Exfoliation of Molecular Solids by the Synergy of Ultrasound and Use of Surfactants: A Novel Method Applied to Boric Acid.

Boric acid, H3BO3, is a molecular solid made up of layers held together by weak van der Waals forces. It can be considered a pseudo "2D" material, like graphite, compared to graphene. The key distinction is that within each individual layer, the molecular units are connected not only by strong covalent bonds but also by hydrogen bonds. Therefore, classic liquid exfoliation is not suitable for this material, and a specific method needs to be developed. Preliminary results of exfoliation of boric acid particles by combination of ultrasound and the use of surfactants are presented. Ultrasound provides the system with the energy needed for the process, and the surfactant can act to keep the crystalline flakes apart. A system consisting of a saturated solution and large excess solid residue of boric acid was treated in this way for a few hours at 40 °C in the presence of various sodium stearate, proving to be very promising, and an incipient exfoliation was achieved.

Correction to "Cathepsin-Targeting SARS-CoV-2 Inhibitors: Design, Synthesis, and Biological Activity".

[This corrects the article DOI: 10.1021/acsptsci.3c00313.].

Cathepsin-Targeting SARS-CoV-2 Inhibitors: Design, Synthesis, and Biological Activity.

Cathepsins (Cats) are proteases that mediate the successful entry of SARS-CoV-2 into host cells. We designed and synthesized a tailored series of 21 peptidomimetics and evaluated their inhibitory activity against human cathepsins L, B, and S. Structural diversity was realized by combinations of different C-terminal warhead functions and N-terminal capping groups, while a central Leu-Phe fragment was maintained. Several compounds were identified as promising cathepsin L and S inhibitors with Ki values in the low nanomolar to subnanomolar range, for example, the peptide aldehydes 9a and 9b (9a, 2.67 nM, CatL; 0.455 nM, CatS; 9b, 1.76 nM, CatL; 0.512 nM, CatS). The compounds' inhibitory activity against the main protease of SARS-CoV-2 (Mpro) was additionally investigated. Based on the results at CatL, CatS, and Mpro, selected inhibitors were subjected to investigations of their antiviral activity in cell-based assays. In particular, the peptide nitrile 11e exhibited promising antiviral activity with an EC50 value of 38.4 nM in Calu-3 cells without showing cytotoxicity. High metabolic stability and favorable pharmacokinetic properties make 11e suitable for further preclinical development.