Synthesis, Anion Sensing And Dna Binding Properties Of Schiff Base Derivatives Of 2-Amino-6-Methoxybenzothiazole And Other Commercially Available Reagents

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Doctor of Philosophy

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The anion sensing properties and DNA binding properties of 1-7 were investigated. Receptors 1-3 (5-nitro-2-hydroxy-benzaldehyde, 2-hydroxy-1,4-naphthoquinone (lawsone dye) and IR 786 perchlorate) are commercially available and were used as purchased. Receptors 4-7 were synthesized as Schiff base derivatives of 2-amino-6-methoxybenzothiazole and an appropriate salicyaldehyde derivative in methanol by reflux method. These receptors were experimentally characterized by FT-IR, 1HNMR and 13CNMR. The anion sensing properties of 1-7 against common anions (CN-, F-, AcO- , OH-, H2PO4-, Br-, Cl-, ClO4-, N3-, and HSO4-) were studied in both organic and aqueous media by optical techniques (colorimetry and fluorescence). In addition, the binding properties of 1-7 were determined by Job’s plots and their respective binding constants calculated using the Benesi-Hildebrand equation. When observed by the naked eye, 1-3 lacked colorimetric selectivity for the most basic anions while under UV illumination they were selective to CN- in both organic and aqueous media. For the same media, 4-7 visually discriminated CN- from other basic anions. Under UV illuminations, 4-7 displayed distinct fluorescence between CN- and OH-. The binding mechanisms for CN- to 4-7 as determined by 1H-NMR was different from other basic anions. CN- was bound through nucleophilic addition reaction while OH-, F-, AcO- and H2PO4- was by deprotonation. Attempts to investigate 4-7 in aqueous media were only successful upto 25% dilution; since the receptors were barely soluble in water. For DNA binding studies, the UV/vis spectroscopy of receptors 4 and 7, showed that Ct-DNA exhibited intercalative binding. This is attributed to inter ligand π-π* transitions via hydrogen bonding to G and C base. In summary, the commercially available reagents (1-3) could be used as anion sensors. However, under the experimental conditions, 1-3 lacked selectivity for the basic anions. The anion sensing properties was further improved by designing 4-7, affording them better selectivity and sensitivity.