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Item Addition of ethyl radicals to nitric oxide(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1974, 70 (10), 1974) Pratt, Graham; Veltman, IanMixtures of methyl and ethyl radicals have been generated at 295 K in a fast flow discharge system by addition of hydrogen atoms to ethylene in helium at total pressures from 6 to 15 Torr (1 Torr = 133 N m–2). Mass spectrometric analysis of the reaction products both with and without added nitric oxide has provided data, numerical analysis of which has given the rate constants of the following reactions, [graphic omitted]Item Selective Free Radical Reactions with Proteins and Enzymes: The Inactivation of Subtilisin Carlsberg and Subtilisin Novo(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1974, 70 (12), 1974) Bisby, Roger H.; Cundall, Robert B.Reactions of the selective inorganic radical anions (SCN)–2 and Br–2, with subtilisins Novo and Carlsberg lead to selective oxidation of the tryptophan, tyrosine, and histidine amino-acid residues. Inactivation studies show that most of the inactivation is caused by oxidation of one or more histidine residues. Oxidation of tryptophan residues has a minor effect upon activity but damage to tyrosine residues does not affect the activity of the two enzymes towards the small synthetic substrate N-acetyl-L-tyrosine ethyl ester. Rate constants for reactions with the radical anions and transient spectra, measured by pulse radiolysis, reflect the differences in amino-acid composition and in structure between the two enzymes.Item Reaction of n-propyl radicals with oxygen, hydrogen and deuterium(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1973, 69 (4), 1973) Baldwin, Roy R.; Walker, Raymond W.; Yorke, David A.n-C3H7 radicals have been produced by the oxidation of n-C3H7CHO at 450°C. By measuring the relative yield of C3H6 and C3H8, a value for the ratio k4/k1= 0.040 ± 0.005 has been obtained. A value of k4 can be obtained, based on the value of 2.9 × 1010 l. mol–1 s–1 assumed for the combination of two C3H7 radicals, which gives k1= 3.1 × 107 at 450°C. By measuring the increased yield of C3H8(or C3H7D) in the presence of H2(or D2), the ratios k1/k2= 347 ± 10, k2/k3= 2.3 ± 0.2 at 450°C are obtained. n-C3H7+ O2→ C3H6+ HO2(1), n-C3H7+ H2→ C3H8+ H (2), n-C3H7+ D2→ C3H7D + D (3), n-C3H7+ C3H7CHO → C3H8+ C3H7CO. (4) The value for k2/k3 suggests that E3–E2= 0.7 kcal mol–1 which indicates a lowering of the zero-point energy in the transition state by about 1.1 kcal mol–1 when H2 is replaced by D2. Using entropy data, and the Arrhenius parameters for reaction (– 2), A2= 2.6 × 109 and E2= 14.8 kcal mol–1.Item Electron Spin Resonance Study of the Reaction of Hydrogen Atoms with Hydrogen Sulphide(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1973, 69 (2), 1973) Bradley, John N.; Trueman, Susan P.; Whytock, David A.; Zaleski, Thomas A.The reaction between H atoms and hydrogen sulphide, with and without added nitric oxide, has been studied by following the H atom, S atom and SH radical concentrations with time using electron spin resonance detection. The results are fully explained by the mechanism (1)–(4) H + H2S→H2+ SH, k1= 5.0 × 108 l. mol–1 s–1(1), H + SH → H2+ S, k2= 2.5 × 1010 l. mol–1 s–1(2), SH + NO → stable species, k3= 6.3 × 108 l. mol–1 s–1(3), SH + SH → H2S + S, k4= 7.8 × 109 l. mol–1 s–1. (4) with no evidence for significant surface effects (the walls were coated with boric acid). The results demonstrate conclusively that reaction (2) is very important in this system and that previous measurements of k1 which neglect this reaction may require correction.Item Oxidation of Carbon Monoxide by Methoxy-radicals(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1973, 69 (2), 1973) Lissi, E. A.; Massiff, G.; Villa, A. E.The thermal decomposition of dimethyl peroxide (DMP) in a static system was investigated over the temperature range 123–153°C