bluuebunny/crossref_metadata_2025 huggingface dataset:
Strahlenchemische Darstellung von Polysulfonen bei Verschiedenen Temperaturen
Authors: Schneider Christel , Denaxas Jannis , Hummel Dieter
Published: June 2010

Under the influence of 60Co‐γ‐rays copolymers of vinyl chloride and sulfur dioxide have been prepared at various temperatures between + 20 and − 75°C.; the molar ratio of vinyl chloride and sulfur dioxide in the polysulfone formed at + 20°C. is about 2. With decreasing temperatures the sulfur content of the polysulfone increases, and at −75°C. the molar ratio VC/SO2 in the copolymer averages about 1.4. For all temperatures used the composition of the polysulfone is independent of the composition of the reaction mixture. However, the polymerization rate is dependent on the vinyl chloride concentration in the feed. The temperature coefficient of the polymerization rate is negative for vinyl chloride concentrations up to 50 mole‐% in the reaction mixture. The reaction mechanism‐according to the reaction temperature–is presumed to be a radical copolymerization between the vinyl chloride monomer and a 1:1 vinyl chloride/SO2 complex, or between two vinyl chloride/SO2 complexes. Furthermore, the eopolymerization of 2‐vinylpyridine, 4‐vinylpyridine, and 4‐vinylcyclohexene with SO2 was investigated. No polysulfone was formed in the case of the vinylpyridines, neither at room temperature nor at low temperatures. 4‐Vinylcyclohexene, on the other hand, formed a polysulfone.
The mechanism of particle formation in polymer hydrosols. I. Kinetics of Aqueous Polymerization of Methyl Methacrylate
Authors: Fitch Robert M. , Prenosil Michael B. , Sprick Karen J.
Published: June 2010

The polymerization of an aqueous solution of methyl methacrylate has been shown to obey classical steady‐state homogeneous kinetics at low initiator concentrations ([I] < 0.463 mM) even though the system is colloidal. At higher [I] (> 0.925 mM) classical heterogeneous kinetics are found. Particle formation, observed by Tyndall scattering, occurs when the polymer concentration reaches approximately 0.03 g/100 ml regardless of the rate of polymerization. This is taken as evidence that in this system particle formation is thermodynamically controlled. The particles are formed during the earliest stages of the polymerization when nonsteady‐state kinetics obtain. In this region the molecular weight of the polymer increases rapidly. After the steady‐state is attained, the average molecular weight remains constant until the Norrish‐Trommsdorff “gel effect” becomes important.
Instabilities in theoretical chemistry. II. Mixing of different instabilities
Authors: Trig C.
Published: June 2010

As discussed in the preceding paper, the Hartree‐Fock instabilities have now been shown1‐3 to occur in a rigid symmetrical lattice, giving rise to lower energy states than the Hartree‐Fock symmetrical wave function. It has also been pointed out already4a, 15 that the charge density waves (“singlet instability”) may possibly enhance a core distortion. As a matter of fact, as far as polyenes are concerned, there are experimental indications that core alternation occurs: for linear polyenes, the relevant experimental data consists of x‐ray analysis of carotenoid crystals, vibrational frequencies spectra,4a and, perhaps less directly, the vibrational coupling in optical spectra4b; even in cyclic polyenes (18‐annulene), core alternation may possibly take place.5 Thus, the first question arises: how can different instabilities coexist in the same ground state? This problem has been partially studied by different authors2a,6, but, as Paldus and Čížek pointed out1,2b, they generally disregarded the possibility that “number density fluctuations” take place between the atoms, inducing or enhancing bond order alternation, and not only on the atoms, inducing alternating electronic charges. Indeed Harris and Falicov6 have considered core alternation together with spin density waves, but, by replacing the long range exchange potential by a constant mean value, they really miss its specific effect on bond alternation. So the question of the nature of the Hartree‐Fock ground state of long chain polyenes is still open. The different types of instability are each characterized by the symmetry properties of the wave function with respect to time reversion, and to the one‐electron space and spin coordinate transformations.2a As these transformations involve different coordinate spaces, they may be compatible; however the onset of one instability generally lessens the other instabilities: in a variational procedure, mixing with excited states is less favorable as soon as an energy gap already exists. Our purpose is to develop some examples of these consistency conditions.
Thermal dehydrochlorination of poly(vinyl chloride) models in the liquid phase
Authors: Mayer Z. , Obereigner B. , Lim D.
Published: June 2010

An investigation was made of the kinetics of thermal dehydrochlorination of 8‐chlorohexadecane, 2,4‐dichloropentadecane, 4‐chloro‐2‐dodecene, 8‐chloro‐6‐tridecene, 6‐chloro‐2,4‐octadiene, and 7‐chloro‐3,5‐nonadiene in the liquid phase in an inert gas.

The course of the reaction is accelerated by the presence of free hydrogen chloride and slowed down by conjugated dienes and trienes. Destruction of the model compounds leads to the formation of oligomers and telomers, some of which were isolated and their elementary composition and molecular weight determined. The reaction occurs much faster in nitrobenzene, compared with the dehydrochlorination of a model without solvent.

With respect to its complicated mechanism, the dehydrochlorination reaction was characterized from the kinetic viewpoint by its initial rate kO. Parameters E and A were estimated from the temperature dependence kO = A exp(−E/RT).

