Solid-state Nuclear Magnetic Resonance (NMR) Spectroscopy

Solid-state nuclear magnetic resonance (NMR) spectroscopy is a technique that uses NMR spectroscopy to provide atomic-level information for solid and semi-solid materials. It is a nondestructive, multinuclear technique that can probe the chemical environment of specific nuclei within a molecule. In addition, it is a quantitative technique that can be used in conjunction with other solid-state techniques such as thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), optical microscopy, infrared (IR) and Raman spectroscopy, and x-ray diffraction techniques (single crystal and powder) ^[1]. Over the past decade or so, the technology has made tremendous strides thanks to huge advances in hardware (such as increasing magnetic field strength) and software (such as improvements in computational simulations and analysis packages).

Today, solid-state NMR spectroscopy will no longer be an alternative and complementary method, but become an independent and often the main tool for elucidating structural, dynamic and other information about materials. Alfa Chemistry believes that the development of solid-state NMR spectroscopy will continue due to the increasing requirements of applications and the growing need for more detailed information on chemical structure and reactivity.

Essential Techniques

The most obvious difference between NMR spectroscopy of solids and liquids is that solids typically produce broader peaks. This difference is largely due to the strong dipole coupling interaction and chemical shift anisotropy (CSA) in solids ^[1]. This has led to a large and continuing effort to improve the sensitivity and resolution of solid-state NMR spectra by averaging or eliminating the anisotropic component of the interactions present. Several essential techniques have emerged for solving the above mentioned problems. Specific as follows.

• Magic angle spinning

Magic angle spinning is one of the most powerful methods used in solid-state NMR spectroscopy to obtain high-resolution NMR spectra. The rapid rotation of the specimen around the axis with a magic angle of 54°44′ to the direction of the applied magnetic field can eliminate many broadening sources of the solid-state NMR spectroscopy and make more refined features appear.

• Cross-polarization

The cross-polarization technique in solid-state NMR spectroscopy is a technique in which polarization from abundant spins is transferred to dilute spins to enhance signal-to-noise ratio ^[2]. It is also used to reduce or eliminate the line broadening observed in solid-state NMR spectroscopy.

• Decoupling

Spin interactions can be removed (decoupled) to improve the resolution of NMR spectra during detection, or to extend the lifetime of nuclear magnetization.

Applications

Solid-state NMR spectroscopy has a wide range of applications in different fields. Its main applications are described below.

Material Science

Solid-state NMR spectroscopy is extensively used for the characterization of various materials such as polymers, ceramics, glasses, and metals.

Pharmaceuticals

Solid-state NMR spectroscopy is used in the pharmaceutical field for the characterization of drug formulations, identification of drug polymorphs, and the study of drug interactions with target molecules.

Geochemistry

Solid-state NMR spectroscopy is used to study the structure and composition of minerals, rocks, and soils.

Catalysis

Solid-state NMR spectroscopy is used to study the structure and dynamics of catalysts, helping to improve their performance in chemical reactions.

Structural Biology

Solid-state NMR spectroscopy is used to study the structure and dynamics of biological macromolecules such as proteins, nucleic acids, and membrane proteins.

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References

1. Tishmack, P. A.; et al. Solid-state nuclear magnetic resonance spectroscopy-pharmaceutical applications. Journal of pharmaceutical sciences. 2003, 92(3): 441-474.
2. Singh, S. S.; et al. Spectroscopy, microscopy, and other techniques for characterization of bacterial nanocellulose and comparison with plant-derived nanocellulose. Microbial and Natural Macromolecules. 2021: 419-454.

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