Amplitude death in complex networks induced by environment

We present a mechanism for amplitude death in coupled nonlinear dynamical systems on a complex network having interactions with a common environment like external system. We develop a general stability analysis that is valid for any network topology and obtain the threshold values of coupling constants for the onset of amplitude death. An important outcome of our study is a universal relation between the critical coupling strength and the largest nonzero eigenvalue of the coupling matrix. Our results are fully supported by the detailed numerical analysis for different network topologies.

Heat and SDS insensitive NDK dimers are largely stabilised by hydrophobic interaction to form functional hexamer in Mycobacterium smegmatis

The primary structure and function of nucleoside diphosphate kinase (NDK), a substrate non-specific enzyme involved in the maintenance of nucleotide pools is also implicated to play pivotal roles in many other cellular processes. NDK is conserved from bacteria to human and forms a homotetramer or hexamer to exhibit its biological activity. However, the nature of the functional oligomeric form of the enzyme differs among different organisms. The functional form of NDKs from many bacterial systems, including that of the human pathogen, Mycobacterium tuberculosis (MtuNDK), is a hexamer, although some bacterial NDKs are tetrameric in nature. The present study addresses the oligomeric property of MsmNDK and how a dimer, the basic subunit of a functional hexamer, is stabilized by hydrogen bonds and hydrophobic interactions. Homology modeling was generated using the three-dimensional structure of MtuNDK as a template; the residues interacting at the monomer-monomer interface of MsmNDK were mapped. Using recombinant enzymes of wild type, catalytically inactive mutant, and monomer-monomer interactive mutants of MsmNDK, the stability of the dimer was verified under heat, SDS, low pH, and methanol. The predicted residues (Gln17, Ser24 and Glu27) were engaged in dimer formation, however the mutated proteins retained the ATPase and GTPase activity even after introducing single (MsmNDK- Q17A, MsmNDK-E27A, and MsmNDK-E27Q) and double (MsmNDK-E27A/Q17A) mutation. However, the monomer monomer interaction could be abolished using methanol, indicating the stabilization of the monomer-monomer interaction by hydrophobic interaction.

Inhibition of cortisol-mediated induction of hepatic tryptophan-2,3-dioxygenase by norepinephrine

Norepinephrine inhibits cortisol-mediated induction of hepatic tryptophan pyrrolase in rats. During cold exposure the stabilization of this enzyme appears to occur by an interaction of corticoids and norepinephrine on the induction process.

The regulation of nitrate reductas enad catalase by amino acids in Neurospora crassa

The induction of nitrate reductase (NADPH:nitrate oxidoreductase, EC 1.6.6.3) by nitrate in Neurospora crassa and its control by amino acids have been studied. The growth-inhibitory amino acids, isoleucine and cysteine as well as the growth-promotory ones, glutamine, asparagine, arginine, histidine and NH4+, repress nitrate reductase effectively. Methionine, tryptophan, proline, aspartic acid and glutamic acid exert little control on nitrate reductase. The repression of nitrate reductase by cysteine, isoleucine, glutamine and asparagine is accompanied by inactivation of the enzyme present initially. The nitrate-induced NADPH-cytochrome c reductase (NADPH:cytochrome c oxidoreductase, EC 1.6.2.3) is also repressed by amino acids which control nitrate reductase, providing further evidence to show that these two enzyme activities may reside in the same protein. Catalase (H2O2:H2O2 oxidoreductase, EC 1.11.1.6) has been found to be induced subsequent to the induction of nitrate reductase by nitrate in N. crassa. The induction of catalase is probably by its substrate H2O2 which would be formed by the interaction of the flavine component of nitrate reductase with oxygen. The amino acids which control nitrate reductase, repress catalase also. The catalase level appears to be determined by the nitrate reductase activity of the mycelia.

Regulation of lipid biosynthesis, sliding motility, and biofilm formation by a membrane-anchored nucleoid-associated protein of mycobacterium tuberculosis

Bacteria use a number of small basic proteins for organization and compaction of their genomes. By their interaction with DNA, these nucleoid-associated proteins (NAPs) also influence gene expression. Rv3852, a NAP of Mycobacterium tuberculosis, is conserved among the pathogenic and slow-growing species of mycobacteria. Here, we show that the protein predominantly localizes in the cell membrane and that the carboxy-terminal region with the propensity to form a transmembrane helix is necessary for its membrane localization. The protein is involved in genome organization, and its ectopic expression in Mycobacterium smegmatis resulted in altered nucleoid morphology, defects in biofilm formation, sliding motility, and change in apolar lipid profile. We demonstrate its crucial role in regulating the expression of KasA, KasB, and GroEL1 proteins, which are in turn involved in controlling the surface phenotypes in mycobacteria.