It follows from the experimental results and from the comparison of thermal dehydrochlorination reactions in the gas and liquid phases and in poly(vinyl chloride) that the reaction under investigation occurs by a ionic mechanism in the liquid phase, and most probably also in the polymer.
Spectroscopy of protein monolayers: A transition in β‐lactoglobulin films
Authors: Loeb George I.
Published: June 2010

Infrared studies of the amide I band of transferred films of β‐lactoglobulin‐B spread on 0.5 M KC1 have been obtained via the multiple internal reflection (MIR) technique. The spectra indicate that the conformations of the films change with surface pressure. The data are consistent with a denatured molecule as the predominant species at high area per molecule and a species whose secondary structure is similar to that of the native molecule at high degree of compression. The transition may be reversed by re‐expansion of the film after compression. Approximately equal amounts of native‐type and denatured type spectral components are found at 6 dynes/cm at room temperature.
The substructure of crystalline cellulose and chitin microfibrils
Authors: Gardner K. H. , Blackwell J.
Published: June 2010

The fine structures of the highly crystalline cellulose microfibrils from the cell walls of the marine algae Valonia ventricosa, and the extra cellular chitin spines of the euryhaline diatoms Thalassiosira fluviatilis, have been investigated by observation of deformed and un‐deformed specimens in the electron microscope. On treatment with ultrasonic vibrations, the purified Valonia cell wall broke down into long microfibrils, with approximate cross section 210 Å × 110Å Some of these microfibrils appeared to have been disruptedby the ultra‐sonic treatment, and consisted of elementary fibrillar fragments, with a regular width of ∼35 Å, or multiples thereof. Deformation by stretching or mylar films separated the micro‐fibril into smaller fibrils with width of ∼35 Å. Striations on the intact microfibrils are in‐terpreted in terms of a substructure of these elementary fibrils.

A similar substructure is observed for the crystalline chitin of the diatom spines. The spines have a lamella morphology, and break down into ribbons with widths of 200‐300 Å, and a thickness of 20 Å. These ribbons were generally observed as lateral or stacked aggregates. Further disruption by ultrasonic vibrations and deformation shows that these ribbons are made up of smaller fibrils with a width of ∼35 Å Striations are observed on the intact ribbons indicating the presence of substructure.
Elementary cellulose fibrils possess an entropic deformation mechanism
Authors: Stöckmann Volker E.
Published: June 2010

In order to obtain information on the structure of cellulose elementary fibrils, temperature coefficients of equilibrium tensile forces were determined. A force‐temperature coefficient is identical with the negative amount of entropy change during deformation. Thus, data on thermoelasticity can provide insight into the basic mechanism of deformation, hence, into the structure of the deformed specimen. The thermoelastic behavior of native and mercerized ramie fibers was investigated as a function of moisture content. All of the measured force‐temperature curves possess positive slopes. The effect of temperature on undeformed length and on moisture content required that temperature coefficients be corrected accordingly. After incorporating the corrections, only moisture‐free fibers possess positive slopes. Water‐swollen fibers show large negative slopes, whereas air‐dried fibers exhibit a behavior between the two extremes. Positive slope implies entropy‐elastic deformation. Because dry fibers deform in an entropy‐elastic manner, disordered regions within elementary fibrils must exist. The degree of disorder must be higher in the mercerized than in the native fibers. Rearrangement of water molecules during deformation towards higher disorder is evoked to account for the increasing entropy of the water‐swollen fibers.
Synthesis of cellulose graft copolymers with mixtures of N‐vinyllactams and vinyl monomers
Authors: Ibraghimov F. , Mukhamedaliyev D. , Gafurov T. G. , Usmanov Kh. U.
Published: June 2010

Synthesis of cellulose graft copolymers with mixtures of N‐vinyllactams (VL) and vinyl monomers (VM), the definition of the copolymer composition of the grafted chain, coefficients of relative monomers reactiveness, solubility, characteristic viscosity, and the effect of the initial monomer ratio on the obtained products properties are reported.

N‐vinylpirrolidone, N‐vinylcaprolactam, and methylmethacrylate butylmethacrylate, acrylonitrile, and β‐hydroxyacrylate glycidic ether were used in the investigations as well as preparations of cotton fibers, fibers of diacetylcellulose, and fibers of viscose staple rayon.

VL and VM were grafted onto cellulose in the oxidative‐reductive systems of bivalent ferrous and hydrogen peroxide at various molar ratio (0.1:0.9; 0.25:0.75; 0.5:0.5; 0.75:0.25; 0.9:0.1). The VL‐VM copolymer side chains were hydrolytically isolated from the grafted part of cellulose. The values of rVL and rVM were plotted as those of rVL and rVM for the static polymerization. It is found that the composition of the grafted cellulose side chains was identical with that of the copolymers, which have been obtained by the bulk method. The copolymers solubility remained the same after the grafted cellulose chain was isolated by the classic method of copolymerization in the absence of cellulose.

The graft copolymers were identified by IR spectra. The mechanism of the graft copolymerization is given for all the abovementioned monomers and cellulose.
The effect of ultraviolet irradiation on photo‐oxidation and crosslinking reactions in a poly(vinyl alcohol)‐ammonium dichromate system
Authors: Bravar M. , Rek V. , Kostelac‐Biffl R.
Published: June 2010

The chemical transformations of poly(vinyl alcohol) (PVA) film by ammonium dichromate on exposure to ultraviolet irradiation have been investigated. The oxidative transformation was followed spectrophotometrically and the extent of crosslinking reaction by measuring the solubility and the viscosity changes of the exposed film. The influence of the time of exposure as well as the concentration of ammonium dichromate on the above reactions has been established.

The ultraviolet and infrared data of exposed film showed that hydroxyl groups are oxidized to carbonyl groups. Absorption bands at 230, 270, and 330 mm, attributed to the presence of the double bond conjugated with carbonyl, were increased during the exposed period.

