The gas phase oxidation of HCOOH by Cl and NH2 radicals. Proton coupled electron transfer versus hydrogen atom transfer*

ABSTRACT

The reaction of formic acid (HCOOH) with chlorine atom and amidogen radical (NH₂) have been investigated using high level theoretical methods such BH&HLYP, MP2, QCISD, and CCSD(T) with the 6–311?+?G(2df,2p), aug-cc-pVTZ, aug-cc-pVQZ and extrapolation to CBS basis sets. The abstraction of the acidic and formyl hydrogen atoms of the acid by the two radicals has been considered, and the different reactions proceed either by a proton coupled electron transfer (pcet) and hydrogen atom transfer (hat) mechanisms. Our calculated rate constant at 298?K for the reaction with Cl is 1.14?×?10^?13?cm³?molecule^?1?s^?1 in good agreement with the experimental value 1.8?±?0.12/2.0?×?10^?13?cm³?molecule^?1?s^?1 and the reaction proceeds exclusively by abstraction of the formyl hydrogen atom, via hat mechanism, producing HOCO+ClH. The calculated rate constant, at 298?K, for the reaction with NH₂ is 1.71?×?10^?15?cm³?molecule^?1?s^?1, and the reaction goes through the abstraction of the acidic hydrogen atom, via a pcet mechanism, leading to the formation of HCOO+NH₃.     

A study of K−p interactions in deuterium in the c.m. energy range from 1.60 to 1.74 GeV

We present results of a K^?d bubble-chamber experiment at four K^? momenta between 680 and 840 MeV/c. The validity of the spectator model for the analysisof KN interactions in deuterium is discussed. Cross sections are determined for the reactions K^?p → Σ^?π⁺, K^?p → Σ⁺π^? and K^?p → Λπ⁺π^? and are compared to those obtain ed on free protons.     

Mechanisms of the Reactions of Radicals with Ozone

The available experimental data (rate constants and activation energies) for the reactions of the hydrogen atom and the R^?, RO^?, RO ₂ ^? , HO^?, and HO ₂ ^? radicals with ozone are analyzed using the method of intersecting parabolas (potential curves). The conclusion is drawn that the primary event in the reactions of H^?, R^?, HO^?, and RO^? with ozone is the addition of the radical to the ozone molecule with the subsequent fast decomposition of the labile polyoxide radical formed. The classical potential barrier for this addition reaction is close to that for the addition of radicals to molecules with multiple bonds. Peroxy radicals react with ozone by the associative decomposition mechanism, RO ₂ ^? + O₃ → RO^? + 2O₂. The ozone molecule reacts with the HO ₂ ^? radical by abstracting its hydrogen atom, O₃ + HO ₂ ^? → HO ₃ ^? + O₂. The experimental data were used to determine the parameters required to calculate the activation energies for the reactions under study.     

Energy dependence of the cross sections for the e<Superscript>+</Superscript>e<Superscript>–</Superscript> → hadrons process near the production threshold for the <Emphasis Type="Italic">N</Emphasis><Emphasis Type="Italic">N̄</Emphasis> pair

The energy dependence of the cross sections for the processes e⁺e^? → π⁺π^?π⁰, K⁺K^?, ηπ⁺π^?, ωπ₀, and K⁺K^?π⁺π^? is studied near the production threshold for a nucleon–antinucleon pair. It is shown that, within the measurement errors, the cross sections in question behave smoothly in this energy region.     

Highly sensitive electrochemical detection of dopamine and uric acid on a novel carbon nanotube-modified ionic liquid-nanozeolite paste electrode

A novel biosensor has been constructed by incorporating modified nanosized natural zeolite and 3-hydroxypropanaminium acetate (HPAA) as a novel room temperature ionic liquid, supported on multiwalled carbon nanotube (MWCNTs) and employed for the simultaneous determination of dopamine (DA) and uric acid (UA). A detailed investigation by transmission electron microscopy and electrochemistry is performed in order to elucidate the preparation process and properties of the composites. The voltammetric studies using the modified carbon paste electrode show two well-resolved anodic peaks for DA and UA with a potential difference of 160 mV, revealing the possibility of the simultaneous electrochemical detection of these compounds. The modified carbon paste electrode shows good conductivity, stability, and extraction effect due to the synergic action of HPAA, MWCNTs, and iron ion-doped natrolite zeolite. Under optimized conditions, the peak currents are linear from 8.12?×?10^?7 to 3.01?×?10^?4?mol?L^?1 and from 9.31?×?10^?7 to 3.36?×?10^?4?mol?L^?1 with detection limits of 1.16?×?10^?7 and 1.33?×?10^?7?mol?L^?1 for DA and UA using the differential pulse voltammetric method, respectively. Finally, the modified carbon paste electrode proved to have good sensitivity and stability and is successfully applied for the simultaneous determination of DA and UA in human blood serum and urine samples.     

