Abstract
A novel naphthoquinone-pyridine hydrazone (NQPH) based chemosensor was synthesized through the condensation reaction of 2-hydroxynaphthoquinone aldehyde and 2-pyridine carboxylic acid hydrazide. The aqueous buffered solution of NQPH quickly changes color from orange to green upon addition of Cu²⁺ ions with appearance of new absorption band at 452 nm. The UV–vis titration indicated binding constant (K) of chemosensor NQPH with Cu²⁺ was determined to be 2.5 × 104 M⁻¹ (log K = 5.39), and the detection limit for Cu²⁺ ions was found to be 4.35 µM. Analysis using a Job plot based on UV–vis data, along with mass spectrometry, indicated a 1:1 stoichiometry between NQPH and Cu²⁺. Density Functional Theory (DFT) calculations were used to determine the minimum energy conformations, molecular properties and vibrational frequency analysis of NQPH and its Cu²⁺ complex. The DFT results showed the reduction in the HOMO-LUMO gap when NQPH interact with Cu²⁺, indicating intramolecular charge transfer (ICT). The practical application of NQPH was demonstrated by creating test strips for the naked-eye detection of Cu²⁺ and by measuring Cu²⁺ in real water samples.
Published Version
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