C1 Introduction

Rapid random molecular motion in liquids usually averages chemical shift anisotropics and J couplings in NMR to discrete isotropic values. Dipolar and quadrupolar interactions are averaged nearly to zero, leaving finite linewidths in solutions that are caused mainly by the inhomogeneity

Figure 8.9 Influence of protein concentration the 'H NMR transverse relaxation rates for dispersions of soybean protein in D20 at 22°C and, in ascending order, pH 4.5, 7.0, 9.1, and 11.0. Solid lines are the best fits to eq. (8.11), after tests with different numbers of parameters. The best fits were obtained using parameters Rm,0, nH, Cp, and B„ for pH 4.5-9.1, and parameters S„,o, nH, Cp, B2. and B0 for pH 11. (Reprinted with permission from [13], copyright by the American Chemical Society.)

Protein Concentration (g/mL)

Figure 8.9 Influence of protein concentration the 'H NMR transverse relaxation rates for dispersions of soybean protein in D20 at 22°C and, in ascending order, pH 4.5, 7.0, 9.1, and 11.0. Solid lines are the best fits to eq. (8.11), after tests with different numbers of parameters. The best fits were obtained using parameters Rm,0, nH, Cp, and B„ for pH 4.5-9.1, and parameters S„,o, nH, Cp, B2. and B0 for pH 11. (Reprinted with permission from [13], copyright by the American Chemical Society.)

of the magnetic field. For samples in the solid state, all of these anisotropic interactions are manifested, to the detriment of the NMR signals.

With the development of cross polarization/magic angle spinning (CP/ MAS) experiments and high-powered decoupling, solid state NMR has become an important technique for characterizing the bulk structures of solids [14, 15], Magic angle spinning simulates motional averaging for the solid, and high-power decoupling minimizes dipolar interactions. Using cross-polarization, a gain in sensitivity for dilute nuclear spin systems such as 13C is achieved via dipolar coupling to the abundant 'H spin system.

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