D meson production and decay in e+e− annihilation at 4.03 and 4 GeV c.m. energy

Decay modes of the charmed mesons, D⁰ and D⁺, are studied in e⁺e^? annihilation data at 4.03 and 4.41 GeV c.m. energy. The products of cross section times branching ratio are measured for the K^?π⁺, K^?π⁺π⁺π^?, K_Sπ⁺π^? and K^?π⁺π⁺ final states. Upper limits are established for the Cabibbo forbidden decays via π⁺π^?, K⁺K^?, K⁺K^? π⁺, K⁺π⁺π^? and π⁺π^?π⁺. The K^?π⁺π⁺π^? final state is shown to be dominated by K^?π⁺ρ⁰.     

Heat capacities of copper(II) formate tetrahydrate and tetradeuterate: A comparative study of phase transitions in layer hydrate crystals

The heat capacities of copper(II) formate tetrahydrate and tetradeuterate have been measured from 12 to 300 K with an adiabatic calorimeter. They have sigmoidal temperature dependence except near the antiferroelectric-paraelectric transition temperatures, 235.78 ± 0.05 K and 245.64 ± 0.05 K, respectively. The corresponding enthalpy changes are 836.0 ± 1.0 J mol^?1 and 936.9 ± 0.5 J mor^?1. The entropy changes are 3.546 ± 0.005 JK^?1mol^?1 and 3.814 ± 0.002 JK^?1 mol^?1. The heat capacities are larger in the high temperature phase than in the low temperature phase, the difference amounting to 5.74 JK^?1 mol^?1 and 7.15 JK^?1 mol^?1 for the hydrate and the deuterate, respectively. The heat capacity anomaly is compared with those in tin(II) chloride dihydrate and potassium hexacyanoferrate trihydrate and discussed in relation to the structure of the hydrogen bond networks in these substances. The discussion is extended to include possible properties of the hydrogen bond frameworks in ices I_h and II.     

Influence of additional metal ions on the ratio of conversion rates of intermediate products of the hydrolysis of adenosine-5′-triphosphoric acid catalyzed by the Cu2+ ion: 1. Experimental study of the influence of Mg2+ ions in the ascending branch of the dependence of the initial hydrolysis rate on pH

The hydrolysis of the dimeric complex (CuATP^2?)₂ to CuADP^? and inorganic phosphate P _i is irreversible. The main intermediate hydrolysis product, whose formation should be taken into account at relatively early steps of hydrolysis, is the pentacovalent intermediate IntK formed in parallel with the hydrolysis to CuADP^? and P _i through the common intermediate product (CuATP^2?)₂OH^? (DOH^?) in step 1, which is the replacement of the nucleophile (OH^?) at the Cu²⁺ ion by OH^? at the positively charged phosphorus atom. The influence of the addition of Mg²⁺ ions is studied (depending on their concentration) on the rate constants of step 1 in the region of pH in the ascending branch of the dependence of the initial hydrolysis rate on pH at two values of pH: 6.48 and 6.70. This region of pH is sensitive to both the rate constant of DOH^? formation and the rate constants of step 1. The rate constant for the formation of DOH^? from D remains unchanged. An increase in the concentration of Mg²⁺ decreases the value of ATP conversion, above which the stationary hydrolysis regime is observed. The ratio [IntK]/[DOH^?] is higher when the stationary regime is attained. The applicability of the method proposed for the formation of the attacking nucleophile and the proposed sequence of steps to the enzymatic phosphoryl transfer processes is discussed.     

Z boson effects in electron positron scattering at epic energies at 14 GeV

We discuss the problem of testing the intermediate vector boson effects in the reactions e^?e⁺ → e^?e⁺ + hadrons, e^?e⁺ → e^?e⁺ + μ^?μ⁺, e^?p → e^?x with the next generation of accelerators, and conclude that these reactions must be considered. The differential cross sections for the one lepton at large four-momentum transfer are obtained, and a significant contribution of Z effects is found.     

