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In the current study, we synthesized new vanadyl complexes of the N,N′-dipyridoxyl(1,2-propanediamine) Schiff bases and characterized them by experimental and theoretical methods. Also, the antibacterial (against strains of S. aureus, P.aeruginosa and E. coli) and cytotoxicity activities of three V(IV) complexes including VO-EN, VO-13 and VO-12 of the pyridoxal SBs were evaluated against human prostate tumor cells (PC3 cell line), where the VO-EN, VO-13 and VO-12 species are V(IV) complexes of the N,N′-dipyridoxyl(ethylenediamine), N,N′-dipyridoxyl(1,3-propanediamine) and N,N′-dipyridoxyl(1,2-propanediamine) Schiff bases, respectively. Deprotonated form of the N,N′-dipyridoxyl(1,2-propanediamine) Schiff base acts as a tetradentate N2O2 ligand, which coordinates to the V(IV) via two phenolate oxygens and two azomethine nitrogens. In the square-pyramidal geometry of the synthesized complex (VO-12), an oxo ligand occupies the apical position. The analyzed results for the VO-12 complex were in agreement with the experimental tests, confirming the suitability of its optimized geometry. The synthesized VO-12 complex displays significant and reusable catalytic activities in synthesis of the tetrahydrobenzo[b]pyrans, where the V4+ central ion is the active site of the catalyst. All investigated SB complexes were active against P.aeruginosa, while VO-13, VO-12 and VO-EN complexes revealed no activity against E. coli and S. aureus, respectively. All complexes showed considerable cytotoxic against PC3 cells. Our results suggested that these complexes decreased the cell viability after 48 h and the VO-12 complex showed the highest cytotoxicity. These observations suggested that the VO-EN, VO-13 and VO-12 species can be cytotoxic materials for pharmaceutical applications. In addition, in a dose-dependent manner, these compounds can be consider as potent antimicrobial agents.

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The dependence of electrical conduction on current frequency has been studied in thin layers of pure metals at temperatures between 4.2°K and 297°K. The experimental data are given for frequencies up to 2 × 10 6 Hz. The thin layers were made by deposition from vapour on to cover glass substrates in a vacuum of 10 −6 mm of Hg. As shown by the experimental data, the decrease in electrical resistance with the increase of the frequency is more pronounced in layers having large dc resistance. In layers with negative temperature coefficients of resistance, this decrease is more rapid at low temperatures. The relation between the relative change in electrical conductance and the frequency drawn on a double logarithmic scale is a straight line with a slope equal to 2. On the assumption of a granular structure of the layers, an interpretation is suggested for these properties using an equivalent electric circuit consisting of an intergranular resistance, a bulk resistance of the metallic grains, and an intergranular capacitance which depends on the gaps between the grains. In some very thin layers the ac resistance diminishes continuously with the increasing frequency tending towards the value zero. The origin of this anomalous effect can be ascribed to stray capacitances. The estimation of the ratio between bulk and intergranular resistances discussed from the viewpoint of this theoretical circuit is compared with data from magnetoresistance measurements on ferromagnetic layers.

A resistance method is given for the determination of the thickness of thin granular metal films based on the use of impedance measurements at frequencies in the order of magnitude of 1 Mc/sec. At these frequencies the intergranular gap resistance can be seen as short circuited by the inter-granular capacitance, so that the measured resistance is that of the metal grains. As shown the resistivity of the individual grains is in general several times greater than the bulk resistivity of the metal. This difference depends strongly on the vacuum conditions and the rates of evaporation.