A Novel Chromone Schiff-Base Fluorescent Chemosensor for Cd(II) Based on C=N Isomerization.

A new chromone Schiff-base fluorescent probe 7'-methoxychromone-3'-methylidene-1,2,4-triazole-3-imine (L) was designed and synthesized for selective recognition Cd(2+). With the fluorescence titration and the ESI-MS data, we reach the conclusion that the binding mode of the ligand-metal (L-Cd (2+) ) complex is 1:1. The sensor showed a strong fluorescence enhancement in ethanol system of Cd(2+) (excitation 409 nm and emission 462 nm) and the sensing mechanism based on the fact that C=N isomerization can be used to explain this phenomenon.

A Chromone-Derived Schiff-Base Ligand as Al(3+) "Turn on" Fluorescent Sensor: Synthesis and Spectroscopic Properties.

In this study, a novel chromone-derived Schiff-base ligand called 6-Hydroxy-3-formylchromone (2'-furan formyl) hydrazone (HCFH) has been designed and synthesized as a "turn on" fluorescent sensor for Al(3+). This sensor HCFH showed high selectivity and sensitivity towards Al(3+) over other metal ions investigated, and most metal ions had nearly no influences on the fluorescence response of HCFH to Al(3+). Additionally, the significant enhancement by about 171-fold in fluorescence emission intensity at 502 nm was observed in the presence of Al(3+) in ethanol, and it was due to the chelation-enhanced fluorescence (CHEF) effect upon complexation of HCFH with Al(3+) which inhibited the photoinduced electron transfer (PET) phenomenon from the Schiff-base nitrogen atom to chromone group. Moreover, this sensor formed a 1 : 1 complex with Al(3+) and the fluorescence response of HCFH to Al(3+) was nearly completed within 1 min. Thus, this sensor HCFH could be used to detect and recognize Al(3+) for real-time detection.

A highly selective turn-on fluorescent chemosensor for zinc ion in aqueous media.

In the paper, a novel rhodamine6G based fluorescent chemosensor bearing 3-carbaldehyde chromone was designed and synthesized. According to the fluorescence behavior toward several metal ions, it showed highly selectivity and sensitivity to Zn(II) over other commonly coexistent metal ions (Cu(II), Cd(II), Hg(II), Mg(II), K(I), Pb(II), Fe(III) and Cr(III)) in aqueous environment (pH = 7.4). Meanwhile the binding constant between Zn(II) and chemosensor achieved 6.21 × 10(11) M(-1) in aqueous media. Moreover, according to the Job plot, 1:1 stoichiometry between Zn(II) and sensor was deduced in aqueous media (pH = 7.4). The good selectivity and sensitivity in aqueous media effectively enhanced the application value of the fluorescent chemosensor for Zn(II).

Synthesis, characterization, DNA binding properties and antioxidant activity of Ln(III) complexes with Schiff base ligand derived from 3-carbaldehyde chromone and aminophenazone.

A novel Schiff base ligand, chromone-3-carbaldehyde-aminophenazone (L) and its Ln(III) (Ln = La, Yb) complexes were synthesized and characterized by physicochemical methods. The interaction between the ligand, Ln(III) complexes and calf thymus DNA in physiological buffer (pH=7.10) was investigated by using UV-vis spectroscopy, fluorescence spectra, ethidium bromide experiments and viscosity measurements, indicating that the studied compounds can all bind to DNA via an intercalation binding mode and the complexes have stronger binding affinity than the free ligand alone. Furthermore, antioxidant activity of the ligand and its complexes was determined by superoxide and hydroxyl radical scavenging methods in vitro, suggesting that Ln(III) complexes inhibit stronger antioxidant activity than the ligand alone and some standard antioxidants, such as mannitol and vitamin C.

Rare earth complexes with 3-carbaldehyde chromone-(benzoyl) hydrazone: synthesis, characterization, DNA binding studies and antioxidant activity.

