Heterocyclic fluorescent Schiff base chemosensors for the detection of Fe(III) and Cu(II) ions

Two new Schiff bases were synthesized from 1-(2,4-dihydroxyphenyl)ethanone and pyridine derivatives. Both compounds were characterized using infrared, UV-Vis., 1H NMR, 13C NMR and mass spectral studies. Density functional theory (DFT) calculations were performed for both the Schiff bases with 6-31G(d, p) as the basis set. Vibrational frequencies calculated using the theoretical method were in good agreement with the experimental values. Both the Schiff bases were highly fluorescent in nature. The cation-recognizing profile of the compounds was investigated in aqueous methanol medium. The Schiff base 4-(1-(pyridin-4-ylimino)ethyl)benzene-1,3-diol (PYEB) was found to interact with Fe(III) and Cu(II) ions, whereas the Schiff base 4,4'-((pyridine-2,3-diylbis(azanylylidene))bis(ethan-1-yl-1-ylidene))bis(benzene-1,3-diol) (PDEB) was found to detect Cu(II) ions. The mechanism of recognition was established as combined excited state intramolecular proton transfer (ESIPT)-chelation-enhanced fluorescence (CHEF) effect and chelation-enhanced quenching (CHEQ) process for the detection of Fe(III) and Cu(II) ions, respectively. The stability constant of the metal complexes formed during the sensing process was determined. The limit of detection for Fe(III) and Cu(II) ions with respect to Schiff base PYEB was found to be 1.64 × 10-6 and 2.16 × 10-7 M, respectively. With respect to Schiff base PDEB, the limit of detection for Cu(II) ion was found to be 4.54 × 10-4 M. The Cu(II) ion sensing property of the Schiff base PDEB was applied in bioimaging studies for the detection of HeLa cells.

Novel Anthracene and Carbazole Based Aggregation Induced Enhanced Emission Active Schiff Base as a Selective Sensor for Cu2+ ions

In present work our group has synthesized two novel Schiff-bases, Di-Carbazole based Schiff-base (DB-1) and Di-Anthracene based Schiff-base (DB-2) using condensation reaction and characterized thorough different spectroscopic techniques such as mass spectrometry, IR spectroscopy, 1H and 13C NMR spectroscopy. Furthermore, the AIE(Aggregation induced emission) studies were done using water-THF mixture. As compared to pure THF, the DB-2 showed a 17.8-fold increase in fluorescence intensity with a bathochromic shift of 64 nm in 80% water: THF mixture. For DB-1increase was seen at 70% water-THF combination. The analysis of the dynamic light scattering (DLS) further supported this excellent AIEE (Aggregation induced enhanced emission) characteristic. Furthermore, the spectrofluorometric techniques were used to examine the capacity of both Schiff bases to detect the heavy metals. It was discovered that only DB-1, with a detection limit of 2.4 × 10-8 M, was selective for the Cu2+ ion, whereas DB-2 had no sensing capability for metal ions. The Job's plot was used to determine the stoichiometry ratio of the DB-1 with Cu2+ to further examine the process. It was discovered that the ratio was 1:1 (DB-1:Cu2+). Additionally, the association constant of DB-1 for Cu2+ was 5.1 × 1011 M-1, demonstrating the excellent binding affinity of DB-1 for the Cu2+ ion.

Rhodamine hydrazide-linked naphthalimide derivative: Selective naked eye detection of Cu2+, S2- and understanding the therapeutic potential of the copper complex as an anti-cervical cancer agent

A naphthalimide-labeled rhodamine hydrazone derivative HL has been synthesized, characterized and examined in metal ion recognition. It shows selective colorimetric detection of Cu2+ over a number of other metal ions with a detection limit of 1.66 × 10-7 M in CH3CN/HEPES buffer (v/v = 2:1, pH = 6.8). The spirolactam ring of rhodamine and the imino-phenol motif of naphthalimide in HL are involved in complexation of Cu2+ as shown by single crystal X-ray. Single crystal of the copper-complex is prepared by utilizing NaSCN and it is characterized as CuL(SCN). The emergence of new absorption at 550 nm in UV-vis and the pink color of the solution reveal the selective interaction toward Cu2+. HL is characterized as a fluorescence resonance energy transfer (FRET) system that remains 'turned OFF' while spirolactam ring exists. In the presence of Cu2+, FRET is 'turned ON' via the opening of spirolactam ring to give emission at 580 nm which is less intense due to the quenching effect of Cu2+ ion. The complexation is reversible and the ensemble of Cu2+.HL selectively recognizes S2- over a series of different anions involving a color change from pink to colorless via the formation of spirolactam ring. The copper complex CuL(SCN) is further employed to understand its efficacy as a therapeutic agent. The complex is cytotoxic to high-risk HPV positive cervical cancer cell lines like SiHa and HeLa and is efficient in the generation and accumulation of reactive oxygen species (ROS). The complex also initiates nuclear blebbing and shows DNA degradation as understood by DNA laddering assay.

