The DQ-HN[CACB] and DQ-HN(CO)[CACB] sequences with evolution of double quantum Calpha-Cbeta coherences

The new variant of known HNCACB and HN(CO)CACB techniques is proposed that employs excitation and evolution of double quantum Calpha-Cbeta coherences. The most important features of the new method are: increased signal dispersion, lack of splittings due to 1J(Calpha-Cbeta) spin-spin couplings, and absence of accidental cancellations of positive and negative signals. The acquisition of both DQ-HN[CACB] and DQ-HN(CO)[CACB] techniques enables sequential assignment of protein backbone, using only Calpha-Cbeta DQ-frequencies. The determination of all Calpha and Cbeta chemical shifts requires, however, a comparison with HN(CO)CA or HNCA spectra. Examples of applications of the DQ-HN[CACB] and DQ-HN(CO)[CACB] experiments are presented, employing the 2D Reduced Dimensionality approach for 13C, 15N-labeled ubiquitin, and the 3D acquisition for 13C, 15N-double labeled Ca2+ -binding bovine S100A1 protein in the apo state (21 kDa) with overall correlation time of 8.1 ns.     

The set of triple-resonance sequences with a multiple quantum coherence evolution period

The new pulse sequence building block that relies on evolution of heteronuclear multiple quantum coherences is proposed. The particular chemical shifts are obtained in multiple quadrature, using linear combinations of frequencies taken from spectra measured at different quantum levels. The pulse sequences designed in this way consist of small number of RF-pulses, are as short as possible, and could be applied for determination of coupling constants. The examples presented involve 2D correlations HNCO, HNCA, HN(CO)CA, and H(N)COCA via heteronuclear zero and double coherences, as well as 2D HNCOCA technique with simultaneous evolution of triple and three distinct single quantum coherences. Applications of the new sequences are presented for 13C,15N-labeled ubiquitin.     

The Intramolecular Spin-Spin Interactions in Ruthenium Complexes of Pyrazole Derivatives

The spin-spin coupling can provide useful information for analysing the structure of a system and the extent of non-covalent bonds interactions. In this study, we present the isotropic NMR properties and spin-spin coupling involving ruthenium-ligand (Ru-L) bonds and other spin-spin interactions obtained from DFT calculations. The proton shift which in close proximity with the Ru and Cl (or O) atoms are characterised with lower and higher chemical shift respectively. Though Ru-Cl bond has longer bond length than all other Ru-L bonds, yet its spin-spin coupling is higher than others because of a very high contribution of PSO which is far higher than the contribution from FC terms. In all other Ru-L bonds, FC is the most significant Ramsey terms that define their spin-spin coupling. Both the isotropic and anisotropic shielding of the Hz of the pyrazole is lower than Hc of the cymene and the spin-spin coupling 3J(Hz…Hz) of the pyrazole are less than half of the 3J(Hc…Hc) of the cymene unit in the complexes. There is a little increase in both the 3J(Hc…Hc) and 3J(Hz…Hz) spin-spin coupling in the hydrolysed complexes compare to the non-hydrolysed complexes. The isotropic and anisotropic shielding tensor of Ru atoms increases in magnitude as the complexes get hydrolysed that could be ascribed to a more deshielding chemical environments.     

Determination of molecular geometry by high-order multiple-quantum evolution in solid-state NMR

The principles of molecular geometry determination by high-quantum heteronuclear local field spectroscopy in solid-state NMR are discussed. The extreme multiple-quantum coherences in a cluster of nuclear spins are allowed to evolve in the presence of heteronuclear through-space couplings to two spins of a different type. The multiple-quantum dephasing curve is independent of the homonuclear spin-spin couplings and may be described in terms of geometric parameters. The triple-quantum version of the experiment is demonstrated by determining the psi torsion angle in a [(15)N(2), (13)C(3)]-labeled sample of the peptide ala-ala-gly. Two regions of torsion angle space fit the experimental data, one in the neighborhood of -152 degrees and one in the neighborhood of +161 degrees. The latter determination is in excellent agreement with the X-ray estimate of +160.5 degrees.     

