共查询到20条相似文献,搜索用时 15 毫秒
1.
Hwang DW Jhao WJ Hwang LP 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2005,172(2):214-221
In this study 2H T2rho DQF NMR spectra of water in MCM-41 were measured. The T2rho double-quantum filtered (DQF) NMR signal is generated by applying a radio frequency (RF) field for various durations and then observed after a monitor RF pulse. It was found that the transfer between different quantum coherences by the couplings during long-duration RF fields (i.e., soft pulses) and that residual quadrupolar interaction dominates the signal decay. Knowledge of coherence transfer during long-RF pulses has special significance for the development of sophisticated multi-quantum NMR experiments especially multi-quantum MRI applications. 相似文献
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报道了一种热转印色带用黄染料的1H、13C NMR , 应用1H NMR、13C NMR、定量碳谱、DEPT、1H-1H COSY、HMQC、HMBC等确定了其在氘代氯仿中的分子结构, 并对全部谱峰进行了归属, 探索了黄染料在氘代氯仿中的结构对13C、1H NMR谱图化学位移及谱峰裂分的影响. 相似文献
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Hauch A Bildsøe H Jakobsen HJ Skibsted J 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2003,165(2):282-292
2H chemical shift anisotropies (CSAs) have been determined for the first time for polycrystalline samples employing 2H MAS NMR spectroscopy at high magnetic field strength (14.1 T). The 2H CSA is reflected as distinct asymmetries in the manifold of spinning sidebands (ssbs) observed for the two overlapping single-quantum transitions. Least-squares fitting to the manifold of ssbs allows determination of the 2H CSA parameters along with the quadrupole coupling parameters. This is demonstrated for KD2PO4, ND4D2PO4, KDSO4, KDCO3, alpha-(COOD)2, alpha-(COOD)2.2D2O, and boehmite (AlOOD) which exhibit 2H shift anisotropies in the range 13< or =deltasigma< or =27 ppm. For fixed values of the shift anisotropy and the 2H quadrupole coupling it is shown that the precision of the CSA parameters depends strongly on the asymmetry parameter (etaQ) for the quadrupole coupling tensor, giving the highest precision for etaQ approximately 0. The 2H CSA parameters (deltasigma and etasigma) are in good agreement with 1H CSA data reported in the literature for the corresponding protonated samples from 1H NMR spectra employing various homonuclear decoupling techniques. The determination of 2H quadrupole coupling parameters and 2H (1H) CSAs from the same 2H MAS NMR experiment may be particularly useful in studies of hydrogen bonding since the 2H quadrupole coupling constant and the CSA appear to characterize bond lengths in a hydrogen bond in a different manner. 相似文献
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1H NMR Detection of superparamagnetic nanoparticles at 1T using a microcoil and novel tuning circuit
Sillerud LO McDowell AF Adolphi NL Serda RE Adams DP Vasile MJ Alam TM 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2006,181(2):181-190
Magnetic beads containing superparamagnetic iron oxide nanoparticles (SPIONs) have been shown to measurably change the nuclear magnetic resonance (NMR) relaxation properties of nearby protons in aqueous solution at distances up to approximately 50 microm. Therefore, the NMR sensitivity for the in vitro detection of single cells or biomolecules labeled with magnetic beads will be maximized with microcoils of this dimension. We have constructed a prototype 550 microm diameter solenoidal microcoil using focused gallium ion milling of a gold/chromium layer. The NMR coil was brought to resonance by means of a novel auxiliary tuning circuit, and used to detect water with a spectral resolution of 2.5 Hz in a 1.04 T (44.2MHz) permanent magnet. The single-scan SNR for water was 137, for a 200 micros pi/2 pulse produced with an RF power of 0.25 mW. The nutation performance of the microcoil was sufficiently good so that the effects of magnetic beads on the relaxation characteristics of the surrounding water could be accurately measured. A solution of magnetic beads (Dynabeads MyOne Streptavidin) in deionized water at a concentration of 1000 beads per nL lowered the T(1) from 1.0 to 0.64 s and the T2 * from 110 to 0.91 ms. Lower concentrations (100 and 10 beads/nL) also resulted in measurable reductions in T2 *, suggesting that low-field, microcoil NMR detection using permanent magnets can serve as a high-sensitivity, miniaturizable detection mechanism for very low concentrations of magnetic beads in biological fluids. 相似文献
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Vignali C Caligiani A Palla G 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2007,187(1):120-125
