An Enantioselective Artificial Suzukiase Based on the Biotin–Streptavidin Technology

Introduction of a biotinylated monophosphine palladium complex within streptavidin affords an enantioselective artificial Suzukiase. Site-directed mutagenesis allowed the optimization of the activity and the enantioselectivity of this artificial metalloenzyme. A variety of atropisomeric biaryls were produced in good yields and up to 90% ee. The hybrid catalyst described herein shows comparable TOF to the previous aqueous-asymmetric Suzuki catalysts, and excellent stability under the reaction conditions to realize higher TON through longer reaction time

Fermi Large Area Telescope Constraints on the Gamma-ray Opacity of the Universe

The Extragalactic Background Light (EBL) includes photons with wavelengths from ultraviolet to infrared, which are effective at attenuating gamma rays with energy above ~10 GeV during propagation from sources at cosmological distances. This results in a redshift- and energy-dependent attenuation of the gamma-ray flux of extragalactic sources such as blazars and Gamma-Ray Bursts (GRBs). The Large Area Telescope onboard Fermi detects a sample of gamma-ray blazars with redshift up to z~3, and GRBs with redshift up to z~4.3. Using photons above 10 GeV collected by Fermi over more than one year of observations for these sources, we investigate the effect of gamma-ray flux attenuation by the EBL. We place upper limits on the gamma-ray opacity of the Universe at various energies and redshifts, and compare this with predictions from well-known EBL models. We find that an EBL intensity in the optical-ultraviolet wavelengths as great as predicted by the "baseline" model of Stecker et al. (2006) can be ruled out with high confidence.Comment: 42 pages, 12 figures, accepted version (24 Aug.2010) for publication in ApJ; Contact authors: A. Bouvier, A. Chen, S. Raino, S. Razzaque, A. Reimer, L.C. Reye

Jet production in ep collisions at high Q(2) and determination of alpha(s)

The production of jets is studied in deep-inelastic e(+/-) p scattering at large negative four momentum transfer squared 150 LT Q(2) LT 15000 GeV2 using HERA data taken in 1999-2007, corresponding to an integrated luminosity of 395 pb(-1). Inclusive jet, 2-jet and 3-jet cross sections, normalised to the neutral current deep-inelastic scattering cross sections, are measured as functions of Q(2), jet transverse momentum and proton momentum fraction. The measurements are well described by perturbative QCD calculations at next-to-leading order corrected for hadronisation effects. The strong coupling as determined from these measurement

Carbon-carbon bond formation methods for the preparation of shape-persistent architectures

Carbon-rich, conjugated organic scaffolding is a popular basis for functional materials, especially for electronic and photonic applications. However, synthetic methods for generating these types of materials lack diversity and, in many cases, efficiency; the insistence of investigators focusing on the properties of the end product, rather than the process in which it was created, has led to the current state of the relatively homogeneous synthetic chemistry of functional organic materials. Because of this, there is plenty of room for improvement at the most basic level. Problems endemic to the preparation of carbon-rich scaffolding can, in many cases, be solved with modern advances in synthetic methodology. We seek to apply this synthesis-focused paradigm to solve problems in the preparation of carbon-rich scaffolds. Herein, the development and utilization of three methodologies: iridium-catalyzed arene C-H borylation; zinc- mediated alkynylations; and Lewis acid promoted Mo nitride-alkyne metathesis, are presented as improvements for the preparation of carbon-rich architectures. In addition, X-ray crystallographic analysis of two classes of compounds are presented. First, an analysis of carbazole-containing arylene ethynylene macrocycles showcases the significance of alkyl chain identity on solid-state morphology. Second, a class of rigid zwitterionic metal-organic compounds display an unusual propensity to crystallize in the absence of inversion symmetry. Hirshfeld surface analysis of these crystalline materials demonstrates that subtle intermolecular interactions are responsible for the overall packing motifs in this class of compounds

Crystal structures of three complexes of zinc chloride with tri-tert-butylphosphane

Under anhydrous conditions and in the absence of a Lewis-base solvent, a zinc chloride complex with tri-tert-butylphosphane as the μ-bridged dimer is formed, viz. di-μ-chlorido-bis[chloridobis(tri-tert-butylphosphane)zinc], [ZnCl4(C12H27P)2], (1), which features a nearly square-shaped (ZnCl)2 cyclic core and whose Cl atoms interact weakly with C—H groups on the phosphane ligand. In the presence of THF, monomeric dichlorido(tetrahydrofuran-κO)(tri-tert-butylphosphane-κP)zinc, [ZnCl2(C4H8O)(C12H27P)] or [P(tBu3)(THF)ZnCl2], (2), is formed. This slightly distorted tetrahedral Zn complex has weak C—H...Cl interactions between the Cl atoms and phosphane and THF C—H groups. Under ambient conditions, the hydrolysed complex tri-tert-butylphosphonium aquatrichloridozincate 1,2-dichloroethane monosolvate, (C12H28P)[ZnCl3(H2O)]·C2H4Cl2 or [HPtBu3]+ [(H2O)ZnCl3]−·C2H4Cl2, (3), is formed. This complex forms chains of [(H2O)ZnCl3]− anions from hydrogen-bonding interactions between the water H atoms and Cl atoms that propagate along the b axis

