Internuclear Distance Measurements up to 0.44 nm for Retinals in the Solid State with 1-D Rotational Resonance 13C MAS NMR Spectroscopy

The results presented in this paper show that accurate through-space internuclear distance measurements can be performed on doubly labeled retinals using the one-dimensional approach to the solid state magic angle spinning (MAS) rotational resonance NMR technique. The apparent splitting Δω1 of the resonances at n = 1 rotational resonance for the labeled vinylic positions of (all-E)-[10,20-13C2]retinal, (all-E)-[11,20-13C2]retinal, and (all-E)-[12,20-13C2]retinal can be simulated with a coherent set of parameters. From a series of simulations with different dipolar coupling constant b IS , it appears that b IS /2π√8 = 1.15(Δω1/2π) + 7 (Hz) to a good approximation. Using this relationship as a calibration, it is demonstrated with a set of model compounds that straightforward Lorentzian fitting to measure Δω1 can be used to determine internuclear distances up to 0.44 nm in doubly labeled retinals in the solid state.