Proximity‐Enabled Protein Crosslinking through Genetically Encoding Haloalkane Unnatural Amino Acids

The selective generation of covalent bonds between and within proteins would provide new avenues for studying protein function and engineering proteins with new properties. New covalent bonds were genetically introduced into proteins by enabling an unnatural amino acid (Uaa) to selectively react with a proximal natural residue. This proximity‐enabled bioreactivity was expanded to a series of haloalkane Uaas. Orthogonal tRNA/synthetase pairs were evolved to incorporate these Uaas, which only form a covalent thioether bond with cysteine when positioned in close proximity. By using the Uaa and cysteine, spontaneous covalent bond formation was demonstrated between an affibody and its substrate Z protein, thereby leading to irreversible binding, and within the affibody to increase its thermostability. This strategy of proximity‐enabled protein crosslinking (PEPC) may be generally expanded to target different natural amino acids, thus providing diversity and flexibility in covalent bond formation for protein research and protein engineering.     

Crystal Structure of Tryptophan Lyase (NosL): Evidence for Radical Formation at the Amino Group of Tryptophan

Streptomyces actuosus tryptophan lyase (NosL) is a radical SAM enzyme which catalyzes the synthesis of 3‐methyl‐2‐indolic acid, a precursor in the synthesis of the promising antibiotic nosiheptide. The reaction involves cleavage of the tryptophan Cα? Cβ bond and recombination of the amino‐acid‐derived ‐COOH fragment at the indole ring. Reported herein is the 1.8 Å resolution crystal structure of NosL complexed with its substrate. Unexpectedly, only one of the tryptophan amino hydrogen atoms is optimally placed for H abstraction by the SAM‐derived 5′‐deoxyadenosyl radical. This orientation, in turn, rules out the previously proposed delocalized indole radical as the species which undergoes Cα? Cβ bond cleavage. Instead, stereochemical considerations indicate that the reactive intermediate is a ^.NH tryptophanyl radical. A structure‐based amino acid sequence comparison of NosL with the tyrosine lyases ThiH and HydG strongly suggests that an equivalent ^.NH radical operates in the latter enzymes.     

Arrays on disc for screening and quantification of pollutants

A rapid compact disc based methodology for screening and quantification of organic pollutants in mandarin juices is presented. The assay is established on the coating conjugate indirect competitive principle and developed under disc-array configuration. The detection is based on the acquisition of attenuated reflective signals that were proportional to optical density of the immunoreaction product. The competitive assay is applied to quantify simultaneously, in a selective manner, non-systemic insecticides in mandarin juices. The detection limits were 0.2 and 0.1 μg L⁻¹ and the sensitivity 2.1 and 1.5 μg L⁻¹, for chlorpyrifos and fenthion, respectively. Pollutants were directly quantified after sample dilution in a total time of 40 min. Also, the implementation of positive and negative controls into the array configuration served as an automatic quality control test. The effect of thermal treatment on pesticide dissipation was studied and found that it was insignificant under the studied conditions. Recovery intervals ranged from 96–105% to 94–103%, for chlorpyrifos and fenthion, respectively and were similar to those obtained with gas chromatography coupled to mass spectrometry. In the current configuration, 64 samples can be simultaneously analyzed on a disc at a very competitive value, demonstrating its potential for high-throughput multiplexed screening applications for controlled monitoring programs in low-level labs or outside the lab setting.     

Thiol Esters in Organic Synthesis XVII.1 S,S′-Diethyl Dithiomalonate as Masked Ethanol Carbanion and 1,3-Diol Equivalent in the Knoevenagel Condensation

S,S′-Diethyl dithiomalonate (1) has been shown to be a useful reagent in the Knoevenagel condensation with aldehydes, using DABCO as the base. The resultant products can be reduced either to 1,3-diols by use of sodium borohydride or to ethanol derivatives using Raney Nickel.     

FRAGRANCE EMULSIONS STABILIZED BY A TRIBLOCK COPOLYMER

The phase diagram was determined of the system a fragrance oil, phenethyl alcohol, a commercial triblock copolymer, PE/L101, and water. The stability of emulsions containing 95 wt% water and various amounts of the fragrance and polymer was investigated both visually and with the aid of an optical microscope. The stability of the two-phase emulsions was explained through the interfacial behavior of the polymer and the density change of the oil phase. Double emulsions were found to form when the oil phase composition is close to that of the L₂ phase with maximum water solubilization.     

Simple and Friendly Sulfones Synthesis Using Aqueous Hydrogen Peroxide with a Reusable Keggin Molybdenum Heteropolyacid,Immobilized on Aminopropyl-Functionalized Silica

Keggin molybdenum heteropolyacid (H₃PMo₁₂O₄₀), immobilized on aminopropyl-functionalized silica catalysts, were made using two immobilization methods: incipient wetness and equilibrium adsorption. The material prepared for the equilibrium adsorption technique was found to be a highly efficient, ecofriendly, and recyclable heterogeneous catalyst for the selective oxidation of sulfides to sulfones in excellent yields, under mild reaction condition using 35% w/v aqueous hydrogen peroxide as the oxidant.     

Exploiting the Burkholderia pseudomallei Acute Phase Antigen BPSL2765 for Structure-Based Epitope Discovery/Design in Structural Vaccinology

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Core–Shell Capsules Based on Supramolecular Hydrogels Show Shell‐Related Erosion and Release Due to Confinement

Hydrogel‐containing core–shell capsules are useful as drug delivery vehicles for many biomedical applications, especially when release of incorporated guests can be controlled. Here, we developed a one‐step organic solvent‐free method to prepare such core–shell capsules using a synthetic and a natural supramolecular hydrogel, for the core and shell, respectively. A solution containing ureido‐pyrimidinone modified poly(ethylene glycol) hydrogelators and calcium chloride was drop‐wise added to an alginate solution, yielding core–shell structures. It was found that the outer shell provides a confined space for the inner supramolecular hydrogel and therefore prevents swelling of the core. This consequently slows down both erosion of the less stable core, and release of dextran guests.

     

Regioselective Generation of Single‐Site Iridium Atoms and Their Evolution into Stabilized Subnanometric Iridium Clusters in MWW Zeolite

Preparation of supported metal catalysts with uniform particle size and coordination environment is a challenging and important topic in materials chemistry and catalysis. In this work, we report the regioselective generation of single‐site Ir atoms and their evolution into stabilized subnanometric Ir clusters in MWW zeolite, which are located at the 10MR window connecting the two neighboring 12MR supercages. The size of the subnanometric Ir clusters can be controlled by the post‐synthesis treatments and maintain below 1 nm even after being reduced at 650 °C, which cannot be readily achieved with samples prepared by conventional impregnation methods. The high structure sensitivity, size‐dependence, of catalytic performance in the alkane hydrogenolysis reaction of Ir clusters in the subnanometric regime is evidenced.