The bromination and hydrogenation of the dissolved films decreased those absorptions. This indicated that the content of the carbonyl groups and double bonds were increased during the irradiation.

The partial insolubilization of the exposed film was attributed to the formation of complexes of alcohol and carbonyl groups to chromic ions formed by reduction of the dichromate.
Effectivity of organic phosphites
Authors: Kovács E. , Wolkóber Z.
Published: June 2010

The behavior of organic phosphites as antioxidants for polyethylene, costabilizer, and metal‐deactivator for poly(vinyl chloride) (PVC), has been studied by Thermox‐meter and Brabander plastograph. It was found, that their antioxidative effectivity is determined by the self‐stability of the investigated phosphites, namely the volatility, the hydrolysis and oxidation sensitivity. At the same time, the stabilizing and metal‐deactivating effect for PVC with this technique did not show significant differences.
Inhibiting activity and thermooxidative stability of the oxidative dehydro‐polycondensation products of diphenylamine
Authors: Berlin A. A. , Ivanov A. A. , Mirotvortsev I. I.
Published: June 2010

Oxidative dehydropolycondensation of diphenylamine (DPA) at 200–260°C leads to the formation of polymers with a system of conjugation, this process being a first order reaction with an activation energy of 20 kcal/mole. Polymeric products of the reaction (PDA) are found to contain fragments of quinone imine and triphenylamine structures and an insignificant quantity of NH groups. PDA reactivity towards peroxide radicals is significantly lower than that of DPA. PDA has higher activity than DPA by the inhibition of thermal oxidation of 1,4‐cis‐polybutadiene, ceresine, and SKN‐26 rubber, the largest effect being observed when PDA mixtures with DPA are used. PDA has high thermal and thermooxidative stability. PDA loses its solubility at the initial stages of destruction, then its destruction rate increases in air and remains constant in argon. Paramagnetic centers of PDA take part in the inhibition of destruction in air until the polymer completely loses its solubility.
Aqueous diffusion through partition membranes
Authors: Lyman Donald J. , Kim Sung Wan
Published: June 2010

Diffusion data obtained from Leonard‐Bluemle cell was interpreted in terms of the extent of interaction between solute and membrane matrix. A new equation was developed to provide linear fit curve for the half‐time data measurements. To develop an understanding of these partition type membranes on the molecular basis, the absolute reaction rate theory has been explored.
Investigation of thermal and thermooxi‐dizing degradation of irradiated polyethylene
Authors: Leshtchenko S. S. , Pavlova Zh. D. , Egorova Z. S. , Karpov V. L.
Published: June 2010

The peculiarities of thermal and thermooxidizing degradation of low‐ and high‐density polyethylene (PELD, PEHD) and the ethylene‐propylene copolymer (CEP‐7) irradiated over the range of 1 to 300 Mrad have been studied.

It was established that the change of structure of polymer by irradiation resulted in an increase of thermostability and a decrease of thermooxidation stability.

The change of content of double bonds as a result of pyrolysis was studied. It was suggested that trans‐vinylene double bonds promoted the development of thermal degradation of irradiated polymer and vinylidene double bonds were slowing down this process. It was found that in nonirradiated branched PELD and CEP‐7 side groups and tertiary carbon atoms oxidized. In nonirradiated linear PEHD the oxidation occurred mainly with the partipation of secondary carbon atoms. The initial polymer structure had an influence on the process of oxidation of irradiated polymers.

Cross‐linking bonds and tertiary carbon atoms were the most vulnerable to the oxidation of irradiated polymers.

Simultaneously with the degradation, during oxidation of irradiated polymers a structuralization with the formation of ether bonds R‐O‐R takes place.
Enzymes covalently bound to acrylic gel beads. II. Practical application of hydrolases covalently bound to hydrophilic anionic gel beads
Authors: Krämer D. M. , Lehmann K. , Plainer H. , Reisner W. , Sprössler B. G.
Published: June 2010

DNase‐free protease covalently bound to hydrophilic anionic gel beads1 can be used to isolate DNA from animal tissue homogenate by simply degrading the protein moiety and precipitating the DNA with isopropanol from the supernatant, the yield being close to 80%. Glucoamylase bound to AM retains 100% activity as compared to the free enzyme. Thus, 30 % solutions of dextrins in water were degraded to glucose and the procedure was repeated with the same beads for 42 times without apparent loss of enzyme activity. From a technical point of view, this system is more efficient than using the free enzyme.
Aminolysis of monoacetyl derivatives of 2,2′ ‐dihydroxydiphenylmethanes
Authors: Böhmer Volker , Wörsdörfer Klaus , Kämmerer Hermann
Published: June 2010

A neighboring group effect was found for the aminolysis of the second acetyl group in acetates of 2,2′‐dihydroxydiphenylmethane derivatives containing a nitrophenol and a methylphenol unit. Kinetic measurements with an excess of n‐butylamine in dioxane were done with 2‐(2‐hydroxy‐3, 5‐dinitrobenzyl)‐4‐methylphenyl acetate (1), 2‐(2‐hydroxy‐5‐nitro‐benzyl)‐4‐methylphenyl acetate (2), and 2‐(2‐hydroxy‐3‐nitro‐5‐methylbenzyl)‐4‐methyl‐phenyl acetate (3). The maximum rate was found for compound 2. When the concentration of n‐butylamine was varied over a large range, the results obtained for compound 2 could be explained best, by assuming that the acetyl group in the methylphenol unit is aminolized faster in the ionic form than as a neutral molecule.
Etude des Activités Catalytiques du Trichlorure de Titane Violet Dans la Polymérisation Haute Température de L'Ethylène
Authors: Machon J. P. , Hermant R. , Houzeaux J. P.
Published: June 2010