Chemical exchange saturation transfer by intermolecular double-quantum coherence

A number of contrast enhancement effects based on the use of intermolecular multiple-quantum coherences, or distant dipolar field effects are known. This phenomenon is characterized by the dependence on the mth power of the initial magnetization (where m is the coherence order used). In this paper, we describe the contrast enhancement based on chemical exchange saturation transfer and NOE, which is achieved by the use of intermolecular double-quantum coherences (iDQC). The method was validated using clinically relevant systems based on glycosaminoglycans and a sample of cartilage tissue, showing that the CEST contrast, as well as, NOE are enhanced by iDQC.     

高分辨核磁共振谱计算机解析方法

本文应用哈密顿矩阵范数逼近方法,利用计算机计算了三自旋、四自旋系统高分辨核磁共振谱的化学位移和偶合常数。与一般迭代程序相比,简化了计算过程,提高了计算精度,并保证了解的唯一性。选择实验能级值作为哈密顿矩阵零级近似,避免了选取初始δ,J值的麻烦。本方法在图谱定量分析中取得了较好效果。     

Hydrogen-mediated spin-spin interaction in ZnCoO

The effect of hydrogen impurities on the electronic and magnetic properties of ZnO-based diluted magnetic semiconductors is examined through first-principles pseudopotential calculations. We suggest that interstitial H can mediate a strong short-ranged ferromagnetic spin-spin interaction between neighboring magnetic impurities through the formation of a bridge bond. Results based on first-principles total-energy calculations and Monte Carlo simulations indicate that such H-mediated spin-spin interactions can lead to high temperature ferromagnetism.     

In phase selective excitation of overlapping multiplets by gradient-enhanced chemical shift selective filters

We have developed gradient-enhanced chemical shift selective filters (ge-CSSF) for inphase excitation of overlapping multiplets 1H. This method relies on the constructive addition of on resonance signal while off resonance magnetization is eliminated by destructive interference due to variable chemical shift evolution. This is achieved by co-addition of several FIDs acquired with a gradually incremented chemical shift evolution period. Two variable-time and one constant-time ge-CSSFs are proposed that can be combined with TOCSY, NOESY, and ROESY mixing schemes yielding highly selective 1D experiments. Analytical and numerical expressions are derived to calculate the excitation profiles of the ge-CSSFs and to examine the effects of spin-spin relaxation, the length of the CSSF increment, and selective inversion pulses. We demonstrate, both theoretically and experimentally, that CSSFs yield fast signal separation for compounds with a range of spin-spin relaxation times and chemical shift differences as small as 1-2 Hz. The use of pulsed field gradients ensures that very clean spectra are obtained. The main application of these techniques lies in analysis of mixtures where severe spectral overlap prevents the use of simple 1D selective methods.     

Detection of correlated dynamics on multiple timescales by measurement of the differential relaxation of zero- and double-quantum coherences involving sidechain methyl groups in proteins

Multiple effects may lead to significant differences between the relaxation rates of zero-quantum coherences (ZQC) and double-quantum coherences (DQC) generated between a pair of nuclei in solution. These include the interference between the anisotropic chemical shifts of the two nuclei participating in formation of the ZQC or DQC, the individual dipolar interactions of each of the two nuclei with the same proton, and the slow modulation of the isotropic chemical shifts of the two nuclei due to conformational exchange. Motional events that occur on a timescale much faster than the rotational correlation time (ps-ns) influence the first two effects, while the third results from processes that occur on a far slower timescale (mus-ms). An analysis of the differential relaxation of ZQC and DQC is thus informative about dynamics on the fast as well as the slow timescales. We present here an experiment that probes the differential relaxation of ZQC and DQC involving methyl groups in protein sidechains as an extension to our recently proposed experiments for the protein backbone. We have applied the methodology to (15)N, (13)C-labeled ubiquitin and used a detailed analysis of the measured relaxation rates using a simple single-axis diffusion model to probe the motional restriction of the C(next)H(next) bond vector where C(next) is the carbon that is directly bonded to a sidechain methyl carbon (C(methyl)). Comparison of the present results with the motional restriction of the C(next)C(methyl) bond (S(axis)(2)) reveals that the single-axis diffusion model, while valid in the fringes of the protein and for shorter chain amino acids, proves inadequate in the central protein core for long chain, asymmetrically branched amino acids where more complex motional models are necessary, as is the inclusion of the possibility of correlation between multiple motional modes. In addition, the present measurements report on the modulation of isotropic chemical shifts due to motion on the mus-ms timescale. Three Leu residues (8, 50, and 56) are found to display these effects. These residues lie in regions where chemical shift modulation had been detected previously both in the backbone and sidechain regions of ubiquitin.     

