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Two-dimensional J-spectra with absorption-mode lineshapes 总被引:1,自引:1,他引:0
Two-dimensional J-spectroscopy offers the possibility of a complete separation of chemical shifts and J-couplings. However, the usefulness of the experiment is considerably reduced by the fact that peaks in the spectra have the phase-twist lineshape. We present a simple new spectroscopic method for recording J-spectra in which the peaks are both in the absorption mode and retain their natural intensities, albeit at the cost of a considerable reduction in the signal-to-noise ratio. No special data-processing is required. The method is tested on quinine, and the steroid dehydroisoandrosterone. 相似文献
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Recep Eryi?it 《International Journal of Theoretical Physics》2009,48(3):885-893
We have analyzed the behavior of multipartite global entanglement and average bipartite concurrence for the sign of quantum
phase transitions in the frustrated J
1−J
2 model by using exact diagonalization technique for a chain of 12 qubits. It is found that although the magnitude of two classes
of the measures show opposite trends the absolute value of their derivatives show similar structure near critical points. 相似文献
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Computer simulation of a many-particle quantum system is bound to reach the inevitable limits of its ability as the system size increases. The primary reason for this is that the memory size used in a classical simulator grows polynomially whereas the Hilbert space of the quantum system does so exponentially. Replacing the classical simulator by a quantum simulator would be an effective method of surmounting this obstacle. The prevailing techniques for simulating quantum systems on a quantum computer have been developed for purposes of computing numerical algorithms designed to obtain approximate physical quantities of interest. The method suggested here requires no numerical algorithms; it is a direct isomorphic translation between a quantum simulator and the quantum system to be simulated. In the quantum simulator, physical parameters of the system, which are the fixed parameters of the simulated quantum system, are under the control of the experimenter. A method of simulating a model for high-temperature superconducting oxides, the t–J model, by optical control, as an example of such a quantum simulation, is presented. 相似文献
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Koźmiński W 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1999,137(2):408-412
A new two-dimensional pulse sequence for accurately determining heteronuclear coupling constants is presented. It is derived from HSQC and HECADE techniques with B0 gradient coherence selection. The main feature of the proposed method is spectra with only one component of the IS doublet; i.e., the final result is equivalent to a selective broadband excitation of either Salpha or Sbeta spin states and a preservation of these states during the entire experiment. The effect is obtained by an appropriate combination of in- and antiphase coherences. It is demonstrated that heteronuclear single-bond as well as long-range coupling constants and their relative signs are readily evaluated. The proposed sequence is equally or less sensitive to a variation of heteronuclear one-bond couplings than previously published, closely related sequences. The new method is applied to a peptide sample for determination of 3JN, Hbeta. 相似文献
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A. Foussats C. Repetto O. P. Zandron O. S. Zandron 《International Journal of Theoretical Physics》2002,41(6):1053-1082
In order to describe the dynamics of the t–J model, two different families of first-order Lagrangians in terms of the generators of the Hubbard algebra are found. Such families correspond to different dynamical second-class constrained systems. The quantization is carried out by using the path-integral formalism. In this context the introduction of proper ghost fields is needed to render the model renormalizable. In each case the standard Feynman diagrammatics is obtained and the renormalized physical quantities are computed and analyzed. In the first case a nonperturbative large-N expansion is considered with the purpose of studying the generalized Hubbard model describing N-fold-degenerate correlated bands. In this case the 1/N correction to the renormalized boson propagator is computed. In the second case the perturbative Lagrangian formalism is developed and it is shown how propagators and vertices can be renormalized to each order. In particular, the renormalized ferromagnetic magnon propagator coming from our formalism is studied in details. As an example the thermal softening of the magnon frequency is computed. The antiferromagnetic case is also analyzed, and the results are confronted with previous one obtained by means of the spin-polaron theories. 相似文献
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A simplified phase-cycling scheme for heteronuclear active-coupling-pattern tilting (ACT) spectroscopy is presented. It is demonstrated that the theoretically expected twofold sensitivity gain over earlier implementations can be experimentally realized. A further intensity increase by a factor of 2 is obtained with standard sensitivity-enhancement pulse-sequence elements. The HSQC-HECADE sequence presented is designed for an accurate determination of heteronuclear one-bond and, with subsequent I-spin isotropic mixing, long-range coupling constants. As an exemplary application, the determination of the (3)J(N,Hbeta) coupling constants in a peptide at natural isotope abundance is demonstrated. Additionally, a new polarization-transfer step for the long-range HSQC-HECADE experiment is proposed which avoids a fixed delay tuned to a specific coupling-constant value. Thus, the long-range correlation experiment does not require prior knowledge of the coupling constants to be measured and yields more uniform cross-peak intensity for a broad range of active coupling constants. 相似文献
