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Structures, g‐tensors, and hyperfine coupling constants of L‐α‐alanine radicals in radiation dosimetry: An ab initio molecular dynamics simulation study
International Journal of Quantum Chemistry ( IF 2.3 ) Pub Date : 2020-03-25 , DOI: 10.1002/qua.26211 Mehdi Janbazi 1 , Yavar T. Azar 2 , Farhood Ziaie 1 , Khashayar Ghandi 3 , Chérif F. Matta 4 , Muhammad Shadman Lakmehsari 5
International Journal of Quantum Chemistry ( IF 2.3 ) Pub Date : 2020-03-25 , DOI: 10.1002/qua.26211 Mehdi Janbazi 1 , Yavar T. Azar 2 , Farhood Ziaie 1 , Khashayar Ghandi 3 , Chérif F. Matta 4 , Muhammad Shadman Lakmehsari 5
Affiliation
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Alanine is used as a transfer standard dosimeter for gamma ray and electron beam calibration. An important factor affecting its dosimetric response is humidity which can lead to errors in absorbed dose calculations. Ab initio molecular dynamics calculations were performed to determine the environmental effects on the electron paramagnetic resonance (EPR) parameters of L‐α‐alanine radicals in acidic and alkaline solutions. A new result, not dissimilar to the closed‐shell amino acid molecule alanine, is that the non‐zwitterionic form of the alanine radical is the stable form in the gas phase while the zwitterionic neutral alanine radical is not a stable structure in the gas phase. Geometric and EPR parameters of radicals in both gas and solution phases are found to be dependent on hydrogen bonding of water molecules with the polar groups and on dynamic solvation. Calculations on the optimized free radicals in the gas phase revealed that for the neutral radical, hydrogen bonding to water molecules drives a decrease in the magnitudes of g‐tensor components g
xx and g
yy without affecting neither g
zz component nor the hyperfine coupling constants (HFCCs). The transfer from the gas to solution phase of the alanine radical anion is accompanied with an increase in the spin density on the carboxylic group's oxygen atoms. However, for the neutral radical, this transfer from gas to solution phase is accompanied with the decrease in the spin density on oxygen atoms. Calculated isotropic HFCCs and g‐tensor of all radicals are in good agreement with experiment in both acidic and alkaline solutions.
中文翻译：
辐射剂量法中L-α-丙氨酸自由基的结构，g张量和超精细偶联常数：从头算分子动力学模拟研究
丙氨酸用作伽马射线和电子束校准的传输标准剂量计。影响其剂量响应的一个重要因素是湿度，湿度会导致吸收剂量计算中的误差。从头开始进行分子动力学计算，以确定环境对酸性和碱性溶液中L-α-丙氨酸自由基的电子顺磁共振（EPR）参数的影响。一个新的结果与闭壳氨基酸分子丙氨酸没有什么不同，是丙氨酸自由基的非两性离子形式在气相中是稳定形式，而两性离子中性丙氨酸自由基在气相中不是稳定结构。 。发现在气相和溶液相中自由基的几何和EPR参数均取决于水分子与极性基团的氢键键合以及动态溶剂化。对气相中最佳自由基的计算表明，对于中性自由基，与水分子键合的氢推动了水分子的数量级降低。g张量分量g xx和g yy既不影响g zz分量也不影响超精细耦合常数（HFCC）。丙氨酸自由基阴离子从气相到溶液相的转移伴随着羧基氧原子上自旋密度的增加。然而，对于中性自由基，这种从气相到固溶相的转移伴随着氧原子上自旋密度的降低。在酸性和碱性溶液中，计算得出的各向同性HFCC和所有自由基的g张量均与实验良好吻合。
更新日期：2020-03-25
中文翻译：
辐射剂量法中L-α-丙氨酸自由基的结构，g张量和超精细偶联常数：从头算分子动力学模拟研究
丙氨酸用作伽马射线和电子束校准的传输标准剂量计。影响其剂量响应的一个重要因素是湿度，湿度会导致吸收剂量计算中的误差。从头开始进行分子动力学计算，以确定环境对酸性和碱性溶液中L-α-丙氨酸自由基的电子顺磁共振（EPR）参数的影响。一个新的结果与闭壳氨基酸分子丙氨酸没有什么不同，是丙氨酸自由基的非两性离子形式在气相中是稳定形式，而两性离子中性丙氨酸自由基在气相中不是稳定结构。 。发现在气相和溶液相中自由基的几何和EPR参数均取决于水分子与极性基团的氢键键合以及动态溶剂化。对气相中最佳自由基的计算表明，对于中性自由基，与水分子键合的氢推动了水分子的数量级降低。g张量分量g xx和g yy既不影响g zz分量也不影响超精细耦合常数（HFCC）。丙氨酸自由基阴离子从气相到溶液相的转移伴随着羧基氧原子上自旋密度的增加。然而，对于中性自由基，这种从气相到固溶相的转移伴随着氧原子上自旋密度的降低。在酸性和碱性溶液中，计算得出的各向同性HFCC和所有自由基的g张量均与实验良好吻合。
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