Theoretical treatment of volume-selective NMR spectroscop (VOSY) applied to coupled spin systems (original) (raw)
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Slice excitation and localized NMR spectroscopy on the basis of spin locking
Journal of Magnetic Resonance (1969), 1989
A new method for the precise selection of thin slices without the need of strong field gradients is presented. The principle is to spin lock the transverse magnetization of the desired slice while homospoiling coherences from the remaining space. The minimum width of the pulse is about 5 ms in total. Beyond this restriction, the pulse length is uncritical and does not affect the thickness of the excited slice. The applicability of this spin-lock-induced slice excitation (SLISE) pulse has been demonstrated in test experiments. The method may be of particular interest for NMR microscopy. The same principle can be used in modified form also as a technique for localized NMR spectroscopy (LOSY). The size of the selected volume can most easily be varied by changing the amplitude of the spin-lock pulse while the field gradients may remain constant. No sophisticated pulse shapes are necessary. Even with comparatively low gradients, a good spatial resolution is achieved by the corresponding reduction of the RF amplitude. Test experiments showed that the irradiated RF energy per cycle is not higher than with other localization techniques.
Volume localized spin echo correlation spectroscopy with suppression of 'diagonal' peaks
Volume localized spectroscopy MRS Volume localized correlation spectroscopy LSECSY Suppression of diagonal or pseudo diagonal peaks LDISSECT a b s t r a c t Two dimensional homonuclear 1 H correlation spectroscopy is of considerable interest for volume localized spectral studies, both in vivo and in vitro, of biological as well as material objects. The information principally sought from correlation spectra resides in the cross-peaks, which are often masked however by the presence of diagonal peaks in COSY, or 'pseudo-diagonal' peaks at F 1 = 0 in SECSY. It has therefore been a concern to suppress these diagonal or 'pseudo-diagonal' peaks, in order to ensure that cross-peak information is fully discernible. We present here a report of our work on volume localized DIagonal Suppressed Spin Echo Correlation specTroscopy (LDISSECT) and demonstrate its performance in comparison to the standard volume localized SECSY experiment, employing brain metabolite phantoms in a gel. The sequence works in the inhomogeneous, multi-component environment by exploiting the short acquisition time to suppress undesired information by employing an additional rf pulse. A brief description of the pulse sequence, its theory, and simulations are also included, besides experimental benchmarking on two brain metabolite phantoms in gel phase.
Journal of Magnetic Resonance, 2022
We demonstrate a new resonance condition that obeys the relation ∆ = /2, where ∆ is the chemical shift difference between two homonuclear-coupled spins, is the magic-angle spinning speed and is an integer. This modulation on the rotational resonance recoupling condition is obtained by the application of rotor-synchronous 1 H pulses when at least one proton is dipolar-coupled to one of the homonuclear-coupled spins. We suggest a new experimental scheme entitled 'pulse induced resonance with angular dependent total enhancement' (PIRATE) that can enhance proton-driven spin diffusion by the application of a single 1 H pulse every rotor period. Experimental evidence is demonstrated on the two carbon spins of glycine and on the Y21M mutant of fd bacteriophage virus. Numerical simulations reveal the existence of the resonances and report on the important interactions governing this phenomena.
Chemical Physics Letters, 2008
Internuclear couplings between selected homonuclear spin pairs in a multiplylabelled spin system are determined by NMR spin echo experiments in the solid state. The spin echoes are induced by an amplitude-modulated shaped pulse. The time shift in the echo modulation curve is treated by average Hamiltonian theory and verified by numerical simulation. The J-couplings may be estimated by experiments on samples spinning at the magic angle, while the direct dipoledipole couplings may be estimated by off-magic-angle spinning. The concept is tested on a uniformly 13 C-enriched sample of L-histidine hydrochloride monohydrate.
Principles of Spin-Echo Modulation byJ-Couplings in Magic-Angle-Spinning Solid-State NMR
ChemPhysChem, 2004
In magic-angle-spinning solid-state NMR, the homonuclear J-couplings between pairs of spin-1/2 nuclei may be determined by studying the modulation of the spin echo induced by a π-pulse, as a function of the echo duration. We present the theory of J-induced spin-echo modulation in magic-angle-spinning solids, and derive a set of modulation regimes which apply under different experimental conditions. In most cases, the dominant spin-echo modulation frequency is exactly equal to the J-coupling and is stabilized by the chemical shift anisotropies and dipole-dipole couplings. The theoretical conclusions are supported by numerical simulations and experimental results obtained for three representative samples containing 13 C spin pairs.
Journal of Magnetic Resonance, 2007
The robustness of the refocused INADEQUATE MAS NMR pulse sequence for probing through-bond connectivities has been demonstrated in a large range of solid-state applications. This pulse sequence nevertheless suffers from artifacts when applied to multispin systems, e.g. uniformly labeled 13 C solids, which distort the lineshapes and can potentially result in misleading correlation peaks. In this paper, we present a detailed account that combines product-operator analysis, numerical simulations and experiments of the behavior of a three-spin system during the refocused INADEQUATE pulse sequence. The origin of undesired anti-phase contributions to the spectral lineshapes are described, and we show that they do not interfere with the observation of long-range correlations (e.g. two-bond 13 C-13 C correlations). The suppression of undesired contributions to the refocused INADEQUATE spectra is shown to require the removal of zero-quantum coherences within a z-filter. A method is proposed to eliminate zero-quantum coherences through dephasing by heteronuclear dipolar couplings, which leads to pure in-phase spectra. 4 Abbreviations: TOBSY, total through-bond spectroscopy; INADE-QUATE, incredible natural abundance double quantum transfer experiment; CR, composite refocusing; UC2QF COSY, uniform-sign cross-peak double quantum filtered correlation spectroscopy; TQ, triplequantum; DD, dipole-dipole; CSA, chemical shift anisotropy, DQ, double quantum; ZQ, zero-quantum; CP, cross polarization; PDSD, protondriven spin diffusion.