Des techniques et méthodes expérimentales développées en réacteurs discontinus et continus permettent d'évaluer les vitesses des réactions concurrentes (polymérisation, désactivation, dimérisation) mises en jeu au cours de la polymérisation Ziegler de l'ethylène à haute tempeéature (160 à 280°C).
Curing of epoxy resins. II. Curing of bisphenol a diglycidyl ether with diamines
Authors: Luňák S. , Dušek K.
Published: June 2010

Structural parameters characterizing the course of curing bisphenol A diglycidyl ether with hexamethylenediamine and 4,4′‐diaminodiphenylmethane in the pre‐ and postgelation stages were determined. Conversion at the gel point, concentration of the tertiary amino groups, and number average molecular weights agree fairly well over a broad range of the stoichiometric ratios of functionalities with the values calculated according to the procedure described in Part I (Dušek, llavský, and Luňák, J. Polym. Sci.: Symp. 53, 29 (1975). A satisfactory agreement was also obtained for lightly crosslinked gel prepared with an excess of the amino component. The optimum values for the reactivity (rate constants) ratio of hydrogen on the secondary and primary amino groups are 0.6–0.7 for hexamethylenediamine and 0.35–0.45 for 4,4′‐diaminodiphenylmethane. The agreement between the course of reaction and the assumed model indicates that not far from the gel point, and at a reaction temperature above the glass transition temperature, the diffusion control does not play any major role and a nonhomogeneous course of the curing reactions is not likely. The authors are indebted to M. Mach, and J. Klaban for the mechanical and spectroscopic measurements.
Network characterization of “viton” ahv fluoroelastomer
Authors: Fogiel A. W.
Published: June 2010

Polymer‐solvent interaction parameter, elastically effective crosslink density Ce, and crosslinking index γ (the number of crosslinked units per polymer chain) have been determined on several vulcanizates of “Viton” AHV fluoroelastomer by means of swelling equilibrium, swollen compression modulus, and sol‐gel analysis. The parameter decreases strongly with increasing Ce for “Viton” AHV/2‐butanone, which suggests that Ce in three‐dimensional expansion (swelling) may not necessarily be equivalent to Ce calculated from uniaxial compression. The relation between γ and Ce is linear and the intercept at Ce = 0 agrees fairly well with Flory's chain‐end correction. The agreement between the initial molecular weight μMn calculated from the slope of this relation is within 25% of μMn measured before crosslinking. In view of the complex cure system the agreement is adequate to conclude that Ce calculated from the swollen compression modulus represents essentially elastically effective crosslinks of chemical nature. For comparable concentrations of the crosslinking agents used, the highest attainable Ce decreases in the order: bisphenol > hydroquinone > diamine. The bisphenol‐cured system yields Ce values far in excess of the theoretical requirements for bisether crosslinks, which is indicative of a more complex crosslinking chemistry than assumed heretofore. The γ‐Ce relation has been applied successfully to distinguish scission in the crosslinks and in the polymer chain during aging at 250°C.
Presence of dual mechanism in poly(vinyl chloride) dehydrochlorination
Authors: Nolan K. P. , Shapiro J. S.
Published: June 2010

Thermal dehydrochlorination of poly(vinyl chloride) was demonstrated to be capable of being maximally inhibited by triphenylmethane. Arrhenius parameters observed under conditions of full inhibition are consistent with a unimolecular loss of hydrogen chloride occurring concurrently with a radical‐chain process. At 194°C, the rate of the molecular process is about 30% of the overall reaction, but at higher temperatures it becomes the predominant pathway.
Some unsolved problems concerned with radiation grafting to natural and synthetic polymers
Authors: Stannett V. , Memetea T.
Published: June 2010

The radiation grafting behavior of styrene to cellulose acetate, polyethylene terephthalate, and wool was examined in some detail. A combination of ESR and an analysis of the grafted products was used. Each system exhibited a certain feature which was difficult to explain. The preirradiation grafting of styrene to cellulose acetate gave a bimodal molecular weight distribution of the grafted side chains, the bulk consisting of an extremely narrow distribution high molecular weight polystyrene. Some possible explanations are presented. The yields of grafted side chains in the case of polyethylene terephthalate were considerably greater than the radical yields determined by ESR. Finally in the case of radiation grafting of styrene to wool, numerous low molecular weight branches were obtained. A backbiting type of chain transfer to polymer mechanism was postulated to explain these results and may also be present in the grafting of styrene to polyethylene terephthalate.
Molecular mechanisms in the formation of polydiacetylenes in the solid state
Authors: Lando J. B. , Day D. , Enkelmann V.
Published: June 2010

Crystals of poly(5, 7–dodecadiinediol‐1, 12–bisphenylurethane) are monoclinic, P2/1 a. The crystal structure has been determined and refined by full matrix least‐squares analysis of diffractometrically measured intensities. The final R index is 0.081 (719 observed reflections). Intramolecular hydrogen bonding, a strong contribution of electron delocalization in the polymer backbone, and unusual C—C bond lengths in the side chain are observed. Polymerized crystals of o,o′‐bisphenyl glutarate diacetylene crystallize in a C2/c monoclinic space group. The x‐ray refinement reveals a solid solution of the monomer and polymer. It was determined that the only movement that occurs during polymerization is in the diacetylene rod (a rotation of 33°) and in adjacent phenyl groups (a rotation of 19° and a swing of 6°) and all other atomic positions in the side group remain essentially the same. An infrared investigation and the final refined atomic coordinates with their standard deviations indicate the BPG crystal was polymerized to an extent of 35%. The final R index is 0.075 (902 observed reflections). Again a strong contribution of electron delocalization in the polymer backbone is observed.
Biological and biochemical activities of protobiopolymers
Authors: Simionescu C. I. , Dénes F. , Brandsch R.
Published: June 2010

