Suzanne Wehrli

Diffusion of Exchangeable Water in Cortical Bone Studied by Nuclear Magnetic Resonance

The rate-limiting step in the delivery of nutrients to osteocytes and the removal of cellular waste products is likely diffusion. The transport of osteoid water across the mineralized matrix of bone was studied by proton nuclear magnetic resonance spectroscopy and imaging by measuring the diffusion fluxes of tissue water in cortical bone specimens from the midshaft of rabbit tibiae immersed in deuterium oxide. From the diffusion coefficient (D(a) = (7.8 +/- 1.5) x 10(-7) cm(2)/s) measured at 40 degrees C (close to physiological temperature), it can be inferred that diffusive transport of small molecules from the bone vascular system to the osteocytes occurs within minutes. The activation energy for water diffusion, calculated from D(a) measured at four different temperatures, suggests that the interactions between water molecules and matrix pores present significant energy barriers to diffusion. The spatially resolved profile of D(a) perpendicular to the cortical surface of the tibia, obtained using a finite difference model, indicates that diffusion rates are higher close to the endosteal and periosteal surfaces, decreasing toward the center of the cortex. Finally, the data reveal a water component (approximately 30%) diffusing four orders of magnitude more slowly, which is ascribed to water tightly bound to the organic matrix and mineral phase.

Water content measured by proton-deuteron exchange NMR predicts bone mineral density and mechanical properties.

NMR was used to measure matrix water content in normal and hypomineralized cortical bone. Water content showed an inverse relationship with mineral content, suggesting it could serve as a surrogate measure for the bones degree of mineralization.

Multipoint mapping for imaging of semi-solid materials.

Multipoint k-space mapping is a hybrid between constant-time (single-point mapping) and spin-warp imaging, involving sampling of a k-line segment of r points per TR cycle. In this work the method was implemented for NMR imaging of semi-solid materials on a 400 MHz micro-imaging system and two different k-space sampling strategies were investigated to minimize the adverse effects from relaxation-induced k-space signal modulation. Signal attenuation from T(2) decay results in artifacts whose nature depends on the k-space sampling strategy. The artifacts can be minimized by increasing the readout gradient amplitude, by PSF deconvolution or by oversampling in readout direction. Finally, implementation of a T(2) selective RF excitation demonstrates the feasibility of obtaining short-T(2) contrast even in the presence of tissues with long-T(2). The methods potential is illustrated with 3D proton images of short-T(2) materials such as synthetic polymers and bone.

Solution complexes of the aluminum halides in acetonitrile and acetonitrile-water studied by high-field 27AI NMR

The complexes coexisting in acetonitrile upon dissolution of AIX3 (X = CI, Br, I) are shown to consist essentially of the pure anionic complex AIX4− and mixed hexacoordinated species of type [A1XnS6−n]3−n (S = acetonitrile), all exhibiting distinctly different 27 Al shieldings. The presence of both geometric isomers was unambiguously established for [AICl2S4]+ and AICl3S3, which could be identified on the basis of their characteristic linewidths, dictated by the distinctly different electric field gradient tensor invariants acting on the Al nucleus. The relative populations of the various mixed species are found to be highly dependent upon solute concentration, and the more chloride-rich species become appreciably populated only at high dilution. By contrast only three different hexacoordinated species were identified for AIBr3 whereas ALL3 provides only AI(CH3CN)63+ and All4−. Addition of small amounts of water consecutively displaces chloride or bromide ions and acetonitrile from the ligand sphere affording mixed solvates of stoichiometry [AlSnH2O)6−n]3+ and, with AICl3, probably also chloride-containing species. All of the complexes described are found to be kinetically inert on the 27Al NMR time scale. Nine out of ten theoretically possible mixed solvates including the cis-trans pairs for [AIS3(H2O)3]3+ and [AIS4(H2O)2]3+ were identified.

Multiple-quantum 113Cd1H correlation spectroscopy as a probe of metal coordination environments in metalloproteins

Utilisation de la RMN multiquantique pour obtenir des spectres RMN de 1 H de proteines de 113 Cd dans lesquels les seules resonances observees proviennent des spins des protons couples au cadmium

An improved method for the detection of malignancy by proton NMR spectroscopy of plasma

The ratio of intensity (RI) of the plasma lipid methyl proton NMR resonance from two Carr-Purcell-Meiboom-Gill spectra acquired with a short (2.4 msec) and long (120 msec) pulse delay time is proposed to provide a potentially more sensitive and less variable marker of human malignancy than the linewidth parameter previously suggested (E.T. Fossel, J.M. Carr, and J. McDonagh (1986) N. Engl. J. Med. 315, 1369-1376). Linewidth and transverse (T2) relaxation data are presented which demonstrate that the observed correlation between methyl and methylene lipid linewidth and the methyl RI parameter arises from a combination of T2 differences and the relative amounts that fast- and slow-relaxing components contribute to the composite methyl resonance.

Evaluation of the rotational barrier in the bis-(dimethylamido) phosphenium cation by spin saturation transfer and 1H and 13C complete bandshape analysis

Abstract The barrier to rotation about the phosphorus-nitrogen bond in the bis(dimethylamido) phosphenium cation has been determined by 13C and 1H DNMR complete bandshape analysis and spin saturation transfer methodologies. Arrhenius activation energies for this simple two-site exchange process as derived from the three techniques are 11.2, 11.0 and 12.7 kcal mol−1, respectively. Corresponding activation enthalpies are 10.7, 10.5 and 12.2 kcal mol−1. Activation energies and enthalpies derived from these methods are thus in agreement within 1.7 kcal of one another.