A novel hydrazide-based selective and sensitive optical chemosensor for the detection of Ni2+ ions: applications in live cell imaging, molecular logic gates and smart phone-based analysis.

A novel flexible "N", "O"-rich hydrazide-based Schiff base chemoreceptor, 2-(benzamido)-N'-((pyridin-2-yl)methylene)benzohydrazide (L), was designed, synthesised and characterised via1H-NMR, IR spectroscopy, ESI-MS spectrometry and single-crystal XRD analysis. The receptor showed a colorimetric and fluorometric "turn on" response in the presence of only Ni2+ ions in methanol-Tris-HCl buffer medium (10 mM, pH 7.2, 1 : 1 v/v). The Job plot analysis revealed that the receptor forms a 2 : 1 complex with Ni2+ ions, which was further confirmed via the ESI-MS analysis. A single crystal of the L-Ni2+ complex (2) was also isolated. The detection limit was calculated to be 1.8 µM colorimetrically and 1.18 µM fluorometrically, which are much lower than those recommended as per the WHO guidelines for drinking water. The experimental results were further supported by DFT studies. The chemosensor L was applied for the recovery of contaminated water samples, building of molecular logic gate, smart phone-based analysis and live cell imaging.

A dual-mode highly selective and sensitive Schiff base chemosensor for fluorescent colorimetric detection of Ni2+ and colorimetric detection of Cu2.

In this paper, a novel flexible Schiff base chemosensor N'-(2-hydroxy-3-methoxybenzylidene)-2-(benzamido)benzohydrazide (L) has been designed, synthesised and characterised by 1H-NMR, IR spectroscopy, ESI-MS spectrometry and single crystal XRD analysis. A significant fluorescence enhancement of L was observed only in the presence of Ni2+ ions with a detection limit of 3.64 µM whereas Cu2+ induced fluorescence quenching, although both the metals showed colorimetric responses in methanol-Tris-HCl buffer (10 mM, pH 7.2) solution (1 : 1, v/v). The single crystal structure of L-Cu2+ has also been determined. No major interference by the other effective background cations (Fe3+, Fe2+, Co2+, Zn2+, Cd2+, Hg2+, Pb2+, Cr3+, Ag+, Al3+ and Mn2+) was observed even at a higher concentration of analytes. The experimental results were further supported by DFT studies. The chemosensor L can be applied to the formation of binary logical devices, recovery of contaminated water samples and living intracellular media.

Triazole-based novel bis Schiff base colorimetric and fluorescent turn-on dual chemosensor for Cu2+ and Pb2+: application to living cell imaging and molecular logic gates.

A triazole-based novel bis Schiff base colorimetric and fluorescent chemosensor (L) has been designed, synthesized and characterized by elemental analysis, 1H-NMR, ESI-MS, FTIR spectra and DFT studies. The receptor L showed selective and sensitive colorimetric sensing ability for Cu2+ and Pb2+ ions by changing color from colorless to yellow and light yellow respectively in CH3OH-tris-buffer (1 : 1, v/v). However, it displayed strong fluorescence enhancement upon the addition of both Cu2+ and Pb2+ ions, attributed to the blocking of PET. The fluorometric detection limits for Cu2+ and Pb2+ were found to be 12 × 10-7 M and 9 × 10-7 M and the colorimetric detection limits were 3.7 × 10-6 M and 1.2 × 10-6 M respectively; which are far below the permissible concentration in drinking water determined by WHO. Moreover, it was found that chemosensor L worked as a reversible fluorescence probe towards Cu2+ and Pb2+ ions by the accumulation of S2- and EDTA respectively. Based on the physicochemical and analytical methods like ESI-mass spectrometry, Job plot, FT-IR, 1H-NMR spectra and DFT studies the detection mechanism may be explained as metal coordination, photoinduced electron transfer (PET) as well as an internal charge transfer (ICT) process. The sensor could work in a pH span of 4.0-12.0. The chemosensor L shows its application potential in the detection of Cu2+ and Pb2+ in real samples, living cells and building of molecular logic gate.

