SELF-ASSOCIATION MECHANISMS IN AQUEOUS-MEDIA - DIMERIZATION VERSUS MICELLIZATION OF ALKYL-ELLIPTICINIUM DERIVATIVES

Self-association mechanisms in aqueous media of ellipticinium (E), 2-m ethylellipticinium (2-NME), oxazolopyridocarbazolium (H-OPC), 10-penty loxazolopyridocarbazolium (10-pentyl-OPC), 2 aminopentyloxazolopyridoc arbazolium (2-aminopentyl-OPC) and 2-pentyloxazolopyridocarbazolium (2 -pentyl-OPC) acetates have been investigated by spectroscopic and kine tic studies. Whereas E, 2-NME, H-OPC, 10-N-pentyl-OPC and 2-aminopenty l-OPC dimerize by self-stacking, the 2-pentyl-OPC displays micellar be haviour (with a critical micellar concentration of 20 mumol dm-3), as a direct consequence of its amphiphilic character. As regards dimeriza tion, both aliphatic substitution (K(d) = 7.6 x 10(3) and 2.4 x 10(4) dm3 mol-1 for E and 2-NME, respectively) and extension of the pi-elect ron aromatic system (K(d) = 1.4 x 10(5) and 4.5 x 10(5) dm3 mol-1 for H-OPC and 10-pentyl-OPC, respectively) significantly increase the dime r stability. From kinetic analysis, dimer stability seems to be contro lled mainly by the reverse rate constants which vary from 4.9 x 10(4) to 1.9 x 10(3) s-1.