Bolch W E, Turner J E, Yoshida H, Jacobson K B, Hamm R N, Crawford O H
Department of Nuclear & Radiological Engineering, University of Florida, Gainesville 32611-8300, USA.
Radiat Environ Biophys. 1998 Oct;37(3):157-66. doi: 10.1007/s004110050111.
The radiation chemistry of photon-irradiated aqueous solutions of biological molecules may be considered under four distinct time regimes: physical transport (< or = 10(-15) s); prechemical conversion of H2O+, H2O*, and subexcitation electrons into free radicals and molecular products (10(-15) s to 10(-12) s); chemical reactions within individual electron tracks (10(-12) s to 10(-6) s); and chemical reactions within overlapping tracks (>10(-6) s). We have previously reported of the use of the Monte Carlo radiation transport/chemistry codes OREC and RADLYS to model the radiolysis of glycylglycine in oxygen-free solution to a time of 1 micros. These simulations successfully predicted the yields of free ammonia, an end product created solely in the reaction of the hydrated electron with the solute within individual tracks. Other measurable products are only partially created during intratrack reactions, and thus one must additionally consider the late, intertrack chemistry of this system. In this paper, we extend our simulations of glycylglycine radiolysis to model for the first time the events which occur during this late chemistry stage. The model considers the product rates of the reactants in bulk solution by using previously available microsecond intratrack yields given by single-track OREC/RADLYS simulations and an x-ray dose rate of 2.80 Gy min(-1) as used in a companion experimental program. These rates are then applied in a series of coupled, differential rate equations that describe the solution chemistry of glycylglycine radiolysis. Product yields are reported as a function of time over a total irradiation period of 10(4) s. Excellent overall agreement is seen between the theoretical predictions and measurements of five radiolysis end products: free ammonia, acetylglycine, diaminosuccinic acid, aspartic acid, and succinic acid. The model also gives the explicit contributions of intratrack and intertrack reactions to the various end products. For example, the model predicts that approximately 56% and 93% of succinic acid and aspartic acid, respectively, are produced during intertrack reactions at a solute concentration of 0.05 M; these contributions drop to 0.07% and 11%, respectively, at 1.2 M.
物理传输（≤10⁻¹⁵秒）；H₂O⁺、H₂O*和亚激发电子预化学转化为自由基和分子产物（10⁻¹⁵秒至10⁻¹²秒）；单个电子径迹内的化学反应（10⁻¹²秒至10⁻⁶秒）；以及重叠径迹内的化学反应（>10⁻⁶秒）。我们之前报道过使用蒙特卡罗辐射传输/化学代码OREC和RADLYS来模拟无氧溶液中甘氨酰甘氨酸的辐射分解至1微秒的时间。这些模拟成功预测了游离氨的产率，游离氨是仅在单个径迹内水合电子与溶质反应中产生的一种终产物。其他可测量的产物仅在径迹内反应期间部分生成，因此必须额外考虑该体系后期的径迹间化学过程。在本文中，我们扩展了对甘氨酰甘氨酸辐射分解的模拟，首次对这一后期化学阶段发生的事件进行建模。该模型通过使用单径迹OREC/RADLYS模拟给出的先前可用的微秒级径迹内产率以及在一个配套实验项目中使用的2.80 Gy min⁻¹的x射线剂量率，来考虑本体溶液中反应物的产物生成速率。然后将这些速率应用于一系列描述甘氨酰甘氨酸辐射分解溶液化学过程的耦合微分速率方程中。在10⁴秒的总辐照期内，产物产率作为时间的函数被报告。在五种辐射分解终产物（游离氨、乙酰甘氨酸、二氨基琥珀酸、天冬氨酸和琥珀酸）的理论预测和测量值之间观察到了极好的总体一致性。该模型还给出了径迹内和径迹间反应对各种终产物的明确贡献。例如，该模型预测，在溶质浓度为0.05 M时，琥珀酸和天冬氨酸分别约有56%和93%是在径迹间反应期间产生的；在1.2 M时，这些贡献分别降至0.07%和11%。
