Geoffrey Bodenhausen

Improved spectral resolution in COSY 1H NMR spectra of proteins via double quantum filtering

A double quantum filter is inserted into a two-dimensional correlated (COSY) 1H NMR experiment to obtain phase-sensitive spectra in which both cross peak and diagonal peak multiplets have anti-phase fine structure, and in which the cross peaks and the major contribution to the diagonal peaks have absorption lineshapes in both dimensions. The elimination of the dispersive character of the diagonal peaks in phase-sensitive, double quantum-filtered COSY spectra allows identification of cross peaks lying immediately adjacent to the diagonal, which represents a significant improvement over the conventional COSY experiment.

Natural abundance nitrogen-15 NMR by enhanced heteronuclear spectroscopy

The detection of NMR spectra of less sensitive nuclei coupled to protons may be significantly improved by a 2-dimensional Fourier transform technique involving a double transfer of polarization. The method is adequate to obtain natural abundance 15N spectra in small sample vols. with a com. spectrometer. [on SciFinder (R)]

Suppression of artifacts in two-dimensional J spectroscopy

Spurious responses, known as phantom and ghost responses, in NMR 2-dimensional J spectroscopy, can be removed by a 4-step sequence where the phase of the C refocusing pulse is cycled through O, 90, 180, 270 Deg while the receiver ref. phase is alternated. This phase-cycling sequence was applied to the 2-dimensional J spectrum of 13C in MeOH obtained by the proton flip technique; both the phantom and ghost multiplets were canceled. [on SciFinder (R)]

Multiple quantum spin-echo spectroscopy

The generation of nuclear magnetic double quantum echoes and their detection by 2-dimensional Fourier transform spectroscopy is reported for partially aligned 1-deuteron systems in a nematic liq. crystal. Phase-cycling techniques which suppress detection of unwanted coherences were developed, and the transverse decay rates of double quantum coherences agree quant. with relaxation results obtained by more conventional methods. [on SciFinder (R)]

Analysis of networks of coupled spins by multiple quantum N.M.R.

It is shown that multiple quantum N.M.R. allows straightforward identification of networks of scalar coupled spins. The information obtained is particularly useful for the identification of magnetic equivalence when multiplet splittings are not fully resolved. The interpretation of multiple quantum spectra is based on a set of simple selection rules which restrict coherence transfer between multiple quantum and single quantum transitions.

Multiple-quantum NMR spectroscopy of S = 3/2 spins in isotropic phase: a new probe for multiexponential relaxation

In nuclear magnetic resonance of quadrupolar spins with S≥3/2, it is shown that excitation and observation of multiple‐quantum coherence is possible in the absence of scalar, dipolar, or quadrupolar splittings, in contrast to the widely accepted view that nonvanishing couplings are a prerequisite for the creation of multiple‐quantum coherence. In the absence of splittings, multiple‐quantum coherence can be excited because the longitudinal (‘‘T1’’) or transverse (‘‘T2’’) relaxation is multiexponential, which occurs if the motional correlation times τc are comparable to or larger than the inverse of the Larmor frequency (violation of the extreme narrowing approximation). Two experiments are described, which combine multiple‐quantum filtration with conventional spin‐echo and inversion‐recovery sequences. For isotropic motion each experiment allows one to determine the motional correlation time without knowledge of the magnitude of the quadrupolar coupling constant.

Correlation of proton and carbon-13 nmr spectra by heteronuclear two-dimensional spectroscopy

A technique is presented for increasing the information content of 13C NMR spectroscopy by introducing correlated proton shift information. It is an application of a general expt. proposed and realized for the indirect detection of 13C resonance by R. R. Ernst and A. A. Maudsley (1977). The application of this technique is illustrated by the shift correlation spectrum of EtOH. Simplification of these 2-dimensional correlations can be achieved by greatly reducing the splitting due to protons in both frequency dimensions. [on SciFinder (R)]

Surface Enhanced NMR Spectroscopy by Dynamic Nuclear Polarization

It is shown that surface NMR spectra can be greatly enhanced using dynamic nuclear polarization. Polarization is transferred from the protons of the solvent to the rare nuclei (here carbon-13 at natural isotopic abundance) at the surface, yielding at least a 50-fold signal enhancement for surface species covalently incorporated into a silica framework.

A simple pulse sequence for selective excitation in Fourier transform NMR

A pulse-repetition rate set to q = 2np radians, i.e., Dfn = n/t, where q = degrees, n = an integer, f = frequency, and t = sec, provides, for a very narrow band of frequencies near the q = 2np conditions, a magnetization vector in which the steps caused by pulses outweigh those caused by precession and which induces a max. NMR signal which is close to the pure absorption-mode condition. Selective excitation by this simple pulse sequence was illustrated by added multiplet subspectra in the Fourier transform 13C NMR of Me2C:CHNMe2. [on SciFinder (R)]

Gaussian pulse cascades: New analytical functions for rectangular selective inversion and in-phase excitation in NMR

New radio-frequency pulse envelopes are presented for selective inversion and in-phase excitation in NMR. The envelope functions consist of superpositions of three or four time-shifted Gaussians with optimized widths and peak amplitudes. The offset dependence closely approaches ideal rectangular functions, as verified by simulation and expt. [on SciFinder (R)]