Albumin-mediated incorporation of water-insoluble therapeutics in layer-by-layer assembled thin films and microcapsules

The present study demonstrates a method to deliver hydrophobic drugs by incorporation into thin films and microcapsules fabricated via a layer-by-layer assembly approach. The hydrophobic molecule binding properties of albumin have been exploited for solubilization of a water-insoluble molecule, pyrene (model drug), by preparation of non-covalent conjugates with bovine serum albumin (BSA). Conjugation with BSA renders a highly negative zeta potential to the previously uncharged pyrene which favors the assembly formation by electrostatic interaction with a positively charged polyelectrolyte, chitosan (at acidic pH). The growth of the assembly was followed by monitoring pyrene absorbance with successive layer deposition. The thin film assembly was demonstrated to be capable of releasing its hydrophobic cargo under physiological conditions. We demonstrated the applicability of this approach by encapsulating a water-insoluble drug, curcumin. These assemblies were further loaded with the anti-cancer drug Doxorubicin. Biocompatible calcium carbonate microparticles were used for capsule preparation. The porous nature of the microparticles allows for the pre-encapsulation of therapeutic macromolecules like protein. The fabrication of protein encapsulated stable microcapsules with hydrophobic molecules incorporated into the shell of the microcapsules has been demonstrated. The microcapsules were further capable of loading hydrophilic molecules like Rhodamine B. Thus, using the approach described, a multi-agent carrier for hydrophobic and hydrophilic drugs as well as therapeutic macromolecules can be envisioned.

Aducts of Lanthanide Perchlorates with N,N,N',N'-Tetramethyl Oxydiacetamide

Lanthanide coordination complexes with unidentate and bidentate amide ligands have been widely reported in the literature[l].In contrast, however, coordination compounds with tridentate ligands and with ligands containing ether oxygen as donor atoms to lanthanides have received little attention. In this paper we report the preparation and characterization of complexes formed by the interaction of the lanthanide perchlorates with N, N, N', N'- tetramethyloxydiacetamide (TMODA). The new complexes have been characterized by analysis, conductance, IR and electronic spectra. In addition, ~H and '3C NMR spectra of the ligand and its diamagnetic La ~+ and y3+ complexes are also discussed.

Nonequilibrium charge transport in an interacting open system: Two-particle resonance and current asymmetry

We use the Lippman-Schwinger scattering theory to study nonequilibrium electron transport through an interacting open quantum dot. The two-particle current is evaluated exactly while we use perturbation theory to calculate the current when the leads are Fermi liquids at different chemical potentials. We find an interesting two-particle resonance induced by the interaction and obtain criteria to observe it when a small bias is applied across the dot. Finally, for a system without spatial inversion symmetry, we find that the two-particle current is quite different depending on whether the electrons are incident from the left or the right lead.

Two-Step Folding of Donor-Acceptor Foldamers

In a series of polymers containing alternately placed electron-rich dialkoxyilaphthalene (DAN) donors and electron-deficient pyromellitic diimide (PDI) acceptors linked by hexa(oxyethylene) (OE-6) segments, the ability to form a folded D-A stack was intentionally disrupted by random inclusion of varying amounts of a comonomer that is devoid of DAN donor units. NMR spectroscopic studies of folding in these copolymers, induced by NH4SCN that coordinates with the OE-6 segments and facilitates the charge-transfer (C-T) induced D-A stacking, clearly reveals the presence of PDI units that are isolated and those that are located at the ends of (D-A),, stacks. Similar conclusions regarding the presence of stacked and unstacked regions along the polymer chain were also inferred from UV-vis spectroscopic studies that probe the evolution of charge-transfer band. One fascinating aspect of these copolymers wits their ability to undergo it two-step folding: first, short (D-A),, stacks are formed by the interaction of the NH4+ ion with some specific regions of the polymer chain, and subsequently these Stacks are further stacked via a two-point interaction with it suitably designed external folding agent that carries a DAN unit and all ammonium group. In the second step, the interaction first occurs by the coordination of the ammonium group of the folding agent with the OE-6 segment, which in turn facilitates the C-T interaction of the DAN unit with the adjacent uncomplexed PDI units along the polymer chain, leading to an increase ill the slacking. Variations of several spectral features, during both UV-vis and NMR spectroscopic titrations, clearly reveal this novel two-step folding process.

