Markov chain modeling of polymer translocation through pores

We solve the Chapman-Kolmogorov equation and study the exact splitting probabilities of the general stochastic process which describes polymer translocation through membrane pores within the broad class of Markov chains. Transition probabilities, which satisfy a specific balance constraint, provide a refinement of the Chuang-Kantor-Kardar relaxation picture of translocation, allowing us to investigate finite size effects in the evaluation of dynamical scaling exponents. We find that (i) previous Langevin simulation results can be recovered only if corrections to the polymer mobility exponent are taken into account and (ii) the dynamical scaling exponents have a slow approach to their predicted asymptotic values as the polymer's length increases. We also address, along with strong support from additional numerical simulations, a critical discussion which points in a clear way the viability of the Markov chain approach put forward in this work.     

Speciation of the Vanadium (III) Complexes with 6-Methylpicolinic Acid,Salicylic Acid and Phthalic Acid

The complex species formed in aqueous solutions (25 °C, I=3.0 mol⋅dm⁻³ KCl ionic medium) between the V(III) cation and the ligands 6-methylpicolinic acid (MePic, HL), salicylic acid (H₂Sal, H₂L) and phthalic acid (H₂Phtha, H₂L) have been studied by potentiometric and spectrophotometric measurements. Application of the least-squares computer program LETAGROP to the experimental emf(H) data, taking into account the hydrolytic species and hydrolysis constants of V(III), indicates that under the employed experimental conditions the complexes [VL]²⁺, [V(OH)L]⁺, [V(OH)₂L], [V(OH)₃L]⁻, [VL₂]⁺, [VL₃] and [V₂OL₄] form in the vanadium(III)–MePic system. Were observed the complexes [VL]⁺, [VL₂]⁻, [V(OH)L₂]²⁻ and [VL₃]³⁻ in the vanadium(III)–H₂Sal system, and the species [VHL]²⁺, [VL]⁺, [V(OH)L], [VHL₂], [VL₂]⁻, [V(OH)L₂]²⁻, [V(OH)₂L₂]³⁻ and [VL₃]³⁻ in the vanadium(III)–H₂Phtha system. The stability constants of these complexes were determined by potentiometric measurements, and spectrophotometric measurements were made in order to perform a qualitative characterization of the complexes formed in aqueous solution.     

Metallomic study on plasma samples from Nile tilapia using SR-XRF and GFAAS after separation by 2D PAGE: initial results

An investigation was made on plasma samples obtained after protein separation. The proteome of the plasma of Nile tilapia (Oreochromis niloticus) was separated by 2D PAGE, and manganese and zinc in protein spots was qualitatively and quantitatively determined by synchrotron radiation X-ray fluorescence (SR-XRF) and graphite furnace atomic absorption spectrometry (GFAAS). Manganese and zinc are present in four and six plasma protein spots, respectively. These ions are bound to proteins with molecular weights ranging from 19 to 70?kDa and with isoelectric point (pI) ranging from 4.7 to 6.3. The concentrations of manganese and zinc bound to these proteins as determined by GFAAS following acid digestion of the spots range from 0.8 to 2.6?mg of manganese, and from 1.0 to 6.3?mg of zinc, respectively, per g of protein.

Infrared (810 nm) low-level laser therapy in rat achilles tendinitis: a consistent alternative to drugs