at varying pressures of carbon monoxide. The reaction of methoxy-radicals with carbon monoxide produces carbon dioxide and methyl radicals. The rate constant of reaction (2) CH3O·+ CO [graphic omitted] CO2+ CH3(2) was determined to be: k2/l. mol–1 s–1= 1010.2 ± 0.6 exp–(11.800 ± 1500/RT)(R in cal mol–1 K–1). At low carbon monoxide pressures production of carbon dioxide is first order in carbon monoxide and half order in DMP while at high carbon monoxide pressures (> 120 Torr) it is zero order in carbon monoxide and first order in DMP. At high pressures of carbon monoxide and at 127°C reaction (2) is the main reaction of methoxy-radicals. These data are rationalized by a simple free-radical mechanism.Item Reaction of Hydrogen Atoms with Nitrous Oxide(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1973, 69 (2), 1973) Baldwin, R. R.; Gethin, A.; Walker, R. W.The velocity constant of the reaction H + N2O → N2+ OH (22) has been obtained at 500°C by the addition of N2O to slowly reacting mixtures of H2+ O2+ He and measurement of the relative rates of formation of N2 and H2O. The ratio k22/k2= 0.64 ± 0.07 gives k22= 2.6 × 106 l. mol–1 s–1, the error of ± 30–40% being largely due to the uncertainty in k2. H + O2→ OH + O. (2) Combination with other measurements gives the Arrhenius parameters A22= 7.6 × 1010 l. mol–1 s–1, E22= 15.1 ± 1.0 kcal mol–1.Item Free Radical Addition to Olefins: Part 8.—Addition of of n-Heptafluoropropyl Radicals to Fluoro-ethylenes(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (1), 1972) Tedder, J. M.; Walton, J. C.; Winton, K. D. R.The light-induced addition of perfluoropropyl iodide to fluoro-ethylenes in the gas phase C3F7·+ RCH[double bond, length as m-dash]CH2→ C3F7CH2ĊHR (2) has been studied, and activation parameters determined by a competitive method. The corresponding differences found are: [graphic omitted] The most striking feature is the similarity to the results for addition of bromotrichloromethane to the same olefins. Relationships between activation energies and some theoretical quantities are discussed.Item Electron Spin Resonance Studies of Elementary Processes in Radiation- and Photo-chemistry: Part 11.—Radical Reactions of α-Aminobutyric Acid between 26 and 440 K(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (9), 1972) Ayscougfi, P. B.; Olsen, K. J.Irradiation of α-aminobutyric acid single crystals with 60Co γ-rays at 26 to 77 K results in the trapping of the protonated molecular-anion CH3CH2CH(NH3+)CO2H–(R1). During thermal annealing to 440 K, six further radicals are formed, including CH3CH2ĊHCO2H(R4), ĊH2CH2CH(NH+3)CO–2(R2), CH3ĊHCH(NH+3)CO–2(R3) and (CH3)2ĊCO2H(R7). The conversion of R1 to R4 and then to R2 and R3 occurs between 100 and 145 K by processes involving only 8–17 kJ mol–1“activation” energy and determined largely by steric considerations. The conversion of R3 to R7 has been followed isothermally between 330 and 365 K and the decay of R7 between 390 and 430 K. These processes have “activation” energies of 71 ± 7 and 83 ± 5 kJ mol–1 respectively and are likely to involve some translational motion of the radicals. A possible mechanism for the radiolysis is discussed.Item γ-Radiolysis of Diethyl Succinate(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (9), 1972) Mills, K. J.; Nosworthy Peto, J. M.Diethyl succinate has been irradiated under vacuum with 60Co γ-radiation. An attempt was made to identify and measure the complete product spectrum. Twenty different products were found after a maximum total dose of 9 × 1023 eV l.–1. The most abundant were ethanol, ethyl propionate, ethane, hydrogen, carbon monoxide, acetaldehyde and carbon dioxide. With the possible exception of acetaldehyde, G-values for these products were independent of the dose in the range studied. Gas yields were also measured in the presence of small amounts of additives (FeCl3, H2O or CH2 : CH2). Possible mechanisms for product formation are discussed.