Solid State H NMR

The phenyl ring motion for peptides and various synthetic polymers have been studied with the solid state H NMR by many workers, undergoing a 180° flipping motion in a two-fold potential. The reported activation energies of the flipping motion reflect the degree of crystallinity, the crystal... 

In general, multiple pulse techniques sufficiently average the dipolar interactions, compress the chemical shift scale, but they do not affect heteronuclear dipolar interactions and the chemical shift anisotropy. A combination of both multiple pulse techniques and magic angle spinning, so-called CRAMPS (Combined Rotational And Multiple Pulse Spectroscopy) is found to yield satisfactory results in the solid state H NMR of solids 186). The limitations of all these techniques, from the analytical point of view, arises from the relatively small chemical shift range (about 10 ppm) as compared with some other frequently studied nuclei. However, high resolution H NMR of solids is useful in studies of molecular dynamics. 

Table I. Solid State H NMR Chemical Shifts of Imidazoles and Hydrogen Bonding Distances in Crystals...

By means of solid-state H-NMR spectroscopy, the open-chain structure of 2-(2-iV-methylaminoethyl)-3-nitrobenzaldoxime (73A) was corroborated (84CB702). In (CD3)2SO solution, the equilibrium 73A 73B was detected (Kt = 0.54, H-NMR). 

The heteropolyanion stabilizes protonated intermediates by coordination in solution and the pseudoliquid phase as well as on the surface, thus lowering the activation energy and accelerating reactions. Several protonated intermediates including the protonated ethanol dimer and monomer [18], the protonated pyridine dimer [12, 19], and protonated methanol [20] have been detected in the pseudoliquid phase directly by use of X-ray diffraction (XRD), IR or solid-state NMR. In solid-state H NMR, the chemical shift for the protonated ethanol dimer, (C2HsOH)2H+ is 9.5 ppm down-field from tetramethylsilane, which lies in the range of supcracids reported by Olah et al. [18]. This fact also supports the strong acidity of heteropolyacids. 

Acid sites of AgjPW C are generated upon the reduction with hydrogen at 573 K [40,42], After the reduction, the catalytic activity (for example, for o-xylene isomerization) develops. The generation of acid sites has been confirmed by pyridine adsorption and solid state H NMR [42]. 

For the partially deuterated benzoic acid (C6D5COOH), the solid state H NMR spectrum is dominated by the intra-dimer H- H dipole-dipole interaction. In a single crystal, both tautomers A and B are characterised by a well-defined interproton vector with respect to the direction of the magnetic field (Fig. 1). Proton motion modulates the H- H dipole-dipole interactions, which in turn affects the H NMR lineshape and the spin-lattice relaxation time. It has been shown that spin-lattice relaxation times are sensitive to the proton dynamics over the temperature range from 10 K to 300 K, and at low temperatures incoherent quantum tunnelling characterises the proton dynamics. A dipolar splitting of about 16 kHz is observed at 20 K. From the orientation dependence of the dipolar splitting, the... 

However, preparation of partially or fully deuterated materials may not always be feasible and single crystal samples are not always available. Hence, techniques have been developed that allow high-resolution solid state H NMR spectra to be recorded for powder samples without any isotope enrichment. Homonuclear H dipole-dipole interactions are typically of the order of 50 kHz leading to very broad spectra as discussed above. In order to alleviate the effects of the homonuclear dipole-dipole interactions and obtain a H NMR spectrum that... 

With A = Rb and Cs, compounds of the type A2[PH] can be prepared containing an isolated hydrogenphosphide anion [PH] , which could also be named for example, as dicesiumphosphanide(l), when starting from phosphane(3). The orientation of the PH unit could not be determined by X-ray analysis, but its existence has been proven by solid-state H-NMR. The metal phosphide Ti3P forms hydrides or deuterides up to a maximum content of 2.6 H (D). The exact crystal structure depends on the H (D) content and the temperature. We note, that exact reliable studies of compounds M/P/H are very rare. 

Bronsted acid sites can be directly probed through solid-state H NMR spectroscopy, as chemical shifts can be correlated with acid strength [195, 197, 198]. The precise chemical shift observed for any given Bronsted acid site is dependent on the material upon which it is located. For instance, on silica values of 1.6ppm are typically observed zirconia has two distinct OH sites, at 2.4 and 4.8ppm while on alumina a typical range may be -0.2 to 4.3 ppm. Early studies employing H NMR to study Bronsted acid sites focused on the characterization of the surface of amorphous silica-alumina materials [165, 199-201]. Extensive work, however. 

Magic Angle Spinning (MAS) Nuclear Magnetic Resonance (NMR) also had some success in determining proton positions. Side-band analysis from solid-state H NMR was used to determine proton positions [19, 20] in ZSM-5 type zeolites. 

Yoshioka, S. Aso, Y. Kojima, S. Determination of molecular mobility of lyophilized bovine serum albumin and (y-globulin by solid-state H NMR and relation to aggregation-susceptibility). Pharm. Res. 1996, 13, 926-930. 

First direct evidence was reported of QEC between two deuterons in a selectively deuterated dihydrogen ruthenium complex 1 (Fig. 3). It was obtained from solid-state H NMR spectra measured for a polycrystalline sample of 1 in the temperature range... 

This article establishes the processing-microstructure-motion-property relationship of high-speed melt-spun nylon-6 fibers. Solid-state H NMR Tip relaxation studies were used to study the structure. 

Brzustowicz MR, Stillwell W, Wassail SR. Molecular organization of cholesterol in polyunsaturated membranes a solid state H NMR investigation. FEBS Lett 1999 451 197-202. 

History of high-resolution solid-state H NMR Features of H CRAMPS NMR Adjustment for H CRAMPS measurements Experimental determination of scaling factor of BR-24 Measurement conditions of H CRAMPS NMR Confirmation of modulation... 

As established by Zilm and coworkers, solid state H NMR is very effective in accurately determining d H because the measurement is unaffected by rotational or other motion of the bound H2 [55]. Only a small amount of solid in powder form is required to observe the signals using broad-line techniques (Fig. 

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