Synthesis, spectral characterization, DFT computational studies and inhibitory activity of novel N 2 S 2 tetradentates Schiff bases on metallo-beta-lactamases of Acinetobacter baumannii

Highly fluorescent new Schiff base chemosensors for the selective detection of Cu(II) and their application in bioimaging technique

A new symmetrical and a new unsymmetrical Schiff bases are synthesized by condensing 1-(2,4-dihydroxyphenyl)ethanone with, Naphthalen-1-amine and Naphthalen-1,8-diamine under solvent free condition and characterized by IR, UV-visible, 1H NMR, 13C NMR and mass spectral studies. Cation recognizing potentiality of both the Schiff bases is explored-of the Schiff base 4-(1-(naphthalen-1-ylimino)ethyl)benzene-1,3-diol (NEBD) in aqueous methanolic medium and of Schiff base 4,4'-((naphthalene-1,8-diylbis(azanylylidene))bis(ethan-1-yl-1-ylidene))bis(benzene-1,3-diol) (NDBD) is scrutinized in aqueous ACN medium through dual modes namely absorption and emission methods. Both the Schiff base sensors are found to detect Cu(II) ion selectively. The detection occurs in an off-on mode (increase of emission intensity of the Schiff base in the presence of Cu(II) ion) and on-off mode (decrease of emission intensity of the Schiff base in the presence of Cu(II) ion) for the Schiff bases NEBD and NDBD respectively. For the Schiff base NEBD LOD for Cu(II) ion is 1.528 × 10-6 M and for NDBD it is 2.871 × 10-7 M. The sensing property is applied in bioimaging technique for the detection of human cancer cells HeLa. Both the Schiff bases are screened for their antimicrobial activities. Schiff base NEBD is found to be more potential than the standard drug amphotericin B towards Aspergillus niger. Regarding Schiff base NDBD, it is as potential as the standard drug towards all the organisms studied.

Heterocyclic fluorescent Schiff base chemosensors for the detection of Fe(III) and Cu(II) ions

Two new Schiff bases were synthesized from 1-(2,4-dihydroxyphenyl)ethanone and pyridine derivatives. Both compounds were characterized using infrared, UV-Vis., 1H NMR, 13C NMR and mass spectral studies. Density functional theory (DFT) calculations were performed for both the Schiff bases with 6-31G(d, p) as the basis set. Vibrational frequencies calculated using the theoretical method were in good agreement with the experimental values. Both the Schiff bases were highly fluorescent in nature. The cation-recognizing profile of the compounds was investigated in aqueous methanol medium. The Schiff base 4-(1-(pyridin-4-ylimino)ethyl)benzene-1,3-diol (PYEB) was found to interact with Fe(III) and Cu(II) ions, whereas the Schiff base 4,4'-((pyridine-2,3-diylbis(azanylylidene))bis(ethan-1-yl-1-ylidene))bis(benzene-1,3-diol) (PDEB) was found to detect Cu(II) ions. The mechanism of recognition was established as combined excited state intramolecular proton transfer (ESIPT)-chelation-enhanced fluorescence (CHEF) effect and chelation-enhanced quenching (CHEQ) process for the detection of Fe(III) and Cu(II) ions, respectively. The stability constant of the metal complexes formed during the sensing process was determined. The limit of detection for Fe(III) and Cu(II) ions with respect to Schiff base PYEB was found to be 1.64 × 10-6 and 2.16 × 10-7 M, respectively. With respect to Schiff base PDEB, the limit of detection for Cu(II) ion was found to be 4.54 × 10-4 M. The Cu(II) ion sensing property of the Schiff base PDEB was applied in bioimaging studies for the detection of HeLa cells.

Investigation of common chemical components and inhibitory effect on GES-type β-lactamase (GES22) in methanolic extracts of Algerian seaweeds

This study aimed to investigate the total phenolic content (TPC), the identification of the common compounds by HPLC-ESI-MS and HPLC-ESI-MS-TOF and the inhibitory effects against class A-type β-lactamase (GES-22 variant, produced recombinantly) in methanolic extracts (MEs) of four Algerian seaweeds [Ulva intestinalis, Codium tomentosum, Dictyota dichotoma and Halopteris scoparia]. The TPC varied among the four species, ranging between 0.93 ± 0.65 and 2.66 ± 1.33 mg GAEs/g DW. C.tomentosum had higher total phenol content than other seaweeds while, all of them inhibited uncompetitively GES-22 activity in a dose-dependent manner. Nitrocefin was used as chromogenic substrate to evaluate the inhibitory effect on GES-22. The methanolic extract of D.dichotoma exhibited significant inhibitory effect on GES-22 (IC50 = 13.01 ± 0.046 μg/mL) more than clavulanate, sulbactam and tazobactam (classical β-lactam inhibitors) (IC50 = 68.38 ± 0.17 μg/mL, 52.68 ± 0.64 μg/mL, and 29.94 ± 0.01 μg/mL, respectively). IC50 of the other ME of U.intestinalis, C.tomentosum, and H.scoparia were 16.87 ± 0.10 μg/mL, 16.54 ± 0.048 μg/mL, and 25.72 ± 0.15 μg/mL, respectively. Except H. scoparia, other three seaweed extracts showed almost two times or more inhibition on GES-22. Furthermore, four common compounds in these MEs were identified, α-linolenic acid (C18:3ω3), linoleic acid (C18:2ω6), oleic acid (C18:1ω9), the eicosanoid precursors ''arachidonic acid'' (C20:4ω6). Baicalein (C15H10O5) was identified in U.intestinalis and D.dichotoma seaweeds. The fact that all seaweed extracts inhibited the GES-22 better than commercial samples makes these seaweeds candidate for discovering new inhibitors against β-lactamases. Besides that, they contain important components with potential health benefits.