Different Behavior (different + behavior)

Distribution by Scientific Domains
Distribution within Chemistry


Selected Abstracts


Different Behavior of the Reaction Between 1,2-Diaza-1,3-butadienes and 1,2-Diamines under Solvent or Solvent-Free Conditions.

CHEMINFORM, Issue 43 2005
Orazio A. Attanasi
Abstract For Abstract see ChemInform Abstract in Full Text. [source]


Assessment of the plasma desorption time-of-flight mass spectrometry technique for pesticide adsorption and degradation on ,as-received' treated soil samples

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 17 2005
J. P. Thomas
The assessment of the plasma desorption time-of-flight mass spectrometry (PD-TOFMS) technique as a tool for direct characterization of pesticides adsorbed on agricultural soil is made for the first time in this study. Pellets of soils impregnated by solutions of three pesticides, namely norflurazon, malathion and oxyfluorfen, as well as deposits of these solutions onto aluminum surfaces, were investigated to this end. The yield values of the most characteristic peaks of the negative ion mass spectra were used to determine both the lowest concentrations detected on soils and limits of detection from thin films. The lowest values on soils are for malathion (1000,ppm range), and the largest for norflurazon (20,000,ppm), which is close to the limit of detection (LOD) found for the pesticide on the aluminum substrate (,0.2,µg,·,cm,2). Different behaviors were observed as a function of time of storage in the ambient atmosphere or under vacuum; norflurazon adsorbed on soil exhibited high stability for a long period of time, and a rapid degradation of malathion with the elapsed time was clearly observed. The behavior of oxyfluorfen was also investigated but segregation processes seem to occur after several days. Although by far less sensitive than conventional methods based on extraction processes and used for real-world analytical applications, this technique is well suited to the study of the transformations occurring at the sample surface. A discussion is presented of the future prospects of such experiments in degradation studies. Copyright © 2005 John Wiley & Sons, Ltd. [source]


Thermal Decomposition Reactions as a Tool for the Synthesis of New Thermodynamic Metastable Modifications: Synthesis, Structures, and Properties of (Formato)nickel(II) Coordination Polymers Based on 4,4,-Bipyridine

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 12 2010
Jan Boeckmann
Abstract The reaction of nickel formate with 4,4,-bipyridine (bipy) in aqueous solution at room temperature leads to the formation of the hydrated compound [Ni(HCO2)2(H2O)(bipy)·4H2O]n (1) reported recently. On heating, compound 1 decomposes into the new anhydrous compound of composition [Ni(HCO2)2(bipy)]n (2II), which decomposes on further heating. Interestingly, if the anhydrous compound is prepared from solution, a new modification 2I is obtained. Investigations on the stability of both forms show that modification 2I presents the thermodynamically most stable form between room and decomposition temperature, whereas modification 2II, which can only be prepared by thermal decomposition, is metastable. In the crystal structure of 2I, the Ni2+ cations are coordinated by four ,2 - anti,anti bridging formato anions and two bridging ,2 -bipy ligands in a slightly distorted octahedralgeometry. The formato anions bridge the metal cations in zigzag chains, which are further connected by ,2 - anti,anti formato anions and bipy ligands to give a three-dimensional coordination network. IR spectroscopic investigations on the metastable form 2II also indicate that all formato anions act as bridging ligands. Magnetic measurements of the hydrated and anhydrous compounds reveal different behavior with a ferromagnetic ordering for compound 2I and an antiferromagnetic ordering for compound 1. For form 2II, only Curie,Weiss paramagnetism was found. [source]


Ligand Effects on the Mechanisms of Thermal Bond Activation in the Gas-Phase Reactions NiX+/CH4,Ni(CH3)+/HX (X=H, CH3, OH, F).

HELVETICA CHIMICA ACTA, Issue 12 2008
Short Communication
Abstract The thermal ion-molecule reactions NiX++CH4,Ni(CH3)++HX (X=H, CH3, OH, F) have been studied by mass spectrometric methods, and the experimental data are complemented by density functional theory (DFT)-based computations. With regard to mechanistic aspects, a rather coherent picture emerges such that, for none of the systems studied, oxidative addition/reductive elimination pathways are involved. Rather, the energetically most favored variant corresponds to a , -complex-assisted metathesis (, -CAM). For X=H and CH3, the ligand exchange follows a ,two-state reactivity (TSR)' scenario such that, in the course of the thermal reaction, a twofold spin inversion, i.e., triplet,singlet,triplet, is involved. This TSR feature bypasses the energetically high-lying transition state of the adiabatic ground-state triplet surface. In contrast, for X=F, the exothermic ligand exchange proceeds adiabatically on the triplet ground state, and some arguments are proposed to account for the different behavior of NiX+/Ni(CH3)+ (X=H, CH3) vs. NiF+. While the couple Ni(OH)+/CH4 does not undergo a thermal ligand switch, the DFT computations suggest a potential-energy surface that is mechanistically comparable to the NiF+/CH4 system. Obviously, the ligands X act as a mechanistic distributor to switch between single vs. two-state reactivity patterns. [source]


