The biological buffer bicarbonate/CO2 potentiates H2O2-mediated inactivation of protein tyrosine phosphatases

Hydrogen peroxide is a cell signaling agent that inactivates protein tyrosine phosphatases (PTPs) via oxidation of their catalytic cysteine residue. PTPs are inactivated rapidly during H(2)O(2)-mediated cellular signal transduction processes, but, paradoxically, hydrogen peroxide is a rather sluggish PTP inactivator in vitro. Here we present evidence that the biological buffer bicarbonate/CO(2) potentiates the ability of H(2)O(2) to inactivate PTPs. The results of biochemical experiments and high-resolution crystallographic analysis are consistent with a mechanism involving oxidation of the catalytic cysteine residue by peroxymonocarbonate generated via the reaction of H(2)O(2) with HCO(3)(-)/CO(2).     

The mechanism of carbon dioxide catalysis in the hydrogen peroxide N-oxidation of amines

The reactivity of the peroxymonocarbonate ion, HCO4- (an active oxidant derived from the equilibrium reaction of hydrogen peroxide and bicarbonate), has been investigated in the oxidation of aliphatic amines. Tertiary aliphatic amines are oxidized to the corresponding N-oxides in high yields, while secondary amines give corresponding nitrones. A closely related mechanism for the H2O2 oxidation of tertiary amines catalyzed by CO2 (under 1 atm) and H2O2 at 25 degrees C is proposed. The rate laws for the oxidation of N-methylmorpholine (1) to N-methylmorpholine N-oxide and N,N-dimethylbenzylamine (2) to N,N-dimethylbenzylamine N-oxide have been obtained. The second-order rate constants for the oxidation by HCO4- are k1 .016 M(-1) s(-1) for 1 in water and k1=0.042 M(-1) s(-1) for 2 in water/acetone (5:1). The second-order rate constants for tertiary amine oxidations by HCO4- are over 400-fold greater than those for H2O2 alone. Activation parameters for oxidation of 1 by HCO4- in water are reported (DeltaH=36+/-2 kJ mol(-1) and DeltaS=-154+/-7 J mol(-1) K(-1)). The BAP (NH4HCO3-activated peroxide) or CO2/H2O2 oxidation reagents are simple and economical methods for the preparation of tertiary amine N-oxides. The reactions proceed to completion, do not require extraction, and afford the pure N-oxides in excellent yields in aqueous media.     

Singlet oxygen generated from the decomposition of peroxymonocarbonate and its observation with chemiluminescence method

The decomposition of peroxymonocarbonate (HCO(4)(-)) has been investigated by flow-injection chemiluminescence (CL) method. An ultraweak CL was observed during mixing the bicarbonate and hydrogen peroxide solution in organic cosolvent. An appropriate amount of fluorescent organic compounds, such as dichlorofluorescein (DCF), was added to the HCO(4)(-) solution, a strong CL was recorded. Based on studies of the spectrum of fluorescence, CL and UV-vis spectra, electron spin trapping (ESR) technique, mass spectra (MS) and comparison with H(2)O(2)/hypochlorite (ClO(-)) and H(2)O(2)/molybdate (MoO(4)(-)) systems, the CL mechanism was proposed. The reaction is initiated by unimolecular homolysis of the peroxo O-O bond in HO-OCOO(-) molecule. It was suggested that the bond rearrangement within radicals yield superoxide ion (O(2)(*-)). The interaction of superoxide ion with perhydroxyl radical produces singlet oxygen ((1)O(2)). The energy transfers from singlet oxygen to DCF forming an excited energy acceptor (DCF*). Luminescence (lambda(max)=509 nm) was emitted during the relaxation of the energy acceptor to the ground state.     

15N CIDNP study of formation and decay of peroxynitric acid: evidence for formation of hydroxyl radicals

