Anisotropic Orientation of Lactate in Skeletal Muscle Observed by Dipolar Coupling in H NMR Spectroscopy

Double quantum (DQ), J-resolved (1)H NMR spectra from rat and bovine skeletal muscle showed a splitting frequency ( approximately 24 Hz) for the lactate methyl protons that varied with the orientation of the muscle fibers relative to the magnetic field. In contrast, spectra of lactate in solution consist of a J-coupled methyl doublet and a J-coupled methine quartet (J(HH) = 7 Hz) with no sensitivity to sample orientation. Spectra acquired in magnetic fields of 4.7, 7, and 11 T showed that the splitting was not due to inhomogeneities in magnetic susceptibility within the muscle, because the magnitude of the splitting did not scale with the strength of B(0) fields. Triple quantum coherence (TQC) spectra revealed two distinct transition frequencies on the methyl resonance. These frequencies resulted from intra-methyl and methine-methyl couplings in this four spin system (A(3)X). Decoupling experiments on the triple quantum coherence showed that the observed frequency splitting was due mainly to the dipolar interactions between the methine and methyl protons of the lactate molecule. Thus, all the proton resonances of the lactate molecules in muscle behave anisotropically in the magnetic field. Adequate design and interpretation of spectroscopic experiments to measure lactate in muscle, and possibly in any cell and organ which contain asymmetric structures, require that both the dipolar coupling described here and the well-known scalar coupling be taken into account.     

Induced spin interactions in the early universe from discrete time quantum theory

By considering a system of spinning particles in an external magnetic field we demonstrate that the system develops non-local spin interactions due to discrete time quantum effects. Such interactions can lead to a domain like structure in the early universe possibly serving as generic seeds to large scale structure.     

Magnetic field dependence of 11B NMR in CeB6

The ¹¹B nuclear magnetic resonance in a dense Kondo system CeB₆ has been observed by the spin echo technique below 4.2 K at fixed frequencies of 2.5, 6.5, 13.33 and 18.00 MHz, which correspond to magnetic fields of 1.83, 4.76, 9.76 and 13.18 KOe for the free ¹¹B nucleus, respectively. The spectra in the phase II appeared to have two peaks in the magnetic field applied in the [111] direction, the spacing of which was found to be very small in zero external field and increased monotonically (up to 0.11 kOe at 2.6 K) with increasing field. On the other hand, the spectra in the phase III were complex. Especially, the spectra observed for [111] at 6.5 MHz were found to spread over 1.9 KOe and to have several peaks. From comparison between the experiments and the dipolar field calculation based on the recent neutron diffraction measurements, possible magnetic structures were examined for the phases II and III.     

Efficiency at high spinning frequencies of heteronuclear decoupling methods designed to quench rotary resonance

The performance of two recently developed heteronuclear decoupling schemes designed to quench rotary resonance, phase-inverted supercycled sequence for attenuation of rotary resonance (PISSARRO) and high-phase two-pulse phase modulation (high-phase TPPM), are probed at high spinning frequencies. High-phase TPPM may be useful at the n=1 rotary resonance condition while PISSARRO permits efficient decoupling over a broad commonly used range of rf amplitudes, even at very high spinning frequencies. New insights into the response of spin systems to both decoupling schemes have been gained. High-phase TPPM is sensitive to the offsets of remote protons, their chemical shift anisotropies, and the relative orientations of the heteronuclear dipolar and proton chemical shift tensors. Since PISSARRO is virtually immune against such effects, the method is especially suited for very high magnetic fields.     

Measurement of Interproton, Nuclear Spin Dipolar Couplings in Liquid Crystalline Samples by Combining Variable Angle Sample Spinning, Isotope Dilution, and Deuterium Decoupling

The proton NMR spectra of liquid crystalline samples can be simplified by selective, partial deuteration followed by deuterium decoupling. This leaves strong peaks from the protons at the undeuterated sites, but also weak resonances from the coupling of these protons to those at low abundance (2% in the present case) at the deuterated sites. The weak resonances can be separated from the strong by recording spectra while spinning the sample at a series of angles to the magnetic field.     

