Kinetics and mechanism of formation and properties of polymers composed of paired macromolecules

The influence of formation conditions on structure and properties of reaction products from two different macromolecules (paired polymers) such as polystyrene and poly(1,1,2-trichlorobutadiene) or polystyrene and poly(vinyl chloride) is investigated. Mechanical properties, molecular mobility, heat resistance, thermostability, and fire resistance are shown to be regulated over a wide range by changing the molecular weight of the initial polymers, their ratio in the reaction mixture, etc. The interaction of different macromolecules in solution to form paired polymers is analyzed theoretically and experimentally. An analysis of structure and properties of the resulting products by refractometry, viscometry, sedimentation velocity, statistical analysis, and others shows that paired polymers are systems of the “coil-in-coil” type held together by chemical bonds in the zones of mutual penetration.     

The effect of active site composition and support structure in supported catalysts on the nascent morphology of polyethylene

The formation process and morphology of polyethylene (PE) produced by the non-porous catalyst species tufa- and kaoline-supported Cr(C₅H₅)₂, Zr(BH₄)₄ and TiCl₄ were studied by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The PE morphology was found to depend upon the catalyst active component composition, the polymer yield and the morphology of the support. A quantitative estimation of the PE coverage of the catalyst particles was made.     

Performance of the ablation index during pulmonary vein isolation: periprocedural data from a multicenter registry

Journal of Interventional Cardiac Electrophysiology - Our study aimed to assess the achievement of target ablation index (AI) values and their impact on first-pass pulmonary vein isolation (FPI) as...     

Correction to: The classification of scoliosis braces developed by SOSORT with SRS,ISPO, and POSNA and approved by ESPRM

European Spine Journal -     

Tetrodotoxins Secretion and Voltage-Gated Sodium Channel Adaptation in the Ribbon Worm Kulikovia alborostrata (Takakura, 1898) (Nemertea)

Nemertea is a phylum of marine worms whose members bear various toxins, including tetrodotoxin (TTX) and its analogues. Despite the more than 30 years of studying TTXs in nemerteans, many questions regarding their functions and the mechanisms ensuring their accumulation and usage remain unclear. In the nemertean Kulikovia alborostrata, we studied TTX and 5,6,11-trideoxyTTX concentrations in body extracts and in released mucus, as well as various aspects of the TTX-positive-cell excretion system and voltage-gated sodium (Nav1) channel subtype 1 mutations contributing to the toxins’ accumulation. For TTX detection, an immunohistological study with an anti-TTX antibody and HPLC-MS/MS were conducted. For Nav1 mutation searching, PCR amplification with specific primers, followed by Sanger sequencing, was used. The investigation revealed that, in response to an external stimulus, subepidermal TTX-positive cells released secretions actively to the body surface. The post-release toxin recovery in these cells was low for TTX and high for 5,6,11-trideoxyTTX in captivity. According to the data obtained, there is low probability of the targeted usage of TTX as a repellent, and targeted 5,6,11-trideoxyTTX secretion by TTX-bearing nemerteans was suggested as a possibility. The Sanger sequencing revealed identical sequences of the P-loop regions of Nav1 domains I–IV in all 17 studied individuals. Mutations comprising amino acid substitutions, probably contributing to nemertean channel resistance to TTX, were shown.     

