RELATIVE BINDING-AFFINITY OF CARBOXYLATE AND ITS ISOSTERES - NITRO, PHOSPHATE, PHOSPHONATE, SULFONATE, AND DELTA-LACTONE

Using the mono and ditopic receptors 1 and 2 (N-n-butyl-N'-p-tolylurea and 4,8-bis[((n-butylamino)carbonyl)amino]dibenz[b, i]acridan), the relative binding affinities of the title functional groups were determined to be ArOPO32- greater than or equal to ArPO32- > ArCOO- greater than or equal to ArP(OH)O-2(-) > ArOP(OH)O-2(-) > ArSO3- > delta-lactone > ArNO2. No evidence of hydrogen bonding of nitrobenzene to 1 was detected in either CDCl3 or DMSO-d(6), but in CCl4, K-assoc = 180 M(-1). Ditopic receptor 2 was designed as a receptor for meta-disubstituted aromatic substrates and binds some (isophthalate and 1,3-C6H4(P(OHO2-)(2)) with high affinity (K-assoc>10(4) M(-1)) in DMSO-d(6). In contrast, the isosteric m-dinitrobenzene is not found by 2 in that solvent, which further illustrates the relatively poor hydrogen bonding ability of nitro groups.