Nucleosynthesis in the outflows associated with accretion disks of type II collapsars

We investigate nucleosynthesis inside the outflows from gamma-ray burst (GRB) accretion disks formed by the Type II collapsars. In these collapsars, massive stars undergo core collapse to form a proto-neutron star initially, and a mild supernova (SN) explosion is driven. The SN ejecta lack momentum, and subsequently this newly formed neutron star gets transformed to a stellar mass black hole via massive fallback. The hydrodynamics and the nucleosynthesis in these accretion disks have been studied extensively in the past. Several heavy elements are synthesized in the disk, and much of these heavy elements are ejected from the disk via winds and outflows. We study nucleosynthesis in the outflows launched from these disks by using an adiabatic, spherically expanding outflow model, to understand which of these elements thus synthesized in the disk survive in the outflow. While studying this, we find that many new elements like isotopes of titanium, copper, zinc, etc., are present in the outflows. Ni-56 is abundantly synthesized in most of the cases in the outflow, which implies that the outflows from these disks in a majority of cases will lead to an observable SN explosion. It is mainly present when outflow is considered from the He-rich, Ni-56/Fe-54-rich zones of the disks. However, outflow from the Si-rich zone of the disk remains rich in silicon. Although emission lines of many of these heavy elements have been observed in the X-ray afterglows of several GRBs by Chandra, BeppoSAX, XMM-Newton, etc., Swift seems to have not yet detected these lines.

Versatility of azide in serendipitous assembly of Copper(II) Magnetic Polyclusters

Engineering at the molecular level is one of the most exciting new developments for the generation of functional materials. However, the concept of designing polynuclear extended structures from bottom up is still not mature. Although progress has been made with secondary building units (SBUs) in metal organic frameworks (MOFs), the control seems to be just an illusion when it comes to bridging ligands such as the azide ion. When we say that the azido ligand is versatile in its bridging capabilities, what we mean is that it would be difficult to predict or control its bridging properties. However, this kind of serendipity is not always bad news. For example, scientists have shown that the azido ligand can mediate magnetic exchanges between paramagnetic metals in a predictable fashion (usually depending upon the bonding geometries). Therefore, it is a well-respected ligand in polynuclear assemblies. Serendipitous assemblies offer new magnetic structures that we may not otherwise even think about synthesizing. The azido ligand forms a variety of complexes with copper(II) using different blocking amines or pyridine based ligands. Its structural nature changes upon changing the substitution on amine, as well as the amount of blocking ligand. In principle, if we take any of these complexes and provide more coordination sites to the bridging azido ligands by removing a fraction of the blocking ligands, we can get new complexes with intricate structural networks and therefore different magnetic properties with the same components as used for the parent complex. In this Account, we mainly discuss the development of a number of new topological and magnetic exchange systems synthesized using this concept. Not all of these new complexes can be grouped according to their basic building structures or even by the ratio of the metal to blocking ligand. Therefore, we divided the discussion by the nuclearity of the basic building structures. Some of the complexes with the same nuclearities have very similar or even almost identical basic structures. However, the way these building units are joined together (by the azido bridges) to form the overall extended structures differ almost in every case. The complexes having the Cu-6 core are particularly interesting from a structural point of view. Although they have almost identical basic structures, some of them are extended in three dimensions, but two of them are extended in two dimensions by two different bridging networks. In the complexes having linear Cu-4 basic units, we find that using similar ligands does not always give the same bridging networks even within the basic building structures. These complexes have also enriched the field of molecular magnetism. One of the complexes with a Cu-3 building unit has provided us with the opportunity to study the competing behavior of two different kinds of magnetic exchange mechanism (ferromagnetic and antiferromagnetic) acting simultaneously between two metal ions. Through density functional theory calculations, we showed how they work independently and their additive nature to produce the overall effect. The exciting methodology for the generation of copper(II) polyclusters presented in this Account will provide the opportunity to explore analogous serendipitous assembly of diverse structures with interesting magnetic behavior using other transition metal ions having more than one unpaired electrons.

