Cyclometalated iridium(III) complex of a 1,2,3-triazole-based ligand for highly selective sensing of pyrophosphate ion.

A new cyclometalated Ir(III) complex of a methylene-bridged benzimidazole-substituted 1,2,3-triazole methanol ligand has been synthesized for the photoluminescent detection of pyrophosphate (H2P2O72-) anions. The solution structure of 1[PF6] was fully characterized by 1D (1H, 13C) and 2D (1H-1H COSY, 1H-13C HSQC, and 1H-13C HMBC) NMR spectroscopy, and ESI-HRMS. The 1[PF6] acted as a highly selective luminescent sensor for H2P2O72- in CH3CN over other competitive ions, including H2PO4-, ATP, ADP and AMP. The PL titration of 1[PF6] with H2P2O72- in CH3CN furnished the association constant Ka = 8.6 × 107 M-1 and a low detection limit of ∼127 nM. The structure of the analyte interacting ligand renders the Ir(III) complex-based probe highly selective for H2P2O72- ions. The PL enhancement with H2P2O72- is due to the hydrogen bonding interaction of H2P2O72- with the triazole C-H, imidazole N-H, methylene hydrogen and hydroxyl groups of the ligand that has been supported by 1H NMR titration. Further, the PL enhancement of 1·H2P2O72- adducts was supported by triplet-state TDDFT calculations. In 1·H2P2O72-, the 3MLCT-3MC energy gap is increased, and the 1·H2P2O72- emits efficiently from the 3MLCT and 3ILCT excited states. Finally, a cytotoxicity study and live-cell imaging were performed. The probe showed low cytotoxicity against HeLa cells and was suitable for intracellular pyrophosphate imaging.

Ruthenium(II) Complex-Based G-quadruplex DNA Selective Luminescent 'Light-up' Probe for RNase H Activity Detection.

A bis-heteroleptic ruthenium(II) complex, 1[PF6 ]2 of benzothiazole amide substituted 2,2'-bipyridine ligand (bmbbipy) has been synthesized for the selective detection of G-quadruplex (GQ) DNA and luminescence-assay-based RNase H activity monitoring. Compound 1[PF6 ]2 exhibited aggregation-caused quenching (ACQ) in water. Aggregate formation was supported by DLS, UV-vis, and 1 H NMR spectroscopy results, and the morphology of aggregated particles was witnessed by SEM and TEM. 1[PF6 ]2 acted as an efficient GQ DNA-selective luminescent light-up probe over single-stranded and double-stranded DNA. The competency of 1[PF6 ]2 for selective GQ structure detection was established by PL and CD spectroscopy. For 1[PF6 ]2 , the PL light-up is exclusively due to the rigidification of the benzothiazole amide side arm in the presence of GQ-DNA. The interaction between the probe and GQ-DNA was analyzed by molecular docking analysis. The GQ structure detection capability of 1[PF6 ]2 was further applied in the luminescent 'off-on' RNase H activity detection. The assay utilized an RNA:DNA hybrid, obtained from 22AG2-RNA and 22AG2-DNA sequences. RNase H solely hydrolyzed the RNA of the RNA:DNA duplex and released G-rich 22AG2-DNA, which was detected via the PL enhancement of 1[PF6 ]2 . The selectivity of RNase H activity detection over various other restriction enzymes was also demonstrated.

Highly Selective Detection of Hypochlorous Acid by a Bis-heteroleptic Ru(II) Complex of Pyridyl-1,2,3-triazole Ligand via C(sp2)-H Hydroxylation.

A Ru(II) complex (Ru-1) of a substituted pyridyl-1,2,3-triazole ligand (BtPT) for highly selective "light-up" detection of hypochlorous acid is presented. An unusual anti-Markovnikov HOCl addition to the C═C bond of 1,2,3-triazole and a highly specific C(sp2)-H hydroxylation over epoxidation made Ru-1 a highly selective luminescent HOCl probe. The abnormal regio- and stereoselective HOCl addition and subsequent hydroxylation mechanism in detail is supported by the combination of ESI-MS, 1H/13C NMR spectroscopy, and 1H NMR titration. The hydroxylation at the C5 center in 1,2,3-triazole increases the electron density and makes BtPT a better σ-donor as well as π-donor, which in turn increases the 3MC-3MLCT energy gap and inhibits the nonradiative decay from the excited state of Ru-1 and is the key reason for luminescence light-up. Most importantly, the exogenous and endogenous HOCl imaging in the living HEK293T cells is also demonstrated. The probe showed low cytotoxicity and efficiently permeated the cell membrane. The cell-imaging experiments revealed rapid staining of the extranuclear region of HEK293T cells which clearly indicates the presence of cytoplasmic HOCl. The endogenous HOCl generation and imaging, stimulated by lipopolysaccharides (LPS) and paraquat in the HEK293T cells, is also demonstrated.

Organoiridium(III) Complexes as Luminescence Color Switching Probes for Selective Detection of Nerve Agent Simulant in Solution and Vapor Phase.

