Finite-size corrections to entanglement in quantum critical systems

We analyze the finite-size corrections to entanglement in quantum critical systems. By using conformal symmetry and density functional theory, we discuss the structure of the finite-size contributions to a general measure of ground state entanglement, which are ruled by the central charge of the underlying conformal field theory. More generally, we show that all conformal towers formed by an infinite number of excited states (as the size of the system L -> infinity) exhibit a unique pattern of entanglement, which differ only at leading order (1/L)(2). In this case, entanglement is also shown to obey a universal structure, given by the anomalous dimensions of the primary operators of the theory. As an illustration, we discuss the behavior of pairwise entanglement for the eigenspectrum of the spin-1/2 XXZ chain with an arbitrary length L for both periodic and twisted boundary conditions.

A comparative solid state (13)C NMR and thermal study of CO(2) capture by amidines PMDBD and DBN

The present work shows study of the CO(2) capture by amidines DBN and PMDBD using (13)C solid-state NMR and thermal techniques. The solid state (13)C NMR analyses demonstrate the formation of a single PMDBD-CO(2) product which was assigned to stable bicarbonate. In the case of DBN, it is shown that two DBN-CO(2) products are formed, which are suggested to be stable bicarbonate and unstable carbamate. The role of water in the DBN-CO(2) capture as well as the stability of the products to environmental moisture was also investigated. The results suggest that the carbamate formation is favored in dry DBN, but in the presence of water it decompose to form bicarbonate. Thermal analysis shows a good gravimetric CO(2) absorption of DBN. Release of CO(2) was found to be almost quantitative from the PMDBDH(+) bicarbonate about 110 degrees C.

Structure of an Odorant-Binding Protein from the Mosquito Aedes aegypti Suggests a Binding Pocket Covered by a pH-Sensitive ""Lid""

Background: The yellow fever mosquito, Aedes aegypti, is the primary vector for the viruses that cause yellow fever, mostly in tropical regions of Africa and in parts of South America, and human dengue, which infects 100 million people yearly in the tropics and subtropics. A better understanding of the structural biology of olfactory proteins may pave the way for the development of environmentally-friendly mosquito attractants and repellents, which may ultimately contribute to reduction of mosquito biting and disease transmission. Methodology: Previously, we isolated and cloned a major, female-enriched odorant-binding protein (OBP) from the yellow fever mosquito, AaegOBP1, which was later inadvertently renamed AaegOBP39. We prepared recombinant samples of AaegOBP1 by using an expression system that allows proper formation of disulfide bridges and generates functional OBPs, which are indistinguishable from native OBPs. We crystallized AaegOBP1 and determined its three-dimensional structure at 1.85 angstrom resolution by molecular replacement based on the structure of the malaria mosquito OBP, AgamOBP1, the only mosquito OBP structure known to date. Conclusion: The structure of AaegOBP1 (= AaegOBP39) shares the common fold of insect OBPs with six alpha-helices knitted by three disulfide bonds. A long molecule of polyethylene glycol (PEG) was built into the electron-density maps identified in a long tunnel formed by a crystallographic dimer of AaegOBP1. Circular dichroism analysis indicated that delipidated AaegOBP1 undergoes a pH-dependent conformational change, which may lead to release of odorant at low pH (as in the environment in the vicinity of odorant receptors). A C-terminal loop covers the binding cavity and this ""lid"" may be opened by disruption of an array of acid-labile hydrogen bonds thus explaining reduced or no binding affinity at low pH.

Imidazolium fumarate

In the title compound, C(3)H(5)N(2)(+)center dot C(4)H(3)O(4)(-), the dihedral angle between the imidazolium ring and the plane formed by the fumarate anion is 80.98 (6)degrees. In the crystal structure, intermolecular O-H center dot center dot center dot O and N-H center dot center dot center dot O hydrogen bonds form extended chains along [100] and [01 (1) over bar], creating a two-dimensional network.

