Reaction Of Hydroxide Ion Research Articles

Binding and Degradation Reaction of Hydroxide Ions with Several Quaternary Ammonium Head Groups of Anion Exchange Membranes Investigated by the DFT Method.

Commercialization of anion exchange membrane fuel cells (AEMFCs) has been limited due to the chemical degradation of various quaternary ammonium (QA) head groups, which affects the transportation of hydroxide () ions in AEMs. Understanding how various QA head groups bind and interact with hydroxide ions at the molecular level is of fundamental importance to developing high-performance AEMs. In this work, the binding and degradation reaction of hydroxide ions with several QA head groups—(a) pyridinium, (b) 1,4-diazabicyclo [2.2.2] octane (DABCO), (c) benzyltrimethylammonium (BTMA), (d) n-methyl piperidinium, (e) guanidium, and (f) trimethylhexylammonium (TMHA)—are investigated using the density functional theory (DFT) method. Results of binding energies (“∆” EBinding) show the following order of the binding strength of hydroxide ions with the six QA head groups: (a) > (c) > (f) > (d) > (e) > (b), suggesting that the group (b) has a high transportation rate of hydroxide ions via QA head groups of the AEM. This trend is in good agreement with the trend of ion exchange capacity from experimental data. Further analysis of the absolute values of the LUMO energies for the six QA head groups suggests the following order for chemical stability: (a) < (b)~(c) < (d) < (e) < (f). Considering the comprehensive studies of the nucleophilic substitution (SN2) degradation reactions for QA head groups (c) and (f), the chemical stability of QA (f) is found to be higher than that of QA (c), because the activation energy (“∆” EA) of QA (c) is lower than that of QA (f), while the reaction energies (“∆” ER) for QA (c) and QA (f) are similar at the different hydration levels (HLs). These results are also in line with the trends of LUMO energies and available chemical stability data found through experiments.

Antibacterial properties of Cu-doped TiO2 prepared by chemical and heat treatment of Ti metal

ABSTRACT In this study, we proposed Cu-doped TiO2, prepared by the alkaline and heat treatment of titanium (Ti) metal, for use in dental applications because of its bone-bonding and antibacterial properties generated by the release of Cu ions and visible-light-responsive photocatalysis. We successfully prepared Cu-doped TiO2 on a Ti chip surface with a Cu content of 7 at.%. The apatite-forming ability of the Cu-doped TiO2 was evaluated using a simulated body fluid and it was found that apatite formation occurred. Hence, we concluded that Cu-doped TiO2 exhibits bone-bonding properties. The antibacterial properties of Cu-doped TiO2 for Escherichia coli were higher than those of non-doped TiO2 under visible light irradiation. The enhanced antibacterial effect was mainly caused by the visible-light-responsive photocatalysis of Cu-doped TiO2. We confirmed that the reactive oxygen species generated by the visible-light-responsive photocatalysis of Cu-doped TiO2 were hydroxyl radicals formed by the reaction of hydroxide ions (OH−) and holes (h+). Our findings are useful for the development of novel bioactive TiO2-based coatings and bulk materials with antibacterial properties by Cu doping.

Characteristics of the voltammetric behavior of the hydroxide ion oxidation at disordered mesoporous titanium dioxide electrocatalyst