The biological and biochemical activity of protobiopolymers and their macromolecular aggregates (microspheres) synthesized in simulative primeval Earth conditions has been investigated. In vitro and in vivo experiments were carried out on bovine albumine and Tubifex egg cells, respectively. The activity of trypsin encapsulated microspheres was studied also. Intense biological and biochemical activities of the protobiopolymers and the trypsin encapsulated microspheres have been observed. It is noteworthy that the development and the division of the egg cells are influenced dramatically.
Molecular degradation of polymers
Authors: Devries K. L. , Igarashi M. , Chao F.
Published: June 2010

An understanding of the transmittal of force or stress through the molecular (or atomic) network of a body should not only be helpful in predicting the load carrying capability of materials but might also provide information on how structure can be altered to enhance properties. A molecular understanding of mechanical properties is particularly difficult in polymers where such factors as molecular weight, tacticity, crystallinity, presence of networks, orientation, etc., may have an influence. In no class of materials are intricacies of physical structure more important than in polymers. Polymers with very similar chemical structures but differing physical structure can have physical properties differing by orders of magnitude. It would obviously be helpful to have means to probe molecular and atomic events and occur during the loading and destruction of the polymer structure. Instruments that have been used for this purpose include: (1) electron spin resonance (ESR) to monitor free radical production resulting from homolytic chain scission, (2) Fourier transform infrared spectroscopy (FTIR) to measure new end groups resulting from molecular chain rupture, and (3) intrinsic viscosity or gel permeation chromotography (GPC) to detect molecular weight changes (MWC) accompanying molecular degradation. This presentation will discuss and compare research results from these methods. Particular emphasis will be placed on recent studies in which computer modeling has been used to identify ESR spectra and a comparison of the results obtained by ESR, FTIR, and MWC for polystyrene.
Structure in dispersions of polymer particles
Authors: Ottewill R. H.
Published: June 2010

In concentrated polymer latex systems where strong repulsive forces, either electrostatic or steric, exist between the particles ordering of the particles occurs. The structure formed can be examined by small angle neutron scattering and experiments indicate that the arrangement of the particles is liquid‐like. Results are reported for a poly(‐styrene) latex in an aqueous electrolyte solution and for a poly(‐deuteromethyl methacrylate) latex, with the particles stabilised by poly‐12‐hydroxy stearic acid in dodecane.
Latex particle size distributions from steady‐state continuous stirred‐tank reactor systems
Authors: Poehlein Gary W. , Lee H. C. , Stubicar Nada
Published: June 2010

The particle size distribution (PSD) of latex produced in a continuous reactor depends on recipe ingredients and reactor design and operation. Alfrey and co‐workers developed theoretical models to predict PSDs for several cases. This work is briefly reviewed in the present paper, and more recent models are presented. The potential use of PSD data for the quantitative determination of kinetic parameters related to free radical desorption from latex particles is discussed.
The dimeric transmembrane domain of prolyl dipeptidase DPP‐IV contributes to its quaternary structure and enzymatic activities
Authors: Chung Kuei‐Min , Cheng Jai‐Hong , Suen Ching‐Shu , Huang Chih‐Hsiang , Tsai Cheng‐Han , Huang Li‐Hao , Chen Yi‐Rong , Wang Andrew H.‐J. , Jiaang Weir‐Torn , Hwang Ming‐Jing , Chen Xin
Published: June 2010

Dipeptidyl peptidase IV (DPP‐IV) is a drug target in the treatment of human type II diabetes. It is a type II membrane protein with a single transmembrane domain (TMD) anchoring the extracellular catalytic domain to the membrane. DPP‐IV is active as a dimer, with two dimer interacting surfaces located extracellularly. In this study, we demonstrate that the TM of DPP‐IV promotes DPP‐IV dimerization and rescues monomeric DPP‐IV mutants into partial dimers, which is specific and irreplaceable by TMs of other type II membrane proteins. By bioluminescence resonance energy transfer (BRET) and peptide electrophoresis, we found that the TM domain of DPP‐IV is dimerized in mammalian cells and in vitro. The TM dimer interaction is very stable, based on our results with TM site‐directed mutagenesis. None of the mutations, including the introduction of two prolines, resulted in their complete disruption to monomers. However, these TM proline mutations result in a significant reduction of DPP‐IV enzymatic activity, comparable to what is found with mutations near the active site. A systematic analysis of TM structures deposited in the Protein Data Bank showed that prolines in the TM generally produce much bigger kinking angles than occur in nonproline‐containing TMs. Thus, the proline‐dependent reduction in enzyme activity may result from propagated conformational changes from the TM to the extracellular active site. Our results demonstrate that TM dimerization and conformation contribute significantly to the structure and activity of DPP‐IV. Optimal enzymatic activity of DPP‐IV requires an optimal interaction of all three dimer interfaces, including its TM.
Characterization of conantokinRl‐A: molecular phylogeny as structure/function study
Authors: Gowd Konkallu H. , Watkins Maren , Twede Vernon D. , Bulaj Grzegorz W. , Olivera Baldomero M.
Published: June 2010

