OPTICAL-PROPERTIES OF CSDNA FILMS AS A FUNCTION OF HYDRATION

The refractive indices of wet-spun films of CsDNA have been measured f or light polarized parallel and perpendicular to the helical axis as a function of relative humidity (RH). These data have been combined wit h previously published data (Biopolymers 30 (1990) 877-887) for the vo lume per base pair and water content as a function of RH in order to e xtract the optical polarizabilities. This work was motivated by the st udy of Weidlich et al. (Biopolymers 26 (1987) 439-453) who reported a similar to 35% increase at the A-to-B transition in the parallel and p erpendicular polarizabilities of NaDNA. In contrast, a much smaller in crease in the polarizabilities of CsDNA is found near the A-to-B trans ition: similar to 12% for the perpendicular direction and less than or equal to 4% for the parallel direction.