Pierre Mutzenhardt

Behavior of cesium and thallium cations inside a calixarene cavity as probed by nuclear spin relaxation. Evidence of cation-pi interactions in water.

We have studied the complexes formed between the p-sulfonatocalix[4]arene and cesium or thallium metal cation, first by carbon-13 longitudinal relaxation of the calixarene molecule at two values of the magnetic field B(0). From the longitudinal relaxation times of an aromatic carbon directly bonded to a proton, thus subjected essentially to the dipolar interaction with that proton, we could obtain the correlation time describing the reorientation of the CH bond. The rest of this study has demonstrated that it is also the correlation time describing the tumbling of the whole calixarene assembly. From three non-proton-bearing carbons of the aromatic cycles (thus subjected to the chemical shift anisotropy and dipolar mechanisms), we have been able to determine the variation of the chemical shift anisotropy when going from the free to the complex form of the calixarene. These variations not only provide the location of the cation inside the calixarene cavity but also constitute a direct experimental proof of the cation-pi interactions. These results are complemented by cesium and thallium relaxation measurements performed again at two values of the magnetic field B(0). An estimation of the mean distance between the cation and the calixarene protons could be obtained. These measurements have also revealed an important chemical shift anisotropy of thallium upon complexation.

Molecular recognition of nucleotides by a new bis(guanidinium)tetrakis(β-cyclodextrin) tetrapod

The facile synthesis of a novel bis(guanidinium)tetrakis(β-cyclodextrin) tetrapod, the first member of a new host family with a pre-defined number of guanidinium centres and cyclodextrins, is presented. Its molecular recognition towards nucleotide guest molecules was investigated. The formation of ditopic bimolecular complexes was observed, combining host–guest hydrophobic inclusion into cyclodextrins and electrostatic interactions between guanidinium and phosphate anions.

Heteronuclear Overhauser effect measurements in surfactant systems. IV. Direct and remote correlations within alkyl chains

This paper deals with the complete interpretation of the heteronuclear Overhauser effect spectroscopy (HOESY) two dimensional nuclear magnetic resonance (NMR) experiment. This experiment aims at the determination of cross relaxation rates (having their origin in dipolar interactions) between two different nuclear species, here proton and carbon‐13. Extra correlation peaks observed in the 2D map of the system under investigation (micellized sodium octanoate) are shown to arise from remote dipolar interactions and not from strong (J) coupling effects. Several experiments have been performed at different mixing times (during which the nuclear Overhauser effect builds up), allowing the observation of the whole carbon‐13 magnetization evolution. Their analysis yields cross‐relaxation rates, refined with respect to those derived from initial behavior. However, this requires inclusion of the effect of spin diffusion, within the proton spin system, in the data treatment. A novel approach is proposed which models ...

Gradient-Enhanced Band-Filtering Experiments

This paper is devoted to sequences involving a selective inverting pulse bracketed by two identicalB0 gradient pulses [pulse field gradient spin echo (PFGSE)]. The merits of a single PFGSE experimentvs. a double PFGSE experiments are discussed. It is shown that the SPFGSE experiment gives results comparable to the DFGSE experiment provided that the selective inverting profile is sufficiently clean. Extension of this type of experiment withB1 gradients is considered.

Behavior of longitudinal spin orders in NMR measurements of self‐diffusion coefficients using radiofrequency field gradients

Weakly coupled spin 1/2 systems of the type AX and AX2 can be easily brought into states of longitudinal order represented (in terms of operator products) by 2IzAIzX and 4IzAIzXIzX′, respectively. It proves possible to follow the evolution of these states under translational diffusion processes through a simple experiment involving two identical radiofrequency field gradient pulses separated by an interval allowing diffusion to take place. Relevant theory and experimental verifications are provided. The main conclusion is that, for a part of the decay, the effective gradient is multiplied by a factor of two in the case of a two spin order (2IzAIzX) and a factor of three in the case of a three spin order (4IzAIzXIzX′). These properties can be employed for accessing to self‐diffusion coefficients, smaller by factors of four and nine respectively, as compared with those measured by conventional methods.

