The radiation chemistry of aqueous benzene solutions has been studied by the electron-pulse radiolysis technique. Ultraviolet absorption spectra of some of the transient species have been recorded by synchronized flash-absorption spectroscopy. The elementary reactions occurring have been observed by fast photoelectric recording of the transient optical density. A transient spectrum having a broad absorption with a strong maximum at 313 mμ has been observed. On the basis of both spectrographic and kinetic evidence this spectrum is assigned to the hydroxycyclohexadienyl radical, (OH)C6H6·. The molar extinction coefficient is estimated to be ε3130=3500±800 M—1cm—1. A number of substituted cyclohexadienyl radicals have been observed in aqueous solution as well as in pure benzene and chloro-benzene. A second transient observed in oxygenated aqueous benzene solution shows an absorption shifted to lower wavelengths. This is attributed to the hydroxycyclohexadienyl peroxy radical, (OH)C6H6O2·. Absolute rate constants have been determined at 23°C for the following reactions: OH+C6H6=(OH)C6H6·(4.3±0.9)×109 M−1sec−1,OH+C6D6=(OH)C6D6·(4.7±0.9)×109 M−1sec−1,(OH)C6H6·+O2=(OH)C6H6O2·(5.0±0.6)×108 M−1sec−1. The yield of phenol in oxygenated solution was found to decrease continuously with increasing pulse intensity. At the highest intensity used, G(C6H5OH) = 0.19 molecules/100 ev. At the lowest pulse intensity used, G(C6H5OH) = 1.9 molecules/100 ev, which approaches the values found in steady irradiations. Some additional phenol is formed in slow post-irradiation reactions. Diphenyl was identified as a product in the deaerated system by gas chromatographic analysis. Its formation is largely the result of post-irradiation reactions, the initial yield being substantially lower than previously reported. The mechanism of the radiation chemical reaction in both deaerated and oxygenated solutions is discussed on the basis of the conclusion that the hydroxyl radical enters the ring to form the hydroxycyclohexadienyl radical.

Relationships among cellular structure, fracturability, and sensory properties in porous, brittle extrudates were investigated. Corn‐based extrudates intentionally processed to exhibit a range of physical structures were characterized in terms of cell size distribution, bulk density, mechanical strength, fracturability, and sensory attributes. These measurements show both mechanical strength, defined by average compressive stress during extended deformation, and fracturability, quantified by fractal and Fourier analyses of stress‐strain functions, increasing with either decreasing mean cell size or increasing bulk density. Fracturability parameters or structural characteristics are furthermore correlated with sensory scores for crunchiness, crispness, hardness and perceived density. These results indicate that cellularity strongly influences the pattern of mechanical failure and that failure characteristics, such as fractal dimension or power spectrum of stress‐strain functions, are reflective of sensory texture.

The one-electron reduction of pentacyanonitrosylferrate(II) ion, Fe(CN)5N02~(nitroprusside ion), in aqueous solution has been studied using continuous and pulse radiolysis techniques, the latter with optical absorption and kinetic conductivity detection. The reducing radicals eaq~, C02~, • 2 , (CH3)2ÓOH, and H react with Fe(CN)5N02™ (k = 1.0 X 10m, 4.0 X 10s, 6.7 X 108, 2.9 X 109, and 7 X 107 M™1 s™1, respectively) to yield Fe(CN)5N03~c haracterized by an absorption spectrum with Xmax 345 and 440 nm (emal 3.5 X 103 and 5.5 x 102 M4 cm™1, respectively); the spectrum is independent of pH (1-8.5). Fe(CN)5N03~undergoes first-order decay with the loss of CN™, presumably from the trans position, to form Fe(CN)4N02~(Xmax 615 nm, emax 3.8 X 102 M™1 cm™1) according to the following reactions: Fe(CN)5N03™ Fe(CN)4N02™ + CN™, K = 6.8 X 10~5; CN™ + H+ <=± HCN, K = 2.0 X 109. The observed first-order rate constant for the disappearance of Fe(CN)5N03™ (2.8 X 102 s™1) is independent of the nature of the reducing radical and pH (4.6-8.5); kobsd increases with increasing [H+] (> 10"4 M) or [CN™]. The relative concentrations of the two reduced species depend markedly on pH and [CN™], but not radiation dose. The reduced species are sensitive to 02 generating Fe(CN)5N02", Fe(CN)4NO(OH)2™, and polymeric species. In solutions c Fe(CN)5N03™ reacts rapidly with -CH2C(CH3)2OH (k = 2.Í cm™1), air-insensitive, moderately stable alkylnitroso complex, has been obtained in a KBr matrix.