The alkaline water electrochemical splitting reactions need economical, very energetic, and durable catalysts. Here, a disordered mesoporous and highly defected titanium dioxide (dom-TiO2) electrocatalyst for the oxidation of hydroxide ion was prepared via ligand-assisted evaporation-induced self-assembly. The (dom-TiO2) electrocatalyst showed significant electrocatalytic performance for the oxidation of hydroxide ion compared to that of non-porous TiO2 (bare-TiO2) and highly-ordered hexagonal mesoporous (hm-TiO2) electrodes. The chemical and electrochemical parameters of the diffusion (D), concentration in the bulk (Cb), the number of transferred electrons (n), rate constant of heterogeneous electron transfer (ks), redox potential (E°), and homogeneous chemical rate constant (kc) for the oxidation of hydroxide ion reaction at the porous TiO2 electrodes were determined via the convolution–deconvolution voltammetry and competed against that of non-porous (bare-TiO2) and hm-TiO2 and catalysts. In addition to the effect of dom-TiO2 film thickness and the type of supporting electrolytes on the electrochemical parameters of the electrocatalytic oxidation of OH– ions have been estimated. The convolutive–deconvoluted results show that the dom-TiO2 electrode catalyst exhibits a superior reaction rate constant among the studied electrodes that depend on the film thickness and type of supporting electrolyte.

Synthesis of dense but microporous graphene by Na+ ions intercalation toward high volumetric performance supercapacitors

With the rapid development of mobile electronics and electric vehicles, supercapacitors need to store as much energy as possible in relatively limited space. For aqueous-electrolyte supercapacitor, it is particularly important to design the electrode materials with high particle density, appropriate pore size distribution and doping degrees. In this work, we report an efficient approach to simultaneous increase the particle density and doping level of graphene-based electrode material. Through the interaction of oxygen functionalized graphene with NaOH solution, the electrostatic adsorption of sodium ions and oxygen-containing functional groups increases the density of the material while the reaction of hydroxide ions with oxygen-containing functional groups can increase the concentration of oxygen-containing functional groups of graphene. The as-prepared graphene displays both high particle density and pseudocapacitance which contributed from oxygen-containing functional groups. The graphene-based electrode delivers high volumetric capacitance of 469 F cm−3 as well as high rate capability (77% capacitance retention at 30 A g−1). Also, the assembled supercapacitor shows the high volumetric energy density of 24.2 Wh L−1, which is higher than most of the carbon materials in aqueous electrolyte. Therefore, this work provides a method to prepare high density and functionalized graphene, which has potential application in energy storage devices.

Understanding hydroxide reactions with guanidinium-based anion exchange polymers under conditions relevant to bipolar membrane electrodialysis

Anion exchange polymers are susceptible to loss of cationic functionality as a result of nucleophilic attack by hydroxide ions. This research investigated the stability of two guanidinium-based cations as anion exchange functional groups under conditions relevant to bipolar membrane electrodialysis. Density functional theory simulations were performed to investigate reaction energies and activation barriers for reactions of hydroxide ions with pentamethylguanidinium (PMG) and hexamethylguanidinium (HMG) cations bound to a diaryl ketone polymer backbone. The effect of physically adsorbed chloride and hydroxide ions, and chemically adsorbed hydroxide ions, on reaction energetics were determined. Fukui functions for nucleophilic attack were used to identify locations most likely to undergo reactions with hydroxide ions. For the PMG species, the most likely bond cleavage reactions were highly exergonic, with ΔGrxno values as large as −46 kcal/mol and activation barriers less than 10 kcal/mol. Chemisorption of hydroxide ions on both PMG and HMG cations was energetically favorable, with activation barriers of 5.3 and 2.7 kcal/mol, and resulted in loss of cationic functionality. Anion adsorption changed the reactivity of both PMG and HMG structures towards nucleophilic attack. For nucleophilic attack at the phenyl carbon atom, adsorption of OH− on the guanidinium carbon atom made PMG less reactive, while adsorption of Cl− made HMG less reactive. Bond cleavage and loss of cationic functionality was a two or three step process involving addition of OH− to the phenyl or guanidinium carbon atoms, followed by bond stretching or deprotonation of the added hydroxide species. For PMG species, deprotonation of the hydroxide resulted in bond cleavage or produced metastable species that decomposed with activation barriers less than 2 kcal/mol. HMG species were more stable with respect to this degradation mechanism, having activation barriers for bond cleavage ranging from 17 to 29 kcal/mol.

