Fluorescence response of a thiazolidine carboxylic acid derivative for the selective and nanomolar detection of Zn( ii ) ions: quantum chemical calculations and application in real samples

• Published in: RSC advances Vol. 5; no. 127; pp. 105453 - 105463
• Main Authors: Balakrishnan, C., Theetharappan, M., Natarajan, Satheesh, Thalamuthu, S., Neelakantan, M. A.
• Format: Journal Article
• Language: English
• Published: 01.01.2015
• Subjects: Carboxylic acids; Complexation; Derivatives; Fluorescence; Mathematical analysis; Nanostructure; Zinc
• ISSN: 2046-2069; 2046-2069
• DOI: 10.1039/C5RA21277D

A thiazolidine carboxylic acid derivative (L) was conveniently synthesized and characterized by spectral techniques and single crystal X-ray crystallography. The complexation of L with zinc (L–Zn 2+ ) was studied by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) and further substantiated by 1 H NMR and ESI-MS analysis. The L showed excellent specificity and sensitivity towards a zinc-induced fluorescence response by forming a 1 : 1 complex (Job's plot) in a 95% (v/v) water–methanol mixture. The presence of zinc ions causes ∼40 fold fluorescence enhancement at 481 nm (quantum yield, Φ = 0.19) and can be detected with the naked eye under a UV-lamp. The L can detect Zn 2+ in nanomolar levels (13.90 nM) with good tolerance in the presence of other interfering metal ions. The reversibility of L–Zn 2+ complexation was checked by EDTA titration. The maximum fluorescence enhancement by Zn 2+ binding of L was observed in the pH range of 7.0–9.0. The dissociation constants of L and the stability constant of the L–Zn 2+ complex in 0.15 M NaClO 4 were determined by pH metrically. Theoretical calculations were done using density functional theory (DFT) to support the above findings. L was successfully applied for the determination of Zn 2+ in water samples. The compound (L) detects the presence of, Klebsiella pneumoniae and E. coli in water samples.