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This article begins with general considerations about enrichment of hydrogen gas into its para isomer (corresponding to nuclear spins in the singlet state); this is a necessary condition to obtain hyperpolarization from transfer of the relevant population excess. This transfer is generally mediated by a hydrogenation reaction such that the two protons become nonequivalent. The energy level populations of this new spin system can be calculated unambiguously using a density matrix formalism. This formalism is reviewed, and the authors propose a simple method that leads to the spin state after the hydrogenation reaction and the insertion of the sample in the NMR magnet. The effect of radio‐frequency pulses is also considered. © 2006 Wiley Periodicals, Inc. Concepts Magn Reson Part A 28A: 321–330, 2006

In part I of this article, it was shown that protein 15N relaxation data at different magnetic fields can be fitted according to a residue‐specific correlation time τeff, which is associated with slow motions sensed by the considered residue. The present article is an attempt to justify the correlation time variations along the backbone by anisotropic overall motion. When an axial rotation‐diffusion tensor is assumed, it is possible to derive simple expressions for relating τeff to τ⊥ and τ// (the two correlation times defining the rotation‐diffusion tensor). A consistent picture is obtained for the most organized parts of the protein C12A‐p8MTCP1 which, as in part I of this article, serves here as an example. By contrast, the model of rotation‐diffusion fails for other less‐organized parts of the protein, suggesting a combination of several slow or intermediate motions. © 2005 Wiley Periodicals, Inc. Concepts Magn Reson Part A 24A: 10–16, 2005.

Comprehensive calculations are performed with the aim of arriving at a ready-to-use form for cross-correlation spectral density functions. Axial symmetry is assumed for tensors associated with the two interactions involved in the cross-correlation spectral density. Moreover, the derived formulas stem from the hypotheses of the “model-free” approach, i.e., a (generally fast) local motion superposed to a (generally slow) molecular tumbling. The restriction of fast local motions imposes the definition of two different order parameters S and S' associated with the principal direction of the two considered interactions and it is the product of these order parameters, which is present in the general expression of a spectral density function. The latter includes two terms. The first one corresponds to fast local motions and involves the factor 1/2(3 cos²α − 1), where α is the angle made by the symmetry axes of the two considered tensors. The second term concerns only molecular tumbling sensed by a (virtual) director. Finally, it is shown that, consistently with the model-free approach, the product SS' can be expressed as 1/2(3 cos²α − 1)S² so that 1/2(3 cos²α − 1) factorizes the spectral density function. © 2003 Wiley Periodicals, Inc. Concepts Magn Reson Part A 19A: 65–70, 2003.

The usual method for probing translational motions is the pulsed gradient spin-echo (PGSE) experiment introduced by Stejskal and Tanner. It employs gradients of the static magnetic field. Most of the drawbacks from which this basic experiment suffers have been successfully circumvented by several modifications and compensations. Thus, it is now possible to obtain very clean experimental results amenable to optimal data processing so that they can be presented as 2D (or 3D) diffusion ordered spectra (DOSY). In first part of this paper, it is shown that radiofrequency field gradients (RFG) are immune to the drawbacks inherent to the basic PGSE sequence, and can give clean, high-resolution diffusion data in a straightforward manner. In the second part, an alternative data processing method for reconstructing DOSY spectra based on the Hankel diagonalization (HD) is introduced. Copyright © 2002 John Wiley & Sons, Ltd.

The assignments of ¹H and ¹³C NMR spectra for three new triterpene saponins from Silene vulgaris (gypsogenin 3-O-glucuronide, quillaic acid 3-O-glucuronide, and gypsogenin 3-O-glycoside) are reported. In addition to 1D NMR methods, 2D NMR techniques (COSY, HSQC, HMBC, and HSQC-TOCSY) were used for the assignments. Copyright © 2002 John Wiley & Sons, Ltd.

The assignments of ¹H and ¹³C NMR spectra for three new triterpene saponins from Silene vulgaris (gypsogenin 3-O-glucuronide, quillaic acid 3-O-glucuronide, and gypsogenin 3-O-glycoside) are reported. In addition to 1D NMR methods, 2D NMR techniques (COSY, HSQC, HMBC, and HSQC-TOCSY) were used for the assignments. Copyright © 2002 John Wiley & Sons, Ltd.