Numerical modeling of creep and creep damage in thin plates of arbitrary shape from materials with different behavior in tension and compression under plane stress conditions

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 11 2009
A. Zolochevsky
Abstract A constitutive model for describing the creep and creep damage in initially isotropic materials with characteristics dependent on the loading type, such as tension, compression and shear, has been applied to the numerical modeling of creep deformation and creep damage growth in thin plates under plane stress conditions. The variational approach of establishing the basic equations of the plane stress problem under consideration has been introduced. For the solution of two-dimensional creep problems, the fourth-order Runge,Kutta,Merson's method of time integration, combined with the Ritz method and R-functions theory, has been used. Numerical solutions to various problems have been obtained, and the processes of creep deformation and creep damage growth in thin plates of arbitrary shape have been investigated. The influence of tension,compression asymmetry on the stress,strain state and damage evolution, with time, in thin plates of arbitrary shape, has been discussed. Copyright © 2009 John Wiley & Sons, Ltd. [source]


Dependence of the wittig reaction mechanism on the environment and on the substituents at the aldehyde group and at the phosphonium ylide

INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 3 2010
Giuliano Alagona
Abstract The B3P86/6-31G* mechanistic results for the Wittig reaction of acetaldehyde, CH3CHO, in vacuo and in tetrahydrofuran (THF) solution in the IEF-PCM framework, with an unsubstituted trimethylphosphonium or triphenylphosphonium ylide, that is Me3PCH2 or Ph3PCH2, have been compared to those recently obtained at the same levels for the reaction of Ph3PCH2 with a bulky chiral aldehyde, (2S,3R)-2,4-dimethyl-3-pyrrol-1-yl-pentanal [TCA (DOI: 10.1007/s00214-009-0521-4)], here named sys for short. The two model systems show distinct, but similar, behaviors that however differ from the large system one. In particular, betaine-type intermediates are not located in vacuo when Me3PCH2 is used, while only a gauche betaine is obtained using Ph3PCH2; the relevant barriers are anyway smaller than those found for sys. Conversely, in THF, the concerted and stepwise mechanisms are both represented and show TS1/TSb barriers, which are negligibly small for sys. Thus, in contrast to assessed literature, models with methyl groups in place of phenyl rings and branched aldehyde chains show a different behavior from realistic systems and prevent inferring general rules from their use, suggesting to resort to Ph3PCH2 whose results in vacuo and in THF are closer to sys. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [source]


Ageing of calcium silicate cements for endodontic use in simulated body fluids: a micro-Raman study

JOURNAL OF RAMAN SPECTROSCOPY, Issue 12 2009
Paola Taddei
Abstract To evaluate bioactivity properties, a calcium silicate experimental cement (wTC) and a phosphate-doped wTC cement (wTC-TCP) were aged for different times (1,180 days) at 37 °C in two simulated body fluids, i.e. Dulbecco's phosphate buffered saline (DPBS) and Hank's balanced salt solution (HBSS). The cements were analyzed by micro-Raman spectroscopy to investigate the presence of calcium phosphate deposits and the composition changes as a function of the storage time (hydration of anhydrite/gypsum and formation of ettringite; hydration of belite/alite and formation of hydrated silicates). After 1 day of ageing in DPBS, the two cements already showed a different behavior: only the surface of wTC-TCP cement showed the band at 965 cm,1, suggesting the formation of a detectably thick calcium phosphate deposit. The trend of the I965/I990 Raman intensity ratio indicated the formation of a meanly thicker apatite deposit on the wTC-TCP cement until 90 days. After 60 days of ageing in DPBS, the thickness of the apatite deposit on wTC and wTC-TCP was about 200 and 500 µm, respectively, whereas at 180 days, the two cements did not appear significantly different (thickness of about 900 µm). The bioactivity of both cements in HBSS was less pronounced than in DPBS, according to the lower phosphate concentration of HBSS; at the same time, higher amounts of calcite were found on the surface of both cements. The wTC-TCP cement showed a higher bioactivity in this medium also; after 180 days, the thickness of the apatite deposit on wTC and wTC-TCP was < 50 µm and about 100 µm, respectively. Copyright © 2009 John Wiley & Sons, Ltd. [source]


EFFECT OF PROCESSING, PRESERVATION AND STORAGE ON RHEOLOGY OF GUAVA PULP

JOURNAL OF TEXTURE STUDIES, Issue 4 2001
S. W. HARNANAN
ABSTRACT Rheological behavior of white and pink guava pulps was investigated using Rheotest 2 coaxial cylinder viscometer over shear rates of 0.6 to 145.8 s,1. The shear rate-shear stress data followed the power law, Casson, Herschel-Bulkley, Michaels and Bolger models. The power law flow behavior index values were in the range of 0.14 to 0.19. Presence of measurable yield stress indicated Bingham model of the pulps. Storage of pulps for 30 weeks had negligible influence on flow behavior index values. The consistency index and yield stress values decreased with extending storage from 0 to 30 weeks. The Michaels and Bolger model distinctly described the non-Newtonian nature of cold- and hot-break pulps as well as different behavior of the pink guava pulps. The structure shear resistance values for hot-break pulps at zero shear rate were considerably higher than those of the cold-break, indicating their high pseudoplasticity. [source]