The reaction of nitrous acid with hydrogen peroxide leads to nitric acid as the only stable product. In the course of this reaction, peroxynitrous acid (ONOOH) and, in the presence of CO(2), a peroxynitrite-CO(2) adduct (ONOOCO(2)(-)) are intermediately formed. Both intermediates decompose to yield highly oxidizing radicals, which subsequently react with excess hydrogen peroxide to yield peroxynitric acid (O(2)NOOH) as a further intermediate. During these reactions, (15)N chemically induced dynamic nuclear polarization (CIDNP) effects are observed, the analysis of the pH dependency of which allows the elucidation of mechanistic details. The formation and decay of peroxynitric acid via free radicals NO(2)(*) and HOO(*) is demonstrated by the appearance of (15)N CIDNP leading to emission (E) in the (15)N NMR signal of O(2)NOOH during its formation and to enhanced absorption (A) during its decay reaction. Additionally, the (15)N NMR signal of the nitrate ion (NO(3)(-)) appears in emission at pH approximately 4.5. These observations are explained by proposing the intermediate formation of short-lived radical anions O(2)NOOH(*)(-) probably generated by electron transfer between peroxynitric acid and peroxynitrate anion, followed by decomposition of O(2)NOOH(*)(-) into NO(3)(-) and HO(*) and NO(2)(-) and HOO(*) radicals, respectively. The feasibility of such reactions is supported by quantum-chemical calculations at the CBS-Q level of theory including PCM solvation model corrections for aqueous solution. The release of free HO(*) radicals during decomposition of O(2)NOOH is supported by (13)C and (1)H NMR product studies of the reaction of preformed peroxynitric acid with [(13)C(2)]DMSO (to yield the typical "HO(*) products" methanesulfonic acid, methanol, and nitromethane) and by ESR spectroscopic detection of the HO(*) and CH(3)(*) radical adducts to the spin trap compound POBN in the absence and presence of isotopically labeled DMSO, respectively.     

Bicarbonate surfoxidants: micellar oxidations of aryl sulfides with bicarbonate-activated hydrogen peroxide

The mechanism and kinetics of bicarbonate-catalyzed oxidations of sulfides by H(2)O(2) at the aqueous /cationic micellar interface have been investigated. The general term surfoxidant is introduced to describe the combination of an ionic surfactant with a reactive counterion that is itself an oxidant or activates an oxidant from the bulk solution to form an oxidant counterion. It is shown that the new catalytic cationic surfoxidant CTAHCO(3) (cetyltrimethylammonium bicarbonate) significantly enhances the overall oxidation rates as compared to the addition of bicarbonate salts to CTACl and CTABr, for which the halide counterions must undergo equilibrium displacement by the oxidant anion (peroxymonocarbonate, HCO(4)(-)). General equations based on the classic pseudophase model have been derived to account for the preequilibrium reaction in the aqueous and micellar phases, and the resulting model can be used to describe any micellar reaction with associated preequilibria. Rate constants and relevant equilibrium constants for HCO(4)(-) oxidations of aryl sulfides at micellar surfaces have been estimated for CTAHCO(3), CTACl, and CTABr. The second-order rate constants in the Stern layer (k(2)(m)) for sulfide oxidations by HCO(4)(-) are estimated to be approximately 50-fold (PhSEtOH) and approximately 180-fold (PhSEt) greater than the background rate constant k(m)(0) for oxidation by H(2)O(2) at the micellar surface. The estimated values of k(2)(m) are lower than the corresponding values in water by a factor of 20-70 depending on the substrate, but the high local concentration of the bicarbonate activator in the surfoxidant and the local accumulation of substrate as a result of strong binding to the micelle lead to a net increase in the observed reaction rates. Comparisons of CTAHCO(3)-activated peroxide to other highly reactive oxidants such as peroxymonosulfate (HSO(5)(-)) in aqueous surfactant media suggest a wide variety of potential applications for this green oxidant.     

Comparison of hydrated hydroperoxide anion (HOO-)(H2O)n clusters with alkaline hydrogen peroxide (HOOH)(OH-)(H2O)(n-1) clusters, n = 1-8, 20: an ab initio study