A new ligand, 3-carbaldehyde chromone-(benzoyl) hydrazone (L), was prepared by condensation of 3-carbaldehyde chromone with benzoyl hydrazine. Its four rare earth complexes have been prepared and characterized on the basis of elemental analyses, molar conductivities, mass spectra, (1)H NMR spectra, UV-vis spectra, fluorescence studies and IR spectra. The Sm(III) complex exhibits red fluorescence under UV light and the fluorescent properties of Sm(III) complex in solid state and different solutions were investigated. In addition, the DNA binding properties of the ligand and its complexes have been investigated by electronic absorption spectroscopy, fluorescence spectra, ethidium bromide displacement experiments, iodide quenching experiments, salt effect and viscosity measurements. Experimental results suggest that all the compounds can bind to DNA via an intercalation binding mode. Furthermore, the antioxidant activities of the ligand and its complexes were determined by superoxide and hydroxyl radical scavenging methods in vitro. The rare earth complexes were found to possess potent antioxidant activities that are better than those of the ligand alone.

Synthesis, characterization, DNA binding properties, fluorescence studies and antioxidant activity of transition metal complexes with hesperetin-2-hydroxy benzoyl hydrazone.

A novel Schiff-base ligand (H(5)L), hesperetin-2-hydroxy benzoyl hydrazone, and its copper (II), zinc (II) and nickel (II) complexes (M.H(3)L) [M(II) = Cu, Zn, Ni], have been synthesized and characterized. The ligand and Zn (II) complex exhibit green and blue fluorescence under UV light and the fluorescent properties of the ligand and Zn (II) complex in solid state and different solutions were investigated. In addition, DNA binding properties of the ligand and its metal complexes have been investigated by electronic absorption spectroscopy, fluorescence spectra, ethidium bromide displacement experiments, iodide quenching experiments, salt effect and viscosity measurements. Results suggest that all the compounds bind to DNA via an intercalation binding mode. Furthermore, the antioxidant activity of the ligand and its metal complexes was determined by superoxide and hydroxyl radical scavenging methods in vitro. The metal complexes were found to possess potent antioxidant activity and be better than the free ligand alone and some standard antioxidants like vitamin C and mannitol.

Two similar Schiff-base receptor based quinoline derivate: Highly selective fluorescent probe for Zn(II).

As is known, Zn2+ plays a vital role in a variety of biological processes but excessive exposure of Zn2+ to human beings can cause toxicity, inducing a series of overt poisoning symptoms and neurodegenerative disorders. Thus, we designed and synthesized two quinoline-derived Schiff-bases HL1 and HL2, and investigated the fluorescence emission responses of these two Schiff-bases to various metal ions. A significant enhancement in fluorescence emission band centered at 450 nm was observed in the ethanolic solution of HL1 with addition of Zn2+, while remarkably lower fluorescence emission enhancement was obtained in the case of HL2 in which one methyl group was introduced to the azomethine carbon. In addition, HL1 showed good selectivity and high sensitivity towards Zn2+ in the existence of other various interfering metal ions, and the reversibility and regeneration of HL1 were also perfect for extending its applications in environmental and biological systems. Therefore, HL1 could be identified as a fluorescent probe for sensing Zn2+ environmentally and biologically.

Study on synthesis and fluorescence property of rhodamine-naphthalene conjugate.

In this study, a novel ligand (HL) consisting of 2-methyl quinoline-4-carboxylic acid, rhodamine and naphthalene moiety, was designed and synthesized, it could be developed a ratiometric fluorescent sensor for selective detection of Al3+ via fluorescence resonance energy transfer (FRET) from naphthalimide moiety to rhodamine moiety. The addition of Al3+ trigger the significant fluorescence enhancement of HL at 550 nm at the expense of the fluorescent emission of HL centered at 524 nm.

Synthesis, characterization and DNA-binding properties of Ln(III) complexes with 6-ethoxy chromone-3-carbaldehyde benzoyl hydrazone.