Applicability of Positive Cooperativity Model of Enzyme Catalysis on Surfactant-Mediated Reaction of Pararosaniline Hydrochloride Carbocation with Hydroxide Ion

The reaction of hydroxide ion with stabilized pararosaniline hydrochloride carbocation was investigated in the presence of cationic micelles of cetyltrimethylammonium bromide (CTAB) and anionic micelles of sodium dodecyl sulfate (SDS). Pseudo-first-order kinetics were followed by the reaction system and rate constant depends on surfactant concentration. The reaction was strongly inhibited in the presence of SDS micelles whereas catalyzed in the presence of CTAB micelles. Micellar data were analyzed by applying positive cooperativity model of enzyme catalysis. The value of index of cooperativity (n) was greater than 1 for all reaction systems. Inhibitory and catalytic effect in the presence of micelles had been explained on the basis of hydrophobic and electrostatic interactions of various species present in the reaction systems. Presence of counterions in the reaction system inhibited the reaction rate.

AM1 Specific Reaction Parameters for Reactions of Hydroxide Ion with Halomethanes in Complex Environments: Development and Testing.

A specific reaction parameters (SRP) approach is used to reparameterize the semiempirical AM1 method to represent two SN2 reactions of OH(-) with halomethanes (CH3F and CH3Cl). The objective is to develop SRP models that are able to accurately reproduce ab initio potential energy surfaces but with a reduction of several orders of magnitude in computational cost. The developed models, labeled AM1-SRP, have been tested in gas and aqueous phases. The results show that the AM1-SRP models are able to predict a minimum reaction path in close agreement with high level ab initio calculations in gas phase. A QM/MM simulation method with the solutes represented by the AM1-SRP models is used to compute the free energy profiles of the reactions in aqueous phase. The AM1-SRP models predict reaction free energies and free energy barriers in good agreement with experimental values. The current study indicates that semiempirical models may be improved to accurately reproduce an ab initio minimum reaction path at a considerably lower cost. The SRP approach is expected to be useful in long time scale molecular dynamics simulations where it is very expensive to use ab initio methods, specially in condensed phases.

Micellar Effect On Dephosphorylation Of Bis-4-Chloro-3,5- Dimethylphenylphosphate Ester By Peroxy Anions

The rate enhancement depends on the hydrophobicity of the nucleophile. The micellar catalyzed reaction between bis-4-chloro-3,5-dimethylphenylphosphate ester and hydroxide or hydroperoxide anions has been examined in buffered medium (pH 8-10). First order rate constant (Kψ) for the reaction of hydroxide ion with bis-4-CDMPP go through maxima with the increasing concentration of cetyltrimethylammoniumbromide (CTABr). Micelles of CTABr very effective catalyst to the reactions of phosphate diesters. Rate constants measured with OH2 - ions are approximately twice and thrice than that of OH - ions in presence of CTABr.

Why Are Hydrophobic/Water Interfaces Negatively Charged?

Impure at heart: A pH-dependent negative charge of the interface between a hydrophobic phase and water results from the reaction of hydroxide ions with traces of fatty acids, contained in the hydrophobic phase (see scheme). This reaction explains the uptake of hydroxide ions by the interface with a large free energy change.

ChemInform Abstract: Kinetics of Reactions of Hydroxide Ion and Water with β-X- Substituted α-Nitrostilbenes (X: Cl, I, SEt, OMe, SCH2CH2OH) in 50% Me2SO-50% Water. Search for the Intermediate in Nucleophilic Vinylic Substitution.

ChemInform Abstract: Kinetics of Reactions of Hydroxide Ion and Water with β-X- Substituted α-Nitrostilbenes (X: Cl, I, SEt, OMe, SCH2CH2OH) in 50% Me2SO-50% Water. Search for the Intermediate in Nucleophilic Vinylic Substitution.

ChemInform Abstract: Kinetic and Equilibrium Studies of σ-Adduct Formation and Nucleophilic Substitution in the Reactions of Hydroxide Ions with 2,4, 6-Trinitrophenyl Sulfides and Ethers.