In this work, cationic organoiridium(III) complex based photoluminescent (PL) probes have been developed to selectively detect the chemical warfare nerve agent mimic, diethyl chlorophosphate(DCP) at nanomolar range by distinct bright green to orange-red luminescence color switching (on-off-on) in solution as well as in the vapor phase. Interference of other chemical warfare agents (CWAs) and their mimics was not observed either by PL spectroscopy or with the naked-eye in solution and gas phase. The detection was attained via a simultaneous nucleophilic attack of two -OH groups of the 4,7-dihydroxy-1,10-phenanthroline ligand with DCP by forming bulkier phosphotriester. The detailed reaction mechanism was established through extensive 1H NMR titration, 31P NMR, and ESI-MS analysis. Finally, a test paper strip and solid poly(ethylene oxide) (PEO) film with iridium(III) complex 1[PF6] were fabricated for the vapor-phase detection of DCP. The solution and vapor-phase detection properties of these luminescent Ir(III) complexes can offer a worthy approach into the design of new metal complex based PL switching probes for chemical warfare agents.

A reusable magnetic nickel nanoparticle based catalyst for the aqueous synthesis of diverse heterocycles and their evaluation as potential anti-bacterial agent.

A library of biologically important heterocycles, viz. pyrazolyl pyrimidine-triones, bis(heterocyclyl)methanes were successfully synthesised by the condensation of barbituric acid, pyrazolone with an aldehyde and dimedone/4-hydoxy coumarin with various substituted aldehydes in aqueous medium at room temperature catalysed by nickel nanoparticles which proved to be an efficient magnetically recyclable catalyst. The method is simple, eco-friendly and gave excellent yields of the products without taking recourse to column chromatographic separation procedures. Computational method was employed to elucidate the selective formation of uncyclised product in reaction course. The biological activity of the synthesized compounds were investigated and the results demonstrated profound antibacterial activity.

A cationic organoiridium(iii) complex-based AIEgen for selective light-up detection of rRNA and nucleolar staining.

A green emissive cationic organoiridium(iii) complex, 2[PF6], with a benzimidazole-substituted 1,2,3-triazole-pyridine (BiPT) ligand has been synthesized for target-specific cellular imaging and selective detection of ribosomal RNA (rRNA) over other competitive biomolecules in aqueous buffer solution at physiological pH. Complex 2 shows aggregation-induced emission enhancement (AIEE) properties and forms nano-aggregates in the presence of poor solvents. DFT and TD-DFT-based quantum mechanical calculations were performed to substantiate some photophysical features and to establish the intermolecular π-π interactions which detain the vibrational as well as rotational motions to form the aggregates, resulting in enhanced photoluminescence (PL). To corroborate the formation of nano-aggregates and to understand the morphology of the aggregated particles, dynamic light scattering (DLS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM) measurements were performed. 2[PF6] showed low cytotoxicity and good biocompatibility and was successfully employed in organelle-specific intracellular imaging. The in vivo and in vitro photoluminescence investigations affirmed that the probe stains cell nucleoli and selectively binds rRNA. It is assumed that the supramolecular π-π interactions between the benzimidazole of the BiPT ligand and the secondary structures of rRNA may facilitate aggregation and enable PL enhancement.

Aggregation-Induced Emission-Active Ruthenium(II) Complex of 4,7-Dichloro Phenanthroline for Selective Luminescent Detection and Ribosomal RNA Imaging.

The development of red emissive aggregation-induced emission (AIE) active probes for organelle-specific imaging is of great importance. Construction of metal complex-based AIE-active materials with metal-to-ligand charge transfer (MLCT), ligand-to-metal charge transfer (LMCT) emission together with the ligand-centered and intraligand (LC/ILCT) emission is a challenging task. We developed a red emissive ruthenium(II) complex, 1[PF6]2, and its perchlorate analogues of the 4,7-dichloro phenanthroline ligand. 1[PF6]2 has been characterized by spectroscopic and single-crystal X-ray diffraction. Complex 1 showed AIE enhancement in water, highly dense polyethylene glycol media, and also in the solid state. The possible reason behind the AIE property may be the weak supramolecular π···π, C-H···π, and C-Cl···H interactions between neighboring phen ligands as well as C-Cl···O halogen bonding (XB). The crystal structures of the two perchlorate analogues revealed C-Cl···O distances shorter than the sum of the van der Waals radii, which confirmed the XB interaction. The AIE property was supported by scanning electron microscopy, transmission electron microscopy, dynamic light scattering, and atomic force microscopy studies. Most importantly, the probe was found to be low cytotoxicity and to efficiently permeate the cell membrane. The cell-imaging experiments revealed rapid staining of the nucleolus in HeLa cells via the interaction with nucleolar ribosomal ribonucleic acid (rRNA). It is expected that the supramolecular interactions as well as C-Cl···O XB interaction with rRNA is the origin of aggregation and possible photoluminescence enhancement. To the best of our knowledge, this is the first report of red emissive ruthenium(II) complex-based probes with AIE characteristics for selective rRNA detection and nucleolar imaging.

