Raman spectral analysis of wet-spun films of CaDNA with varying amounts of CaCl$_{2}$ as a function of relative humidity

Raman spectroscopy has been used to probe the amount of DNA in the B conformation in wet-spun films of CaDNA which contain varying amounts of CaCl$_{2}$ as a function of relative humidity. This determination is made by measuring the intensity of the B-form marker band (at about 834 cm$^{-1})$ relative to a vibrational mode localized in the bases. Our experiments show that CaDNA is in the B conformation from 98{\%} relative humidity (rh) down to 75{\%} and is disordered at lower humidities. Interestingly, a maximum in the relative amount of B-DNA is observed near 80{\%} rh.