Noncovalent Hydrogen Isotope Effects in Paramagnetic Molecules

Zero-point energies (ZPE) of intermolecular, non-bonded vibrations and isotope effects, induced by noncovalent interactions, are computed for paramagnetic molecules. They appear to be not significant for complexation of HO₂ and oxygen with C–H bonds and results to isotope effect, which deviates from unit by 5–10%. However, ZPE and isotope effects in complexes of HO₂ and nitroxyl radicals with water are larger and reach 50–70%. The largest effect, about 12, is found for complexation of hydrogen atom with water. Complexation of nitroxyl and peroxy radicals by hydrogen bonds is accompanied by transfer of spin density of unpaired electron from radical to the ligand molecules and induces high field paramagnetic shifts of the ligand NMR lines. It evidences that the spin transfer via intermolecular bonds occurs by mechanism of spin polarization.     

Hydrogen Isotope Effects in Electrochemical Reductions of Organic Chloro Compounds

Abstract

The kinetic hydrogen isotope effects in electrochemical reductions of CCl₃COOD, CDCl₂COOD, CCl₄, CDCl₃, benzyl chloride, 1-chloronaphthalene and 4-chlorobenzonitrile in deuterated reaction media were determined. The aliphatic chloro compounds are reduced with rather small isotope effects k_H/k_D = 1.2…1.7, as expected if anionic intermediates are formed and protonated. Benzyl chloride is reduced with an apparent k_H/k_D = 2.1, which is probably too high due to radical reactions. Aromatic chloro compounds are reduced with significant participation of a second mechanism via radical intermediates which abstract carbon-bound hydrogen atoms from the components of the reaction system. The resulting isotope effects are k_H/k_D = 1.2 for the part of the reduction which proceeds via anions and k_H/k_D ～ 2.5 for the competing radical reaction.     

Theory of Isotope Effects on He+ Trapping in Solid Hydrogen

We are currently investigating the influence of vibrational effects on the strength of trapping of He⁺ in solid hydrogen. Such effects can lead to an isotope dependence of the trapping energy associated with the hydrogen molecules and He⁺ ion. At the present time, our focus is on the isotope effect for ³He⁺ and ⁴He⁺, which we are studying through the vibrational motions of the trapped He⁺ ions in the potential they experience as they move about their equilibrium positions. The potential governing the vibrations has been obtained from Hartree–Fock cluster calculations of the total energy of the cluster composed of the He⁺ ion and up to the third nearest neighbor hydrogen molecules as a function of the displacement of the He⁺ ion from its trapped position. The energy eigenvalues for the ground vibrational states of ³He⁺ and ⁴He⁺ in this potential come out as 1.29 and 0.96 meV, respectively, leading to corresponding reductions by these amounts in the binding energy of 8.6 eV for both ions without vibrational effects. The difference of these reductions can be considered as an isotope shift, its value for this case being 0.33 meV. From the analysis for these results, it is suggested that isotope shift effects for deuteron and triton in solid D–T would have the same order of magnitude. A procedure for more accurate investigations of the isotope shifts is discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

An Insight into the Biophysical Characterization of Insoluble Collagen Aggregates: Implication for Arthritis

Misfolding and aggregation of proteins is involved in some of the most prevalent neurodegenerative disorders. The importance of collagen stems from the fact that it is one of the dominant component used for tissue engineering and drug delivery applications and is a major component of skin, tendon, bone and other connective tissues. A systematic investigation on the conformation of collagen at various concentrations of glyoxal is studied by various biophysical techniques such as Trp fluorescence, ANS binding, Circular dichroism (CD), ATR-FTIR, Congo red (CR) assay, Rayleigh light scattering and Turbidity measurements. At 60 % (v/v) glyoxal, collagen retains native-like secondary structure, altered Trp environment and high ANS fluorescence, characteristic of molten globule (MG) state. At 80 % (v/v) glyoxal, insoluble collagen aggregates are detected as confirmed by decrease in Trp and ANS fluorescence, increase in non-native β sheet structure as evident from far-UV CD and FTIR spectra, increase in Thioflavin T fluorescence, Rayleigh light scattering, Turbidity measurements, as well as red shift in CR absorbance.     

