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)ų, Z= 2] shows that the four charged ammonium groups point inside the macrocyclic cavity.