Hydroperoxide anion (HOO(-)), the conjugate base of hydrogen peroxide (HOOH), has been relatively little studied despite the importance of HOOH in commercial processes, atmospheric science, and biology. The anion has been shown to exist as a stable species in alkaline water. This project explored the structure of gas phase (HOO(-))(H(2)O)(n) clusters and identified the lowest energy configurations for n ≤ 8 at the B3LYP/6-311++G** level of theory and for n ≤ 6 at the MP2/aug-cc-pVTZ level of theory. As a start toward understanding equilibration between HOO(-) and HOOH in an alkaline environment, (HOOH)(OH(-))(H(2)O)(n-1) clusters were likewise examined, and the lowest energy configurations were determined for n ≤ 8 (B3LYP/6-311++G**) and n ≤ 6 (MP2/aug-cc-pVTZ). Some studies were also done for n = 20. The two species have very different solvation behaviors. In low energy (HOOH)(OH(-))(H(2)O)(n-1) clusters, HOOH sits on the surface of the cluster, is 4-coordinated (each O is donor once and acceptor once), and donates to the hydroxide ion. In contrast, in low energy (HOO(-))(H(2)O)(n) clusters, (HOO(-)) takes a position in the cluster center surrounded on all sides by water molecules, and its optimum coordination number appears to be 7 (one O is donor-acceptor-acceptor while the other is a 4-fold acceptor). For n ≤ 6 the lowest (HOOH)(OH(-))(H(2)O)(n-1) cluster lies 1.0-2.1 kcal/mol below the lowest (HOO(-))(H(2)O)(n) cluster, but the lowest clusters found for n = 20 favor (HOO(-))(H(2)O)(20). The results suggest that ambient water could act as a substantial kinetic brake that slows equilibration between (HOOH)(OH(-)) and (HOO(-))(H(2)O) because extensive rearrangement of solvation shells is necessary to restabilize either species after proton transfer.     

Mechanism of the reaction of radicals with peroxides and dimethyl sulfoxide in aqueous solution

The reactions of methyl and methylperoxyl radicals derived from dimethyl sulfoxide (DMSO) with hydrogen peroxide, peroxymonocarbonate (HCO4 (-)), and persulfate were studied. The major reaction observed for the hydroperoxides was the abstraction of the hydrogen atom by the radicals. The radicals interact with a lone pair of electrons on the peroxide to produce methanol and formaldehyde. Furthermore, the results indicate that in RO2H and RO2R', electron-withdrawing groups cause a considerable increase in the reactivity of the peroxides towards the radicals and not only towards nucleophiles. The HO2 (.)/O2 (.-) and CO3 (.-) radicals react with DMSO to produce methyl radicals. Thus, the formation of the (.)CH3 radicals in the presence of DMSO is not proof of the formation of the (.)OH radicals in the system. These reactions must be considered when radical processes, such as in biological and catalytic systems, are studied. Especially, the plausible role of HCO4 (-) ions in biological systems as a source of oxidative stress cannot be overlooked.     

Formation and characterization of water-soluble hydrido-ruthenium(II) complexes of 1,3,5-triaza-7-phosphaadamantane and their catalytic activity in hydrogenation of CO2 and HCO3- in aqueous solution

The water-soluble tertiary phosphine complex of ruthenium(II), [RuCl2(PTA)4], (PTA = 1,3,5-triaza-7-phosphaadamantane) was used as catalyst precursor for hydrogenation of CO2 and bicarbonate in aqueous solution, in the absence of amine or other additives, under mild conditions. Reaction of [RuCl2(PTA)4] and H2 (60 bar) gives the hydrides [RuH2(PTA)4] (at pH = 12.0) and [RuH(PTA)4X] (X = Cl- or H2O) (at pH = 2.0). In presence of excess PTA, formation of the unparalleled cationic pentakis-phosphino species, [HRu(PTA)5]+, was unambiguously established by 1H and 31P NMR measurements. The same hydrides were observed when [Ru(H2O)6][tos]2 (tos = toluene-4-sulfonate) reacted with PTA under H2 pressure. The rate of CO2 hydrogenation strongly depends on the pH. The highest initial reaction rate (TOF = 807.3 h(-1)) was determined for a 10% HCO3-/90% CO2 mixture (pH = 5.86), whereas the reduction was very slow both at low and high pH (CO2 and Na2CO3 solutions, respectively). 1H and 31P NMR studies together with the kinetic measurements suggested that HCO3- was the real substrate and [RuH(PTA)4X] the catalytically active hydride species in this reaction. Hydrogenation of HCO3- showed an induction period which could be ascribed to the slow formation of the catalytically active hydride species.     

