脱水淫羊藿素─3─O─甙类化合物的核磁共振谱研究

用远程１Ｈ－１３ＣＣＯＳＹ（ＨＭＢＣ）技术研究了从朝鲜淫羊藿中分离出的二个脱水淫羊藿素─３－Ｏ－甙类化合物，朝藿甙Ａ和箭藿甙Ｂ，确定了其骨架碳的化学位移．并重新评估了前期文献对该类化合物Ｃ－５、Ｃ－７和Ｃ－４′信号的归属．     

脱水淫羊藿素-3-O-甙类化合物的核磁共振谱研究

用远程¹H-¹³C COSY (HMBC)技术研究了从朝鲜淫羊藿中分离出的二个脱水淫羊藿素-3-O-甙类化合物,朝藿甙A和箭藿甙B,确定了其骨架碳的化学位移.并重新评估了前期文献对该类化合物C-5、C-7和C-4'信号的归属.     

13C NMR Chemical Shifts of Heterocycles: Empirical Substituent Effects in 5-Halomethylisoxazoles

Evaluation by empirically derived equations for the Substituent effect (α, β, γ, δ) on the ¹³C NMR chemical shifts for C-3, C-4. C-5 and halomethyl-substituent carbon (C-6) in isoxazoles 1-5 [where C-3 substituent (R¹) = H, alkyl or phenyl, C-4 Substituent (R²) = H, alkyl, and C-5 substituent (R³) = di-or trihalomethyl, methyl and H], taking as reference the compound la, is reported. From the calculated values for the α, β, γ, δ effects for each substituent it was possible to estimate the chemical shift of each carbon of the compounds 1–5. The ¹³ C chemical shifts of the C-3, C-4, C-5, C-6 of these compounds, can be estimated with good precision: 94% of the calculated chemical shifts are found to be within ±1.0ppm, and 100% are found to be within ±1.5ppm.     

On the Role of Aluminum in Finemet

The role of aluminum with respect of its influence on some intrinsic magnetic properties of the nanocrystalline Finemet, such as saturation magnetization, Curie temperature, spin-wave stiffness constant and hyperfine magnetic fields was investigated. The strengthening effect of Al on the exchange interaction was observed for the alloys with small Al content (up to 3 at.%). Higher concentration of Al (5-7 at.%) led to considerably suppressed exchange interaction.     

甲苯羰基化的^13C—NMR研究：Ⅰ甲苯的质子化

本文报导了甲苯—三氯化铝—氯化氢体系的~(13)C—NMR室温谱.实验证实在溶液中,不仅在甲苯分子与络合物分子之间,而且在络合物分子之间均存在着快速的化学交换.本文还解释了实验中出现的异常现象.     

13C NMR Chemical Shifts of Heterocycles: 3∗. Empirical Substituent Effects in 2-Halomethyl-2-hydroxy-tetrahydrofurans and -5,6-tetrahydro-4H-pyrans

Abstract

Evaluation by empirically derived equations for the Substituent effect (α, β, γ, δ) on the ¹³C NMR chemical shifts for C-2, C-3, C-4, C-5, C-6, the halomethyl-substituted carbon (C-7) and the cyano or oxymic carbon (C-8) in 2-halomethyl-2-hydroxy-tetrahydrofurans 1a-c, 2, 3a, b, 4a and -5,6-tetrahydro-4H-pyrans 5a-c, 6a [with C-2-substituents (R²): CF₃, CCl₃ or CHCl₂, C-3-substituents (R³): CN, C(Me)=NOH, CH=NOMe, C(Me)=NOMe or CH=NOH], taking as reference the 2-trifluoromethyl-2-hydroxy-tetrahydrofuran (la), is reported. From the additivity properties of the α-, β-, γ-, δ-and ?-effects for each Substituent it is possible to predict the chemical shift of each carbon of the compounds 1–6.

     

Electronic structures and magnetic couplings of B-, C-, and N-doped BeO

The electronic structures and magnetic properties of B-, C-, and N-doped BeO supercells are investigated by means of ab initio calculations using density functional theory. The magnetic exchange constants of C-doped BeO at different doping levels are also calculated. A phenomenological band structure model based on p-d exchange-like p-p level repulsion between the dopants is proposed to explain the magnetic ground states in B-, C-, and N-doped BeO systems. The evolution from the antiferromagnetic phase to the ferromagnetic phase of C-doped BeO supercell with C concentration decreasing can also be well explained using this model. The findings in this study provide a simple guide for the design of band structure for a magnetic sp-electron semiconductor.     