Biotransformations of Substituted Phenylethanols and Acetophenones by Environmental Bacteria

Whole cells of hydrocarbon-degrading bacteria, isolated from polluted sediments in the Santos Estuary (Baixada Santista, Sao Paulo, Brazil), were able to catalyse oxidoreduction reactions with various substituted phenylethanols and acetophenones as substrates. A number of substituted phenylethanols were formed with high (>99 %) enantiomeric excess. The results of microbial oxidation of phenylethanols 2, 3, 5-7 by Acinetobacter sp. 6.4T and the reduction of acetophenones 1a-6a by Serratia marcescens 5.4T showed that the bacteria used as biocatalysts in this study present significant potential for exploitation in biotechnological processes. The reduction of prochiral acetophenones by Serratia marcescens 3.5T yielded optically active alcohols with 90-99 % enantiomeric excess, and Acinetobacter sp. 6.4T is a potential biocatalyst for the oxidation of alcohols.

Identification of archaeal proteins that affect the exosome function in vitro

Background: The archaeal exosome is formed by a hexameric RNase PH ring and three RNA binding subunits and has been shown to bind and degrade RNA in vitro. Despite extensive studies on the eukaryotic exosome and on the proteins interacting with this complex, little information is yet available on the identification and function of archaeal exosome regulatory factors. Results: Here, we show that the proteins PaSBDS and PaNip7, which bind preferentially to poly-A and AU-rich RNAs, respectively, affect the Pyrococcus abyssi exosome activity in vitro. PaSBDS inhibits slightly degradation of a poly-rA substrate, while PaNip7 strongly inhibits the degradation of poly-A and poly-AU by the exosome. The exosome inhibition by PaNip7 appears to depend at least partially on its interaction with RNA, since mutants of PaNip7 that no longer bind RNA, inhibit the exosome less strongly. We also show that FITC-labeled PaNip7 associates with the exosome in the absence of substrate RNA. Conclusions: Given the high structural homology between the archaeal and eukaryotic proteins, the effect of archaeal Nip7 and SBDS on the exosome provides a model for an evolutionarily conserved exosome control mechanism.

Direct evidence of singlet molecular oxygen generation from peroxynitrate, a decomposition product of peroxynitrite

The decomposition of peroxynitrite to nitrite and dioxygen at neutral pH follows complex kinetics, compared to its isomerization to nitrate at low pH. Decomposition may involve radicals or proceed by way of the classical peracid decomposition mechanism. Peroxynitrite (ONOOH/ONOO(-)) decomposition has been proposed to involve formation of peroxynitrate (O(2)NOOH/O(2)NOO(-)) at neutral pH (D. Gupta, B. Harish, R. Kissner and W. H. Koppenol, Dalton Trans., 2009, DOI: 10.1039/b905535e, see accompanying paper in this issue). Peroxynitrate is unstable and decomposes to nitrite and dioxygen. This study aimed to investigate whether O(2)NOO(-) formed upon ONOOH/ONOO(-) decomposition generates singlet molecular oxygen [O(2) ((1)Delta(g))]. As unequivocally revealed by the measurement of monomol light emission in the near infrared region at 1270 nm and by chemical trapping experiments, the decomposition of ONOO(-) or O(2)NOOH at neutral to alkaline pH generates O(2) ((1)Delta(g)) at a yield of ca. 1% and 2-10%, respectively. Characteristic light emission, corresponding to O(2) ((1)Delta(g)) monomolecular decay was observed for ONOO(-) and for O(2)NOOH prepared by reaction of H(2)O(2) with NO(2)BF(4) and of H(2)O(2) with NO(2)(-) in HClO(4). The generation of O(2) ((1)Delta(g)) from ONOO(-) increased in a concentration-dependent manner in the range of 0.1-2.5 mM and was dependent on pH, giving a sigmoid pro. le with an apparent pK(a) around pD 8.1 (pH 7.7). Taken together, our results clearly identify the generation of O(2) ((1)Delta(g)) from peroxynitrate [O(2)NOO(-) -> NO(2)(-) + O(2) ((1)Delta(g))] generated from peroxynitrite and also from the reactions of H(2)O(2) with either NO(2)BF(4) or NO(2)(-) in acidic media.