A multidisciplinary strategy for discovery of newConusvenom peptides combines molecular genetics and phylogenetics with peptide chemistry and neuropharmacology. Here we describe application of this approach to the conantokin family of conopeptides targeting NMDA receptors. A new conantokin fromConus rolani, ConRl‐A, was identified using molecular phylogeny and subsequently synthesized and functionally characterized. ConRl‐A is a 24‐residue peptide containing three γ‐carboxyglutamic acid residues with a number of unique sequence features compared to conantokins previously characterized. The HPLC elution of ConRl‐A suggested that this peptide exists as two distinct, slowly exchanging conformers. ConRl‐A is predominantly helical (estimated helicity of 50%), both in the presence and absence of Ca++. The order of potency for blocking the four NMDA receptor subtypes by ConRl‐A was NR2B > NR2D > NR2A > NR2C. This peptide has a greater discrimination between NR2B and NR2C than any other ligand reported so far. In summary, ConRl‐A is a new member of the conantokin family that expands our understanding of structure/function of this group of peptidic ligands targeted to NMDA receptors. Thus, incorporating phylogeny in the discovery of novel ligands for the given family of ion channels or receptors is an efficient means of exploring the megadiverse group of peptides from the genusConus. Copyright © 2010 European Peptide Society and John Wiley & Sons, Ltd.
Adsorbate‐induced modification of the surface electric field of GaAs (001)‐c(4 × 4) measured via the linear electro‐optic effect
Authors: Bruhn T. , Passmann R. , Fimland B. O. , Kneissl M. , Esser N. , Vogt P.
Published: June 2010

We have investigated the modification of the surface electric field (SEF) of the GaAs (001)‐c(4 × 4) surface during the adsorption of cyclopentene and 1,4‐cyclohexadiene molecules by reflectance anisotropy spectroscopy (RAS) in the spectral range from 1.5 to 5.0 eV. At around 3 eV the RAS line shape originates from the so‐called linear electro‐optic effect (LEO). The amplitude of the LEO oscillation scales linearly with the SEF within the RAS penetration depth and is thus a measure for it. For the separation of the LEO from the RAS spectra several different methods are described in the literature. Here, we present a modified method which allows the LEO separation in particular for interfaces between GaAs and organic molecules. The results obtained this way show a significant increase of the LEO effect upon molecule adsorption indicating a higher SEF. The observed changes of the surface electronic properties are probably related to a modification of surface strain upon molecule adsorption.
Hydrogenated amorphous silicon based surface passivation of c‐Si at high deposition temperature and rate
Authors: Illiberi A. , Creatore M. , Kessels W. M. M. , van de Sanden M. C. M.
Published: June 2010

Low substrate temperature during deposition of a‐Si:H is considered a necessary condition to reach excellent surface passivation of c‐Si wafers, such as a hydrogen‐rich and atomically abrupt a‐Si:H/c‐Si interface forms. From a comparison between surface passivation levels achieved by different deposition methods, delivering a broad range of a‐Si:H growth rates, we show that a high a‐Si:H deposition rate (∼3 nm/s) is crucial in achieving an excellent level of surface passivation at high deposition temperatures (>425 °C) compatible with emerging post‐deposition thermal treatments of solar cells. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Adaptive discrete neural observer design for nonlinear systems with unknown time‐delay
Authors: Na Jing , Herrmann Guido , Ren Xuemei , Barber Phil
Published: June 2010

This paper focuses on the adaptive observer design for nonlinear discrete‐time MIMO systems with unknown time‐delay and nonlinear dynamics. The delayed states involved in the system are arguments of a nonlinear function and only the estimated delay is utilized. By constructing an appropriate Lyapunov–Krasovskii function, the delay estimation error is considered in the observer parameter design. The proposed method is then extended to the system with a nonlinear output measurement equation and the delayed dynamics. With the help of a high‐order neural network (HONN), the requirement for a precise system model, the linear‐in‐the‐parameters (LIP) assumption of the delayed states, the Lipschitz or norm‐boundedness assumption of unknown nonlinearities are removed. A novel converse Lyapunov technical lemma is also developed and used to prove the uniform ultimate boundedness of the proposed observer. The effectiveness of the proposed results is verified by simulations. Copyright © 2010 John Wiley & Sons, Ltd.
Robust consensus of multiple inertial agents with coupling delays and variable topologies
Authors: Chen Gang , Lewis Frank L.
Published: June 2010

In this paper, we consider the exponential second‐order consensus problem of a network of inertial agents with time‐varying coupling delays and variable balanced topologies. The passive decomposition approach is employed to incorporate the agents' inertial effect into the distributed control design. The sufficient conditions for the exponential second‐order consensus are provided, both when the topology is switched arbitrarily (without dwell time between consecutive switches) and when it is switched with average dwell time. The results present conditions that must be satisfied by the controller design parameters and performance requirements. Furthermore, an approach to the design of consensus protocol is presented, which is robust to the time delays and the dynamically changing interaction topologies. Numerical examples are given to illustrate our theoretical results. Copyright © 2010 John Wiley & Sons, Ltd.
Robust stability of nonlinear time‐delay systems with interval time‐varying delay
Authors: Orihuela L. , Millan P. , Vivas C. , Rubio F. R.
Published: June 2010

