Dmitriy A. Lukoyanov, Zhi-Yong Yang, Krista Shisler, John W. Peters, Simone Raugei, Dennis R. Dean, Lance C. Seefeldt and Brian M. Hoffman
{"title":"A conformational equilibrium in the nitrogenase MoFe protein with an α-V70I amino acid substitution illuminates the mechanism of H2 formation†","authors":"Dmitriy A. Lukoyanov, Zhi-Yong Yang, Krista Shisler, John W. Peters, Simone Raugei, Dennis R. Dean, Lance C. Seefeldt and Brian M. Hoffman","doi":"10.1039/D2FD00153E","DOIUrl":"https://doi.org/10.1039/D2FD00153E","url":null,"abstract":"<p >Study of α-V70I-substituted nitrogenase MoFe protein identified Fe6 of FeMo-cofactor (Fe<small><sub>7</sub></small>S<small><sub>9</sub></small>MoC-homocitrate) as a critical N<small><sub>2</sub></small> binding/reduction site. Freeze-trapping this enzyme during Ar turnover captured the key catalytic intermediate in high occupancy, denoted E<small><sub>4</sub></small>(4H), which has accumulated 4[e<small><sup>?</sup></small>/H<small><sup>+</sup></small>] as two bridging hydrides, Fe2–H–Fe6 and Fe3–H–Fe7, and protons bound to two sulfurs. E<small><sub>4</sub></small>(4H) is poised to bind/reduce N<small><sub>2</sub></small> as driven by mechanistically-coupled H<small><sub>2</sub></small> reductive-elimination of the hydrides. This process must compete with ongoing hydride protonation (HP), which releases H<small><sub>2</sub></small> as the enzyme relaxes to state E<small><sub>2</sub></small>(2H), containing 2[e<small><sup>?</sup></small>/H<small><sup>+</sup></small>] as a hydride and sulfur-bound proton; accumulation of E<small><sub>4</sub></small>(4H) in α-V70I is enhanced by HP suppression. EPR and <small><sup>95</sup></small>Mo ENDOR spectroscopies now show that resting-state α-V70I enzyme exists in two conformational states, both in solution and as crystallized, one with wild type (WT)-like FeMo-co and one with perturbed FeMo-co. These reflect two conformations of the Ile residue, as visualized in a reanalysis of the X-ray diffraction data of α-V70I and confirmed by computations. EPR measurements show delivery of 2[e<small><sup>?</sup></small>/H<small><sup>+</sup></small>] to the E<small><sub>0</sub></small> state of the WT MoFe protein and to both α-V70I conformations generating E<small><sub>2</sub></small>(2H) that contains the Fe3–H–Fe7 bridging hydride; accumulation of another 2[e<small><sup>?</sup></small>/H<small><sup>+</sup></small>] generates E<small><sub>4</sub></small>(4H) with Fe2–H–Fe6 as the second hydride. E<small><sub>4</sub></small>(4H) in WT enzyme and a minority α-V70I E<small><sub>4</sub></small>(4H) conformation as visualized by QM/MM computations relax to resting-state through two HP steps that reverse the formation process: HP of Fe2–H–Fe6 followed by slower HP of Fe3–H–Fe7, which leads to transient accumulation of E<small><sub>2</sub></small>(2H) containing Fe3–H–Fe7. In the dominant α-V70I E<small><sub>4</sub></small>(4H) conformation, HP of Fe2–H–Fe6 is passively suppressed by the positioning of the Ile sidechain; slow HP of Fe3–H–Fe7 occurs first and the resulting E<small><sub>2</sub></small>(2H) contains Fe2–H–Fe6. It is this HP suppression in E<small><sub>4</sub></small>(4H) that enables α-V70I MoFe to accumulate E<small><sub>4</sub></small>(4H) in high occupancy. In addition, HP suppression in α-V70I E<small><sub>4</sub></small>(4H) kinetically unmasks hydride reductive-elimination without N<small><sub>2</sub></small>-binding, a process that is precluded in WT enzyme.</p>","PeriodicalId":76,"journal":{"name":"Faraday Discussions","volume":"243 ","pages":" 231-252"},"PeriodicalIF":3.4,"publicationDate":"2023-01-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"3936035","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Boosting the activity of Mizoroki–Heck cross-coupling reactions with a supramolecular palladium catalyst favouring remote Zn⋯pyridine interactions†","authors":"Naba Abuhafez and Rafael Gramage-Doria","doi":"10.1039/D2FD00165A","DOIUrl":"https://doi.org/10.1039/D2FD00165A","url":null,"abstract":"<p >Transition metal catalysis benefitting from supramolecular interactions in the secondary coordination sphere in order to pre-organize substrates around the active site and reach a specific selectivity typically occurs under long reaction times and mild reaction temperatures with the aim to maximize such subtle effects. Herein, we demonstrate that the kinetically labile Zn⋯N interaction between a pyridine substrate and a zinc–porphyrin site serving for substrate binding is a unique type of weak interaction that enables identification of supramolecular effects in transition metal catalysis after one hour at a high reaction temperature of 130 °C. Under carefully selected reaction conditions, supramolecularly-regulated palladium-catalyzed Mizoroki–Heck reactions between 3-bromopyridine and terminal olefins (acrylates or styrenes) proceeded in a more efficient manner compared to the non-supramolecular version. The supramolecular catalysis developed here also displayed interesting substrate-selectivity patterns.</p>","PeriodicalId":76,"journal":{"name":"Faraday Discussions","volume":"244 ","pages":" 186-198"},"PeriodicalIF":3.4,"publicationDate":"2023-01-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://pubs.rsc.org/en/content/articlepdf/2023/fd/d2fd00165a?page=search","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"3693584","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Arnau Vicens, Laia Vicens, Giorgio Olivo, Osvaldo Lanzalunga, Stefano Di Stefano and Miquel Costas
{"title":"Site-selective methylene C–H oxidation of an alkyl diamine enabled by supramolecular recognition using a bioinspired manganese catalyst†","authors":"Arnau Vicens, Laia Vicens, Giorgio Olivo, Osvaldo Lanzalunga, Stefano Di Stefano and Miquel Costas","doi":"10.1039/D2FD00177B","DOIUrl":"https://doi.org/10.1039/D2FD00177B","url":null,"abstract":"<p >Site-selective oxidation of aliphatic C–H bonds is a powerful synthetic tool because it enables rapid build-up of product complexity and diversity from simple precursors. Besides the poor reactivity of alkyl C–H bonds, the main challenge in this reaction consists in differentiating between the multiple similar sites present in most organic molecules. Herein, a manganese oxidation catalyst equipped with two 18-benzo-6-crown ether receptors has been employed in the oxidation of the long chain tetradecane-1,14-diamine. <small><sup>1</sup></small>H-NMR studies evidence simultaneous binding of the two protonated amine moieties to the crown ether receptors. This recognition has been used to pursue site-selective oxidation of a methylenic site, using hydrogen peroxide as oxidant in the presence of carboxylic acids as co-ligands. Excellent site-selectivity towards the central methylenic sites (C6 and C7) is observed, overcoming selectivity parameters derived from polar deactivation by simple amine protonation and selectivity observed in the oxidation of related monoprotonated amines.</p>","PeriodicalId":76,"journal":{"name":"Faraday Discussions","volume":"244 ","pages":" 51-61"},"PeriodicalIF":3.4,"publicationDate":"2023-01-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://pubs.rsc.org/en/content/articlepdf/2023/fd/d2fd00177b?page=search","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"3936058","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
求助内容：
应助结果提醒方式：
京公网安备 11010802042870号