1-Bromomethyl-4-aza-1-azoniabicyclo[2.2.2]octane bromide

The title compound, C7H14BrN2+·Br−, was prepared by nucleophilic substitution of DABCO (systematic name: 1,4-diazabicyclo[2.2.2]octane) with dibromomethane in acetone. The structure features Br...H close contacts (2.79 and 2.90 Å) as well as a weak bromine–bromide interaction [3.6625 (6) Å]

Data-collection strategy for challenging native SAD phasing

Recent improvements in data-collection strategies have pushed the limits of native SAD (single-wavelength anomalous diffraction) phasing, a method that uses the weak anomalous signal of light elements naturally present in macromolecules. These involve the merging of multiple data sets from either multiple crystals or from a single crystal collected in multiple orientations at a low X-ray dose. Both approaches yield data of high multiplicity while minimizing radiation damage and systematic error, thus ensuring accurate measurements of the anomalous differences. Here, the combined use of these two strategies is described to solve cases of native SAD phasing that were particular challenges: the integral membrane diacylglycerol kinase (DgkA) with a low Bijvoet ratio of 1% and the large 200 kDa complex of the CRISPR-associated endonuclease (Cas9) bound to guide RNA and target DNA crystallized in the low-symmetry space group C2. The optimal native SAD data-collection strategy based on systematic measurements performed on the 266 kDa multiprotein/multiligand tubulin complex is discussed

A Review of Pet Food Recalls from 2003 Through 2022

This is a review of U.S. Food and Drug Administration (FDA) recalls of products that are for dogs and cats which took place from 2003 through 2022. It includes recalls for pet foods (food, treats, and chews), ingredients, supplements (vitamins and minerals), and drugs. There were 3,691 recalls during this period: 51% were Class I, 35% were Class II, and 14% were Class III. Food items and ingredients accounted for the majority or 68%, drugs for 27%, and supplements (vitamins and minerals) accounted for 5% of these recalls. Recalls that could be associated with dogs only accounted for 42%, with cats only 18%, and with multiple species 40%. The primary reasons for the recalls were biological contamination at 35%, chemical contamination at 32%, and cGMP violations at 8%. Almost 25% of the total recalls in the past 20 years were due to a melamine incident in 2007/2008 (73% of those were Class I). Salmonella recalls for the 20 years accounted for 23% of the total recalls (94 % of those were Class I). Although the recalls for vitamins and minerals accounted for only 5.6% percent of the total, 70% of those were Class I and 30% Class II. Pet food is a complex part of the processed food industry, and the processing of pet food is subject to at least 40 different federal regulations. To avoid recalls and be successful, pet food manufacturers need a robust food safety culture to meet all of these requirements to produce a safe product. In contrast, the melamine contamination (an adulteration event) in 2007/2008 which resulted in animal deaths and recalls is a prime example of the need for an effective and robust supplier approval program in order to avoid fraudulent suppliers in the future

Synthesis of Cyano-Substituted Diaryltetracenes from Tetraaryl[3] cumulenes**

A versatile, two-step synthesis of highly substituted, cyano-functionalized diaryltetracenes has been developed, starting from easily accessible tetraaryl[3]cumulenes. This unprecedented transformation is initiated by [2+2] cycloaddition of tetracyanoethylene (TCNE) to the proacetylenic central double bond of the cumulenes to give an intermediate zwitterion, which after an electrocyclization cascade and dehydrogenation yields 5,5,11,11-tetracyano-5,11-dihydrotetracenes in a one-pot procedure. A subsequent copper-assisted decyanation/aromatization provided the target 5,11-dicyano-6,12-diaryltetracene derivatives. All of the postulated structures were confirmed by X-ray crystallography. The new chromophores are thermally highly stable and feature promising fluorescence properties for potential use in optoelectronic devices. They are selective chemosensors for Cu-I ions, which coordinate to one of the CN substituents and form a 1:1 complex with an association constant of K-a=1.5x10(5)Lmol(-1) at 298K