Nonlinear regression models of multicomponent interactions of anhydropolyols with aqueous ammonium ion by carbon-13 nuclear magnetic resonance

1983 ◽  
Vol 87 (23) ◽  
pp. 4720-4724 ◽  
Author(s):  
David G. Naugler ◽  
Robert J. Cushley
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Nonlinear Regression ◽  
Regression Models ◽  
Ammonium Ion ◽  
Nonlinear Regression Models ◽  
Nuclear Magnetic

Low temperature nuclear magnetic resonance studies of NH4ClO4

1976 ◽  
Vol 54 (3) ◽  
pp. 239-251 ◽  
Author(s):  
R. F. Code ◽  
J. Higinbotham ◽  
A. R. Sharp
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Low Temperature ◽  
Relaxation Times ◽  
Ammonium Ion ◽  
Proton Relaxation ◽  
Spin Conversion ◽  
Type Symmetry ◽  
Symmetry Species ◽  
Nuclear Magnetic

The properties of ammonium perchlorate were investigated in the temperature range between 1.3 and 50 K by nuclear magnetic resonance and relaxation experiments. The observed increase in the proton second moment from its high temperature value of ~ 1.18 G2 to the value of 4.30 G2 below 4.2 K was associated with a characteristic activation energy of ~ 4 × 10−21 J molecule−1 (~ 0.6 kcal mole−1). No evidence could be found for nuclear spin conversion between the symmetry species of the ammonium ion from measurements of the static proton magnetic susceptibility above 1.3 K. An asymptotic analysis of the low temperature proton lineshapes identified the broad wings of the lines with ammonium ions of T type symmetry. Measurements of the proton relaxation times T1 and T1ρ agreed with previous work by others on NH4ClO4, and were similar to observations on other ammonium compounds having low reorientational barriers.

14N nuclear magnetic resonance: amines and ammonium ions

1969 ◽  
Vol 47 (8) ◽  
pp. 1321-1325 ◽  
Author(s):  
M. Witanowski ◽  
H. Januszewski
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Chemical Shift ◽  
Nitrogen Atom ◽  
Excited States ◽  
Ammonium Ion ◽  
Ammonium Ions ◽  
Alkyl Groups ◽  
Phenyl Vinyl ◽  
Nuclear Magnetic

The 14N nuclear magnetic resonance (n.m.r.) signals of alkylamines and ammonium ions are shifted to lower magnetic fields with the increasing number of alkyl groups at the carbon atom directly bonded to the nitrogen atom, and at the nitrogen atom itself. The resonance of an ammonium ion always occurs at a field lower than that for the corresponding amine. It seems that high-lying excited states, not only those corresponding to lowest-wavelength transitions, are important for an explanation of the observed resonance shifts. A downfield shift of the 14N resonance and a substantial increase in signal width, as compared with the spectra of neat amines, are observed for aqueous solutions of amines. There is a very characteristic chemical shift for the R—CH2—NH2 molecules (R = alkyl, phenyl, vinyl) in the 14N n.m.r. spectra.

An emerging technology: Nuclear magnetic resonance microscopy

1988 ◽  
Vol 46 ◽  
pp. 1000-1001
Author(s):  
M.J. Hennessy ◽  
E. Kwok
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Relaxation Times ◽  
Basic Research ◽  
Local Environment ◽  
Magnetic Resonance Images ◽  
Nmr Microscopy ◽  
Mri Scans ◽  
Temperature Relaxation ◽  
Nuclear Magnetic

Much progress in nuclear magnetic resonance microscope has been made in the last few years as a result of improved instrumentation and techniques being made available through basic research in magnetic resonance imaging (MRI) technologies for medicine. Nuclear magnetic resonance (NMR) was first observed in the hydrogen nucleus in water by Bloch, Purcell and Pound over 40 years ago. Today, in medicine, virtually all commercial MRI scans are made of water bound in tissue. This is also true for NMR microscopy, which has focussed mainly on biological applications. The reason water is the favored molecule for NMR is because water is,the most abundant molecule in biology. It is also the most NMR sensitive having the largest nuclear magnetic moment and having reasonable room temperature relaxation times (from 10 ms to 3 sec). The contrast seen in magnetic resonance images is due mostly to distribution of water relaxation times in sample which are extremely sensitive to the local environment.

Nuclear magnetic resonance microscopy

1989 ◽  
Vol 47 ◽  
pp. 828-829
Author(s):  
Paul C. Lauterbur
Keyword(s):  
Magnetic Field ◽  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Magnetic Fields ◽  
Signal To Noise ◽  
Field Gradients ◽  
Useful Signal ◽  
Magnetic Field Gradients ◽  
Observation Times ◽  
Nuclear Magnetic

Nuclear magnetic resonance imaging can reach microscopic resolution, as was noted many years ago, but the first serious attempt to explore the limits of the possibilities was made by Hedges. Resolution is ultimately limited under most circumstances by the signal-to-noise ratio, which is greater for small radio receiver coils, high magnetic fields and long observation times. The strongest signals in biological applications are obtained from water protons; for the usual magnetic fields used in NMR experiments (2-14 tesla), receiver coils of one to several millimeters in diameter, and observation times of a number of minutes, the volume resolution will be limited to a few hundred or thousand cubic micrometers. The proportions of voxels may be freely chosen within wide limits by varying the details of the imaging procedure. For isotropic resolution, therefore, objects of the order of (10μm) may be distinguished.Because the spatial coordinates are encoded by magnetic field gradients, the NMR resonance frequency differences, which determine the potential spatial resolution, may be made very large. As noted above, however, the corresponding volumes may become too small to give useful signal-to-noise ratios. In the presence of magnetic field gradients there will also be a loss of signal strength and resolution because molecular diffusion causes the coherence of the NMR signal to decay more rapidly than it otherwise would. This phenomenon is especially important in microscopic imaging.

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