The infrared spectrum and structure of the type I complex of silver and DNA.

Infrared spectroscopy was used to study films of the type I complex of Ag+ and DNA as a function of hydration with the following conclusions. Ag+ binds to guanine residues but not to cytosine or thymine residues. Cytosine becomes protonated as Ag+ binds to guanine. (These conclusions confirm previous models.) The type I complex remains in the B family of structures with slight modifications of the sugar-phosphate geometry. This modified B structure remains stable at lower values of hydration for which pure DNA is in the A form. Binding of Ag+ to PO2-, O-P-O or the deoxyribose oxygen is excluded.