Spectroscopic Description of the E1 State of Mo Nitrogenase Based on Mo and Fe X‑ray Absorption and Mössbauer Studies

Mo nitrogenase (N2ase) utilizes a two-component protein system, the catalytic MoFe and its electron-transfer partner FeP, to reduce atmospheric dinitrogen (N2) to ammonia (NH3). The FeMo cofactor contained in the MoFe protein serves as the catalytic center for this reaction and has long inspired model chemistry oriented toward activating N2. This field of chemistry has relied heavily on the detailed characterization of how Mo N2ase accomplishes this feat. Understanding the reaction mechanism of Mo N2ase itself has presented one of the most challenging problems in bioinorganic chemistry because of the ephemeral nature of its catalytic intermediates, which are difficult, if not impossible, to singly isolate. This is further exacerbated by the near necessity of FeP to reduce native MoFe, rendering most traditional means of selective reduction inept. We have now investigated the first fundamental intermediate of the MoFe catalytic cycle, E1, as prepared both by low-flux turnover and radiolytic cryoreduction, using a combination of Mo Kα highenergy-resolution fluorescence detection and Fe K-edge partial-fluorescence-yield X-ray absorption spectroscopy techniques. The results demonstrate that the formation of this state is the result of an Fe-centered reduction and that Mo remains redoxinnocent. Furthermore, using Fe X-ray absorption and 57Fe Mössbauer spectroscopies, we correlate a previously reported unique species formed under cryoreducing conditions to the natively formed E1 state through annealing, demonstrating the viability of cryoreduction in studying the catalytic intermediates of MoFe

Simple Preparation of LaPO4:Ce, Tb Phosphors by an Ionic-Liquid-Driven Supported Liquid Membrane System

In this work, LaPO4:Ce, Tb phosphors were prepared by firing a LaPO4:Ce, Tb precipitate using an ionic-liquid-driven supported liquid membrane system. The entire system consisted of three parts: a mixed rare earth ion supply phase, a phosphate supply phase, and an ionic-liquid-driven supporting liquid membrane phase. This method showed the advantages of a high flux, high efficiency, and more controllable reaction process. The release rate of PO43− from the liquid film under different types of ionic liquid, the ratio of the rare earth ions in the precursor mixture, and the structure, morphology, and photoluminescence properties of LaPO4:Ce, Tb were investigated by inductively coupled plasma-atomic emission spectroscopy, X-ray diffraction, Raman spectra, scanning electron microscopy, and photoluminescence emission spectra methods. The results showed that a pure phase of lanthanum orthophosphate with a monoclinic structure can be formed. Due to differences in the anions in the rare earth supply phase, the prepared phosphors showed micro-spherical (when using rare earth sulfate as the raw material) and nanoscale stone-shape (when using rare earth nitrate as the raw material) morphologies. Moreover, the phosphors prepared by this method had good luminescent properties, reaching a maximum emission intensity under 277 nm excitation with a predominant green emission at 543 nm which corresponded to the 5D4-7F5 transition of Tb3+

Modeling Non-Heme Iron Halogenases: High-Spin Oxoiron(IV)–Halide Complexes That Halogenate C–H Bonds

The non-heme iron halogenases CytC3 and SyrB2 catalyze C–H bond halogenation in the biosynthesis of some natural products via <i>S</i> = 2 oxoiron­(IV)–halide intermediates. These oxidants abstract a hydrogen atom from a substrate C–H bond to generate an alkyl radical that reacts with the bound halide to form a C–X bond chemoselectively. The origin of this selectivity has been explored in biological systems but has not yet been investigated with synthetic models. Here we report the characterization of <i>S</i> = 2 [Fe^IV(O)­(TQA)­(Cl/Br)]⁺ (TQA = tris­(quinolyl-2-methyl)­amine) complexes that can preferentially halogenate cyclohexane. These are the first synthetic oxoiron­(IV)–halide complexes that serve as spectroscopic and functional models for the halogenase intermediates. Interestingly, the nascent substrate radicals generated by these synthetic complexes are not as short-lived as those obtained from heme-based oxidants and can be intercepted by O₂ to prevent halogenation, supporting an emerging notion that rapid rebound may not necessarily occur in non-heme oxoiron­(IV) oxidations