Nonsteroidal anti-inflammatory drugs (NSAIDs) are widely used and can reduce musculoskeletal pain in spite of the cost of adverse reactions like gastrointestinal ulcers or cardiovascular events. The current study investigates if a safer treatment such as low-level laser therapy (LLLT) could reduce tendinitis inflammation, and whether a possible pathway could be through inhibition of either of the two-cyclooxygenase (COX) isoforms in inflammation. Wistar rats (six animals per group) were injected with saline (control) or collagenase in their Achilles tendons. Then, we treated them with three different doses of IR LLLT (810 nm; 100 mW; 10 s, 30 s and 60 s; 3.57 W cm(-2); 1 J, 3 J, 6 J) at the sites of the injections, or intramuscular diclofenac, a nonselective COX inhibitor/NSAID. We found that LLLT dose of 3 J significantly reduced inflammation through less COX-2-derived gene expression and PGE(2) production, and less edema formation compared to nonirradiated controls. Diclofenac controls exhibited significantly lower PGE(2) cytokine levels at 6 h than collagenase control, but COX isoform 1-derived gene expression and cytokine PGE(2) levels were not affected by treatments. As LLLT seems to act on inflammation through a selective inhibition of the COX-2 isoform in collagenase-induced tendinitis, LLLT may have potential to become a new and safer nondrug alternative to coxibs.     

Interfacial behavior of OEG-linear dendron monolayers: aggregation, nanostructuring, and electropolymerizability

We report on the interesting interfacial behavior of oligoethylene glycol or OEGylated linear dendron monolayers at the air-water interface as a function of (a) carbazole dendron generation, (b) the length of the OEG units, and (c) the surface pressure applied upon compression. Surface pressure-area isotherms, hysteresis studies, and isobaric creep measurement revealed a structure-property relationship consistent with the hydrophilic-lipophilic balance of a linear dendron with the OEG group serving as the surface anchor to the water subphase. AFM studies revealed that all the OEGylated carbazole dendrons self-assemble into spherical morphology at low surface pressures but form ribbonlike structures as the surface pressure is increased. This nanostructuring is primarily imparted by the increase in van der Waals forces with increasing amount of carbazole units per dendron generation on a hydrophilic mica surface. Further, electrochemical cross-linking of the carbazole molecules by cyclic voltammetery (CV) on doped Si wafer has enabled the formation of an LB film monolayer with a secondary level of organization in the monolayer imparted by the inter- and intramolecular cross-linking among the carbazole units. This study should provide a basis for monolayer film materials based on combining the LB technique and electrochemical cross-linking for nanostructuring superstructures at the air-water interface.     

Dissociation of deprotonated microcystin variants by collision-induced dissociation following electrospray ionization

Microcystins (MC) are a family of hepatotoxic cyclic heptapeptides produced by a number of different cyanobacterial species. Considering the recent advances in the characterization of deprotonated peptides by mass spectrometry, the fragmentation behavior of four structurally related microcystin compounds was investigated using collision-induced dissociation (CID) experiments on an orbitrap mass spectrometer. It is demonstrated in this study that significant structural information can be obtained from the CID spectra of deprotonated microcystins. A predominant ring-opening reaction at the isoMeAsp residue, as well as two major complementary fragmentation pathways, was observed, reducing the complexity of the product ion spectra in comparison with spectra observed from protonated species. This proposed fragmentation behavior was applied to characterize [Leu(1)]MC-LR from a cyanobacterial cell extract. In conclusion, CID spectra of microcystins in the negative ion mode provide rich structurally informative mass spectra which greatly enhance confidence in structural assignments, in particular when combined with complementary positive ion CID spectra.     

Synthesis and application of imprinted polyvinylimidazole-silica hybrid copolymer for Pb2+ determination by flow-injection thermospray flame furnace atomic absorption spectrometry