Ethylene and Propylene Polymerization Using In Situ Supported Me2Si(Ind)2ZrCl2 Catalyst: Experimental and Theoretical Study

MACROMOLECULAR MATERIALS & ENGINEERING, Issue 3 2006
Fernando C. Franceschini
Abstract Summary: Me2Si(Ind)2ZrCl2 was in situ immobilized onto SMAO and used for ethylene and propylene polymerization in the presence of TEA or TIBA as cocatalyst. The catalytic system Me2Si(Ind)2ZrCl2/SMAO exhibited different behavior depending on the amount and nature of the alkylaluminum employed and on the monomer type. The catalyst activity was nearly 0.4 kg polymer,·,g cat,1,·,h,1 with both cocatalysts for propylene polymerization. Similar activities were observed for ethylene polymerization in the presence of TIBA. When ethylene was polymerized using TEA at an Al/Zr molar ratio of 250, the activity was 10 times higher. Polyethylenes made by in situ supported or homogeneous catalyst systems had practically the same melting point (Tm). On the other hand, poly(propylenes) made using in situ supported catalyst systems had a slightly lower Tm than poly(propylenes) made using homogeneous catalyst systems. The nature and amount of the alkylaluminum also influenced the molar mass. The poly(propylene) molar mass was higher when TIBA was the cocatalyst. The opposite behavior was observed for the polyethylenes. Concerning the alkylaluminum concentration, the molar mass of the polymers decreased as the amount of TEA increased. In the presence of TIBA, the polyethylene's molar mass was almost the same, independent of the alkylaluminum concentration, and the poly(propylene) molar mass increased with increasing amounts of cocatalyst. The deconvolution of the GPC curves showed 2 peaks for the homogeneous system and 3 peaks for the heterogeneous in situ supported system. The only exception was observed when TEA was used at an Al/Zr molar ratio of 500, where the best fit was obtained with 2 peaks. Based on the GPC deconvolution results and on the theoretical modeling, a proposal for the active site structure was made. Molar mass distribution deconvolution of polyethylene prepared with the system Me2Si(Ind)2ZrCl2/SMAO/TIBA with 500 mol/mol of alkylaluminum as cocatalyst. [source]


The dependence on temperature and concentration of 129Xe NMR chemical shift values of organoxenon(II) salts [RXe][Y] and of the parent molecule XeF2

MAGNETIC RESONANCE IN CHEMISTRY, Issue 6 2006
Vadim V. Bardin
Abstract The dependence of the 129Xe NMR chemical shift value of XeF2 on temperature and concentration was determined in a variety of prototypic media: in acidic (anhydrous HF, aHF), nonprotic but polar (dichloromethane), and basic (CD3CN-EtCN, 1:3 v/v) solvents. The 129Xe NMR spectra of a representative series of organoxenon(II) salts [RXe][Y] (R = C6F5, heptafluoro-1,4-cyclohexadien-1-yl (cyclo -1,4-C6F7), pentafluoro-1,4-cyclohexadien-3-on-1-yl (cyclo -3-O-1,4-C6F5), CF2 = C(CF3), (CF3)2CFC,C, C4H9C,C; Y = BF4, AsF6) in aHF showed, compared with XeF2aHF, a quantitatively less distinct but qualitatively related dependence of ,(129Xe) vs temperature. The dependence of their ,(129Xe) values on concentration in aHF is negligible. An explanation for the different behavior of [RXe][Y] and XeF2 is offered. Copyright © 2006 John Wiley & Sons, Ltd. [source]


Adult primary extragonadal germ cell tumors: Treatment results and long-term follow-up

PEDIATRIC BLOOD & CANCER, Issue 1 2003
Argon Andac MD
Abstract Background Primary extragonadal germ cell tumors (PEGCT) are rare neoplasms. They have a poor prognosis, different behavior, and natural course compared to their gonadal counterparts. Both primary and salvage treatment of these tumors constitute a challenge. We retrospectively evaluated the clinicopathologic status, therapeutic implications, and outcome of our patients with PEGCT. Procedure Between 1991 and 2000, 18 patients with PEGCT (median age 31 years; range 17,63), diagnosed with tru-cut biopsy and treated with cisplatin-based chemotherapy, were evaluated in respect to treatment response and outcome. Results Cisplatin-based chemotherapy achieved a complete response rate of 27.8% and a partial response rate of 55.5%. Overall response rate was 83.3%. Only three patients were unresponsive to chemotherapy; an additional six patients with residual mass underwent surgical resection and were rendered disease-free by surgery. The 5-year actuarial event-free and overall survival were 63.4 and 71.3%, respectively. Conclusions The outcomes of our patients with extragonadal primaries including mediastinal localization appear to be slightly better than those previously reported. Multimodality therapy is essential for these patients and given the relatively poor prognosis, prospective trials with large sample sizes, and new treatment approaches to improve outcome are required. Med Pediatr Oncol 2003;41:49,53. © 2003 Wiley-Liss, Inc. [source]


