A spectroscopic study of poly(dA-dT)•poly(dA-dT) in microemulsions

The behaviour of high molecular weight [poly(dA-dT) . poly(dA-dT)] (polyAT) [(0.9-1.9) x 10(6) Da] in the quaternary water-in-oil microemulsion CTAB-n-pentanol-n-hexane-water has been studied as a function of temperature and NaCl concentration by means of UV and circular dichroism (CD) spectroscopy. Solubilization in the microemulsion stabilises the polymer double helix and no helix-to-coil thermal transition has been observed. At increasing NaCl concentration, the CD spectrum of polyAT exhibits dramatic changes and for salt concentrations greater than or equal to 7.5 x 10(-1) M the spectral pattern suggests the formation of aggregates of the psi(-) type. Condensation is induced by the peculiar characteristics of the aqueous core of the microemulsion. The condensates seem to destabilise the microemulsive system and, with time, separate from it.