Résonance magnétique nucléaire

vignette|175px|Spectromètre de résonance magnétique nucléaire. L'aimant de 21,2 T permet à l'hydrogène (H) de résonner à . La résonance magnétique nucléaire (RMN) est une propriété de certains noyaux atomiques possédant un spin nucléaire (par exemple H, C, O, F, P, Xe…), placés dans un champ magnétique. Lorsqu'ils sont soumis à un rayonnement électromagnétique (radiofréquence), le plus souvent appliqué sous forme d'impulsions, les noyaux atomiques peuvent absorber l'énergie du rayonnement puis la relâcher lors de la relaxation. L'énergie mise en jeu lors de ce phénomène de résonance correspond à une fréquence très précise, dépendant du champ magnétique et d'autres facteurs moléculaires. Ce phénomène permet donc l'observation des propriétés quantiques magnétiques des noyaux dans les phases gaz, liquide ou solide. Seuls les atomes dont les noyaux possèdent un moment magnétique donnent lieu au phénomène de résonance. Le phénomène RMN est exploité par la spectroscopie de résonance magné

Metrological Characterization of Nuclear Magnetic Resonance Markers for Real-Time Field Control of the CERN ELENA Ring Dipoles

Anthony Jean Beaumont, Marco Buzio

Field markers in particle accelerators are used to provide a digital trigger when the magnetic field reaches a preset threshold. This paper describes the results of a test campaign performed on the extra low energy antiproton decelerator's main bending dipoles at the European Organization for Nuclear Research (CERN) investigating the behavior of nuclear magnetic resonance (NMR) markers in ramping fields. Following the conclusions of an off-line study using a spare dipole, a series of tests performed on the reference magnet powered in series with the ring showed an NMR signal with a reproducibility better than 9 mu T at field levels lower than 47 mT, using slow ramp rates. This is promising for the real-time field control of the decelerator. For a high-field marker using high ramp rates, the reproducibility of the signal was found to be better than 3 mu T.

2018

Chemical exchange in proteins

Mariachiara Verde

Nuclear Magnetic Resonance (NMR) spectroscopy offers many ways to investigate dynamic properties of molecules. A wide variety of experimental techniques can probe molecular dynamics on time scales that range from 10-12 to 103 seconds. Many lines of evidence point to the existence of large scale dynamics on milli- to microsecond time scale that are essential to molecular function. Those conformational motions can give rise to chemical exchange effects. So far in the literature two methods have been mainly used to study such processes: CPMG echo trains and R1ρ spin-lock relaxation experiments. The former is suited to investigate processes on the millisecond time scale, whereas R1ρ can probe processes ranging from milliseconds down to ca. microseconds. CPMG and R1ρ studies of the relaxation rates of single quantum (SQ) coherences can be complemented by multiple quantum coherence (MQ) coherences experiments which can provide information whether two (or more) spins are affected simultaneously by chemical exchange. The goal of this thesis is to characterize chemical exchange in proteins by new (Heteronuclear Double Resonance, HDR) and existing (relaxation compensated CPMG) methods. The presence of chemical exchange has been identified in APO-rMUP using the classical CPMG experiment on single quantum 15N magnetization, whereas in HOLO-rMUP no presence of chemical exchange has been found. Most of the thesis is dedicated to the analysis and the application of a new method, HDR, which is designed to determine the cross-relaxation rates between MQ operators. In fact, in heteronuclear systems, correlated chemical exchange contributes to cross-relaxation between MQ coherences 2IxSx and 2IySy. This method, based on MLEV-32 and WALTZ-16 used in double resonance mode, is designed to effectively preserve all relevant MQ coherences simultaneously so that the interconversion between MQ operators can only arise through cross-relaxation. This is an essential requirement if we want to measure, for example, small cross-relaxation rates between MQ operators. We have treated the effects of coherent evolution during the HDR sequences by numerical simulations and Average Hamiltonian Theory (AHT) showing that, under most conditions, the dynamics of MQ coherences is not affected by coherent evolution. This result is proved experimentally on the 15N-1H pair of selectively deuterated tBoc-glycine. The effect of relaxation during HDR sequences leads to an effective relaxation superoperator which is explored by numerical simulations and predicted by Average Liouvillian Theory (ALT). Finally the HDR MLEV-32 sequence is applied to amide 1H-15N pairs in ubiquitin and KIX proteins. In the case of ubiquitin the HDR MLEV-32 experiments and the numerical simulations run with parameters obtained from the literature are in good agreement, suggesting that HDR sequences could be used as a tool to obtain information about the dynamics of the system.

EPFL2009

Structural determination of biomolecular interfaces by nuclear magnetic resonance of proteins with reduced proton density

Fabien Ferrage

Protein interactions are important for understanding many molecular mechanisms underlying cellular processes. So far, interfaces between interacting proteins have been characterized by NMR spectroscopy mostly by using chemical shift perturbations and cross-saturation via intermolecular cross-relaxation. Although powerful, these techniques cannot provide unambiguous estimates of intermolecular distances between interacting proteins. Here, we present an alternative approach, called REDSPRINT (REDduced/Standard PRoton density INTerface identification), to map protein interfaces with greater accuracy by using multiple NMR probes. Our approach is based on monitoring the cross-relaxation from a source protein (or from an arbitrary ligand that need not be a protein) with high proton density to a target protein (or other biomolecule) with low proton density by using isotope-filtered nuclear Overhauser spectroscopy (NOESY). This methodology uses different isotropic labeling for the source and target proteins to identify the source-target interface and also determine the proton density of the source protein at the interface for protein-protein or protein-ligand docking. Simulation indicates significant gains in sensitivity because of the resultant relaxation properties, and the utility of this technique, including a method for direct determination of the protein interface, is demonstrated for two different protein–protein complexes.

Springer Verlag2010

Chemical exchange in proteins

Mariachiara Verde

EPFL2009