A novel 6-ethoxy chromone-3-carbaldehyde benzoyl hydrazone (L) and its Ln(III) complexes, [Ln = Sm (1), Eu (2), Gd (3), Tb (4)], have been synthesized and characterized. The fluorescence properties of the Eu(III) and Sm(III) complexes in solid state and Eu(III) complex in different solutions (DMF, DMSO, methanol and acetonitrile) were investigated. At the same time, the DNA-binding properties of the two complexes are investigated using UV-Vis absorption spectroscopy, fluorescence spectroscopy, viscosity measurement. All the experimental evidences indicate that the two complexes can bind to CT-DNA via an intercalation mechanism. Furthermore, antioxidant activity tests in vitro showed that the complexes have significant antioxidative activity against hydroxyl free radicals from the Fenton reaction.

Fluorescence and biological evaluation of the La(III) and Eu(III) complexes with 7-methoxychromone-3-carbaldehyde benzoyl hydrazone Schiff base.

A novel Schiff base ligand (L = 7-methoxychromone-3-carbaldehyde benzoyl hydrazone) and its La(III) and Eu(III) complexes have been successfully prepared. The crystal structure of [LaL(2)(NO(3))(3)].H(2)O was characterized by X-ray crystallography. It crystallizes in monoclinic, space group C2/c with crystallographic data: a = 27.7173(17) A, b = 10.0002(6) A, c = 14.7884(9) A, beta = 102.6870(10) degrees and Z = 4. In the structure, the La(III) ion satisfies 12 coordination and three nitrate coordinate as bidentate ligand. The biological experiments show that the ligand and its two complexes can strongly bind to DNA through intercalation mode, and the three compounds also exhibit good antioxidant activities against OH(*) and O(2) (-*). Moreover, it is found that the Eu(III) complex exhibits characteristic fluorescence of europium ion in different organic solvent.

Crystal structures, antioxidation and DNA binding properties of Yb(III) complexes with Schiff-base ligands derived from 8-hydroxyquinoline-2-carbaldehyde and four aroylhydrazines.

X-ray crystal and other structural analyses indicate that Yb(III) and all four newly synthesized ligands can form a binuclear Yb(III) complex with a 1:1 metal to ligand stoichiometry by octacoordination at the Yb(III) center. Investigations of DNA binding properties show that all the ligands and Yb(III) complexes can bind to Calf thymus DNA through intercalations with the binding constants at the order of magnitude 10(5)-10(7) M(-1), but Yb(III) complexes present stronger affinities to DNA than ligands. All the ligands and Yb(III) complexes may be used as potential anticancer drugs. Investigations of antioxidation properties show that all the ligands and Yb(III) complexes have strong scavenging effects for hydroxyl radicals and superoxide radicals but Yb(III) complexes show stronger scavenging effects for hydroxyl radicals than ligands.

Crystal structures, DNA-binding studies and antioxidant activities of the Ln(III) complexes with 7-methoxychromone- 3-carbaldehyde-isonicotinoyl hydrazone.

The neutral mononuclear Ln(III) complexes (Ln = La, Sm) with 7-methoxychrom-one-3-carbaldehyde-isonicotinoyl hydrazone ligand (L) have been synthesized, characterized and investigated their interactions with calf-thymus DNA. The results show that the binding affinity of the La(III) complex is stronger than that of the Sm(III) complex and that of the ligand (L). Furthermore, the antioxidant activities of the ligand (L) and its Ln(III) complexes (Ln = La, Sm) were studied in detail.

A Schiff-base receptor based chromone derivate: Highly selective fluorescent and colorimetric probe for Al(III).

