Self-association mechanisms in aqueous media: dimerization versus micellization of alkyl-ellipticinium derivatives

Abstract

Self-association mechanisms in aqueous media of ellipticinium (E), 2-methylellipticinium (2-NME), oxazolopyridocarbazolium (H-OPC), 10-pentyloxazolopyridocarbazolium (10-pentyl-OPC), 2 aminopentyloxazolopyridocarbazolium (2-aminopentyl-OPC) and 2-pentyloxazolopyridocarbazolium (2-pentyl-OPC) acetates have been investigated by spectroscopic and kinetic studies. Whereas E, 2-NME, H-OPC, 10-N-pentyl-OPC and 2-aminopentyl-OPC dimerize by self-stacking, the 2-pentyl-OPC displays micellar behaviour (with a critical micellar concentration of 20 µmol dm^–3), as a direct consequence of its amphiphilic character. As regards dimerization, both aliphatic substitution (K_d= 7.6 × 10³ and 2.4 × 10⁴ dm³ mol^–1 for E and 2-NME, respectively) and extension of the π-electron aromatic system (K_d= 1.4 × 10⁵ and 4.5 × 10⁵ dm³ mol^–1 for H-OPC and 10-pentyl-OPC, respectively) significantly increase the dimer stability. From kinetic analysis, dimer stability seems to be controlled mainly by the reverse rate constants which vary from 4.9 × 10⁴ to 1.9 × 10³s^–1.