Improvement of resolution in solid state NMR spectra with J-decoupling: an analysis of lineshape contributions in uniformly C-enriched amino acids and proteins

In magic angle spinning (MAS) NMR spectra of highly and uniformly 13C,15N-enriched amino acids and proteins, homo-nuclear coupling interactions contribute significantly to the 13C linewidths, particularly for moderate applied magnetic field strengths and sample spinning frequencies. In this work, we attempted to dissect, analyze, and control the contributions of J-coupling and residual homo-nuclear dipolar coupling interactions to the linewidths of uniformly 13C,15N-enriched crystalline alanine; these studies were carried out at 9.4 T using a range of spinning frequencies from 5 to 15 kHz. The anisotropic second-order dipolar shifts and the J-splittings are comparable in their contribution to the linewidths, but behave very differently in terms of experimental protocols for line narrowing. In contrast to the J-coupling interactions, the second-order dipolar broadening cannot be refocused using selective pulses on the passively coupled spin. We carried out experiments to remove or refocus the 13C J-coupling interactions (omega1 J-decoupling) using a selective DANTE pulse in the center of the indirect evolution period. Inversion profiles and bandwidths of selective DANTE pulses acting on transverse magnetization, in the regime of moderate spinning frequencies, were characterized computationally and experimentally. A dramatic improvement in the resolution of the 2D spectrum was achieved when this decoupling protocol was employed.     

Improvement of resolution in solid state NMR spectra with J-decoupling: an analysis of lineshape contributions in uniformly 13C-enriched amino acids and proteins

In magic angle spinning (MAS) NMR spectra of highly and uniformly 13C,15N-enriched amino acids and proteins, homo-nuclear coupling interactions contribute significantly to the 13C linewidths, particularly for moderate applied magnetic field strengths and sample spinning frequencies. In this work, we attempted to dissect, analyze, and control the contributions of J-coupling and residual homo-nuclear dipolar coupling interactions to the linewidths of uniformly 13C,15N-enriched crystalline alanine; these studies were carried out at 9.4 T using a range of spinning frequencies from 5 to 15 kHz. The anisotropic second-order dipolar shifts and the J-splittings are comparable in their contribution to the linewidths, but behave very differently in terms of experimental protocols for line narrowing. In contrast to the J-coupling interactions, the second-order dipolar broadening cannot be refocused using selective pulses on the passively coupled spin. We carried out experiments to remove or refocus the 13C J-coupling interactions (omega1 J-decoupling) using a selective DANTE pulse in the center of the indirect evolution period. Inversion profiles and bandwidths of selective DANTE pulses acting on transverse magnetization, in the regime of moderate spinning frequencies, were characterized computationally and experimentally. A dramatic improvement in the resolution of the 2D spectrum was achieved when this decoupling protocol was employed.     

Lienard-Wiechert potentials and synchrotron radiation from a relativistic spinning particle in pseudoclassical theory

For a relativistic spinning particle with an anomalous magnetic moment, Lienard-Wiechert potentials are constructed within the pseudoclassical approach. Some specific cases of the motion of a spinning particle are considered on the basis of general expressions obtained in this study for the Lienard-Wiechert potentials. In particular, the intensity of the synchrotron radiation from a transversely polarized particle moving along a circle at a constant speed is investigated as a function of the particle spin. In the specific case of particles having no anomalous magnetic moment and moving in an external uniform magnetic field, the resulting expressions coincide with familiar formulas from the quantum theory of radiation. The spin dependence of the polarization of synchrotron radiation is investigated.     