An Ingenious Approach of Determining Hydrogen Isotope Solubilities, Diffusivities and Permeabilities in GWHER-1 Stainless Steel

To predict the total tritium inventory for starting up a fusion reactor and the tritium distribution in all components of reactor system including test blanket module （TBM）, the hydrogen isotope solubilities, diffusivities and permeabilities are urgently required. Moreover, the neutral hydrogen isotopes released from the plasma facing component materials and their retention in blanket structural materials have notable impacts on either neutral particle transport, recycling in the edge plasma, and density profile control during discharge in present devices, or tritium extraction and recovery in future tokamak reactors. The experimental investigations of hydrogen isotope diffusivities and solubilities in GWHER-1 steel （hydrogen- embrittlement-resistant stainless steel made by China-great-wall-steel-mill） have been performed.     

Quantization of Magnetic Flux Through the Orbits of the Hydrogen Atom

The quantization of magnetic flux through the orbits of the hydrogen atom is investigated on the basis of the Rutherford-Bohr model of the atom. In contrast to earlier studies based on magnetic fields originating from the magnetic moment of the proton, here the origin of the magnetic flux is taken to be the orbiting electron itself. The effect of the magnetic moment of the proton on the magnetic flux through the orbit is studied in more detail. The energy difference due to opposite directions of the magnetic moment of the proton is shown to result in a fractional amount of 3/8 of the hyperfine level splitting of the lowest Bohr orbit. This ratio was also observed for the fine structure energy level splitting when the spin of the electron is neglected.     

Carbon Isotope Fractionation in the Decarboxylation of Phenylpropiolic Acid in Hydrogen Donating Media

Abstract

¹³C kinetic isotope effect (KIE) in the decarboxylation of phenylpropiolic acid (PPA) in tetralin medium (Tn) has been determined at 409–432 K and found to be of magnitude similar to the ¹³C KIE observed in the decarboxylation of malonic acid where the rupture of the C-C bond is the rate determining step. ¹³C KIE equals 1.0318/at 136°C in the decarboxylation of PPA in Tn medium. Intramolecular ¹³C KIE in the decarboxylation of malonic acid equals 1.0316 at this temperature. Thus it has been shown that the nearly “full” ¹³C KIE can be achieved by providing the excess hydrogen to C _x of PPA (or to triple acetylene bond) using not only strong mineral acids as the source of protons but also by carrying out the decarboxylation in organic medium like tetralin. A mechanism of decarboxylation of PPA in Tn is suggested.     

质谱法精密测定重水中的氢同位素丰度

介绍了用高分辨气体质谱计精密测定重水中氢同位素丰度的分析方法．实验自制了一套重水分解系统,以金属铀作还原剂,在一定的温度下还原重水为氘气．采用低温活性碳作为吸收剂,将样品分解、制备成气体试样,用高分辨气体质谱计测定重水中氢同位素丰度．该方法测定高浓度（〉99％）重水的氘丰度,测量结果的相对标准偏差不大于0．02％。     

New Methods for Fully Automated Isotope Ratio Determination from Hydrogen at the Natural Abundance Level

Abstract

A variety of methods for measurement of ²H/¹H from H₂ are evaluated for their ability to be fully automated and for applicability to automated isotopic analysis of water and organic compounds. Equilibration of water with H₂ gas with the aid of a platinum catalyst has been commercialized into a fully automated sample preparation device. A second and newer technique, involving injecting water, methane, or other volatile organic compounds onto hot chromium in a reactor attached to the dual inlet system of a gas isotope ratio mass spectrometer, can be integrated with a conventional GC-autosampler to allow automated analysis of a variety of substrates. Both techniques result in precisions around 1‰ (δ notation) on the VSMOW scale, and are fast and accurate, and with appropriate mass spectrometers require only negligible scaling for the SLAP/VSMOW difference. Several experimental methods which show considerable promise employ “isotope ratio monitoring” (irm) inlet systems, in which a carrier gas is used for transport of H₂ to the mass spectrometer. Any such method has to address the problem of He ions corrupting the measurement of the H₂ ions. One such approach uses a heated palladium membrane for selective introduction of H₂ into the mass spectrometer, and a second involves modifications to the ion optics to control the stray helium ions. Both approaches have significant limitations that must be overcome before irm techniques can be used in routine applications, in particular for measuring hydrogen isotopes from GC effluents (irm-GCMS).     