Upon excitation of the visible light, probes show colorimetric and fluorescent responses to the specific metal ion, which can be easily detected by the naked eye. Owing to the excitation of the visible light at 423 nm, a novel and simple Schiff-base receptor based chromone derivative called 7-methoxychromone-3-carbaldehyde-(indole-3-formyl) hydrazone (MCIH2) had been investigated as a selective and sensitive probe for Al3+ with colorimetric and fluorescent responses. Upon addition of Al3+ to compound MCIH2 solution, compound MCIH2 could respond to Al3+ with a good selective colorimetric signal, which was easily observed from colorless to yellow-green by the naked eye. Furthermore, a remarkable fluorescence emission enhancement with an "OFF-ON" signal by over 700-fold was triggered, but other various metal ions had no such significant effects on the fluorescence emission. In addition, the detection limit of compound MCIH2 for recognizing Al3+ was evaluated to be as low as 1 × 10-7 M level, which was sufficiently low for sensing Al3+ widely distributed in various environmental and biological systems.

Synthesis, characterization and DNA-binding properties of four Zn(II) complexes with bis(pyrrol-2-yl-methyleneamine) ligands.

A novel series of bis(pyrrol-2-yl-methyleneamine) ligands H2L(n) (n = 1-4) were synthesized via condensation of diamines with two equivalents of 2-formyl-pyrrole (2). Their Zn(II) complexes were characterized by elemental analyses, mass spectra and IR spectra. The crystal structures of [ZnL(1)]2 and [ZnL(4)]2 obtained from ethanol solution was determined by X-ray diffraction analysis, each of them possesses a double-stranded helical geometry. In addition, the DNA-binding properties of the compounds have been fully investigated by absorption, fluorescence and viscosity measurements.

Synthesis, characterization, antioxidant activity and DNA-binding studies of two rare earth(III) complexes with naringenin-2-hydroxy benzoyl hydrazone ligand.

Two novel rare earth complexes, Y(III) complex (1) and Eu(III) complex (2), with naringenin-2-hydroxy benzoyl hydrazone ligand were synthesized and characterized. The interaction of the two metal complexes and the free ligand with calf thymus DNA (CT DNA) was investigated by electronic absorption spectroscopy, fluorescence spectroscopy and viscosity measurement. All the experimental evidences indicate that these three compounds can strongly bind to CT DNA via an intercalation mechanism. The intrinsic binding constants of the Y(III) complex (1), Eu(III) complex (2) and the free ligand with CT DNA were 2.1 x 10(4), 8.5 x 10(4) and 1.6 x 10(4) M(-1), respectively. Furthermore, the antioxidant activity of the metal complexes was determined by hydroxyl radical scavenging method in vitro.

A novel chromone and rhodamine derivative as fluorescent probe for the detection of Zn(II) and Al(III) based on two different mechanisms.

In this study, a novel fluorescent probe, 6­hydroxychromone­3­carbaldehyde­(rhodamine B carbonyl) hydrazine (L), for Zn2+ and Al3+ was designed and synthesized. Initially, this probe L exhibited inferior fluorescence emission peak centered at 488 nm in EtOH/HEPES solution (3/1, 10.0 µM HEPES, pH 7.4) when excited at 421 nm. After the addition of Zn2+, this probe L displayed excellent selectivity towards Zn2+ with obvious fluorescence color change from colorless to yellow, which might be attributed to the formation of a 1:1 ligand-metal complex resulting in the inhibition of photo-induced electron transfer phenomenon. Whereas, the prepared Zn2+ complex of L could be used as a ratiometric fluorescent probe to detect Al3+ on the basis of fluorescence resonance energy transfer mechanism. This ligand-metal complex of Zn2+ (LZn) showed high selectivity towards Al3+ with obvious enhancement in fluorescence emission intensity at 580 nm and remarkable decrease in fluorescence emission intensity at 488 nm, and the fluorescence color also changed from yellow to pink. Furthermore, the detection limit of the probe L, LZn towards Zn2+, Al3+ were 1.25 × 10-7 M and 3.179 × 10-6 M, respectively. Additionally, the complexation properties of L towards Zn2+ and LZn towards Al3+ were studied in detail.

