Redox-inactive and -active metal ions that act as Lewis acids are essential cofactors in modulating the redox reactivity of metal–oxygen complexes and metalloenzymes, such as the manganese(V)-oxo intermediate in the oxygen-evolving complex, where Ca²⁺ in the Mn₄CaO₅ cluster is indispensable for the catalytic water oxidation in Photosystem II. Zinc ion is also an essential cofactor in Cu-Zn superoxide dismutases (Cu,Zn-SOD), in which binding of O₂⁻ to Zn²⁺ facilitates the electron-transfer reduction of O₂⁻, whereas Zn²⁺ ion that is bridged with Cu²⁺ by imidazolate accelerates the electron-transfer oxidation of O₂⁻. This review focuses on the effects of redox-inactive and –active metal ions that act as Lewis acids on the electron-transfer and redox reactivity of metal–oxygen intermediates such as metal-oxo, metal-peroxo and metal-superoxo complexes. Such electron-transfer reactions from electron donors to acceptors enhanced by binding of metal ions to electron acceptors is referred as metal ion-coupled electron transfer (MCET). Lewis acid metal ions can bind to metal-oxo, metal-peroxo and metal-superoxo complexes to enhance the MCET reactivity of these metal–oxygen species. A quantitative measure of Lewis acidity of redox-inactive diamagnetic metal ions is obtained from the g_zz values of EPR spectra of O₂⁻–metal ion complexes, whereas a quantitative measure of Lewis acidity of paramagnetic redox-active metal ions such as Fe³⁺ and Co²⁺ is provided from the emission maxima of 10-methylacridone–metal ion complexes. The MCET reactivity of Fe^IV-oxo, Mn^IV-oxo, Fe^III-peroxo, and Cr^III-superoxo complexes is enhanced by Lewis acids and the logarithm of the enhancement of the rate constant by metal ions is correlated linearly with the quantitative measure of Lewis acidity of metal ions obtained from the g_zz values of EPR spectra of O₂⁻–metal ion complexes and the emission maxima of metal ion–10-methylacridone complexes.

充当路易斯酸的氧化还原无活性和活化金属离子是调节金属-氧配合物和金属酶（例如，放氧复合物中的锰（V）-氧代中间体）的氧化还原反应的重要辅助因子，其中Ca ²⁺ Mn ₄ CaO ₅团簇中的碳原子对于光系统II中的催化水氧化是必不可少的。锌离子也是Cu-Zn类超氧化物歧化酶（铜，锌-SOD）的重要辅助因子，其中的O-结合₂ ^-对于Zn ²⁺便于0的电子转移还原₂ ^- ，而锌²⁺离子即与Cu ²⁺桥接通过咪唑酯加速的O的电子转移的氧化₂ ^- 。这篇综述着重讨论了充当路易斯酸的氧化还原无活性和活性金属离子对金属-氧中间体（如金属-氧，金属-过氧和金属-超氧配合物）的电子转移和氧化还原反应的影响。从电子供体到通过金属离子与电子受体结合而增强的受体的这种电子转移反应称为金属离子偶联电子转移（MCET）。路易斯酸性金属离子可与金属-氧，金属-过氧和金属-超氧配合物结合，从而增强这些金属-氧物种的MCET反应性。从O的EPR光谱的g _zz值获得了对氧化还原惰性的反磁性金属离子的Lewis酸度的定量测量₂ ^- -金属离子复合物，而顺磁性氧化还原活性的金属离子，例如Fe的路易斯酸性的定量量度³⁺和Co ²⁺是从10甲基吖啶酮-金属离子复合物的发射最大值提供。路易斯酸可增强Fe ^IV-氧，Mn ^IV-氧，Fe ^III-过氧和Cr ^III-超氧配合物的MCET反应性，并且金属离子提高速率常数的对数与定量方法线性相关从得到的金属离子的路易斯酸性克_ZZ EPR光谱的O值₂ ^-–金属离子配合物和金属离子–10-甲基ac啶酮配合物的发射最大值。