Electron impact ionisation cross sections of cis- and trans-diamminedichloridoplatinum(II) and its hydrolysis products

ABSTRACT

We report total electron-impact ionisation cross sections (EICSs) of cisplatin, its hydrolysis products and transplatin in the energy range from threshold to 10?keV using the binary-encounter-Bethe (BEB) and its relativistic variant (RBEB), and the Deutsch-Märk (DM) methods. We find reasonable agreement between all three methods, and we also note that the RBEB and the BEB methods yield very similar (almost identical) results in the considered energy range. For cisplatin, the resulting EICSs yield cross section maxima of 22.09?×?10^?20?m² at 55.4?eV for the DM method and 18.67?×?10^?20?m² at 79.2?eV for the (R)BEB method(s). The EICSs of monoaquated cisplatin yield maxima of 12.54?×?10^?20?m² at 82.8?eV for the DM method and of 9.74?×?10^?20?m² at 106?eV for the (R)BEB method(s), diaquated cisplatin yields maxima of 7.56?×?10^?20?m² at 118.5?eV for the DM method and of 5.77?×?10^?20?m² at 136?eV for the (R)BEB method(s). Molecular geometry does not affect the resulting EICS significantly, which is also reflected in very similar EICSs of the cis- and trans-isomer. Limitations of the work as well as desirable future directions in the research area are discussed.     

Validated HPLC-Fl Method for the Analysis of S-Adenosylmethionine and S-Adenosylhomocysteine Biomarkers in Human Blood

The natural methyl donor group, S-adenosylmethionine and its product, S-adenosylhomocysteine play an important role in many biochemical reactions involving transmethylation reactions. These compounds can be used as biomarkers in incipient diagnosis of various pathological disorders therefore the validation of a suitable method to routinely analysis of these compounds is very important. In this paper, a high performance liquid chromatrography method for S-adenosylmethionine and S-adenosylhomocysteine measurement as fluorescent 1,N ⁶-ethanoderivatives from biological samples was validated in terms of selectivity, linearity range of the response (R?>?0.9993), detection limit (9?×?10^?9 and 4.4?×?10^?9 molL^?1), the limit of quantitation (9.7?×?10^?9 and 5.7?×?10^?9?mol?L^?1), precision, trueness and robustness. The method for quantification simultaneous of these compounds is rapid, sensitive and precise and appropriate for clinical analysis.     

Search for heavy neutral leptons in e+e− annihilations at 29 GeV

A search was made in 29 GeV e⁺e^? annihilations for heavy, neutral leptons decaying to e^±X^?(ν), where X is a muon or charged meson. Six events with isolated e^±X^? pairs were found for an intergrated luminosity of 106 pb^?1. The expected background is 5.5 ± 2.2 events. Limits on $\text{σ}\text{s}\text{?}\text{B}$ depend on mass and range from 8 to 20 × 10^?5 nb.     

Molecular dynamics simulation of methane in sodium montmorillonite clay hydrates at elevated pressures and temperatures

Computer simulation has been used to study the structure and dynamics of methane in hydrated sodium montmorillonite clays under conditions encountered in sedimentary basins. Systems containing approximately one, two, three and four molecuiar layers of water have followed gradients of 150 bar km^?1 and 30Kkm^?1, to a maximum burial depth of 6 km (900 bar and 460 K). Methane is coordinated to approximately 19 oxygen atoms, of which typically 6 are provided by the clay surface. Only in the three- and four-layer hydrates is methane able to leave the clay surface. Diffusion depends strongly on the porosity (water content) and burial deth self-diffusion coefficients are in the range 0.12 × 10^?9m²S^?1 < D < 12.65 × 10^?9m²s^?1 for water and 0.04 × 10^?9m²s^?1 < D < 8.64 × 10^?9m²s^?1 for methane. Bearing in mind that porosity decreases with burial depth, it is estimated that maximum diffusion occurs at around 3 km. This is in good agreement with the known location of methane reservoirs in sedimentary basins.     

