dyes were eosinY and its ester derivatives with methyl, butyl and decyl alkyl groups. In aqueous media at physiological pH eosin is present as dianionic protolytic form while its esters are monoanionic. Analysis of the water/octanol partition coefficient showed that the eosin is the most hydrophilic compound and the hydrophobicity increases as the alkyl chain of the ester increases: eosin < methyl