SDS-capped 1-pyrenecarboxaldehyde nanoprobe for selective detection of Cu2+ ion from water samples: Spectroscopic approach

Sodium dodecyl sulfate (SDS)-capped 1-pyrenecarboxaldehyde nanoparticles (PyalNPs) were prepared using a reprecipitation method in an aqueous medium and exhibited red-shifted aggregation-induced enhanced emission (AIEE). The dynamic light scattering (DLS) examination showed narrower particle size distribution with an average particle size of 41 nm, whereas -34.5 mV zeta potential value indicate the negative surface charge and good stability of nanoparticles (NPs) in an aqueous medium. The AIEE was seen at λmax  = 473 nm in a fluorescence spectrum of a PyalNP suspension. In the presence of Cu2+ ions, the fluorescence of PyalNPs quenches very significantly, even in the presence of other metal ions like Ba2+ , Ca2+ , Cd2+ , Co2+ , Al3+ , Fe2+ , Hg2+ , Ni2+ and Mg2+ . The changes in the fluorescence lifetime of PyalNPs in the presence of Cu2+ ions suggested that the type of quenching was dynamic. The fluorescence quenching data for the NPs suspension fitted well into a typical Stern-Volmer relationship in the concentration range 1.0-25 μg/ml of Cu2+ ions. The estimated value of the correlation coefficient R2  = 0.9877 was close to 1 and showed the linear relationship between quenching data and Cu2+ ion concentration. The limit of detection (LOD) was found to be 0.94 ng/ml and is far below the tolerable intake limit value of 1.3 μg/ml accepted by the World Health Organization for Cu2+ ions in drinking water. The fluorescence quenching approach for a SDS-capped Pyal nanosuspension for copper ion quantification is of high specificity and coexisting ions were found to interfere very negligibly. The developed method was successfully applied for the estimation of copper ions in river water samples.

A rapid responsive coumarin-naphthalene derivative for the detection of cyanide ions in cell culture

Cyanide ion (CN^-) is widely used in many industrial processes; however, it causes several diseases in humans. Therefore, rapid and accurate detection of CN^- is very important and urgent. In this study, a CN^- sensor (MH-2) which was capable of detecting CN^- ions in living cell was developed. MH-2 gives a rapid color change, absorbance and fluorescence response to CN^- in the presence of the anions tested in the working system. The binding ratio between the sensor and CN^- was demonstrated by some spectrophotometric methods and the sensing mechanism was investigated by NMR titration experiments, suggesting that MH-2 gives response to CN^- via the nucleophilic addition reaction. The fluorescence detection limit and the absorbance detection limit were calculated as 0.056 μM and 0.11 μM, respectively. Both of these detection limits are below the tolerable limit recommended by WHO for CN^- in the drinking water (1.9 μM). MH-2 was also applied to living cells for bio-imaging and the results showed that the sensor penetrates the cells and can detect cyanide ions in living cells.

A reaction-based system for the colorimetric detection of glyphosate in real samples

Glyphosate is widely used herbicides and causes several diseases in humans. Therefore, the detection of glyphosate is curial and urgent. Studies on the detection of glyphosate in literature are often based on inhibition of the enzyme acetylcholinesterase. In this study, we developed two simple colorimetric sensors, BP-Cl and CP-Cl, by linking 3-chloro-4-methylpyridine with 4-(dimethylamino)cinnamaldehyde or 4-(dimethylamino)benzaldehyde in a one-step reaction. The colorimetric and optical sensing properties of these compounds were investigated by the naked-eye and UV-Vis spectrophotometer in ACN/HEPES buffer (5 mM pH 8.0, 1:1 v/v). The sensors displayed high sensitivity and selectivity for glyphosate by color changes, which ranged from colorless to yellow for BP-Cl and yellow to orange for CP-Cl. The detection limits of BP-Cl and CP-Cl by the naked-eye detection were found as 15 µM and 10 µM. On the other hand, the detection limits of BP-Cl and CP-Cl via UV-Vis measurements were calculated as 0.847 µM and 1.23 µM, respectively. Moreover, the sensors were able to monitor glyphosate in water samples using the naked-eye, UV-Vis spectroscopy, and filter paper strips.

Highly Sensitive and Selective Spiropyran-Based Sensor for Copper(II) Quantification

The metal-binding capabilities of the spiropyran family of molecular switches have been explored for several purposes from sensing to optical circuits. Metal-selective sensing has been of great interest for applications ranging from environmental assays to industrial quality control, but sensitive metal detection for field-based assays has been elusive. In this work, we demonstrate colorimetric copper sensing at low micromolar levels. Dimethylamine-functionalized spiropyran (SP1) was synthesized and its metal-sensing properties were investigated using UV-vis spectrophotometry. The formation of a metal complex between SP1 and Cu²⁺ was associated with a color change that can be observed by the naked eye as low as ≈6 μM and the limit of detection was found to be 0.11 μM via UV-vis spectrometry. Colorimetric data showed linearity of response in a physiologically relevant range (0-20 μM Cu²⁺) with high selectivity for Cu²⁺ ions over biologically and environmentally relevant metals such as Na⁺, K⁺, Mn²⁺, Ca²⁺, Zn²⁺, Co²⁺, Mg²⁺, Ni²⁺, Fe³⁺, Cd²⁺, and Pb²⁺. Since the color change accompanying SP1-Cu²⁺ complex formation could be detected at low micromolar concentrations, SP1 could be viable for field testing of trace Cu²⁺ ions.