This paper deals with the problem of obtaining delay‐dependent stability conditions and L2‐gain analysis for a class of nonlinear time‐delay systems with norm‐bounded and possibly time‐varying uncertainties. No restrictions on the derivative of the time‐varying delay are imposed, though lower and upper bounds of the delay interval are assumed to be known. A Lyapunov–Krasovskii functional approach is proposed to derive novel delay‐dependent stability conditions which are expressed in terms of linear matrix inequalities (LMIs). To reduce conservatism, the work exploits the idea of splitting the delay interval in multiple regions, so that specific conditions can be imposed to a unique functional in the different regions. This improves the computed bounds for certain delay‐dependent integral terms, providing less conservative LMI conditions. Examples are provided to demonstrate the reduced conservatism with respect to the available results in the literature. Copyright © 2010 John Wiley & Sons, Ltd.
ℒ︁2gain analysis of linear systems with a single switching
Authors: Sebe Noboru , Suyama Koichi
Published: June 2010

For analysis and design of fault‐tolerant control systems, it is very important to evaluate the effects of failures, especially the transient responses caused by failures. This paper considers the ℒ︁2gain analysis of linear systems with a single switching, and gives necessary and sufficient conditions for the analysis. Also, the worst disturbance corresponding to the switching ℒ︁2gain is explicitly characterized. Copyright © 2010 John Wiley & Sons, Ltd.
Auswirkungen der Vorspannung auf das Tragverhalten von SL‐Verbindungen
Authors: Lange Jörg , Friede Roland
Published: June 2010

Der Tragsicherheitsnachweis für Schrauben mit Zug‐ und Querbelastung erfolgt nach DIN 18800‐1 (810) durch die quadratische Interaktion. Dabei stellt sich die Frage, ob bei reiner Querbeanspruchung eine Vorspannkraft als Zuganteil berücksichtigt werden muss. Um diese Frage zu klären, wurden am Fachgebiet Stahlbau der TU Darmstadt Abscherversuche an Schrauben mit unterschiedlichen Vorspanngraden durchgeführt. In diesem Beitrag werden die Versuche vorgestellt und Empfehlungen zur Behandlung der Vorspannkraft ausgesprochen.

Influence of the preload on the resistance of bearing‐type connections. The design resistance of bolts under tension and shear is given in DIN 18800‐1 (810) by a quadratic interaction. The question is, whether the tension due to a preload has to be taken into account. The workgroup steel construction of the Technische Universität Darmstadt, Germany, has run tests to assess the influence of the preload in bearing‐type connections. In this paper the tests are presented and recommendations to take the preload into account are given.
Die Edelstahlrampen im Haus der Musiker der Stiftung Insel Hombroich – Konstruktion und Ausführung
Authors: Kappauf Horst
Published: June 2010

Das Haus der Musiker am westlichen Rand der Insel Hombroich bei Neuss wurde von dem New Yorker Architekten Raimund Abraham entworfen. Der Entwurf wurde erstmals 1996 auf der Architektur‐Biennale in Venedig vorgestellt. Nach einem langen Reifungsprozess wurde 2006 mit dem Bau der Studier‐ und Begegnungsstätte für junge Künstler begonnen. 2010 wurden die Rampen, Bühnen und Wendeltreppen, mit denen das Obergeschoss erschlossen wird, fertiggestellt. Mit seinen klaren Formen und seinen klaren Funktionen ist es ist ein typischer Abraham‐Bau.

Dieser Aufsatz ist meinem Freund Raimund Abraham gewidmet, einem großen Architekten, der am 4. März 2010 in Los Angeles nach einem Vortrag am Southern California Institut of Architecture bei einem Autounfall um Leben kam und damit die Fertigstellung des Hauses nicht mehr erleben kann. Für den Bauherrn und Kunstsammler Karl‐Heinrich Müller, der 2007 verstorben ist, und auch für den Architekten sowie für den Statiker war es eine große Herausforderung und Ehre Raimund Abrahams Ideen umzusetzen zu dürfen. Raimund Abraham wird auch in diesem Haus weiterleben.

The stainless‐steel ramps inside the Haus der Musiker of the Foundation Insel Hombroich – Structure and Execution. The Haus der Musiker (House of Musicians) near Neuss, Germany, has been designed by the New York Architect Raimund Abraham. The design was presented for the first time in 1996 at the architecture‐biennale at Venice. After a longer period of reflection the construction of the building started in 2006, the ramps, the steel platforms and the screw‐stairs – necessary to enter the upper living rooms – were completed in 2010. The house shall be a studying place and a meeting center for young artists.
Arbitrage‐free implementation of implied volatility binomial trees
Authors: Bušić Boris
Published: June 2010

We examine the long‐standing issue of arbitrage violations in implementations of implied volatility binomial trees believed to be the consequence of the inherent limitations imposed by the requirement that such trees be recombining and/or arbitrage violations embedded in the underlying implied volatility function. We disprove the latter on general grounds by demonstrating the possibility of arbitrage violations when implied volatility functions are arbitrage‐free, and the former by formulating an implementation which is arbitrage‐free within the limits imposed by the numerical constraints. Copyright © 2010 Wilmott Magazine Ltd.
Swaptions in Libor Market Model with local volatility
Authors: Henrard Marc
Published: June 2010

The Libor Market Model (LMM) describes the evolution of a yield curve through equations for a discrete set of forward rates. In the original version, the rate dynamic was log‐normal. The rate dynamic has been extended. The main result presented here is a generic approximation that provides an explicit European swaptions price for local volatilities LMM. The approximation is based on an initial freeze approximation very efficient in the Bond Market Model and an original corrector‐type approach. The approximation is strike dependent, allowing a smile calibration. The approximation efficiency is analyzed in details in the displaced diffusion case by comparison to precise Monte Carlo simulations. Copyright © 2010 Wilmott Magazine Ltd.
A note on the Black–Scholes implied volatility with default risk
Authors: Ohsaki Shuichi , Ozeki Takaaki , Umezawa Yuji , Yamazaki Akira
Published: June 2010

