[IR-spectroscopic study of the interaction of chromium salts with native DNA]

Infrared spectra of some unoriented films of DNA contained CrCl3, K2Cr2O7 and Cr2(SO4)3 have been obtained at relative humidities (r.h.) 0 to 93%. Chromium cations were shown to interact with phosphoric groups of DNA molecules. Cr2(SO4)3 or K2Cr2O7 content exceeds 0.1 Cr/P, the sugar-phosphate backbone of the double helix becomes irregular and nucleic bases unstacked, i.e. denaturation of DNA occurs. A very small amount of the salt, less than 0.01 Cr/P contained in DNA films prevents the conformational transition of the double helix from the B to A form induced by r.h. decreasing. The efficiency of the chromium salts in preventing the transition falls in the row: Cr2(SO4)3 > K2Cr2O7-CrCl3.