Adeola A. Nejo

Synthesis, characterization, antibacterial, and thermal studies of unsymmetrical Schiff-base complexes of cobalt(II)

Cobalt(II) complexes of a new series of unsymmetrical Schiff bases have been synthesized and characterized by their elemental analyses, melting points, magnetic susceptibility, thermogravimetric analysis, differential scanning calorimetry, infrared (IR), and electronic spectral measurements. The purity of the ligands and the metal complexes are confirmed by microanalysis, while the unsymmetrical nature of the ligands was further corroborated by 1H-NMR. Comparison of the IR spectra of the Schiff bases and their metal complexes confirm that the Schiff bases are tetradentate and coordinated via N2O2 chromophore. The magnetic moments and electronic spectral data support square-planar geometry for the cobalt(II) complexes. The complexes were thermally stable to 372.3°C and their thermal decomposition was generally via the partial loss of the organic moiety. The Schiff bases and their complexes were screened for in vitro antibacterial activities against 10 human pathogenic bacteria and their minimum inhibitory concentrations were determined. Both the free ligands and cobalt(II) complexes exhibit antibacterial activities against some strains of the microorganisms, which in a number of cases were comparable with, or higher than, that of chloramphenicol.

Synthesis, characterization, and insulin-enhancing studies of unsymmetrical tetradentate Schiff-base complexes of oxovanadium(IV)

A series of unsymmetrical tetradentate Schiff bases were synthesized by interaction of 2-hydroxy-1-naphthaldehyde, phenylenediamine and salicylaldehyde, or substituted salicylaldehyde in an ethanolic medium. The oxovanadium(IV) complexes and the ligands were synthesized and characterized by elemental analyses, 1H NMR, infrared, electron paramagnetic resonance, electronic spectra, cyclic voltammetry, and room temperature magnetic susceptibility measurements. The elemental analyses for both the ligands and the metal complexes confirmed purity of the compounds as formulated. Electron paramagnetic resonance spectra of the complexes were measured as powder and in toluene/dichloromethane (9 : 1, v/v) solution at room and liquid N2 temperatures. The g values, g o = 1.971, g ⊥ = 1.978, and g = 1.950, are the same for all the complexes examined. The vanadium nuclear hyperfine splitting, A o = 101–99, A ⊥ = 65–64, A ∥ = 179–177, vary slightly with substituents on the salicylaldehyde. Infrared spectra reveal strong V=O stretching bands in the range 970–988 cm−1, typical of monomeric five-coordinate complexes. The room temperature magnetic moments of 1.6–1.8 BM for the complexes confirmed that the complexes are V(IV) complexes, with d1 configuration. Only one quasi-reversible wave is observed for each compound and they all showed redox couples with peak-to-peak separation values (ΔE p) ranging from 78 to 83 mV, indicating a single step one electron transfer process. Insulin-mimetic tests on C2C12 muscle cells using Biovision glucose assay showed that all the complexes significantly stimulated cell glucose utilization with negligible cytotoxicity at 0.05 µg µL−1.

Heterocyclic dithiocarbamates: precursors for shape controlled growth of CdS nanoparticles

We report the synthesis of hexadecylamine (HDA) and tri-n-octylphosphine oxide (TOPO) capped CdS nanoparticles using cadmium piperidine dithiocarbamate (DTC) and cadmium tetrahydroquinoline dithiocarbamate complexes as single source precursors. These complexes are easy to prepare, air stable for long periods and pyrolyze to give high quality nanoparticles. The nanoparticles obtained showed quantum confinement with near band edge luminescence. The reaction conditions such as the amount of capping group and reaction temperature were varied to study their influence on the properties and morphology of the nanoparticles. Elongated CdS particles in the form of rods, bipods and tripods were obtained for the HDA capped CdS whereas spherical particles were observed when TOPO was used as the capping material. The X-ray diffraction studies revealed the hexagonal phase to be dominant. Details on the particle crystallinity, size and size distribution were investigated by transmission electron microscopy (TEM) and high resolution TEM.

Spectral, magnetic, biological, and thermal studies of metal(II) complexes of some unsymmetrical Schiff bases

New nickel(II) and copper(II) complexes with unsymmetrical Schiff bases derived from aromatic 2-hydroxy aldehydes were synthesized and characterized by elemental analyses, melting points, 1H-NMR, magnetic susceptibility, thermogravimetric analysis, differential scanning calorimetry (DSC), infrared (IR), and electronic spectral measurements. Comparison of IR spectra of the Schiff bases and their metal complexes indicated that the Schiff bases are tetradentate, coordinated via the two azomethine nitrogens and the two phenolic oxygens. Magnetic moments and electronic spectral data confirm square-planar geometry for the complexes. Thermal studies reveal a general decomposition pattern, whereby the complexes decomposed partially in a single step due to loss of part of the organic moiety. A single endothermic profile, corresponding to melting point, was observed from the DSC of all complexes, except those whose ligand contained the nitro group, which decomposed exothermally without melting. The Schiff bases and their complexes were screened in vitro against 10 human pathogenic bacteria. The metal(II) complexes exhibited higher antibacterial activity than their corresponding Schiff bases.

An in vitro assessment of the interaction of cadmium selenide quantum dots with DNA, iron, and blood platelets

Cadmium selenide (CdSe) quantum dots have gained increased attention for their potential use in biomedical applications. This has raised interest in assessing their toxicity. In this study, water‐soluble, cysteine‐capped CdSe nanocrystals with an average size of 15 nm were prepared through a one‐pot solution‐based method. The CdSe nanoparticles were synthesized in batches in which the concentration of the capping agent was varied with the aim of stabilizing the quantum dot core. The effects of the CdSe quantum dots on DNA stability, aggregation of blood platelets, and reducing activity of iron were evaluated in vitro . DNA damage was observed at a concentration of 200 μg/mL of CdSe quantum dots. Furthermore, the CdSe nanocrystals exhibited high reducing power and chelating activity, suggesting that they may impair the function of haemoglobin by interacting with iron. In addition, the CdSe quantum dots promoted aggregation of blood platelets in a dose dependent manner.

Synthesis, Structural, and Insulin-Enhancing Studies of Oxovanadium(IV) Complexes

Oxovanadium(iv) complexes with Schiff bases derived from substituted salicylaldehyde and diamine have been prepared and characterized. 1H NMR and IR spectral data revealed that the symmetrical Schiff base was isolated, and elemental analysis confirmed the purity of all the compounds as formulated. The room-temperature magnetic moments of 1.6–1.8 Bohr magneton for the complexes confirmed that the complexes are VIV complexes, with d1 configuration. Cyclic voltammetry revealed only one quasi-reversible wave for each complex and they all showed redox couples with peak-to-peak separation values (ΔEp) ranging from 76 to 84 mV, indicating a single-step one-electron transfer process. An oral administration of these complexes supplied at a dose of 0.2 mmol kg–1 to streptozotocin-induced diabetic rats elicited a progressive reduction in plasma glucose over 6-h periods. Two of the complexes produced significant and consistent reduction in fasting blood glucose levels over a 6-h monitoring period.