Vertical Migration and Motility Responses in Three Marine Phytoplankton Species Exposed to Solar Radiation,

PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 4 2007
Peter R. Richter
ABSTRACT Diurnal vertical migration in the water column and the impact of solar radiation on motility were investigated in three marine phytoplankton species: Tetraselmis suecica, Dunaliella salina and Gymnodinium chlorophorum. Cells were exposed to solar radiation either in ultraviolet radiation (UVR, 280,400 nm) transparent Plexiglas tubes (45 cm length, 10 cm diameter) or in quartz tubes under three radiation treatments: PAB (280,700 nm), PA (320,700 nm) and P (400,700 nm). The three species displayed different behavior after exposure to solar radiation. Tetraselmis suecica was insensitive to UVR and under high solar radiation levels, cells accumulated preferentially near the surface. Exposure experiments did not indicate any significant changes in swimming speed nor in the percentage of motile cells after 5 h of exposure. On the other hand, D. salina was sensitive to UV-B displaying a significant decrease in swimming speed and percentage of motile cells after 2,3 h of exposure. Moreover, D. salina cells migrated deep in the water column when irradiance was high. The response of G. chlorophorum was in between that of the other two species tested, with a slight (but significant) decrease in swimming speed and percentage of motile cells in all radiation treatments after 5 h of exposure. While G. chlorophorum cells were more or less homogenously distributed in the water column, a slight (but significant) avoidance response to high radiation was observed at local noon, with cells migrating deep in the water column. Our data clearly indicate that these sub-lethal effects of solar radiation are species-specific and they might have important implications for the aquatic ecosystem. [source]


Implementation of the GaN lateral polarity junction in a MESFET utilizing polar doping selectivity

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2010
Ramón Collazo
Abstract The difference in surface energies between the Ga-polar orientation and the N-polar orientation of GaN translates into a completely different behavior for the incorporation of intentional and unintentional impurities. Oxygen is found to be an impurity with higher concentration in the N-polar films than in Ga-polar films and is the cause of n-type conductivity observed in N-polar films. Utilizing this doping selectivity we fabricated a depletion-mode metal-semiconductor field effect transistor (MESFET) with n-type N-polar domains as source and drain and a Ga-polar channel on polarity-patterned wafers. The difference in the electronic properties of the different domains, i.e., as-grown N-polar domains are n-type conductive and Ga-polar domains are insulating, allows for laterally selective doped areas that can be realized for improving contact resistance to the n-type conduction channel. Basically, the N-polar domains acted as the ohmic contacts to the channel localized in a Ga-polar domain. A MESFET with a Schottky gate was fabricated as an example of implementation of this novel structure showing a lowering in the specific contact resistivity. [source]


Half-metallicity and magnetism at Heusler alloy surfaces: Co2MSi(001) (M = Ti, Cr)

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 8 2008
Ying Jiu Jin
Abstract We investigated the electronic structures, magnetism, and half-metallicity at the (001) surfaces of full-Heusler alloys, Co2MSi (M = Ti, Cr), by using the all-electron full-potential linearized augmented plane wave method within the generalized gradient approximation. Both the Co-terminated (Co-term) and the MSi-terminated (MSi-term) surfaces were considered. From the calculated atom-resolved density of states, we found that the half-metallicity was destroyed at the Co-term surfaces for both alloys. The electronic structures at the MSi-term surfaces of the two alloys showed much different behavior. The half-metallicity was retained at the TiSi-term for Co2TiSi(001) but the minority spin gap was much reduced due to surface states located just below the Fermi level. On the other hand the half-metallicity was destroyed at the CrSi-term of Co2CrSi(001) due to the surface states located at the Fermi level. The calculated magnetic moment of the surface Co atom of the Co-term for Co2CrSi(001) was increased slightly to 1.05,B with respect to that of the deep inner layers (,1.00,B), while that for Co2TiSi(001) was decreased to 0.88,B. Large enhancement of the magnetic moment was found for the surface Ti atoms at TiSi-term of Co2TiSi(001) and Cr atoms at CrSi-term of Co2CrSi(001) with values of 0.07,B and 2.91(B, respectively. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Thermodynamic characterization of two homologous protein complexes: Associations of the semaphorin receptor plexin-B1 RhoGTPase binding domain with Rnd1 and active Rac1