A dipodal molecular probe for naked eye detection of trivalent cations (Al3+, Fe3+and Cr3+) in aqueous medium and its applications in real sample analysis and molecular logic gates.

A simple and low cost multifunctional colorimetric receptor L has been designed, synthesized and characterized by 1H-NMR, IR spectroscopy, ESI-MS spectrometry and elemental analysis. The chemosensor L can selectively detect three biologically and environmentally important trivalent metal ions (Al3+, Fe3+and Cr3+) both visually and spectrophotometrically in CH3CN-H2O (1 : 1, v/v) solution in the presence of other biologically relevant metal ions. The Job's plot analyses indicate the 2 : 2 binding stereochemistry for Al3+, Fe3+ and Cr3+ ions with L, which was further confirmed by 1H-NMR and ESI-MS studies. The binding constant values were found to be 2.9 × 104 M-1 for Al3+, 1.079 × 105 M-1 for Fe3+ and 1.366 × 105 M-1 for Cr3+ respectively. The detections limits of the sensor for Al3+ (2.8 × 10-7 M), Fe3+ (1.9 × 10-7 M) and Cr3+ (2.5 × 10-7 M) are far below than the limit set by the World Health Organization (WHO) for drinking water. Moreover, colorimetric test kits for rapid detection of Al3+, Fe3+, and Cr3+ could be successively applied for all practical purposes, indicating its potential use in environmental samples. It has also been used in building molecular logic gates.

Solvent-dependent fluorescent-colorimetric probe for dual monitoring of Al(3+) and Cu(2+) in aqueous solution: an application to bio-imaging.

A novel, quinoline-based smart probe L has been designed for the detection of Al(3+) and Cu(2+) at physiological range. The unprecedented solvent-dependent sensitivities of the probe L for simultaneous detection of Al(3+) and Cu(2+) ions with high selectivity and sensitivity have been observed for the first time. It displays quick responses through visible colorimetric as well as fluorogenic changes towards both Al(3+) and Cu(2+), as delineated by absorption and fluorescence titrations. The sensitivity of the fluorescence-based assay (12.6 nM) for Al(3+) and (18.4 nM) for Cu(2+) is far below the limit recommended in the World Health Organization (WHO) guidelines for drinking water. From (1)H NMR data, the Job plot and the ESI-MS spectrum, 1 : 2 stoichiometric complexations between L and both metals have been established. The geometry and spectral property of L and its metal complexes have been well rationalized by DFT calculations. This probe L has been tested as being highly suitable for mapping Al(3+) and Cu(2+) in human breast cancer cells, MCF7, thus providing a wonderful candidate for tracking Al(3+) and Cu(2+) in biological organisms and processes. The proposed chemosensor L has also been successfully applied for analysis of real samples.

A reversible fluorescent-colorimetric imino-pyridyl bis-Schiff base sensor for expeditious detection of Al(3+) and HSO3(-) in aqueous media.

A reversible fluorescent-colorimetric imino-pyridyl bis-Schiff base receptor (N(1)E,N(4)E)-N(1),N(4)-bis(pyridine-4-ylmethylene)benzene-1,4-diamine for the detection of both Al(3+) and HSO3(-) in aqueous medium has been developed. Receptor exhibits an excellent selective fluorescent-colorimetric response toward Al(3+). The sensitivity of the fluorescent based assay (0.903 µM) for Al(3+) is far below the limit recommended in the World Health Organization (WHO) guidelines for drinking water (7.41 µM). From (1)H NMR data, the Job plot and the ESI-MS spectrum, 1 : 2 stoichiometric complexation between and Al(3+) has been established. Receptor shows remarkable detection ability in a wide pH range of 4-11 and was successfully utilised in the determination of Al(3+) in aqueous solution of bovine serum albumin protein, and of HSO3(-) in real food samples. Moreover, shows a highly selective colorimetric response to HSO3(-) by changing its colour from yellow to colorless immediately without any interference from other anions.

catena-Poly[[(triphenyl-phosphane)copper(I)]-di-µ-iodido-[(triphenyl-phosphane)copper(I)]-µ-{1,2-bis-[1-(pyridin-4-yl)ethyl-idene]hydrazine}].

