Spin-orbit coupling and zero-field splitting of the high-spin ferric enzyme-substrate complex： Protocatechuate 3,4-dioxygenase complexed with 3,4-dihydroxyphenylacetate

• Published in: Chinese science bulletin 2013-02, Vol.58 (6), p.627-633
• Main Authors: Lü, LingLing, Zhu, YuanCheng, Wang, XiaoFang, Zuo, GuoFang, Guo, Feng, Zhao, SuRui, Wang, YongCheng
• Format: Article
• Language: English
• Subjects: Charge transfer; Chemistry/Food Science; Earth Sciences; Electronics; Engineering; Humanities and Social Sciences; iron; Life Sciences; Magnetic properties; Mathematical analysis; multidisciplinary; Orbitals; Origins; oxygenases; phenolic acids; Physics; Science; Science (multidisciplinary); Spin-orbit interactions; Splitting; 原儿茶酸; 双加氧酶; 复合物; 密度泛函计算; 底物; 自旋轨道耦合; 零场分裂; 高自旋
• ISSN: 1001-6538; 1861-9541
• DOI: 10.1007/s11434-012-5316-7

We used density functional calculations to investigate the electronic origins of the magnetic properties of the high-spin ferric en- zyme-substrate complex protocatechuate 3,4-dioxygenase （3,4-PCD）. The calculated g-tensors show that ligand-to-metal charge transfer transitions are from the protocatechuate （PCA） and Tyr408 orbitals to the Fe dπ orbitals, which lead to x- and y-polarized transitions. These polarized transitions require a spin-orbit coupling （SOC） matrix element in the z-direction, Lz （z = z＇）, resulting in a gz＇ value of 2.0158, significantly deviating from 2.0023. A large zero-field splitting parameter value of ＋1.147 cm-1 is due to AS = -1 spin-orbit mixing with the quartet states for the sextet ground state, accounting for around 73% of the SOC contribution. The SOC matrix elements indicate that the high-spin d5 system Fe（III）, 3,4-PCD-PCA is a weak spin-crossover compound with an SOC of 31.56 cm-1.