Phase transformation, oxidation and hydration of raseodymium sesquioxide

The C→A transformation of Pr2O3 has been examined. The transformation is sluggish and takes place at and above 750°C. C-Pr2O3 is oxidized at a lower temperature than the A-form and oxidation proceeds in two stages in both cases. A hydrate Pr 2O3 . H2O, formed by the interaction of C-Pr2O3 and water at relatively high temperature, is described and its behaviour compared with that of Pr(OH)3. The C-form undergoes hydration at 40°C while the A-form does not. All the observations have been explained in terms of the defect structure of C-Pr2O 3.

Rapid isolation of lysyl-tRNA synthetase from rat liver

The high molecular weight aminoacyl-tRNA synthetase complex (the 24S complex) was isolated from rat liver by ultracentrifugation. The lysyl-tRNA synthetase (E.C. 6.1.1.6) was selectively dissociated by hydrophobic interaction chromatography on 1,6 diaminohexyl agarose followed by hydroxylapatite chromatography and DEAE chromatography. The lysyl-tRNA synthetase dissociated from the 24S synthetase complex was purified approximately to 2700 fold with 14% yield.

Performance comparison of dynamical decoupling sequences for a qubit in a rapidly fluctuating spin bath

Avoiding the loss of coherence of quantum mechanical states is an important prerequisite for quantum information processing. Dynamical decoupling (DD) is one of the most effective experimental methods for maintaining coherence, especially when one can access only the qubit system and not its environment (bath). It involves the application of pulses to the system whose net effect is a reversal of the system-environment interaction. In any real system, however, the environment is not static, and therefore the reversal of the system-environment interaction becomes imperfect if the spacing between refocusing pulses becomes comparable to or longer than the correlation time of the environment. The efficiency of the refocusing improves therefore if the spacing between the pulses is reduced. Here, we quantify the efficiency of different DD sequences in preserving different quantum states. We use C-13 nuclear spins as qubits and an environment of H-1 nuclear spins as the environment, which couples to the qubit via magnetic dipole-dipole couplings. Strong dipole-dipole couplings between the proton spins result in a rapidly fluctuating environment with a correlation time of the order of 100 mu s. Our experimental results show that short delays between the pulses yield better performance if they are compared with the bath correlation time. However, as the pulse spacing becomes shorter than the bath correlation time, an optimum is reached. For even shorter delays, the pulse imperfections dominate over the decoherence losses and cause the quantum state to decay.

Physicochemical behaviour of polyperoxide

Polymeric peroxides are equimolar alternating copolymers formed by the reaction of vinyl monomers with oxygen. Physicochemical studies on the microstructure and chain dynamics of poly(styrene peroxide) PSP were first carried out by Cais and Bovey. We have found that polyperoxides are formed as main intermediates in solid-propellant combustion by the interaction of the monomer and oxygen generated by the decomposition of the polymeric binder and the oxidizer ammonium perchlorate. The experimentally determined heat of degradation and that calculated from thermochemical considerations reveal that polyperoxides undergo highly exothermic primary degradation, the rate-controlling step being the O-O bond dissociation. A random-chain scission mechanism for the thermal degradation of polyperoxides has been proposed. The prediction of unusual exothermic degradation of polyperoxides has resulted in the discovery of an interesting new phenomenon of 'autopyrolysability' in polymers. Several new polyperoxides based on vinyl naphthalene have been synthesized. We have also found that PSP, in conjunction with amines, can be used as initiator at ambient temperature for the radical polymerization of vinyl monomers.

Specificity in the regulation of eukaryotic gene transcription

The regulation of eukaryotic gene transcription poses major challenges in terms of the innumerable protein factors required to ensure tissue or cell-type specificity. While this specificity is sought to be explained by the interaction of cis-acting DNA elements and thetrans-acting protein factor(s), considerable amount of degeneracy has been observed in this interaction. Immunoglobulin heavy chain gene expression in B cells and liver-specific gene expression are discussed as examples of this complexity in this article. Heterodimerization and post-translational modification of transcription factors and the organization of composite promoter elements are strategies by which diverse sets of genes can be regulated in a specific manner using a finite number of protein factors