Hydration and counterion binding of aqueous acetylcholine chloride and carbamoylcholine chloride

The hydration and Cl- ion binding of the neurot(dagger)ransmitter acetylcholine (ACh(+)) and its synthetic analogue, carbamoylcholine (CCh(+)), were studied by combining dilute-solution conductivity measurements with dielectric relaxation spectroscopy and statistical mechanics calculations at 1D-RISM and 3D-RISM level. Chloride ion binding was found to be weak but not negligible. From the similar to 30 water molecules coordinating ACh and CCh(+) only similar to 1/3 is affected in its rotational dynamics by the cation, with the majority - situated close to the hydrophobic moieties - only retarded by a factor of similar to 2.5. At vanishing solute concentration cations and the similar to 3-4 H2O molecules hydrogen bonding to the C=O group of the solute exhibit similar rotational dynamics but increasing concentration and temperature markedly dehydrates ACh(+) and CCh(+).

Automated summary

The hydration and Cl- ion binding of the neurotransmitter acetylcholine (ACh(+)) and its synthetic analogue, carbamoylcholine (CCh(+)), have been studied. Weak but not negligible chloro ion binding was observed, with only about 1/3 of water molecules being affected by the cation. Increasing concentration and temperature significantly dehydrate ACh(+) and CCh(+).