Schiff bases are diverse organic compounds with an azomethine structure (–C=N–), holding potential in both chemistry and biology. They serve as catalysts, stabilizers, and exhibit various biological activities. The molecular structure of Schiff bases influences their biological properties, including antimicrobial effects. Redox-active compounds with more negative potentials tend to be more effective against microbes. In one of our recent studies, we explored the antimicrobial properties of two Schiff bases derivatives, SB-1 ((E)-4-amino-3-((3,5-di-tert-butyl-2-hydroxybenzylidene)amino) and SB-2 ((E)-2-((4-nitrobenzilidene)amino)aniline). SB-1 showed antibacterial activity against certain Gram-positive bacteria, while SB-2 did not. The difference in their cyclic voltametric profiles, especially SB-1’s more negative reduction potential, prompted us to carry out further characterizations, including scan-rate studies, solvent analysis, and computational calculations. We found that SB-1, which presents a stable intramolecular hydrogen bond, undergoes irreversible oxidation, likely at the –NH2 group, and a quasi-reversible reduction via an intramolecular reductive coupling of the (–C=N–) azomethine group, supported by orbital theoretical calculations. This research sheds light on the potential applications of Schiff bases in antimicrobial contexts, guided by their redox properties and structure. –C=N–, CN –C=N– , C N biology catalysts stabilizers activities effects Redoxactive Redox active microbes studies derivatives SB1 SB 1 SB- E4amino33,5ditertbutyl2hydroxybenzylideneamino E4amino335ditertbutyl2hydroxybenzylideneamino Eaminoditertbutylhydroxybenzylideneamino E 4 amino 3 3,5 di tert butyl 2 hydroxybenzylidene 5 ((E)-4-amino-3-((3,5-di-tert-butyl-2-hydroxybenzylidene)amino SB2 E24nitrobenzilideneaminoaniline. E24nitrobenzilideneaminoaniline Enitrobenzilideneaminoaniline nitrobenzilidene aniline . ((E)-2-((4-nitrobenzilidene)amino)aniline) Grampositive Gram positive bacteria not profiles SB1s SBs s characterizations scanrate scan rate analysis calculations SB1, 1, bond oxidation NH2 NH –NH group quasireversible quasi reversible (–C=N– contexts –C=N E4amino33 5ditertbutyl2hydroxybenzylideneamino ditertbutyl hydroxybenzylideneamino 35 3, nitrobenzilideneaminoaniline ((E)-2-((4-nitrobenzilidene)amino)aniline (–C=N Eamino E4amino3 ditertbutylhydroxybenzylideneamino E4amino

ABSTRACT Botrytis cinerea is a ubiquitous necrotrophic filamentous fungal pathogen, causing the “grey mold” disease in a wide range of plants, including species of importance in the food industry. Recently, we reported the use of fac-[Re(I)(CO)3(2,2’-bpy)L]PF6 (C3) and fac-[Re(I)(CO)3(4,4′-dimethyl-2,2′-bpy)L]PF6 (C4) complexes as biomarkers for yeasts and bacteria. Nevertheless, the use of these complexes to stain filamentous fungi, such as Botrytis cinerea, has not been explored so far. Since Botrytis cinerea exhibits a dynamic multilayer cell wall that changes the composition during normal growth, in both their hyphae and conidia, is not possible to directly extrapolate the use of both C3 and C4 as biomarkers for Botrytis cinerea without an experimental approach. In this work, we explored new features of the luminescent compounds C3 and C4 as biomarkers for the higher filamentous fungi Botrytis cinerea, including conidia and juvenile hyphae. We found that, with the new protocol proposed, both C3 and C4 were suitable to stain conidia with a simple procedure since no cell permeabilization is required. Additionally, these results suggest that C3 and C4 can selectively stain living conidia, allowing the differentiation from non-germinating conidia. This point opens a new focus of development for rhenium (I) tricarbonyl complexes as new fluorescent biomarkers for Botrytis cinerea with potential properties as vital staining.

BACKGROUND: Salmonella enterica serovar Typhi (S. Typhi) stg operon, encoding a chaperone/usher fimbria (CU), contributes to an increased adherence to human epithelial cells. However, one report suggests that the presence of the Stg fimbria impairs the monocyte-bacteria association, as deduced by the lower level of invasion to macrophage-like cells observed when the stg fimbrial cluster was overexpressed. Nevertheless, since other CU fimbrial structures increase the entry of S. Typhi into macrophages, and considering that transcriptomic analyses revealed that stg operon is indeed expressed in macrophages, we reassessed the role of the stg operon in the interaction between S. Typhi strain STH2370 and human cells, including macrophage-like cells and mononuclear cells directly taken from human peripheral blood. RESULTS: We compared S. Typhi STH2370 WT, a Chilean clinical strain, and the S. Typhi STH2370 Astg mutant with respect to association and invasion using epithelial and macrophage-like cells. We observed that deletion of stg operon reduced the association and invasion of S. Typhi, in both cellular types. The presence of the cloned stg operon restored the WT phenotype in all the cases. Moreover, we compared Salmonella enterica sv. Typhimurium 14028s (S. Typhimurium, a serovar lacking stg operon) and S. Typhimurium heterologously expressing S. Typhi stg. We found that the latter presents an increased cell disruption of polarized epithelial cells and an increased association in both epithelial and macrophage-like cells. CONCLUSIONS: S. Typhi stg operon encodes a functional adhesin that participates in the interaction bacteria-eukary-otic cells, including epithelial cells and macrophages-like cells. The phenotypes associated to stg operon include increased association and consequent invasion in bacteria-eukaryotic cells, and cell disruption.