PROTEIN SCIENCE, Issue 5 2009
Prasanta K. Hota
Abstract Plexin receptors function in response to semaphorin guidance cues in a variety of developmental processes involving cell motility. Interactions with Rho, as well as Ras family small GTPases are critical events in the cell signaling mechanism. We have recently determined the structure of a cytoplasmic domain (RBD) of plexin-B1 and mapped its binding interface with several Rho-GTPases, Rac1, Rnd1, and RhoD. All three GTPases associate with a similar region of this plexin domain, but show different functional behavior in cells. To understand whether thermodynamic properties of the GTPase,RBD interaction contribute to such different behavior, we have examined the interaction at different temperatures, buffer, and pH conditions. Although the binding affinity of both Rnd1 and Rac1 with the plexin-B1 RBD is similar, the detailed thermodynamic properties of the interactions are considerably different. These data suggest that on Rac1 binding to the plexin-B1 RBD, the proteins become more rigid in the complex. By contrast, Rnd1 binding is consistent with unchanged or slightly increased flexibility in one or both proteins. Both GTPases show an appreciable reduction in affinity for the dimeric plexin-B1 RBD indicating that GTPase binding is not cooperative with dimer formation, but that a partial steric hindrance destabilizes the dimer. However, a reduced affinity binding mode to a disulphide stabilized model for the dimeric RBD is also possible. Consistent with cellular studies, the interaction thermodynamics imply that further levels of regulation involving additional binding partners and/or regions outside of the RhoGTPase binding domain are required for receptor activation. [source]


Routing complexity of faulty networks

RANDOM STRUCTURES AND ALGORITHMS, Issue 1 2008
Omer Angel
Abstract One of the fundamental problems in distributed computing is how to efficiently perform routing in a faulty network in which each link fails with some probability. This article investigates how big the failure probability can be, before the capability to efficiently find a path in the network is lost. Our main results show tight upper and lower bounds for the failure probability, which permits routing both for the hypercube and for the d -dimensional mesh. We use tools from percolation theory to show that in the d -dimensional mesh, once a giant component appears,efficient routing is possible. A different behavior is observed when the hypercube is considered. In the hypercube there is a range of failure probabilities in which short paths exist with high probability, yet finding them must involve querying essentially the entire network. Thus the routing complexity of the hypercube shows an asymptotic phase transition. The critical probability with respect to routing complexity lies in a different location than that of the critical probability with respect to connectivity. Finally we show that an oracle access to links (as opposed to local routing) may reduce significantly the complexity of the routing problem. We demonstrate this fact by providing tight upper and lower bounds for the complexity of routing in the random graph Gn,p. © 2007 Wiley Periodicals, Inc. Random Struct. Alg., 2008 [source]


The problem of phase mixed shear Alfvén waves in the solar corona revisited

ASTRONOMISCHE NACHRICHTEN, Issue 8 2008
G. Mocanu
Abstract The problem of phase mixing of shear Alfvén waves is revisited taking into account dissipative phenomena specific for the solar corona. In regions of space plasmas where the dynamics is controlled by the magnetic field, transport coefficients become anisotropic with transport mechanism having different behavior and magnitude depending on the orientation with respect to the ambient magnetic field. Taking into account realistic values for dissipative coefficients we obtain that the previous results derived in context of torsional Alfvén wave phase mixing are actually heavily underestimated so phase mixing cannot be used to explain the damping of torsional Alfvén waves and heating of open coronal structures. The presented results indicate that in order for phase mixing to still be a viable mechanism to explain heating or wave damping unrealistic assumptions have to be made. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Theoretical Study of Catalytic Efficiency of a Diels,Alderase Catalytic Antibody: An Indirect Effect Produced During the Maturation Process

CHEMISTRY - A EUROPEAN JOURNAL, Issue 2 2008
Sergio Martí Dr.
Abstract The Diels,Alder reaction is one of the most important and versatile transformations available to organic chemists for the construction of complex natural products, therapeutics agents, and synthetic materials. Given the lack of efficient enzymes capable of catalyzing this kind of reaction, it is of interest to ask whether a biological catalyst could be designed from an antibody-combining site. In the present work, a theoretical study of the different behavior of a germline catalytic antibody (CA) and its matured form, 39,A-11, that catalyze a Diels,Alder reaction has been carried out. A free-energy perturbation technique based on a hybrid quantum-mechanics/molecular-mechanics scheme, together with internal energy minimizations, has allowed free-energy profiles to be obtained for both CAs. The profiles show a smaller barrier for the matured form, which is in agreement with the experimental observation. Free-energy profiles were obtained with this methodology, thereby avoiding the much more demanding two-dimensional calculations of the energy surfaces that are normally required to study this kind of reaction. Structural analysis and energy evaluations of substrate,protein interactions have been performed from averaged structures, which allows understanding of how the single mutations carried out during the maturation process can be responsible for the observed fourfold enhancement of the catalytic rate constant. The conclusion is that the mutation effect in this studied germline CA produces a complex indirect effect through coupled movements of the backbone of the protein and the substrate. [source]


