In a previous article (Concepts Magn Reson 22A(1) 37-49 (2004)), the initial setup of the C-13 CP/MAS experiment was described. The advantages of the experiment over direct C-13 excitation were also given. In this article, the experiment is applied to three polymorphic structures of glycine. Temperature calibration of the experiment to investigate molecular dynamics as a function of temperature is also described. Though the C-13 CP/MAS experiment is widely applicable, it cannot be universally used. The C-13 CP/MAS experiment works at ambient temperature for both the alpha and gamma polymorphic structures of glycine. However, the cross-polarization technique fails to provide a signal at low temperature from either polymorph. The failure of the technique for both polymorphs arises from the shortened H-1 T-1rho at low temperatures. This shortened T-1rho results from the hindered rotation of the -NH3 group. The technique even fails at ambient temperature for beta-glycine. Again, the reason is a shortened H-1 T-1rho. (C) 2004 Wiley Periodicals, Inc.

The C-13 cross-polarization (CP) technique combined with magic angle spinning (MAS) has become one of the more commonly performed solid-state nuclear magnetic resonance (NMR) experiments. The basics of initially setting up the experiment are given and used to illustrate such NMR phenomena as rotational echoes, homogeneous and inhomogeneous interactions, continuous wave H-1 decoupling, and coupling of quadrupolar N-14 nuclei to C-13 nuclei. The polarization transfer from the protons to the carbons is described briefly with the usual thermodynamic and quantum mechanical models. The setup and use of the experiment for routine analyses are discussed. (C) 2004 Wiley Periodicals, Inc.

Proton NMR spin-lattice relaxation times in the laboratory frame (T1) and in the rotating frame (T1ρ) were measured as a function of temperature for a static sample of α-glycine. Both T1 and T1ρ data can be fit quantitatively by a single thermally-activated motion (the modulation of the dipolar coupling by random hopping about the threefold axis of the -NH3 group), with no addition of other mechanisms at any temperature between 173 K and 415 K. An activation energy of 21.7 ± 1 kJ/mol was extracted and is compared with previously reported values for both α- and γ-glycine. Such comparisons allow the correction of glycine polymorphs misidentified in the literature. The minimum in T1 at 325 K corresponds to a correlation time of 0.53 ns. Chemical shifts as a function of temperature were measured by 1H CRAMPS and by 13C and 15N CP/MAS experiments. These results are discussed relative to a previous report of anomalous electrical behavior in α-glycine within this temperature range.

The principal elements of the 199Hg chemical-shift (CS) tensors of the mercuric halides (HgX2, X = F, Cl, Br, and I) and the mercurous halides (Hg2X2, X = F and Cl) were determined from spectra of static polycrystalline powders and from magic-angle spinning (MAS) spectra. The CS tensors of both HgCl2 and Hg2Cl2 are axially symmetric (η = 0) within experimental error, differing from literature reports of η=0.12 and η=0.14, respectively. The principal elements of the axially symmetric CS tensor in HgBr2 were also measured using a static sample, and the wideline spectra of HgF2 and HgI2 (red polymorph) give chemical-shift tensors that suggest, within experimental error, that the mercury sits in sites of cubic symmetry. The 199Hg CS tensor for Hg2F2 is asymmetric. Experiments with static polycrystalline samples may allow the determination of the elements of the 199Hg CS tensors even when MAS fails to completely average the dipolar coupling of the spin-½ 199Hg and the quadrupolar halide nucleus.

We observe non-monotonic development of the 13C magnetization in polycrystalline samples of glycine, sucrose, and adamantine during cross-polarization. We demonstrate, by fitting the time dependence, that the development quantitatively results from dipolar oscillations. To fit the data quantitatively requires one to assume two types of spin-diffusion behavior.

19F and 199Hg high-resolution solution NMR spectra were acquired for cyclic trimeric perfluoro-ortho-phenylenemercury. Even with the high superconducting magnetic fields currently available, the 19F spectrum was not interpretable with a simple first-order analysis. Spectroscopic parameters for chemical shift and scalar coupling interactions in the NMR spectra were extracted from four- and five-spin simulations. Differential line widths in the 19F spectrum result from scalar coupling to the 199Hg.

The scientific literature contains reports of external magnetic fields affecting the fundamental properties and structure of water, including a report of the rotational motion of water molecules being slowed due to increased hydrogen bonding resulting from magnetic treatment. To investigate such a change in molecular motion, 1H spin-lattice relaxation times of water were measured at increasing magnetic field strengths. Strong radiation damping was observed at each magnetic field strength when using inversion-recovery experiments. To measure the relaxation times in the presence of radiation damping, several experimental methods of saturation recovery to measure spin-lattice relaxation were applied to a 90% H2O sample to obtain results as a function of field strength for proton frequencies from 300 to 800 MHz.

Mobility in γ-glycine can be measured by proton relaxation or line-shape analysis of wide-line 2H spectra of deuterium-substituted γ-glycine. The temperature dependence of the wide-line 2H spectra indicates an activation energy of 33 +/- 2 kJ/mol, in agreement with the activation energy extracted from proton spin-lattice relaxation times. The proton spin-lattice relaxation time of the protons in partially deuterated γ-glycine is 78 sec, much longer than the 4-s T1 of the undeuterated material. The comparison demonstrates how effectively the amine protons act as a relaxation sink.

Proton NMR spin-lattice relaxation times T1 were measured for urea as a function of temperature. An activation energy of 46.3 ± 4.7 kJ/mol was extracted and compared with the range of 38-65 kJ/mol previously reported in the literature as measured by different magnetic resonance techniques. In addition, proton NMR spin-lattice relaxation times in the rotating frame T1ρ were measured as a function of temperature. These measurements provide acquisition conditions for the 13C and 15N CP/MAS spectra of pure urea in the crystalline phase.

The 199Hg chemical-shift tensor of solid HgCl2 was determined from spectra of polycrystalline materials, using static and magic-angle spinning (MAS) techniques at multiple spinning frequencies and field strengths. The chemical-shift tensor of solid HgCl2 is axially symmetric (η = 0) within experimental error. The 199Hg chemical-shift anisotropy (CSA) of HgCl2 in a frozen solution in dimethylsulfoxide (DMSO) is significantly smaller than that of the solid, implying that the local electronic structure in the solid is different from that of the material in solution. The experimental chemical-shift results (solution and solid-state) are compared with those predicted by density functional theory (DFT) calculations using the zeroth-order regular approximation (ZORA) to account for relativistic effects.

199Hg spin-lattice relaxation of HgCl2 dissolved in DMSO is dominated by a CSA mechanism, but a second contribution to relaxation arises from ligand exchange. Relaxation in the solid state is independent of temperature, suggesting relaxation by paramagnetic impurities or defects.