共查询到20条相似文献,搜索用时 31 毫秒
1.
Katalin E. Kvr Victor J. Hruby Du
an Uhrín 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1997,129(2):125-129
A pulsed field gradient version of the sensitivity-enhanced 2D HSQC–TOCSY experiment is proposed for measurement of long-range heteronuclear coupling constants. The coupling constants are obtained by computer-aided analysis of mixed-phase multiplets with and without the heteronuclear splitting. Generation of pure phase data is not required. Since large1JXHandJHHcouplings are used for coherence transfer, smallnJXHcan be measured accurately, which could be difficult to obtain from purely heteronuclear polarization transfer experiments. 相似文献
2.
The spatial localization of the heteronuclear coherence transfer from scalar order was analyzed for a rectangular and an adiabatic remagnetization contact pulses. The transferred coherence amplitudes with and without localization were evaluated for different experimental conditions and an AX-1/2 spin-pair system. The use of this method for13C localized spectroscopy is discussed. 相似文献
3.
《Journal of magnetic resonance. Series B》1993,101(3):240-247
Hydrogen-detected NOE-relayed heteronuclear correlation via single-quantum coherence spectra (SQC-NOESY) may be affected by second-order anomalies when |(ωI ± πJIS) − ωI′| ≤ 20πJII′, where I and I′ are protons and S the heterospin coupled only to I. When the above condition applies, coherences of type SαIβ (α, β = x, y, z) undergo oscillatory transfer to SαI′β coherences without the need for any pulse perturbation. Thus the INEPT transfers, as well as the t1 precession step of the SQC-NOESY scheme, will no longer be effective in sorting out only antiphase or transverse coherences of the proton spin directly coupled to the heteronucleus S. In practice the process leads to measurable amplitude contributions to both auto- and cross-peak volumes, despite the fact that the effects developed during the INEPT steps are often negligible and the theoretical net transfer expected from the t1 evolution is null. Since during tm and t2 (provided heteronuclear decoupling is applied) no effect is expected from the direct-heteronuclear-coupling operator, any strong-coupling contribution arising in these conditions can be computed using the specific parameters of the system under investigation. Thus auto- and cross-peak volumes can be corrected before internuclear distances are evaluated, In natural-abundance or slightly enriched 1H-13C biopolymer systems, assuming JII′/JIS = 0.06 and t1 = 10-20 ms, a correction amounting to 0-7% of the auto- and cross-peak volume sum should be applied to the connectivities of the strongly coupled pair, depending on ΔωI. 相似文献
4.
The spatial localization of the heteronuclear scalar order produced for an AX N spin-1/2 system by adiabatic demagnetization in the rotating frame is discussed. The density operator formalism is used for an exact evaluation of the produced scalar order in the presence of the main field gradient. A pulse sequence to record the scalar order profile is presented. 相似文献
5.
Dušan Uhr?&#x;n Gyula Batta Victor J. Hruby Paul N. Barlow Katalin E. Kövér 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1998,130(2):155-161
An enhanced version of the X(ω1) half-filtered TOCSY experiment for measurement of long-range heteronuclear coupling constants is proposed which yields high-quality spectra with substantially increased sensitivity and resolution. The modified method features gradient-enhanced X filtering sequences, broadband homonuclear decoupling duringt1, optional1JXHscaling in theF1domain, and gradient coherence selection in combination with the sensitivity-enhanced protocol for the TOCSY transfer. These modifications extend the applicability of the method—coupling constants can be measured accurately for natural abundance samples at low concentrations and for compounds yielding complex spectra. Computer-aided analysis of E.COSY-type multiplets is applied for the determination of heteronuclear long-range coupling constants. 相似文献
6.
Coherence transfer between heteronuclear spin species in the rotating frame is analysed in view of application to heteronuclear two-dimensional cross-correlation spectroscopy in liquids. The general formalism and applications to simple spin systems are presented. In particular, the longitudinal and transverse coherence transfer functions are evaluated and discussed in terms of transfer efficiency, oscillation frequencies, phase anomalies and multiplet effects. 相似文献
7.
Double-quantum heteronuclear coherence transfer in solids shows a strong spatial dependence when performed in the presence of a magnetic field gradient. This is a direct consequence of the off-resonance sensitivity of the coherence transfer process and represents a new principle for localized NMR spectroscopy of quadrupole nuclei in solids. Since the slice-selective excitation is achieved simultaneously to the cross-polarization, the suggested pulse sequences avoid the use of shaped pulses, the application of which is problematic in solids. In the present work, the localization efficiency of this new slice-selection principle was analyzed in dependence on the experimental parameters for a spin system consisting of abundant spin-1/2 and rare spin-1 nuclei. The resulting slice profiles and the calculated dependences of the slice thickness for the basic coherence transfer procedures are discussed on the example of1H?2H in monodeuterated benzene. The proposed method opens the possibility of volume-selective investigations of the structure and dynamics of materials using the well-established methodology of deuteron-NMR spectroscopy. 相似文献
8.
