The amide I maximum in 2H2O, at 1645 cm-1, is typical of unordered proteins with C = O groups deuterium-bonded predominantly to 2H2O. Addition of DMSO disrupts such interactions by competing with the peptide C = O group for the deuterium bond donor capacity of the 2H2O, and so progressively increases the amide I maximum until it stabilizes at 1663 cm-1, a position indicative of free C = O groups.