Fractional dependence of the free energy of activation on the driving force of charge transfer in the quenching of the excited states of substituted phenanthroline homoleptic ruthenium(ii) complexes in aqueous medium.

The photophysical characteristics of some homoleptic ruthenium(ii) phenanthroline derivatives are investigated in aqueous medium. The lifetimes of the excited 3MLCT state of the studied complexes were found to be very sensitive to the type of the substituents on the phenanthroline ligand and were found to increase from about 0.96 µs in case of the parent [Ru(Phen)3]2+ complex to 2.97 µs in case of [Ru(DPPhen)3]2+. The transient absorption spectra of the current set of complexes were studied also in aqueous medium. Quenching of the excited 3MLCT states of the studied complexes by molecular oxygen were studied and quenching rate constants were found to be in the range 1.02-4.83 × 109 M-1 s-1. Values of singlet oxygen quantum yields were found to be in the range 0.01 to 0.25, and the corresponding efficiencies of singlet oxygen thereby produced, f T Δ, were in the range 0.03-0.52. The mechanism by which the excited 3MLCT state is quenched by oxygen is discussed in light of the spin statistical factor rate constants and the competition between charge transfer and non-charge transfer quenching pathways. The partial charge transfer parameters, p CT, were obtained and found to be about 0.88 for all complexes except for complexes with f T Δ values lower than 0.25. The correlation of the activation free energies ΔG ≠ of the exciplexes formation with the driving force for charge transfer, ΔG CET, gives a charge transfer character of the exciplexes of about 35.0%.

Design, synthesis, biomedical investigation, DFT calculation and molecular docking of novel Ru(II)-mixed ligand complexes.

A novel series of bioactive water-soluble mononuclear Ru(II)-mixed ligand complexes of 2,2'-bipyridyl and V-shaped Schiff base ligands were synthesized and structurally characterized. Biomedical activities of Ru(II) complexes have been tested in view of antioxidant activities, interaction with calf thymus DNA (CT-DNA), and anticancer performance. The optimized structure of these complexes has been further supported by density functional theory (DFT) calculations. Further, validation of the interaction studies of some complexes was accomplished by carrying out molecular docking studies with DNA using molecular operating environment (MOE) software are reported.Communicated by Ramaswamy H. Sarma.

Some novel rare earth metal ions complexes: Synthesis, characterization, luminescence and biocidal efficiency.

New lanthanide complexes (1-3) of the general formulae [Ln(L)(NO3)(H2O)] have been synthesized by reaction of Ln(NO3)3 {Ln = La (1), Sm (2) and Yb (3)} with 2,2'-(((1E,1'E)-thiophene-2,5-diylbis(methaneylylidene))bis(azaneylylidene))diphenol (H2L). Based on elemental analysis, spectroscopic studies (UV-Vis., FT-IR, ESI-MS, 1H/13C NMR), molar conductance and thermogravimetric analysis, the Schiff base ligand was suggested to coordinate Ln(III) ions through the azomethine nitrogens, deprotonated hydroxyl groups, and thiophene sulphur atom. The interaction of the synthetic compounds with CT-DNA has been studied by the electronic spectroscopy, fluorometric competition studies with ethidium bromide and DNA viscosity measurements. Furthermore, due to the ligand and its Ln(III) complexes exhibit good DNA binding affinity, it is considered worthwhile to investigate their antioxidant activity. The data have shown that, the complexes are more effective inhibitors towards reactive oxygen species (ROS), such as superoxide anion and hydroxyl radical. The activity of test compounds in ascending order (1) > (2) > (3) > H2L in terms of IC50 value. The anticancer activities of the complexes have also been studied towards human colon carcinoma cancer (HCT-116) and human breast cancer (MCF-7) cell lines.

Synthesis, Spectral Characterization, SEM, Antimicrobial, Antioxidative Activity Evaluation, DNA Binding and DNA Cleavage Investigation of Transition Metal(II) Complexes Derived from a tetradentate Schiff base bearing thiophene moiety.

