Nuclear magnetic resonance spectroscopy. A stereospecific ^3J_(CF) coupling in the low-temperature ^(13)C nmr spectrum of 1,1-difluorocyclohexane

The proton-decoupled ^(13)C nmr spectrum of 1,1-difluorocyclohexane has been examined at room temperature and at -90 degrees C. There are only minor changes in the one-bond and two-bond carbon-fluorine scalar coupling constants at the lower temperature; however, the triplet observed for C-3 (^3J_(CF) = 4.7 Hz) collapses to a doublet (3JCF = 9.5 Hz) at -90 °C. It is proposed that only the equatorial fluorine is coupled with the C-3 carbon as the result of operation of a back-lobe orbital interaction

Merlin controls the repair capacity of Schwann cells after injury by regulating Hippo/YAP activity

Loss of the Merlin tumor suppressor and activation of the Hippo signaling pathway play major roles in the control of cell proliferation and tumorigenesis. We have identified completely novel roles for Merlin and the Hippo pathway effector Yes-associated protein (YAP) in the control of Schwann cell (SC) plasticity and peripheral nerve repair after injury. Injury to the peripheral nervous system (PNS) causes a dramatic shift in SC molecular phenotype and the generation of repair-competent SCs, which direct functional repair. We find that loss of Merlin in these cells causes a catastrophic failure of axonal regeneration and remyelination in the PNS. This effect is mediated by activation of YAP expression in Merlin-null SCs, and loss of YAP restores axonal regrowth and functional repair. This work identifies new mechanisms that control the regenerative potential of SCs and gives new insight into understanding the correct control of functional nerve repair in the PNS

A segmentation-based and partial-volume-compensated method for an accurate measurement of lateral ventricular volumes on T-1-weighted magnetic resonance images

Lateral ventricular volumes based on segmented brain MR images can be significantly underestimated if partial volume effects are not considered. This is because a group of voxels in the neighborhood of lateral ventricles is often mis-classified as gray matter voxels due to partial volume effects. This group of voxels is actually a mixture of ventricular cerebro-spinal fluid and the white matter and therefore, a portion of it should be included as part of the lateral ventricular structure. In this note, we describe an automated method for the measurement of lateral ventricular volumes on segmented brain MR images. Image segmentation was carried in combination of intensity correction and thresholding. The method is featured with a procedure for addressing mis-classified voxels in the surrounding of lateral ventricles. A detailed analysis showed that lateral ventricular volumes could be underestimated by 10 to 30% depending upon the size of the lateral ventricular structure, if mis-classified voxels were not included. Validation of the method was done through comparison with the averaged manually traced volumes. Finally, the merit of the method is demonstrated in the evaluation of the rate of lateral ventricular enlargement. (C) 2001 Elsevier Science Inc. All rights reserved

Nuclear Magnetic Resonance Spectroscopy. Observation of Carbon-13 Resonances in a Paramagnetic Transition Metal Complex. Nickel(II) N,N'-di(p-tolyl)aminotroponiminate

The discovery of the extraordinary chemical shifts of the proton magnetic resonances of paramagnetic Ni(II) aminotroponiminates has been of great value for probing the nature of metal-ligand bonding especially because sharp resonances are observed as the result of the short electronic relaxation times of the tetrahedral forms which are associated with the squareplanar (diamagnetic) ⇌ tetrahedral (paramagnetic) equilibria. These complexes are expected to provide a useful starting point for natural-abundance nmr studies of paramagnetic transition metal complexes. We report in this study observation of eight of the possible nine carbon resonances of the N,N’-di(ptolyl) derivative 1, and present evidence for nonzero spin density in the σ framework of the ligand

Nuclear Magnetic Resonance Spectroscopy. Carbon-13 Spectra of n-Alkyl Nickel(II) Aminotroponiminates

In a previous communication from these laboratories we reported the ^(13)C nmr spectrum of nickel(II) N,N'-di(p-tolyl)aminotroponiminate and proposed that, at least qualitatively, the ^(13)C isotropic shifts were consistent with the propagation of unpaired spin density by way of both the π and σ electrons of the ligand. This analysis assumed that the π contribution to the ^(13)C hyperfine coupling constant, ɑ^c_i, could be approximated by the Karplus-Fraenkel equation (eq 1), where S^c is the proportionality factor for the polarization of the 1s electrons and the Q's are the proportionality factors for the 2s electrons

In vivo localized1 H spectroscopy of the rat eye at 7 T: preliminary studies

Preliminary in vivo proton spectroscopic studies of the posterior chamber of the rat eye have been undertaken at 7 T. The Spatial and Chemical shift encoded Excitation (SPACE) localization sequence was used to acquire signals from 10-μl voxels and demonstrate the presence of metabolites associated with the vitreous humor, lens, retina, and the optic nerve. Localized T2 and T1 measurements of water in the vitreous humor indicate a relatively fluid environment. Susceptibility maps are used to demonstrate the difficulties of in vivo spectroscopic investigations in the anterior regions of the eye. Comments are made concerning the implications for spectral resolution in these regions