Pt-6(II) nanoscopic cages with an organometallic backbone as sensors for picric acid

An organometallic building block 1,3,5-tris(4-trans-Pt(PEt3)(2)I(ethynyl)phenyl)benzene (1) incorporating Pt-ethynyl functionality has been synthesized and characterized. 2 + 3] self-assembly of its nitrate analogue 1,3,5-tris(4-trans-Pt(PEt3)(2)(ONO2)(ethynyl)phenyl)benzene (2) with ``clip'' type bidentate donors (L-1-L-3) separately afforded three trigonal prismatic architectures (3a-3c), respectively. All these prisms were characterized and their shapes/sizes are predicted through geometry optimization employing molecular mechanics universal force field (MMUFF) simulation. The extended p-conjugation including the presence of Pt-ethynyl functionality makes them electron rich as well as luminescent in nature. Macrocycles 3b and 3c exhibit fluorescence quenching in solution upon addition of picric acid PA], which is a common constituent of many explosives. Interestingly, the non-responsive nature of fluorescent intensity towards other electron-deficient nitro-aromatic explosives (NAEs) makes them promising selective sensors for PA with a detection limit predicted to be ppb level. Furthermore, solid-state quenching of fluorescent intensity of the thin film of 3b upon exposure to saturated vapor of picric acid has drawn special attention for infield applications.

Remarkable anticancer activity of ferrocenylterpyridine platinum(II) complexes in visible light with low dark toxicity

Ferrocenyl platinum(II) complexes (1-3), viz. Pt(Fc-tpy)Cl]Cl (1), Pt(Fc-tpy)(NPC)]Cl (2, HNPC = N-propargyl carbazole) and Pt(Fc-bpa)Cl]Cl (3), were prepared, characterized and their anti-proliferative properties in visible light in human keratinocyte (HaCaT) cell lines have been studied. Pt(Ph-tpy)Cl]Cl (4) was prepared and used as a control. Complexes 1 and 3, structurally characterized by X-ray crystallography, show distorted square-planar geometry for the platinum(II) centre. Complexes 1 and 2 having the Fc-tpy ligand showed an intense absorption band at similar to 590 nm. The ferrocenyl complexes are redox active showing the Fc(+)-Fc couple near 0.6 V vs. SCE in DMF-0.1 M tetrabutylammonium perchlorate (TBAP). Complexes 1-3 showed external binding to calf thymus DNA. Both 1 and 2 showed remarkable photocytotoxicity in HaCaT cell lines giving respective IC50 values of 9.8 and 12.0 mu M in visible light of 400-700 nm with low dark toxicity (IC50 > 60 mu M). Fluorescent imaging studies showed the spread of the complexes throughout the cell localising both in cytoplasm and the nucleus. The ferrocenyl complexes triggered apoptosis on light exposure as evidenced from the Annexin V-FITC/PI and DNA ladder formation assays. Spectral studies revealed the formation of ferrocenium ions upon photo-irradiation generating cytotoxic hydroxyl radicals via a Fenton type mechanism. The results are rationalized from a TDDFT study that shows involvement of ferrocene and the platinum coordinated terpyridine moiety as respective HOMO and LUMO.

D-A-D-structured conducting polymer-modified electrodes for detection of lead(II) ions in water

Donor-acceptor-donor-structured thiophene derivative-based conducting polymer poly(7,9-dithiophene-2yl-8H-cyclopentaa]acenaphthalene-8-one) was chemically synthesized. This polymer was used to modify both glassy-carbon and carbon-paste electrode, which was used to detect lead(II) ions present in water in the range of 1 mM to 0.1 mu M. Cyclic voltammetry confirms the formation of the co-ordination complex between the soft segment of polymer and the dissolved lead ion. Anodic stripping voltammetry was carried out by the modified electrode to determine the lower limit of detection of dissolved lead(II) species in the solution. Differential adsorptive stripping and impedance measurements were also conducted to find the lowest possible response of the as-synthesized polymer to lead(II) ion in water. The electrochemical performance of the modified electrodes at different pH (4, 7 and 9) environments was carried out by stripping voltammetry, to get optimum sensitivity and stability under these conditions. Finally, interference analysis was carried out to detect the modified electrode's sensitivity towards lead ion affinity in water.

