Sacrificial substrates that react with the photochemically formed holes in the valence band are often used to study the mechanism of H2 production, as they scavenge the holes and hinder charge carrier recombination (electron‐hole pairs). Here, we show that the desired sacrificial agent is one forming a radical that is a fairly strong reducing agent, and whose oxidized form is not a good electron acceptor that might suppress the hydrogen evolution reaction (HER). In an acidic medium, methanol was found to fulfill both these requirements better than ethanol and propan‐2‐ol in the TiO2‐(M0‐NPs) (M=Au or Pt) system, whereas in an alkaline medium, the alcohols exhibit a reverse order of activity. Moreover, we report that CH2(OH)2 is by far the most efficient sacrificial agent in a nontrivial mechanism in acidic media. Our study provides general guidelines for choosing an appropriate sacrificial substrate and helps to explain the variance in the performance of alcohol scavenger‐based photocatalytic systems. [ABSTRACT FROM AUTHOR]

Binding NiII to the terminal amine of a peptide depresses totally its nucleophilic character as measured by the rate constant of the reaction of the peptide with 4-nitrophenyl acetate. The structure of NiII(GGGGG) in aqueous solutions was determined by this technique. The results indicate that the ratio of complexes in which the nickel is bound to four deprotonated peptide nitrogen atoms to those in which the nickel is bound to the terminal amine and three deprotonated peptide nitrogen atoms increases as the pH increases. At pH 9.0, this ratio is approximately 1. [ABSTRACT FROM AUTHOR]

Abstract: Literature reports provide evidence that nanomolar concentrations of spaghetti-like, high molecular weight polymers decrease the hydrodynamic resistance of blood thereby improving impaired blood circulation. It has been suggested that the polymer-induced drag reduction is caused by the corralling of red blood cells (RBCs) among extended macromolecules aligned in the flow direction. This mechanism predicts that drag-reducing polymers must affect the conductivity of completely dispersed blood, time-dependent and steady state structural organization of aggregated RBCs at rest. However, experimental results obtained at the concentration of poly(ethylene oxide) (PEO, MW=4×106) of 35ppm show that neither the conductivity of completely dispersed blood, nor the kinetics of RBC aggregation occurring after the stoppage of flow, nor the structural organization of aggregated RBCs in the quiescent blood are affected by PEO. As these results are at odds with the “corralling” hypothesis, it is assumed that the effect of these polymers on the drag is associated with their interactions with local irregularities of disturbed laminar blood flow. [Copyright &y& Elsevier]

The effects of 10 paramagnetic metal complexes (FeIIIEDTA(H2O), FeIIIEDTA(OH)2-, FeIIIPDTA-, FeIIIDTPA2, FeIII2O(TTHA)2-, FeIII(CN)63-, MnIIEDTA(H2O)2-, MnIIPDTA2-, MnIIβ-EDDADP2-, and MnIIPO4-) on F- ion 19F NMR transverse relaxation rates (R2 = 1/T2) were studied in aqueous solutions as a function of temperature. Consistent with efficient relaxation requiring formation of a metal/F- bond, only the substitution inert complexes FeIII(CN)63- and FeIIIEDTA(OH)2- had no measured effect on T2 relaxation of the F- 19F resonance. For the remaining eight complexes, kinetic parameters (apparent second-order rate constants and activation enthalpies) for metal/F- association were determined from the dependence of the observed relaxation enhancements on complex concentration and temperature. Apparent metal/F association rate constants for these complexes (kapp,F-) spanned 5 orders of magnitude. In addition, we measured the rates at which O2·- reacts with FeIIIPDTA-, MnIIEDTA(H2O)2-, MnIIPDTA2-, and MnIIβ-EDDADP2- by pulse radiolysis. Although no intermediate is observed during the reduction of FeIIIDTA- by O2·-, each of the MnII complexes reacts with formation of a transient intermediate presumed to form via ligand exchange. These reactivity patterns are consistent with literature precedents for similar complexes. With these data, both kapp.O2- and kapp.F- are available for each of the eight reactive complexes. A plot of log(kapp.O2-) versus log(kapp,F-) for these eight showed a linear correlation with a slope 1. This correlation suggests that rapid metal/O2·- reactions of these complexes occur via an inner-sphere mechanism whereas formation of an intermediate coordination complex limits the overall rate. This hypothesis is also supported by the very low rates at which the substitution inert complexes (FeIII(CN)63- and FeIIIEDTA(OH)2-). are reduced by O2·-. These results suggest that F- 19F NMR relaxation can be used to predict the reactivities of other FeIII complexes toward reduction by O2·-, a key step in the biological production of reactive oxygen species. [ABSTRACT FROM AUTHOR]

