A novel fluorescence platform for portable and visual monitoring of meat freshness.

Biogenic amines (BAs) are crucial markers of meat spoilage. Developing practical and effective BAs detection methods is essential for monitoring meat freshness and ensuring daily consumption safety. This study prepared several naphthalene-based fluorescent compounds to visually monitor meat freshness in real-time. These probes show a colorimetric fluorescence response to putrescine and cadaverine (typical spoilage indicators) through nucleophilic addition/elimination reaction. The detectability of these probes can be optimized by altering the electronegativity and substitution position of the recognition group. Among these compounds, 2-((6-(4-(diphenylamino)phenyl)naphthalen-2-yl)methylene)malono nitrile (TNMA) demonstrated exceptional sensing performance toward putrescine and cadaverine, including high-contrast fluorescence color transition (red to blue), rapid response times (∼30 s), high selectivity and sensitivity (detection limit for putrescine: 2.69 ppm, cadaverine: 6.11 ppm). Furthermore, the B/R values of TNMA test strips output by RGB analysis presented a linear correlation with total volatile basic nitrogen (TVBN, an international standard for evaluating food spoilage) values in pork. Based on this correlation, we utilized smartphone applications to construct an intelligent evaluation system, enabling visual monitoring of pork, chicken, and shrimp freshness under various storage conditions. The TNMA-based system offers a reliable platform for real-time, portable and visual monitoring of meat freshness for consumers and suppliers in the food industry.

Post-Assembly Modification of Head-to-Tail Cyclic Peptides by Methionine-Directed ß-C(sp3)-H Arylation.

Peptide modification by C(sp3)-H functionalization of internal residues remains a major challenge due to the inhibitory effect of peptide bonds. In this work, we developed a methionine-directed ß-C(sp3)-H arylation method for internal alanine functionalization. By tuning the σC-C bond rotation of internal Ala through head-to-tail cyclization, we overcame the inhibitory effect and functionalized a wide range of head-to-tail cyclic peptides with aryl iodides with excellent position selectivity.

Peptide Modification via N-Terminal-Residue-Directed γ-C(sp3)-H Arylation.

Postassembly modification of peptides via C(sp3)-H functionalization provides an efficient way to prepare functionalized peptides for biological study and pharmaceutical development. In this work, we developed a new method for γ-C(sp3)-H functionalization of aliphatic side chains of N-terminus-unprotected peptides. With the N-terminal residues as directing groups, a wide range of di-, tri-, tetra-, and pentapeptides underwent C-H arylation of the residues (Val, Ile, Tle) at the +2 position from the N-terminus.

Site-Selective Modification of α-Amino Acids and Oligopeptides via Native Amine-Directed γ-C(sp3)-H Arylation.

Site-selective modification of chemically and biologically valuable α-amino acids and peptides is of great importance for biochemical study and pharmaceutical development. Few methods based on remote C(sp3)-H functionalization of aliphatic side-chains of peptides has been disclosed in recent years. In this report, we developed a novel approach for γ-C(sp3)-H and γ-/δ-C(sp2)-H arylation of α-amino acids with α-hydrogen by native amine-directed C-H functionalization and further realized the γ-C(sp3)-H arylation of N-terminally unprotected peptides.