ChemInform Abstract: Kinetic and Equilibrium Studies of σ-Adduct Formation and Nucleophilic Substitution in the Reactions of Hydroxide Ions with 2,4, 6-Trinitrophenyl Sulfides and Ethers.

Reaction kinetics on hydrolysis of substituted di-phenyl phosphate ester in different borate buffers

The reaction of hydroxide ion with di-4-methyl phenyl phosphate has been studied in the presence of micelles of cationic detergent. It has been investigated at pH 8.0 to 10.0 at 40 ± 0.10 °C in aqueous dioxane di-phosphate esters. Pseudo-first order rate constants k ψ and k' w have been measured spectrophotometrically by rate of appearance of inorganic phosphate during hydrolysis. k ψ and k' w were rate constants with and without CTAB, which varied in between 0.02 x 10 -3 to 2 × 10 -3 mol dm -3 and the concentration of phosphate was restricted to 5.0 x 10- 3 s -1 . Rate constants increase with concentrations of CTAB, giving at rate maximum. k ψ = 67.03 × 10 -5 s -1 at 18 x 10- 3 mol dm -3 CTAB and k ψ = 52.43 × 10 -5 s -1 at 16 x 10- 3 mol dm -3 CTAB respectively at pH 8.0 and 9.0 for di-anions of 4-mpp. The values of ion exchange parameter calculated at pH 8.0 and 9.0 by using various ion exchange equations have been summarized. The activation energy is 25.08 kcal/mol and entropy is 52.07 [-ΔS(eu)], which has been found at pH 8.0 and used borate buffer 3.9 x 10 -3 mol dm -3 [OH - ].

Guest-host interactions in the alkaline bleaching of triphenylmethane dyes catalysed by β-cyclodextrin

The rates of alkaline bleaching of triphenylmethane dyes crystal violet (CV), malachite green (MG) and rosaniline (RA) have been measured spectrophotometrically in an aqueous medium at 30°C in the presence of β-cyclodextrin (CD). At lower concentrations of CD, CV forms productive 1: 1 (G: H) complex. At higher concentrations of CD, it forms unproductive 1: 2 (G: H) complex. For the bleaching of MG, CD accelerates or decelerates the rate depending on pH of the medium by forming 1: 1 (G: H) inclusion complex. Analysis of rate data shows that MG undergoes fading by mixed order process. CD decelerates the water reaction and accelerates hydroxide ion reaction. In the case of RA, both water reaction as well as hydroxide ion reaction are retarded by CD by the formation of inclusion complex.

Controlled Growth of Iron Oxide Nanoparticles in the Aqueous Microdroplets

Magnetite nanoparticles were synthesized by chemical coprecipitation of ferric and ferrous aqueous solutions via regulation of the microenvironment at ambient conditions. Nanocrystals having an average diameter of 6 to 12 nm were obtained by picoliter droplets, whereas only 9 nm diameter nanocrystals were prepared by microliter droplets. The size of the nanocrystals was controlled by a precise balance of reactions of hydroxide ions with positive ions at the surface layer and inner layers of the droplets. The crystal structure and average size were analyzed by X-ray diffraction pattern and transmission electron microscope images. The field dependence and temperature dependence on magnetization measured by a superconducting quantum interference device demonstrate that the as-synthesized particles are superparamagnetic at room temperature and have a size-dependent magnetic property. The anisotropy constant calculated by the blocking temperature and particle size was found to decrease with increasing particle size.