Electronic structure and magnetic properties of SmCo7-x Tix

Electronic structure of SmCo7-xTix alloy has been studied by means of the spin-polarized MS-X( method. It is shown that a few of electrons are transferred to Sm(5d) orbital due to orbital hybridization between Sm and Co atoms. The exchange interaction between 5d-3d electrons is stronger, which is the main reason resulting in the long-range ferromagnetic order between Co and Sm atoms. The Curie temperature of SmCo7-xTix is generally lower than that of pure Co metal, which may be explained by the weaker average of coupling strength between Co sites due to some negative exchange couplings occurring mainly at 2e site. The calculated results for the Sm5Co28Ti6 cluster may lead to a better understanding of why SmCo7-xTix is stable phase. Since the negative interaction of 2e sites weakens and the bonding at EF strengthens with increasing Ti concentration, which result in the decrease in the free energy of the alloy, the stable ferromagnetic order forms inside SmCo7-xTix. Considering the localization of 4f states and 5d moment arising from the orbital hybridization, the calculated moment is 9.47μB per formula unit that is in agreement with experiments.     

Multiple-quantum relaxation in the magic-angle-spinning NMR of 13C spin pairs.

We determine the decay rate constants of zero-, double- and single-quantum coherence for 13C spin pairs in magic-angle-spinning solid-state NMR. The double-quantum coherence is excited by a C7 pulse sequence and converted into zero-quantum coherence by a frequency-selective pair of pi/2 pulses. The zero-quantum coherence is reconverted into observable magnetization by a second pair of pi/2 pulses followed by a second C7 sequence. In a magnetically dilute system where the 13C-13C distance is 0.296 nm, the relaxation rate constants are consistent with a model of uncorrelated random fields at the two labeled 13C sites. In a fully-labelled system with a short 13C-13C distance of 0.153 nm, the measured rate constants are inconsistent with the uncorrelated random field model.     

Ionization and electron capture in neon K vacancy production from NNe collisions

Our measurements of Ne K and N K X-ray cross sections for N^{3+,4+,5+,6+,7+,} ions incident on a thin Ne target at energies from 9 to 54 MeV indicate that charge exchange plays a minor role compared to ionization in producing Ne K vacancies over that energy range.     

Magnetization reversal in perpendicular exchange-biased multilayers

Co/Pt multilayers with perpendicular magnetic anisotropy exhibit an exchange bias when covered with an IrMn layer. The exchange bias field, which is about 7 mT for 3 Co/Pt bilayer repetitions and a Co layer thickness of 5 Å, can be increased up to 16.5 mT by the insertion of a thin Pt layer at the Co/IrMn interface. The interfacial magnetic anisotropy of the Co/IrMn interface (KSCo/IrMn =-0.09 mJ/m2) favours in-plane magnetization and tends to tilt the Co spins away from the film normal. Dynamical measurements of the magnetization reversal process reveal that both thermally activated spin reversal in the IrMn layer and domain wall nucleation in the Co/Pt multilayer influence the interfacial spin structure and therefore the strength of the perpendicular exchange bias field.     

Direct decays of heavy quarkonia

The branching ratios are evaluated of the ψ (3770) and (4S) decays into ππ, , ωπ⁰, ωη, ωη ′, π, η, η′, , . They arise due to the transition through the real intermediate states and , respectively. It is shown that some branching ratios exceed the three-gluon one by an order of magnitude. The rates of the decays ,

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and are evaluated also. τ-C and B factories coul be good tools for studying all decays mentioned.     

13C NMR lineshapes of acetone adsorbed on silica

¹³C NMR data, obtained as a function of temperature with magic-angle spinning (MAS) and either cross polarization or direct polarization, are reported on acetone and a sample of acetone (an approximately equal mixture with ¹³C labels at C-1 or C-2) adsorbed on dry silica gel. Various contributions to the observed linewidths and T^C₂ values are considered in terms of a previously established model of the acetone/SiO₂ system; in that model, acetone species are in equilibrium between a physisorbed-acetone (non-hydrogen-bonded) state and a state consisting of acetone units that are hydrogen bonded to silanol moieties on the silica surface. Spin dynamics simulations are useful in interpreting the effects of variations of experimental parameters. It is concluded that the main linewidth contributions, which increase at lower temperatures, are: (a) a dispersion of chemical shifts in the hydrogen-bonded state, associated with the inhomogeneous character of the silica surface; (b) the interference between MAS averaging of the chemical shift anisotropy (especially for the carbonyl carbon) and molecular motion and/or chemical exchange; and (c) chemical exchange broadening. Prominence of the last of these contributions is most consistent with data obtained as a function of magnetic field strength, MAS speed, and temperature.     

Three-dimensional 13C shift/1H-15N coupling/15N shift solid-state NMR correlation spectroscopy.

