Tri-armed Schiff base fluorescent sensor for the rapid recognition of Zn(II): application in live cell imaging, test strips and TLC.

Various metal ions exist in nature and human beings and play limitless vital roles in both the atmosphere and biology. A fundamental and useful aspect is the qualitative and quantitative assessment of Zn(II) at concentration levels as low as parts per billion (ppb). Thus, the design and development of novel fluorescent turn-on receptors have gained significant interest because of their potential for use in live cell imaging to detect biologically relevant metal ions with high selectivity and sensitivity. The present research illustrates the design and synthesis of a novel fluorescent sensor [(1,3,5-triazine-2,4,6-triyl)tris(hydrazine-2-yl-1-ylidene)tris(methaneylylidene)]tris(2,4-di-tert-butylphenol) (THDBP) for the selective and sensitive probing of Zn(II). The sensor exhibited a fluorescence turn-on mechanism upon treatment with Zn(II) ions at λemi. 503 nm in aq. acetonitrile. The formation of a 1 : 3 complex between THDBP and Zn(II) is confirmed from the Job plot and ESI-MS spectrum. The evaluated limit of detection (LOD) and association constant (Ka) of the sensor THDBP for Zn(II) were found to be 1.03 × 10-10 M and 2.33 × 108 M-1, respectively. Further research demonstrates the practical application of the sensor for the detection of Zn(II) ions in live cells. The sensing ability of the sensor THDBP was also explored through inexpensive test strips and TLC sheets.

A pyrene-induced PET-based chemosensor for biologically important Zn(II) ions: application in test strips and live cell imaging studies.

Cation and anion sensing is vital owing to their universal dispersion in ecosystems and biological functions. It has been shown that fluorescent receptors based on organic platforms are efficient for detecting a number of ions and have many advantages such as low cost, superior sensitivity and simplicity in installation. This study demonstrates the design and synthesis of a novel receptor (E)-3-[(3,5-di-tert-butyl-2-hydroxybenzylidene)amino]-2-(pyren-1-yl)-2,3-dihydroquinazolin-4(1H)-one (DTQ) for the rapid recognition of Zn(II) ions. DTQ exhibited a significant fluorometric "turn-on" characteristic towards Zn(II) at λmax 444 nm in aqueous acetonitrile by inhibiting the photo-induced electron transfer (PET) and -CN- process. The ESI-MS analysis and Job's plot experimental results confirmed stoichiometric 1 : 1 complex formation between DTQ and Zn(II). Fluorometric investigations revealed the detection limit and association constant of DTQ towards Zn(II), which were found to be 13.4 nM and 1.47 × 105 M-1, respectively. DTQ was employed to sense Zn(II) on low-cost test strips. The present research findings imply that DTQ can function as an effective sensor for Zn(II).

Luminescent Pyrene-based Schiff base Receptor for Hazardous Mercury(II) Detection Demonstrated by Cell Imaging and Test Strip.

Qualitative and quantitative analysis of mercury at concentration levels as low as parts per billion (ppb) is a basic and practical concern. The vast majority of research in this field has centered on the development of potent chemosensor to monitor mercuric (Hg2+) ions. Mercury exists in three oxidation states, + 2, + 1 and 0, all of which are highly poisonous. In this study, (N1E,N2E)-N1,N2-bis(pyrene-1-ylmethylene)benzene-1,2-diamine (PAPM), a novel photoluminescent sensor based on pyrene platform was synthesized. Over the tested metal ions (Cd2+, Co2+, Cu2+, Mg2+, Mn2+, Ni2+, K+, Na+, Zn2+, Sr2+, Pb2+, Al3+, Cr3+ and Fe3+) the sensor responds only to Hg2+ by showing high selectivity and sensitivity. After treatment with mercuric ions at room temperature, the luminescence intensity of probe was quenched at 456 nm. The quenching of fluorescence intensity of probe upon addition of mercury is due to the effect of "turn-off" chelation enhanced quenching (CHEQ) by the formation of 1:1 complex. The ESI-MS spectrum and the Job's experimental results confirm the formation of 1:1 complex between PAPM and Hg2+. The detection limit and association constant of sensor for mercury is computed using fluorescence titration data and were found to be 9.0 × 10-8 M and 1.29 × 105 M-1 respectively. The practical application of sensor towards recognition of mercury(II) ions was explored through economically viable test strips and also using cell imaging studies.

Effect of Hydroxyl Group on Photo-Physical Properties and Dipole Moments of Fluorescent Dyes: An Experimental and Computational Approach.

In this work, structurally similar, (E)-N'-(2-hydroxybenzylidene)-3,5-di-tert-butyl-2-hydroxybenzohydrazide (A) and (E)-N'-(2-4-dihydroxybenzylidene)-3,5-di-tert-butyl-2-hydroxybenzohydrazide (A-OH) dyes dissolved in general solvents have been studied to explore photo-physical properties, employing solvatochromic shift method, thereby determining their dipole moments in the ground (µg) and excited (µe) states. The molecule A shows a bathochromic shift of fluorescence emission maxima in aprotic solvents whereas a hypsochromic shift in protic solvents. Interestingly, A-OH follows a hypsochromic shift in both protic and aprotic solvents with increasing solvent polarity. The effect of hydroxyl substituent on UV-Visible absorption, fluorescence emission, and dipole moment of the titled organic molecules was explained. Theoretical methods such as Bilot-Kawski method for determination of µg and µe and Bakshiev, Kawski-Chamma-Viallet, Lippert-Mataga equations for µe, and Reichardt method for the difference between µg and µe were employed. It is observed that µe is higher than that of µg for both the molecules, and interestingly, upon substituting an additional hydroxyl group the value of µg has increased while µe is decreased. The DFT calculations have been performed to support experimental results by employing DFT/B3LYP/6-311G + (d) and TD-DFT/B3LYP/6-311G + (d) method using Gaussian09 software. The electrophilic and nucleophilic sites on the molecules were studied with the help of MEP. The NBO analysis results show that the interaction N24 (σ) → C22-O23 (π*) is found to be stronger in both the molecules with energy 68.90 kJ/mol and the effect of hydroxyl group is also discussed on the basis of HOMO and LUMO.

A novel switch on and reversible optical sensor as an efficient, selective receptor for Zn(II) ion and its biological application.

In the present study, a promising optical sensor (TR) was designed, synthesized, characterized and its chemosensing mechanism has been explored through 1H NMR, ESI-MS, UV-Vis absorption and emission spectral studies. This compound exhibits a drastic change in its optical properties when treated with Zn2+, whereas other metal ions do not respond. This provides a naked eye detection for Zn2+ ion. In methanolic medium, Zn2+ ion induces strong fluorescence in TR with large Stokes shifts up to ∼132 nm. A 5-fold increase in fluorescence intensity of TR in presence Zn2+ ion is due to inhibition of ESIPT (Excited State Intramolecular Proton Transfer) and -C=N isomerization with large increase in the ICT (Intramolecular Charge Transfer) character of TR in the excited state. The Job's plot and BH plots reveal the formation of 1: 1 stoichiometry with an estimated binding constant of 3.9 × 107 M-1. The detection limit of TR was found to be 3.85 nM. The TR could be regenerated by adding EDTA solution to the complex formed during interaction. The pH studies indicate that TR could render pH dependent fluorescence measurements in a live physiological environment. Computational technique was used to optimize the structures and the theoretical results are correlated with the experimental results. The possible utilization of TR as bio-imaging fluorescent sensor with 98.57% cell viability to detect Zn2+ in HeLa cells was also explored by fluorescent cell imager.