The protonation state of ascorbate peroxidase compound II (APX-II) has been a subject of debate. A combined X-ray/neutron crystallographic study reported that APX-II is best described as an iron(IV)hydroxide species with an FeO distance of 1.88 Å (Kwon, et al. Nat Commun 2016, 7, 13,445), while X-ray absorption spectroscopy (XAS) experiments (utilizing extended X-ray absorption fine structure (EXAFS) and pre-edge analyses) indicate APX-II is an authentic iron(IV)oxo species with an FeO distance 1.68 Å (Ledray, et al. Journal of the American Chemical Society 2020, 142, 20,419). Previous debates concerning ferryl protonation states have been resolved through the application of Badger's rule, which correlates FeO bond distances with FeO vibrational frequencies. To obtain the required vibrational data, we have collected Nuclear Resonance Vibrational Spectroscopy (NRVS) data for APX-II. We observe a broad vibrational feature in the range associated with iron(IV)oxo stretching (700–800 cm⁻¹). This feature appears to have two peaks at 732 cm⁻¹ and 770 cm⁻¹, corresponding to FeO distances of 1.69 and 1.67 Å, respectively. The broad vibrational envelope and the presence of multiple resonances could reflect a distribution of hydrogen bonding interactions within the active-site pocket.

抗坏血酸过氧化物酶化合物 II (APX-II) 的质子化状态一直是争论的主题。一项联合 X 射线/中子晶体学研究报告称，APX-II 最好被描述为一种铁 ​​( IV ) 氢氧化物，Fe O 距离为 1.88 Å (Kwon, et al. Nat Commun 2016 , 7, 13,445)，而 X射线吸收光谱 (XAS) 实验（利用扩展的 X 射线吸收精细结构 (EXAFS) 和前边缘分析）表明 APX-II 是一种真正的铁 ( IV ) 氧代物种，Fe O 距离为 1.68 Å (Ledray, et al.美国化学学会杂志 2020, 142, 20,419)。以前关于ferrl 质子化状态的争论已经通过应用Badger 规则得到解决，该规则将Fe O 键距离与Fe O 振动频率相关联。为了获得所需的振动数据，我们收集了 APX-II 的核共振振动光谱 (NRVS) 数据。我们观察到与铁（ IV）氧拉伸（700-800 cm ^-1 ）相关的范围内的广泛振动特征。该特征似乎在 732 cm ^-1和 770 cm ^-1处有两个峰，对应于 FeO 距离分别为 1.69 和 1.67 Å。广泛的振动包络和多个共振的存在可以反映活性位点口袋内氢键相互作用的分布。