A novel series of Co(II), Ni(II), Cu(II) and Zn(II) mononuclear complexes have been synthesized involving a potentially tetradentate Schiff base ligand, which was obtained by condensation of 2-aminophenol with 2,5-thiophene-dicarboxaldehyde. The complexes were synthesized via reflux reaction of methanolic solution of the appropriate Schiff base ligand with one equivalent of corresponding metal acetate salt. Based on different techniques including micro analysis, FT-IR, NMR, UV-Vis, ESR, ESI-mass and conductivity measurements, four-coordinated geometry was assigned for all complexes. Spectroscopic data have shown that, the reported Schiff base coordinated to metal ions as a dibasic tetradentate ligand through the phenolic oxygen and the azomethine nitrogen. The antimicrobial activities of the parent ligand and its complexes were investigated by using the agar disk diffusion method. Antioxidation properties of the novel complexes were investigated and it was found that all the complexes have good radical scavenging properties. The binding of complexes to calf thymus DNA (CT-DNA) was investigated by absorption, emission and viscosity measurements. Binding studies have shown that all the complexes interacted with CT-DNA via intercalation mode and the binding affinity varies with relative order as Cu(II) complex > Co(II) complex > Zn(II) complex > Ni(II) complex. Furthermore, DNA cleavage properties of the metal complexes were also investigated. The results suggested the possible utilization of novel complexes for pharmaceutical applications.

A Novel Fluorimetric Bulk Optode Membrane Based on NOS Tridentate Schiff Base for Selective Optical Sensing of Al3+ Ions.

A novel fluorimetric optode has been developed for the highly selective and sensitive for the determination of ultra trace amounts of Al3+ ions. The proposed fluorescent optode is based on the incorporation of a simple and effective fluorescent sensor tridentate NOS Schiff base N-(2-hydroxynaphthylidene)-2-aminothiophenol (H2L) in a plasticized PVC containing KTpClPB as a lipophilic anionic additive. H2L was synthesized by a facile one-step Schiff base reaction. The plasticized PVC-membrane displays a calibration response for Al3+ ions over a wide concentration range from 1.0 × 10-9 to 4.4 × 10-3 mol/L. The fluorescence signal of the optode membrane can be easily recovered by immersion in 0.01 M EDTA. In addition to high stability and reproducibility, the sensor shows a unique selectivity towards Al3+ ion with respect to common co-existing cations, particularly Ga3+and In3+. The proposed optode was applied successfully for determination of Al3+ in some real samples, including bottled drinking waters, bottled mineral waters and soft drinks.

A Novel Fluorescent Optode for Recognition of Zn(2+) ion Based on N,N(')-bis-(1-Hydroxypheylimine)2,5-Thiophenedicarobxaldehyde (HPTD) Schiff Base.

A novel fluorescent sensing film has been proposed for sensitive determination of Zn(2+) ion in EtOH-HEPES buffer solution (20 mM HEPES, 50:50, v/v, pH 7.0). The novel sensor based on incorporating a novel qaudridentate Schiff base N,N(')-bis-(1-hydroxypheylimine)2,5-thiophenedicarobxaldehyde (HPTD) as ionophore in the plasticized PVC membrane containing bis(2-ethylhexyl)sebecate (DOS) as plasticizer. The novel optode membrane works on the basis of a cation-exchange mechanism and shows a significant fluorescent emission enhancement on exposure to HEPES buffer solution of pH 7.0 containing Zn(2+) ion. Under optimal conditions, the proposed sensing film displays a linear range of 1.0 × 10(-12) to 8.6 × 10(-4) M with a limit of detection 5.3 × 10(-13) M. The response characteristics of the sensor including reversibility, reproducibility, response time and lifetime are discussed in detail. The optode membrane has been applied to determine Zn(2+) in various real water samples.

Spectral, electrochemical, thermal, DNA binding ability, antioxidant and antibacterial studies of novel Ru(III) Schiff base complexes.

