Different factors affecting polyAT conformation in microemulsions: effects of variable Po and KCl concentration

The behaviour of the synthetic polynucleotide polyAT entrapped in the inner core of a quaternary cationic microemulsion has been investigated by means of CD and UV spectroscopies in the presence of KCl (variable temperature at constant W0 = [H2O]/[CTAB] and P0 = [cosurfactant]/[CTAB]) and NaCl (variable P0 at constant W0 and temperature). While the presence of KCl gives rise to effects which are not substantially different from those already reported for NaCl (absence of thermal melting and formation of compact ψ(−) structures), the peculiar results obtained as a consequence of the progressive addition of cosurfactant (denaturation of the polymer at low [NaCl] and W0; transition from B- to A-form at intermediate [NaCl], formation of ψ(−) aggregates at high [NaCl]) can be attributed to the characteristics of the microemulsive system (restricted volume), of the micellar water (low dielectric constant and reduced activity) and of the interface (progressively higher cosurfactant concentration).