A microscopic view of substitution reactions solvated by ionic liquids

The solvation effect of the ionic liquid 1-N-butyl-3-methylimidazolium hexafluorophosphate on nucleophilic substitution reactions of halides toward the aliphatic carbon of methyl p-nitrobenzenesulfonate (pNBS) was investigated by computer simulations. The calculations were performed by using a hybrid quantum-mechanical/molecular-mechanical (QM/MM) methodology. A semiempirical Hamiltonian was first parametrized on the basis of comparison with ab initio calculations for Cl(-) and Br(-) reaction with pNBS at gas phase. In condensed phase, free energy profiles were obtained for both reactions. The calculated reaction barriers are in agreement with experiment. The structure of species solvated by the ionic liquid was followed along the reaction progress from the reagents, through the transition state, to the final products. The simulations indicate that this substitution reaction in the ionic liquid is slower than in nonpolar molecular solvents proper to significant stabilization of the halide anion by the ionic liquid in comparison with the transition state with delocalized charge. Solute-solvent interactions in the first solvation shell contain several hydrogen bonds that are formed or broken in response to charge density variation along the reaction coordinate. The detailed structural analysis can be used to rationalize the design of new ionic liquids with tailored solvation properties. (c) 2008 American Institute of Physics.

DNA damage by sulfite autoxidation catalyzed by cobalt complexes

DNA damage was investigated in the presence of sulfite, dissolved oxygen and cobalt(II) complexes with glycylglycylhistidine, glycylhistidyllysine, glycylglycyltyrosylarginine and tetraglycine. These studies indicated that only Co(II) complexed with glycylglycylhistidine (GGH) induced DNA strand breaks at low sulfite concentrations (1-80 mu M) via strong oxidants formed in the reaction. In the presence of the other complexes, some damage occurred only in the presence of high sulfite concentrations (0.1-2.0 mM) after incubation for 4 h. In the presence of GGH, Co(II) and dissolved O(2), DNA damage must involve a reactive high-valent cobalt complex. The damaging effect was increased by adding S(IV), due to the oxysulfur radicals formed as intermediates in S(IV) autoxidation catalyzed by the complex. SO(3)(center dot)-S-, HO(center dot) and H(center dot) radicals were detected by EPR-spin trapping experiments with DMPO (5,5-dimethyl-1-pyrroline N-oxide). The results indicate that Co(II) binds O2 in the presence of GGH, and leads to the formation of a DMPO-HO(center dot) adduct without first forming free superoxide or hydroxyl radical, supporting the participation of a reactive high-valent cobalt complex.

Hybrid layer-by-layer assembly based on animal and vegetable structural materials: multilayered films of collagen and cellulose nanowhiskers

Layer-by-layer (LBL) assembly was used to combine crystalline rod-like nanoparticles obtained from a vegetable source, cellulose nanowhiskers (CNWs), with collagen, the main component of skin and connective tissue found exclusively in animals. The film growth of the multilayered collagen/CNW was monitored by UV-Vis spectroscopy and ellipsometry measurements, whereas the film morphology and surface roughness were characterized by SEM and AFM. UV-Vis spectra showed the deposition of the same amount of collagen, 5 mg m(-2), in each dipping cycle. Ellipsometry data showed an increment in thickness with the number of layers, and the average thickness of each bilayer was found to be 8.6 nm. The multilayered bio-based nanocomposites were formed by single layers of densely packed CNWs adsorbed on top of each thin collagen layer where the hydrogen bonding between collagen amide groups and OH groups of the CNWs plays a mandatory role in the build-up of the thin films. The approach used in this work represents a potential strategy to mimic the characteristics of natural extracellular matrix (ECM) which can be used for applications in the biomedical field.

Cloud point extraction to avoid interferences by structured background on nickel determination in plant materials by FAAS

An analytical procedure based on microwave-assisted digestion with diluted acid and a double cloud point extraction is proposed for nickel determination in plant materials by flame atomic absorption spectrometry. Extraction in micellar medium was successfully applied for sample clean up, aiming to remove organic species containing phosphorous that caused spectral interferences by structured background attributed to the formation of PO species in the flame. Cloud point extraction of nickel complexes formed with 1,2-thiazolylazo-2-naphthol was explored for pre-concentration, with enrichment factor estimated as 30, detection limit of 5 mu g L(-1) (99.7% confidence level) and linear response up to 80 mu g L(-1). The accuracy of the procedure was evaluated by nickel determinations in reference materials and the results agreed with the certified values at the 95% confidence level.