An Insight into the Diffusion of Unsaturated Polyester (UP) Resin into Expanded Graphite (EG) to Improve the Mechanical Properties of the UP/EG Composites

Abstract

Polymer/expanded graphite (EG) nanocomposites have great importance in many industrial applications mainly due to their high electrical/thermal conductivity or flame retardancy. However, to fully employ the benefits of polymer/EG nanocomposites one must consider the high degree of porosity of EG. The high degree of porosity of EG can deteriorate the composites’ mechanical properties if the polymer chains cannot diffuse completely into the EG pores. In this article, an insight is given into the diffusion of unsaturated isophthalic polyester (UP) resin, consisting of a combination of maleic anhydride and isophthalic anhydride in the resin backbone, with two viscosities, into the pores of the EG particles of various degrees of porosity. The diffusion experiments were carried out on compressed EG tablets with the same density but different porosity due to the different porosity of the EG particles. The results showed that the diffusion rate of the UP resin with higher viscosity slightly decreased when the EG porosity decreased but, in the opposite way, it strongly increased for the low viscosity UP resin. The EG nanocomposites samples were molded at varying pressures. The micrographs of the fractured surfaces of the EG nanocomposites showed that the EG pores were not filled with resin, thus the EG nanocomposites had residual pores. It was found that composites containing EGs with higher expansion ratio and larger particles and pores showed larger residual pores. Furthermore, the composites prepared with the more viscous UP resin showed more residual pores. By applying a pressure of 10?bar instead of 1?bar, a reduction of 7–20% in the residual pores of the nanocomposites was observed which led to improved mechanical properties by up to 20% in flexural strength for the EG with the highest expansion ratio.     

NMR Spin Trapping: Insight into the Hidden Life of Free Radical Adducts

In our original work (V. Khramtsov, L.J. Berliner and T.L. Clanton, Magn. Reson. Med. 42:228??34, 1999), a ³¹P nuclear magnetic resonance spin trapping (ST NMR) approach aimed to overcome comparatively short lifetimes of the paramagnetic adducts by detecting stable diamagnetic adducts of the degradation of phosphorous-containing nitrone was proposed. High stability of the NMR adducts of the nitrone spin traps with C-centered radicals and the ability to track their origin from paramagnetic adducts make ST NMR a valuable tool for the studies of these radicals in chemical and biological systems. Complementary ST NMR and electron paramagnetic resonance studies of the nitrone adducts derived from the addition of O- and S-centered radicals and nucleophiles revealed new insights into the pathways of the paramagnetic and diamagnetic adduct formation and degradation. In particular, use of ST NMR allowed for observation of reversible nucleophilic addition to the nitrones. On one hand, nucleophilic addition may result in a possible spin trapping artifact via the Forrester–Hepburn mechanism; whereas, on the other hand, the reverse reaction provides the key step in the “recycling??mechanism that is important for the antioxidant actions of the nitrones.     

Electromagnetic Transition Strengths and New Insight into the Chirality in ^106Ag

Excited states in ^106Ag are populated through the heavy-ion fusion evaporation reaction ^100Mo（ll B,5n）^106Ag at a beam energy of 60MeV. Lifetimes are measured for transitions of the two negative-parity rotational bands in the nucleus ^106Ag. The reduced transition probabilities show a great difference between the two bands. The staggering of the B（M1） and B（M1）/B（E2） values with spin are not observed. The bands are identified to be built on two distinct quasiparticle configurations. These results are contrary to an earlier suggestion that the pair of bands in ^106Ag are chiral doublet bands.     

Insight into the role of instantons and their zero modes from lattice QCD

Evidence from lattice QCD calculations is presented showing that instantons and their associated zero modes play a major role in the physics of light hadrons and the propagation of ight quarks in the QCD vacuum.     

Insight into the f-derived Fermi surface of the heavy-fermion compound YbRh2Si2

Angle-resolved photoelectron spectroscopy (ARPES) was used to study the Fermi surface of the heavy-fermion system YbRh(2)Si(2) at a temperature of about 10 K, i.e., a factor of 2 below the Kondo energy scale. We observed sharp structures with a well-defined topology, which were analyzed by comparing with results of band-structure calculations based on the local-density approximation (LDA). The observed bulk Fermi surface presents strong similarities with that expected for a trivalent Yb state, but is slightly larger, has a strong Yb-4f character, and deviates from the LDA results by a larger region without states around the Γ point. These properties are qualitatively explained in the framework of a simple f-d hybridization model. Our analysis highlights the importance of taking into account surface states and doing an appropriate projection along k(z) when comparing ARPES data with results from theoretical calculations.     

