Curcumin-Derived Turn-Off Fluorescent Probe for Copper (II) Ion Detection and Live Cell Imaging Applications

A curcumin-derived chemosensor 4,4'-((1E,3Z,5Z,6E)-3,5-bis((2hydroxyphenyl)imino) hepta-1,6-diene-1,7-diyl)bis(2-methoxyphenol) (HIBMP) was developed from curcumin and o-aminophenol using Schiff base condensation method. HIBMP selectively recognizes Cu (II) ion (Cu (II)) relative to other tested metal ions. Selective binding of Cu (II) ion turns off the fluorescent property of HIBMP and shows no interference with other metal ions. Moreover, the favourable binding of Cu (II) with HIBMP was noticed by a good linearity between the fluorescence intensity and concentration of Cu (II) with a range of 0-15.6 × 10-7 M, and the limit of detection was determined to be as low as 30.1 nM. Furthermore a 1:1 stoichiometry was identified from the results of Job's plot and HR-MS. Density functional theory (DFT) calculation results expressed that the intramolecular charge transfer (ICT) during chelation is responsible for quenching of fluorescence. Besides, the fluorescence life time measurement and ethylenediaminetetraacetic acid (EDTA) titration method revealed the stability and reversibility of the sensor. Practical use of the sensor was achieved through the quantitative analysis of spiked Cu (II) ion in real water samples with good recoveries, and biological experiments exposed that the sensor was less toxic and could be applied in fluorescence imaging of Cu (II) in living cells.

Eco-friendly Fluorescent Sensor for Sensitive and Selective Detection of Zn2+ and Fe3+ Ions: Applications in Human Hair Samples

A new eco-friendly sensor, 3-((6-((4-chlorobenzylidene)amino)pyridin-2-yl)imino)indolin-2-one (CBAPI) was synthesized and well characterized. The CBAPI sensor was employed for detecting Zn2+ and Fe3+ ions. It exhibited a low limit of detection at pH 6.0, with values of 2.90, for Zn2+ and 3.59 nmol L-1 for Fe3+ ions. The sensor demonstrated high selectivity over other interfering cations. Additionally, the high binding constants reflect the great affinity of sensor towards Zn2+ and Fe3+ ions. To further validate its quantification ability for Zn2+ ions, the synthesized CBAPI sensor was used to determine Zn levels in human hair samples, and the results were confirmed using atomic absorption spectroscopy (AAS). The AGREE metric tool was used to assess the method's environmental impact and practical applicability. These positive outcomes indicated that the new method for detecting Zn2+ and Fe3+ ions is environmentally friendly and safe for humans. The developed CBAPI sensor represents a potential development in metal ion detection, combining sensitivity, selectivity, and rapidity.

Naphthalimide-based new architecture for fluorescence turn-on sensing of Cu2+ and colorimetric detection of F-/CN. Methods 2024;225:13-19. [PMID: 38438060 DOI: 10.1016/j.ymeth.2024.02.009] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

A new molecular structure 1 has been developed on naphthalimide motif. The amine and triazole binding groups have been employed at the 4-position of naphthalimide to explore the sensing behavior of molecule 1. Single crystal x-ray diffraction and other spectroscopic techniques confirm the identity of 1. Compound 1 exhibits high selectivity and sensitivity for Cu2+ ions in CH3CN. The binding of Cu2+ shows ∼ 70-fold enhancement in emission at 520 nm. The binding follows 1:1 interaction and the detection limit is determined to be 6.49 × 10-7 M. The amine-triazole binding site in 1 also corroborates the detection of F- through a colour change in CH3CN. Initially H-bonding and then deprotonation of amine -NH- in the presence of F- are the sequential steps involved in F- recognition with a detection limit of 4.13 × 10-7 M. Compound 1 is also sensible to CN- like F- ion and they are distinguished by Fe3+ ion. Cu2+-ensemble of 1 fluorimetrically recognizes F- among the tested anions and vice-versa. The collaborative effect of amine and triazole motifs in the binding of both Cu2+ and F-/CN- has been explained by DFT calculation.

S-S bridged Schiff bases as versatile ionophores: Synthesis and application for electrochemical sensing of Copper(II) and Mercury(II)

Schiff base derivates (3, 4 and 5) comprising pseudo cavity with different heteroatoms (O, N and S) were designed, synthesized and explored for their detection behaviour towards diverse metal ions. In UV and fluorescence studies, all three receptors exhibited sensitive response towards Cu2+ while 5 showed sensitivity for Hg2+ also. To explore the synthesized receptors for electrochemical behaviour, voltammetric studies were conducted where 3, 4 and 5 exhibited sensitive response towards Cu2+ with detection limits of 9.8 × 10-7 M, 9.0 × 10-7 M and 1.41 × 10-7 M, respectively. The receptor 5 also showed response towards Hg2+ with detection limit of 5.61 × 10-8 M. The formation of complexes, 3/4+Cu2+ and 5+Cu2+/Hg2+ was supported by large values of binding constant and associated negative free energy change. The binding mechanism of 3, 4 and 5 towards respective metal ions was confirmed using 1H-NMR and HR-MS studies. Further, to utilize the proposed sensors for on-site monitoring of analyte metal ions, carbon paste electrodes (CPEs) were constructed by incorporating 3, 4 and 5. All CPEs showed Nernstian response with lower detection limits and excellent selectivity and successfully utilized for the determination of Cu2+ and Hg2+ in groundwater samples.

A highly selective and sensitive fluorescent sensor based on a 1,8-naphthalimide with a Schiff base function for Hg2+ in aqueous media

A new fluorescent sensor, N-allyl-4-[(2-(3-methoxysalicylaldimino)ethylamino]-1,8-naphthalimide (HL), for Hg2+ has been developed where the Schiff base substituent acts as a recognition group. This sensor shows a large Stokes shift of 3535–4042 cm−1 and a general fluorescence quantum yield of 0.05, 249–0.11, 866 in organic solvents of different polarity as expected. It also exhibits highly selective and a sensitive response to Hg2+ (Ф Hg+HL/Ф HL = 2.28) over other metal ions (Na+, K+, Ca2+, Mg2+, Al3+, Pb2+, Fe3+, Ni2+, Zn2+, Cu2+, Ag+, Co2+, Cr3+, Mn2+ and Cd2+) in solution (DMF/Tris-HCl buffer, 1:1, v/v, pH = 7.2). The Hg2+-induced fluorescence enhancement at 526 nm is proportional to the concentration of Hg2+ in the range of 0.5–4.0 µm with a detection limit of 0.18 µm. Based on the fluorescence titration and a Job’s plot analysis, the metal-to-ligand ratio of the complex is 2:1 with a binding constant of 1.56 × 1012 m −1.