. . "The incorporation of the non-functional-group remaining A substituents listed above can be used to enhance the affinity of the ion-selective molecule for polycations (such as the lower alkyl groups, methyl and ethyl) or lessen the affinity (such as carboxylic acid derivatives, nitro, cyano, trifluoromethyl and halogens such as chlorine, bromine and iodine)." . . . .