AI Article Synopsis

  • - The text discusses a new theoretical method for understanding multiple-quantum excitation and mixing in nuclear magnetic resonance (NMR) specifically for half-integer quadrupolar nuclei, simplifying the complex behavior into more manageable curves using scaling techniques.
  • - It introduces an efficient algorithm that simulates the multiple-quantum magic-angle-spinning (MQ-MAS) spectra, allowing for variable radio frequency (RF) field strengths, pulse durations, and spinning rates, while focusing on static limit approximations.
  • - Additionally, the paper highlights strategies to reduce experimental errors and enhance the accuracy of analyzing MQ-MAS spectra by optimizing RF field strength and pulse durations, as well as improving least-squares analysis through affine transformations.

Article Abstract

A simplified theoretical description of multiple-quantum excitation and mixing for nuclear magnetic resonance of half-integer quadrupolar nuclei is presented. The approach recasts the multiple-quantum nutation behavior in terms of reduced excitation and mixing curves through a scaling of the first-order offset frequency by the quadrupolar coupling constant. The two-dimensional correlation of the static first-order anisotropic line shape to the second-order anisotropic magic-angle-spinning (MAS) line shape is utilized to transform the three-dimensional integral over the three Euler angles into a single integral over the dimensionless first-order offset parameter. These transformations lead to a highly efficient algorithm for simulating the multiple-quantum (MQ)-MAS spectrum for arbitrary excitation and mixing radio frequency (RF) field strengths, pulse durations, and MAS rates within the static limit approximation, which is defined in terms of the rotation period, pulse duration, RF field strength, and quadrupolar coupling parameters. This algorithm enables a more accurate determination of the relative site populations and quadrupolar coupling parameters in a least-squares analysis of MQ-MAS spectra. Furthermore, this article examines practical considerations for eliminating experimental artifacts and employing affine transformations to improve least-squares analyses of MQ-MAS spectra. The optimum ratio of RF field strength to the quadrupolar coupling constant and the corresponding pulse durations that maximize sensitivity within experimental constraints are also examined.

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http://dx.doi.org/10.1063/5.0240970DOI Listing

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