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    Colorimetric chemical sensing properties of 3-amino-4-hydroxybenzene- sulfonic acid-based Schiff bases containing electron donor-acceptor groups
    (Elsevier, 2023) Yildiz, Elif Akhuseyin; Pepe, Yasemin; Erdener, Digdem; Karatay, Ahmet; Boyacioglu, Bahadir; Unver, Huseyin; Yapar, Gonul
    A new series of aminobenzene sulfonic acid-based Schiff bases (1-3) were synthesized from the reaction of 3-amino-4-hydroxybenzenesulfonic acid with 5-methyl, 5-nitro and 5-bromo-salicylaldehyde. The colorimetric and UV-Vis spectroscopic responses of compounds in DMSO to addition of equivalent number of anions (F-, Br-, I-, CN-, SCN-, ClO4-, HSO4-, AcO-, H2PO4-, N3- and OH-) were investigated. Additionally, biological activities of the compounds; antimicrobial and DNA binding properties, were investigated. A DPPH (2,2-diphenyl-1-picryl-hydrazyl-hydrate) free radical method was used to measure antioxidant activity, and 4-hydroxy-3-(2-hydroxy-5-methylbenzylideneamino)benzene sulfonic acid (1) displayed greater antioxidant activity than butylated hydroxytoluene (BHT). Studied compounds demonstrated emission properties over a wide range of visible spectrum, and compound 4-hydroxy-3-(2-hydroxy-5-nitrobenzylideneamino)benzenesulfonic acid (2) has hyp-sochromic shift by incorporating NO2 in comparison with other compounds. Femtosecond transient absorption spectroscopy measurements showed that compounds 4-hydroxy-3-(2-hydroxy-5-nitrobenzylideneamino)benze-nesulfonic acid (2) and 3-(5-bromo-2-hydroxybenzylideneamino)-4-hydroxybenzenesulfonic acid (3), incorpo-rated nitro and bromine groups and possessing electron accepting features have fast triplet transition. This study provides a novel design strategy for biological activity and colorimetric probing features of aminobenzene sul-fonic acid-based Schiff bases.
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    Synthesis and characterization of 2-aminoethylphosphonic acid-functionalized graphene quantum dots: biological activity, antioxidant activity and cell viability
    (Natl Inst Science Communication-Niscair, 2020) Yapar, Gonul; Senel, Behiye; Demir, Neslihan; Yıldız, Mustafa
    A facile, environmentally friendly one-step reaction for the preparation of luminescent N-doped graphene quantum dots (GQDs) involving a hydrothermal reaction between citric acid and 2-aminoethylphosphonic acid has been designed. Graphene quantum dots have been characterized by UV-visible absorption, FTIR spectroscopy, transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX) and dynamic light scattering (DLS) techniques. Furthermore, the biological activity of the GQDs has been studied. UV-visible spectroscopy studies of the interactions between the GQDs and calf thymus DNA (CT-DNA) showed that the compound interacts with CT-DNA via intercalative binding. DNA cleavage study showed that the GQDs cleaved DNA oxidatively. In addition, antioxidant activity of N-doped GQDs was measured using the DPPH method. As the concentration of the compound increased, the antioxidant activity also has increased. According to cell viability analyses results, the N-doped GQDs showed cell viability (70%) when the concentration reaches 228 mu g/mL for A549, 200 mu g/mL for MDA-MB-231 and 140 mu g/mL for NIH-3T3 cell lines with 24 h incubation.
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    Synthesis, Biological Activities, Antioxidant Properties, and Molecular Docking Studies of Novel Bis-Schiff Base Podands as Responsive Chemosensors for Anions
    (Elsevier, 2022) Yapar, Gonul; Demir, Neslihan; Kiraz, Askin; Ozkat, Gozde Yalcin; Yıldız, Mustafa
    In this study, bis-carbonyl podand (triethylene glycol bis(2-carbonylphenyl)ether) ( 1 ) was synthesized from the reaction of triethylene glycol dichloride with salicylaldehyde. Then, Schiff base podans ( 2 and 3 ) were prepared from the interaction of bis(carbonyl) podand with 2-amino-4-methylphenol and 2-amino3-hydroxypyridine in ethanol medium. The structures of podands have been investigated by elementary analysis, FT-IR, UV-Vis,H- 1-NMR, C-13-NMR and MS spectroscopy. The antimicrobial activities of the podands have been investigated for their minimum inhibitory concentration (MIC) to bacteria and yeast cultures. Furthermore, the interactions of Schiff base podands with DNA were investigated by UV-Vis spectra and gel electrophoresis method. The efficiency of molecules in DNA cleavage has also been investigated by computational examination of the interaction between Schiff base podands and human topoisomerase II alpha (hTop alpha) enzyme by molecular docking method. Docking results of podands were compared with known topo inhibitors. UV-Vis spectroscopy studies of the interactions between the podands and calf thymus DNA (CT-DNA) showed that the compounds interact with CT-DNA via electrostatic binding. DNA cleavage study showed that the podands cleaved DNA oxidatively. It has been observed that especially podand 2 shows the best interactions with the hTop alpha's binding site by molecular docking method compared to known inhibitors. In addition, antioxidant activities of Schiff base podands were measured using the DPPH method. Podands showed similar antioxidant activity with BHT. It was also found that activity increased with increasing concentration of compounds. In addition, the anion recognition ability of all Schiff bases was examined by colorimetric, UV-Vis and fluorescence spectroscopy. Schiff base podand 2 showed a visually and spectroscopically detectable color and absorbance change against fluoride, cyanide and hydroxyl anions, while Schiff base podand 3 showed the same change against fluoride, cyanide, acetate, dihydrogen phosphate and hydroxyl anions. No significant color and absorbance change were observed upon addition of other anions such as bromide, iodide, thiocyanate, perchlorate, and hydrogen sulphate.(c) 2022 Elsevier B.V. All rights reserved.
