Proton Nuclear Magnetic Resonance Spin Research Articles

Phase modulated Lee–Goldburg magic angle spinning proton nuclear magnetic resonance experiments in the solid state: A bimodal Floquet theoretical treatment

Interference phenomena between sample spinning and radio frequency (RF) irradiation in solid state high resolution proton nuclear magnetic resonance (NMR) spectroscopy are examined. A bimodal Floquet treatment is exploited in order to overcome the limitations of the average Hamiltonian theory (AHT) approach. Frequency switched Lee Goldburg (FSLG) and its variant, phase modulated Lee Goldburg (PMLG-n), homonuclear dipolar decoupling experiments on protons that are rotating at the magic angle are examined. Average Hamiltonian theory (AHT) is used for the synchronous application of FSLG and PMLG-n RF sequences with the sample spinning. A bimodal Floquet approach is introduced to treat both synchronous and nonsynchronous cases. The Floquet approach, providing a general theoretical framework for describing rotating spin systems exposed to periodically applied RF field, reveals several features of the interference between the sample spinning and the RF irradiation. These features can be characterized by mapping out resonance conditions in terms of the Floquet energy level crossings. Line broadening effects occurring when the RF sequences are applied synchronously with the sample spinning are discussed. The appearances of RF-rotor frequency lines in the decoupled spectra are explained. In addition PMLG-n magic angle spinning (MAS) experiments with a reduced number of phases, n⩾3, per RF cycle are explored. All theoretical predictions are verified by simulations of proton spectra and by PMLG-n-MAS experiments on uniformly labeled C13− tyrosine.

Classification of human liposarcoma and lipoma using ex vivo proton NMR spectroscopy.

Prognostication in patients with liposarcoma is a complex and controversial subject based on recognition of lipoblasts, adipocyte nuclear atypia, and qualitative estimations of cellularity and cell size. We show here that for 30 patients with liposarcoma and 5 patients with lipoma, spectral differences on high-resolution, magic angle spinning proton nuclear magnetic resonance (hr-MAS 1H-NMR) spectroscopy relate to known biochemical changes and correlate with adipocyte tissue differentiation, histologic cell type, and cellularity. The NMR-visible level of triglyceride is shown to correlate with liposarcoma differentiation, since the triglyceride level in well-differentiated liposarcoma is 33-fold higher on average than for myxoid/round cell liposarcoma, which in turn is 6-fold higher than the dedifferentiated and/or pleomorphic subtypes. The NMR-visible phosphatidylcholine level serves as an estimate of total tissue cell membrane phospholipid mass and was found to correlate with liposarcoma subtype. Pleomorphic liposarcoma, the most aggressive and metastatic subtype, was found to have a threefold increase in NMR-visible phosphatidylcholine level compared with dedifferentiated liposarcoma. The level of NMR-visible phosphatidylcholine was twofold greater in well-differentiated liposarcoma compared with lipoma and was threefold larger for the hypercellular myxoid/round cell subtype compared with the pure myxoid histology. Thus, NMR-derived parameters of tissue lipid may be used for objective distinction of liposarcoma histologic subtype/grade and lipoma from liposarcoma. These biochemical parameters may ultimately improve prognostication in patients with liposarcoma.

Classification of human liposarcoma and lipoma using ex vivo proton NMR spectroscopy

Prognostication in patients with liposarcoma is a complex and controversial subject based on recognition of lipoblasts, adipocyte nuclear atypia, and qualitative estimations of cellularity and cell size. We show here that for 30 patients with liposarcoma and 5 patients with lipoma, spectral differences on high-resolution, magic angle spinning proton nuclear magnetic resonance (hr-MAS 1H-NMR) spectroscopy relate to known biochemical changes and correlate with adipocyte tissue differentiation, histologic cell type, and cellularity. The NMR-visible level of triglyceride is shown to correlate with liposarcoma differentiation, since the triglyceride level in well-differentiated liposarcoma is 33-fold higher on average than for myxoid/round cell liposarcoma, which in turn is 6-fold higher than the dedifferentiated and/or pleomorphic subtypes. The NMR-visible phosphatidylcholine level serves as an estimate of total tissue cell membrane phospholipid mass and was found to correlate with liposarcoma subtype. Pleomorphic liposarcoma, the most aggressive and metastatic subtype, was found to have a threefold increase in NMR-visible phosphatidylcholine level compared with dedifferentiated liposarcoma. The level of NMR-visible phosphatidylcholine was twofold greater in well-differentiated liposarcoma compared with lipoma and was threefold larger for the hypercellular myxoid/round cell subtype compared with the pure myxoid histology. Thus, NMR-derived parameters of tissue lipid may be used for objective distinction of liposarcoma histologic subtype/grade and lipoma from liposarcoma. These biochemical parameters may ultimately improve prognostication in patients with liposarcoma. Magn Reson Med 41:257–267, 1999. © 1999 Wiley-Liss, Inc.

