Measurement of cross-correlation of fluctuations of dipolar couplings and anisotropic chemical shifts by selective spin locking

New exptl. methods are presented that allow one to measure cross-correlation between the fluctuations of dipolar interactions and chem. shift anisotropy (CSA) in scalar coupled systems with two and three spins I = 1/2 in isotropic soln. The methods involve selective excitation of the transverse magnetization IAx of a chosen spin A, followed by selective spin locking of this magnetization. If the spin locking radiofrequency (RF) field is exactly on-resonance for spin A while leaving the other spins M and X unaffected, there is no cross-relaxation (Overhauser effect) in the rotating frame, i.e., no transfer from IAx to IxM or IXx. By contrast, cross-correlation between different relaxation mechanisms may give rise to single-quantum coherence of higher rank. In particular, CSA-dipolar cross-correlation may lead to a partial conversion of IAx into 2IAxIMz or 2IAxIXz, while interference between two dipole-dipole interactions leads to the appearance of terms such as 3IAxIMzIXz. [on SciFinder (R)]

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Geoffrey Bodenhausen, Robert Konrat
1992
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https://infoscience.epfl.ch/record/80299?ln=en

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Related concepts (12)

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Related publications

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Measurement of cross relaxation between two selected nuclei by synchronous nutation of magnetization in nuclear magnetic resonance

Geoffrey Bodenhausen, Robert Konrat

A novel technique is described that allows one to measure cross-relaxation rates (Overhauser effects) between 2 selected nuclei in high-resoln. NMR. The 2 chosen sites are irradiated simultaneously with the sidebands of an amplitude-modulated radiofrequency field, so that their magnetization vectors are forced to undergo a simultaneous motion, which is referred to as synchronous nutation. From the time-dependence obsd. for different initial conditions, one may derive cross-relaxation rates, and hence det. internuclear distances. The scalar interactions between the selected spins and other spins belonging to the same coupling network are effectively decoupled. Also, cross relaxation to other spins in the environment does not affect the transient response of the selected spins, which are therefore in effect isolated from their environment in terms of dipolar interactions. The method is particularly suitable to study cases where normal Overhauser effects are perturbed by spin-diffusion effects due to the presence of further spins. The technique is applied to the protein bovine pancreatic trypsin inhibitor. [on SciFinder (R)]

1993

Coherence transfer in nuclear magnetic resonance by selective homonuclear Hartmann-Hahn correlation spectroscopy

Geoffrey Bodenhausen, Robert Konrat

New NMR techniques are described for transferring transverse magnetization between scalar-coupled nuclei in the rotating frame. The methods involve simultaneous spin-locking of two selected spins A and X, using cosinusoidal modulation of the radio frequency (rf) carrier. If transverse magnetization of spin A is excited selectively before spin-locking, for example with a self-refocusing 270 Deg Gaussian pulse, in-phase magnetization will be transferred from spin A to spin X, and in-phase multiplets are obtained in both one- and two-dimensional spectra. The method allows one to verify whether two particular spins are connected by a scalar coupling. Examples are shown for peptides and basic pancreatic trypsin inhibitor (BPTI). The fine structure of the multiplets yields information on couplings to further spins. In contrast to nonselective spin-lock expts., the magnetization cannot diffuse to a manifold of coupling partners. If relayed coherence transfer is to be achieved deliberately, several spins may be locked simultaneously by imposing an addnl. modulation on the rf carrier. [on SciFinder (R)]

1991

In crowded NMR spectra, it is shown how longitudinal relaxation rates (lab.-frame rates 1/T1) can be measured by selective inversion-recovery of a chosen site A followed by selective transfer of magnetization to another site X through a scalar coupling JAX, prior to observation of the signal. Relaxation rates in the presence of spin-locking (rotating frame rates 1/T1r) can be measured by first transferring transverse magnetization selectively from site X to A, followed by selective spin-locking of the magnetization of A, which can then be obsd. after partial decay. In both cases, the transfer can be achieved by a doubly-selective homonuclear Hartmann-Hahn method that uses simultaneous spin-locking of the transverse magnetization components of sites A and X by sidebands of an audio-modulated radio-frequency field. Provided the A-X cross-peak multiplet in a two-dimensional correlation ("COSY") spectrum does not suffer from overlap, there is no ambiguity in the one-dimensional spectra resulting from the novel methods. The techniques make it possible to measure accurate self-relaxation rates r or rt (diagonal elements of the Solomon matrixes), which are important for a quant. anal. of Overhauser effects in either lab. or rotating frames. The methods are applied to the protein bovine pancreatic trypsin inhibitor (BPTI) and to the cyclic undecapeptide cyclosporin A (CsA). [on SciFinder (R)]

1992