2H MAS NMR

Fig. 6 (a) SQ and (b) DQ rotor-synchronized 2H MAS NMR spectra of sodium tetrathionate dihydrate-d4 (solid lines). The dashed line in (a) represents the exact numerical simulation of the SQ spectrum for random molecular motion with the rate constant k given in the figure, (c) The corresponding experimental and simulated static 2H quadrupolar-echo spectra, (d) Simulated SQ (solid line) and DQ (dashed line) linewidths as functions of k. (Reproduced with permission from [88])... 

Fig. 2. Theoretical 2H MAS NMR spectra calculated with quadrupolar coupling constant Cq = 200 kHz, asymmetry parameter r Q = 0.10, rotation frequency = 5.0 kHz (left) and uT = 10.0 kHz (right). The spectra represent (a) ideal RF irradiation conditions with RF field strength i/Rf = 100 kHz and optimum pulse length Tp = 2.25 fis, and (b, c) nonideal RF irradiation conditions with i rf = 25 kHz and tp = 4.25 fjbs. The phase distortion effects are illustrated in (b), while (c) demonstrates the result of performing a first-order phase correction. (Adapted from Kristensen et alP with permission.)...

Figure 5 11B MAS NMR spectra (a) pristine phenyl modified elastomer (b) heated at 480°C for 2 h (c) heated at 580°C for 2h (d) after 1 MGy gamma exposure. ( represents spinning sidebands.)...

Solid state 2H NMR parameters are almost exclusively governed by the quadrupole interaction with the electric field gradient (EFG) tensor at the deuteron site.1 8 The EFG is entirely intramolecular in nature. Thus molecular order and mobility are monitored through the orientation of individual C-2H bond directions. Therefore, 2H NMR is a powerful technique for studying local molecular motions. It enables us to discriminate different types of motions and their correlation times over a wide frequency range. Dynamics of numerous polymers has been examined by solid state 2H NMR.1 3,7,9 Dynamic information on polypeptides by NMR is however limited,10 26 although the main-chain secondary structures of polypeptides in the solid have been extensively evaluated by 13C and 15N CP/MAS NMR.27,28... 

As an example. Fig. 18 shows CP/MAS NMR spectra recorded during the investigation of surface ethoxy species (7S) formed on acidic zeolite HY ( si/ Ai = 2.7) by a SF protocol. Figure 18a shows the CP/MAS NMR spectrum recorded after a continuous injection of C-1-enriched ethanol, CHI CHzOH, into the MAS NMR rotor reactor containing calcined zeolite HY. The ethanol was injected at room temperature for 10 min. Subsequently, the loaded zeolite was purged with dry nitrogen (200 mL/min) at room temperature for 2h. 

Fig. 33. Y HPDEC/MAS NMR (left) and CP/MAS NMR (right) spectra of zeolite HY (na/ Wai = 2.7) recorded during the formation of methoxy species (56.2 ppm) at various temperatures. The spectra were obtained after a continuous injection of C-enriched methanol into the MAS NMR rotor reactor at room temperature for 20 min (a) and after a subsequent purging with dry nitrogen (200 mL/ min) at 298 K (b), 373 K (c), 413 K (d), 433 K (e), 453 K (1), and 473 K (g). The temperature treatments were performed for 2h at each step. Asterisks denote spinning sidebands. Reproduced with permission from (262). Copyright 2003 Elsevier Science.

Fig. 37. C CF MAS NMR (left) and UV/Vis (right) spectra of a dealuminated zeolite HZSM-5 recorded during conversion of ( -enriched methanol (W/F = 25gh/mol) at 413 K for 2h (a), during a subsequent conversion of T l U = T l U (W/F = 10 g h/mol) at 413 K for 1 h (b), and during conversion of V H2 = V H2 (W/F= 10 g h/mol) at 413 K on a fresh catalyst for 2 h (c). Asterisks denote spinning sidebands. The narrow peaks at ca. 500 nm in UV spectra were caused by the equipment. Reproduced with permission from 168). Copyright 2004 The Royal Society of Chemistry.

Sepiolite clay (<100 mesh) was heated in air at 120°C in order to remove the zeolitic and surface bound water molecules. The partially dehydrated clay mineral was subsequently exposed to acetone vapor at room temperature for a period of four days. H and 29Si CP MAS-NMR experiments revealed that the acetone molecules penetrated into the microporous channels of the sepiolite structure. Broad line 2H NMR studies using acetone-d6 revealed that, in addition to fast methyl group rotations, the guest acetone-d6 molecules were also undergoing 2-fold re-orientations about the carbonyl bond. The presence of acetone-d6 molecules adsorbed on the exterior surfaces of the sepiolite crystals was also detected at room temperature. 