Insight into the calcium carboxylate release behavior during Zhundong coal pyrolysis and combustion

In this paper, the dynamic behavior of calcium carboxylate release during Zhundong coal pyrolysis and combustion is studied via reactive molecular dynamics (ReaxFF MD) simulation. The molecular structure model of Zhundong coal is constructed based on the combination of the classic Hatcher coal model and experimental characterizations. Pyrolysis simulations on the coal model are performed at different temperatures ranging from 2000 K to 2800 K. The pyrolysis experiments are also carried out to validate the ReaxFF simulation. The results show that most of the calcium are released into the volatiles by the thermal decomposition of CM-Ca (coal/char matrix with calcium bonded) after releasing CO₂. The distributions of the calcium bonded to gas, tar and inorganics as well as the atomic calcium in the volatiles are quantitatively classified. The thermal cracking of tar fragments are significant at high temperatures leading to the conversion of calcium from tar into the organic gas. Furthermore, the nascent char model is constructed to study the release behavior of calcium in char combustion stage. The calcium is initially released in the form of oxidized calcium and atomic calcium. With increasing temperature, the oxidized calcium trends to convert to the organically bonded calcium. By using the Arrhenius expression, the kinetic parameters for the release of calcium into various species during pyrolysis and char combustion stages are quantitatively determined.     

Isotope effect in electron capture by protons into the 2S-state of hydrogen

We have investigated the isotope effect for electron capture into the 2S-state of hydrogen in close collisions for the processes H⁺ in H₂ and H⁺ in D₂. The differential cross sections and transition probabilities P_2S obtained for capture into H(2S) as a function of energy at a fixed angle of θ = 1° exhibit distinctive features, but no apparent isotope effects are detected.     

Insight into the magnetic behavior of Sr2IrO4: A spontaneous magnetization study

Sr₂IrO₄ is a weak ferromagnet where the spin arrangement is canted anti-ferromagnetic (AF). Moreover, the spin-structure coupling plays an important role in magnetic behavior of Sr₂IrO₄. In this concern the magnetization under zero applied field i.e. spontaneous magnetization would be interesting to study and would give insight into the novel magnetic behavior of Sr₂IrO₄. Sophisticated techniques like neutron diffraction, μSR etc has been used to understand the magnetic behavior of Sr₂IrO₄ under zero applied field. To understand the magnetic behavior we have performed field and temperature dependent magnetization study. The measured field and temperature dependent magnetic data is analyzed rigorously. We have attempted to understand the temperature dependance of spontaneous magnetization, remanent magnetization and coercive force. We observe that the spontaneous magnetization extracted from Arrott plot shows that the Sr₂IrO₄ is not an ideal ferromagnet. The temperature dependent coercive field follows Guant's model of strong domain wall pinning. Our investigation explicit the temperature dependence of various magnetic properties shows the magnetic transitions from paramagnetic to ferromagnetic phase with $T_c$ around 225 K and a low temperature evolution of magnetic moment around $T_M～90$ K.     

Isotope Effects in the Electrochemical Reduction of Oxalic Acid-D2 and Benzoic Acid-D

Abstract

The electrochemical reduction of model carboxylic acid at lead cathodes in deuterated media was studied for potential use in the synthesis of special deuterated compounds.

Oxalic acid-d₂ in D₂O gives good yields of glyoxylic acid-d₂. An unexpected large isotope effect of 5.3 ± 1.7 was found in this reaction, leading to significant depletion of deuterium content in the aldehyde group.

Benzoic acid-d in CD₃OD/diluted D₂SO₄ yields benzyl alcohol-d, 7,7-d₂. The isotope effect of 2.4 ± 1.0 is within the expected range. No deuterium is incorporated into the aromatic nucleus. Essentially unlabelled benzyl alcohol is obtained in CD₃OH/dil. H₂SO₄.     

Exploratory Insight into the Long-Term Photostability of the Brilliant Cresyl Blue Based Electrolyte Solution of Photogalvanic Cells

Journal of Applied Spectroscopy - Photogalvanic cells have been studied with respect to the photostability of the Brilliant Cresyl Blue (ВСВ) dye sensitizer Fructose reductant...