Cellular uptake and remarkable photocytotoxicity of pyrenylter pyridine oxovanadium(IV) complexes of dipyridophenazine bases

Pyrenylterpyridine (pytpy) oxovanadium(IV) complexes VO(pytpy)(L)]Cl-2 (1-6) of the dipyridophenazine bases (L), viz., dipyrido-6,7,8,9-tetrahydrophenazine (dpqC in 1), dipyrido3,2-a:2',3'-c]phenazine-2-carboxylic acid (dppzc in 2), dipyrido3,2-a:2',3'-c]phenazine-11-sulfonic acid (dppzs in 3), 7-aminodipyrido3,2-a:2',3'-c]phenazine (dppza in 4), benzo-i]dipyrido3,2-a:2',3'-c]phenazine (dppn in 5) and dipyrido3,2-a:2',3'-c]phenazine (dppz in 6) were prepared, characterized and their DNA binding, photocleavage activity and photocytotoxicity studied. The complexes which showed a d-d band near 750 nm in DMF are efficient binders to calf thymus DNA (K-b: 3.2 x 10(5)-2.9 x 10(6) M-1). The complexes showed significant pUC19 DNA cleavage in near-IR light of 785 nm forming center dot OH radicals and photocytotoxicity in HeLa cells in visible light with the benzo-i] dipyrido3,2-a:2',3'-c]phenazine complex 5 showing a remarkably low IC50 value of 0.036 mu M. Flow-cytometric analysis shows a high sub-G1 phase cell cycle arrest in HeLa cells by the complexes on photo-irradiation. The photocytotoxicity correlates well with the hydrophobicity, photosensitizing ability and DNA binding propensity of the complexes. (C) 2012 Elsevier B.V. All rights reserved.

Euglena sp as a suitable source of lipids for potential use as biofuel and sustainable wastewater treatment

Prolific algal growth in sewage ponds with high organic loads in the tropical regions can provide cost-effective and efficient wastewater treatment and biofuel production. This work examines the ability of Euglena sp. growing in wastewater ponds for biofuel production and treatment of wastewater. The algae were isolated from the sewage treatment plants and were tested for their nutrient removal capability. Compared to other algae, Euglena sp. showed faster growth rates with high biomass density at elevated concentrations of ammonium nitrogen (NH4-N) and organic carbon (C). Profuse growth of these species was observed in untreated wastewaters with a mean specific growth rate (mu) of 0.28 day(-1) and biomass productivities of 132 mg L-1 day(-1). The algae cultured within a short period of 8 days resulted in the 98 % removal of NH4-N, 93 % of total nitrogen 85 % of ortho-phosphate, 66 % of total phosphate and 92 % total organic carbon. Euglenoids achieved a maximum lipid content of 24.6 % (w/w) with a biomass density of 1.24 g L-1 (dry wt.). Fourier transform infrared spectra showed clear transitions in biochemical compositions with increased lipid/protein ratio at the end of the culture. Gas chromatography and mass spectrometry indicated the presence of high contents of palmitic, linolenic and linoleic acids (46, 23 and 22 %, respectively), adding to the biodiesel quality. Good lipid content (comprised quality fatty acids), efficient nutrient uptake and profuse biomass productivity make the Euglena sp. as a viable source for biofuel production in wastewaters.

Dinuclear zinc bis(thiosemicarbazone) complexes: Synthesis, in vitro anticancer activity, cellular uptake and DNA interaction study

Four dinucleating bis(thiosemicarbazone) ligands and their zinc complexes have been synthesized and characterized by multinuclear NMR (H-1 and C-13), IR, UV-Vis, ESI-MS and fluorescence spectroscopic techniques. Their purity was assessed by elemental analysis. Cytotoxicity was tested against five human cancer cell lines using the sulphorhodamine B (SRB) assay, where one of the complexes, 1,3-bis{biacetyl-2'-(4 `'-N-pyrrolidinylthiosemicarbazone)-3'-(4 `'-N-pyrrolidinylthiosemicarbazone) zinc(II)} propane (6), was found to be quite cytotoxic against MCF-7 (breast cancer) and HepG2 (hepatoma cancer) cell lines, with a potency similar to that of the well known anticancer drug adriamycin. It is evident from the cellular uptake studies that the uptake is same for the active complex 6 and the inactive complex 8 (1,6-bis{biacetyl- 2'-(4 `'-N-pyrrolidinylthiosemicarbazone)-3'-(4 `'-N-pyrrolidinylthiosemicarbazone) zinc(II)} hexane) in MCF-7 and HepG2 cell lines. In vitro DNA binding and cleavage studies revealed that all complexes bind with DNA through electrostatic interaction, and cause no significant cleavage of DNA. (C) 2'13 Elsevier B. V. All rights reserved.