New insight into solvent effects on the formal HOO. + HOO. reaction

The 2,2'-azobis(isobutyronitrile)(AIBN)-induced autoxidation of gamma-terpinene (TH) at 50 degrees C produces p-cymene and hydrogen peroxide in a radical-chain reaction having HOO* as one of the chain-carrying radicals. The kinetics of this reaction in cyclohexane and tert-butyl alcohol show that chain termination involves the formal HOO. + HOO. self-reaction over a wide range of gamma-terpinene, AIBN, and O2 concentrations. However, in acetonitrile this termination process is accompanied by termination via the cross-reaction of the terpinenyl radical, T., with the HOO. radical under conditions of relatively high [TH] (140-1000 mM) and low [O2] (2.0-5.5 mM). This is because the formal HOO. + HOO. reaction is comparatively slow in acetonitrile (2k approximately 8 x 10(7) M(-1) s(-1)), whereas, this reaction is almost diffusion-controlled in tert-butyl alcohol and cyclohexane, 2k approximately 6.5 x 10(8) and 1.3 x 10(9) M(-1) s(-1), respectively. Three mechanisms for the bimolecular self-reaction of HOO. radicals are considered: 1) a head-to-tail hydrogen-atom transfer from one radical to the other, 2) a head-to-head reaction to form an intermediate tetroxide, and 3) an electron-transfer between HOO. and its conjugate base, the superoxide radical anion, O2-.. The rate constant for reaction by mechanism (1) is shown to be dependent on the hydrogen bond (HB) accepting ability of the solvent; that by mechanism (2) is shown to be too slow for this process to be of any importance; and that by mechanism (3) is dependent on the pH of the solvent and its ability to support ionization. Mechanism (3) was found to be the main termination process in tert-butyl alcohol and acetonitrile. In the gas phase, the rate constant for the HOO. + HOO. reaction (mechanism (1)) is about 1.8 x 10(9) M(-1) s(-1) but in water at pH< or =2 where the ionization of HOO. is completely suppressed, this rate constant is only 8.6 x 10(5) M(-1) s(-1). The very large retarding effect of water on this reaction has not previously been explained. We find that it can be quantitatively accounted for by using Abraham's HB acceptor parameter, beta(2)(H), for water of 0.38 and an estimated HB donor parameter, alpha(2)(H), for HOO. of about 0.87. These Abraham parameters allow us to predict a rate constant for the HOO. + HOO. reaction in water at 25 degrees C of 1.2 x 10(6) M(-1) s(-1) in excellent agreement with experiment.     

pH-oscillations in a closed chemical system of CaSO3-H2O2-HCO3(-)

Long-lasting large amplitude periodic change of the pH is measured in an aqueous suspension of CaSO(3)-H(2)O(2)-HCO(3)(-) at 2.0-10.0 °C in a closed reactor. The amplitude can be as large as 2 pH units between pH 5 and 7. The observed phenomenon is explained and simulated by taking into account a slow dissolution of CaSO(3), which serves as a continuous supply of HSO(3)(-) for a H(+)-producing autocatalytic composite reaction between H(2)O(2) and HSO(3)(-). Protonation of HCO(3)(-) to form CO(2) in a reversible reaction provides for the necessary negative feedback in [H(+)].     

The onset of calcium carbonate nucleation: a density functional theory molecular dynamics and hybrid microsolvation/continuum study

Density functional theory (Perdew-Burke-Ernzerhof) based methods have been used to study the structure and hydration environment of the building blocks of CaCO 3 in aqueous solutions of calcium bicarbonate and calcium carbonate. Car-Parrinello molecular dynamics simulations of Ca(2+)/CO3(2-) and Ca (2+)/HCO3(-) in explicit water were performed to investigate the formation of CaCO3 and the hydration shell of the solvated hetero-ion pair. Our simulations show that the formation of the monomer of CaCO3 occurs with an associative mechanism and that the dominant building block of calcium (bi)carbonate in aqueous solution is Ca[eta(1)-(H)CO3](H2O)5, i.e., the preferred hydration number is five, while the (bi)carbonate is coordinated to the calcium in a monodentate mode. This result agrees with static calculations, where a hybrid approach using a combination of explicit solvent molecules and a polarizable continuum model has been applied to compute the solvation free energies of calcium bicarbonate species. Furthermore, the discrete-continuum calculations predict that the Ca(HCO3)2 and Ca(HCO3)3(-) species are stable in an aqueous environment preferentially as Ca(HCO3)2(H2O)4 and Ca(HCO3)3(H2O)2(-), respectively.     