Triple-resonance experiments capable of correlating directly bonded and proximate carbon and nitrogen backbone sites of uniformly 13C- and 15N-labeled peptides in stationary oriented samples are described. The pulse sequences integrate cross-polarization from 1H to 13C and from 13C to 15N with flip-flop (phase and frequency switched) Lee-Goldburg irradiation for both 13C homonuclear decoupling and 1H-15N spin exchange at the magic angle. Because heteronuclear decoupling is applied throughout, the three-dimensional pulse sequence yields 13C shift/1H-15N coupling/15N shift correlation spectra with single-line resonances in all three frequency dimensions. Not only do the three-dimensional spectra correlate 13C and 15N resonances, they are well resolved due to the three independent frequency dimensions, and they can provide up to four orientationally dependent frequencies as input for structure determination. These experiments have the potential to make sequential backbone resonance assignments in uniformly 13C- and 15N-labeled proteins.     

A step towards nanoionics

The interaction of finely focused 20–100 keV electron beam at 10–1000 A/cm² current densities with 30–150 nm films of the RbAg₄I₅-family solid electrolytes has been studied. The results obtained show that it is possible to form arrays of electrochemical devices with single elements ≈ 10 nm in size in the films. Arrays of 100×100 nm structures consisting of a solid electrolyte film on C-, Au-and Ag-thin supports are demonstrated.     

Solvent Dependence on Structure and Electronic Properties of 7-(Diethylamino) - 2H -1- Benzopyran-2- one (C-466) Laser Dye

In this work, we studied influences on the absorption and fluorescence emission spectra of coumarin-4066 (C-466) with different solvent polarity scale. The spectral shifts reflect the effect of the equilibrium solvents association across the energized solute particle, which adjusts inertially as a result of quick charge realignment upon radiative deactivation to the lowest electronic state. The dipole moments of C-466 are determined by employing the Bakhshiev, Kawski-Chamma-Viallet, Lippert-Mataga and McRae relations. The results from all these methods are, excited state dipole moment of C-466 is higher than the ground state dipole moments and which indicates molecule is less polar in the ground state. Theoretical analysis was also carried out by Density Functional theory (DFT and TD –DFT) employing the BECKE-1998 (exchange)/STO-6G basic set in ethanol solvent and in vacuum medium. The HOMO-LUMO, Solvent Accessible Surfaces (SAS) and Molecular Electrostatic Potential (MEP) were analysed to acquire additional knowledge of the molecular arrangement and electronic properties of C-466. These photophysical properties suggest delineation can be mauled for laying out new luminescent tests for various solvents microenvironment.     

Exchange bias studies of NiFe/FeMn/NiFe trilayer by ion beam etching

Effect of low energy ion beam etching on exchange bias in NiFe/FeMn/NiFe trilayer is investigated in multilayers prepared by rf magnetron sputtering. Stepwise etching and magnetization measurement of FeMn layer in an NiFe/FeMn bilayer show increase of bias as etching proceeds and FeMn thickness decreases. The bias show a maximum around 7 nm FeMn thickness and then fall sharply below 5 nm, broadly in line with the exchange bias variation at increasing FeMn thickness but in reverse order, particularly at low FeMn thickness. Progressive etching of top NiFe layer in the NiFe/FeMn/NiFe trilayer shows an initial gradual increase in bias followed by a sharp increase below 7 nm thickness of top NiFe layer, with a maximum at 2 nm thickness for both NiFe layers and greater bias for seed NiFe layer.     

Higgs-pair production and decay in simplest little Higgs model

In the framework of the simplest little Higgs model (SLHM), we study the production of a pair of neutral CP-even Higgs bosons at the LHC. First, we examine the production rate and find that it can be significantly larger than the SM prediction. Then we investigate the decays of the Higgs-pair and find that for a low Higgs mass their dominant decay mode is hh→ηηηη (η is a CP-odd scalar) while and hh→ηηWW may also have sizable ratios. Finally, we comparatively study the rates of , , and pp→hh→WWWW in the SLHM and the littlest Higgs models (LHT). We find that for a light Higgs, compared with the SM predictions, all the three rates can be sizably enhanced in the LHT but severely suppressed in the SLHM; while for an intermediately heavy Higgs, both the LHT and SLHM can enhance sizably the SM predictions.     

Vlasov-kinetic computer simulations of electrostatic waves in dusty plasmas: an overview of recent results

We have performed calculations for collisions between fully stripped ions, C⁶⁺ and N⁷⁺, and atomic hydrogen, in both its ground and first excited energy levels. We have employed the Classical Trajectory Monte Carlo method to obtain total ionization and charge exchange cross sections and state selective charge exchange cross sections in the 5–500 keV/amu energy range.