Four new air stable low spin Ru(III) complexes of the type [Ru(L(1-4))(H2O)2]Cl have been synthesized, where L=dianion of the tetradentate Schiff base ligands namely N,N'bis(salicylaldehyde)4,5-dimethy-l,2-phenylendiammine (L(1)H2), N,N'bis(salicylaldehyde)4,5-dichloro 1,2-phenylendiammine (L(2)H2), N,N'bis(o-vanillin)4,5-dimethy-1,2-phenylendiammine (L(3)H2) and N,N'bis(o-vanillin)4,5-dichloro-1,2-phenylendiammine (L(4)H2). The complexes have been fully characterized by elemental analysis, infrared spectroscopy, electronic spectroscopy, magnetic susceptibility and electron spin resonance spectroscopy. Elemental analyses and spectroscopic data have been showed that, the stoichiometries of complexes were 1:1 with an octahedral geometry for all the complexes. Thermal analysis measurements indicated that the complexes have good thermal stability. The redox behavior of the complexes has been investigated by the cyclic voltammetric technique. The interaction of these complexes with calf thymus DNA (CT-DNA) was explored by different techniques which revealed that the complexes could bind to CT-DNA through an intercalative mode. Furthermore, the antioxidant activity of the Ru(III) complexes against superoxide and hydroxyl radicals was evaluated by using spectrophotometer methods in vitro. The experiments on antioxidant activity show that the complexes were found to possess potent antioxidant activity. Additionally, as a potential application the antibacterial activity of the complexes was assessed by testing their effect on the growth of various strains of bacteria.

Synthesis, spectroscopic, photoluminescence properties and biological evaluation of novel Zn(II) and Al(III) complexes of NOON tetradentate Schiff bases.

Novel mononuclear Zn(II) and Al(III) complexes were synthesized from the reactions of Zn(OAc)(2).2H(2)O and anhydrous AlCl(3) with neutral N2O2 donor tetradentate Schiff bases; N,N'bis(salicylaldehyde)4,5-dimethyl-1,2-phenylenediamine (H(2)L(1)) and N,N'bis(salicylaldehyde)4,5-dichloro-1,2-phenylenediamine (H(2)L(2)). The new complexes were fully characterized by using micro analyses (CHN), FT-IR, (1)H NMR, UV-Vis spectra and thermal analysis. The analytical data have been showed that, the stoichiometry of the complexes is 1:1. Spectroscopic data suggested tetrahedral and square pyramidal geometries for Zn(II) and Al(III) complexes, respectively. The synthesized Zn(II), and Al(III) complexes exhibited intense fluorescence emission in the visible region upon UV-excitation in methylene chloride solution at ambient temperature. This high fluorescence emission was assigned to the strong coordination of the ligands to the small and the highly charged Zn(II) and Al(III) ions. Such strong coordination seems to extend the π-conjugation of the complexes. Thermal analysis measurements indicated that the complexes have good thermal stability. As a potential application the biological activity (e.g., antimicrobial action) of the prepared ligands and complexes was assessed by in-vitro testing of their effect on the growth of various strains of bacteria and fungi.

Determination of melamine in different milk batches using a novel chemosensor based on the luminescence quenching of Ru(II) carbonyl complex.

A novel, simple, sensitive and precise spectrofluorimetric method was developed for measuring the melamine concentration in different milk batch samples. The method was based upon measuring the quenching of the luminescence intensity of the produced yellow colored ruthenium((II)) carbonyl complex of the general formula [Ru(CO)(2)(L)] (where L=anion of tetradentate Schiff base). The Ru((II)) complex exhibited characteristic luminescence band in the visible region. The remarkable quenching of the luminescence intensity of [Ru(CO)(2)(L)] complex by various concentrations of melamine was successfully used as a chemosensor for the assessment of melamine in different milk samples at λ(ex)=400 nm and pH 7.4 in DMSO with a linear dynamic range 1.0 × 10(-6) to 3.0 × 10(-9) mol L(-1) and lower detection limit (LOD) and quantification detection limit (QOD) of 3.3 × 10(-10) and 1.0 × 10(-9) mol L(-1), respectively.