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Yang J McAteer K Silks LA Wu R Isern NG Unkefer CJ Kennedy MA 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2000,146(2):260-276
Stereo-selectivedeuteration has been explored as an approach for improving the accuracy of NMR-derived, three-bond vicinal proton-proton coupling constants in the 12-base-pair DNA Dickerson sequence [d(CGCGAATTCGCG)(2)]. The coupling constants are useful for DNA structure determination in restrained molecular dynamics calculations. Specifically, the A5 and A6 residues were prepared with the H2" proton stereo-selectively replaced with a deuteron. Deuteration of the H2" leads to a 42-fold reduction in the transverse cross-relaxation rate of the H2' spin, effectively negating the contribution of transverse cross relaxation to the cross peak frequencies and phases. Calculated linewidth and polarization transfer functions indicated that the reduced dipolar interaction is also expected to result in a significant increase in intensity for all cross peaks involving the H1', H2', or H3' spin. The spectral complexity is also reduced by selective deuteration. Time-shared homonuclear decoupling of passive spins during acquisition was implemented, reducing the spin system, in some cases, to an effectively isolated two-spin system. This enables the use of a 90 degrees mixing pulse instead of the 35 degrees pulse commonly used in standard P.E.COSY experiments, leading to an additional 75% increase in signal intensity. Selective excitation pulses were used to reduce the number of increments required in the indirect dimension by as much as a factor of 4. The cumulative improvement in sensitivity is striking, approaching three orders of magnitude per unit time. Separate experiments, referred to as Stripe-COSY and Superstripe-COSY, were optimized for each coupling constant measured. Finally, J-doubling was used to obtain the most accurate peak separations. This comprehensive approach shows promise as an effective method for extracting highly accurate homonuclear vicinal coupling constants in DNA. 相似文献
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The technique of multiple-quantum J-resolved NMR spectroscopy (MQ-JRES) is introduced and applied to the spin system SI3–M (such as in the example given here, the 13CH3–12CH in alanine). The SI3 spin system was excited to its highest quantum state (8SyIxIyIy), which consists of four coherences: quadruple quantum of (3I + S), double quantum of (3I − S), double quantum of (I + S), and zero quantum of (I − S). In the MQ spectrum generated from the projection onto the F1 dimension, the resonances of the different multiple-quantum coherences are resolved by their coupling constants to the remote spin (M). The absorptive lineshapes in both F1 and F2 dimensions enable accurate measurements of transverse relaxation rates, and both amplitude and relative signs of the long-range coupling constants are to be derived from either frequency or time domain data. The selective detection of MQ-JRES spectra of the individual MQ coherences using either phase cycling or pulsed field gradients is presented. 相似文献
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Nuzillard JM 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2007,187(2):193-198
The SERF experiment is a variant of the homonuclear J-resolved experiment, in which a single coupling constant is measured. It consists of a single chemical shift selective excitation that is followed by a biselective spin echo. Recent articles mention the existence of artefacts in SERF spectra that are supposedly related to pulse imperfections. This article presents a detailed study of the biselective refocusing pulses. It also reports a method for predicting the position and amplitude of the expected and unexpected 2D spectral peaks in SERF spectra. Artefacts can be partially eliminated by phase cycling or by the introduction of static field gradient pulses in the acquisition sequence. A procedure to obtain of pure absorption peaks in SERF spectra is proposed. 相似文献
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Schmedt auf der Günne J 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2006,180(2):186-196
It is shown how homonuclear distances and homonuclear dipolar lattice sums between spin-1/2 nuclei can be measured by a pulsed solid-state NMR experiment under magic-angle spinning conditions. The presented technique is based on double-quantum coherence filtering. Instead of measuring a build-up of double-quantum coherence the pulse sequence is designed to dephase double-quantum coherence. This is achieved by exciting double-quantum coherence either with the help of the through-space dipolar coupling or the through-bond dipolar coupling while the dephasing relies on the through-space dipolar coupling as selected by a gamma-encoded pulse sequence from the C/R symmetry class. Since dephasing curves can be normalized on zero dephasing, it is possible to analyze the initial dephasing regime and hence determine dipolar lattice sums (effective dipolar couplings) in multiple-spin systems. A formula for the effective dipolar coupling is derived theoretically and validated by numerical calculations and experiments on crystalline model compounds for (13)C and (31)P spin systems. The double-quantum dephasing experiment can be combined with constant-time data sampling to compensate for relaxation effects, consequently only two experimental data points are necessary for a single distance measurement. The phase cycling overhead for the constant-time experiment is minimal because a short cogwheel phase cycle exists. A 2D implementation is demonstrated on [(13)C(3)]alanine. 相似文献
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Katalin E. Kvr Gyula Batta 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2004,170(2):341
