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

A series of oxovanadium(IV) symmetrical tetradentate Schiff base complexes have been isolated from the reaction of VOSO₄ with Schiff bases obtained from the condensation of 2-hydroxybenzophenone or 2-hydroxy-5-chlorosalicylaldehyde with various aliphatic diamines. The compounds were characterized by elemental analyses, ¹H NMR, infrared, electron paramagnetic resonance, electronic spectral, cyclic voltammetry and room temperature magnetic susceptibility measurements. The solution EPR spectra are consistent with square pyramidal complexes with C_4v symmetry. The IR spectra confirmed that the complexes are all monomeric except for [VO(Clsal)₂tn] which polymerizes via OV?VO linkages. The electronic spectra indicate a square pyramidal geometry in both non-coordinating and coordinating solvents except for [VO(bp₂-pn)] which appears to be octahedral in DMSO. The room temperature magnetic moments of 1.7-1.8 B.M. are normal for V(IV) d¹ configuration. Evidence for electrochemical pseudo-reversibility is presented for four of the complexes. In vitro studies revealed that two of the compounds, [VO(bp₂-en] and [VO(bp₂-tn)MeOH], significantly increased glucose uptake when compared to the basal glucose uptake in transformed and sensitized C1C12 cells, but not at the same level as insulin.     

Synthesis of an amphiphilic ruthenium complex with swallow-tail bipyridyl ligand and its application in nc-DSC

An amphiphilic swallow-tail bipyridyl ligand, 4,4′-bis(dihexylmethyl)-2,2′-bipyridine, and its heteroleptic ruthenium (II) complex were synthesized starting from dichloro-(p-cymene)ruthenium (II) dimer. The complex was characterized by UV/Vis and FTIR spectrophotometers, NMR spectroscopy and cyclic voltammetry. The performance of this complex as charge transfer photosensitizer in nc-TiO₂ based dye sensitized solar cells was studied under standard AM 1.5 sunlight and by using an electrolyte consisting of 0.6 M N-methyl-N-butyl imidazolium iodide (BMII), 0.1 M LiI, 0.05 M I₂, 0.5 M 4-tert-butyl pyridine (TBP) in acetonitrile. The complex, CS9 in DMF, gave a photocurrent density of 12.62 mA/cm², 630 mV open circuit potential and 0.62 fill factor yielding 5.68% efficiency.     

Photosynthetic energy storage efficiency,oxygen evolution and chloroplast movement

When there is a saturating supply of dissolved carbon available, photosynthetic energy storage efficiency (ES) varies linearly with light fluence rate (I) for both Vallisneria americana and Pisum sativum leaves. The frequently reported hyperbolic relationship between ES and I occurs only when low levels of dissolved carbon are present in the medium. The linear relationship has its origin in intracellular events and implies that two heat-producing processes limit the value of ES. The rate of one process varies as I and the other varies as I². The rates of both processes were changed after a 2 hour exposure to 400 μmol photons m⁻² s⁻¹ of red light, speeding up the process that depends linearly on I and slowing the other. Illumination for 1 hour with 100 μmol photons m⁻² s⁻¹ of blue (but not red) light moves many chloroplasts from the periclinal to the anticlinal cell walls [Inoue and Shibata (1973) Planta 114: 341–358]. Blue light exposure of V. americana leaf sections (a) reduced the rate of oxygen evolution under light-limiting conditions by about 22%; (b) increased the value of ES by an amount dependent on the light fluence rate; and (c) decreased the slope of (ES v I). The slope change indicated that light absorption had fallen by 26% after blue light exposure. The rate of oxygen evolution (V) was measured under light-limiting conditions with leaf sections in which the chloroplasts had been immobilised after blue or red light exposure. With both red and blue-exposed leaf sections, V fell by about 50% after exposure to 1 hour of 1250 μmol photons m⁻² s⁻¹ of white light. Thus accumulation of chloroplasts on anticlinal walls did not protect the leaf from photoinactivation by a high light fluence rate. This revised version was published online in August 2006 with corrections to the Cover Date.     

Cytochrome c decelerates channel kinetics of negatively charged gramicidin due to electrostatic interaction

The effect of cytochrome c on the kinetic properties of ion channels formed by O-pyromellitylgramicidin (OPg), the negatively charged analogue of gramicidin A (gA), in bilayer lipid membranes was studied by the method of sensitized photoinactivation. The addition of cytochrome c to both sides of the membrane caused substantial deceleration of the photoinactivation kinetics of OPg channels which expose three negative charges to the aqueous phase at both sides of the membrane. By contrast, the gA photoinactivation kinetics was unaltered by the addition of cytochrome c. Based on the sensitivity of the observed effect to the ionic strength of the bathing solution, the cytochrome c-induced deceleration of the OPg photoinactivation kinetics reflecting the increase in the OPg channel lifetime was ascribed to electrostatic interaction of positive charges of cytochrome c with negative charges of OPg that resulted in channel clustering. Formation of clusters of OPg channels was previously inferred to explain the polylysine effect on the OPg channel kinetics. The decelerating effect of cytochrome c on OPg channels was observed only at a high number of OPg channels in the membrane, thus suggesting that the interaction between cytochrome c and the charged transmembrane protein requires sufficiently high negative charge density on the surface of the membrane.     