The assignments of ¹H and ¹³C NMR spectra for three new triterpene saponins from Silene vulgaris (gypsogenin 3-O-glucuronide, quillaic acid 3-O-glucuronide, and gypsogenin 3-O-glycoside) are reported. In addition to 1D NMR methods, 2D NMR techniques (COSY, HSQC, HMBC, and HSQC-TOCSY) were used for the assignments. Copyright © 2002 John Wiley & Sons, Ltd.

It is shown that fully J-decoupled homonuclear spectra involving Lorentzian lines can be readily obtained by straightforward processing of the 2D data arising from a conventional spin echo sequence (π/2–t1/2–π–t1/2–Acq(t2)) used in the so-called J-resolved experiment. The method simply rests on power spectra with the drawback of lines having meaningless relative intensities. In principle, the experiment should also yield transverse relaxation times. Several tests demonstrate that this is not so, due to pulse imperfections and nonresolved long-range Jcouplings. Conversely, longitudinal and rotating frame relaxation times can be easily determined by means of an appropriate preparation period (for instance, a saturation-recovery period in the case of longitudinal relaxation) inserted before the 2D spin echo sequence. Since one is dealing with a single line per nucleus, relaxation measurements become reliable and accurate.

The phase-twisted lines, resulting from a double complex Fourier transform, can greatly alter the quality of two-dimensional spectra. This problem, which is generally overcome by experimental procedures (requiring twice as much time as a standard measurement), is inevitable in the two-dimensional J-resolved experiment. This experiment is revisited theoretically and a postprocessing treatment, leading to pure 2D J-spectra, is deduced. Quantitative fully J-decoupled homonuclear spectra are accordingly obtained by means of a projection onto the F2 axis after a 45° tilt.

Analytical solutions are provided for a set of three simultaneous first-order differential equations which describe either cross relaxation among three groupings of spin-12nuclei (regardless of the number of spins within each grouping) or the complete longitudinal relaxation of a system of two spins-12, including CSA-dipolar interference terms (which couple the longitudinal spin order to conventional longitudinal magnetizations). In spite of their complexity, the expressions so obtained afford a time savings by a factor of 50 when used in a computer program. The efficiency of the method is illustrated by the fit of experimental data, exhibiting an unusual evolution due to both intra- and intermolecular dipolar couplings.

This paper reports a method of NMR microimaging which employs exclusively radiofrequency field gradients, one in the transverse direction created by a single-turn coil and the other along the longitudinal direction generated by the saddle coil of the conventional probe used with vertical superconducting magnets. The basic experiment involves slice selection by means of the longitudinal gradient followed by the acquisition of the NMR signal in the presence of the transverse gradient. By rotating the object around the vertical axis in a stepped manner, a series of profiles is obtained whose analysis, including inter alia the filtered back-projection algorithm, provides a two-dimensional image. The experiment can be run routinely with a slightly modified conventional NMR spectrometer; emphasis is put on its relative immunity to B₀ inhomogeneities and/or magnetic susceptibility variations across the object under investigation.Copyright 1994, 1999 Academic Press, Inc.

Traditional multiple-quantum filtering in nuclear magnetic resonance spectroscopy relies on the acquisition of several transients along with appropriate phase cycling. It is shown that similar results can be obtained in one transient by using a cluster of two radiofrequency field (B1) gradient pulses (g1)x(rg1)y where g1 and rg1 denote the durations of the B1 gradient pulses and the subscripts x and y the transmitter phases. This filter acts on single-quantum antiphase coherences and is of high-pass nature. The choice of r determines the order of the filter (according to the number of spins belonging to the system considered). This property is demonstrated theoretically and verified experimentally by dedicated one-dimensional experiments and COSY-type two-dimensional experiments.