A novel ion imprinted polyvinylimidazole-silica hybrid copolymer (IIHC) was synthesized and used as a selective solid sorbent for Pb(2+) ions preconcentration using an on-line solid phase extraction (SPE) system coupled to TS-FF-AAS. The ionic hybrid sorbent was prepared using 1-vinylimidazole and 3-(trimethoxysilyl)propylmethacrylate as monomers, Pb(2+) ions as template, tetraethoxysilane as reticulating agent and 2,2'-azobis-isobutyronitrile as initiator. The best on-line SPE conditions concerning sorption behavior, including sample pH (6.46), buffer concentration (9.0 mmol L(-1)), eluent (HNO(3)) concentration (0.5 mol L(-1)) and preconcentration flow rate (4.0 mL min(-1)), were optimized by means of full factorial design and Doehlert matrix. The analytical curve ranged from 2.5 to 65.0 μg L(-1) (r=0.999) with limit of detection of 0.75 μg L(-1); the precision (repeatability) calculated as relative standard deviation (n=10) was 5.0 and 3.6% for Pb(2+) concentration of 10.0 and 60.0 μg L(-1), respectively. From on-line breakthrough curve, column capacity was 3.5 mg g(-1). Preconcentration factor (PF), consumptive index (CI) and concentration efficiency (CE) were 128.0, 0.16 mL and 25.6 min(-1), respectively. The selective performance of the sorbent, based on relative selectivity coefficient, was compared to NIC (non imprinted copolymer) for the binary mixture Pb(2+)/Cd(2+), Pb(2+)/Cu(2+) and Pb(2+)/Zn(2+). The results showed that ion imprinted polyvinylimidazole-silica hybrid polymer had higher selectivity for Pb(2+) than NIC at 64.9, 16.0 and 8.8 folds. The developed method was successfully applied for highly sensitive and selective Pb(2+) determination in different kinds of water samples, parenteral solutions and urine. Accuracy was also assessed by analyzing certified reference fish protein (DORM-3) and marine sediment (MESS-3 and PACS-2) with satisfactory results.     

Chemical constituents of the methanolic extract of leaves of Leiothrix spiralis Ruhland and their antimicrobial activity

Chemical fractionation of the methanolic extract of leaves of Leiothrix spiralis Ruhland afforded the flavonoids luteolin-6-C-β-D-glucopyranoside (1), 7-methoxyluteolin-6-C-β-D-glucopyranoside (2), 7-methoxyluteolin-8-C-β-D-glucopyranoside (3), 4'-methoxyluteolin-6-C-β-D-glucopyranoside (4), and 6-hydroxy-7-methoxyluteolin (5), and the xanthones 8-carboxymethyl-1,5,6-trihydroxy-3-methoxyxanthone (6), 8-carboxy-methyl-1,3,5,6-tetrahydroxyxanthone (7). Methanolic extract, fractions, and isolated compounds of the leaves of L. spiralis were assayed against Gram-positive (Staphylococcus aureus, Bacillus subtilis and Enterococcus faecalis) and Gram-negative bacteria (Escherichia coli, Pseudomonas aeruginosa, Salmonella setubal and Helicobacter pylori) and fungi (the yeasts Candida albicans, C. tropicalis, C. krusei and C. parapsilosis). We observed the best minimum inhibitory concentration values for the methanolic extract against Candida parapsilosis, for the fraction 5 + 6 against Gram-negative bacteria E. coli and P. aeruginosa, and compound 7 against all tested Candida strains. The methanolic extract contents suggest that this species may be a promising source of compounds to produce natural phytomedicines.     

A Neumann problem for the KdV equation with Landau damping on a half-line

We consider the initial-boundary value problem on a half-line for the KdV equation with Landau damping. We study traditionally important problems of the theory of nonlinear partial differential equations, such as global in time existence of solutions to the initial-boundary value problem and the asymptotic behavior of solutions for large time.     

Examples of almost Einstein structures on products and in cohomogeneity one

Almost Einstein manifolds are conformally Einstein up to a scale singularity, in general. This notion comes from conformal tractor calculus. In the current paper we discuss almost Einstein structures on closed Riemannian product manifolds and on 4-manifolds of cohomogeneity one. Explicit solutions are found by solving ordinary differential equations. In particular, we construct three families of closed 4-manifolds with almost Einstein structure corresponding to the boundary data of certain unimodular Lie groups. Two of these families are Bach-flat, but neither (globally) conformally Einstein nor half conformally flat. On products with a 2-sphere we find an exotic family of almost Einstein structures with hypersurface singularity as well.