Gas Phase Oxygen Quenching Studies of Ketone Tracers for Laser-Induced Fluorescence Applications in Nitrogen Bath Gas

In this paper we report the quantitative oxygen quenching effect on laser-induced fluorescence of acetone, methyl ethyl ketone, and 3-pentanone at low pressures (approximate to 700torr) with oxygen partial pressures up to 450torr. Nitrogen was used as a bath gas in which these molecular tracers were added in different quantities according to their vapor pressure at room temperature. These tracers were excited by using a frequency-quadrupled, Q-switched, Nd:YAG laser (266nm). Stern-Volmer plots were found to be linear for all the tracers, suggesting that quenching is collisional in nature. Stern-Volmer coefficients (k(sv)) and quenching rate constants (k(q)) were calculated from Stern-Volmer plots. The effects of oxygen on the laser-induced fluorescence of acetone, methyl ethyl ketone, and 3-pentanone were compared with each other. Further, the Smoluchowski theory was used to calculate the quenching parameters and compared with the experimental results.

Supercapacitors based on nitrogen-doped reduced graphene oxide and borocarbonitrides

Nitrogen-doped reduced giaphene oxide (RGO) samples with different nitrogen content, prepared by two different methods, as well as nitrogen-doped few-layer graphene have been investigated as supercapacitor electrodes. Two electrode measurements have been carried out both in aqueous (6 M KOH) and in ionic liquid media. Nitrogen-doped reduced graphene oxides exhibit satisfactory specific capacitance, the values reaching 126 F/g at a scan rate of 10 mV/s in aqueous medium. Besides providing supercapacitor characteristics, the study has shown the nitrogen content and surface area to be important factors. High surface-area borocarbonitrides, BxCyNz, prepared by the urea route appear to be excellent supercapacitor electrode materials. Thus, BC4.5N exhibits a specific capacitance of 169 F/g at a scan rate of 10 mV/s in aqueous medium. In an ionic liquid medium, nitrogen-doped RGO and BC4.5N exhibit specific capacitance values of 258 F/g and 240 F/g at a scan rate of 5 mV/s. The ionic liquid enables a larger operating voltage range of 0.0-2.5 V compared to 0.0-1 V in aqueous medium. (C) 2013 Elsevier Ltd. All rights reserved.

Efficient Dendrimer-DNA Complexation and Gene Delivery Vector Properties of Nitrogen-Core Poly(propyl ether imine) Dendrimer in Mammalian Cells

Dendrimers as vectors for gene delivery were established, primarily by utilizing few prominent dendrimer types so far. We report herein studies of DNA complexation efficacies and gene delivery vector properties of a nitrogen-core poly(propyl ether imine) (PETIM) dendrimer, constituted with 22 tertiary amine internal branches and 24 primary amines at the periphery. The interaction of the dendrimer with pEGFPDNA was evaluated through UV-vis, circular dichroism (CD) spectral studies, ethidium bromide fluorescence emission quenching, thermal melting, and gel retardation assays, from which most changes to DNA structure during complexation was found to occur at a weight ratio of dendrimer:DNA similar to 2:1. The zeta potential measurements further confirmed this stoichiometry at electroneutrality. The structure of a DNA oligomer upon dendrimer complexation was simulated through molecular modeling and the simulation showed that the dendrimer enfolded DNA oligomer along both major and minor grooves, without causing DNA deformation, in 1:1 and 2:1 dendrimer-to-DNA complexes. Atomic force microscopy (AFM) studies on dendrimer-pEGFP DNA complex showed an increase in the average z-height as a result of dendrimers decorating the DNA, without causing a distortion of the DNA structure. Cytotoxicity studies involving five different mammalian cell lines, using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide] (MTT) assay, reveal the dendrimer toxicity profile (IC50) values of similar to 400-1000 mu g mL(-1), depending on the cell line tested. Quantitative estimation, using luciferase assay, showed that the gene transfection was at least 100 times higher when compared to poly(ethylene imine) branched polymer, having similar number of cationic sites as the dendrimer. The present study establishes the physicochemical behavior of new nitrogen-core PETIM dendrimer-DNA complexes, their lower toxicities, and efficient gene delivery vector properties.