The broad line 2H NMR results, combined with the H and 29Si MAS-NMR results, confirm that acetone-d6 molecules are able to penetrate into the microporous channels of sepiolite, and cannot be removed by heating to only 60°C. This result is in agreement with a previous study that found, on the basis of BET surface area measurements, that molecules such water, ammonia, ethanol, benzene and pyridine were small enough to fit inside the microporous channels [10],... 

The potential of other nuclei for the study of surfaces is yet to be explored. Gottlieb and Luz (388) measured 2H spectra of a number of perdeuterated molecules adsorbed on active alumina and interpreted the results in terms of quadrupolar tensors. Yesinowski and Mobley (369) have shown that 19F MAS NMR can provide useful information about fluorinated surfaces of calcium hydroxyapatite, Cas(0H)(P04)3. In particular, l9F, 2H, and H MAS NMR may become powerful techniques for the study of interface systems in general. 

This work foreshadows one way in which mechanistic studies of conventional (heterogeneous) and biological catalysts may proceed in future. When one recognizes that parallel H and 2H CP/MAS NMR studies could also be carried out in situ, there are good prospects that kinetic isotope effects will prove directly accessible through the agency of high-resolution solid-state NMR. 

We have characterized (8e-i) this intermediate using solid-state 13C CP/MAS NMR, 2H NMR, and two dimensional (2D). /-resolved 3C NMR spectroscopy in the course of dehydration of isobutyl alcohol and /er/-butyl alcohol in HZSM-... 

Structure identification, quantifying relative cage occupancies. 1II NMR has been used for ethane, propane, and isobutane hydrates (Davidson et al., 1977 Garg et al., 1977), while 2H, 19F, 31P, and 77 Se NMR have been used for several si guests (Collins et al., 1990). 13C cross-polarization and magic angle spinning (MAS) NMR techniques have been applied to study hydrates of carbon dioxide, methane, and propane (Ripmeester and Ratcliffe, 1988, 1999 Wilson et al., 2002 Kini et al., 2004). 

Figure 9.8 13 C CP MAS NMR spectra of dry treated APTS-modified silica (a) 2h, 383K air precured (b) 423K vacuum cured.

Fig. 2. Calculated 2H NMR spectra for the situation illustrated in Fig. 1, where nuclei can move between potential wells and diffuse under the governing potential within wells, (a) 2H MAS spectra, (b) Static 2H spectra. The spectra are calculated as a function of D, the diffusion coefficient and Efi, the potential barrier between wells. Spectra are taken from reference 6.

A systematic investigation of the application of Lie algebra to NMR was presented.29 The symmetry properties of the nuclear spin systems were naturally included in selection of the sets of the basis operators. With this theoretical framework, the existing sets of basis operators used for various specific purposes can be treated in a unified manner and their respective advantages and disadvantages can be evaluated. A number of 2H MAS spectra calculated on the basis of that theoretical framework are shown in Fig. 2. The... 

N MAS-NMR spectra, with 23Na-15N and 27A1-15N TRAPDOR and - N CP/MAS-NMR experiments, gave details on NH3 binding sites on 3A zeolite molecular sieves, and dynamics between two primary adsorbed NH3 environments.653 2H and 13C solid-state MAS-NMR data were used to follow the dynamics of deuteriated p-nitroaniline molecules in zeolite ZSM-5 pores.654,655 ll and 13C CP/MAS-NMR spectra were able to probe host-guest interactions between Me3N+(CH2)nN+Me3 (where n = 3 = 10) and zeolites.656... 

Fig. 24. Calculated 2H quadrupole echo and MAS NMR spectra for a two-site reorientation35 such that the 2H quadrupole coupling tensor unique principal axis moves through 106°, i.e. the motion appropriate for the two-site motion of the methyl groups in deuterated DMS. The simulations assume an inhomogeneous symmetric log-Gaussian distribution of correlation times with a mean correlation time of 5 x 10 5s and a standard deviation ranging from 0 to 3 decades, (a) Quadrupole echo spectra with echo delay time t = 30 /is. (b) MAS spectra.

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