Exploration of Molecular Structure, DFT Calculations, and Antioxidant Activity of a Hydrazone Derivative.

The hydrazine derivatives are known to possess several biological activities including anticancer, antibacterial and anti-fungal, anticonvulsant, and antioxidant. This communication presents the synthesis, X-ray crystal structure analysis, DFT calculations, cell cytotoxicity, and antioxidant activity of the Schiff base 4,4'-((1E,1'E)-hydrazine-1,2-diylidenebis(ethan-1-yl-1-ylidene))bis(benzene-1,3-diol) (compound 2). We have also isolated the side product compound 1 and characterized it using single X-ray crystallography. The crystal structure of compound 1 depicts that the ensuing C-H···N hydrogen bonding interaction is presented and discussed herein. In addition, the calculations using density functional theory (DFT) approximation supported by experimental 1H and 13C NMR studies on the key compound 2 are reported. The results of theoretical and experimental 1H and 13C NMR were concordant. The antioxidant activity of compound 2 was determined by using 2,2'-azinobis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS•+) radical cation assays and 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical assay. Compound 2 demonstrated excellent antioxidant activity in ABTS assay (IC50 = 4.30 ± 0.21 µM) and DPPH assay (IC50 = 81.06 ± 0.72 µM) with almost no cytotoxicity below 25 µM.

Exploration of highly selective fluorogenic 'on-off' chemosensor for H2 PO4 - ions: ICT-based sensing and ATPase activity profiling.

In this study, the recognition contour of Chemosensor 1 was investigated using semiaqueous methanol (XH , mole fraction = 0.31) for a range of anions and bioactive species. Host-receptor signalling based on the internal charge transfer mechanism for Chemosensor 1 was explored and reported. Structure of Chemosensor 1 and its plausible anion coordination based on hydrogen bonding is complemented with density functional theory. Consequently, we investigated the applicability of the synthesized probe in blood plasma, urine, tap water samples, and for monitoring of ATP in lysosomes by apyrase enzyme.

Highly selective optical and reversible dual-path chemosensor for cyanide detection and its application in live cells imaging.

A new biocompatible fluorescent receptor 1 was synthesized by conjugating diaminomaleonitrile (DMN) with benzothiazole unit, and characterized by single X-ray. In DMF/water (1:1, v/v), the receptor 1 showed a selectivity turn-on fluorescence at 517nm in the presence of CN-. Receptor 1 showed a detection limit down to 0.16µM without any interference from other tested anions. The reversibility and reusability of 1 for the detection of CN- ion was also tested for five cycles indicating the probe 1 could be used in a reversible manner. Importantly, the receptor 1 showed excellent cells viability and was successfully applied for the detection of CN- in live mouse fibroblast cells L929 cells.

Selective ciprofloxacin antibiotic detection by fluorescent siderophore pyoverdin.

Fluorescent siderophore pyoverdin (PVD) was produced from a soil isolate Pseudomonas monteilii strain MKP 213. The PVD was purified near to homogeneity and applied for the fluorescent chemosensing of various antibiotics in aqueous solution (pH=7.0). Upon addition of ciprofloxacin, PVD showed new UV-vis absorption bands at 252 and 321nm due to an internal charge transfer mechanism. Also, the addition of ciprofloxacin induced a highly selective fluorescence enhancement of PVD with a 13nm blue shift from 458 to 445nm. The combination of a long peptide chain along with the chromophore unit of PVD generates a converging cleft for ciprofloxacin recognition with LOD and LOQ of 7.13µM and 21.6µM, respectively without interference from other studied antibiotics. The association constant (Ka) of PVD with ciprofloxacin was calculated to be as low as 1.40×10(5)M(-1) using Benesi-Hildebrand plot depicting its significance in detection. The pharmaceutical tablet analysis measures the sensing with negligible matrix effect and quantitative recovery.

A novel zinc(II) and hydrogen sulphate selective fluorescent "turn-on" chemosensor based on isonicotiamide: INHIBIT type's logic gate and application in cancer cell imaging.

We have developed a novel isonicotiamide-based fluorescent "turn-on" chemosensor 1 for the selective detection of Zn(2+) and HSO4(-). The sensor 1 can detect Zn(2+) and HSO4(-) with a detection limit down to the nanomolar level by forming a complex in 1 : 1 stoichiometry in the presence of other anions and 2 : 1 in presence of cations in aqueous solution. Density functional theory calculations on 1 and the 1-Zn(2+)/HSO4(-) complexes are consistent with the experimental results. We have successfully utilized the above cation and anion for the fabrication of INHIBIT molecular logic gates. Furthermore the receptor 1 successfully detected the Zn(2+) and HSO4(-) ions in HeLa cells cultured in Zn(2+) and HSO4(-) enriched medium.

