Uncoupling effect of lipid peroxidation in spinach thylakoids exposed to peroxyl radicals generated by 2,2′-azobis (2-amidinopropane) dihydrochloride

In this study, we characterized how lipid peroxidation alters the functionality of spinach thylakoids exposed to peroxyl radicals generated by the azo compound 2,2-azobis(2-amidinopropane) dihydrochloride (AAPH). Incubation of thylakoids in presence of different concentrations (0 to 200 mM) of AAPH inhibited the formation of ΔpH (IC50 ≈ 1.5 mM) estimated by the quenching of 9-aminoacridine fluorescence (Q9-AA). The Q9-AA inhibition was correlated (R2=0.98) to the extent of lipid peroxidation determined by the accumulation of thiobarbituric acid reactive substances (TBARS). Much higher AAPH concentrations were required to inhibit the maximum (Fv/Fm) and effective (ΔF/Fm’) photochemical efficiencies of photosystem II (IC50 ≈ 120 mM and 50 mM respectively), indicating that moderate lipid peroxidation caused the uncoupling of spinach thylakoids. This was confirmed by the 62 % stimulation of the O2 uptake rates measured without the artificial uncoupler NH4Cl when the AAPH concentrations increased from 0 to at 20 mM, reaching similar values to the rates measured in presence of NH4Cl. Above 20 mM AAPH, the O2 uptake rates measured with and without NH4Cl declined similarly to the decrease of ΔF/Fm’. These results suggest that the increased H+-leakiness of thylakoid membranes could be one of the primary effects of oxidative stress.

5-((8-Hydroxyquinolin-5-yl)diazenyl)-3-methyl-1H-pyrazole-4-carboxylic Acid

A new azo compound was prepared via the azo coupling reaction between 4-(ethoxycarbonyl)-3-methyl-1H-pyrazole-5-diazonium chloride and 8-hydroxyquinoline (oxine). The ester functional group of the obtained compound was hydrolyzed and thus a new chemical structure with a carboxylic functional group resulted. The structures of the new compounds were fully characterized by: UV–Vis, FT-IR, 1D and 2D NMR spectroscopy, and HRMS spectrometry.

Synthesis, characterization and antimicrobial properties of two derivatives of pyrrolidine-2,5-dione fused at positions-3,4 to a dibenzobarrelene backbone

Background : The present study describes for the first time, the synthesis of two pyrrolidine-2,5-dione derivatives that belong to N-arylsuccinimid (compound 5) and of azo (compound 8) class of molecules. The initial step of the reaction involved the preparation of the intermediate compound (9R, 10R, 11S)-9, 10-dihydro-9, 10-[3, 4] furanoanthracene-12, 14-dione (3) through [4 + 2]-cycloaddition between anthracene and maleic anhydride in xylene which was then condensed with para-hydroxyaniline to give compound 5. Subsequent coupling of 5 with the aryldiazonium ion of aniline gave compound 8.Results: These compounds were characterized by their physical, elemental, and spectroscopic data. 2D-NMR (COSY, HSQC, and HMBC) techniques were used to complete the elucidation of their structures. Compounds 5 (MIC = 32–128µg/mL) and 8 (MIC = 16–256µg/mL) along with the precursor 3 (MIC = 64–128µg/mL) displayed moderate antimicrobial activities against selected bacterial and fungal species when compared with those of nystatin (MIC = 0.50–2µg/mL) and ciprofloxacin (MIC = 0.50–16µg/mL) used as reference drugs.Conclusion: The results of biological tests showed that compounds 3, 5, 8 possess antimicrobial activities. Although being less active than the compound taken as a reference, the azo compound has better antibacterial activity than the other two compounds especially on Staphylococcus aureus, V. choleraeSG24 and, V. choleraeCO6 strains. These results show that the azo function (N = N) is indeed a pharmacophore and would be responsible for the biological activity in the azo molecules.

Azo synthesis meets molecular iodine catalysis

An innovative metal-free oxidative protocol for azo compound formation catalyzed by substoichiometric amounts of molecular iodine (2 mol%) is disclosed.