Purpose: To examine the role of the water-soluble antioxidants glutathione and ascorbic acid in the irrigating solution on corneal endothelial cells following exposure to high-intensity ultrasound energy. Setting: Goldschleger Eye Research Institute, Sheba Medical Center, Tel-Aviv University, Tel Aviv, Israel. Methods: Thirty-two rabbit eyes were subjected to prolonged exposure to the phacoemulsification device in the anterior chamber. The eyes were divided into 4 groups that differed only in the composition of the irrigating solution applied to the eyes: balanced salt solution (BSS) BSS Plus BSS containing additional soluble components including glutathione, BSS with 10−3 M of oxidized glutathione (GSSG), and BSS with 10−2 M of ascorbic acid. Specular microscopy was performed preoperatively and 1 week after surgery. Results: The BSS group exhibited the highest endothelial cell loss (19.3%), followed by the BSS Plus group (10.6%), the GSSG group (5.2%), and the ascorbic acid group (0.9%). An overall difference was found between the groups (F = 11.046, P<.0001), and all groups demonstrated a statistically significant difference from the control BSS group (P<.02, P = .001, and P<.0001, respectively). Conclusions: Damage to the cornea is largely due to the free radicals generated by high-intensity ultrasound energy during phacoemulsification. Adding the antioxidants ascorbic acid and GSSG to the irrigation solution significantly reduced the endothelial corneal cell damage. Ascorbic acid in the concentration of 10−2 M had the highest protective effect; thus, it should be evaluated for clinical use. [Copyright &y& Elsevier]

The reactions of several radicals of the type ·CR¹R²CR³R4X (where X = OH or NH3+) with metal powders that have been immersed in aqueous solutions were studied. The radicals were formed by radiation chemical techniques. One of the products in all these reactions is the corresponding alkene, R¹R²CCR³R4. The results are in accord with a mechanism in which the radicals react with the metals that are forming transients with metal-carbon σ bonds. The latter transients decompose via two competing reactions: (a) heterolysis of the metal-carbon σ bond and (b) β-elimination of X-. Moreover, the dehalogenation of BrCH2CH2NH3+ and ClCH2(CH3)2COH by metal powders was studied. Also in these reactions, the corresponding alkene is one of the products. This result is consistent with the suggestion that, in the dehalogenation reaction, an alkyl radical is formed in the first step. This radical then reacts with the metal. Alternatively, the transients with metal-carbon π bonds in the dehalogenation processes might be formed via a concerted mechanism. [ABSTRACT FROM AUTHOR]

Abstract: CR1R2OH, R i =CH3 or H, react with the complex [CoIII(NH3)5CN]2+ to form an observable intermediate probably via bonding to the nitrogen of the cyanide. This intermediate isomerizes to form a second intermediate. The second intermediate decomposes into Co2+(aq), 5NH4 +, CN− and R1R2CO. The plausible structures of the intermediates are discussed. The radicals CH3, CH2CHO, , and are considerably less reactive towards this complex, the formation of intermediates in their presence is not observed. [Copyright &y& Elsevier]

The reactions of RO2· radicals with Fe(H2O)62+ were studied, R=H; CH3; CH2COOH; CH2CN; CH2C(CH3)2OH; CH2OH; CHCl2/CCl3. All these processes involve the following reactions:(1)Fe(H2O)62++RO2·⇄(H2O)5FeIII–OOR2+ K1∼250 M−1(2)(H2O)5FeIII–OOR2++H3O+/H2O→Fe(H2O)63++ROOH+H2O/OH−(3)(H2O)5FeIII–OOR2++2Fe(H2O)62+→3Fe(H2O)63++ROH(4)2 RO2·→Products(5)RO2·+(H2O)5FeIII–OOR2+→Fe(H2O)62++productsThe values of k1 and k3 [reaction is clearly not an elementary reaction] approach the ligand exchange rate of Fe(H2O)62+, i.e. these reactions follow an inner sphere mechanism and the rate determining step is the ligand exchange step. The rate of reaction is several orders of magnitude faster than that of the Fenton reaction.Surprisingly enough the K1 values are nearly independent of the redox potential of the radical and are considerably higher than calculated from the relevant redox potentials. These results indicate that the ROO− ligands considerably stabilise the Fe(III) complex, this stabilisation is smaller for radicals with electron withdrawing groups which raise the redox potential of the radical but decrease the basicity of the ROO− ligands, two effects which seem to nearly cancel each other. Finally, the results clearly indicate that reaction (5) is relatively fast and affects the nature of the final products. The contribution of these reactions to oxidation processes involving ‘Fenton-like’ processes is discussed. [Copyright &y& Elsevier]

Methyl radicals play key roles in various chemical and biological processes. Mechanistic studies of methyl radicals with their precursor, Dimethyl Sulfoxide (DMSO), were extensively studied. Though the involved mechanisms seemed to be clarified, essentially none of the studies have been performed at conditions relevant to both biological and catalytic systems, i.e. low steady state radical concentrations. A chain-like reaction, as an inverse function of the radicals concentrations ([•CH 3 ] ss), increases the methyl radical yields. The nature of the additional products obtained differs from those commonly observed. Furthermore it is shown that methyl radicals abstract a methyl group from DMSO to yield ethane. Herein we report a novel mechanism relevant mainly at low steady state radical concentrations, which may change the understanding of certain reaction routes present in both biological systems and catalytic chemical systems. Thus the results point out that mechanistic studies have to be carried out at dose rates forming radicals at analogous concentrations to those present in the process of interest. Image 1 • Low steady state concentrations of radicals alter the reaction mechanism. • Several new reaction paths, that produce new radicals, have been identified. • Processes in living systems might differ from those observed in model studies. [ABSTRACT FROM AUTHOR]

