Tetracationic-to-dianionic tetraamino-dihydroxy-tetraoxacalix[4]arene: A paraquat receptor for all seasons

•• Two novel water-soluble, proton-ionizable, isomeric tetraamino-dihydroxy-tetraoxacalix[4]arene were synthesized.•• Six protonation constants were determined, and the distribution diagrams for the seven protonated species were calculated.•• The phloroglucinol-derived oxacalix[4]arene 1·H2 was successfully employed to complex paraquat both at low and high pH.•• Combination of protonation and apparent binding constants gave association constants for the differently-charged complexes.