The class of diamino-naphthalene exhibits antioxidant properties, which are partly related to the relative positions of the two amino groups. This study demonstrates how the reactivity of one of these compounds, 1,5-diamino-naphthalene (DAN), can be adjusted by introducing a single amide bond through a simple thermal coupling with l-pyroglutamic acid (PyroGlu). The solventless thermal reaction between PyroGlu and DAN at 160 °C yielded a new mono-pyroglutanilide compound (PyroDAN) that was characterized using various analytical techniques, including a thermal and infrared analysis, HRMS (ESI), and one- (1D) and two-dimensional (2D) NMR. The optical properties were investigated using UV-Vis and fluorescence spectroscopy. Additionally, two chemical standard assays were used to measure both the antioxidant and pro-oxidant properties of PyroDAN. The molecule has shown nearly negligible pro-oxidant activity, while a mild antioxidant activity is still retained. These findings indicate that the transformation of DAN into a mono-pyroglutanilide derivative breaks the original molecular symmetry and effectively modifies the electronic distribution of the aromatic system, suppressing the oxidant properties while keeping a mild antioxidant activity. Furthermore, the tuneable fluorescent properties of PyroDAN—the mild antioxidant activity and the inhibition of the cytologically harmful pro-oxidant properties—suggest promising applications in bioimaging and other biological fields.

The synthesis of biocidal peptide materials using simple, low-cost, solvent-free methods is a crucial challenge for developing new antimicrobial approaches. In this study, we produced proteinoid nanostructures through simple, inexpensive, and environmentally friendly thermal reactions between glutamic acid (Glu) and tyrosine (Tyr) in various molar ratios. Mechanistically, the thermal cyclization of glutamic acid into pyroglutamic acid (pGlu) facilitated the formation of short peptide chains containing pGlu as the N-terminus moiety and subsequent L-tyrosine or glutamic acid residues, which self-assembled into nanometric spheroidal structures that exhibit blue emission. Spectroscopic (FTIR, UV-Vis, photoluminescence) and mass (LC-MS) analyses confirmed the formation of mixed pGlu-/Tyr/Glu peptides. All products exhibit dose-dependent antimicrobial activity against Methicillin-Resistant Staphylococcus aureus (MRSA), with a minimum inhibitory concentration (MIC) of 25 mg mL⁻¹ for the GluTyr 1:1 and 2:1 proteinoids. The outcomes observed following 24 h exposure of the HEK293 cell line to the materials indicate their suitability for integration into hybrid systems for antimicrobial surfaces. This work is the first to demonstrate a direct antibacterial activity of proteinoids obtained by thermal condensation, opening up the possibility of designing a new class of synthetic antimicrobial peptides.