Buffering dissociation/formation reaction of biogenic calcium carbonate

The oscillating stability of coral reef seawater pH has been maintained at around physiological pH values over the past 300 years (Pelejero et al., 2005). The stability mechanism of its pH has been interpreted in terms of the buffering dissolution/formation reaction of CaCO(3) as well as the proton consumption/generation reaction in CaCO(3)-saturated water. Here the pH-dependent solubility product [HCO(3)(-)][Ca(2+)] has been derived on the basis of the actual pH-dependent reactions for the atmospheric CO(2)/CO(2 (aq.))/HCO(3)(-)/CO(3)(2-)/Ca(2+)/CaCO(3) system. Overbasic pH peaks appeared between pH approximately 8 and approximately 9.5 during sodium hydroxide titration, as a result of simultaneous CaCO(3) formation and proton generation. The spontaneous and prompt water pH recovery from the acidic to the physiological range has been confirmed by the observation of acid/base time evolution, because of simultaneous CaCO(3) dissolution and proton consumption. The dissolution/formation of CaCO(3) in water at pH 7.5-9 does not take place without a proton consumption/generation reaction, or a buffering chemical reaction of HCO(3)(-)+Ca(2+)right arrow over left arrowCaCO(3)+H(+). SEM images of the CaCO(3) fragments showed that the acid water ate away at the CaCO(3) formed at physiological pH values. Natural coral reefs can thus recover the physiological pH levels of seawater from the acidic range through partial dissolution of their own skeletons.     

O-H...O interactions involving doubly charged anions: charge compression in carbonate-bicarbonate crystals

The O-H...O interaction formed by the anions HCO(3)(-) and CO(3)(2-) has been investigated on the basis of data retrieved from the Inorganic Crystal Structure Database (ICSD) and by means of ab initio computations. It has been shown that the O-H...O separations associated with HCO(3)(-)...(3)(2-) interactions are shorter than those found in crystals containing hydrogen carbonate monoanions such as HCO(3)(-)...HCO(3)(-). Ab initio MP2/6-311G++(2d,2p) computations on the crystal Na(3)(HCO(3))(CO(3)).2H(2)O have shown that the interaction between the monoanion donor and the dianion acceptor, for example HCO(3)(-)...CO(3)(2-), is more repulsive than that between singly charged ions, for example HCO(3)(-)...HCO(3)(-), but is largely overcompensated for by anion-cation electrostatic attractions. The shortening of the (-)O-H...O(2-) interaction relative to the (-)O-H...O(-) interaction has been explained as a consequence of the increased charge compression, that is of the stronger cation-anion interactions established by the CO(3)(2-) dianions with respect to those established by monoanions, and does not reflect an increase in the strength of the (-)O-H ...O(-) interaction. To expand the structural sample in the crystal packing analysis, the structure of the novel mixed salt K(2)Na(HCO(3))(CO(3)).2H(2)O has been determined by single-crystal X-ray diffraction and compared with the structure of the salt Na(3)(HCO(3))(CO(3)).2H(2)O used in the computations.     

Carbonate complexation of Mn2+ in the aqueous phase: redox behavior and ligand binding modes by electrochemistry and EPR spectroscopy

The chemical speciation of Mn2+ within cells is critical for its transport, availability, and redox properties. Herein we investigate the redox behavior and complexation equilibria of Mn2+ in aqueous solutions of bicarbonate by voltammetry and electron paramagnetic resonance (EPR) spectroscopy and discuss the implications for the uptake of Mn2+ by mangano-cluster enzymes such as photosystem II (PSII). Both the electrochemical reduction of Mn2+ to Mn0 at an Hg electrode and EPR (in the absence of a polarizing electrode) revealed the formation of 1:1 and 1:2 Mn-(bi)carbonate complexes as a function of Mn2+ and bicarbonate concentrations. Pulsed EPR spectroscopy, including ENDOR, ESEEM, and 2D-HYSCORE, were used to probe the hyperfine couplings to 1H and 13C nuclei of the ligand(s) bound to Mn2+. For the 1:2 complex, the complete 13C hyperfine tensor for one of the (bi)carbonate ligands was determined and it was established that this ligand coordinates to Mn2+ in bidentate mode with a 13C-Mn distance of 2.85 +/- 0.1 angstroms. The second (bi)carbonate ligand in the 1:2 complex coordinates possibly in monodentate mode, which is structurally less defined, and its 13C signal is broad and unobservable. 1H ENDOR reveals that 1-2 water ligands are lost upon binding of one bicarbonate ion in the 1:1 complex while 3-4 water ligands are lost upon forming the 1:2 complex. Thus, we deduce that the dominant species above 0.1 M bicarbonate concentration is the 1:2 complex, [Mn(CO3)(HCO3)(OH2)3]-.     

