No abstract

Electrochemical reduction of carbon dioxide (CO2RR) into value‐added chemicals is a promising tactic to mitigate global warming. However, this process resists catalyst preparation, low faradaic efficiency (FE%) towards multi‐carbon products, and insights into mechanistic understanding. Indeed, it is demonstrated that this Fe single‐atom catalyst (Fe SAC) exists in three oxygen coordination of Fe–(O)3 configuration in Nafion coated functionalized multi‐wall carbon nanotubes (Fe‐n‐f‐CNTs), which is obtained via a simple ionic exchange method under ambient conditions. The electrochemical performance reveals that Fe SACs achieve an FE of 45% and a yield rate of 56.42 µmol cm−2 h−1 at −0.8 VRHE for ethanol. In situ X‐ray analysis reveals that the Fe SACs have variable electronic states and keeps close +3 of the oxidation state at the potential range of CO2RR. The catalytic feature reduces the reaction energy and induces the electrons transferred to the adsorbed products intermediates of *COOH and *OCHO, thus promoting CO. The carboxylic functional group on the CNTs stabilizes the Fe active sites via electrostatic interaction, verified by density functional theory calculations. The yield rate of Fe SACs indicates that the Fe single‐atom site can instantly provide a large CO to help conversion of CO2‐to‐C2 product on the CNTs.

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The β-sheet is one of the common protein secondary structures, and the aberrant aggregation of β-sheets is implicated in various neurodegenerative diseases. Cross-strand interactions are an important determinant of β-sheet stability. Accordingly, both diagonal and lateral cross-strand interactions have been studied. Surprisingly, diagonal cross-strand ion-pairing interactions have yet to be investigated. Herein, we present a systematic study on the effects of charged amino acid side-chain length on a diagonal ion-pairing interaction between carboxylate- and ammonium-containing residues in a β-hairpin. To this end, 2D-NMR was used to investigate the conformation of the peptides. The fraction folded population and the folding free energy were derived from the chemical shift data. The fraction folded population for these peptides with potential diagonal ion pairs was mostly lower compared to the corresponding peptide with a potential lateral ion pair. The diagonal ion-pairing interaction energy was derived using double mutant cycle analysis. The Asp2-Dab9 (Asp: one methylene; Dab: two methylenes) interaction was the most stabilizing (−0.79 ± 0.14 kcal/mol), most likely representing an optimal balance between the entropic penalty to enable the ion-pairing interaction and the number of side-chain conformations that can accommodate the interaction. These results should be useful for designing β-sheet containing molecular entities for various applications.

In this study, a methodology utilizing peptide conformational imprints (PCIs) as a tool to specifically immobilize porcine pancreatic alpha-trypsin (PPT) at a targeted position is demonstrated. Owing to the fabrication of segment-mediated PCIs on the magnetic particles (PCIMPs), elegant cavities complementary to the PPT structure are constructed. Based on the sequence on targeted PPT, the individual region of the enzyme is trapped with different template-derived PCIMPs to show certain types of inhibition. Upon hydrolysis, N-benzoyl-L-arginine ethyl ester (BAEE) is employed to assess the hydrolytic activity of PCIMPs bound to the trypsin using high-performance liquid chromatography (HPLC) analysis. Further, the kinetic data of four different PCIMPs are compared. As a result, the PCIMPs presented non-competitive inhibition toward trypsin, according to the Lineweaver-Burk plot. Further, the kinetic analysis confirmed that the best parameters of PPT/PCIMPs 233–245+G were Vmax = 1.47 × 10−3 mM s−1, Km = 0.42 mM, kcat = 1.16 s−1, and kcat/Km = 2.79 mM−1 s−1. As PPT is bound tightly to the correct position, its catalytic activities could be sustained. Additionally, our findings stated that the immobilized PPT could maintain stable activity even after four successive cycles.