UNDERSTANDING CACO3-Mg(OH)2 SCALE FORMATION: A SEMI-EMPIRICAL MINDO-FORCES STUDY OF CO2-H2O SYSTEM

In this work, the CO 2 -H 2 O system species and the preferential precipitation of either CaCO 3 or Mg(OH) 2 have been studied by the MINDO-Forces method. The calculations were carried out using the standard MINDO-Forces procedure with standard parameters for the included atoms. The potential energies of the LUMO of CO 2 , , and are positive, and this clearly indicates that there is a kinetic barrier to overcome. The activation energy (Ea) of the reaction of H 2 O with CO 2 is about 14.3 eV and this indicates that the reaction is not likely to occur. On the other hand, the reaction of hydroxide ion with CO 2 has a much smaller activation energy (3.4 eV). When the two reactions run simultaneously, the one with lower activation energy occurs preferentially. The pH value plays a decisive role in Mg(OH) 2 scale precipitation. At higher pH, the alkaline mechanism is predominant, and the net reaction () is preferred. Increasing the temperature has similar effect since the pH value increases due to the CO 2 release. Values of pH in the evaporator stages were 0.2 to 0.7 unit higher than seawater feed. At high pH values, Mg(OH) 2 precipitates preferentially.

Solvent Isotope Effects in Reactions of Human Medium-Chain Acyl-CoA Dehydrogenase Active Site Mutants

Glu376, the base involved in substrate alphaH+ abstraction at the active center of medium-chain acyl-CoA dehydrogenase (MCAD), has been mutated to Gln and Gly. The mutants are active; however, their rates of dehydrogenation are lowered by approximately 5 orders of magnitude. Binding of the substrate octanoyl-CoA to Glu376Gln-MCAD involves (at least) two steps. The ensuing dehydrogenation reaction that corresponds to reduction of the flavin cofactor also occurs in two phases. These are interpreted to consist of a first, reversible step, followed by a slower, practically irreversible one. For Glu376Gln-MCAD, the log of the rates of dehydrogenation increases linearly with pH (slope = 1) in the pH range of 6-10, suggesting HO- as a reactant. The rates of the same reactions in D2O have the same pD profile and reflect a solvent kinetic isotope effect (SKIE) of approximately 8.5. Glu376Gln+Glu99Gly-MCAD (studied to assess the role of Glu99 also present at the bottom of the active center cavity) has activities and activity profiles similar to those of Glu376Gln-MCAD. This excludes Glu99 as the active center base for Glu376Gln-MCAD catalysis. Proton inventories for the two phases of the dehydrogenation reaction were investigated at 4 and 25 degrees C. The inventories at 25 degrees C reflect a SKIE of approximately 4.5; the profiles are "bowl-shaped", in which a transition-state contribution predominates. The profiles for the 4 degrees C reaction are very unusual. That for the first phase can be analyzed on a two-step model with one step (80% rate-limiting) having a conformational reorganization with an isotope effect of 90-100, from small isotope effects at many protein sites, and the other step (20% rate-limiting) having an inverse isotope effect of ca. 2, characteristic of the reaction of hydroxide ion as a base. For the second phase, only a contribution from many protein sites with a KIE of approximately 4.5 is observed. The results are compatible with a very rigid active site framework that must undergo rearrangements for dehydrogenation to take place, and specifically to allow access of HO-, the reactant that must neutralize the H+ abstracted from the alphaC-H substrate. The large isotope effects are attributed to the changes in state of several H-bonds that occur during the process.

Transition metal carbene chemistry 6: Kinetic studies of the reactions of hydroxide ion with (CO) 5Mo [dbnd]C(XCH 2CH 2OH)(C 6H 5) (X = O and S) and (CO) 5W [dbnd]C(OCH 2CH 2OH)(C 6H 4–Z)

A kinetic study of the reaction of hydroxide ion with (CO) 5Mo C(XCH 2CH 2OH)(C 6H 5) (X = O for Mo–OR, and X = S for Mo–SR), and (CO) 5W C(OCH 2CH 2OH)(C 6H 4–Z) ( W–OR(Z)) is reported. The results are consistent with a pathway in basic solution that involves rapid deprotonation of the OH group followed by rate-limiting cyclization. The parameter k 1 K OH for the reaction of W–OR(Z) was determined as a function of the phenyl substituents. They were found to correlate well with the Hammett equation. The dependence of the reactivity on the metal atoms in the complexes M–OR (M = Cr, Mo and W) shows that the reactivity decreases slightly down the group of the Periodic Table, while for M–SR the reactivity increases slightly down the group. A plausible explanation of these results is offered based on electronegativity values of the metal atoms. The much higher ρ( k 1 K OH) value for W–OR(Z) over W–SR(Z) arises mainly due to the stabilization of the reactant carbene complex by the stronger π-donor effect of oxygen over sulfur.