The Migration of Samarium(Ⅲ)across Oil/water Interface

钐离子在油／水界面迁移的电化学行为①狄俊伟＊徐肖邢＊＊吴莹范瑞溪（苏州大学化学化工学院苏州２１５００６）近年来，人们对中性载体推动金属离子在油／水界面转移的报道较多［１～４］．通常的实验研究大多采用水相中的金属离子ＭＺ＋大大过量，而于油相中溶解少量的...The migration of Samarium(Ⅲ)across water/nitrobenzene (w/nb) interface facilitated by diantipyrylmethane (DAM) and the electrochemical behaviour affected by emulsifier OP in the nb phase have been studied by normal and convolute cyclic voltammetry. It is concluded that the formation of the complex occurs at w/nb interface and the mechanism of the samarium(Ⅲ)transfer across w/nb interface facilitated by DAM is E mechanism.作者联系地址：苏州大学化学化工学院Author's Address: School of Chem. and Chemical Eng., Suzhou Univ., Suzhou 21500

Timing of formation of the Hongdonggou Pb-Zn polymetallic ore deposit, Henan Province, China: Evidence from Rb-Sr isotopic dating of sphalerites

The Hongdonggou Pb-Zn polymetallic ore deposit, located in the southwestern part of the Luanchuan Mo-W-Pb-Zn-Ag polymetallic ore mineralization in Henan Province, China, is an important part of the East Qinling metallogenic belt. The orebodies in the deposit, which are vein, bedded and lenticular, are mainly hosted in the syenite porphyry, and formed within the carbonate and clastic rocks of the Yuku and Qiumugou formations partially. The genesis of the deposit has previously been argued to be of hydrothermal-vein type or of skarn-hydrothermal type. In this study, we report the results of Rb-Sr isotopic dating based on sphalerites from the main orebody of the Hongdonggou Pb-Zn polymetallic ore deposit, which yield an isochron age of 135.7 ± 3.2 Ma, constraining the timing of mineralization as early Cretaceous. The age is close to those reported for the Pb-Zn deposits in the Luanchuan ore belt. The (87Sr/86Sr)i values of the sphalerites (0.71127 ± 0.00010) are lower than that of terrigenous silicates (0.720) and higher than the mantle (0.707), suggesting that the metallogenic components were mainly derived through crust-mantle mixing. Combining the results from this study with those from previous work, we propose that the Hongdonggou Pb-Zn polymetallic ore deposit is a hydrothermal-vein deposit associated with the early Cretaceous tectonothermal event, and the mineralization is controlled by NW- and near EW-trending faults in the Luanchuan Mo-W-Pb-Zn-Ag polymetallic ore concentration belt

Design and application of a pharyngeal swab samples collection device (一种咽拭子采集装置的设计及应用)

Objective To explore the clinical application effect of a pharyngeal swab samples collection device in nucleic acid testing. Methods A total of 120 hospital staff members who conducted nucleic acid testing were randomly divided into the control group and study group, with 60 cases in each group. The control group adopted regular method of pharyngeal swab samples collection, while the study group used the new type device for pharyngeal swab samples collection. The time cost in sample collection was recorded. The degree of comfort and satisfaction in objects of sample collection were measured. Results The time spent in sample collection was (22. 84±2. 57)s in the study group, which was shorter than that in the control group (P＜0. 05). The degree of comfort and satisfaction in objects of sample collection were higher than in the study group than those in the control group (P＜0. 05). Conclusion The new type of pharyngeal swab samples collection device is effective to improve the efficiency of sampling in nucleic acid testing. (目的 探讨一种新型咽拭子采集装置在核酸检测中的应用效果。方法 选取核酸采集点进行采样的医务人员120人, 随机分为试验组和对照组, 各60人。对照组采用常规咽拭子采集方法, 试验组采用新型咽拭子采集装置采集。记录两组咽拭子采集时间, 评价被采集对象的舒适度和满意度。结果 试验组咽拭子采集时间(22. 84±2. 57)s, 短于对照组(27. 56±2. 44)s, 差异有统计学意义(P＜0. 05)。试验组舒适度和满意度均高于对照组, 差异有统计学意义(P＜0. 05)。结论 新型咽拭子采集装置能有效提高采样效率。