Reversible catalytic dehydrogenation of alcohols for energy storage

Reversibility of a dehydrogenation/hydrogenation catalytic reaction has been an elusive target for homogeneous catalysis. In this report, reversible acceptorless dehydrogenation of secondary alcohols and diols on iron pincer complexes and reversible oxidative dehydrogenation of primary alcohols/reduction of aldehydes with separate transfer of protons and electrons on iridium complexes are shown. This reactivity suggests a strategy for the development of reversible fuel cell electrocatalysts for partial oxidation (dehydrogenation) of hydroxyl-containing fuels.Hydrogenation and dehydrogenation reactions are fundamental in synthetic organic chemistry and used in a variety of large- and small-scale processes for manufacturing chemicals, pharmaceuticals, foods, and fuels. An increased need for energy storage technologies, in large part because of the recent deployment of intermittent renewable energy sources, has generated a renewed interest in hydrogen as a form of chemical energy storage. Hydrogen, which may be used in fuel cells or internal combustion engines, is best-suited for longer-term energy storage and can be stored in the form of a compressed gas or a cryogenic liquid or chemically bonded in hydrides (1). The most attractive hydrogen storage media are liquid organic hydrogen carriers (LOHCs), because they have relatively high hydrogen content and can be transported and distributed using the existing liquid fuel infrastructure (2–5).Two strategies for coupling the chemical energy stored in these LOHCs with an energy storage device include thermal dehydrogenation to provide H₂(g) for a polymer electrolyte membrane (PEM) fuel cell (expression 1) (6) and electrochemical dehydrogenation to yield protons and electrons in a direct alcohol fuel cell (expressions 2 and 3) (2, 7). In the former (acceptorless strategy), hydrogen release from LOHCs frequently requires high reaction temperatures and expensive platinum group metal (PGM) catalysts. Regeneration of the hydrogen-depleted compounds can be achieved with both PGM and less expensive non-PGM catalysts (e.g., nickel-based); however, elevated hydrogen pressures are needed (8, 9). The latter was the basis for an Energy Frontier Research Center around Electrocatalysis, Transport Phenomena, and Materials for Innovative Energy Storage funded by the Department of Energy (Acknowledgments), which assumed the use of a single electrocatalyst for dehydrogenation and hydrogenation of LOHCs that would also simplify the conventional hydrogen storage process (10). The envisioned partial electrochemical dehydrogenation of LOHCs typically involves expensive PGM catalysts (11–18), with weak bases to serve as proton scavengers in lieu of a proton exchange membrane. Reversing the applied potential in the presence of these same components provides a mechanism for regenerating the LOHCs without the need for elevated hydrogen pressure:LH_n ? L + n/2?H₂, [1]LH_n ? L + n?H⁺ + n?e^?, [2]andn/2?O₂ + n?H⁺ + n?e^? ? n/2?H₂O.[3]A thermodynamic analysis of a variety of potential LOHCs showed that cyclic hydrocarbons exhibit high hydrogen contents but that nitrogen heterocycles exhibit lower reaction enthalpies (9, 10). Nitrogen heterocycles are also more practical, because they display energy densities that are comparable with those of liquid hydrogen, and the theoretical open cell potentials of these materials are calculated to be close to or exceed the potential of the hydrogen–oxygen fuel cell (11). In addition, the overpotential of their electrooxidation is also smaller compared with cyclic hydrocarbons (12). However, basic nitrogen heterocycles are not compatible with commonly used acidic proton exchange membranes because of the formation of a nonconductive salt. One alternative class of LOHCs that does not suffer from this problem is hydroxyl-containing compounds (e.g., alcohols and diols) that feature reasonable hydrogen content and low oxidation potentials. Both mono- and polysubstituted alcohols have been proposed as hydrogen storage materials (13) and used as fuel for direct alcohol fuel cells, usually in the form of an aqueous alkaline solution (14).Homogeneous catalysts for the acceptorless dehydrogenation of primary and secondary alcohols for the most part contain precious metals, such as Ru (19), Rh (20), and Ir (21). By comparison, the same reaction with nonprecious, earth-abundant metal catalysts is, so far, a relatively unexplored area in the literature. The first cobalt catalyst bearing a noninnocent bis(dicyclohexylphosphino)amine (PNP^Cy) ligand for acceptorless dehydrogenation of alcohols was reported by Hanson and coworkers (22, 23). Recently, Beller and coworkers (24) have shown hydrogen production from methanol in the presence of KOH with octahedral iron complexes (PNP^iPr)Fe(H)(CO)X [X = BH₄ (1) and X = Br (2)]. Remarkably, very low catalyst loadings (parts per million level) were used, and catalysis was performed at 91 °C, which suggests high thermal stability of these iron complexes and related intermediate species. However, Guan and coworkers (25) have accomplished ester hydrogenation using catalyst 1. In addition to these studies, it was recently shown that the same iron complexes can also efficiently catalyze the reversible dehydrogenation–hydrogenation of N-heterocycles (26). Yamaguchi et al. (27) have also reported Cp*Ir complexes with substituted pyridonate ligands that catalyze the reversible acceptorless dehydrogenation of 1,2,3,4-tetrahydroquinoline to quinoline in boiling xylene. Dehydrogenation is harder and routinely produced lower yields than hydrogenation, but with the 5-trifluoromethylpyridonate ligand, a quantitative yield was achieved in both directions (27). A computational analysis of the proposed catalytic cycle showed that two major pathways are possible: through a bifunctional species with coordinated pyridonate ligand or through a monomeric Cp*Ir(H)Cl complex (28).As part of our ongoing effort to develop another strategy, specifically electrocatalysts for reversible partial oxidation (dehydrogenation) of alcohol-based fuels, we concentrated on the possibility of converting a known dehydrogenation catalyst to an electrocatalyst through separation of protons and electrons. We regard separately extracting protons and electrons in a catalytic dehydrogenation reaction together with the microscopic reverse (29) (i.e., separately injecting protons and electrons to effect substrate hydrogenation) as fundamental in the development of a reversible alcohol dehydrogenation–hydrogenation electrocatalyst. It was clear at the outset that the possibility of oxidation of intermediate species containing metals in low-oxidation states during dehydrogenation and the competing proton reduction to H₂ in the reverse reaction substantially limited our selection of possible candidates. We recently reported electrocatalytic properties of an iridium amino-olefin complex [Ir(trop₂DACH)][OTf], which is capable of catalyzing alcohol dehydrogenation with chemical oxidants as well as electrocatalytic dehydrogenation of primary alcohols with excellent faradaic efficiency (30). Two catalytic systems capable of oxidizing alcohols with a chemical oxidant (ferrocenium cation) in the presence of a base as a proton acceptor have been very recently described in literature (30, 31).In this report, we describe catalytic systems that address both strategies outlined above as part of a unified effort to develop catalysts for reversible dehydrogenation of organic fuels in energy generation and storage reactions. These catalysts show reversible acceptorless (expression 1) and partial oxidative (expression 2) dehydrogenation of alcohols using non-PGM (iron-based) and PGM (iridium-based) catalysts, respectively.     