Recombinant Whole-Cell Mediated Baeyer,Villiger Oxidation of Perhydropyran-Type Ketones

CHEMISTRY & BIODIVERSITY, Issue 3 2008
Marko
Abstract Recombinant Escherichia coli cells expressing eight Baeyer,Villiger monooxygenases of bacterial origin have been utilized to oxidize prochiral heterocyclic ketones containing a pyran ring system. Within the biotransformation, two stereogenic centers were introduced with high control of enantioselectivity. The chemoselectivity of the enzymatic reaction was found to be high in favor of the Baeyer,Villiger process when using substituted ketone precursors incorporating functional groups labile to oxidation. A significantly different behavior was observed for two groups of monooxygenases with respect to substrate acceptance, which is consistent with our previous classification into two enzyme clusters. [source]


On Differences between Hydrogen Bonding and Improper Blue-Shifting Hydrogen Bonding

CHEMPHYSCHEM, Issue 4 2005
Wiktor Zierkiewicz Dr.
Abstract Twenty two hydrogen-bonded and improper blue-shifting hydrogen-bonded complexes were studied by means of the HF, MP2 and B3LYP methods using the 6-31G(d,p) and 6,311++G(d,p) basis sets. In contrast to the standard H bonding, the origin of the improper blue-shifting H bonding is still not fully understood. Contrary to a frequently presented idea, the electric field of the proton acceptor cannot solely explain the different behavior of the H-bonded and improper blue-shifting H-bonded complexes. Compression of the hydrogen bond due to different attractive forces,dispersion or electrostatics,makes an important contribution as well. The symmetry-adapted perturbation theory (SAPT) has been utilized to decompose the total interaction energy into physically meaningful contributions. In the red-shifting complexes, the induction energy is mostly larger than the dispersion energy while, in the case of blue-shifting complexes, the situation is opposite. Dispersion as an attractive force increases the blue shift in the blue-shifting complexes as it compresses the H bond and, therefore, it increases the Pauli repulsion. On the other hand, dispersion in the red-shifting complexes increases their red shift. [source]


Investigation of the Effect of Different Glassy Carbon Materials on the Performance of Prussian Blue Based Sensors for Hydrogen Peroxide

ELECTROANALYSIS, Issue 3 2003
Francesco Ricci
Abstract Three different kinds of glassy carbon (GC-R, GC-K, GC-G) were equally pretreated, further modified with electrochemically deposited Prussian Blue and used as sensors for hydrogen peroxide at an applied potential of ,50,mV (vs. Ag|AgCl). Their performance was evaluated with respect to the following parameters: the coverage and electrochemistry of the electrodeposited Prussian Blue, the sensitivity and the lower limit of detection for hydrogen peroxide, and the operational stability of the sensors. GC-R showed the best behavior concerning the surface coverage and the operational stability of the electrodeposited Prussian Blue. For this electrode the sensitivity for hydrogen peroxide (10,,M) was 0.25,A/M cm2 and the detection limit was 0.1,,M. Scanning electron microscopy was used to study the surfaces of the three electrodes before and after the electrodeposition of Prussian Blue and to search for the reason for the three different behaviors between the different glassy carbon materials. The Prussian Blue modified GC-R was also used for the construction of a glucose biosensor based on immobilizing glucose oxidase in Nafion membranes on top of electrodeposited Prussian Blue layer. The operational stability of the glucose biosensors was studied in the flow injection mode at an applied potential of ,50,mV (vs. Ag|AgCl) and alternatively injecting standard solutions of hydrogen peroxide (10,,M) and glucose (1,mM) for 3,h. For the GC-R based biosensor a 2.8% decrease of the initial glucose response was observed. [source]


Sentinel node biopsy and head and neck tumors,Where do we stand today?

HEAD & NECK: JOURNAL FOR THE SCIENCES & SPECIALTIES OF THE HEAD AND NECK, Issue 12 2006
FCAP, Kenneth O. Devaney MD
Abstract Background. Sentinel lymph node sampling may be studied profitably in series of patients with 1 tumor type, such as breast carcinoma, in 1 anatomic locale. The present work analyzes the efficacy of sentinel node sampling in a pathologically diverse group of lesions from an anatomically diverse region such as the head and neck; however, there are risks conflating the findings in different tumors with radically different behaviors, in the process producing muddled data. This report reviews the head and neck experience with sentinel sampling and concludes that certain tumor types that have a known propensity for aggressive behavior are the best candidates for trials employing sentinel node sampling; candidates include many cutaneous melanomas of the head and neck, oropharyngeal squamous carcinomas, and selected thyroid carcinomas. Despite the growing popularity of sentinel node sampling in a variety of regions of the body, however, at this juncture this technique remains an investigational procedure, pending demonstration of a tangible improvement in patient outcome through its use. It is recommended that studies of the efficacy of this technique strive, whenever possible, to segregate results of different tumor types in different head and neck locales from one another so as to produce more focused findings for discrete types of malignancies, and not group together tumor types that may in reality exhibit different biological behaviors. © 2006 Wiley Periodicals, Inc. Head Neck, 2006 [source]