Simultaneous Multi-Slice Excitation in Spatially Encoded NMR Experiments
Chemistry - A European Journal, 2013
Recently, there has been a growing interest in spatially localized NMR spectroscopic techniques based on the incorporation of the traditional slice selection concept implemented in magnetic resonance imaging (MRI) applications. Several high-resolution NMR methods applying spatial frequency encoded excitation along an NMR tube have been suggested as means of obtaining specific information from a particular slice. For instance, selective spin-lattice T 1 relaxation times [1] and all proton-proton coupling constants for a selected proton resonance from a slice-selective J-resolved (G-SERF) experiment have been measured, [2] broadband homodecoupled 1 H spectra with the Zangger-Sterk (ZS) method have been obtained, [3-5] slice-selective diffusion experiments have been carried out [6] and diagonal-suppressed 2D experiments are also possible. [7] Sequential multi-slice selection has been exploited for cases in which nuclear spins in different parts of the NMR tube are exclusively excited during subsequent transients by changing the offset frequency while the previously used spins have time to relax towards equilibrium before being excited again, resulting in significantly shorter overall acquisition times. Examples have been utilized to accelerate data acquisition in multidimensional NMR experiments, [8] to improve the signal-tonoise ratio (SNR) per time unit in the ZS method [9] or to study the kinetics of a reaction on the ms time scale. [10] The use of multiple-frequency pulses [11] has been recently suggested as a method of effective broadband 13 C homodecoupling in slice-selected HSQC experiments for highly-enriched 13 C samples. [12] Experimentally, spatial frequency encoding is achieved easily by simultaneous application of a frequency-selective 908 or 1808 1 H pulse and a spatial-encoding gradient, G s. The range of sampled frequencies (SW G) is defined by the strength of G s according to SW G = g L G S, in which g is the gyromagnetic ratio of the spatially encoded nucleus and L is the active volume coil length. On the other hand, the carrier frequency (W) and the selective pulse bandwidth (Dw) determine the z-position of each nuclear spin
Superior pulse schemes for spin-echo and other two-dimensional homonuclear correlated spectroscopies
Journal of Magnetic Resonance (1969), 1985
pulse schemes are sugg&cd which remove the antiphase intensity character from the muhiplets of cross peaks and introduce antiphase intensity chamcter into the multipkts of diagonal peaks in spinecho correlated 2D spectroscopy (SECSY) and in relay coherence transfer 2D spectroscopy (RCOSY). These are suggested with the aim of enhancing the intensity of cross peaks in situations of limited digital resolution. Q 1985 Academic FWs, Inc. Two-dimensional NMR spectroscopy has had a revolutionary effect on the practice of NMR in biological systems. Essentially total resonance assignments have become possible (1-6) with the help of correlated two-dimensional spectroscopy (COSY) (7), spin-echo correlated spectroscopy (SEC!!%) (a), nuclear Overhauser effect spectroscopy (NOESY) (9), relayed coherence transfer spectroscopy (RCOSY) (IO-Z2), and multiplequantum transition (MQT) spectroscopies (13-17). COSY and SECSY, which yield information on resonances which are spin coupled, have proved to be extremely useful and have become widely used experiments for resonance assignments in many systems. In biomolecules, however, t&se experiments require samples having reasonably good concentration of biomolecules and several hours of data accumulation. We have recently pointed out that the COSY experiment can be very much improved by addition of fixed time delays in the evolution and detection periods (18). These delays remove antiphase character from the multiplets of the cross peaks and introduce antiphase character into the multiplets of the diagonal peaks, achieving many improvements in the COSY spectrum. The scheme, named SUPER COSY, drastically enhances the sensitivity of detection of the cross peaks under conditions of limited digital resolution, reduces the dynamic range of diagonal to cross peaks, and allows J tuning of the COSY spectra for detection of particular couplings (I 9). In this paper we describe similar improvements in the other schemes used for homonuclear 2D correlation, namely SECSY and RCOSY. SECSY EXPERIMENTS The experimental schemes for SECSY and two versions of SUPER SECSY are given in Fig. 1. Standard phase-cycling procedure needed for cancellation of P peaks
Magnetic Resonance in Chemistry, 2005
New NMR pulse schemes completely driven under homonuclear and heteronuclear cross-polarization conditions are proposed for the study and the measurement of coupling constants in symmetrical molecules in solution. The appropriate superimposition of independent magnetization components can afford several spin-selective multiplet patterns that are suitable for the determination of the magnitude and the sign of proton-proton and proton-carbon coupling constants with optimum sensitivity levels. A detailed product operator formalism analysis for the proposed doubly selective 1D and nonselective 2D HCP-TOCSY versions is provided and experimental verification for the configurational analysis of symmetric olefinic systems having chemical equivalence is demonstrated.