Du
an Uhrín Gyula Batta Victor J. Hruby Paul N. Barlow Katalin E. Kvr 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1998,130(2)
An enhanced version of the X(ω1) half-filtered TOCSY experiment for measurement of long-range heteronuclear coupling constants is proposed which yields high-quality spectra with substantially increased sensitivity and resolution. The modified method features gradient-enhanced X filtering sequences, broadband homonuclear decoupling duringt1, optional1JXHscaling in theF1domain, and gradient coherence selection in combination with the sensitivity-enhanced protocol for the TOCSY transfer. These modifications extend the applicability of the method—coupling constants can be measured accurately for natural abundance samples at low concentrations and for compounds yielding complex spectra. Computer-aided analysis of E.COSY-type multiplets is applied for the determination of heteronuclear long-range coupling constants. 相似文献
9.
The 19F-13C heteronuclear single quantum coherence (HSQC) experiment is vital for the structural elucidation of polyfluorinated organic species, yet its sensitivity and phaseability are limited by difficulties in uniform excitation of the widely disperse 19F spectral window. Adiabatic pulses of different types have previously been employed to generate effective π pulses for inversion and refocussing, but a systematic comparison of various adiabatic and other inversion pulses has not been published. In this work, it was observed that the use of a broadband inversion pulse (BIP) during the t 1 evolution period resulted in properly phaseable spectra for experiments optimized to detect 1 J CF, in contrast to CHIRP or WURST adiabatic pulses. For the INEPT and reverse-INEPT transfer segments of the HSQC, optimal sensitivity for resonances distant from the transmitter frequency was afforded by optimized universal rotation (BURBOP) or CHIRP pulses. In HSQC experiments with delays optimized for two-bond correlations, only the use of BURBOP pulses in INEPT and reverse-INEPT sequences afforded spectra cleanly phaseable across the F 2 and F 1 spectral windows. This observation is supported by off-resonance pulsed field gradient spin-echo experiments. 相似文献
10.
《Journal of Magnetic Resonance, Series A》1993,101(1):41-46
A simple modification of BIRD pulses, which removes the inversion effect on an X nucleus and retains a chemical-shift evolution of the heterospin, is proposed. This modification extends the possibilities for manipulation of heteronuclear spin systems. The concept of group-selective π pulses was shown to be useful in systematic design of pulse sequences in heteronuclear NMR spectroscopy. This approach was illustrated for the proton-carbon chemical-shift-correlated experiment, a new method for measurement of 1J(C, H) from correlated spectra. 相似文献
11.
Photo-initiated charge transfer reactions in solution proceed via a radical pair intermediate which in most cases will separate on a time scale of several nanoseconds. The non-adiabicity of this process is the source of coherences in the spin system. A quantitative discussion of the observability of the resulting quantum beats using Fourier-transform EPR is presented. We also show experimental evidence for the predicted quantum beats using the photo-initiated charge transfer reaction of Zn-Tetraphenylporphyrin and benzoquinone in 2-propanol. The analysis of the beat frequency leads to an estimate of the exchamge couplingJ≈2.6·106 s?1 of the Coulomb-coupled radical pair. 相似文献
12.
《Journal of Magnetic Resonance (1969)》1990,86(1):110-126
Several new techniques, requiring 15N incorporation, are described for measuring NHCαH J couplings in proteins. 1H-detected heteronuclear 1H15N multiple-quantum correlation spectra retain the homonuclear J coupling information. Because of the favorable relaxation properties of 15N1H zero- and double-quantum coherences, significant line narrowing occurs in the F1, dimension compared to the regular NH 1H linewidth, permitting high accuracy measurements of J splittings, even for medium sized proteins. Methods for convenient analysis of such coupling information are described, correcting for linewidth and dispersion mode contributions. The new approach is demonstrated for the protein staphylococcal nuclease (18 kDa), complexed with pdTp and calcium. 相似文献
13.
《Journal of Magnetic Resonance (1969)》1982,46(2):306-318
The resolution in heteronuclear two-dimensional NMR spectroscopy is affected by coherence transfer echoes. By introducing a delay between the transfer of coherence and the signal observation, the resolution in the crucial ω1 dimension can be enhanced. This procedure removes the symmetry of the multiplet structure, and an additional pulse is required to realign the signals in the two-dimensional spectra. The methods are illustrated by applications to the indirect observation of scalar proton-proton couplings through phosphorus-31 in phosphothreonine. 相似文献
14.