On lepton-pair production in neutrino-nucleus collisions

A calculation of the cross section for the reaction νγ → νμ ⁺ μ ^? which is induced by the neutrino magnetic moment, is described in detail. The expression obtained for this cross section is used to determine the asymptotic behavior of the cross section for the reaction νN → νNμ ⁺ μ ^? by the Weiszäcker-Williams method. It is shown that, upon going over from the nucleus involved to a structureless particle (for example, an electron), the resulting expression is doubled owing to integration with respect to the virtual-photon momentum over the region m _μ?Q?E _ν, where the Weiszäcker-Williams approximation is not applicable. The method developed here makes it possible to obtain straightforwardly the known asymptotic expressions for the cross sections describing the reactions eN → eNμ ⁺ μ ^? and e ⁺ e ^? → W ⁺ W ^? e ⁺ e ^?.     

Effect of hydrostatic pressure on the magnetocrystalline anisotropy constant K1 of iron and nickel

Previous values of the pressure dependence of the magnetocrystalline anisotropy constant K₁ of iron and nickel were revised. These values of K₁^?1 ($\text{dK}{}_1\text{dp}$) depend on the magnetic field for iron, and do not for nickel. The value in iron extrapolated to infinitely strong magnetic field is ?7.8×10^?6 bar^?1 at room temperature and ?7.3×10^?6 bar^?1 at 77K, and in nickel at 15 KOe is ?7.5×10^?6 bar^?1 at room temperature and ?2.8×10^?6 bar^?1 at 77K.     

Electronic structure and fluorescence spectrum of the HeO+ cation

Quantum-mechanical calculations of the potential curves of the HeO⁺ ion are preformed which correlate with four lower dissociation limits and indicate the excimer type of the ion. The transition dipole moments of the 2²Σ^?→1²Σ^? and 2⁴Σ^?→1⁴Σ ^? transitions are calculated. The energies and radiative lifetimes of vibrational levels are determined and structural and spectroscopic constants of the states 1²Σ^?, 2²Σ^?, 1⁴Σ^?, and 2⁴Σ^? are calculated. The fluorescence spectrum corresponding to the 2²Σ^?→1²Σ^? and 2⁴Σ^?→1⁴Σ ^? transitions is also calculated. The possibility of lasing at these transitions is discussed.     

Hard photon corrections for Bhabha scattering

Numerical results for the α³ differential cross section for e⁺e^? → e⁺e^? are presented for the case of e⁺e^? colliding beams. Special care is given to the hard photon corrections. Acoplanarity distributions for e⁺e^? → e⁺e^?γ are also presented. Attention is drawn to experimental conditions which require the calculation of still higher order corrections.     

Di-Lepton events in the BEBC narrow-band beam neutrino experiment

In film taken with BEBC filled with a Ne(74%mol)/H₂ mixture and exposed to the CERN narrow-band neutrino beam (200 GeV), tenμ^?μ⁺, one μ^?μ⁺μ^?and five μ^?e⁺ events were found in the ν exposure and two μ⁺μ^? events and one μ⁺e^? event in the $\text{ν}$ exposure. Assuming the same production mechanism for μμ and μe events, the relative rates, corrected for identification inefficiency and background, can be combined and are (1.3 ± 0.4)% for (μ^?e⁺ + μ^?μ⁺)/μ^? in neutrino interactions, and (1.2 ± 0.5)% for (μ⁺e^? + μ⁺μ^?)/μ⁺ antineutrino interactions. Eight out of the sixteen μ^??⁺ events have a V⁰, leading to a corrected K⁰-multiplicity of 1.7 ± 0.7. No evidence is found for heavy-lepton production.     

Volume properties and compressibility of the graphite-potassium-mercury compounds

Abstract

The volume properties of graphite intercalation compounds (GIGS) C4KHg and of the initial intermetallic compounds KHg and KHg₂ have been investigated in the piston-cylinder apparatus, using the direct volumetric technique, under pressures up to 25 kbar. The compounds, average compressibility K₊, was determined to be 3.8×10^?3 kbar^?1 for C₄KHg, 3.0×10^?3 kbar-^?1 for C₈KHg, 4.8×10^?1 kbar^?1 for KHg, and 4.0 ×10^?1 kbar^?1 for KHg₂ at pressures of 0-20 kbar. The compressibility of the “two-dimensional” KHg layer in the GIC under various pressure conditions has been estimated. These estimates permit comparison of KHg properties in the “three dimensional” and “quasi-two dimensional” states. It was concluded that the influence of the graphite matrix on the intercalant is insignificant for this type ternary GIC.