Solid-state NMR measurement

Figure 13 Model of statherin on the HAp surface based on solid-state NMR measurements. (Reprinted with permission from Ref. 125. 2010 Elsevier.)...

By comparison, a saturated methine carbon (C-H) has a CSA of only 25 ppm because the mobility of electrons around the carbon nucleus is much less in an sp3-hybridized carbon and depends much less on the orientation of the C-H bond with respect to B0. In solution-state NMR we only see the isotropic chemical shift, < iso, and the fixed-position chemical shifts and the CSA value are obtained from solid-state NMR measurements. Although CSA does not affect chemical shifts in solution, it does contribute to NMR relaxation and can be exploited to sharpen peaks of large molecules such as proteins in solution. For large molecules, such as proteins, nucleic acids, and polymers, or in viscous solutions, molecular tumbling is slow and CSA broadens NMR lines due to incomplete averaging of the three principle chemical shift values on the NMR timescale. Like isotropic chemical shifts, CSA in parts per million is independent of magnetic field strength B0 but is proportional to B0 when expressed in hertz. Because linewidths are measured in... 

So far, most of the quantum-chemical computations of solid compounds have assumed a free molecular model that is the intermolecular effects are initially not considered. Although these second-order effects are minor in many cases and do not cause much disagreement with solid-state NMR measurements, they might become significant and should not be neglected. Recently a series of publications has addressed this problem, based on a supercell technique.38-41 The appealing feature of this new method is that it can deal not only with free molecules but also with crystals, amorphous materials or materials with defects. 

T. Melchior and C. F. Pictroski for solid state nmr measurements, A. J. Jacobson for helpful discussions, and L. B. McKusker for providing a version of and interfaces to G. S. Pawley s allhkl program [53]. 

The structural features of dealuminated zeolite samples were characterized using X-ray powder diffraction, porosimetry and solid-state NMR measurements. Hexadecane cracking was used as a probe reaction to investigate catalytic properties of pure zeolites. 

Coal, Soil Organic Matter and Other Related Materials. - 5.5.1 Coals and Carbonaceous Materials. C - The extract from carbon disulfide/AT-methyl-2-pyrrolidinone mixed solvent extraction of Upper Freeport coal at room temperature has been fractionated with acetone and pyridine into three fractions, and solid-state NMR measurements of these fractions have been measured. 

H, C, N - Since the prediction of the potential extraordinary mechanical properties of crystalline P-C3N4, many authors have attempted its synthesis. To aid this H, C and N solid-state NMR measurements for the determination of the bonding types in amorphous CN films are given. ... 

The H chemical shift moves downfield (in some cases up to 20 ppm), and A- -X distance versus shift correlations have been established, based on H solid-state NMR measurements and geometries from neutron crystal structures. These correlations have also been successfully applied to hydrogen bonds in the liquid state [43]. The shift is also known to be proportional to the number of hydrogen bonds [21]. 

Table 21.4. spin-lattice relaxation times (T) in s) of PHB, PPL and P(3HB-co-3HP) on the assumption of a biexponential decay obtained by 67.9 MHz high-resolution solid-state NMR measurements... 

NMR spectroscopy probes atomic environments based on the different resonance frequencies exhibited by nuclei in a strong magnetic field. Many different nuclei are observable by the NMR technique, but those of hydrogen and carbon atoms are most frequently studied. NMR spectroscopy of solutions is commonly used for structure elucidation. However, solid-state NMR measurements are extremely useful for characterizing the crystal forms of pharmaceutical solids. 

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