Mechanism for Six-Electron Aryl-N-Oxygenation by the Non-Heme Diiron Enzyme CmlI

The ultimate step in chloramphenicol (CAM) biosynthesis is a six-electron oxidation of an aryl-amine precursor (NH₂-CAM) to the aryl-nitro group of CAM catalyzed by the non-heme diiron cluster-containing oxygenase CmlI. Upon exposure of the diferrous cluster to O₂, CmlI forms a long-lived peroxo intermediate, <b>P</b>, which reacts with NH₂-CAM to form CAM. Since <b>P</b> is capable of at most a two-electron oxidation, the overall reaction must occur in several steps. It is unknown whether <b>P</b> is the oxidant in each step or whether another oxidizing species participates in the reaction. Mass spectrometry product analysis of reactions under ¹⁸O₂ show that both oxygen atoms in the nitro function of CAM derive from O₂. However, when the single-turnover reaction between ¹⁸O₂-<b>P</b> and NH₂-CAM is carried out in an ¹⁶O₂ atmosphere, CAM nitro groups contain both ¹⁸O and ¹⁶O, suggesting that <b>P</b> can be reformed during the reaction sequence. Such reformation would require reduction by a pathway intermediate, shown here to be NH­(OH)-CAM. Accordingly, the aerobic reaction of NH­(OH)-CAM with diferric CmlI yields <b>P</b> and then CAM without an external reductant. A catalytic cycle is proposed in which NH₂-CAM reacts with <b>P</b> to form NH­(OH)-CAM and diferric CmlI. Then the NH­(OH)-CAM rereduces the enzyme diiron cluster, allowing <b>P</b> to reform upon O₂ binding, while itself being oxidized to NO-CAM. Finally, the reformed <b>P</b> oxidizes NO-CAM to CAM with incorporation of a second O₂-derived oxygen atom. The complete six-electron oxidation requires only two exogenous electrons and could occur in one active site

NMR and Mössbauer Studies Reveal a Temperature-Dependent Switch from S = 1 to 2 in a Nonheme Oxoiron(IV) Complex with Faster C-H Bond Cleavage Rates

S = 2 FeIV═O centers generated in the active sites of nonheme iron oxygenases cleave substrate C-H bonds at rates significantly faster than most known synthetic FeIV═O complexes. Unlike the majority of the latter, which are S = 1 complexes, [FeIV(O)(tris(2-quinolylmethyl)amine)(MeCN)]2+ (3) is a rare example of a synthetic S = 2 FeIV═O complex that cleaves C-H bonds 1000-fold faster than the related [FeIV(O)(tris(pyridyl-2-methyl)amine)(MeCN)]2+ complex (0). To rationalize this significant difference, a systematic comparison of properties has been carried out on 0 and 3 as well as related complexes 1 and 2 with mixed pyridine (Py)/quinoline (Q) ligation. Interestingly, 2 with a 2-Q-1-Py donor combination cleaves C-H bonds at 233 K with rates approaching those of 3, even though Mössbauer analysis reveals 2 to be S = 1 at 4 K. At 233 K however, 2 becomes S = 2, as shown by its 1H NMR spectrum. These results demonstrate a unique temperature-dependent spin-state transition from triplet to quintet in oxoiron(IV) chemistry that gives rise to the high C-H bond cleaving reactivity observed for 2.</p