Rashba coupling induced spin susceptibility and magnetic phase transition of conduction electrons in monolayer graphene

Isolated graphene cannot be obtained by the known synthesis processes and it should be placed on a substrate. This substrate introduces a new type of spin–orbit interaction known as Rashba coupling. Using the Kubo formalism, the magnetic properties of the system in the linear regime have been investigated. Mainly the effect of non-magnetic substrate on the spin susceptibility is calculated. Results show that the Rashba coupling has a central role in the magnetic response function of the system and it is really remarkable since this type of spin orbit coupling can be effectively controlled by an external gate voltage. Most importantly, it was shown that, in the presence of the Rashba interaction a magnetic phase transition could be observed. This magnetic phase corresponds to a magnetic order of conduction electrons that takes place at some special frequencies of external magnetic field.     

Spin state of ortho-parawater molecules in liquid

The state of the nuclear spin moments of two protons in the water molecule is considered when the latter is subjected to surrounding liquid and, for this reason, is an open quantum system. The form of the density operator of the mixed state for spin moments is postulated. Spin degrees of freedom of the molecule appear strongly protected against external influences and are not susceptible to external magnetic fields due to the zero nuclear magnetic moment.     

Double resonance experiments in low magnetic field: Dynamic polarization of protons by N and measurement of low NQR frequencies

The possibilities of dynamically polarizing proton spin system via the quadrupole ¹⁴N spin system in low magnetic field are analyzed. The increase of the proton magnetization is calculated. The polarization rate of the proton spin system is related to the transition probabilities per unit time between the ¹⁴N quadrupole energy levels and proton energy levels. The experiments performed in 1,3,5-triazine confirm the results of the theoretical analysis. A new double resonance technique is proposed for the measurement of nuclear quadrupole resonance frequencies ν_Q of the order of 100 kHz and lower. The technique is based on magnetic field cycling between a high and a low static magnetic field and observation of the proton NMR signal in the high magnetic field. In the low magnetic field the quadrupole nuclei and protons resonantly interact at the proton Larmor frequency ν_H = ν_Q/2. The quadrupole nuclei are simultaneously excited by a resonant rf magnetic field oriented along the direction of the low static magnetic field. The experimental procedure is described and the sensitivity of the new technique is estimated. Some examples of the measurement of low ¹⁴N and ²H nuclear quadrupole resonance frequencies are presented.     

Chemical shift referencing in MAS solid state NMR

Solid state 13C magic angle spinning (MAS) NMR spectra are typically referenced externally using a probe which does not incorporate a field frequency lock. Solution NMR shifts on the other hand are more often determined with respect to an internal reference and using a deuterium based field frequency lock. Further differences arise in solution NMR of proteins and nucleic acids where both 13C and 1H shifts are referenced by recording the frequency of the 1H resonance of DSS (sodium salt of 2,2-dimethyl-2-silapentane-5-sulphonic acid) instead of TMS (tetramethylsilane). In this note we investigate the difficulties in relating shifts measured relative to TMS and DSS by these various approaches in solution and solids NMR, and calibrate adamantane as an external 13C standard for solids NMR. We find that external chemical shift referencing of magic angle spinning spectra is typically quite reproducible and accurate, with better than +/-0.03 ppm accuracy being straight forward to achieve. Solid state and liquid phase NMR shifts obtained by magic angle spinning with external referencing agree with those measured using typical solution NMR hardware with the sample tube aligned with the applied field as long as magnetic susceptibility corrections and solvent shifts are taken into account. The DSS and TMS reference scales for 13C and 1H are related accurately using MAS NMR. Large solvent shifts for the 13C resonance in TMS in either deuterochloroform or methanol are observed, being +0.71 ppm and -0.74 ppm from external TMS, respectively. The ratio of the 13C resonance frequencies for the two carbons in solid adamantane to the 1H resonance of TMS is reported.     

