Electrochemical and spectroscopic effects of mixed substituents in bis(phenolate)-copper(II) galactose oxidase model complexes.
Electrochemical and spectroscopic effects of mixed substituents in bis(phenolate)-copper(II) galactose oxidase model complexes.
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DOI：
10.1021/ja211247f
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发表时间：
2012-05-02
影响因子：
15
通讯作者：
Stack TD
中科院分区：
文献类型：
--
作者：
Pratt RC;Lyons CT;Wasinger EC;Stack TD
非对称取代的Salen（1 R1，R2）和减少的Salen（2 R1，R2）铜II-苯氧基配合物与tBu，SiPr和-OMe取代基的组合导致其氧化还原和光谱性质的显着差异，提供洞察半胱氨酸修饰的酪氨酸辅因子在酶半乳糖氧化酶（GO）的影响。使用改进的Marcus-Hush分析，氧化铜配合物的特征在于由于两个取代的酚盐之间的电子分化为II类混合价。硫K边X-射线吸收光谱（XAS）评估自由基离域到7%的非对称[1 tBu，SMe]+的单个硫原子上的程度，与其他光谱和电化学结果一致，表明优先氧化的-SMe轴承酚盐。对[1 R1，R2]+和[2 R1，R2]+的两个定域态之间的热力学自由能差（ΔG_（11））和重组能（λ R1 R2）的估计导致对光谱观察到的IVCT跃迁能的准确预测。使用[2 R1，R2]+确定的参数对GO应用改进的Marcus-Hush分析，预测Vmax约为13600 cm−1，正好在酶显示的宽可见-近红外带的能量范围内。
Non-symmetric substitution of salen (1R1,R2) and reduced salen (2R1,R2) CuII-phenoxyl complexes with a combination of -tBu, -SiPr, and -OMe substituents leads to dramatic differences in their redox and spectroscopic properties, providing insight into the influence of the cysteine-modified tyrosine cofactor in the enzyme galactose oxidase (GO). Using a modified Marcus-Hush analysis, the oxidized copper complexes are characterized as Class II mixed-valent due to the electronic differentiation between the two substituted phenolates. Sulfur K-edge X-ray absorption spectroscopy (XAS) assesses the degree of radical delocalization onto the single sulfur atom of non-symmetric [1tBu,SMe]+ at 7%, consistent with other spectroscopic and electrochemical results that suggest preferential oxidation of the -SMe bearing phenolate. Estimates of the thermodynamic free-energy difference between the two localized states (ΔG∘) and reorganizational energies (λR1R2) of [1R1,R2]+ and [2R1,R2]+ leads to accurate predictions of the spectroscopically observed IVCT transition energies. Application of the modified Marcus-Hush analysis to GO using parameters determined for [2R1,R2]+ predicts a νmax of ~ 13600 cm−1, well within the energy range of the broad Vis-NIR band displayed by the enzyme.
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