Dieting history in obese youngsters with and without disordered eating

INTERNATIONAL JOURNAL OF EATING DISORDERS, Issue 8 2006
Line Claus MA
Abstract Objective: This article examines the relationship between the emergence of disordered eating and the history of weight and dieting in obese youngsters. Method: Both child and parent reports were obtained from 40 obese disordered eaters (objective bulimic episodes, n = 20; objective overeating episodes, n = 20) and 40 obese matched controls aged 10,16 years. Results: No significant differences between subsamples with regard to weight and dieting history were found. In dieters, it was shown that overweight onset preceded dieting onset, which in turn preceded dietary restraint onset. Despite some discordance regarding precise onset ages of different behaviors, parent and child re ports revealed the same temporal sequences. Conclusion: A developmental pathway from weight problems through dieting to binge eating is plausible for a subgroup of obese children. Convergence between parent and child reports supports the assumption that children's reports are a viable means of monitoring dieting and weight behaviors. © 2006 by Wiley Periodicals, Inc. Int J Eat Disord 2006; 39:721,728 [source]


The Right Gastroepiploic Artery in Coronary Artery Bypass Grafting

JOURNAL OF CARDIAC SURGERY, Issue 4 2008
Hideki Sasaki M.D.
Although some reports presenting good results justify its use in clinical settings, there is still much concern about using the RGEA in bypass surgery. The RGEA demonstrates different behaviors from the internal thoracic artery (ITA) in bypass surgery due to its histological characteristics and anatomical difference, which might contribute to the long-term outcome. Now that left ITA (LITA) to left anterior descending artery (LAD) is the gold standard, other grafts are expected to cover the rest of the coronary arteries. It should be elucidated how we can use other grafts and what we can expect from them. RGEA, as an arterial graft, can be used as an in situ graft or a free graft. The RGEA is mainly used to graft to the right coronary artery (RCA) because of its anatomical position, and its patency is not inferior to that of the saphenous vein (SVG). The RGEA can cover the lateral walls when its length is long enough or by making a composite graft with other grafts. However, when used to graft to the LAD, its mid-term patency is not favorable. [source]


EFFECT OF ARTIFICIAL FEEDING ON DIGESTIVE EFFICIENCY, GROWTH AND QUALITIES OF MUSCLE AND OOCYTE OF MATURING ATLANTIC MACKEREL (SCOMBER SCOMBRUS L.)

JOURNAL OF FOOD BIOCHEMISTRY, Issue 6 2007
KRISNA RUNGRUANGSAK-TORRISSEN
ABSTRACT Maturing Atlantic mackerel with and without artificial feeding, kept in sea pens (September to May), showed differences in digestive efficiency (protease activity ratio of trypsin to chymotrypsin), muscle growth (concentrations of RNA, protein, RNA/protein ratio and free amino acids [FAA]) and oocyte quality (trypsin-like specific activity, and concentrations of RNA, RNA/protein ratio and FAA). The artificially fed mackerel had higher body weights (1.7 times) but with less white muscle protein concentration (0.5 time), compared to the control group. Both groups showed higher levels of capacity for protein synthesis in the oocytes than in the white muscle, but it was about two times higher in the artificially fed fish whereas about four times higher in the control group. This indicated that, during maturation, development of oocytes and muscle for growth occurred concurrently in higher growth mackerel, while development of oocytes dominated in slower growth fish. A higher trypsin-like specific activity with higher FAA levels in the oocytes from females fed with an artificial diet, compared to the control group, suggested differences in development and quality between the gametes of the fish with different feedings. PRACTICAL APPLICATIONS The work illustrates differences in digestive efficiency and the quality of growth performance (growth and protein metabolism in muscle and oocytes) in fish with different feedings. The use of various methods for evaluating digestive efficiency and the quality of fish growth performance could provide reasonable information for some important biological differences between fish groups, especially when the number of samples are low. It is more advantageous to apply different methods simultaneously than using growth parameter alone in order to study for precise evaluation of the quality of fish growth performance. The methods are very practical for studying food utilization and growth quality of fish in different environmental conditions and with different behaviors in aquaculture as well as in natural ecosystem where food consumption rate and feeding regime cannot be under control. [source]


Growth model on (1 + 1) dimensions with local relaxation and discrete number of orientations