Solid State 1H-Mas-Nmr and Spin Densities on Protons of the Organic Ferromagnetic Tempo Derivatives

Electron spin densities on hydrogen atoms of 4-(arylmethyleneamino)-2,2,6,6-tetramethylpiperidin-1-oxyls (abbreviated as Ar-CH=N-TEMPO), which show ferromagnetic behavior at low temperatures, were determined in their crystal phases from the temperature dependence of the Fermi contact shift measured by high speed magic angle spinning proton nuclear magnetic resonance. This method revealed a large negative hyperfine coupling constant for the methyl and methylene protons, A = -1.00 MHz for Ar = p-C1-ph and A = -1.32 MHz for Ar = ph, and very small one for the aryl group protons, |A| < 0.01 MHz for p-Cl-ph and A = +0.04 MHz for ph. The observed negative hyperfine coupling constant (negative spin density) of methyl and methylene protons matches with spin alternation for the intermolecular spin polarization mechanism through the contact of methyl and/or methylene protons to adjacent N-O radical group. This contact potentially contributes to the intermolecular ferromagnetic interaction.

High resolution nuclear magnetic resonance imaging of the spinal cord in experimental demyelinating disease.

Chronic recurrent experimental allergic encephalomyelitis was induced in a strain 13 guinea pig by inoculation of isologous spinal cord homogenate. The spinal cord was obtained after perfusion with 4% paraformaldehyde and examined with nuclear magnetic resonance (NMR) imaging. Proton NMR spin echo images (repetition time: 3 s; echo times: 20 and 60 ms) were obtained from intact, isolated spinal cord in a 4.7 Tesla, 50 mm bore magnet. The slice thickness of the images was 380 microns and the inplane resolution was 40 X 40 microns. The images showed superficial areas of low signal intensity in the lateroventral regions of the white matter, in some instances with a seam of higher signal intensity. Neuropathologically, these abnormalities corresponded exactly to areas of demyelination. Control images did not show these abnormalities. The present high resolution imaging allowed a correlation between demyelination and abnormal NMR signals in a small laboratory animal with an inflammatory demyelinating disease.

The effect of hydration on the mobility of phospholipids in the gel state. A proton nuclear magnetic resonance spin echo study

Proton nuclear magnetic resonance (NMR) dipolar echo studies are presented for the gel state of dipalmitoylglycerophosphocholine (dipalmitoyl-GPC) — heavy water dispersions. The mobility and the mean order of the chains and the head group of dipalmitoyl-GPC were determined for different water concentrations and temperatures. For smaller than 5 mol D 2O per mol dipalmitoyl-GPC the molecule undergoes temperature- and hydration-dependent restricted rotational oscillations about the long axis of the molecule. For hydration numbers equal or larger than 5 mol D 2O per mol dipalmitoyl-GPC the molecules rotate effectively about their long axes and intermolecular dipolar interactions between proton groups of neighbour molecules are averaged. The onset of the lateral diffusion of dipalmitoyl-GPC is observed which averages out all intermolecular dipolar interactions. Deviations of the individual segments of the chains from the all- trans state have to be considered. The widely accepted model that the dipalmitoyl-GPC molecules rotate about their long axes with stiff all- trans chains should be modified. The polar head groups of dipalmitoyl-GPC effectively rotate about the bilayer-normal and restricted rotations about single bonds in the head group are allowed. An order parameter of about 0.6 for the head group was obtained for fully hydrated dipalmitoyl-GPC molecules at ambient temperature.

Varied magnetic field, multiple-pulse, and magic-angle spinning proton nuclear magnetic resonance study of muscle water

The nuclear magnetic resonance linewidth of 1H in water of frog muscle was studied as a function of magnetic field strength and angle of orientation. The results suggest that the observed spectra are dominated by demagnetization field anisotropy and dispersion, but a small static dipolar interaction of the order of a few hertz man be present. Data from line-narrowing, multiple-pulse experiments also indicate the presence of a small dipolar broadening.

Experimental evidence for the role of cross-relaxation in proton nuclear magnetic resonance spin lattice relaxation time measurements in proteins

Proton nuclear magnetic resonance (NMR) spin lattice relaxation time (T1) and spin-spin relaxation time (T2) measurements are presented for a number of proteins with molecular weights spanning the range of 6,500-150,000 daltons. These measurements provide experimental evidence for the role of cross-relaxation in 1H NMR T1 measurements in proteins. The relationship between these measurements and the theory recently presented by Kalk and Berendsen is discussed. The results indicate that cross-relaxation dominates the T1 measurements for the larger proteins, even at relatively low resonance frequencies such as 100 MHz.