Multiple-quantum coherences of molecular groups:19F in CF3COOAg

The three (3Q) and six (6Q) quantum coherences of two proximate methyl groups were studied to find out if they can be used to determine the possible nonequivalence of the groups relative to chemical shifts. Numerical calculations of the efficiency of excitation and detection of 3Q and 6Q coherences in reorienting and static methyl group pairs were performed. The crystal orientation, resonance offset, chemical shifts and finite value of the RF field were taken into account. Experimental¹⁹F 2D NMR spectra were obtained from a single crystal of CF₃COOAg. To record 6Q spectra in pure absorption mode in presence of chemical shifts, the data were acquired according to the hypercomplex method. 3Q spectra of the same sample were recorded in absolute-value mode.     

利用CαH系统的零量子-双量子混合相干的弛豫测量研究蛋白质动力学(英文)

越来越多的证据说明,"传统"的弛豫测量(T1, T2, NOE)不足以完整描述蛋白质的复杂动态,如化学交换、构型交换或相互作用导致的动态改变.涉及到多量子相干弛豫机制可以提供额外的动态信息.该文测量2个蛋白质的CαH系统的混合零量子和双量子弛豫速率随CPMG序列中脉冲间隔及温度的变化来探讨蛋白质中的动态及温度的影响.发现2种蛋白之质中均存在可观的交换效应,且与残基位置有关.进一步的分析表明,两位点交换模型不足以解释蛋白质的复杂动态.     

Shielding and spin-spin coupling constants from gas-phase NMR

Intermolecular interactions modify nuclear magnetic resonance (NMR) chemical shifts and spin-spin coupling constants. The intermolecular effects can be determined if the NMR parameters for an isolated molecule are known. Gas-phase NMR spectroscopy offers such methods which allow one to measure the shielding and spin-spin coupling constants at the zero-density limit where the NMR parameters are free from intermolecular contributions. It is also shown that at present the multinuclear NMR spectra can easily be obtained for gaseous samples containing several micrograms of a solute compound.     

不同算法原子电荷下的~1J_(CH)理论计算

用一种计算直接键连原子核自旋耦合常数的半经验公式,结合量子化学计算得到的32种有机分子稳定几何构型的7种不同算法下的原子电荷,探究原子电荷算法的不同对1JCH理论计算的影响,拟合出基于7种原子电荷的耦合常数计算公式,并利用拟合公式对5种分子进行了检验.计算结果表明拟合的32种分子及检验的5种分子的耦合常数的计算值均与实验值较好的符合,拟合得到的基于7种原子电荷的计算公式均可以对其他分子体系的耦合常数进行预测.另外,计算结果同样显示原子电荷算法的不同对1JCH理论计算值有一定的影响却不显著,其中基于电荷均衡方法电荷(QEq)得出的耦合常数计算值与实验值的偏差较其它6种原子电荷的小,结果更可靠.     

MO LCAO calculation of the effect of the reaction electric field on the constant of the spin-spin interaction for P31 and H1 in phosphine

Perturbation theory is used in the MO LCAO approximation to derive a general relation between the constant of the spin-spin interaction and the reaction electric field. This relation predicts possible changes in this constant when there are changes in the dielectric constant of the solvent. The magnitude and nature of these changes depend on the magnitude and orientation of the dipole moment of the dissolved molecule with respect to the direction of the chemical bonds of the interacting nuclei in this molecule. A quantitative calculation is carried out for the effect of the reaction electric field on the spin-spin constant in the PH₃ molecule. A satisfactory agreement is found with experiment.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 10, pp. 38–41, October, 1970.     

Multiple Quantum NMR in One-Dimensional and Nano-Scale Systems: Theory and Computer Simulations

We investigate several exactly solvable models of multiple quantum (MQ) NMR dynamics. We study MQ NMR dynamics of one-dimensional systems (chains and rings) and nano-voids filled with spin-carrying atoms or molecules in a strong external magnetic field. Our focus is the problem of the profile of MQ NMR coherences (i.e., the dependence of the intensities of MQ NMR coherences on their orders). We find that integrable one-dimensional systems exhibit peculiar behavior that does not shed much light on a more generic situation. On the other hand, important lessons can be extracted from our solution for the nano-scale systems. We find that the profile of the intensities of the MQ NMR coherences is rather exponential than Gaussian as was proposed earlier. We also address the cluster growth in the course of the evolution of MQ NMR coherences.     

