Synthesis, crystal structures and protease activity of amino acid Schiff base iron(III) complexes

Iron(III) complexes, (NHEt3)[Fe(III)(sal-met)(2)] and (NHEt3)[Fe(III)(sal-phe)(2)], of amino acid Schiffbase ligands, viz., N-salicylidene-L-methionine and N-salicylidene L-phenylalanine, have been prepared and their binding to bovine serum albumin (BSA) and photo-induced BSA cleavage activity have been investigated. The complexes are structurally characterized by single crystal X-ray crystallography. The crystal Structures of the discrete mononuclear rnonoanionic complexes show FeN2O4 octahedral coordination geometry in which the tridentate dianionic amino acid Schiff base ligand binds through phenolate and carboxylate oxygen and imine nitrogen atoms. The imine nitrogen atoms are trans to each other. The Fe-O and Fe-N bond distances range between 1.9 and 2.1 angstrom. The sal-met complex has two pendant thiomethyl groups. The high-spin iron(III) complexes (mu(eff) similar to 5.9 mu(B)) exhibit quasi-reversible Fe(III)/Fe(II) redox process near -0.6 V vs. SCE in water. These complexes display a visible electronic hand near 480 nm in tris-HCl buffer assignable to the phenolate-to-iron(III) charge transfer transition. The water soluble complexes bind to BSA giving binding constant values of similar to 10(5) M-1. The Complexes show non-specific oxidative cleavage of BSA protein on photo-irradiation with UV-A light of 365 nm.

Structure-thermal behaviour studies on the salicylato complex of cobalt

The salicylato complex of cobalt was synthesized and its structure established to be [Co(sal)2] · 4 H2O, where, sal =, from elemental analysis, IR spectroscopy, magnetic susceptibility, cryoscopy and conductivity. The X-ray diffractogram of the complex has been given. Thermal decomposition has been studied in air by thermogravimetry (TG), differential thermal analysis and differential scanning calorimetry. TG shows three main steps of decomposition. The intermediates formed at various stages were collected and analysed. From the TG results and chemical analysis of the intermediates, a mechanism has been proposed for the thermal decomposition of the complex, leading to the oxide formation in the final stage.

Iron(III) Schiff base complexes of arginine and lysine as netropsin mimics showing AT-selective DNA binding and photonuclease activity

Iron(III) complexes [Fe(L)(2)]Cl (1-3), where L is monoanionic N-salicylidene-arginine (sal-argH for 1), hydroxynaphthylidene-arginine (nap-argH for 2) and N-salicylidene-lysine (sal-lysH for 3), were prepared and their DNA binding and photo-induced DNA cleavage activity studied. Complex 3 as its hexafluorophosphate salt [Fe(sal-lysH)(2)](PF6)center dot 6H(2)O (3a) was structurally characterized by single crystal Xray crystallography. The crystals belonged to the triclinic space group P-1. The complex has two tridentate ligands in FeN2O4 coordination geometry with two pendant cationic amine moieties. Complexes 1 and 2 with two pendant cationic guanidinium moieties are the structural models for the antitumor antibiotics netropsin. The complexes are stable and soluble in water. They showed quasi-reversible Fe(III)/Fe(II) redox couple near 0.6 V in H2O-0.1 M KCl. The high-spin 3d(5)-iron(III) complexes with mu(eff) value of similar to 5.9 mu(B) displayed ligand-to-metal charge transfer electronic band near 500 mm in Tris-HCl buffer. The complexes show binding to Calf Thymus (CT) DNA. Complex 2 showed better binding propensity to the synthetic oligomer poly(dA)center dot poly(dT) than to CT-DNA or poly(dG)center dot poly(dC). All the complexes displayed chemical nuclease activity in the presence of 3-mercaptopropionic acid as a reducing agent and cleaved supercoiled pUC19 DNA to its nicked circular form. They exhibited photo-induced DNA cleavage activity in UV-A light and visible light via a mechanistic pathway that involves the formation of reactive hydroxyl radical species. (C) 2010 Elsevier Inc. All rights reserved.