Self-assembly of discrete metallamacrocycles employing half-sandwich octahedral diruthenium(II) building units and imidazole-based ligands

Equimolar combination of a series of binuclear half-sandwich p-cymene ruthenium(II) building units Ru-2(mu-eta(4)-C2O4)(MeOH)(2)(eta(6)-p-cymene)(2)](OTf)(2) 1a](OTf)(2), Ru-2(mu-eta(4)-N,N'-diphenyloxamidato)( MeOH)(2)(eta(6)-p-cymene)(2)](OTf)(2) 1b](OTf)(2) and Ru-2(mu-eta(4)-C6H2O4)(MeOH)(2)(eta(6)-p-cymene)(2)](OTf)(2) 1c](OTf)(2) separately with imidazole-based ditopic ligands (L-1-L-2) in methanol yielded a series of tetranuclear metallamacrocycles 2-7](OTf)(4), respectively L-1 = 1,4-bis(imidazole-1-yl)benzene; L-2 = 4,4'-bis(imidazole-1-yl)biphenyl; OTf- = O3SCF3-]. Similarly, the reaction of Ru-2(mu-eta(4)-C2O4)(MeOH)(2)(eta(6)-p-cymene)2](OTf)(2) 1a](OTf)(2) with a triazine-based tritopic ligand 1,3,5-tris(imidazole-1-yl) triazine (L3) in 3: 2 M ratio afforded an unexpected tetranuclear macrocycle 8](OTf)(4) instead of an expected trigonal prismatic cage 8a](OTf)(6). All the self-assembled macrocycles 2-8](OTf)(4) were isolated in moderate to high yields and were fully characterized by multinuclear H-1, F-19] NMR, IR and electrospray ionization mass spectrometry (ESI-MS). In addition, X-ray diffraction study on the single crystals of 3](OTf)(4) and 8](OTf)(4) also indicated the formation 2 + 2] self-assembled macrocycles. Despite the possibility of formation of different conformational isomeric macrocycles (syn-and anti) and polymeric product due to free rotation of ligand sites of imidazole linkers, the selective formation of single conformational isomer (anti) as the only product is quite interesting. Furthermore, the photo-and electrochemical properties of these assemblies have been studied using UV/Vis absorption and cyclic voltammetry analysis. (c) 2013 Elsevier B.V. All rights reserved.

Transcriptional Repression of Tumor Suppressor CDC73, Encoding an RNA Polymerase II Interactor, by Wilms Tumor 1 Protein (WT1) Promotes Cell Proliferation IMPLICATION FOR CANCER THERAPEUTICS

The Wilms tumor 1 gene (WT1) can either repress or induce the expression of genes. Inconsistent with its tumor suppressor role, elevated WT1 levels have been observed in leukemia and solid tumors. WT1 has also been suggested to act as an oncogene by inducing the expression of MYC and BCL-2. However, these are only the correlational studies, and no functional study has been performed to date. Consistent with its tumor suppressor role, CDC73 binds to RNA polymerase II as part of a PAF1 transcriptional regulatory complex and causes transcriptional repression of oncogenes MYC and CCND1. It also represses beta-catenin-mediated transcription. Based on the reduced level of CDC73 in oral squamous cell carcinoma (OSCC) samples in the absence of loss-of-heterozygosity, promoter methylation, and mutations, we speculated that an inhibitory transcription factor is regulating its expression. The bioinformatics analysis predicted WT1 as an inhibitory transcription factor to regulate the CDC73 level. Our results showed that overexpression of WT1 decreased CDC73 levels and promoted proliferation of OSCC cells. ChIP and EMSA results demonstrated binding of WT1 to the CDC73 promoter. The 5-azacytidine treatment of OSCC cells led to an up-regulation of WT1 with a concomitant down-regulation of CDC73, further suggesting regulation of CDC73 by WT1. Exogenous CDC73 attenuated the protumorigenic activity of WT1 by apoptosis induction. An inverse correlation between expression levels of CDC73 and WT1 was observed in OSCC samples. These observations indicated that WT1 functions as an oncogene by repressing the expression of CDC73 in OSCC. We suggest that targeting WT1 could be a therapeutic strategy for cancer, including OSCC.

