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首页> 外文期刊>Dalton transactions: An international journal of inorganic chemistry >Vitamin B_12 as an allosteric cofactor;dual fluorescence,hysteresis,oscillations and the selection of corrin over porphyrin
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Vitamin B_12 as an allosteric cofactor;dual fluorescence,hysteresis,oscillations and the selection of corrin over porphyrin

机译：维生素B_12作为变构辅因子;双荧光，迟滞，振荡和卟啉比卟啉的选择

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Studies of the emission spectra of four Co(III)cobinamides(diaquo-,aquohydroxo-,dihydroxo-and dicyano-)show(1)that the excited states corresponding to the alpha beta and 8 absorption bands behave like the S_1 and S_2 levels in the non-alternant hydrocarbon azulene(with emission from S_2 S_1 in violation of Kasha's rule)and(2)that the excited states include a TICT(twisted intramolecular charge transfer)mechanism,as in the simpler cyanines,but where the TICT state gives rise to dual fluorescence instead of cis-trans isomerisation.Combined with the previously reported dual fluorescence from the S_1 level in synthetic metal corrinoids and in the naturally-occurring metal-free corrin,this provides evidence that the existence of an additional(metastable)ground state with a significantly different vibronic splitting and nuclear configuration is an intrinsic property of the basic corrin ligand(irrespective of the nature of the side-chains and the metal ion or even the absence of a metal)which distinguishes it from porphyrin.The occurrence of hysteresis(and its associated oscillations)in redox reactions of the cobinamides involving both the Co~III/II and Co_II/I couples indicates that the corrin ligand also has an intrinsic ability to exist in different conformations or"allosteric"forms with differing redox potential,which further distinguishes it from the porphyrin ligand.Possible links between the existence of an additional metastable ground state and of allosteric changes and the likely reasons for the selection of corrin over a porphyrin for the vitamin B_12-dependent enzymes are discussed.
机译：四种Co（III）cobinamides（双-，aquahydroxo-，dihydroxo-和dicyano-）的发射光谱研究表明：（1）对应于αβ和8个吸收带的激发态表现出与S_1和S_2的能级相似非交替碳氢z（具有从S_2 S_1的排放，违反了Kasha规则）和（2）激发态包括TICT（扭曲的分子内电荷转移）机制，如较简单的花菁一样，但TICT处于产生双荧光而不是顺反异构化。结合先前报道的合成金属类皮质醇和天然存在的不含金属的柯林中S_1级的双重荧光，这提供了另外一种（可转移的）存在的证据基波林配体的内在特性是具有基本的电子振动分裂和核构型的基态（无论侧链和金属离子的性质，甚至不存在金属） h区别于卟啉。在Co〜III / II和Co_II / I对的共结合酰胺的氧化还原反应中出现的迟滞（及其相关的振荡）表明，corrin配体也具有固有的能力以不同的构象存在氧化还原电位不同的“变构”或“变构”形式，这进一步与卟啉配体区分开。另外的亚稳态基态和变构变化的存在与维生素B_12取代卟啉时选择卟啉的可能原因之间可能存在联系依赖性酶被讨论。

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