Relaxation Dispersion NMR to Reveal Fast Dynamics in Bronsted Acid Catalysis: Influence of Sterics and H-Bond Strength on Conformations and Substrate Hopping.

ABSTRACT: NMR provides both structural and dynamic information, which is key to connecting intermediates and to understanding reaction pathways. However, fast exchanging catalytic intermediates are often inaccessible by conventional NMR due its limited time resolution. Here, we show the combined application of the 1H off-resonance R1ρ NMR method and low temperature (185-175 K) to resolve intermediates exchanging on a μs time scale (ns at room temperature). The potential of the approach is demonstrated on chiral phosphoric acid (CPA) catalysts in their complexes with imines. The otherwise inaccessible exchange kinetics of the E-I ⇌ E-II imine conformations and thermodynamic E-I:E-II imine ratios inside the catalyst pocket are experimentally determined and corroborated by calculations. The E-I ⇌ E-II

SUBMITTER: Lokesh N 

PROVIDER: S-EPMC6863621 | biostudies-literature | 2019 Oct

REPOSITORIES: biostudies-literature