第二配位层的氧化还原活性二茂铁促使铁卟啉在氧存在下发生质子还原

采用洁净、可持续的替代能源以解决化石燃料的过度消耗及因其燃烧而导致的日益加剧的全球变暖问题已经成为当务之急.其中,如何实现在大气含氧条件下的析氢反应成为需要攻克的重大挑战.氧还原在热力学上比质子还原更容易进行,并且氧气部分还原时通常产生活性氧物种,致使催化剂失活.因此,需要开发在氧气存在情况下能够有效还原质子的催化剂.本文设计了一种四苯基铁卟啉分子,该分子通过三氮唑将四个二茂铁连接在苯基邻位,并证明该催化剂能够在有氧气的情况下高效还原质子,产生氢气.作为铁卟啉类化合物催化质子还原的活性物种,Fe(0)发生质子还原比发生O2还原的动力学速率快得多,从而为氧气存在下的选择性质子还原奠定了基础.     

Novel Metal- and Mineral-Acid–Free Synthesis of Organic Ammonium Tribromides and Application of Ethylenephenanthrolium Bistribromide for Bromination of Active Methylene Group of 1,3-Diketones and β-Ketoesters

A novel procedure for the preparation of organic ammonium tribromides (OATBs) is described from their corresponding bromides. Quaternary ammonium bromides (QABs) and a N,N′-heterocyclic dibromide are efficiently oxidized to their corresponding monotribromides and bistribromide by m-chloroperbenzoic acid (MCPBA) in the presence of 2 and 4 equiv of KBr, respectively. The reactions are carried out in an aqueous medium without the use of any mineral acid or metal catalyst/promoters. A variety of tribromides are synthesized in very good yields including a hitherto unknown reagent, 1,10-(ethane-1, 2-diyl)phenanthrolinediium bistribromide (EPDBT). EPDBT is investigated as brominating agent and found to be highly effective for selective bromination of active methylene groups of a variety of 1,3-diketones and β-ketoesters.     

Composite lifting of group inequalities and an application to two-row mixing inequalities

Given a valid inequality for the mixed integer infinite group relaxation, a composite lifting approach that combines sequential lifting and the use of a fill-in function is proposed that can be used to strengthen this inequality. Properties of this composite lifting such as bounds on the solution of the lifting problem and some necessary conditions for the lifted inequality to be minimal for the mixed integer infinite group relaxation are presented. Finally, this composite lifting approach is used to generate a strengthened version of the two-row mixing inequality that provides a new class of extreme inequalities for the two-row mixed integer infinite group relaxation.     

Triboluminescence in sodium chloride

The emission of light due to rubbing or impact of two surfaces (Triboluminescence) has been traditionally studied under visible and ultraviolet spectrum. The current study provides an experimental insight into infrared emission occurring during low velocity impact on common salt crystals. The high speed IR imaging done using a whole field IR camera is first of its kind of measurement that provides experimental verification of IR emission occurring in these events. It was observed that the nature of impact surface and the crystalline structure of the material have a marked role in the IR emission. Of the existing theories that explain the origin of light emission in TL, the model provided by Chapman, that TL is a thermal radiation from high temperature regions, which propagate along with the crack, matches closely with the current experimental observations.     

On the Importance of Anion–π Interactions in the Mechanism of Sulfide:Quinone Oxidoreductase

Sulfide:quinone oxidoreductase (SQR) is a flavin‐dependent enzyme that plays a physiological role in two important processes. First, it is responsible for sulfide detoxification by oxidizing sulfide ions (S^2? and HS^?) to elementary sulfur and the electrons are first transferred to flavin adenine dinucleotide (FAD), which in turn passes them to the quinone pool in the membrane. Second, in sulfidotrophic bacteria, SQRs play a key role in the sulfide‐dependent respiration and anaerobic photosynthesis, deriving energy for their growth from reduced sulfur. Two mechanisms of action for SQR have been proposed: first, nucleophilic attack of a Cys residue on the C4 of FAD, and second, an alternate anionic radical mechanism by direct electron transfer from Cys to the isoalloxazine ring of FAD. Both mechanisms involve a common anionic intermediate that it is stabilized by a relevant anion–π interaction and its previous formation (from HS^? and Cys‐S‐S‐Cys) is also facilitated by reducing the transition‐state barrier, owing to an interaction that involves the π system of FAD. By analyzing the X‐ray structures of SQRs available in the Protein Data Bank (PDB) and using DFT calculations, we demonstrate the relevance of the anion–π interaction in the enzymatic mechanism.     

Neptunium estimation in the spent fuel dissolver solution by inductively coupled plasma-atomic emission spectroscopy

This paper deals with the optimization of experimental conditions for the estimation of Np in spent fuel dissolver solution using 2-thenoyltrifluoroacetone (HTTA) as extractant. The quantitative extraction of Np from the dissolver solution employing 0.5 M HTTA/xylene was followed by its estimation by Inductively Coupled Plasma-Atomic Emission Spectroscopy (ICP-AES) after stripping it from the organic phase with 8 M HNO₃. The reliability of the method was checked by standard addition technique. The method is precise and accurate yielding Np analytical recovery of 99 ± 1%.