Analysis of the beta-glucoside utilization (bgl) genes of Shigella sonnei: evolutionary implications for their maintenance in a cryptic state

The pattern of expression of the genes involved in the utilization of aryl beta-glucosides such as arbutin and salicin is different in the genus Shigella compared to Escherichia coli. The results presented here indicate that the homologue of the cryptic bgl operon of E. coli is conserved in Shigella sonnei and is the primary system involved in beta-glucoside utilization in the organism. The organization of the bgl genes in 5. sonnei is similar to that of E. coli; however there are three major differences in terms of their pattern of expression. (i) The bglB gene, encoding phospho-beta-glucosidase B, is insertionally inactivated in 5. sonnei. As a result, mutational activation of the silent bgl promoter confers an Arbutin-positive (Arb(+)) phenotype to the cells in a single step; however, acquiring a Salicin-positive (Sal(+)) phenotype requires the reversion or suppression of the bglB mutation in addition. (ii) Unlike in E. coli, a majority of the activating mutations (conferring the Arb(+) phenotype) map within the unlinked hns locus, whereas activation of the E. coli bgl operon under the same conditions is predominantly due to insertions within the bglR locus. (iii) Although the bgl promoter is silent in the wild-type strain of 5. sonnei (as in the case of E. coli), transcriptional and functional analyses indicated a higher basal level of transcription of the downstream genes. This was correlated with a 1 bp deletion within the putative Rho-independent terminator present in the leader sequence preceding the homologue of the bglG gene. The possible evolutionary implications of these differences for the maintenance of the genes in the cryptic state are discussed.

Photocytotoxicity and DNA cleavage activity of L-arg and L-lys Schiff base oxovanadium(IV) complexes having phenanthroline bases

Oxovanadium(IV) complexes [VO(sal-argH)(B)] Cl (1-3) and [VO(sal-lysH)(B)] Cl (4-6), where sal-argH2 and sal-lysH(2) are N-salicylidene-L-arginine and N-salicylidene-L-lysine Schiff bases and B is a phenanthroline base, viz. 1,10-phenanthroline (phen in 1 and 4); dipyrido[3,2-d: 2', 3'-f] quinoxaline (dpq in 2 and 5) and dipyrido[3,2-a: 2', 3'-c] phenazine (dppz in 3 and 6), have been prepared, characterized and their DNA photocleavage activity studied. Complex 1, characterized by X-ray crystallography, shows the presence of a vanadyl group in VIVO3N3 coordination geometry with a tridentate Schiff base having a pendant guanidinium moiety and bidentate phen ligand. The complexes exhibit a d-d band at similar to 715 nm in 20% DMF-Tris-HCl buffer. The complexes are redox active showing cathodic and anodic responses near -1.0 V and 0.85 V (vs. SCE) for the V(IV)-V(III) and V(V)-V(IV) couples, respectively, in DMF-Tris-HCl buffer. The complexes bind to calf thymus DNA giving Kb values in the range of 3.8 x 10(4) to 1.6 x 10(5) M-1. Thermal denaturation and viscosity data suggest DNA groove binding nature of the complexes. The complexes do not show any `chemical nuclease'' activity in dark in the presence of 3-mercaptopropionic acid or H2O2. The dpq and dppz complexes are efficient photocleavers of plasmid DNA in UV-A (365 nm) and red light (676 nm) via singlet oxygen pathway. The dppz complexes exhibit photocytotoxicity in HeLa cancer cells giving IC50 values of 15.4 mu M for 3 and 17.5 mu M for 6 in visible light while being non-toxic in dark giving IC50 values of > 100 mu M.

Synthesis and Studies of Pb0.76Ca0.24TiO3 Nanoparticles Derived by Sol-Gel

Pb0.76Ca0.24TiO3 (PCT24) nanoparticles were synthesized by modified sal gel method and characterized by a number of experimental techniques such as X-ray diffraction, TGA-DTA, FTIR and transmission electron microscopy equipped with energy-dispersive X-ray spectroscopy (EDX). X-ray diffraction (XRD) and selected-area electron diffraction (SAED) investigations demonstrated that the postannealed (650 degrees C for 1 h) PCT24 nanoparticles have tetragonal perovskite crystal structure. TEM have been employed to characterize the morphology, structure and composition of the as prepared nanoparticles. Dielectric results indicates the evidence for relaxor type behavior while observed leaky ferroelectric loops may be because of the defects such as grain boundaries and the pores in the sample as the sample was not heated at higher temperature, to retain the nanosize dimension of the particles.