In the title coordination polymer, [Cu(2)I(2)(C(14)H(14)N(4))(C(18)H(15)P)(2)](n), the Cu(I) atom is coordinated by two I atoms, one P atom and one N atom in a fairly regular tetra-hedral arrangement. A crystallographic inversion centre generates a Cu(2)I(2) diamond with a Cu-Cu separation of 3.0120 (5) Å. The complete N,N'-(1-pyridin-4-yl-ethethyl-idene)-hydrazine mol-ecule is also generated by inversion symmetry, and this bridging ligand leads to [011] polymeric chains in the crystal structure.

Metal binding to bipyridine-modified PNA.

Substitution of natural nucleobases in PNA oligomers with ligands is a strategy for directing metal ion incorporation to specific locations within a PNA duplex. In this study, we have synthesized PNA oligomers that contain up to three adjacent bipyridine ligands and examined the interaction with Ni2+ and Cu2+ of these oligomers and of duplexes formed from them. Variable-temperature UV spectroscopy showed that duplexes containing one terminal pair of bipyridine ligands are more stable upon metal binding than their nonmodified counterparts. While binding of one metal ion to duplexes that contain two adjacent bipyridine pairs makes the duplexes more stable, additional metal ions lower the duplex stability, with electrostatic repulsions being, most likely, an important contributor to the destabilization. UV titrations showed that the presence of several bipyridine ligands in close proximity of each other in PNA oligomers exerts a chelate effect. A supramolecular chelate effect occurs when several bipyridines are brought next to each other by hybridization of PNA duplexes. EPR spectroscopy studies indicate that even when two Cu2+ ions coordinate to a PNA duplex in which two bipyridine pairs are next to each other, the two metal-ligand complexes that form in the duplex are far enough from each other that the dipolar coupling is very weak. EXAFS and XANES show that the Ni2+-bipyridine bond lengths are typical for [Ni(bipy)2]2+ and [Ni(bipy)3]2+ complexes.

Influence of metal coordination on the mismatch tolerance of ligand-modified PNA duplexes.

Recent studies on metal incorporation in ligand-modified nucleic acids have focused on the effect of metal coordination on the stability of metal-containing duplexes or triplexes and on the metal binding selectivity but did not address the effect of the sequence of the nucleic acid in which the ligands are incorporated. We have introduced 8-hydroxyquinoline Q in 10-mer PNA strands with various sequences and have investigated the properties of the duplexes formed from these strands upon binding of Cu(2+). Variable-temperature UV-vis spectroscopy shows that, in the presence of Cu(2+), duplexes are formed even from ligand-modified Q-PNA strands that have a large number of mismatches. Spectrophotometric titrations demonstrate that at any temperature, one Cu(2+) ion binds a pair of Q-PNA strands that each contain one 8-hydroxyquinoline, but below the melting temperature, the PNA duplex exerts a supramolecular chelate effect, which prevents the transformation in the presence of excess Cu(2+) of the 1:2 Cu(2+):Q-PNA complexes into 1:1 complexes. EPR spectroscopy gives further support for the existence in the duplexes of [CuQ(2)] moieties that are similar to the corresponding square planar synthetic complex formed between Cu(2+) and 8-hydroxyquinoline. As PNA duplexes show a preferred handedness due to the chiral induction effect of a C-terminal l-lysine, which is transmitted through stacking interactions within the duplex, only if the metal-containing duplex has complementary strands, does it show a chiral excess measured by CD spectroscopy. The strong effect of the metal-ligand moiety is suggestive of an increased correlation length in PNA duplexes that contain such moieties. These results indicate that strong metal-ligand alternative base pairs significantly diminish the importance of Watson-Crick base pairing for the formation of a stable PNA duplex and lead to high mismatch tolerance, a principle that can be used in the construction of hybrid inorganic-nucleic acid nanostructures.