Coherence Evolution and Transfer Supplemented by Sender’s Initial-State Restoring

The evolution of quantum coherences comes with a set of conservation laws provided that the Hamiltonian governing this evolution conserves the spin-excitation number. At that, coherences do not intertwist during the evolution. Using the transmission line and the receiver in the initial ground state we can transfer the coherences to the receiver without interaction between them, although the matrix elements contributing to each particular coherence intertwist in the receiver’s state. Therefore we propose a tool based on the unitary transformation at the receiver side to untwist these elements and thus restore (at least partially) the structure of the sender’s initial density matrix. A communication line with two-qubit sender and receiver is considered as an example of implementation of this technique.     

Spin-Spin Interactions in Gauge Theory of Gravity, Violation of Weak Equivalence Principle and New Classical Test of General Relativity

For a long time, it has been generally believed that spin-spin interactions can only exist in a theory where Lorentz symmetry is gauged, and a theory with spin-spin interactions is not perturbatively renormalizable. But this is not true. By studying the motion of a spinning particle in gravitational field, it is found that there exist spin-spin interactions in gauge theory of gravity. Its mechanism is that a spinning particle will generate gravitomagnetic field in space-time, and this gravitomagnetic field will interact with the spin of another particle, which will cause spin-spin interactions. So, spin-spin interactions are transmitted by gravitational field. The form of spin-spin interactions in post Newtonian approximations is deduced. This result can also be deduced from the Papapetrou equation. This kind of interaction will not affect the renormalizability of the theory. The spin-spin interactions will violate the weak equivalence principle, and the violation effects are detectable. An experiment is proposed to detect the effects of the violation of the weak equivalence principle.     

Fresco paintings studied by unilateral NMR

Unilateral NMR has been used to monitor the state of conservation of frescoes in the Vasari's house in Florence. The causes of deterioration of ancient frescoes are varied, which result in the detachment and crumbling of the painted film from the supporting plaster and in the outcropping of salts. Unilateral measurements of Hahn echo performed on such frescoes have allowed a perfect identification of the detachment of the painted film from the plaster. The presence of soluble salts on the pictorial film affects the spin-spin relaxation times, T(2). It is then possible using this technique, to characterize the effect of chemical treatments, of cleansing and consolidation procedures using the distribution of T(2) spin-spin relaxation times.     

Multiple quantum dynamics in linear chains and rings of nuclear spins in solids at low temperatures

Multiple quantum spin dynamics is studied using analytical and numerical methods for one-dimensional finite systems of nuclear spins 12 coupled by dipole-dipole interactions at low temperatures. Exact expressions for intensities of multiple quantum coherences at low temperatures were obtained in the approximation of the nearest neighbor interactions. The time growth of multiple quantum coherences was analyzed numerically when all the dipole-dipole interactions in one-dimensional systems consisting of 6/8 spins were taken into account. It is shown that the growth of multiple quantum coherences gets faster when the temperature decreases, and the intensities of multiple quantum coherences can be negative at low temperatures.     

The Effect of Spin-Orbit Coupling and Spin-Spin Coupling of Compact Binaries on Chaos

There are spin-orbit interaction and spin-spin interaction in a generic post-Newtonian Lagrangian formu-lation of comparable mass spinning compact binaries. The spin-orbit coupling or the spin-spin coupling plays a quite important role in changing the evolution of the system and may sometime cause chaotic behavior. How do the two types of couplings exert together any influences on chaos in this formulation? To answer it, we simply take the Lagrangian formulation of a special binary system, including the Newtonian term and the leading-order spin-orbit and spin-spin couplings. The key to this question can be found from a Hamiltonian formulation that is completely identical to the Lagrangian formulation. If the Lagrangian does not include the spin-spin coupling, its equivalent Hamiltonian has an additional term (i.e. the next-order spin-spin coupling) as well as those terms of the Lagrangian. The spin-spin coupling rather than the spin-orbit coupling makes the Hamiltonian typically nonintegrable and probably chaotic when two objects spin. When the leading-order spin-spin coupling is also added to the Lagrangian, it still appears in the Hamiltonian. In this sense, the total Hamiltonian contains the leading-order spin-spin coupling and the next-order spin-spin coupling, which have different signs. Therefore, the chaos resulting from the spin-spin interaction in the Legrangian formulations is somewhat weakened by the spin-orbit coupling.