Metal-metal charge transfer and interfacial charge transfer mechanism for the visible light photocatalytic activity of cerium and nitrogen co-doped TiO2

Nanosized cerium and nitrogen co-doped TiO2 (Ce-TiO2-xNx) was synthesized by sol gel method and characterized by powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), FESEM, Fourier transform infrared, N-2 adsorption and desorption methods, photoluminescence and ultraviolet-visible (UV-vis) DRS techniques. PXRD analysis shows the dopant decreases the crystallite sizes and slows the crystallization of the titania matrix. XPS confirm the existence of cerium ion in +3 or +4 state, and nitrogen in -3 state in Ce-TiO2-xNx. The modified surface of TiO2 provides highly active sites for the dyes at the periphery of the Ce-O-Ti interface and also inhibits Ce particles from sintering. UV-visible DRS studies show that the metal-metal charge transfer (MMCT) of Ti/Ce assembly (Ti4+/Ce3+ -> Ti3+/Ce4+) is responsible for the visible light photocatalytic activity. Photoluminescence was used to determine the effect of cerium ion on the electron-hole pair separation between the two interfaces Ce-TiO2-xNx and Ce2O3. This separation increases with the increase of cerium and nitrogen ion concentrations of doped samples. The degradation kinetics of methylene blue and methyl violet dyes in the presence of sol gel TiO2, Ce-TiO2-xNx and commercial Degussa P25 was determined. The higher visible light activity of Ce-TiO2-xNx was due to the participation of MMCT and interfacial charge transfer mechanism.

Synthesis, properties and applications of graphene doped with boron, nitrogen and other elements

Chemical doping of graphene becomes necessary to create a band gap which is useful for various applications. Furthermore, chemical doping of elements like boron and nitrogen in graphene gives rise to useful properties. Since chemically doped graphene is both of academic and technical importance, we have prepared this article on the present status of various aspects of this important class of materials. In doing so, we have covered the recent literature on this subject citing all the major references. Some of the aspects that we have covered are the synthesis of chemically doped graphene followed by properties and applications. The applications discussed relate to gas adsorption, lithium batteries, supercapacitors, oxygen reduction reaction, field emission and photochemical water splitting. Characterization of chemically doped graphene also included. We believe that the article will be useful to all those interested in graphene and related materials and provides the present status of the subject. (C) 2014 Elsevier Ltd. All rights reserved.

Hexamethylenetetramine mediated simultaneous nitrogen doping and reduction of graphene oxide for a metal-free SERS substrate

We report a one-pot hydrothermal synthesis of nitrogen doped reduced graphene oxide (N-rGO) and Ag nanoparticle decorated N-rGO hybrid nanostructures from graphene oxide (GO), metal ions and hexamethylenetetramine (HMT). HMT not only reduces GO and metal ions simultaneously but also acts as the source for the nitrogen (N) dopant. We show that the N-rGO can be used as a metal-free surface enhanced Raman spectroscopy (SERS) substrate, while the Ag nano-particles decorated N-rGO can be used as an effective SERS substrate as well as a template for decorating various other nanostructures on N-rGO.

Experimental validation of `pnicogen bonding' in nitrogen by charge density analysis

The participation of a nitrogen atom acting as an electrophile in pnicogen bonding, a hitherto unexplored interaction has been established by experimental charge density analysis. QTAIM and NBO analyses ratify this observation.

2-(Phenylazo)pyridineplatinum(II) Catecholates Showing Photocytotoxicity, Nuclear Uptake, and Glutathione-Triggered Ligand Release

Platinum(II) complexes Pt(pap)(an-cat)] (1) and Pt(pap)(py-cat)] (2) with 2-(phenylazo)pyridine (pap), 4-2-(anthracen-9-ylmethylene)amino]ethyl]benzene-1,2-diol (H(2)an-cat), and 4-2-(pyren-1-ylmethylene)amino]ethyl]benzene-1,2-diol (H2py-cat) were prepared, and their photoinduced cytotoxicity was studied. The complexes were found to release catecholate ligand in the presence of excess glutathione (GSH), resulting in cellular toxicity in the cancer cells. The catecholate complex Pt(pap)(cat)] (3) was prepared and used as a control. Complex 3, which is structurally characterized by X-ray crystallography, has platinum(II) in a distorted square-planar geometry. The complexes are redox-active, showing responses near 0.6 and 1.0 V versus SCE in N,N-dimethylformamide/0.1 M tetrabutylammonium perchlorate corresponding to a two-step catechol oxidation process and at -0.3 and -1.3 V for reduction of the pap ligand. Complex 1 showed remarkable light-induced cytotoxicity in HaCaT (human skin keratinocytes) and MCF-7 (human breast cancer) cells, giving IC50 value of similar to 5 mu M in visible light of 400-700 nm and >40 mu M in the dark. The 2',7'-dichlorofluorescein diacetate (DCFDA) assay showed the generation of reactive oxygen species (ROS), which seems to trigger apoptosis, as is evident from the annexin V-fluorescein isothiocyanate (FITC)/propidium iodide (PI) assay. The fluorescence microscopic images showed significant nuclear localization of the complexes and free ligands. A mechanistic study revealed possible reduction of the coordinated azo bond of pap by cellular GSH, releasing the catecholate ligand and resulting in remarkable photochemotherapeutic action of the complexes.