Diverse pathways for salicin utilization in Shigella sonnei and Escherichia coli carrying an impaired bgl operon

Utilization of the aryl-beta-glucosides salicin or arbutin in most wild-type strains of E. coli is achieved by a single-step mutational activation of the bgl operon. Shigella sonnei, a branch of the diverse E. coli strain tree, requires two sequential mutational steps for achieving salicin utilization as the bglB gene, encoding the phospho-beta-glucosidase B, harbors an inactivating insertion. We show that in a natural isolate of S. sonnei, transcriptional activation of the gene SSO1595, encoding a phospho-beta-glucosidase, enables salicin utilization with the permease function being provided by the activated bgl operon. SSO1595 is absent in most commensal strains of E. coli, but is present in extra-intestinal pathogens as bgcA, a component of the bgc operon that enables beta-glucoside utilization at low temperature. Salicin utilization in an E. coli bglB laboratory strain also requires a two-step activation process leading to expression of BglF, the PTS-associated permease encoded by the bgl operon and AscB, the phospho-beta-glucosidase B encoded by the silent asc operon. BglF function is needed since AscF is unable to transport beta-glucosides as it lacks the IIA domain involved in phopho-relay. Activation of the asc operon in the Sal(+) mutant is by a promoter-up mutation and the activated operon is subject to induction. The pathway to achieve salicin utilization is therefore diverse in these two evolutionarily related organisms; however, both show cooperation between two silent genetic systems to achieve a new metabolic capability under selection.

Synthesis and structural characterization of perovskite 0.65Pb(Mg1/3Nb2/3)O-3-0.35PbTiO(3) nanotubes

We report the synthesis and structural characterization of 0.65Pb(Mg1/3Nb2/3)O-3-0.35PbTiO(3) (PMN-PT) nanotubes prepared by a novel sal-gel template method. X-ray diffraction (XRD) and selected-area electron diffraction (SAED) investigations demonstrated that the postannealed (650 degrees C for 1 h) PMN-PT nanotubes were polycrystalline with perovskite crystal structure. The field emission scanning electron microscope (FE-SEM) shows that as prepared PMN-PT nanotubes were hollow with diameter to be about 200 nm. High resolution transmission electron microscope (HRTEM) analysis confirmed that the obtained PMN-PT nanotubes made up of nanoparticles (10-20 nm) which were randomly aligned in the nanotubes. Energy-dispersive X-ray spectroscopy (EDX) analysis confirmed the stoichiometric 0.65Pb(Mg1/3Nb2/3)O-3-0.35PbTiO(3). The possible formation mechanism of PMN-PT nanotubes was proposed at the end. (C) 2011 Elsevier B.V. All rights reserved.

PAMAM Dendrimer-Drug Interactions: Effect of pH on the Binding and Release Pattern

Understanding the dendrimer-drug interaction is of great importance to design and optimize the dendrimer-based drug delivery system. Using atomistic molecular dynamics (MD) simulations, we have analyzed the release pattern of four ligands (two soluble drugs, namely, salicylic acid (Sal), L-alanine (Ala), and two insoluble drugs, namely, phenylbutazone (Pbz) and primidone (Prim)), which were initially encapsulated inside the ethylenediamine (EDA) cored polyamidoamine (PAMAM) dendrimer using the docking method. We have computed the potential of mean force (PMF) variation with generation 5 (G5)-PAMAM dendrimer complexed with drug molecules using umbrella sampling. From our calculated PMF values, we observe that soluble drugs (Sal and Ala) have lower energy barriers than insoluble drugs (Pbz and Prim). The order of ease of release pattern for these drugs from G5 protonated PAMAM dendrimer was found to be Ala > Sal > Prim > Pbz. In the case of insoluble drugs (Prim and Pbz), because of larger size, we observe much nonpolar contribution, and thus, their larger energy barriers can be reasoned to van der Waals contribution. From the hydrogen bonding analysis of the four PAMAM drug complexes under study, we found intermolecular hydrogen bonding to show less significant contribution to the free energy barrier. Another interesting feature appears while calculating the PMF profile of G5NP (nonprotonated)-PAMAM Pbz and G5NP (nonprotonated)-PAMAM-Sal complex. The PMF was found to be less when the drug is bound to nonprotonated dendrimer compared to the protonated dendrimer. Our results suggest that encapsulation of the drug molecule into the host PAMAM dendrimer should be carried out at higher pH values (near pH 10). When such complex enters the human body, the pH is around 7.4 and at that physiological pH, the dendrimer holds the drug tightly. Hence the release of drug can occur at a controlled rate into the bloodstream. Thus, our findings provide a microscopic picture of the encapsulation and controlled release of drugs in the case of dendrimer-based host-guest systems.