Kinetics of the iodate reduction by hydrogen peroxide and relation with the Briggs-Rauscher and Bray-Liebhafsky oscillating reactions

The iodate reduction by hydrogen peroxide in acidic solutions is part of the Bray-Liebhafsky and Briggs-Rauscher oscillating reactions. At low hydrogen peroxide concentrations, typical of the Bray-Liebhafsky reaction, its rate law is -d[IO(-)(3)]/dt = (k'(R) + k"(R)[H(+)])[IO(-)(3)][H(2)O(2)] with k'(R) = 1.3 × 10(-7)(20°), 7.8 × 10(-7) (39°), 1.4 × 10(-5) M(-1) s(-1) (60°) and k"(R) = 1.5 × 10(-5) (25°), 6.2 × 10(-5) (39°), 6.3 × 10(-4) M(-2) s(-1) (60°). It is explained by a non-radical mechanism. At high hydrogen peroxide concentrations, typical of the Briggs-Rauscher reaction, a new reaction pathway appears with a rate more than proportional to [H(2)O(2)](2) and nearly independent of [IO(3)(-)] > 0.01 M. This pathway is inhibited by scavengers of free radicals. We suggest that it has a radical mechanism starting with IOH + H(2)O(2)? IOOH + H(2)O and IOOH+H(2)O(2)→ IO˙ + H(2)O+HOO˙.     

Theoretical Investigation of CH3CF2O2+HOO Reaction

The reactions of CH3CF2O2 with HOO are important chemical cyclic processes of photochemical contamination. In this paper, the reaction pathways and reaction mechanism of CH3CF2O2+HOO are investigated extensively with the Gaussian 98 package at the B3LYP/6-311++G** basis sets. The use of vibrational mode analysis and electron population analysis to reveal the reaction mechanism is firstly reported. The study shows that CH3CF2CO2+HOO→IM1→TS1→CH3CF2O2H+O2 channel is the energetically most favorable, CH3CF2CO2H and O2 are the principal products, and the formation of CH3OH and CF2O is also possible.     

Hydride ion transfer from ruthenium(II) complexes in water: kinetics and mechanism

Reactions of hydride complexes of ruthenium(II) with hydride acceptors have been examined for Ru(terpy)(bpy)H(+), Ru(terpy)(dmb)H(+), and Ru(η(6)-C(6)Me(6))(bpy)(H)(+) in aqueous media at 25 °C (terpy = 2,2';6',2'-terpyridine, bpy = 2,2'-bipyridine, dmb = 4,4'-dimethyl-2,2'-bipyridine). The acceptors include CO(2), CO, CH(2)O, and H(3)O(+). CO reacts with Ru(terpy)(dmb)H(+) with a rate constant of 1.2 (0.2) × 10(1) M(-1) s(-1), but for Ru(η(6)-C(6)Me(6))(bpy)(H)(+), the reaction was very slow, k ≤ 0.1 M(-1) s(-1). Ru(terpy)(bpy)H(+) and Ru(η(6)-C(6)Me(6))(bpy)(H)(+) react with CH(2)O with rate constants of (6 ± 4) × 10(6) and 1.1 × 10(3) M(-1) s(-1), respectively. The reaction of Ru(η(6)-C(6)Me(6))(bpy)(H)(+) with acid exhibits straightforward, second-order kinetics, with the rate proportional to [Ru(η(6)-C(6)Me(6))(bpy)(H)(+)] and [H(3)O(+)] and k = 2.2 × 10(1) M(-1) s(-1) (μ = 0.1 M, Na(2)SO(4) medium). However, for the case of Ru(terpy)(bpy)H(+), the protonation step is very rapid, and only the formation of the product Ru(terpy)(bpy)(H(2)O)(2+) (presumably via a dihydrogen or dihydride complex) is observed with a k(obs) of ca. 4 s(-1). The hydricities of HCO(2)(-), HCO(-), and H(3)CO(-) in water are estimated as +1.48, -0.76, and +1.57 eV/molecule (+34, -17.5, +36 kcal/mol), respectively. Theoretical studies of the reactions with CO(2) reveal a "product-like" transition state with short C-H and long M-H distances. (Reactant) Ru-H stretched 0.68 ?; (product) C-H stretched only 0.04 ?. The role of water solvent was explored by including one, two, or three water molecules in the calculation.     

