Essentially the same spectrum is produced by addition of H atoms to phenylalanine, acetylphenylalanine or acetylphenylalanylamide at pH 2.0 and 6.4. This spectrum closely resembles the most prominent feature in the primary transient spectrum produced by the addition of H atoms to ribonuclease-S-peptide and can be assigned to cyclohexadienyl radicals. Specific rates of reaction of H atoms with phenylalanine, acetylphenylalanine, acetylphenylalanylamide and acetylmethionine have been determined. The decay of cyclohexadienyl radicals followed strictly second order kinetics in the absence or presence of methionyl compounds and the radicals formed by the action of H atoms upon them. No reaction of cyclohexadienyl radicals with parent methionyl compounds was detectable. The bimolecular radical-radical reactions observed with monomeric radicals take place on a time scale over which only intramolecular transformations occur in the radicals produced by the addition of H atoms to the ribonuclease-S-peptide molecule. The virtually identical reactivity of monomeric phenylalanyl and methionyl compounds to reaction with H atoms can be compared to evidence that the reaction of H atoms with ribonuclease-S-peptide takes place about five times as often at the methionyl as at the phenylalanyl residue.

The reactions of H atoms with ribonuclease-S-peptide and ribonuclease-S-protein at pH 2.2 and 6.6 have been investigated by means of pulse radiolysis-kinetic spectrometry and compared with those of intact ribonuclease. Initial spectra were observed after 100-nsec pulses of 5 MeV electrons under conditions such that only H atoms reacted with substrate. The resulting spectra are due to addition of one H atom to a substrate molecule. Their subsequent transformations were studied over periods ranging from several microseconds to several seconds. The specific rates of reaction of H atoms with S-protein and with intact ribonuclease (1) are the same, while S-peptide reacts about half as rapidly. For both substrates the subsequent transformations are first order and presumably correspond to intramolecular chemical reactions. The data implicate aromatic and sulfur-containing amino acid residues as transient radical sites. The data for S-peptide establish that intramolecular radical transfer is a reaction of polypeptide as well as of protein. The types of residues involved as radical sites and the intramolecular nature of sequential transformations are similar to those observed (1) in the reaction of intact ribonuclease with H atoms, but significant differences are observed in specific rates and spectra. The sum of the effects of H atoms on S-peptide and on S-protein separately is not identical with the action of H atoms on structurally intact ribonuclease.

Yields per 100 eV of products of 60 Co gamma-radiolysis of anhydrous liquid formamide at room temperature, which are either gaseous under ordinary conditions or are less volatile than formamide, obtained with 10-Mrad dose, were <tex-math>$G({\rm H}_{2})=0.8_{7}$</tex-math>; <tex-math>$G({\rm CO})=0.6_{1}$</tex-math>; <tex-math>$G({\rm CO}_{2})=0.2;G({\rm NH}_{3})=0.7$</tex-math>; <tex-math>$G[({\rm CONH}_{2})_{2}]=0.2$</tex-math>; <tex-math>$G[({\rm HCONH})_{2}]=0.04$</tex-math>; <tex-math>$G({\rm C}_{4}{\rm H}_{8}{\rm N}_{2}{\rm O})=0.06$</tex-math>; polymer, mol. wt. 1655, G = 0.006; and G(HCN), trace. <tex-math>$G({\rm NH}_{3})$</tex-math> and G(HCN) decrease sharply with increasing dose amounting to 2.6 and 0.3 molecules/100 eV, respectively, with a dose of 0.16 Mrad. <tex-math>$G({\rm CO}_{2})$</tex-math> is similarly dose dependent, but <tex-math>$G({\rm H}_{2})$</tex-math> and G(CO) are not. N 2 O up to concentrations of the order of <tex-math>$4\times 10^{-2}$</tex-math> M has little or no effect on <tex-math>$G({\rm H}_{2})$</tex-math> and G(CO), although substantial amounts of N 2 are produced. Water at concentrations up to 0.1 M did not influence <tex-math>$G({\rm H}_{2})$</tex-math>, G(CO), or <tex-math>$G({\rm CO}_{2})$</tex-math> significantly. The isotopic composition of hydrogen produced by radiolysis of <tex-math>${\rm HCOND}_{2}$</tex-math> in the liquid and solid states indicates selective detachment from carbon. Selectivity is more pronounced in the solid state. The chemical significance of the data is discussed.