Dipole moment of acetylcholine and its relevance to the chemical synaptic transmission.

The dipole moment of acetylcholine (AcCh) has been measured in chloroform and a value of 8.49 D was obtained. Such a value actually represents the total dipole moment of the ion pair (AcCh)(+)(Cl)(-). The dipole moment of the (AcCh)(+) cation alone turned out to be 2.65 D whereas its theoretical value obtained after a vectorial calculation was 1.65 D. The discrepancy was related to an interaction between AcCh and the solvent. The meaning of the measured value is discussed on the basis of a recent theory of chemical synaptic transmission based on the assumption of a much higher dipole moment value for the AcCh molecule.