Enhancing the magnetic characteristics of BiFeO3 nanoparticles by Ca, Ba co-doping

Multiferroic nanoparticles (NPs) of pristine and Ca, Ba co-doped BiFeO3 were synthesized by a facile sal gel route. Co-doping was done by fixing the total dopant concentration at 5 mol% and then the relative concentrations of Ca and Ba was varied. Structural, optical and magnetic properties of the NPs were investigated using different techniques. UV-Vis absorption spectra of BiFeO3 NPs showed a substantial blue shift of similar to 100 nm (530 nm -> 430 nm) on Ca. Ba co-doping which corresponds to increase in band gap by 0.5 eV. Fe-57 Mossbauer spectroscopy confirmed that iron is present only in 3(+) valence state in all co-doped samples. The coercive field increased by 18 times for Bi0.95Ca0.01Ba0.04FeO3 samples, which is the maximum enhancement, observed amongst all the 5 mol% doped samples. At the equimolar (2.5 mol % each) concentration of co-dopants, the coercive field shows a significant enhancement of about 9 times (220 Oe -> 2014 Oe) with concomitant increase in saturation magnetization by 7 times. Thus, equimolar co-doping causes simultaneous enhancement of the twin aspects of magnetic properties thereby making them better suited for device applications. (C) 2012 Elsevier B.V. All rights reserved.

Metal doped nanosized titania used for the photocatalytic degradation of rhodamine B dye under visible-light

Metal-doped anatase nanosized titania photocatalysts were successfully synthesized using a sal gel process. Different amounts of the dopants (0.2, 0.4, 0.6, 0.8 and 1.0%) of the metals (Ag, Ni, Co and Pd) were utilized. The UV-Vis spectra (solid state diffuse reflectance spectra) of the doped nanoparticles exhibited a red shift in the absorption edge as a result of metal doping. The metal-doped nanoparticles were investigated for their photocatalytic activity under visible-light irradiation using Rhodamine B (Rh B) as a control pollutant. The results obtained indicate that the metal-doped titania had the highest activity at 0.4% metal loading. The kinetic models revealed that the photodegradation of Rh B followed a pseudo first order reaction. From ion chromatography (IC) analysis the degradation by-products Rhodamine B fragments were found to be acetate, chloride, nitrite, carbonate and nitrate ions.

Mitochondria-Targeting Oxidovanadium(IV) Complex as a Near-IR Light Photocytotoxic Agent

Oxidovanadium(IV) complexes VO(L-1)(phen)]Cl (1) and VO(L-2)(L-3)]Cl (2), in which HL1 is 2-{(benzimidazol-2-yl)methylimino]-methyl}phenol (sal-ambmz), HL2 is 2-({1-(anthracen-9-yl)methyl]-benzimidazol-2-yl}methylimino)-met hyl]phenol (sal-an-ambmz), phen is 1,10-phenanthroline and L-3 is dipyrido3,2-a:2,3-c]phenazine (dppz) conjugated to a Gly-Gly-OMe dipeptide moiety, were prepared, characterized, and their DNA binding, photoinduced DNA-cleavage, and photocytotoxic properties were studied. Fluorescence microscopy studies were performed by using complex 2 in HeLa and HaCaT cells. Complex 1, structurally characterized by X-ray crystallography, has a vanadyl group in VO2N4 core with the VO2+ moiety bonded to N,N-donor phen and a N,N,O-donor Schiff base. Complex 2, having an anthracenyl fluorophore, showed fluorescence emission bands at 397, 419, and 443nm. The complexes are redox-active exhibiting the V(IV)/V(III) redox couple near -0.85V versus SCE in DMF 0.1M tetrabutylammonium perchlorate (TBAP). Complex 2, having a dipeptide moiety, showed specific binding towards poly(dAdT)(2) sequence. The dppz-Gly-Gly-OMe complex showed significant DNA photocleavage activity in red light of 705nm through a hydroxyl radical ((OH)-O-.) pathway. Complex 2 showed photocytotoxicity in HaCaT and HeLa cells in visible light (400-700nm) and red light (620-700nm), however, the complex was less toxic in the dark. Fluorescence microscopy revealed the localization of complex 2 primarily in mitochondria. Apoptosis was found to occur inside mitochondria (intrinsic pathway) caused by ROS generation.