Magnetic-field dependent optically detected ESR in the photoexcited triplet states of bridged Zr(IV) metallocenes

We report on the magnetic-field-dependent optically detected magnetic resonance (ODMR) spectra for polycrystalline samples of the bridged Zr(IV) metallocenes, Me₂Si<(Cp₂)ZrCl₂ ( (dimethylsilylbis(cyclopentadienyl)zirconium-dichloride) and Me₂C<(Cp₂)ZrCl₂ (iso-propylidenebis(cyclopentadienyl)zirconium-dichloride). ODMR spectra at zero magnetic field were recorded by frequency sweeping a microwave source from 0.1 to 10 GHz with the sample contained in a microwave helix. ODMR spectra at finite magnetic fields were recorded with the sample contained in either a helix or a slotted-tube resonator with a fixed microwave frequency and sweeping the magnetic field. For all experiments, the sample and microwave probes were contained in an immersion dewar cryostat, and the temperature was held at about 2 K. All three zero field ODMR transitions (2|E|, and |D| − |E| and |D|+|E|) were observed in the frequency-swept ODMR spectra recorded at zero and small magnetic fields. The zero-field frequency-swept spectra allowed the determination ofD andE values uniquely. For frequency-swept small-field ODMR spectra recorded at successively higher magnetic fields, each of the ODMR line intensities was observed to increase with increasing magnetic field. This intensity increase was observed for all three ODMR lines, reflecting an increase in the total intensity rather than simply a change in the polarization of the triplet sublevels. The latter would result in a change in the relative intensities of the ODMR lines but would not change simultaneously the intensities of all three lines. The ODMR line intensities increase in proportion toB ⁿ, wheren<1. This field dependence is weaker than the expected proportionalB ² dependence from the Zeeman effect, which likely originates from the magnetic field dependence of the spin relaxation rates between the triplet sublevels. Magnetic-field-swept ODMR spectra recorded at fixed microwave frequencies in the X-band frequency range (9.8 GHz) do not show all three expected classic Pake powder pattern line shape profiles, exhibited by the molecules with their magneticZ, Y, andX axes parallel to the external magnetic field. In particular, the intensity for molecular magneticY-axes parallel to the external magnetic field is completely suppressed. In addition, an external magnetic field dependence in field-swept ODMR spectra was observed, which results in a linear decrease of the ODMR intensity with increasing strength of the external magnetic field over and above that would be expected in a polycrystalline spectrum. The data are analyzed by simulation of the continuous-wave ESR spectrum with the eigenvalues and eigenvectors of the spin Hamiltonian matrix characterizing the triplet state exhibiting the ODMR spectrum, in conjunction with homotopy, as a function of the orientations of the magnetic axes of the various molecules in a polycrystalline sample. This approach is useful to interpret the experimentally observed ODMR transition frequencies andg-values but does not take the amplitudes in the ODMR spectrum. The corrections required to modify the continuous-wave ESR spectral amplitudes that reproduce the observed ODMR amplitudes are effects associated with the ODMR processes.     

Zitterbewegung in External Magnetic Field: Classic versus Quantum Approach

We investigate variations of the Zitterbewegung frequency of electron due to an external static and uniform magnetic field employing the expectation value quantum approach, and compare our results with the classical model of spinning particles. We demonstrate that these two so far compatible approaches are not in agreement in the presence of an external uniform static magnetic field, in which the classical approach breaks the usual symmetry of free particles and antiparticles states, i.e. it leads to CP violation. Hence, regarding the Zitterbewegung frequency of electron, the classical approach in the presence of an external magnetic field is unlikely to correctly describe the spin of electron, while the quantum approach does, as expected. We also show that the results obtained via the expectation value are in close agreement with the quantum approach of the Heisenberg picture derived in the literature. However, the method we use is capable of being compared with the classical approach regarding the spin aspects. The classical interpretation of spin produced by the altered Zitterbewegung frequency, in the presence of an external magnetic field, are discussed.     