Kinetic and equilibrium study of the reaction of nitroprusside and hydroxide ions: Influence of ionic strength using Pitzer model

AbstractA kinetic and equilibrium study of the addition reaction of hydroxide ions to nitroprusside has been carried out in this paper. Rate and equilibrium constants at different salt concentrations (up to 4 mol kg−1) were obtained, and the influence of ionic strength was studied by means of Pitzer equations. This model is of special interest because it is able to explain the experimental behavior at high ionic strength, when Debye–Huckel limiting law is no longer valid. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 650–660, 2004

Catalytic and inhibitory effects of β‐cyclodextrin on the hydrolysis of benzoic anhydride

AbstractThe hydrolysis of benzoic anhydride (Bz2O) in the presence of β‐cyclodextrin (β‐CD) was studied in aqueous solution as a function of pH, temperature and ionic strength, at 25°C. The experimental rate constant versus pH profiles show that, in the region of spontaneous water reaction (pH 3.0–6.5), β‐CD inhibits the reaction and the isotope effect $(k_{{\rm H_2 O}} / k_{{\rm D_2 O}} = 4.7)$ indicates that the rate determining step of the reaction corresponds to the water‐catalyzed nucleophilic attack of water on the carbonyl group of Bz2O. Conversely, whereas inhibition is observed at pH 6.0, catalysis of the hydroxide ion reaction is observed at pH 8.0 and it is found that the activation entropy is responsible for the catalytic phenomena in the basic hydrolysis of benzoic anhydride. Copyright © 2004 John Wiley &amp; Sons, Ltd.

Kinetics of the Reactions of Water, Hydroxide Ion and Sulfide Species with CO2, OCS and CS2: Frontier Molecular Orbital Considerations

The kinetics of the reactions of water, hydroxide ion and sulfide species with CO2, OCS and CS2 are investigated using the molecular orbital approach and available kinetic data. Although these reactions are symmetry allowed, the lowest unoccupied molecular orbital (LUMO) for CO2 is a poor electron accepting orbital as it has a positive potential energy. At low pH, hydration of CO2 requires that the waters interact with CO2 via hydrogen bonding for subsequent formation of H2CO3 in an effort to overcome the high energy of activation. These factors are significant for the slow kinetics of hydration and the persistence of CO2 in water. The reaction of hydroxide ion with CO2 has a much smaller energy of activation. For the isoelectronic species OCS and CS2, their LUMO orbitals are good electron acceptor orbitals, and the energy of activation is less than that for the corresponding CO2 reactions. The LUMO orbitals for OCS and CS2 have less carbon character whereas the LUMO for CO2 has more carbon character. The relative rates of these reactions (CO2 > OCS > CS2) reflect the increased carbon character of the π* LUMO orbital for CO2 over CS2 and the fact that the LUMO for OCS is σ*, which when filled can readily break the C—S bond leading to sulfide (even though the C character of the LUMO is less than those for CO2 and CS2). Also, the higher hydrogen bonding interactions with nearest water molecules is in the order CO2 > OCS > CS2 indicating that hydrolysis via water catalysis is retarded as the number of S atoms increases. Solid phase FeS has a highest occupied molecular orbital (HOMO) with a potential energy similar to that of CO2 and can activate (or bond with) the carbon atom in CO2 so that organic compounds can be produced under hydrothermal vent conditions.