Fluorescence spectroscopic analysis of the hydrogen bonding properties of catecholamines,resorcinolamines, and related compounds with phosphate and other anionic species in aqueous solution††

Fluorescence spectroscopic analysis based upon the difference in fluorescent behaviour of several phenol, catechol and resorcinol derivatives in 0·2 M phosphate and water, at different pH values ranging from 7·4 to 1·0, produced evidence for the existence of complexes between phosphate anions and these compounds. This complex formation was also found with acetate, citrate and glutamate but not with sulphate and borate. A comparison of different ligand structures revealed that the complex formation observed with unsubstituted phenol, catechol or resorcinol was not influenced by ethyl substitution; however, ethylamine or ethanolamine substitution favoured the formation of the complex. The findings indicate the formation of 1:1 intermolecular complexes between mono- and dihydroxyphenethylamines and several anionic species with participation of two hydrogen bonds. The predictions of a theoretical model describing this interaction are confirmed by the experimental data. Association constants of isoprenaline with phosphate and glutamate were found to be 5·1 and 26·6 litres mol^?1 respectively; for the complexes of m-tyramine and terbutaline with phosphate, association constants of 15·3 and 6·9 litres mol^?1 respectively, were obtained.