The cover picture shows the 5‐metallacrown‐5 complex, which is obtained by the self‐assembly of five copper(II) ions, five 2‐picolinehydroximate ligands (picha) and the central mercury(II) ion. The (15‐metallacrown‐5)HgII and ‐PbII complexes have been obtained in the crystalline form as pyridine adducts [HgCu5(picha)5(py)7](NO3)2 and [PbCu5(picha)5(py)6](NO3)2 (axial pyridine molecules are not shown). Unlike the analogous lanthanide(III) derivatives, which are essentially flat, the presented 15‐metallacrown‐5 system is dome‐shaped, although not as convex as the shell of the turtle Gubi (shown in the background). Gubi is the favorite pet of the daughter of one of the authors. Details are discussed in the article by J. Lisowski et al. on p. 3015 ff.
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.
The tetradentate Schiff base ligand (SB), N,N′-bis-(2-mercaptophenylimine)-2,5thiophenedicarboxaldehyde was prepared via condensation of 2,5-thiophenedicarboxaldehyde with 2-aminothiophenol in a 1:2 molar ratio by conventional method. Additionally, its Co(II), Ni(II), Cu(II) and Zn(II) complexes have been synthesized and fully characterized by elemental analysis, FT-IR, 1 H NMR, 13 C NMR, UV-Vis, ESR, ESI-mass, conductivity and magnetic susceptibility measurements. Spectral studies suggested that, the Schiff base coordinate metal ions through the azomethine N-and deprotonated thiol S-atoms. Based on UV-Vis absorption and magnetic susceptibility data, tetrahedral geometry was assigned for both Co(II) and Zn(II) complexes, whereas on the other hand, square planar geometry for both Ni(II) and Cu(II) complexes. The Schiff base and its metal complexes were screened for their in vitro antimicrobial activity by minimum inhibitory concentration (MIC) method. Free radical scavenging activity of the novel compounds was determined by elimination of 2,2-diphenyl-1-picrylhydrazyl (DPPH) radicals. In addition, the interactions of the free ligand and its complexes with calf thymus DNA (CT-DNA) were explored using absorption, emission and viscosity measurements techniques.
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.
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