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 5 2004
W. L. Cavalcanti
Abstract We introduced in this work a simple model for studying the texture formation during the electrodeposition process. Monte Carlo simulations were used to describe the formation of the deposits, and scaling concepts were also employed to characterize their growth and roughness properties. Particles are randomly deposited on a substrate, and their main axis can be aligned in a discrete set of possible directions. The final orientation of the deposited particle is determined by the interaction energy with its first neighboring particles and substrate temperature. Particle interactions are chosen according to the q -state ferromagnetic Potts model hamiltonian. Simulations were performed on (1 + 1) dimensions, for different values of temperature and substrate size. We have found different behaviors at low and high temperatures. Only at zero temperature the system reaches an absorbing state with all the layers occupied by particles oriented in the same direction. At this temperature we found the dynamic, roughness and growth exponents of the model, which satisfies the well known Family,Vicsek scaling relation for the self-affine interfaces. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Central L-cysteine induces sleep, and D-cysteine induces sleep and abnormal behavior during acute stress in neonatal chicks

ANIMAL SCIENCE JOURNAL, Issue 4 2009
Haruka YAMANE
ABSTRACT L-Cysteine (L-Cys) is a non-essential and glycogenic amino acid. Previously, we reported that the intracerebroventricular (i.c.v.) injection of L-Cys induced sedative effects under isolation-induced stress in neonatal chicks. L-Cys has an optical isomer, D-Cys. The aim of this study was to clarify the effect of L-Cys and D-Cys during a stressful condition in chicks. The i.c.v. injection of L-Cys and D-Cys (0.84 µmol) decreased both distress vocalization and spontaneous activity induced by isolation. However, the two cysteine isomers induced different behaviors. L-Cys increased sleep-like behavior while D-Cys caused abnormal behavior including syncope as well as sleep-like behavior. In conclusion, while both L-Cys and D-Cys caused a sedative effect when injected i.c.v, D-Cys caused abnormal behavior and may be detrimental to neonatal chicks. [source]


Exploring the interactions of gliadins with model membranes: Effect of confined geometry and interfaces

BIOPOLYMERS, Issue 8 2009
Amélie Banc
Abstract Mechanisms leading to the assembly of wheat storage proteins into proteins bodies within the endoplasmic reticulum (ER) of endosperm cells are unresolved today. In this work, physical chemistry parameters which could be involved in these processes were explored. To model the confined environment of proteins within the ER, the dynamic behavior of ,-gliadins inserted inside lyotropic lamellar phases was studied using FRAP experiments. The evolution of the diffusion coefficient as a function of the lamellar periodicity enabled to propose the hypothesis of an interaction between ,-gliadins and membranes. This interaction was further studied with the help of phospholipid Langmuir monolayers. ,- and ,-gliadins were injected under DMPC and DMPG monolayers and the two-dimensional (2D) systems were studied by Brewster angle microscopy (BAM), polarization modulation infrared reflection-absorption spectroscopy (PM-IRRAS), and surface tension measurements. Results showed that both gliadins adsorbed under phospholipid monolayers, considered as biological membrane models, and formed micrometer-sized domains at equilibrium. However, their thicknesses, probed by reflectance measurements, were different: ,-gliadins aggregates displayed a constant thickness, consistent with a monolayer, while the thickness of ,-gliadins aggregates increased with the quantity of protein injected. These different behaviors could find some explanations in the difference of aminoacid sequence distribution: an alternate repeated - unrepeated domain within ,-gliadin sequence, while one unique repeated domain was present within ,-gliadin sequence. All these findings enabled to propose a model of gliadins self-assembly via a membrane interface and to highlight the predominant role of wheat prolamin repeated domain in the membrane interaction. In the biological context, these results would mean that the repeated domain could be considered as an anchor for the interaction with the ER membrane and a nucleus point for the formation and growth of protein bodies within endosperm cells. © 2009 Wiley Periodicals, Inc. Biopolymers 91: 610,622, 2009. This article was originally published online as an accepted preprint. The "Published Online" date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com [source]


Octanuclear Oxothiomolybdate(V) Rings: Structure and Ionic-Conducting Properties

CHEMISTRY - A EUROPEAN JOURNAL, Issue 12 2004
Charlotte du Peloux Dr.
Abstract A family of alkali salts of octanuclear oxothiomolybdate rings has been synthesized by crystallization of the [Mo8S8O8(OH)8{HMO5(H2O)}]3, (noted HMo8M3,; M=Mo, W) and [Mo8S8O8(OH)8(C2O4)]2, (noted Mo8ox2,) anions in an aqueous solution of ACl (A=Li, Na, K, Rb). Single-crystal X-ray diffraction experiments have been performed showing that the alkali salts exhibit a similar three-dimensional structure. Disordered alkali ions form columns to which the anionic rings are anchored. Ionic-conductivity measurements on pressed pellets have revealed two different behaviors. The lithium salts of HMo8M3, (M=Mo, W) are moderately good proton conductors at room temperature (,=10,5 S,cm,1) and the profile of conductivity as a function of relative humidity shows that the conductivity is due to surface-proton motion (particle-hydrate-type mechanism). On the other hand, the lithium salt of Mo8ox2, competes with the best crystalline lithium conductors at room temperature (,=10,3 S,cm,1), and 7Li NMR experiments confirm the mobility of the lithium ions along the one-dimensional channels of this material. [source]