This paper focuses on a theoretical aspect of relations between the Black–Scholes implied volatility and the default probability in a general framework that the stock price is fixed at zero after default occurs. It is shown that the default probability of the company under a risk‐neutral measure significantly links to the implied volatility skew at extremely small strike. Moreover, it is proved that the divergence speed of the implied volatility must be determined uniquely in any defaultable economy under arbitrage‐free condition. Finally, through a numerical test, we show whether our model‐free formula is applicable or not in practice. Copyright © 2010 Wilmott Magazine Ltd.
Viroids: self‐replicating, mobile, and fast‐evolving noncoding regulatory RNAs
Authors: Ding Biao
Published: June 2010

Viroids are small, circular, and noncoding RNAs that infect plants. They replicate in the nucleus or chloroplast and then traffic from cell to cell and from organ to organ to establish systemic infection. Viroids achieve nearly all of the biological functions by directly interacting with host cellular factors. Viroid replication, together with replication of human hepatitis delta virus, demonstrates the biological novelty and significance of RNA‐dependent RNA polymerase activities of DNA‐dependent RNA polymerases. Viroid systemic infection uncovers a new biological principle—the role of three‐dimensional RNA structural motifs mediating RNA trafficking between specific cells. Viroid diseases are virtually the consequences of host gene regulation by noncoding RNAs. A viroid RNA has the highest in vivo mutation rate among all known nucleic acid replicons. The host range of many viroids is expanding, essentially as a result of continuing and fast evolution of noncoding sequences/structures to gain new biological functions. Here, I discuss recent progress in these areas, emphasizing the broad significance of viroid research to the discovery of fundamental biological principles. Copyright © 2010 John Wiley & Sons, Ltd.

This article is categorized under:

Regulatory RNAs/RNAi/Riboswitches > Regulatory RNAs

RNA in Disease and Development > RNA in Disease

RNA in Disease and Development > RNA in Development
Determination of Alcohol Ethoxylates derivatized with Naphthoyl Chloride, in Waste Water Treatment Plant Influent, Effluent and Sludge Samples by Liquid Chromatography Mass Spectrometry
Authors: Cassani Giorgio , Tibaldi Francesca , Donato Graziano , Andriollo Nunzio
Published: June 2010

A new analytical procedure for the determination of alcohol ethoxylates (AE) in environmental samples such as influents, effluents and sludge from waste water treatment plants (WWTPs) was developed. Although some work had been previously published on the detection of AE in water samples, this is the first paper that deals with AE in sludge. Alcohol ethoxylates were removed from water samples by sorption on polymeric discs followed by extraction with methanol. The methanol extracts were cleaned up with two alumina solid‐phase extractions (SPE) at different conditions of solvent polarity, one before and the other after derivatization with naphthoyl chloride. A final polishing step was carried out on a Florisil SPE column. Liquid chromatography/mass spectrometry with electrospray ionization was used to quantify AE as naphthoyl derivatives. The detection limits for AE ethoxymers range from 0.07 to 0.005 μg/L in water samples. The method was applied to an Italian WWTP in order to follow the fate of AE during treatment, AE concentrations of 839 μg/L, 0.46 μg/L and 10.6 mg/kg were respectively found in the inlet, outlet and sludge samples. AE removals of each ethoxymer in the plant were in the range 99.6–100% and no difference was observed between high or low‐mole ethoxymers and between AE with odd or even carbon chain lengths. An overall 99.7% removal was also determined on the mass balance of AE in the inlet, the outlet, and sludge of the plant.
Electronegative Low‐Density Lipoprotein is Associated with Dense Low‐Density Lipoprotein in Subjects with Different Levels of Cardiovascular Risk
Authors: de Queiroz Mello Ana Paula , da Silva Isis Tande , Oliveira Aline Silva , Nunes Valéria Sutti , Abdalla Dulcineia Saes Parra , Gidlund Magnus , Damasceno Nágila Raquel Teixeira
Published: June 2010

Dyslipidemias and physicochemical changes in low‐density lipoprotein (LDL) are very important factors for the development of coronary artery disease (CAD). However, pathophysiological properties of electronegative low‐density lipoprotein [LDL(−)] remain a controversial issue. Our objective was to investigate LDL(−) content in LDL and its subfractions (phenotypes A and B) of subjects with different cardiovascular risk. Seventy‐three subjects were randomized into three groups: normolipidemic (N; n = 30) and hypercholesterolemic (HC; n = 33) subjects and patients with CAD (n = 10). After fasting, blood samples were collected and total, dense and light LDL were isolated. LDL(−) content in total LDL and its subfractions was determined by ELISA. LDL(−) content in total LDL was lower in the N group as compared to the HC (P < 0.001) and CAD (P = 0.006) groups. In the total sample and in those of the N, HC, and CAD groups, LDL(−) content in dense LDL was higher than in light LDL (P = 0.001, 0.001, 0.001, and 0.033, respectively) The impact of LDL(−) on cardiovascular risk was reinforced when LDL(−) content in LDL showed itself to have a positive association with total cholesterol (β = 0.003; P < 0.001), LDL‐C (β = 0.003; p < 0.001), and non‐HDL‐C (β = 0.003; P < 0.001) and a negative association with HDL‐C (β = −0.32; P = 0.04). Therefore, LDL(−) is an important biomarker that showed association with the lipid profile and the level of cardiovascular risk.