The thermodynamically favored reaction between water and magnesium, Mg + 2H2O → Mg(OH)2 + H2, is normally sluggish, but it becomes reasonably rapid when a milled composite of powdered magnesium metal and powdered iron (1−10 mol %) is used with sodium chloride solutions. Iron functions as an activator, and chloride functions as a catalyst that depassivates the outermost oxide/hydroxide layer and allows water to penetrate to the activated magnesium surface. Adding solutes such as sodium nitrate, copper(II) chloride, and sodium trichloroacetate to the reaction mixture suppresses the yield of dihydrogen. Manometric and calorimetric studies on the stoichiometry and kinetics of the reaction between Mg(Fe) powders and aqueous solutions demonstrate that short-lived, partially, and fully solvated electrons ( and ) are precursors of dihydrogen and that they and the hydrogen atoms (H•) formed from them can be scavenged, resulting in suppressed dihydrogen yields.

Neutral, crystalline ice samples were pulse irradiated in order to study phase and temperature effects on the properties of transient intermediates produced in radiolyzed water. These studies demonstrate that optical absorption bands with peaks near 670, at 280 ± 5, and at 230 ± 8 nm are detectable. The transient visible absorption is attributed to a solvated electron es−. Its spectrum, though unaffected by phase change, is influenced by temperature, dEmax / dT being −1.2 × 10−3 eV/deg. Ges− also depends on temperature, decreasing markedly from −5° to −40°C, but only slowly thereafter. The decay of es−, which is second order at −14°C (k = 1.5 × 1011 M−1·sec−1) and partly first order from −40° to −100°C [k(−60°C) = 1.1 × 104sec−1; ΔEact = 9 ± 2 kcal/mole], becomes slower with decreasing temperature. Over-all spectral, yield and kinetic considerations indicate that es− is structurally similar to eaq−, forms via pre-existing traps, and though immobile as a unit, decays both by reaction with H3O+ and by means of an equilibrial, mobile partner em−. These findings are viewed in terms of the polaron theory and other models for the solvated electron. The transient 280-nm absorption is assigned to a hydrogen-bonded hydroxyl radical OHt·. ESR data showing chemical and kinetic characteristics similar to the optical results confirm this assignment. Its molar extinction coefficient at −196°C is estimated as ε280 = 560 ± 50 M−1·cm−1 [using GOHt· (stable) = 0.8]. The over-all OHt· decay is complex. After prolonged irradiation, pseudo-first-order kinetics representing reaction with H2 and/or H2O2 is primarily observed. For low doses and at temperatures below −100°C, separate fast and slow decaying portions can be distinguished, the former attributable to H· reacting with OHt·, the latter to reaction involving only OHt·. Based on an empirical 32-order kinetic treatment [k(−59°C) ≤ 1 × 104 M−1 / 2·sec−1], ΔEact for the slow decay is determined to be 5.7 ± 0.7 kcal/mole. Qualitatively, this decay and the reaction with products are reconcilable with a mechanism involving OHt· in equilibrium with a mobile species OHm·. Second-order kinetic behavior observed at −14°C (k appears to be ∼108 M−1·sec−1) may also be consistent with this scheme. The full transient yield at −131°C is estimated to be 1.2. These findings imply that OH· is structurally different in both phases, but chemically similar. The relatively stable absorption at 230 nm is ascribed to HO2·. Spectral, chemical, and possibly, ESR evidence support this identification. Its yield is low, and it decays only very slowly at −14°C.

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The "quasi-chemical" kinetics model accounts for all 4 phases of the microbial lifecycle based on a proposed series of chemical rate equations. The model fits continuous growth-death kinetics for Staphylococcus aureus in intermediate moisture bread in various conditions of water activity, pH, and temperature. Growth rates evaluated using the quasi-chemical model are compared with values obtained with the Gompertz model. Kinetics data obtained with the quasi-chemical model are integrated with a probabilistic approach to estimate the boundary between growth and no-growth conditions. Continuous modeling of microbial growth/death kinetics in actual foods advances predictive modeling that conventionally separates growth and death models.

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