Search PubMed⌕ Search

Biomedical subjects

G Bodenhausen

Publications and source records attributed to G Bodenhausen.

27 records · Page 2Linked to original sources
PubMed1996

Divergent double chirp pulses for refocusing quadrupolar interactions.

To excite and refocus single quantum coherences in a three-level system with a quadrupolar interaction, it is possible to use frequency-modulated pulses with two diverging frequency components that are swept simultaneously through the two single-quantum transitions. This is achieved by time-dependent amplitude-modulation of the carrier frequency, so as to generate two sidebands with frequencies that are diverging (or converging) symmetrically with respect to the carrier frequency. Simulations and experiments show that such modulated pulses can be used to refocus single quantum coherences to form quadrupole echoes, using much weaker RF amplitudes than in conventional echo sequences. To visualize the evolution of the coherences in a three-level system, a graphical representation of the density operator components is proposed.

Magnetic Resonance Spectroscopy↗
PubMed1994

Methods for reconstructing phase sensitive slice profiles in magnetic resonance imaging.

The experimental determination of slice profiles excited by applying radiofrequency pulses in the presence of a gradient generally results in magnitude profiles. The conditions necessary to obtain a phase-sensitive picture of the profile of a slice are discussed. A distinction is made between the "excitation profile" (distribution of the transverse magnetization immediately after the RF pulse) and the "slice profile" (distribution after refocusing by gradient reversal and/or imperfect gradient switching). Methods are presented that allow one to obtain either the excitation profile or the slice profile. It is shown that phase encoding along the direction of the slice selection gradient provides a convenient protocol for obtaining the distribution of both the real and imaginary parts of the slice profile. The phase sensitive excitation profile can be obtained by frequency encoding. These methods were used to evaluate the performance of various shaped pulses.

Algorithms↗
PubMed1991

NMR studies of an oligoproline-containing peptide analogue that binds specifically to the H-2Kd histocompatibility molecule.

T lymphocytes expressing variable cell surface antigen receptors recognize "processed" forms of antigen, presented on the surface of other cells by molecules of the major histocompatibility complex (MHC). Naturally processed antigenic peptides can be replaced by synthetic ones. The synthetic peptide AYPPPPPTLA (P5) is an active competitor to the antigenic peptide HLA A24 170-182 (sequence RYLENGKETLQRA) that is recognized by A24 specific T cells in association with the H-2Kd class I MHC molecule. In P5 the five prolines were designed to play the role of a rigid spacer between the residue Y and the T-L unit, so as to mimic the role of Y171, T178, and L179 in the HLA A24 antigenic peptide, since these residues have proven to be the most important with respect to the binding of the HLA A24 peptide with the H-2Kd MHC molecule. Nuclear magnetic resonance studies allow us to demonstrate that in aqueous solution P5 adopts at least three long-lived conformations that can be classified with respect to the Y2-P3-P4 amide bonds as trans-trans, cis-trans, and cis-cis. Among these, the trans-trans form is present in 67% of the molecules while the two others share the remaining 33%.

Amino Acid Sequence↗
PubMed1989

Self-refocusing 270 degrees Gaussian pulses for slice selection without gradient reversal in magnetic resonance imaging.

It is demonstrated, on the grounds of simulations, how 270 degrees Gaussian pulses can be used for slice selection in nuclear magnetic resonance imaging experiments. It is shown that the usual gradient reversal procedure can be omitted if the selective 90 degrees pulse normally used is replaced by a self-refocusing 270 degrees pulse with a Gaussian time-domain amplitude profile, and some of the properties which are specific to this type of pulse are explored.

Magnetic Resonance Imaging↗
PubMed1983

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.

Magnetic Resonance Spectroscopy↗
PubMedDate not supplied

Solid-state NMR for the study of membrane systems: the use of anisotropic interactions.

The use of solid-state nuclear magnetic resonance (NMR) as a tool to determine the structure of membrane molecules is reviewed with a particular emphasis on techniques that provide information on orientation or order. Experiments reported here have been performed in membranes, rather than in micelles or organic solvents. Several ways to prepare and handle the samples are discussed, like sample orientation and magic-angle spinning (MAS). Results concerning lipids, membrane peptides and proteins are included, as well as a discussion regarding the potential of such methods and their pitfalls.

Anisotropy↗