Conventional peptide synthesis involves multiple protection and deprotection steps, and typically relies on stoichiometric amounts of coupling reagents and additives. This makes the process cumbersome, and results in poor atom economy and hazardous waste generation. Therefore, direct peptide bond formation using unprotected amino acids is a promising alternative. However, this approach presents some challenges: 1) Solubility of unprotected amino acids in organic solvents; 2) Control of undesired side reactions; 3) Chemo-selective activation of the carboxylic acid group in the presence of an amine functionality; and 4) Epimerization. To address these challenges, we developed tris(2,2,2-trifluoroethoxy)silane [H-Si(OCH₂CF₃)₃], a cost-effective and accessible coupling reagent. This single reagent efficiently synthesizes N-terminal free peptides from unprotected amino acids and amino acid tert-butyl esters, without the need for any additives. H-Si(OCH₂CF₃)₃ enhances amino acid solubility through coordinating with both termini and plays a dual role, serving as a transient amine-protecting group and as a carboxylic acid activating or promoting reagent for peptide bond formation. This method is operationally simple and versatile, enabling the efficient synthesis of N-terminal free peptides from unprotected amino acids and amino acid tert-butyl esters, with good yields, high optical purity, and broad side-chain compatibility.

We previously reported that Ag^I- and Hg^II-mediated primer extension reactions with a dT template are highly selective for dC and dT triphosphate incorporation, forming T-Ag^I-C and T-Hg^II-T base pairs, respectively. This study investigates the impact of 5-substitution of templated thymine and pH on Klenow fragment (KF) catalyzed metal-mediated primer extension reactions, as well as the thermal stability of DNA duplexes with a 5-substituted uracil derivative. The findings reveal that the selective base recognition of Ag^I and Hg^II ions, leading to T-Ag^I-C and T-Hg^II-T formation in metal-mediated primer extension, is likely governed by the absence of net charge in the resulting base pairs, the abstraction of thymine’s N3 imino proton by Ag^I, and the stability of the Hg^II-N3 bond. These findings may be useful for designing novel regulated replicating systems utilizing metal-mediated base pairs.

Real-time detection and identification of modified cysteine sulfhydryl (Cys-SH) residues are important because supersulfidation (S-sulfhydrylation) alters protein function and thereby modulates the activity of biological systems. Although fluorescence probes for rapid, sensitive detection and biotin tag-switch methods for comprehensive labeling of modified residues at the proteome level have been developed, simultaneous detection and labeling have not been achieved in a single system. Herein, we describe dinitrobenzene-based fluorogenic probes with tunable electrophilicity, which react rapidly and selectively with highly nucleophilic supersulfides such as cysteine persulfide (Cys-SSH) and Na₂S₂ and simultaneously label Cys-SSH itself with a dinitrobenzene tag.

Efficient cytosolic delivery of functional proteins such as therapeutic antibodies remains a major challenge in drug development. In this study, we sought to optimize the cytosolic delivery peptide Mel-V8G12, a melittin derivative, through structure-guided design and functional screening of its amino acid substitutions. Among seven derivatives, VG-6, featuring A10L, T11E, and S18K substitutions demonstrated superior cytosolic delivery efficiency compared with the parental Mel-V8G12, while maintaining low cytotoxicity. Notably, VG-6 exhibited enhanced membrane-lytic activity toward neutral lipid membranes, yet did not increase cellular toxicity, suggesting a delivery mechanism distinct from conventional pH-responsive endosomolytic peptides. Mechanistic studies revealed that, in contrast to Mel-V8G12 which predominantly utilizes actin-mediated endocytosis, VG-6 additionally engages caveolae-mediated endocytosis, contributing to its enhanced cytosolic delivery. Furthermore, VG-6 enabled successful cytosolic delivery of functional Cre recombinase and immunoglobulin G (IgG), facilitating biological activity and subcellular targeting. These findings suggest that VG-6 is a promising tool for intracellular delivery of protein therapeutics via a unique membrane-interacting and endocytic pathway.

Structural transformation changes the activity of biological reactions. Neurotransmitter aralkylamines, such as phenethylamine, tyramine, dopamine, tryptamine, serotonin, and histamine, absorb aerial CO₂, and heteronuclear multiple bond connectivity (HMBC) correlations between the carbon derived from CO₂ and the α-hydrogen of the several amines were confirmed in the D₂O solution. The isolation of methyl carbamate from phenethylamine and CO₂ in water with TMSCHN₂ also supported the formation of covalently bound carbamic acid in the amine aqueous solution containing CO₂. Therefore, it is suggested that CO₂ produced in the body would react with neurotransmitter amines to form covalently bound carbamic acid, which might affect biological reactions.