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    Synthesis, characterization, biological activity and theoretical studies of a 2-amino-6-methoxybenzothiazole-based fluorescent Schiff base
    (Elsevier, 2019) Alpaslan, Gokhan; Boyacioglu, Bahadir; Demir, Neslihan; Tumer, Yasemin; Yapar, Gonul; Yildirim, Nuray; Yıldız, Mustafa
    A new Schiff base, (E)-3,5-dimethoxy-2-((6-methoxybenzo[d]thiazol-2-ylimino)methyl)- phenol, was prepared from the reaction of 2-amino-6-methoxybenzothiazole and 2-hydroxy-4,6-dimethoxybenzaldehyde and characterized with elemental analysis, FTIR, UV-VIS, NMR and single crystal X-ray diffraction techniques. Frontier molecular orbitals, molecular electrostatic potential, and chemical reactivity descriptors of the synthesized compound were studied using molecular modeling methods. The antibacterial and antifungal activities of the Schiff base were studied for its minimum inhibitory concentration. The compound showed a higher effect on yeast than against bacteria. The interactions of the compound with DNA were studied with the ultraviolet-visible (UV-VIS) spectra and gel electrophoresis method. The experimental results indicated that the 2-amino-6-methoxybenzothiazole-based Schiff base could bind to DNA via an intercalative mode and showed that it cleaved DNA without the need for external agents. Additionally, the Schiff base showed colorimetric sensor properties for fluoride and cyanide anions in dimethyl sulfoxide.
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    Synthesis, Quantum Chemical Calculations and Molecular Docking Studies, Biological and Anion Sensor Properties of (E)-4-[(4-ethoxy-phenylimino)methyl]-2-methoxyphenol
    (Croatian Chemical Soc, 2018) Zeyrek, Celal Tugrul; Unver, Huseyin; Boyacioglu, Bahadir; Demir, Neslihan; Yapar, Gonul; Dal, Hakan; Yıldız, Mustafa
    We report the synthesis and characterization, biological activity, DNA binding, colorimetric anion sensor properties, computational (HF) and molecular docking studies of a novel Schiff base (E)-4-[(4-ethoxyphenylimino)methyl]-2-methoxyphenol. The molecular structure of the title compound was experimentally determined using spectroscopic data and was compared to the structure predicted by theoretical calculations using density functional theory (DFT). In addition, atomic charges, molecular electrostatic potential (MEP), nonlinear optical (NLO) effects, the potential energy surface (PES) scans about two important torsion angles and thermodynamic properties of the title compound were predicted using DFT. The antimicrobial activity of the compound was investigated for minimum inhibitory concentration. UV-Vis spectroscopy studies of the interactions between the compound and calf thymus DNA (CT-DNA) showed that the compound interacts with CT-DNA via intercalative binding. The colorimetric response of the Schiff base receptors in DMSO was investigated. The most discernable color change in the Schiff base was caused by CN-, which demonstrated that the ligand can be used to selectively detect CN-.
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    UV-Vis spectroscopic and colorimetric anion detection and fluorescence properties of new 3-amino-4-hydroxybenzenesulfonic acid-based Schiff bases depending on the strength and position of the electron donor substitution
    (Iop Publishing Ltd, 2023) Yildiz, Elif Akhuseyin; Pepe, Yasemin; Erdener, Digdem; Karatay, Ahmet; Boyacioglu, Bahadir; Unver, Hueseyin; Yapar, Gonul
    In this study, 3-amino-4-hydroxybenzenesulfonic acid-based imine compounds; 3-(2,5-dihydroxybenzylideneamino)-4-hydroxybenzenesulfonic acid (1), 3-(2,4-dihydroxybenzylideneamino)-4-hydroxybenzenesulfonic acid (2) and 4-hydroxy-3-(2-hydroxy-3-methoxybenzylideneamino)-4-hydroxybenzenesulfonic acid (3) was synthesized. The compounds were analyzed using various spectroscopy methods, and the experimental UV-vis data matched the theoretical predictions. The compound 1 displayed lower stability, higher reactivity, and easier photoexcitation due to a smaller HOMO-LUMO energy gap. The investigated compounds 1-3 showed promise as chemosensors for anions, providing visible detection in daylight conditions. The compound 3 exhibited selective fluorescence at specific wavelengths. The compounds 1-3 interacted with DNA through electrostatic interactions. Also, compounds 1-3 showed higher antioxidant activity than BHT. However, fluorescence measurements indicated that the emission signals were strongly influenced by the position and strength of the electron-donating group. Adding a hydroxy or methoxy moiety near the -OH group on the phenyl ring decreased the fluorescence signal due to intersystem crossing and intramolecular charge transfer mechanisms, respectively. These findings were supported by femtosecond transient absorption spectroscopy measurements. The results emphasize the significance of substituents in imines derived from 3-amino-4-hydroxybenzenesulfonic acid in determining their biological activities, as well as their optical and sensor properties.