Vacuum ultraviolet spark emission spectra of fluorine and some polyatomic fluorides in noble gases

Spark emission spectra in the vacuum ultraviolet are reported for several polyatomic fluorides in He + Ar mixtures, and for pure fluorine. These results are discussed in terms of the potential of a given fluorine compound for ArF formation. The 158 nm emission in fluorine is tentatively assigned to the ³Π_g → ³Π_u.     

Heteropoly acids in the determination of phosphorus by neutron activation analysis

Phosphorus is selectively extracted as molybdovanadophosphoric acid (MVPA) and determined indirectly using⁵²V. Silicon, germanium, arsenic, fluoride and tannic acid do not interfere. The sensitivity for phosphorus was 1421±13 counts⁵²V per ng P ml^–1 with a detection limit of 0.2 ng P ml^–1. The precision is ±10% over the range 0.7±70 ng P ml^–1. The sensitivity is four orders of magnitude greater than for conventional neutron activation analysis (NAA) using the³¹P(n, )²⁸ Al reaction and a SLOWPOKE II reactor. Greater selectivity for phosphorus is obtained than by direct measurement of³²P by beta ray spectroscopy.     

Isonitrile Formation by a Non‐Heme Iron(II)‐Dependent Oxidase/Decarboxylase

The electron‐rich isonitrile is an important functionality in bioactive natural products, but its biosynthesis has been restricted to the IsnA family of isonitrile synthases. We herein provide the first structural and biochemical evidence of an alternative mechanism for isonitrile formation. ScoE, a putative non‐heme iron(II)‐dependent enzyme from Streptomyces coeruleorubidus, was shown to catalyze the conversion of (R)‐3‐((carboxymethyl)amino)butanoic acid to (R)‐3‐isocyanobutanoic acid through an oxidative decarboxylation mechanism. This work further provides a revised scheme for the biosynthesis of a unique class of isonitrile lipopeptides, of which several members are critical for the virulence of pathogenic mycobacteria.     

An Immobilized‐Dirhodium Hollow‐Fiber Flow Reactor for Scalable and Sustainable C−H Functionalization in Continuous Flow

A scalable flow reactor is demonstrated for enantioselective and regioselective rhodium carbene reactions (cyclopropanation and C?H functionalization) by developing cascade reaction methods employing a microfluidic flow reactor system containing immobilized dirhodium catalysts in conjunction with the flow synthesis of diazo compounds. This allows the utilization of the energetic diazo compounds in a safe manner and the recycling of the dirhodium catalysts multiple times. This approach is amenable to application in a bulk‐scale synthesis employing asymmetric C?H functionalization by stacking multiple fibers in one reactor module. The products from this sequential flow–flow reactor are compared with a conventional batch reactor or flow–batch reactor in terms of yield, regioselectivity, and enantioselectivity.     

Two‐Color Valence‐to‐Core X‐ray Emission Spectroscopy Tracks Cofactor Protonation State in a Class I Ribonucleotide Reductase

Proton transfer reactions are of central importance to a wide variety of biochemical processes, though determining proton location and monitoring proton transfers in biological systems is often extremely challenging. Herein, we use two‐color valence‐to‐core X‐ray emission spectroscopy (VtC XES) to identify protonation events across three oxidation states of the O₂‐activating, radical‐initiating manganese–iron heterodinuclear cofactor in a class I‐c ribonucleotide reductase. This is the first application of VtC XES to an enzyme intermediate and the first simultaneous measurement of two‐color VtC spectra. In contrast to more conventional methods of assessing protonation state, VtC XES is a more direct probe applicable to a wide range of metalloenzyme systems. These data, coupled to insight provided by DFT calculations, allow the inorganic cores of the Mn^IVFe^IV and Mn^IVFe^III states of the enzyme to be assigned as Mn^IV(μ‐O)₂Fe^IV and Mn^IV(μ‐O)(μ‐OH)Fe^III, respectively.     

Oxidopyrylium [5+2] cycloaddition chemistry: Historical perspective and recent advances (2008–2018)

The following review article provides an overview of oxidopyrylium [5+2] cycloaddition chemistry, with a particular emphasis placed on seminal historical developments and advancements made over the last decade. It is our hope this review serves as a valuable resource to those interested in the oxidopyrylium cycloaddition chemistry, and helps inspire future advancements.     

Indyllithium and the Indyl Anion [InL]−: Heavy Analogues of N‐Heterocyclic Carbenes

Reduction of the indate complex In(NON^Ar)(μ‐Cl)₂Li(OEt₂)₂ (NON^Ar=[O(SiMe₂NAr)₂]^2?; Ar=2,6‐iPr₂C₆H₃) with sodium generates the In^II diindane species [In(NON^Ar)]₂. Further reduction with a mixture of potassium and [2.2.2]crypt affords the In^I N‐heterocyclic indyl anion [In(NON^Ar)]^?, which crystallizes with a non‐contacted [K([2.2.2]crypt)]⁺ cation. The indyl anion can also be isolated as the indyllithium compound In(NON^Ar)(Li{THF}₃), which contains an In?Li bond. Density functional theory calculations show that the HOMO of the indyl anion is a metal‐centred lone pair, and preliminary reactivity studies confirm its nucleophilic behaviour.     

Characterization of hydrates of norfloxacin

Norfloxacin, a nalidixic acid analog with antimicrobial properties, exists in different hydrated forms. Three of these crystal forms were reproducibly prepared and characterized by analytical techniques that included infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, differential scanning calorimetry, solution microcalorimetry and pulsed nuclear-magnetic resonance spectroscopy.These studies showed that the dihydrate is the thermodynamically stable entity at ambient temperatures and humidities.