1,10-Dimethyl-1,4,7,10,13,16-hexaazacyclooctadecane L and 1,4,7-trimethyl-1,4,7,10,13,16,19-heptaazacyclohenicosane L1: two new macrocyclic receptors for ATP binding. Synthesis, solution equilibria and the crystal structure of (H₄L)(ClO₄)₄

Abstract

The synthesis of two new methylated ligands 1,10-dimethyl-1,4,7,10,13,16-hexaazacyclooctadecane L and 1,4,7-trimethyl-1,4,7,10,13,16,19-heptaazacyclohenicosane L1 is described. Basicity constants and protonation enthalpies of both ligands have been determined by potentiometric and microcalorimetric measurements in 0.15 mol dm–3 NaClO4 at 298.1 K. The protonated forms of these cyclic polyamines bind ATP in solution. The equilibrium constants of the species formed have been determined (0.15 mol dm–3 NaClO4, 298.1 K). The results presented for L and L1 are compared with those previously obtained for the related ligands 1,4,7,10,13,16-hexaazacyclooctadecane, 1,4,7,10,13,16,19-heptaazacyclohenicosane and 1,4,7,13-tetramethyl-1,4,7,10,13,16-hexaazacyclooctadecane. Among these macrocycles Lis a selective receptor for ATP binding.The crystal structure of the compound (H4L)(ClO4)4[space group P21/c, a= 9.257(4), b= 8.600(2). c= 17.990(10)Å, β= 101.74(4)°, V= 1402(1)Å3, Z= 2] shows that the four charged ammonium groups point inside the macrocyclic cavity.