Solvent effects in the 2JHH, 3JHH, 1JNC and 2JNC coupling constants in the NMR spectrum of acetylcholine chloride

Coupling constant values (J(NH) and J(NC)) obtained from H-1 and C-13 NMR spectra of acetylcholine chloride (ACh) in several solvents with a wide range of permittivity constants (epsilon) are remarkably invariant, indicating the absence of solvent effects in the conformational equilibrium of this compound. The values show that the OCH2CH2N+ system occurs in a gauche arrangement. J(NH) and J(NC) are observable in most solvents, but not in chlorine-containing solvents, and are not dependent on solvent viscosity. This behavior was explained using data from T-1 measurements. The measurement of NMR diffusion coefficients shows that ACh has a greater tendency to aggregate when dissolved in chlorinated solvents, a fact that could explain the observed differences in N-14 T-1. (c) 2006 Elsevier B.V. All rights reserved.