Field cycling by fast NMR probe transfer: Design and application in field-dependent CIDNP experiments

A novel field-cycling unit with fast digital positioning of a high-resolution nuclear magnetic resonance probe in a spatially varying magnetic field is described and used to measure CIDNP spectra of the amino acid-dye (histidine-bipyridyl) photoreaction system in the range between 0 and 7 T. The pattern of nuclear polarization varies with the magnetic field. In particular, strong polarization with an emission/absorption pattern (multiplet effect) is found at low field for two histidine ringprotons with scalar coupling below 3 Hz visible only because of the high resolution made possible by the new field-cycling setup. Also for the CH₂ protons in the β-position a multiplet effect is observed having a pattern changing with magnetic field. By analysis of the spin nutation the non-Boltzmann population differences of the nuclear levels have been determined.     

Rescaling of 2D ESEEM Data as a Tool for Inverse Problem Solving

A rescaling procedure is proposed for electron spin echo envelope modulation spectra observed at several electron paramagnetic resonance transitions. Analytical expressions describing the relations between the rescaled frequencies and hyperfine and quadrupole parameters of the remote nucleus are obtained. The dependences of the rescaled data on the external magnetic field and spin projections of the ion nucleus and the remote nuclei are used to derive the parameters of the nuclear state in the crystals Y₂SiO₅ and YVO₄ doped by ion Nd³⁺.     

磁性纳米结构中由激光引起的超快自旋动力学研究

以单个磁性中心的NiO以及由Co和Ni等元素构成的双磁性中心的纳米结构为例,总结了近年所做的主要工作.为了在理论上实现磁性纳米结构中的超快自旋翻转和转移,提出了一种称为Λ进程(Λ process)的超快自旋转换机理.在实际计算中,首先采用量子化学第一性原理计算得到磁性纳米结构中精确的隙间d电子态,然后考虑外加磁场和自旋轨道耦合分析磁性原子中的自旋局域化程度,最后引入激光脉冲项,研究在其作用下材料的自旋态经由Λ进程实现转换的时间历程.研究结果表明自旋翻转和转移可以在线偏振光的作用下在亚皮秒的时间尺度内完成. 关键词： 超快自旋动力学 第一性原理计算 Λ进程 磁性纳米结构     

自旋为1/2的XY模型亚铁磁棱型链的物性和有序-无序竞争

利用不变本征算符法, 计算低温下自旋为1/2的XY模型一维亚铁磁棱型链系统的元激发谱, 讨论在此系统中不同的特殊情形下的元激发能量, 从而给出体系的三个临界磁场强度的解析解H_C1, H_C2, H_peak. 分析不同外磁场下 体系的磁化强度随温度的变化规律, 发现三个临界磁场强度的解析解H_C1, H_C2, H_peak是正确的, 并从三个元激发对磁化强度的贡献进行了说明. 低温下磁化强度随外磁场的变化呈现1/3磁化平台. 体系的磁化率随温度或者外磁场的变化都出现了双峰现象. 这说明双峰源于二聚体分子内电子自旋平行排列的铁磁交换作 用能和二聚体与单基体分子间电子自旋反平行排列的反铁磁交换作用能, 热无序能, 外磁场强度相关的自旋磁矩势能之间的竞争.     

~(13)C CP/MAS OF MOTIONS IN SOLID POLYMERS

High-resolution 13C spectra of solid polymers are often acquired with cross polarization with magic angle spinning (CP/MAS) to take advantage of the abunda ntly available protons in the polymer chains. The sequence for transferring mag netization from 1H to13C using Hartmann-Hahn spin locking in the rotating frame is now a standard in commercial solidstate NMR spectrometers.     

PRISE THE SECRET OF HETEROGENEITY OUT OF BIOPOLYMER SYSTEMS

High-resolution 13C spectra of solid polymers are often acquired with cross polarization with magic angle spinning (CP/MAS) to take advantage of the abunda ntly available protons in the polymer chains. The sequence for transferring mag netization from 1H to13C using Hartmann-Hahn spin locking in the rotating frame is now a standard in commercial solidstate NMR spectrometers.