A highly selective and sensitive fluorescent chemosensor and its application for rapid on-site detection of Al3.

In this paper, a simple naphthalene-based derivative (HL) has been designed and synthesized as a Al3+-selective fluorescent chemosensor based on the PET mechanism. HL exhibited high selectivity and sensitivity towards Al3+ over other commonly coexisting metal ions in ethanol with a detection limit of 2.72nM. The 1:1 binding stoichiometry of the complex (HL-Al3+) was determined from the Job's plot based on fluorescence titrations and the ESI-MS spectrum data. Moreover, the binding site of HL with Al3+ was assured by the 1H NMR titration experiment. The binding constant (Ka) of the complex (HL-Al3+) was calculated to be 5.06×104M-1 according to the Benesi-Hildebrand equation. In addition, the recognizing process of HL towards Al3+ was chemically reversible by adding Na2EDTA. Importantly, HL could directly and rapidly detect aluminum ion through the filter paper without resorting to additional instrumental analysis.

Synthesis, crystal structure and DNA-binding studies of the Ln(III) complex with 6-hydroxychromone-3-carbaldehyde benzoyl hydrazone.

A novel 6-hydroxy chromone-3-carbaldehyde benzoyl hydrazone ligand (L) and its Ln(III) complexes, [Ln=La(1) and Sm(2)], have been prepared and characterized. The crystal and molecular structures of complexes 1 and 2 were determined by single-crystal X-ray diffraction. Antioxidative activity tests in vitro showed that L and its complexes have significant antioxidative activity against hydroxyl free radicals from the Fenton reaction and also oxygen free radicals, and that the effect of the La(III) complex 1 is stronger than that of mannitol and the other compounds. The compounds were tested against tumor cell lines including HL-60 and A-549. The data shows that the suppression rate of complexes 1 and 2 against the tested tumor cells are superior to the free ligand (L). The interactions of complexes 1 and 2, and L, with calf thymus DNA were investigated by UV-visible (UV-vis), fluorescence, denaturation experiments and viscosity measurements. Experimental results indicated that complexes 1 and 2, and L can bind to DNA via the intercalation mode, and that the binding affinity of complex 1 is higher than that of complex 2 and of free ligand (L). The intrinsic binding constants of complexes 1 and 2, and L were (7.62+/-0.56)x10(6), (3.70+/-0.47)x10(6) and (2.41+/-0.46)x10(6)M(-1), respectively.

Synthesis, characterization and DNA-binding studies of 2-carboxybenzaldehydeisonicotinoylhydrazone and its La(III), Sm(III) and Eu(III) complexes.

2-Carboxybenzaldehydeisonicotinoylhydrazone (HL), and its three lanthanide complexes, LnL(3).4H2O [Ln=La(1), Sm(2), Eu(3)], have been synthesized and characterized on the basis of elemental analyses, molar conductivities, IR spectra and thermal analyses. In addition, the DNA-binding properties of the ligand and its complexes have been investigated by absorption, fluorescence and viscosity measurements. The experimental results indicated that the complexes (2) and (3) can bind to DNA, but the ligand and the complex (1) cannot; the binding affinity of the complex (3) is higher than that of the complex (2) and the intrinsic binding constant Kb of the complex (3) is 7.86x10(4) M-1.

Infrared and DNA-binding on ultraviolet and fluorescence spectra of new copper and zinc complexes with a naringenin Schiff-base ligand.

A naringenin Schiff-base ligand (H(3)L) and its copper(II) and zinc(II) complexes have been synthesized and characterized by elemental analyses, molar conductivities, (1)H NMR, IR spectra, UV spectra and thermal analyses. The DNA-binding properties of the Cu(II) and Zn(II) complexes have been investigated by fluorescence spectroscopy, ultraviolet spectroscopy and by viscosity measurements. The results indicate that complexes and ligand may bind to DNA by intercalation modes, but the binding affinity of the complexes is much higher than that of the ligand.