Department of Chemistry, Stanford University, Stanford, California 94305, USA.
J Am Chem Soc. 2012 May 2;134(17):7367-77. doi: 10.1021/ja211247f. Epub 2012 Apr 23.
Nonsymmetric substitution of salen (1(R(1),R(2))) and reduced salen (2(R(1),R(2))) Cu(II)-phenoxyl complexes with a combination of -(t)Bu, -S(i)Pr, 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 nonsymmetric 1((t)Bu,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(o)) and reorganizational energies (λ(R(1)R(2))) of 1(R(1),R(2)) and 2(R(1),R(2)) lead to accurate predictions of the spectroscopically observed IVCT transition energies. Application of the modified Marcus-Hush analysis to GO using parameters determined for 2(R(1),R(2)) predicts a ν(max) of ∼13600 cm(-1), well within the energy range of the broad Vis-NIR band displayed by the enzyme.
非对称取代手性水杨醛亚胺（1(R(1),R(2)))和还原水杨醛亚胺（2(R(1),R(2)))Cu(II)-苯氧自由基配合物，与-(t)Bu、-S(i)Pr 和-OMe 取代基结合，导致其氧化还原和光谱性质发生显著变化，为研究半胱氨酸修饰的酪氨酸辅因子在半乳糖氧化酶（GO）中的影响提供了深入了解。使用改进的马库斯-休斯分析，氧化态铜配合物被表征为 II 类混合价态，这是由于两个取代苯氧自由基之间的电子区分。硫 K 边 X 射线吸收光谱（XAS）评估了非对称 1((t)Bu,SMe)中单硫原子自由基离域的程度为 7%，这与其他光谱和电化学结果一致，表明优先氧化带有-SMe 的苯氧自由基。两个局域态（ΔG(o)）和 1(R(1),R(2))和 2(R(1),R(2))的重组能（λ(R(1)R(2)))之间的热力学自由能差（ΔG(o)）的估计值，导致对光谱观察到的 IVCT 跃迁能量进行了准确预测。使用为 2(R(1),R(2))确定的参数对 GO 应用改进的马库斯-休斯分析，预测ν(max)约为 13600 cm(-1)，在酶显示的宽可见-近红外带的能量范围内。