An inexpensive external unit that allows the use of the commercial high-resolution NMR spectrometer for (2)H observation with an (1)H lock system is described. The external unit does not require any tuning, is extremely easy to use, and could be a cheaper and more straightforward alternative to the more expensive (19)F lock configuration. An application for the quantitative determination of the natural isotopic ratio (2)H/(1)H of ethanol and acetic acid is reported. 相似文献
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K. Fujiwara K. Ichinose H. Nagai A. Tsujimura 《Journal of magnetism and magnetic materials》1987,70(1-3):184-186
In the hydrides YMn2H3.0, the nuclear magnetic resonance of 1H nuclei has been measured under external fields up to 50 kOe at 4.2 K and three 1H NMR signals have been observed. The 1H hyperfine fields corresponding to these NMR signals can be discussed in terms of the dipole interaction between the H nuclei and the localized moments of the Mn(or Fe) atoms surrounding H atoms. 相似文献
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O.J. Zogal A.H. Vuorimäki E.E. Ylinen 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(2):201-207
2H NMR spectra and spin-lattice relaxation rates, R1 are measured as functions of temperature (4.2-310 K) for YD1.99 and YD1.99+0.04. In YD1.99 the measured temperature dependence of R1 is explained by the interaction of deuteron spins with conduction electrons and the value s-1 K-1 is obtained for the inverse Korringa product . Most of the spectral features in the “rigid” lattice regime are described by the dipolar interaction. No evidence of the
deuterium self-diffusion was observed in the measured temperature range. The low-temperature spectra in YD1.99+0.04 consisted of two components: a central line and a doublet characteristic for the quadrupole interaction. The central line
corresponds to zero electric field gradients (EFG) at the sites of the deuterons which have a surrounding with cubic symmetry
like in YD1.99. The doublet indicates a non-zero EFG which can be explained in terms of the presence of short-range ordered domains of the
hypothetical YD2.25 stoichiometry. Other possible interpretations of the spectra are also discussed. In the vicinity of 250 K both spectra and
R1 reflect the onset of the rapid motion of deuterium atoms. The linear dependence of R1 at low temperatures yields s-1 K-1.
Received 8 September 1998 相似文献
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Fojud Z Szcześniak E Jurga S Stapf S Kimmich R 《Solid state nuclear magnetic resonance》2004,25(1-3):200-206
Molecular dynamics in n-dodecylammonium chloride/water solutions for concentrations of 34 and 45 wt% was studied by 2H NMR and by 1H NMR dispersion of spin-lattice relaxation in the 2 kHz-90 MHz frequency range. The system exhibits a number of lyotropic liquid crystalline phases, which differ in symmetry and involve motions characterized by a wide frequency scale. The analysis of 2H NMR lineshapes of selectively deuterated DDACl molecules gave us an evidence for local trans-gauche conformational changes in the chains, whereas the dispersion of spin-lattice relaxation times T1 explored by fast field cycling method revealed fast local motions, translational diffusion and collective molecular dynamics of the chains. In particular, we have found that the order director fluctuation mechanism in smectic and nematic phases dominates spin-lattice relaxation below 1 MHz and that local motions and translational diffusion are responsible for the spin-lattice relaxation in the higher Larmor frequency range. 相似文献
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2H NMR测定了酒中氢同位素氘的分布。发现随水质不同氘含量将变化;且在亚基甲中氘含量变化幅度大。而由不同原料酿造的酒的氘含量的区别主要表现在甲基上的变化。因而获得用2H NMR监测化合物质量及探究生化机制有意义的方法。 相似文献
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Macdonald PM Crowell KJ Franzin CM Mitrakos P Semchyschyn D 《Solid state nuclear magnetic resonance》2000,16(1-2):21-36
2H NMR studies of polyelectrolyte-induced domain formation in lipid bilayer membranes are reviewed. The 2H NMR spectrum of choline-deuterated phosphatidylcholine (PC) reports on any and all sources of lipid bilayer surface charge, since these produce a conformation change in the choline head group of PC, manifest as a change in the 2H NMR quadrupolar splitting. In addition, homogeneous and inhomogeneous surface charge distributions are differentiated. Adding polyelectrolytes to lipid bilayers consisting of mixtures of oppositely charged and zwitterionic lipids produces 2H NMR spectra which are superpositions of two Pake sub-spectra: one corresponding to a polyelectrolyte-bound lipid population and the other to a polyelectrolyte-free lipid population. Quantitative analysis of the quadrupolar splittings and spectral intensities of the two sub-spectra indicate that the polyelectrolyte-bound populations is enriched with oppositely charged lipid, while the polyelectrolyte-free lipid population is correspondingly depleted. The