Highly Sensitive Bifunctional Probe for Colorimetric Cyanide and Fluorometric H2S Detection and Bioimaging: Spontaneous Resolution, Aggregation, and Multicolor Fluorescence of Bisulfide Adduct.

A 4-methylbenzothiazole linked maleimide-based single molecular bifunctional probe 1 has been synthesized for the colorimetric and fluorometric detection of highly competitive H2S and cyanide ion in aqueous DMSO media. The probe 1 selectively detected CN- under the UV-vis spectroscopy through the rapid appearance of deep pink color. The bright pink color developed due to ICT in the moderately stable cyano substituted enolate intermediate. The absorbance titration of 1 with CN- revealed a new band at 540 nm and the nonlinear curve fitting analysis showed good fit with 1:1 model. In fluorescence channel, 1 was found to be highly selective to H2S in 50% aqueous buffer (pH 7). It exhibited ∼16-fold fluorescence intensity enhancement at 435 nm after reaction with 1 equiv of H2S due to the inhibition of PET. The 1-SH adduct showed TICT phenomenon and behaved like molecular rotor. It further displayed aggregation behavior at higher concentration and excitation wavelength dependent multicolor emission properties. Most interestingly, the spontaneous resolution of chiral S-isomer of the 1-SH adduct occurred during crystallization. The cell imaging study revealed the staining of the cell and multicolor emission in the presence of H2S.

Ruthenium(II) Complex-Based Luminescent Bifunctional Probe for Ag+ and Phosphate Ions: Ag+-Assisted Detection and Imaging of rRNA.

A new bis-heteroleptic Ru(II) complex (1) of benzimidazole-substituted 1,2,3-triazole pyridine ligand has been designed and constructed for the photoluminescent detection of cationic and anionic analytes, Ag+ and phosphate ions. Compound, 1[PF6]2 was fully characterized by various spectroscopic techniques and the solid-state structure was determined via single-crystal X-ray diffraction. The cation and anion sensing properties in 50% aqueous buffer (pH 9.2) and pure acetonitrile were carefully examined in photoluminescence (PL) spectroscopy. The 1[PF6]2 was found to be highly selective to pyrophosphate; PPi/HP2O73- and H2PO4- ions in CH3CN. It showed ∼10-fold PL intensity enhancement at 583 nm in the presence of only 1 and 2 equiv of PPi and H2PO4- ions, respectively. The PL titrations of 1[PF6]2 with PPi and H2PO4- in CH3CN furnished the association constant (Ka = 3.3 × 103 M-1 and 6.8 × 103 M-1) and the detection limit was as low as 5.73 and 5.19 ppb, respectively. The 1[PF6]2 also selectively detected Ag+ over other competitive cations through the luminescence light up in 50% aqueous buffer (pH 9.2) media. The PL titration of 1[PF6]2 with Ag+ showed ∼8-fold luminescence enhancement at 591 nm and yielded association constant, Ka = 3.5 × 104 M-1 and the detection limit was determined to be 5.05 ppb. A new cation sensing mechanism has been established where the Ag+ ion is detected in photoluminescence spectroscopy through the unique cyclometalated Ag+-triazolide complex formation. The high selectivity of 1[PF6]2 for phosphates and Ag+ was established by PL in the presence of various competing ions. Finally, for biological application, the cytotoxicity study was performed. The probe showed low cytotoxicity and was suitable for intracellular Ag+ imaging. The cell imaging and in vitro photoluminescence study revealed that the probe stained the cell nucleoli and specifically bind with ribosomal RNA (rRNA) and, therefore, it can also serve as a luminescent probe for rRNA in the presence of Ag+.

A coumarin based Schiff base probe for selective fluorescence detection of Al3+ and its application in live cell imaging.

A new coumarin based Schiff base compound, CSB-1 has been synthesized to detect metal ion based on the chelation enhanced fluorescence (CHEF). The cation binding properties of CSB-1 was thoroughly examined in UV-vis and fluorescence spectroscopy. In fluorescence spectroscopy the compound showed high selectivity toward Al3+ ion and the Al3+ can be quantified in mixed aqueous buffer solution (MeOH: 0.01M HEPES Buffer; 9:1; v/v) at pH7.4 as well as in BSA media. The fluorescence intensity of CSB-1 was enhanced by ~24 fold after addition of only five equivalents of Al3+. The fluorescence titration of CSB-1 with Al3+ in mixed aqueous buffer afforded a binding constant, Ka=(1.06±0.2)×104M-1. The colour change from light yellow to colourless and the appearance of blue fluorescence, which can be observed by the naked eye, provides a real-time method for Al3+ sensing. Further the live cell imaging study indicated that the detection of intracellular Al3+ ions are also readily possible in living cell.