Template-free multicomponent coordination-driven self-assembly of Pd(II)/Pt(II) molecular cages

Recent years have seen a tremendous increase in the interest for constructing hollowed-out molecular frameworks, for their potential uses. Metal-ligand coordination-driven self-assembly has provided multitudes of opportunities in the formation of molecular architectures of desired shapes and sizes, with the help of the information already coded in the components. This article summarizes the recent developments in the construction of multicomponent molecular cages through this process, with a focus on the decreasing relevance of templates, and use of these systems in catalysis/host-guest chemistry.

mu-Oxamido binuclear copper (II) complexes: Synthesis, crystal structure, DNA interaction and antibacterial studies

Four binuclear copper (II) complexes Cu(oxpn)Cu(B)](2+) (2-5) bridged by N, N'-bis3-(methylamino) propyl] oxamide (oxpn), where, B is N, N-donor heterocyclic bases (viz. 2,2'-bipyridine (bpy, 2), 1,10-phenathroline (phen, 3), dipyrido3,2-d:2',3'-f]quinoxaline (dpq, 4) and dipyrido3,2-a:2',3'-c]phenazine (dppz, 5) are synthesized, characterized by different spectroscopic and single crystal X-ray data technique. The phen (3) and dpq (4) complexes were structurally characterized by X-ray data analysis. Their DNA binding, oxidative cleavage and antibactirial activities were studied. The dpq (4) and dppz (5) complexes are avid binders to the Calf thymus DNA (CT-DNA). The phen (3), dpq (4) and dppz (5) complexes show efficient oxidative cleavage of supercoiled DNA (SC DNA) through hydroxyl radical ((OH)-O-center dot) pathway in the presence of Mercaptopropionic acid (MPA). (C) 2013 Elsevier Ltd. All rights reserved.

Synthesis, crystal structure, DNA interaction and cleavage activities of mononuclear and trinuclear copper(II) complexes

Mono- and trinuclear copper(II) complexes with 2-1-(2-dimethylamino-ethylamino)-ethyl]-phenol (HL) have been synthesized and structurally characterized. The mononuclear complex Cu(L)(H2O)(ONO2)] (1) crystallizes in monoclinic space group P2(1) /n with a square pyramidal Cu(II) center coordinated by the tridentate Schiff base (L) and a water ligand in the equatorial plane and an oxygen atom from nitrate in the axial position. The trinuclear complex (CuL)(3)(mu(3)-OH)](ClO4)(2)center dot H2O (2) crystallizes in hexagonal space group P6(3); all three copper atoms are five-coordinate with square pyramidal geometries. The interactions of these complexes with calf-thymus DNA have been investigated using absorption spectrophotometry. The mononuclear complex binds more strongly than the trinuclear complex. The DNA cleavage activity of these complexes has been studied on double-stranded pBR 322 plasmid DNA by gel electrophoresis experiments in the absence and in the presence of added oxidant (H2O2). The trinuclear complex cleaves DNA more efficiently than the mononuclear complex in the presence of H2O2.

Dynamics of H-atom exchange in stable cis-dihydrogen/hydride complexes of ruthenium( II) bearing phosphine and N-N bidentate ligands

Synthesis and characterization of cis, trans-RuH(eta(2)-H-2)(PPh3)(2)(N-N)]OTf] (N-N = 2,2'-bipyridyl (bpy) 1a, 2,2'-bipyrimidine (bpm) 2a; OTf = trifluoromethane sulfonate (CF3SO3)) complexes are reported. The cis-H-2/hydride ligands are involved in H-atom site exchange between the two moieties. This dynamics was investigated by variable temperature NMR spectral studies based on which the mechanism of the exchange process was deduced. The Delta G(#) for the exchange of H-atoms between the eta(2)-H-2 and hydride ligands was determined to be around 8 and 13 kJ mol(-1), respectively, for 1a and 2a. The H-H distances (d(HH), A) in complexes 1a and 2a have been calculated from the T-1(minimum) and (1)J(H, D) and are found to be 1.07 A (slow) and 0.95 A for 1a and 1.04 A (slow) and 0.94 A for 2a, respectively. The molecular structure of 1a was determined by X-ray crystallography.

