Solid-State 17O NMR Studies of Sulfonate Jump Dynamics in Crystalline Sulfonic Acids: Insights into the Hydrogen Bonding Effect.

Abstract

We report variable-temperature (VT) 17O solid-state nuclear magnetic resonance (NMR) spectra for three crystalline sulfonic acids: l-cysteic acid monohydrate (CA), 3-pyridinesulfonic acid (PSA), and p-toluenesulfonic acid monohydrate (TSA). We were able to analyze the experimental VT 17O NMR spectra to obtain the activation barriers for SO3- jumps in these systems. Using the density functional-based tight-binding (DFTB) method, we performed potential energy surface scans for SO3- jumps in the crystal lattice of CA, PSA, and TSA, as well as for three related crystalline sulfonic acids (taurine, homotaurine, and 4-aminobutane-1-sulfonic acid) for which relevant 17O solid-state NMR data are available in the literature. The calculated activation barriers are in reasonable agreement with the experimental values. On the basis of the DFTB results, we hypothesized that activation barriers for SO3- jumps in the crystal lattice depend largely on the hydrogen bonding energy difference between the ground state and the transition state.