Sites of Attack of Hydroxyl Radicals on Amides in Aqueous Solution

Authors: E. Hayon, T. Ibata, N. N. Lichtin, M. Simic

The reactivity and sites of attack of hydroxyl radicals on simple amides in aqueous solution were studied. The following amides were examined: formamide (F), N-methylformamide (NMF), N,N-dimethylformamide (DMF), acetamide (A), N-methylacetamide (NMA), and , -dimethylacetamide (DMA). The rate constants for reaction of OH radical with NMF, DMF, NMA, and DMA fall in the range (1.0-3.5) X 109 M~l sec-1, but the reactivity with F and A is significantly lower. The absorption spectra in the wavelength range 225-600 nm and the specific rates of decay of the transient species produced by the reaction of OH radicals with amides were determined and their structures assigned. With F and A, OH radicals attack at both sites on the molecule to give HCOÑH, CONH2, CH3COÑH, and CH2CONH2 radicals. With the N-methylated amides, abstraction by OH radicals takes place mainly from the N-methyl group, e.g., OH + CH3CON(CH3)2 —CH3CON(CH2)(CH3) + H20. The implications of these results with respect to the radiolysis of peptides are discussed.

https://doi.org/10.1021/ja00716a011