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.     

基于显微光谱的组织切片细胞纳米结构研究

细胞纳米结构的探测对癌症的早期诊断以及筛查具有非常重要的意义。空域低相干相位显微镜可以探测细胞的纳米结构获取系统参数,但是显微镜的系统参数和细胞纳米结构参数之间存在着复杂的非线性相关关系,需要研究方法加以定量分析。因此,基于一维高斯场模型加一维多层介质模型模拟空域低相干相位显微镜的背散射光谱,实验结果表明模型预测结果与实际测量结果基本一致。对已知纳米结构的组织切片光谱建模, 通过统计方法分析了系统参数与细胞纳米结构参数的相关关系,验证了系统参数确实能反映细胞纳米结构参数的变化,并量化了系统参数的反映水平。研究成果为基于空域低相干相位显微镜的癌症早期诊断提供了新的理论基础和方法依据。     

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.     

Insight into the growth mechanism of black phosphorus

Two-dimensional (2D) black phosphorus (BP) has attracted great attention in recent years in fundamental research as well as optoelectronics applications. The controllable synthesis of high-quality BP is vital to the investigation of its intrinsic physical properties and versatile applications. Originally, BP was mostly synthesized under high temperatures and pressures. Subsequently, metal flux, wet chemical and chemical vapor transport (CVT) methods had been appeared successively. The pulsed laser deposition (PLD) and CVT methods have been used to prepare high-quality BP thin films on silicon substrates, which is significant for its monolithic integration and practical applications. To meet the demand of the scalable applications of BP, the direct preparation of BP films on dielectric substrates that avoids additional transfer process, is crucial to high-performance device implementation. In this review, the growing methods and corresponding mechanisms of BP are summarized and analyzed. Meanwhile, the view on the controllable growth of large-area, high-quality BP films is envisioned.     

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.     

Insight into the chemomechanical coupling mechanism of kinesin molecular motors

Kinesin is a two-headed biological molecular motor that can walk processively on microtubule via consumption of ATP molecules. The central issue for the molecular motor is how the chemical energy released from ATP hydrolysis is converted to the kinetic energy of the mechanical motion, namely the mechanism of chemomechanical coupling. To address the issue, diverse experimental methods have been employed and a lot of models have been proposed. This review focuses on the proposed models as well as the qualitative and quantitative comparisons between the results derived from the models and those from the structural, biochemical and single-molecule experimental studies.     

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％。     

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.     

Insight into the inner structure of stretched premixed ammonia-air flames

Ammonia as a fuel has sparked significant interest in the combustion community. Although, using ammonia has a lot of advantages including no carbon emissions, ammonia-air flames are characterized as thick flames with low flame speeds. It is important to understand the flame structure to know the combustion process better. Flame thickness is an important property of the flame which characterizes the reactivity of the flame. Identifying the preheat zone is necessary to determine the fresh gas surface which is used to determine flame speed. Also, understanding the behavior of the important species emitted helps to demonstrate the reaction pathway which may be implemented in chemical kinetics schemes. Further, it is interesting to know the effect of curvature on the emission of excited species which gives direct knowledge on the influence of curvature on the flame reactivity. It was seen that the change in reactivity was manifested as a change in thickness of the species. The experiments presented here were performed on a Bunsen burner at atmospheric conditions. The laminar flame speeds have been evaluated over a range of equivalence ratios by choosing the isotherm as specified by the definition of the flame speed which are slightly higher than the values obtained from the literature. Chemiluminescence from NH* and NH₂* was studied for different equivalence ratios. A 1D simulation performed in Chemkin-Pro-was used to compare the behavior of the counterpart non-excited species. This comparison helps to correlate excited and non-excited species and also to define the structure of the ammonia-air flame. Both NH* and NH₂* have been determined as heat release rate markers.     

Isotope Studies of Hydrogen and Oxygen in Ground Ice - Experiences with the Equilibration Technique

Abstract

Equilibration technique suitable for a large amount ofsamples is described for hydrogen and oxygen isotope analyses of ground ice, especially ice wedges, including the sampling strategy and the analytical procedure as well as the calibration of the Finnigan MAT Delta-S mass spectrometer in June, 1999. Since for future analyses of ice wedges, a higher sampling resolution with limited sample volume is required, the limit of the equliibration technique for small water samples size of between 0.05 and 5 ml was checked. For water samples smaller than 1ml, corresponding to a molar ratio [H₂O]/[H₂] of smaller than 0.994, a balance correction has to be applied. The experimental errors due to partial evaporation during evacuation, the balance calcultion of the isotope equilibration process, the linearity as well as memory effects of the mass spectrometer for smaples with large differences in δ¹⁸O and δD are tackled in this paper. In the polar regions of Northern Siberia without Late Pleistocene and Holocene glaciation, ground ice is used as an archive for paleoclimate studies. First results of stable isotope measurements on ice wedges clearly show a shift towards heavier isotopes and thus warmer winter temperatures as well as a change in the source of the precipitation between Late Pleistocene and Holocene. These results indicate the high potential of ground ice for paleoclimate studies.     

Insight into the magnetic behavior and magnetocaloric effect of a borophene monolayer

The successful discovery of borophene has opened a new door for the development of 2D materials. Due to its excellent chemical, electronic and thermal properties, borophene has shown considerable potential in supercapacitors, hydrogen storage and batteries. In this paper, the thermodynamic characteristics and magnetocaloric effect of borophene are specifically studied using the Monte Carlo method. We find that there is an opposite impact between the spin quantum number and the crystal field on t...     

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.     

拉曼光谱研究苯-重水间氢同位素分馏效应

应用金刚石压腔结合拉曼光谱技术研究了封闭体系内氢同位素在苯和重水之间的分馏效应。物相间达到同位素交换平衡是测定稳定同位素分馏系数的前提。与高温高压条件下水抑制正烷烃、环烷烃等烷烃的氢同位素分馏不同,苯的特殊结构可促使其在实验条件下与重水发生氢同位素分馏。通过逐步升高体系温度、增大苯和重水的接触面积、300 ℃下恒温足够长时间等实验手段促使苯和液态重水间达到氢同位素交换平衡,测得300 ℃条件下苯和重水之间的氢同位素分馏系数为0.909 9。证明了原位拉曼技术测定不同液相间氢同位素分馏系数的可行性,同时扩展了金刚石压腔结合拉曼光谱技术测定不同物相间稳定同位素分馏系数的应用范围。     

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.