Hydrogen bond of radicals: Interaction of HNO with HCO,HNO, and HOO

Ab initio quantum mechanics methods are employed to investigate hydrogen bonding interactions between HNO and HCO, HOO radicals, and closed‐shell HNO. The systems were calculated at MP2/6‐311++G (2d, 2p) level and G2MP2 level. The topological and NBO analysis were investigated the origin of hydrogen bonds red‐ or blue‐shifts. In addition, the comparisons were performed between HNO‐opened‐shell radical (HCO, HOO) complexes and HNO‐corresponding closed‐shell molecule (H₂CO, HOOH) complexes. It is found that the stabilities of complexes increase from HNO‐HCO to HNO‐HOO. There are blue‐shifts of N? H, C? H stretching vibrational frequencies and a red‐shift of O? H stretching vibrational frequency in the complexes. Rehybridization and electron density redistribution contribute to the blue‐shifts of C? H and N? H stretching vibrational frequencies. Compared with the closed‐shell H₂CO, HCO is weaker proton donor and weaker proton acceptor. For the HOO, it is stronger proton donor and weaker proton acceptor than the HOOH is. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Exchange equilibria between bicarbonate, carbonate, chloride and bromide on dowex 1 x 8

The exchange reaction 2R(+)HCO(3)(2-) + CO(3)(2-) right harpoon over left harpoon R(2)(+) CO(3)(2-) + 2HCO(3)(2-) has been studied on Dowex 1 x 8 in the presence of bicarbonate solution in equilibrium with atmospheric carbon dioxide (open system). The experiments showed, as theory predicts, that the composition of the resin phase is independent of the concentration of the bicarbonate solution. The mole fraction of carbonate at equilibrium is about 0.4 and the equilibrium constant is 0.15M at 20 degrees . With this value of the constant, the composition of the ion-exchanger for various bicarbonate concentrations has been calculated for a closed system. At [HCO(3)(-)] < 0.01M a substantial part of the resin is in the carbonate form, whereas for [HCO(3)(-)] 0.05M the resin is present almost exclusively in bicarbonate form. The exchange constants of bromide at trace level have been determined for the bicarbonate and mixed carbonate forms of the ion-exchanger. The exchange constant K(Cl)(HCO(3)) has been determined over the whole composition range and the results can be represented by K(Cl)(HCO(3))= 0.428 -0.063x(Cl) -0.115x(Cl)(2), where X(Cl) is the mole fraction of chloride in the resin. The constants are used to discuss the conditions for the Chromatographie enrichment of bromide from fresh water.     

Uptake of CO2, SO2, HNO3 and HCl on calcite (CaCO3) at 300 K: mechanism and the role of adsorbed water

All experimental observations of the uptake of the four title compounds on calcite are consistent with the presence of a reactive bifunctional surface intermediate Ca(OH)(HCO3) that has been proposed in the literature. The uptake of CO2 and SO2 occurs on specific adsorption sites of crystalline CaCO3(s) rather than by dissolution in adsorbed water, H2O(ads). SO2 primarily interacts with the bicarbonate moiety whereas CO2, HNO3 and HCl all react first with the hydroxyl group of the surface intermediate. Subsequently, the latter two react with the bicarbonate group to presumably form Ca(NO3)2 and CaCl2.2H2O. The effective equilibrium constant of the interaction of CO2 with calcite in the presence of H2O(ads) is kappa = deltaCO2/(H2O(ads)[CO2]) = 1.62 x 10(3) bar(-1), where CO2 is the quantity of CO2 adsorbed on CaCO3. The reaction mechanism involves a weakly bound precursor species that is reversibly adsorbed and undergoes rate-controlling concurrent reactions with both functionalities of the surface intermediate. The initial uptake coefficients gamma0 on calcite powder depend on the abundance of H2O(ads) under the present experimental conditions and are on the order of 10(-4) for CO2 and 0.1 for SO2, HNO3 and HCl, with gamma(ss) being significantly smaller than gamma0 for HNO3 and HCl, thus indicating partial saturation of the uptake. At 33% relative humidity and 300 K there are 3.5 layers of H2O adsorbed on calcite that reduce to a fraction of a monolayer of weakly and strongly bound water upon pumping and/or heating.