Since the introduction of RDCs in high-resolution NMR studies of macromolecules, there is a growing interest in the development of accurate, and sensitive methods for determining coupling constants. Most methods for extracting these couplings are based on the measurement of the splitting between multiplet components in J-coupled spectra. However, these methods are often unreliable since undesired multiple-bond couplings can considerably broaden the multiplet components and consequently make accurate determination of their position difficult. To demonstrate one approach to this problem, G-BIRD(r) decoupled TROSY sequences are proposed for the measurement of 1JNH and 1JNC′ coupling constants. Resolved or unresolved splittings due to remote protons are removed by a G-BIRD(r) module employed during t1 and as a result, spectra with narrow, well-resolved peaks are obtained from which heteronuclear one-bond couplings can be accurately measured. Moreover, introduction of a spin-state-selective α/β-filter in the TROSY sequence allows the separation of the 1JNC′ doublet components into two subspectra which contain the same number of peaks as the regular TROSY spectrum. The 1JNC′ couplings are obtained from the displacement between the corresponding peaks in the subspectra. 相似文献
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Andrew P. Davison Jonathan A. Jones Ruth M. Dixon 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1999,137(2):448
NMR detection of multiply labeled compounds in biological samples is often used to follow metabolic pathways. Detection of protons bound to13C atoms offers a more sensitive approach than direct13C detection, but generally results in the loss of carbon–carbon coupling information. We have modified an HSQC sequence to refocus the carbon chemical shifts in order to obtain a proton-correlated13C homonuclearJspectrum, which allows us to measure singly and doubly labeled compounds in the same spectrum. 相似文献
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Yizhou Liu James H. Prestegard 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2009,200(1):109-118
Residual dipolar couplings (RDCs) between NC′ and NCα atoms in polypeptide backbones of proteins contain information on the orientation of bond vectors that is complementary to that contained in NH RDCs. The 1JNCα and 2JNCα scalar couplings between these atoms also display a Karplus relation with the backbone torsion angles and report on secondary structure. However, these N–C couplings tend to be small and they are frequently unresolvable in frequency domain spectra having the broad lines characteristic of large proteins. Here a TROSY-based J-modulated approach for the measurement of small 15N–13C couplings in large proteins is described. The cross-correlation interference effects inherent in TROSY methods improve resolution and signal to noise ratios for large proteins, and the use of J-modulation to encode couplings eliminates the need to remove frequency distortions from overlapping peaks during data analysis. The utility of the method is demonstrated by measurement of 1JNC′, 1JNCα, and 2JNCα scalar couplings and 1DNC′ and 1DNCα residual dipolar couplings for the myristoylated yeast ARF1·GTPγs protein bound to small lipid bicelles, a system with an effective molecule weight of 70 kDa. 相似文献
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The dynamics of hydration-water in several phospholipid membranes of different compositions is studied by 2D (1)H-(31)P heteronuclear correlation NMR under magic-angle spinning. By using a (1)H T(2) filter before and a (1)H mixing-time after the evolution period and (31)P detection, inter-bilayer water is selectively detected without resonance overlap from bulk water outside the multilamellar vesicles. Moreover the (1)H T(2) relaxation time of the inter-bilayer water is measured. Lipid membranes with labile protons either in the lipid headgroup or in sterols exhibit water-(31)P correlation peaks while membranes free of exchangeable protons do not, indicating that the mechanism for water-lipid correlation is chemical exchange followed by relayed magnetization transfer to (31)P. In the absence of membrane proteins, the inter-bilayer water (1)H T(2)'s are several tens of milliseconds. Incorporation of charged membrane peptides shortened this inter-bilayer water T(2) significantly. This T(2) reduction is attributed to the peptides' exchangeable protons, molecular motion and intermolecular hydrogen bonding, which affect the water dynamics and the chemically relayed magnetization transfer process. 相似文献
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T. Watanabe H. Yokoyama M. Ogata 《Physica C: Superconductivity and its Applications》2009,469(15-20):1009-1012
To consider the origin of a pseudogap and a superconducting (SC) gap found in the high-Tc cuprates, we evaluated the momentum dependence of the singlet gap corresponding to the pseudogap and the SC gap in the t–J model, using an optimization variational Monte Carlo (VMC) method. In the underdoped regime, the singlet gap is significantly modified from the simple dx2-y2(d)-wave gap (∝ cos kx − cos ky) by the contribution of long-range pairings. Its angular dependence at the quasi Fermi surface is qualitatively consistent with those experimentally observed in both hole and electron-doped cuprates. On the other hand, a SC gap is almost unchanged, preserving the original simple d-wave form. Thus, it seems that the incoherent part of the singlet gap mainly influences the forms of observed gaps. 相似文献
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A. V. Sorokin 《Journal of Applied Spectroscopy》2009,76(2):234-239
The effect of various additives (NaCl, DNA, and CPB surfactant) on the structure and optical properties of luminescent molecular
nanoclusters, J-aggregates of L-21 polymethine dye, has been investigated using stationary and time-resolved optical spectroscopy. It has
been shown that all investigated additives enhance the dye aggregation and change its aggregate structure as manifested in
a change of tilt angle between molecules in the molecular chain. Salt causes the biggest change of tilt angle whereas surfactant
causes the smallest. It has been found that a decrease of tilt angle leads to an increase of J-aggregate luminescence intensity. The addition of CPB surfactant is shown to modify the exciton dynamics in J-aggregates whereas the other additives affect only their structure.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 2, pp. 250–255, March–April, 2009. 相似文献