same domain-segregation effect is produced whether cationic polyelectrolytes are added to anionic lipid bilayers or anionic polyelectrolytes are added to cationic lipid bilayers. The 2H NMR spectra permit a complete characterization of domain composition and size. The anion:cation ratio within the domains is always stoichiometric, as expected for a process driven by Coulombic interactions. The zwitterionic lipid content of the domains is always statistical, reflecting the systems tendency to minimize the entropic cost of demixing charged lipids into domains. Domain formation is observed even with rather short polyelectrolytes, suggesting that individual polyelectrolyte chains aggregate at the surface to form "superdomains". Overall, the polyelectrolyte bound at the lipid bilayer surface appears to lie flat along the surface and to be essentially immobilized through its multiple electrostatic contacts. 相似文献
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V. P. Tarasov Yu. B. Muravlev V. N. Fokin Yu. M Shul'ga 《Journal of Applied Spectroscopy》2003,70(2):315-318
Deuterofullerites C60D
x
have been studied by means of 2H NMR spectroscopy. It has been established that there are two types of carbon–deuterium bindings in the samples under study: tip C–D with quadrupole constant coupling (QCC) 171 kHz and bridge –C...D...C– with QCC 56 kHz. It is possible that the latter bond is a result of the rigidity of the lattice, which is unusual for fullerene compounds. 相似文献
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G.V. Lecomte N.S. VanderVen S.A. Friedberg 《Journal of Physics and Chemistry of Solids》1981,42(12):1087-1089
Previous studies have shown that NiZrF6.6H2O can be described by an axial spin Hamiltonian with parameters g = 2.33 and , and exhibits ferromagnetic ordering at Tc = 164mK. Our room temperature X-ray measurements confirm that NiZrF6·.6H2O is isomorphous with NiSnCl6·.6H2O and give lattice parameters of and α = 96°09′. Proton NMR measurements show that there exist important molecular motions at room temperature and that the space group remains down to liquid helium temperatures. The positions of all twelve protons have been determined and are found to lie on a sphere of radius 2.9 Å centered on the nickel ion. 相似文献
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The free-electron laser FLASH at DESY in Hamburg, Germany, has been extended by a second undulator line in a separate tunnel and a new experimental hall (Figure 1). The existing undulator line, called FLASH1, and the new one, which includes provisions for external seeding to be realized later, called FLASH2, both use the same linear accelerator. They are operated in tandem by separating the pulse train into two sections, which are then directed to the different undulators. The linac energy is determined by the needs of the experiments at FLASH1, whereas the wavelength at FLASH2 can be varied in the limits of the tuning range of the undulators. 相似文献
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Rossi C Boss A Haap M Martirosian P Claussen CD Schick F 《Magnetic resonance imaging》2009,27(4):489-496
This study investigated the feasibility of an MRI protocol providing whole-body T2* maps at 1.5 T. Seven healthy volunteers (mean age=30.1+/-3.7, three women and four men) and two patients (both male, 53 and 46 years old) affected by transfusion-dependent anemias participated in the study. Coronally oriented images of five subsequent body levels were acquired using a fat-suppressed multiecho 2D gradient-echo sequence (12 echo times ranging from 4.8 to 76.3 ms were selected) and afterwards composed. Parametrical T2* maps of the whole body were reconstructed on a pixel-by-pixel basis. For both, healthy volunteers and patients, representative T2* values were computed from extended regions of interest (ROIs). Good-quality whole-body T2* maps were computed in all volunteers and patients. In healthy volunteers, T2* values were assessed in the cerebral white (58.5+/-4.2 ms) and gray (81.4+/-5.5 ms) matter, liver (34.3+/-7.0 ms), spleen (63.5+/-3.3 ms), kidneys (65.4+/-10.3 ms) and skeletal muscles (~30 ms). The liver presented faster relaxation rates in males as compared to females. One patient (serum ferritin concentration=927 microg/dl) showed shortened T2* values in liver (3.6+/-5.5 ms), spleen (3.1+/-4.8 ms), kidneys (11.1+/-7.1 ms) and muscles (25.1+/-3.4 ms). The second patient (serum ferritin concentration=346 microg/dl) presented reduced T2* values in liver (3.9+/-7.3 ms), spleen (20.1+/-9.8 ms) and kidneys (24.6+/-7.7 ms). The presented technique may find clinical application in the assessment of the iron burden in the entire body, and in monitoring of chelation therapies in patients treated with frequent blood transfusions. 相似文献