Band Edge Modulated Polymer Layer to Decrease Back Electron Transfer and Increase Efficiency in Sensitized Solar Cells

Recombination of charges residing in the TiO₂ and redox electrolyte is one of the factors affecting the efficiency of dye sensitized solar cells (DSSCs). To circumvent this recombination, inorganic oxide barrier layers and organic silanes have been coated on TiO₂/dyes. Due to the insulating nature of these layers, the efficiency increase is not very impressive. Conducting polymers with different band edges are used to suppress the charge recombination. Amongst the four polymers that are used as barrier layers, a polymer with a highest occupied molecular orbital energy at ?5.8 eV and lowest unoccupied molecular orbital at ?3.1 eV is found to increase the electron life time at TiO₂ and decrease the charge recombination. The electron life time is found to be 88 ms. In addition to the long electron life time, the recombination resistance of this polymer is also high (91 Ω). This resistance is 18% higher than that measured for DSSCs without polymer barrier layer. These factors impact the efficiency of DSSCs. DSSCs fabricated with this polymer as barrier layer exhibit an efficiency of 9.2%, which is 22% higher than that of DSSCs without polymer barrier layer.     

Determination of fluoxetine in pharmaceutical and biological samples based on the silver nanoparticle enhanced fluorescence of fluoxetine–terbium complex

In this study, a simple and sensitive spectrofluorimetric method is presented for the determination of fluoxetine based on the enhancing effect of silver nanoparticles (AgNPs) on the terbium–fluoxetine fluorescence emission. The AgNPs were prepared by a simple reduction method and characterized by UV–Vis spectroscopy and transmission electron microscopy. It was indicated that these AgNPs have a remarkable amplifying effect on the terbium‐sensitized fluorescence of fluoxetine. The effects of various parameters such as AgNP and Tb³⁺ concentration and the pH of the media were investigated. Under obtained optimal conditions, the fluorescence intensity of the terbium–fluoxetine–AgNP system was enhanced linearly by increasing the concentration of fluoxetine in the range of 0.008 to 19 mg/L. The limit of detection (b + 3s) was 8.3 × 10^‐4 mg/L. The interference effects of common species found in real samples were also studied. The method had good linearity, recovery, reproducibility and sensitivity, and was satisfactorily applied for the determination of fluoxetine in tablet formulations, human urine and plasma samples. Copyright © 2016 John Wiley & Sons, Ltd.     

Effects of bicarbonate and oxygen concentration on photoinhibition of thylakoid membranes

The effects of bicarbonate and oxygen on photoinhibition of thylakoid membranes were investigated by varying their concentrations independently of each other. A pretreatment of the thylakoid suspension which lowered the bicarbonate concentration of the medium without affecting its oxygen content, increased the degree of photoinhibition upon illumination. This showed that the normal bicarbonate content of a thylakoid suspension, originating from dissolved carbondioxide from the air, protects against photoinhibition. The resistance against photoinhibition was further increased by addition of extra NaHCO₃ up to about 5 mM. The normal oxygen content can be decreased profoundly without affecting the degree of photoinhibition; in contrast, even small changes from the normal bicarbonate content affected photoinhibition.At oxygen concentrations approximately below 25 M, added NaHCO₃ not only did not protect, but caused a more severe PS 2 inactivation. This was due to a blockage by added NaHCO₃ of the recovery from a reversible photoinhibited state.Furthermore, it is shown that if the bicarbonate ions bound to high-affinity sites in PS 2 were replaced by formate ions, the thylakoid membranes became less susceptible to photoinhibition under normal oxygen tension.Abbreviations chl chlorophyll - HEPES (N-[2-Hydroxyethyl]piperazine-N-[2-ethanesulfonic acid]) - PpBQ phenyl-p-benzoquinone - PS 2 Photosystem 2 - Q_A and Q_B primary and secondary quinone acceptors of Photosystem 2     

Cryoconcentration of flavonoid extract for enhanced biophotovoltaics and pH sensitive thin films

Flavonoids are important value added products for dye sensitized solar cells biosensors, functional foods, medicinal supplements, nanomaterial synthesis, and other applications. Brassica oleracea contains high levels of anthocyanins in leaf sap vacuoles, and there are many viable extraction techniques that vary in terms of simplicity, environmental impact, cost, and extract photochemical/electrochemical properties. The efficiency of value added biotechnologies from flavonoid is a function of anthocyanin activity/concentration and molecule stability (i.e., ability to retain molecular resonance under a wide range of conditions). In this paper, we show that block cryoconcentration and partial thawing of anthocyanin from B. oleracea is a green, facile, and highly efficient technique that does not require any special equipment or protocols for producing enhanced value added products. Cryoconcentration increased anthocyanin activity and total phenol content approximately 10 times compared with common extraction techniques. Cryoconcentrated extract had enhanced electrochemical properties (higher oxidation potential), improved chroma, and higher UV absorbance than extract produced with other methods for a pH range of 2–12, with minimal effect on the diffusion coefficient of the extract. As a proof of concept for energy harvesting and sensor applications, dye sensitized solar cells and pH‐sensitive thin films were prepared and tested. These devices were comparable with other recently published biotechnologies in terms of efficacy, but did not require expensive/environmentally detrimental extraction or concentration methods. This low cost, biorenewable, and simple method can be used for development of a variety of value added products. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 34:206–217, 2018