An Atypical Naturally Split Intein Engineered for Highly Efficient Protein Labeling

Protein trans‐splicing catalyzed by split inteins is a powerful technique for assembling a polypeptide backbone from two separate parts. However, split inteins with robust efficiencies and short fragments suitable for peptide synthesis are rare and have mostly been artificially created. The novel split intein AceL‐TerL was identified from metagenomic data and characterized. It represents the first naturally occurring, atypically split intein. The N‐terminal fragment of only 25 amino acids is the shortest natural intein fragment to date and was easily amenable to chemical synthesis with a fluorescent label. Optimal protein trans‐splicing activity was observed at low temperatures. Further improved mutants were selected by directed protein evolution. The engineered intein variants with up to 50‐fold increased rates showed unprecedented efficiency in chemically labeling of a diverse set of proteins. These inteins should prove valuable tools for protein semi‐synthesis and other intein‐related biotechnological applications.     

Hydrogen-Chlorate Electric Power Source: Feasibility of the Device,Discharge Characteristics and Modes of Operation

A power source based on the current-generating reaction of aqueous chlorate-to-chloride reduction by molecular hydrogen would provide as much as 1150 Wh per 1 L of reagent storage (for a combination of 700 atm compressed hydrogen and saturated aqueous solution of lithium chlorate) at room temperature, but direct electroreduction of chlorate only proceeds with unacceptably high overvoltages, even for the most catalytically active electrodes. In the present study, we experimentally demonstrated that this process can be performed via redox-mediator catalysis by intermediate products of chlorate reduction, owing to their participation in homogeneous com- and disproportionation reactions. A series of current–voltage and discharge characteristics were measured for hydrogen-chlorate membrane–electrode assembly (MEA) cells at various concentrations of chlorate and sulfuric acid under operando spectrophotometric monitoring of the electrolyte composition during the discharge. We established that chlorine dioxide (ClO₂) is the key intermediate product; its fraction in the electrolyte solution increases progressively, up to its maximum, equal to 0.4–0.6 of the initial amount of chlorate anions, whereas the ClO₂ amount decreases gradually to a zero value in the later stage. In most discharge experiments, the Faradaic yield exceeded 90% (maximal value: 99%), providing approximately 48% chemical energy storage-to-electricity conversion efficiency at maximal power of the discharge (max value: 402 mW/cm²). These results support prospect of a hydrogen-chlorate flow current generator as a highly specific energy-capacity source for airless media.     

Autocatalytic Formation of High-Entropy Alloy Nanoparticles

High-entropy alloy (HEA) nanoparticles hold great promise as tunable catalysts. Despite the fact that alloy formation is typically difficult in oxygen-rich environments, we found that Pt-Ir-Pd-Rh-Ru nanoparticles can be synthesized under benign low-temperature solvothermal conditions. In situ X-ray scattering and transmission electron microscopy reveal the solvothermal formation mechanism of Pt-Ir-Pd-Rh-Ru nanoparticles. For the individual metal acetylacetonate precursors, formation of single metal nanoparticles takes place at temperatures spanning from ca. 150 °C for Pd to ca. 350 °C for Ir. However, for the mixture, homogenous Pt-Ir-Pd-Rh-Ru HEA nanoparticles can be obtained around 200 °C due to autocatalyzed metal reduction at the (111) facets of the forming crystallites. The autocatalytic formation mechanism suggests that many types of HEA nanocatalysts should accessible with scalable solvothermal reactions, thereby providing broad availability and tunability.     

Observation of a Transient Intermediate in Soai's Asymmetric Autocatalysis: Insights from (1) H NMR Turnover in Real Time

Caught in the act: (1) H?NMR spectroscopy was used to monitor the loss of reactant and formation of product during the induction and burst phases of Soai's autocatalysis reaction. A transient intermediate was observed at 0?°C and identified as an alkoxyacetal formed from one aldehyde and two alkoxide moieties.     

An Adaptor Domain‐Mediated Autocatalytic Interfacial Kinase Reaction

This paper describes a model system for studying the autocatalytic phosphorylation of an immobilized substrate by a kinase enzyme. This work uses self‐assembled monolayers (SAMs) of alkanethiolates on gold to present the peptide substrate on a planar surface. Treatment of the monolayer with Abl kinase results in phosphorylation of the substrate. The phosphorylated peptide then serves as a ligand for the SH2 adaptor domain of the kinase and thereby directs the kinase activity to nearby peptide substrates. This directed reaction is intramolecular and proceeds with a faster rate than does the initial, intermolecular reaction, making this an autocatalytic process. The kinetic non‐linearity gives rise to properties that have no counterpart in the corresponding homogeneous phase reaction: in one example, the rate for phosphorylation of a mixture of two peptides is faster than the sum of the rates for phosphorylation of each peptide when presented alone. This work highlights the use of an adaptor domain in modulating the activity of a kinase enzyme for an immobilized substrate and offers a new approach for studying biochemical reactions in spatially inhomogeneous settings.     

Systematic Studies using 2‐(1‐Adamantylethynyl)pyrimidine‐5‐carbaldehyde as a Starting Material in Soai’s Asymmetric Autocatalysis

Herein, we present a new substrate for the Soai reaction, which has an adamantylethynyl residue ( 1 g ) and exhibits asymmetric autocatalysis, yielding products with enantiomeric excesses above 99 %. For the first time, all reactions were performed on a parallel synthesizer system to ensure identical reaction conditions. A detailed systematic study of reaction parameters was performed and we report the highest enhancements of enantiomeric excess reported so far in the Soai reaction in one reaction cycle (7.2→94.1 % ee or 3.1→92.1 % ee). Our results led to a set of reaction parameters that yield reproducible results. Therefore, our new starting material 1 g is suitable for systematic and mechanistic studies on this remarkable reaction. A series of experiments designed to quantify the amplification of enantiomeric excess demonstrated that the reaction can be used in principle as a tool for the detection of low enantiomeric excesses: under definite conditions, an unknown low enantiomeric excess (0.1–7 %) was amplified to a detectable one. A back calculation to the original value offers a new method for the determination of small enantiomeric excesses.     

On the Autocatalysis of Methane Pyrolysis

Methane pyrolysis has been performed in a recycled flow system in the temperature range of 1103 to 1220 K to investigate the time profile of product distribution. Hydrogen, ethylene, and benzene are found to be the major products before the soot formation. Similar to the literature reports of studies in conventional flow systems, the rate of methane conversion is slow at the beginning of the decomposition and becomes fast after an incubation period. This increase in the decomposition rate after the incubation period is generally called autocatalysis. The proposed reason for this autocatalysis has been the catalytic effect of the secondary products, i.e., soots and carbon deposits. The present study showed that autocatalysis started before the accumulation of these products, and that decomposition of propylene and other minor but reactive products might be attributed to this autocatalysis effect.