CoII salts in the presence of HCO3−/CO32− in aqueous solutions act as electrocatalysts for water oxidation. It comprises of several key steps: (i) A relatively small wave at Epa≈0.71 V (vs. Ag/AgCl) owing to the CoIII/II redox couple. (ii) A second wave is observed at Epa≈1.10 V with a considerably larger current. In which the CoIII undergoes oxidation to form a CoIV species. The large current is attributed to catalytic oxidation of HCO3−/CO32− to HCO4−. (iii) A process with very large currents at >1.2 V owing to the formation of CoV(CO3)3−, which oxidizes both water and HCO3−/CO32−. These processes depend on [CoII], [NaHCO3], and pH. Chronoamperometry at 1.3 V gives a green deposit. It acts as a heterogeneous catalyst for water oxidation. DFT calculations point out that Con(CO3)3n−6, n=4, 5 are attainable at potentials similar to those experimentally observed. [ABSTRACT FROM AUTHOR]

Abstract The Fenton reaction, Fe(H 2 O) 6 2+ + H 2 O 2 → Oxidizing product, is of major importance in biology as the major cause of oxidative stress, and in advanced oxidation processes. It is commonly assumed that · OH is the product of the Fenton reaction. The results presented herein point out that · OH is indeed the oxidizing product in acidic solutions for [Fe(H 2 O) 6 2+] > [H 2 O 2 ]; FeIV aq is the active oxidizing product in neutral solutions; in slightly acidic solutions for [H 2 O 2 ] > [Fe(H 2 O) 6 2+] a mixture of · OH and FeIV aq is formed. However CO 3 · - is the active oxidizing product in neutral solutions containing HCO 3 - even at low concentrations, i.e. under physiological conditions. The implications to our understanding of the origins of oxidative stress and of catalytic oxidations in advanced oxidation processes are discussed. Graphical abstract fx1 Highlights • CO 3 ·- is the oxidizing agent of the Fenton reaction in neutral solutions containing HCO 3 -. • CO 3 ·-, and not ·OH is the major cause of oxidative stress in biological systems. • Under catalytic conditions FeIV=O2+ aq is a major product of the Fenton reaction. [ABSTRACT FROM AUTHOR]

Abstract: Recently it was reported that copper bicarbonate/carbonate complexes are good electro‐catalysts for water oxidation. However, the results did not enable a decision whether the active oxidant is a CuIII or a CuIV complex. Kinetic analysis of pulse radiolysis measurements coupled with DFT calculations point out that CuIII(CO3)n3−2n complexes are the active intermediates in the electrolysis of CuII(CO3)n2−2n solution. The results enable the evaluation of E°[(CuIII/II(CO3)n)aq]≈1.42 V versus NHE at pH 8.4. This redox potential is in accord with the electrochemical report. As opposed to literature suggestions for water oxidation, the present results rule out single‐electron transfer from CuIII(CO3)n3−2n to yield hydroxyl radicals. Significant charge transfer from the coordinated carbonate to CuIII results in the formation of C2O62− by means of a second‐order reaction of CuIII(CO3)n3−2n. The results point out that carbonate stabilizes transition‐metal cations at high oxidation states, not only as a good sigma donor, but also as a non‐innocent ligand. [ABSTRACT FROM AUTHOR]

Polyoxometalates (POMs), Na 3 PW 12 O 40 and H 5 AlW 12 O 40 were entrapped in silica matrices using the sol-gel process and utilized as reducing electron exchange columns for the reduction of bromate. Bromate is a toxic disinfection by-product, generated during the ozonation process of water. The results distinctly show that this hazardous compound can be efficiently removed from aqueous media at different pH values without the addition of any chemicals to the media. Furthermore, the reducing capacity of the matrices can be recharged without loss of activity. This is the first reported practicable application of reducing electron exchange columns. [ABSTRACT FROM AUTHOR]

The electrocatalytic reduction of bromoacetic, chloroacetic, bromobenzoic and chlorobenzoic acids by four Ni macrocyclic complexes (Ni II L i ) 2+ , was studied in both homogeneous and heterogeneous systems using glassy-carbon, nafion and carbon-paste modified electrodes. The results indicate that the electrocatalytic reduction of the bromo-compounds is more efficient than that of the chloro-compounds. The electrocatalytic activity increases with the redox potential of the electrocatalyst. The nafion-modified electrodes show poor electrocatalytic ability, whereas the carbon-paste electrodes are good electrocatalysts for the reduction of bromo-alkyls only. For this purpose, the latter electrode is better than the bare glassy-carbon electrode. The results show that the rates of reduction of the halo-organic compounds by the (Ni I L i ) + are slowed down when the complexes are incorporated into the modified electrodes. [ABSTRACT FROM AUTHOR]