A highly selective fluorescent 'turn-on' chemosensor for Zn(2+) based on a benzothiazole conjugate: their applicability in live cell imaging and use of the resultant complex as a secondary sensor of CN(-).

A benzothiazole derivative linked "off-on" multi-responsive and selective chemosensor has been synthesized and evaluated for cation recognition properties. The receptor shows a high sensitivity and selectivity for Zn(2+) through a 'turn-on' fluorescence response over the other tested cations with a detection limit as low as 0.67 µM. The receptor was successfully applied for the detection of Zn(2+) in live HeLa cells. Then, the Zn(2+) complex of receptor was also used for cyanide detection and recognition.

Fluorogenic ratiometric dipodal optode containing imine-amide linkages: exploiting subtle thorium (IV) ion sensing.

The (13E,19E)-N1',N3'-bis[4-(diethylamino)-2-hydroxybenzylidene]malonohydrazide (L) has been developed for the detection of Th(4+) ions using dual channel signalling system. The UV-vis absorbance and fluorescence spectroscopic data revealed the formation of L-Th(4+) complex in 1:1 equilibrium. The density functional theory (DFT) also confirms the optimum binding cavity for the recognition of metal ion. The binding constant computed from different mathematical models for an assembly of L-Th(4+). The detection limit of L for Th(4+) recognition is to a concentration down to 0.1 µM (0.023 µg g(-1)). The present sensing system is also successfully applied for the detection of Th(4+) ion present in soil near nuclear atomic plants.

Ratiometric fluorescent scaffold giving discrete response towards iodide ion: a combined experimental and DFT study.

A novel ratiometric fluorescent receptor (Z)-2-(4-[diethylamino]-2-hydroxybenzylideneamino) pyridine-3-carbaldehyde (3) bearing one phenolic OH and one aldehyde group as recognition sites was synthesized and characterized. The anion recognition behaviour of receptor 3 was evaluated by various spectroscopic (UV-visible, fluorescence and (1) H nuclear magnetic resonance) methods and was validated by computational studies. The receptor showed fast response time, excellent selectivity and reproducibility towards iodide ion detection among the other surveyed anions, with a binding constant of 6.12 × 10(4) M(-1) and a detection limit of 0.24 µM, thus confirming its potential applicability as a fluorescent sensor for iodide.

Highly selective turn-on fluorescent sensor for nanomolar detection of biologically important Zn2+ based on isonicotinohydrazide derivative: application in cellular imaging.

A new Zn(2+) selective chemosensor (3) was synthesized by condensation of commercially available substituted salicylaldehyde and isonicotinohydrazide, and characterized by single crystal X-ray crystallography. Receptor 3 with Zn(2+) exhibited a highly selective and pronounced enhancement in the fluorescence emission among different cations by forming a 2:1 complex. The receptor can detect Zn(2+) up to nanomolar level (6.75 nM) with good tolerance of other metal ions and can be used for in vitro cellular imaging.

"Turn-on" fluorescent chemosensor for zinc(II) dipodal ratiometric receptor: application in live cell imaging.

A dipodal ligand 2,2'-((ethane-1,2-diylbis(azanediyl))bis(ethane-1,1-diyl))diphenol was synthesized through a condensation reaction and was characterized with IR, (1)H NMR, (13)C-NMR, and mass spectroscopy. The receptor 2 has shown marked enhancement in fluorescence intensity (emission signal at 341 nm) on binding with Zn(2+) as compared to other surveyed metal ions. The sensor has shown dramatic changes in dual channel fluorescence emission with λmax at 300 and 341 nm. The successive addition of Zn(2+) to the solution of the sensor led to a blue shift of the peak maxima and interestingly upon addition of higher equivalents of Zn(2+) quenched the fluorescence intensity of the sensor, and ultimately the original fluorescent profile of sensor was restored. The structures of 2 and 3 were optimized with B3LYP/LanL2DZ basis sets. The receptor 2 successfully detect the Zn(2+) ion in HeLa cells cultured in Zn(2+) enriched medium.

A novel urea-linked dipodal naphthalene-based fluorescent sensor for Hg(II) and its application in live cell imaging.

