The molal volumes of atropine and hyoscine in relation to their respective potencies.
The partial molal volumes, V2, at infinite dilution of atropine and hyoscine were determined in each of eight different solvents having cohesive energy densities in the range 64 to 144 cal cm-3. V2 for hyoscine in a given solvent was invariably and significantly smaller than that of atropine in the same solvent. The difference being 1.58 cm3 mol-1 in the least polar solvent (n-propylbenzene) and 4.29 cm3 mol-1 in the most polar one (acetonitrile) in the series studied. It is proposed that the lower affinity of atropine relative to that of hyoscine for the muscarinic cholinoceptor could be accounted for by the relative increase in enthalpy in the adsorption of atropine to the receptor with respect to the same process with hyoscine.
D001285:Atropine / Q000494:pharmacology*; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D009994:Osmolar Concentration; D012601:Scopolamine / Q000494:pharmacology*; D012995:Solubility
D001285:Atropine; D012601:Scopolamine