S. Westermann T. Amthor A. L. de Oliveira J. Deiglmayr M. Reetz-Lamour M. Weidemüller 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,40(1):37-43
We investigate excitation transfer and migration
processes in a cold gas of rubidium Rydberg atoms.
Density-dependent measurements of the resonant population exchange
for atoms initially excited into the 32P3/2(|mJ|=3/2) state
are compared with a Monte Carlo model for coherent energy
transfer. The model is based on simulations of small atom
subensembles involving up to ten atoms interacting via coherent
pair processes. The role of interatomic mechanical forces due to the
resonant dipole-dipole interaction is investigated.
Good agreement is found between the experimental data and the
predictions of the model, from which we infer that atomic motion
has negligible influence on the energy transfer up to Rydberg
densities of 108 cm-3, that the system has to be described in terms
of many-body dynamics, and that the energy transfer
preserves coherence on microsecond timescales. 相似文献
15.
《Journal of Magnetic Resonance, Series A》1993,101(3):277-284
This work has two objectives. First, heteronuclear editing was considered, with particular aim at proton-detected NMR spectroscopy of rare nuclei. The second aspect refers to localized heteronuclear NMR spectroscopy, implying the editing option. The common basis of both techniques is J cross polarization (or coherent rotating-frame polarization transfer). In the presence of magnetic field gradients this process is slice selective and is introduced as a principle for localized liquid-state NMR, particularly of heteronuclear spins. Heteronuclear editing of NMR lines is performed by the aid of a cyclic cross-polarization pathway. Both methods can be combined to a technique for localized proton-detected NMR spectroscopy of rare nuclei. Test experiments demonstrating the slice selectivity of the transfer process and the efficiency of the cyclic cross-polarization editing procedure are reported. Applications to localized homo- or heteronuclear spectroscopy and imaging are discussed. 相似文献
16.
J.C. Bacelar R. Chapman J.R. Leslie J.C. Lisle J.N. Mo E. Paul A. Simcock J.C. Willmott J.D. Garrett G.B. Hagemann B. Herskind A. Holm P.M. Walker 《Nuclear Physics A》1985,442(3):547-577
High-spin data are presented for 170Ta and 171Ta for the first time, and the known level scheme of 173Ta is extended to higher spins. Anomalies found in the crossing frequencies for the alignment of a pair of neutrons are considered. At high spin a large and constant value of J(2), with J(2) > J(1), is found for two 171Ta bands and the implications of this are discussed. The πi13/2 [660]1/2+, α = + 1/2 orbital is identified as it crosses the rotational band built on the [402]5/2+, α = + 1/2 orbital in 171Ta. Magnetic transition probabilities obtained from measured branching ratios show the effects of the aligning pair of neutrons and the spectator orbital. The data are interpreted using cranked shell-model calculations and a semiclassical vector-coupling scheme developed by Donau and Frauendorf. 相似文献
17.
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19.
《Journal of Magnetic Resonance (1969)》1987,71(2):283-293
A method for obtaining complete two-dimensional 1H NMR amide proton-Cα proton J-connectivity maps for proteins (the “fingerprint”) is describe. The method relies on the conversion of antiphase single-quantum coherence into longitudinal two-spin order which is made observable by utilizing a selective solvent-suppression readout pulse. Since irradiation of the solvent resonance is unnecessary in this experiment, J connectivities are observable even for protons resonating exactly at the solvent frequency. Thus, a complete protein fingerprint is obtained at a single set of experimental conditions. The method is demonstrated for a 75-amino-acid protein. 相似文献
20.
Chandrakumar N Kimmich R 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1999,137(1):100-107
In this work, we present a family of pulse sequences for selective heteronuclear J cross-polarization (JCP), which we have developed especially for indirect 13C imaging using JCP, for example in the CYCLCROP environment. The sequences are straightforward to implement and operate reliably. Results of an average Hamiltonian analysis are given for the basic sequence, which we term PRAWN (pulsed rotating frame transfer sequence with windows). It is shown experimentally that the pulse sequence, which operates efficiently with low RF duty cycles down to a few percent, has a useful tolerance range to absolute Hartmann-Hahn mismatch and generates coherence transfer spectra in close correspondence with the JCP average Hamiltonian. Computer simulation of the performance of the basic sequence on a heteronuclear spin-(1/2) AX system is also presented. The mismatch compensation of PRAWN may be markedly enhanced further by issuing a pi pulse to each spin halfway through the basic PRAWN train and in phase quadrature to it. A simple analysis of this modified sequence, PRAWN-pi, is given under conditions of mismatch and off-resonance irradiation. 相似文献