A novel cell-permeable urea-linked dipodal naphthalene-based fluorescent receptor 1 (1,1'-(1,5,5-trimethyl-3-oxocyclohexane-1,2-diyl)bis(3-(naphthalen-2-yl)urea) was designed and synthesized. The cation recognition ability of 1 was evaluated with a library of metal ions in DMSO/H2O (9:1, v/v). The receptor showed a selective chromogenic and fluorescent turn-off response towards Hg(2+) among the surveyed metal ions. The developed sensor was successfully applied to image intracellular Hg(2+) in living cells and also for the determination of Hg(2+) content in real water samples. Moreover, the DFT calculations were performed to complement the experimental evidences.

2,2'-[Benzene-1,2-diylbis(iminomethanediyl)]diphenol derivative bearing two amine and hydroxyl groups as fluorescent receptor for Zinc(II) ion.

A new non-natural receptor 2,2'-[benzene-1,2-diylbis(iminomethanediyl)]diphenol (4) was synthesized, and it is fluorogenic behaviour toward various metal ions were investigated. Receptor 4 exhibited pronounced fluorescence enhancement in the presence of Zn(2+), which can visually be discernible by an orchid fluorescence in compared to other metal ions. The receptor 4 shows high sensitivity and selectivity for Zn(2+) through changes in the fluorescence intensity based on chelation-enhanced fluorescence (CHEF). The binding modes of the complexes were investigated by Job's plot and density functional theory (DFT).

Exploration of selective recognition of iodide with dipodal sensor: 2,2'-[ethane-1,2-diylbis(iminoethane-1,1-diyl)]diphenol.

A dipodal fluorescent receptor, 2,2'-[ethane-1,2-diylbis(iminoethane-1,1-diyl)]diphenol (), with amine and hydroxyl moieties as binding sites has been synthesised and characterized with spectroscopic methods and single crystal X-ray techniques. The recognition of the anions with receptor was studied using UV-Vis and fluorescence spectroscopy. The (1)H-NMR spectroscopic and DFT studies revealed the distinct recognition of I(-) ions over the other surveyed anions.

Al3+ selective colorimetric and fluorescent red shifting chemosensor: application in living cell imaging.

We report the development of a fluorescent probe based on the benzothiazole unit to monitor intracellular Al(3+) levels in living cells. The fluorescent probe exhibits a fluorescence response towards Al(3+) under physiological conditions with high sensitivity and selectivity and even facilitates naked-eye detection of Al(3+). The fluorescence intensity was significantly quenched with red shifting upon addition of 0.5 equiv. of Al(3+). The simple and cost effective receptor avails rapid detection of Al(3+) ions at concentrations as low as 0.42 µM and is expected to be effective for the design of efficient biological sensor.

An amide based dipodal Zn(2+) complex: nano-molar detection of HSO(4) (−) in a semi-aqueous system.

A new chromogenic dipodal Zn2+ complex (4) bearing an amide group has been synthesized. The anion binding profile of this sensor was investigated with fluorescence and UV-Vis spectroscopy. The receptor 4 has high affinity for HSO4 − with a binding constant of 3.5 × 104 M−1 and a detection limit of 50 nM. The binding ability was confirmed with spectroscopic methods and density functional theory calculation (DFT).

Design and Synthesis of a Pyridine Based Chemosensor: Highly Selective Fluorescent Probe For Pb2+

A pyridine based imine-linked chemosensor has been synthesized and evaluated its binding affinity with library of transition metal ions. It has prominent selectivity towards Pb2+ among other metal ions in DMF/H2O (9:1, v/v) solvent system. The 1:1 stoichiometric was confirmed by job's plot and has a binding constant (Ka) = 5.142 × 103 M-1 on fluorescence. A B3LYP/6-31G and B3LYP/LanL2DZ basis sets were employed for optimization of 3 and 3.Pb2+.

Bis(2-hydroxy-3-isopropyl-6-methyl-benzaldehyde)ethylenediamine: a novel cation sensor.

Novel substituted phenol-based new symmetrical bis(2-hydroxy-3-isopropyl-6-methyl-benzaldehyde)ethylenediamine (1) has been designed and synthesized. The compound 1 fluorometrically recognized Cu(2+) ion in CH3OH/H2O (90:10, v/v) by exhibiting an increase in emission upon complexation. In addition, Cu(2+) gave rise to a change in colour of the solution of compound 1, which was clearly visible to the naked eye under UV irradiation. The association constant (K) of compound 1 with Cu(2+) ion was computed with the Benesi-Hildebrand plot and Scatchard plot at 43,000 M(-1) and 43,011 M(-1) respectively.