Allosteric regulation and substrate activation in cytosolic nucleotidase II from Legionella pneumophila

Cytosolic nucleotidase II (cN-II) from Legionellapneumophila (Lp) catalyzes the hydrolysis of GMP and dGMP displaying sigmoidal curves, whereas catalysis of IMP hydrolysis displayed a biphasic curve in the initial rate versus substrate concentration plots. Allosteric modulators of mammalian cN-II did not activate LpcN-II although GTP, GDP and the substrate GMP were specific activators. Crystal structures of the tetrameric LpcN-II revealed an activator-binding site at the dimer interface. A double mutation in this allosteric-binding site abolished activation, confirming the structural observations. The substrate GMP acting as an activator, partitioning between the allosteric and active site, is the basis for the sigmoidicity of the initial velocity versus GMP concentration plot. The LpcN-II tetramer showed differences in subunit organization upon activator binding that are absent in the activator-bound human cN-II structure. This is the first observation of a structural change induced by activator binding in cN-II that may be the molecular mechanism for enzyme activation. DatabaseThe coordinates and structure factors reported in this paper have been submitted to the Protein Data Bank under the accession numbers and . The accession number of GMP complexed LpcN-II is . Structured digital abstract andby() andby() Structured digital abstract was added on 5 March 2014 after original online publication]

A Dinuclear Cadmium(II) Schiff Base Thiocyanato Complex: Crystal Structure and Fluorescence

A new dinuclear cadmium(II) complex, Cd(L)(NCS)](2) (1) has been synthesized using a potentially tetradentate Schiff base ligand HL, 2-((E)-(2-(diethylamino) ethylimino) methyl)-6-methoxyphenol, obtained by the condensation of 2-diethylaminoethylamine and o-vanillin, and characterized by different physicochemical techniques. Crystal structure of the title complex was unambiguously established by single crystal X-ray diffraction which reveals that metal centers are connected by bridging phenolato and chelating methoxy oxygen atoms of the coordinating Schiff bases and embedded in severely distorted octahedral geometries. Fluorescence properties of the ligand and its complex, studied at room temperature indicate that later may serve as strong fluorescent

Effects of temperature on complexes I and II mediated respiration, ROS generation and oxidative stress status in isolated gill mitochondria of the mud crab Scylla serrata

Effects of fluctuations in habitat temperature (18-30 degrees) on mitochondrial respiratory behavior and oxidative metabolic responses in the euryhaline ectotherm Scylla serrate are not fully understood. In the present study, effects of different temperatures ranging from 12 to 40 degrees C on glutamate and succinate mediated mitochondrial respiration, respiratory control ratio (RCR), ATP generation rate, ratio for the utilization of phosphate molecules per atomic oxygen consumption (P/O), levels of lipid peroxidation and H2O2 in isolated gill mitochondria of S. serrata are reported. The pattern of variation in the studied parameters was similar for the two substrates at different temperatures. The values recorded for RCR ( >= 3) and P/O ratio (1.4-2.7) at the temperature range of 15-25 degrees C were within the normal range reported for other animals (3-10 for RCR and 1.5-3 for P/O). Values for P/O ratio, ATP generation rate and RCR were highest at 18 degrees C when compared to the other assay temperatures. However, at low and high extreme temperatures, i.e. at 12 and 40 degrees C, states III and IV respiration rates were not clearly distinguishable from each other indicating that mitochondria were completely uncoupled. Positive correlations were noticed between temperature and the levels of both lipid peroxidation and H2O2. It is inferred that fluctuations on either side of ambient habitat temperature may adversely influence mitochondria respiration and oxidative metabolism in S. serrata. The results provide baseline data to understand the impacts of acute changes in temperature on ectotherms inhabiting estuarine or marine environments. (C) 2014 Elsevier Ltd. All rights reserved.

Inhibition of Mycobacterium tuberculosis topoisomerase I by m-AMSA, a eukaryotic type II topoisomerase poison

m-AMSA, an established inhibitor of eukaryotic type II topoisomerases, exerts its cidal effect by binding to the enzyme-DNA complex thus inhibiting the DNA religation step. The molecule and its analogues have been successfully used as chemotherapeutic agents against different forms of cancer. After virtual screening using a homology model of the Mycobacterium tuberculosis topoisomerase I, we identified m-AMSA as a high scoring hit. We demonstrate that m-AMSA can inhibit the DNA relaxation activity of topoisomerase I from M. tuberculosis and Mycobacterium smegmatis. In a whole cell assay, m-AMSA inhibited the growth of both the mycobacteria. (C) 2014 Elsevier Inc. All rights reserved.