International use of an academic nephrology World Wide Web site: from medical information resource to business tool

BACKGROUND: Studies of the use of the World Wide Web to obtain medical knowledge have largely focused on patients. In particular, neither the international use of academic nephrology World Wide Web sites (websites) as primary information sources nor the use of search engines (and search strategies) to obtain medical information have been described. METHODS: Visits ("hits") to the Walter Reed Army Medical Center (WRAMC) Nephrology Service website from April 30, 2000, to March 14, 2001, were analyzed for the location of originating source using Webtrends, and search engines (Google, Lycos, etc.) were analyzed manually for search strategies used. RESULTS: From April 30, 2000 to March 14, 2001, the WRAMC Nephrology Service website received 1,007,103 hits and 12,175 visits. These visits were from 33 different countries, and the most frequent regions were Western Europe, Asia, Australia, the Middle East, Pacific Islands, and South America. The most frequent organization using the site was the military Internet system, followed by America Online and automated search programs of online search engines, most commonly Google. The online lecture series was the most frequently visited section of the website. Search strategies used in search engines were extremely technical. CONCLUSIONS: The use of "robots" by standard Internet search engines to locate websites, which may be blocked by mandatory registration, has allowed users worldwide to access the WRAMC Nephrology Service website to answer very technical questions. This suggests that it is being used as an alternative to other primary sources of medical information and that the use of mandatory registration may hinder users from finding valuable sites. With current Internet technology, even a single service can become a worldwide information resource without sacrificing its primary customers.     

The classification of scoliosis braces developed by SOSORT with SRS,ISPO, and POSNA and approved by ESPRM

Purpose

Studies have shown that bracing is an effective treatment for patients with idiopathic scoliosis. According to the current classification, almost all braces fall in the thoracolumbosacral orthosis (TLSO) category. Consequently, the generalization of scientific results is either impossible or misleading. This study aims to produce a classification of the brace types.

Methods

Four scientific societies (SOSORT, SRS, ISPO, and POSNA) invited all their members to be part of the study. Six level 1 experts developed the initial classifications. At a consensus meeting with 26 other experts and societies’ officials, thematic analysis and general discussion allowed to define the classification (minimum 80% agreement). The classification was applied to the braces published in the literature and officially approved by the 4 scientific societies and by ESPRM.

Results

The classification is based on the following classificatory items: anatomy (CTLSO, TLSO, LSO), rigidity (very rigid, rigid, elastic), primary corrective plane (frontal, sagittal, transverse, frontal & sagittal, frontal & transverse, sagittal & transverse, three-dimensional), construction—valves (monocot, bivalve, multisegmented), construction—closure (dorsal, lateral, ventral), and primary action (bending, detorsion, elongation, movement, push-up, three points). The experts developed a definition for each item and were able to classify the 15 published braces into nine groups.

Conclusion

The classification is based on the best current expertise (the lowest level of evidence). Experts recognize that this is the first edition and will change with future understanding and research. The broad application of this classification could have value for brace research, education, clinical practice, and growth in this field.

     

Interpolymer complexes of (co)poly(vinyl ethers) of glycols and poly(carboxylic acids)

The complex formation reaction of poly(vinyl ethers) of ethylene glycol ( 1 ), poly(vinyl ether) of diethylene glycol ( 2 ), copolymers of vinyl ether of ethylene glycol and vinyl butyl ether ( 3a–3c ) with poly(acrylic acid) (PAA) and poly(methacrylic acid) (PMAA) was studied by conductimetric, viscometric and spectroturbidimetric methods in aqueous solution. It is shown that 1 and 2 do not form polycomplexes with PAA. While an introduction of hydrophobic vinyl butyl ether fragments into the structure of 1 enhances the complexation processes with respect to poly(carboxylic acids), the composition of the polycomplexes is independent of the mixing order of interacting components, temperature and composition of the copolymers. An addition of organic solvents to the aqueous solution of the polycomplexes leads to the cooperative destruction of polycomplex particles. An analysis of IR spectra of the polycomplex films shows the existence of ? COOH dimers, hydrogen bonds between hydroxyl groups and carboxylic groups as well as ester bonds.