Measurement of weak heteronuclear (13C–1H) Overhauser effects involving carbons not directly bonded to protons

Abstract Although proton detected heteronuclear Overhauser effect spectroscopy is known to be an efficient tool for probing molecular structure and dynamics, it is shown that, in practice, the method fails for observing weak 13 C– 1 H heteronuclear Overhauser effect when the considered carbon-13 (in natural abundance) is not directly bonded to proton(s). Such a weak heteronuclear Overhauser effect has been successfully measured using a modified pulse sequence made of a selective TOCSY block followed by a classical (carbon-13 observation) one-dimensional HOESY sequence. The potentialities of this tool have been illustrated by the confirmation of the preferential conformation of uridine in water.

Structural and motional features of benzene-solvated C60 as revealed by high-resolution solid state NMR

Abstract Structural and motional features of C 60 · 4C 6 H 6 solvate has been investigated by high-resolution 13 C solid-state NMR spectroscopy. 13 C line shape analysis of the cross-polarization spectrum for the static sample at 293 K shows an unusual motional restriction of benzene molecules in this solvate. The existence of highly anisotropic motion of benzene fraction is visualized also by the detection of important homo and heteronuclear dipolar interactions. 13 C magic-angle spinning spectra reveal a complex character of the C 60 NMR signal composed of three components with slightly different isotropic chemical shifts indicating the existence of magnetically nonequivalent positions or sites.

Feasibility of NMR imaging by a single radiofrequency field gradient and the separation of two species with different chemical shifts

The idea of substituting RF field gradients for static field gradients for localization or imaging purposes goes back to Hoult’s rotating-frame zeugmatography ( 1): further developments of this technique have been recently published (2). Obvious advantages of RF gradients lie in the possibility of rapid switching and in the simplicity of the experimental device, which essentially includes a single-turn coil in addition to a classical NMR probe. Most practical applications rely on two-dimensional methods (3-IO), the first dimension referring to a single spatial dimension, the other to a chemical-shift scale; such experiments therefore provide the distribution of different chemical species along that spatial direction. The present work is part of a project aimed at the use of a linear RF gradient for various NMR applications. These include measurements of self-diffusion coefficients (II), spatial localization by the adaptation of the classical DANTE sequence (12), slice selection, and ID imaging (13) through the recently proposed DANTE-Z procedure ( 14). We demonstrate here the possibility of obtaining a two-dimensional (eventually three-dimensional) image by means of a single coil delivering a RF gradient, in contrast with the applications mentioned, which concern only the examination of a single dimension. The successive exploration of the two dimensions is achieved by a fast rotation of the sample during an interval in an appropriate pulse sequence. Moreover, it is shown that a simple variant of this experiment allows one to perform imaging of two chemically shifted species within the same experiment. The experimental arrangement in use ( I1 -13) can be summarized as follows: (i) surrounding the sample is a normal saddle-shaped coil which is employed for generating hard homogeneous pulses and for detecting the NMR signal, (ii) a single-turn coil, orthogonal to the saddle-shaped coil, delivers a linear RF gradient in the sample region (Fig. 1). and (iii) two different transmitters feed these two coils, at the same RF frequency, but with the possibility of adjusting their relative phases so that they can operate in the same rotating frame. The rotation of the object under investigation could be replaced (and probably will be in the near future) by a rotation of the two-coil system.

Algorithm based on a new proof of HSVD equations derived without invoking singular-value decomposition

Abstract The spectral characteristics of all signals contained in a FID are obtained on the basis of pure matrix calculations. The algorithm bears some resemblance to HSVD ( H. Barkhuijsen, R. de Beer, and D. van Ormondt, J. Magn. Reson. 73 , 553, (1987 ), although it does not rely on singular-value decomposition, but rather on the specific properties of XX † , where X is the signal matrix. The eficiency of themethod is demonstrated by the complete analysis of the proton NMR spectrum of ethanol, including carbon-13 satellites.

Location of a Metallic Cation Complexed in a Calixarene Cavity As Determined by Calixarene 13C Spin Relaxation. Application to Cesium and Thallium Complexed by p-Sulfonatocalix[4]arene in Water

This study deals with the exact location of the monovalent metal cations Cs(+) and Tl(+) which are complexed by the p-sulfonatocalix[4]arene in water. This determination rests on the measurements of longitudinal relaxation times of carbon-13 not directly bonded to protons. The difference between the relaxation times of the free calixarene and of the complex definitely demonstrates that the monovalent metal cation is well inside the calixarene cavity. These features are in fact enhanced by the presence of paramagnetic species which act in a different way in the complexed form. Experimental results also show without any ambiguity that the calixarene cavity is essentially hydrophobic. Finally, it is observed that thallium is more mobile than cesium within the calixarene cavity.