Distinguishing between COOH, COO- , and hydrogen disordered COOH sites in solids with 13 C chemical shift anisotropy and T1 measurements

Ryan Toomey; Jacob Powell; Jacob Cheever; James K Harper

doi:10.1002/mrc.5425

Distinguishing between COOH, COO^- , and hydrogen disordered COOH sites in solids with ¹³ C chemical shift anisotropy and T₁ measurements

Magn Reson Chem. 2024 Mar;62(3):190-197. doi: 10.1002/mrc.5425. Epub 2024 Jan 18.

Authors

Ryan Toomey¹, Jacob Powell², Jacob Cheever¹, James K Harper¹

Affiliations

¹ Department of Chemistry and Biochemistry, Brigham Young University, Provo, Utah, USA.
² Department of Chemistry, Drexel University, Philadelphia, Pennsylvania, USA.

PMID: 38237932
DOI: 10.1002/mrc.5425

Abstract

Since 1993, it has been known that ¹³ C chemical shift tensor (i.e., δ₁₁ , δ₂₂ , and δ₃₃ ) provides information sufficient to distinguish between COOH and COO^- sites. Herein, four previously unreported metrics are proposed for differentiating COOH/COO^- moieties. A new relationship is also introduced that correlates the asymmetry (i.e., δ₁₁ -δ₂₂ ) of COOH sites to the proximity of hydrogen bond donating partners within 2.6 Å with high accuracy (±0.05 Å). Conversely, a limitation to all proposed metrics is that they fail to distinguish between COO^- and hydrogen disordered COOH sites. To reconcile this omission, a new approach is proposed based on T₁ measurements of both ¹ H and ¹³ C. The ¹³ C T₁ values are particularly sensitive with the T₁ for hydrogen disordered COOH moieties found to be nearly six times smaller than T₁ 's from COO^- sites.

Keywords: COOH; T1 relaxation; chemical shift anisotropy; hydrogen disorder.