Copper-Catalyzed Direct Transformation of Secondary Allylic and Benzylic Alcohols into Azides and Amides: An Efficient Utility of Azide as a Nitrogen Source

A mild and convenient method for the synthesis of amides has been explored by using secondary alcohols, Cu(ClO4)(2)6H(2)O as a catalyst, and trimethylsilyl azide (TMSN3) as a nitrogen source in the presence of 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) at ambient temperature. This method has been successfully adapted to the preparation of azides directly from their corresponding alcohols and offers excellent chemoselectivity in the formation of -halo azides and the azidation of allylic alcohols in the presence of a benzyl alcohol moiety. In addition, this strategy provides an opportunity to synthesize azides that can serve as precursors to -amino acids.

Iron(III) Complexes of a Pyridoxal Schiff Base for Enhanced Cellular Uptake with Selectivity and Remarkable Photocytotoxicity

Iron(III) complexes of pyridoxal (vitamin B6, VB6) or salicylaldehyde Schiff bases and modified dipicolylamines, namely, Fe(B)(L)](NO3) (15), where B is phenyl-N,N-bis((pyridin-2-yl)methyl)methanamine (phbpa in 1), (anthracen-9-yl)-N,N-bis((pyridin-2-yl)methyl)methanamine (anbpa in 2, 4) and (pyren-1-yl)-N,N-bis((pyridin-2-yl)methyl)methanamine (pybpa in 3, 5) (H2L1 is 3-hydroxy-5-(hydroxymethyl)-4-(((2-hydroxyphenyl)imino)methyl)-2-methylp yridine (13) and H2L2 is 2-(2-hydroxyphenyl-imino)methyl]phenol), were prepared and their uptake in cancer cells and photocytotoxicity were studied. Complexes 4 and 5, having a non-pyridoxal Schiff base, were prepared to probe the role of the pyridoxal group in tumor targeting and cellular uptake. The PF6 salt (1a) of complex 1 is structurally characterized. The complexes have a distorted six-coordinate FeN4O2 core where the metal is in the +3 oxidation state with five unpaired electrons. The complexes display a ligand to metal charge transfer band near 520 and 420 nm from phenolate to the iron(III) center. The photophysical properties of the complexes are explained from the time dependent density functional theory calculations. The redox active complexes show a quasi-reversible Fe(III)/Fe(II) response near -0.3 V vs saturated calomel electrode. Complexes 2 and 3 exhibit remarkable photocytotoxicity in various cancer cells with IC50 values ranging from 0.4 to 5 mu M with 10-fold lower dark toxicity. The cell death proceeded by the apoptotic pathway due to generation of reactive oxygen species upon light exposure. The nonvitamin complexes 4 and 5 display 3-fold lower photocytotoxicity compared to their VB6 analogues, possibly due to preferential and faster uptake of the vitamin complexes in the cancer cells. Complexes 2 and 3 show significant uptake in the endoplasmic reticulum, while complexes 4 and 5 are distributed throughout the cells without any specific localization pattern.

Supercapacitors based on composites of PANI with nanosheets of nitrogen-doped RGO, BC1.5N, MoS2 and WS2

Performance of supercapacitors based on 1:1 (by weight) composites of polyaniline (PANI) with nanosheets of nitrogenated reduced graphene oxide (NRGO), BC1.5N, MoS2 and WS2 has been investigated in detail. The highest specific capacitance is found with the 1:1 NRGO-PANI composite, the value being 561 F/g at a current density of 0.2 A/g. All the 1:1 nanocomposites show good cyclability. Increasing the PANI content increases the specific capacitance and the highest value found being 715 F/g at a current density of 0.5 A/g in the case of the 1:6 NRGO-PANI composite. However, all the 1:6 composites show a marked decrease in specific capacitance with increase in current density. The energy density of 1:6 NRGO-PANI is similar to 25 Wh/Kg at 0.5 A/g and 1:1 NRGO-PANI is similar to 19 Wh/Kg at 0.2 A/g. NRGO-PANI composites clearly stand out as viable materials for practical applications. (C) 2014 Elsevier Ltd. All rights reserved.