This paper deals with the extraction of accurate cross-relaxation rates from two-dimensional HOESY experiments. Data treatment is performed in part by a variant (dubbed HD, for Hankel decomposition) of the HSVD algorithm. The first 2D experiment (corresponding to the first t₁ value) is subjected to a whole HD treatment; this yields in particular the frequencies and the damping factors which are then kept as they are for the subsequent experiments, from which only amplitudes and phases are determined by means of a least-squares procedure. These latter parameters are used to reconstruct a limited number of FIDs in the t₁ dimension (one FID per line in the ƒ₂ dimension). The amplitude of signals entering these FIDs (treated by the whole HD algorithm) are directly comparable to those of a conventional (reference) experiment, thus eliminating the major difficulties encountered in the quantitation of heteronuclear two-dimensional experiments.Copyright 1993, 1999 Academic Press

Simple pulse sequences have been used to determine and isolate most carbon-13 and fluorine-19 longitudinal relaxation parameters in pure hexafluorobenzene (carbon-13 in natural abundance). The derived parameters include fluorine-19 and carbon-13 specific relaxation rates (at different field values), dipolar fluorine-carbon cross-relaxation rate, and dipolar (¹³C−¹⁹F)-chemical shift anisotropy (¹³C or ¹⁹F) cross-correlation rates. From these experimental parameters, it was possible to estimate the reorientational anisotropy of liquid hexafluorobenzene and to extract the shielding tensor elements of fluorine-19 and carbon-13. Comparison with those elements as determined from solid-state NMR shows a good agreement for fluorine-19 but one important difference (for one element) in the carbon-13 shielding tensor. This feature is confirmed by quantum chemistry calculations and can be explained by the particular ordering in pure solid.

Simple pulse sequences have been used to determine and isolate most carbon-13 and proton longitudinal relaxation parameters in pure liquid benzene (carbon-13 in natural abundance). The derived parameters include specific longitudinal proton and carbon-13 relaxation rates, direct and remote proton−carbon cross-relaxation rates, proton−proton cross-relaxation rates, and the cross-correlation rate involving direct proton−carbon dipolar interaction and carbon shielding anisotropy (the latter being derived from the evolution of the initially created longitudinal spin order). From these data, it was possible to estimate the dipolar intermolecular contributions to proton and carbon longitudinal nuclear relaxations and the anisotropy of molecular reorientation (the two relevant correlation times are found to be at 25 °C:  τ∥ = 0.58 ps and τ⊥ = 1.62 ps; τ⊥ associated with the tumbling of the symmetry axis perpendicular to the molecular plane and τ∥ associated with rotation around this axis).

A new C2-symmetric chiral lariat ether has been prepared by 1 : 1 cyclocondensation of a contrafunctional amine easily obtained from L-serine. Its ¹H and ¹³C spectra were completely assigned using the two-dimensional gradient enhanced one-bond (HMQC) and multiple-bond (HMBC) heteronuclear techniques together with the homonuclear DQF COSY correlation technique. Copyright © 2001 John Wiley & Sons, Ltd.

It is shown that the proton chemical-shift anisotropy of hydrate crystals affect dipolar powder pattern at 7.0 T. This may be clearly observed via an asymmetric envelope of dipolar spinning sidebands in magic-angle spinning proton spectra.

The principle ofquenchingundesirableindirectexternaltrouble innuclearOverhausereffectspectroscopy(QUIET-NOESY) relies on a doubly selective inversion of the longitudinal magnetization components of a source spinAand a target spinXto measure the cross-relaxation rate (Overhauser effect) betweenAandXwithout significant perturbation by spin diffusion. In15N-enriched proteins, this can be achieved by using abilinearrotationdecoupling (BIRD) sequence for the selective inversion of amide protons that have a scalar coupling to nitrogen-15. The procedure can be improved by using editing techniques to simplify the resulting NOESY spectra.

Two tagging reagents using a quinoxalinone fluorophore were synthesized and, for the first time, completely physico-chemically characterized. The ¹H and ¹³C spectra were entirely assigned using a combination of two-dimensional gradient enhanced HMQC, HMBC experiments and one-dimensional NOE difference experiments. © 1997 John Wiley & Sons, Ltd.

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