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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Electronic Structure of a Transient Histidine Radical in Liquid Aqueous Solution: EPR Continuous-Flow Studies and Density Functional Calculations
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Electronic Structure of a Transient Histidine Radical in Liquid Aqueous Solution: EPR Continuous-Flow Studies and Density Functional Calculations

机译：溶液中瞬态组氨酸自由基的电子结构：EPR连续流研究和密度泛函计算

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摘要

Transient histidine radicals formed in aqueous solutions by oxidation of histidine with a Ti~(3+)/H_2O_2 Fenton system at pH 2.0 have been studied by EPR using a fast continuous-flow setup and a dielectric ring resonator equipped with a mixing chamber. A histidine peroxy radical with a single EPR line at g = 2.0151 and a histidine cation radical with a complex hyperfine structure and g = 2.0023 have been detected. The hyperfine structure of the latter radical was analyzed by investigating two selectively deuterated histidines and using an EPR simulation and fit program for analysis of the spectra. Isotropic hyperfine coupling constants of two #beta#-protons, three ring protons, and two nitrogen nuclei have been determined in this way and assigned to a histidine-OH adduct cation radical. Density functional theory (DFT) calculations at the B3LYP and PWP86 levels have been performed on protonated cation radicals of 4-ethylimidazole (as histidine models), yielding isotropic hyperfine coupling constants for three different positions of OH addition. The C5 position for OH addition (a 5-oxohistidine cation radical) is clearly supported by the calculated hyperfine coupling constants. The agreement between DFT and EPR is further improved when hydrogen-bonding interactions to the N1 and C2 protons are introduced in the calculations.
机译：通过使用快速连续流装置和配备有混合室的介电环共振器的EPR，研究了在pH 2.0的条件下用Ti〜（3 +）/ H_2O_2 Fenton系统氧化组氨酸而在水溶液中形成的瞬态组氨酸自由基。已检测到在g = 2.0151处具有单个EPR线的组氨酸过氧自由基和具有复杂的超精细结构且g = 2.0023的组氨酸阳离子自由基。通过研究两个选择性氘化的组氨酸，并使用EPR模拟和拟合程序对光谱进行分析，分析了后者的超精细结构。已经以这种方式确定了两个＃β＃质子，三个环质子和两个氮核的各向同性超精细偶合常数，并将其分配给组氨酸-OH加合物阳离子自由基。已对4-乙基咪唑的质子化阳离子自由基（作为组氨酸模型）进行了B3LYP和PWP86浓度的密度泛函理论（DFT）计算，从而为OH加成的三个不同位置产生了各向同性的超精细偶合常数。 OH加成（5-氧代组氨酸阳离子基团）的C5位置清楚地由计算的超精细偶合常数支持。当在计算中引入与N1和C2质子的氢键相互作用时，DFT和EPR之间的一致性得到进一步改善。

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