Quantification of some nonsteroidal anti-inflammatory drugs as reducing agents of Cu(II)/4,4 '-dicarboxy-2,2 '-biquinoline complexes in cationic micellar medium

A simple method was developed for spectrophotometric determination of some nonsteroidal anti-inflammatory drugs (meloxicam, piroxicam and tenoxicam) based on the reduction of copper(II) in buffered solution (pH 7.0) and micellar medium containing 4,4'-dicarboxy-2,2'-buffered solution (pH 7.0) and micellar medium containing 4,4'-dicarboxy-2,2'-biquinoline acid. The-biquinoline acid. The absorbance values at 558 nm, characteristic of the formed Cu(I)/4,4'-dicarboxy-2,2'-biquinoline complexes, are linear with the concentrations (5.7-40 mmol L(-1), n = 5) of these oxicams (meloxicam r = 0.998; piroxicam and tenoxicam r = 0.999). The limit of detection values, in mmol L(-1), calculated for meloxicam (2.7), piroxicam (1.2) and tenoxicam (1.3) was obtained with 99% confidence level and the relative standard deviations for meloxicam (3.1%), piroxicam (5.1%) and tenoxicam (1.2%) were calculated using a 25 mmol L(-1) solution (n = 7). Mean recovery values for meloxicam, piroxicam and tenoxicam forms were 100 +/- 6.9, 98.6 +/- 3.6 and 99.4 +/- 2.5%, respectively. The conditional potential of Cu(II)/Cu(I) in complex medium of 7.5 mmol L(-1) BCA was determined to be 629 +/- 11 mV vs. NHE.

On the stabilization of conducting pernigraniline salt by the synthesis and oxidation of polyaniline in hydrophobic ionic liquids

The electrochemical polymerization of aniline in a hydrophobic room-temperature ionic liquid and the spectroelectrochemical characterization of the formed film are presented. The polymerization occurs without the presence of acid in 1-butyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide (BMMITFSI), leading to a very stable electroactive material where no degradation was observed even at high applied potentials. Both in situ UV-Vis and Raman spectroscopic studies provided evidence for the stabilization of pernigraniline salt at high oxidation potentials and that this polyaniline state is the conducting form, as was corroborated by in situ resistance measurements. These data are indicative that low conductivity is not an intrinsic property of pernigraniline salt and this point must be reconsidered.

The role of the steps in the cleavage of the C-C bond during ethanol oxidation on platinum electrodes

Ethanol oxidation has been studied on stepped platinum single crystal electrodes in acid media using electrochemical and Fourier transform infrared (FTIR) techniques. The electrodes used belong to two different series of stepped surfaces: those having (111) terraces with (100) monoatomic steps and those with (111) terraces with (110) monoatomic steps. The behaviors of the two series of stepped surfaces for the oxidation of ethanol are very different. On the one hand, the presence of (100) steps on the (111) terraces provides no significant enhancement of the activity of the surfaces. On the other hand, (110) steps have a double effect on the ethanol oxidation reaction. At potentials below 0.7 V, the step catalyzes the C-C bond cleavage and also the oxidation of the adsorbed CO species formed. At higher potentials, the step is not only able to break the C-C bond, but also to catalyze the oxidation of ethanol to acetic acid and acetaldehyde. The highest catalytic activity from voltammetry for ethanol oxidation was obtained with the Pt(554) electrode.

Surface structure effects on the electrochemical oxidation of ethanol on platinum single crystal electrodes

Ethanol oxidation has been studied on Pt(111), Pt(100) and Pt(110) electrodes in order to investigate the effect of the surface structure and adsorbing anions using electrochemical and FTIR techniques. The results indicate that the surface structure and anion adsorption affect significantly the reactivity of the electrode. Thus, the main product of the oxidation of ethanol on the Pt(111) electrode is acetic acid, and acetaldehyde is formed as secondary product. Moreover, the amount of CO formed is very small, and probably associated with the defects present on the electrode surface. For that reason, the amount of CO(2) is also small. This electrode has the highest catalytic activity for the formation of acetic acid in perchloric acid. However, the formation of acetic acid is inhibited by the presence of specifically adsorbed anions, such as (bi) sulfate or acetate, which is the result of the formation of acetic acid. On the other hand, CO is readily formed at low potentials on the Pt(100) electrode, blocking completely the surface. Between 0.65 and 0.80 V, the CO layer is oxidized and the production of acetaldehyde and acetic acid is detected. The Pt(110) electrode displays the highest catalytic activity for the splitting of the C-C bond. Reactions giving rise to CO formation, from either ethanol or acetaldehyde, occur at high rate at any potential. On the other hand, the oxidation of acetaldehyde to acetic acid has probably the lower reaction rate of the three basal planes.