bluuebunny/crossref_metadata_2025_split huggingface dataset:
Lipid coated chitosan microparticles as protein carriers
Authors: Sommerwerk Anett , Brüßler Jana , Schäfer Jens , Baginski Leonie , Bandulik Mario , Bakowsky Udo 
Published: May 2011

AbstractIn this study, a novel protein‐loaded and lipid‐coated drug carrier system for pulmonary application was developed. In a first step, spherically shaped chitosan particles were produced by spray‐drying. The produced particles showed sizes between 2 μm and 3.5 µm and zeta potentials ranged between 1.4 mV and 37.9 mV. Due to the positive charge of the particles, they could easily be loaded with the model protein drug Bovine Serum Albumine (BSA) via electrostatic interaction. In a final step, the prepared BSA loaded chitosan microparticles were coated with a lipid layer to improve drug delivery via the pulmonary and nasal route. This lipid‐based surface modification changed the physico‐chemical characteristics of the drug carrier systems. While unmodified chitosan particles showed a fast burst release of the protein, the lipid coated particles released the protein over a time period of 2 days. In Conclusion, the lipid‐coated particles show characteristics which make them a promising vehicle for pulmonary administration of proteins. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Selective interactions of concanavalin A‐modified tetraether lipid liposomes
Authors: Ozcetin Aybike , Dayyoub Eyas , Hobler Christian , Keusgen Michael , Bakowsky Udo 
Published: May 2011

AbstractFor the development of site specific liposomes, high stability and long circulation properties are very promising for the improvement of drug targeting and drug delivery system as well as improvement of bioavailability of efficient bioactive drugs. Tetraether lipids (TELs) are very stabile lipids, extracted from Thermoplasma acidophilum. Because of its high chemical stability and its biocompatibility, Tetraether lipid liposomes prepared with TELs are excellent candidates for liposomal drug delivery. In this study a model protein, Concanavalin A (ConA) was chosen for a simulation of a specific adsorbtion onto mannan surface. Concanavalin A (ConA) is a lectin, extracted from Canavalia ensiformis, which interacts with sugar domains localized on inflammatory active tissues or tumors. In this study, stable TEL liposomes were prepared and characterized. Furthermore to develop side specific liposomes, tetraether lipids were activated and, ConA was covalently bond onto the surface of the prepared liposomes. Interaction of ConA conjugated liposomes with mannan‐modified surfaces was investigated by Biomolecular Interaction Analysis (BIA) via Reflectometric Interference Spectroscopy (RIfS). This provides real time observation of interactions between carbohydrate structure and TEL liposomes. Specific interaction was also visualised by AFM imaging subsequent to the RIfS measurements. According to the results, with ConA conjugated liposomes, high specific adsorption efficiency was observed. Consequently, this specific adsorption assay between ConA and mannan surface can be considered as a model for the further studies utilized with specific biomarkers for a selective active agent transfer to tumors and inflammatory active tissues. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The role of cold fronts in the onset of the monsoon season in the South Atlantic convergence zone
Authors: Nieto‐Ferreira Rosana , Rickenbach Thomas M. , Wright Emily A. 
Published: May 2011

AbstractThe onset of the South American monsoon season culminates with the abrupt establishment of the South American convergence zone (SACZ). The impact of cold fronts on the abrupt establishment of the SACZ is studied using an 11‐year composite analysis of the dynamic and thermodynamic structures, intensity and propagation of cold fronts that occur prior to, during, and after monsoon onset in the SACZ. A significant change in the structure and propagation of cold fronts is observed at the time of monsoon onset in the SACZ, with cold fronts suddenly stalling and becoming stationary in southeastern Brazil. It is proposed that this regime change of the structure and propagation of cold fronts causes the abrupt onset of the monsoon in the SACZ. A mechanism for this sudden change in cold front behaviour is suggested by analyzing changes in the observed upper‐level structure of midlatitude waves. Our observations show that, at the time of monsoon onset in the SACZ, midlatitude waves develop a ‘thinning trough’ behaviour, with upper‐level troughs becoming thinner, westward tilted, and sometimes forming cut‐off lows. This behaviour is characteristic of midlatitude waves that develop in the region of anticyclonic shear on the equatorward side of the upper‐level midlatitude jet. During the austral spring, the upper‐level midlatitude jet over South America migrates southward leaving subtropical South America in the equatorward, anticyclonic shear side of the jet. It is hypothesized that, as the meridional shear on the equatorward side of the upper‐level jet gradually becomes more anticyclonic, it suddenly crosses the critical threshold of horizontal shear that has been shown to produce a sudden transition to a ‘thinning trough’ midlatitude wave regime. At this time a regime change occurs whereby the character of frontal systems crossing South America changes abruptly, causing the onset of the monsoon season in the SACZ. Copyright © 2011 Royal Meteorological Society
Quantum topological molecular descriptors in QSAR analysis of organophosphorus compounds
Authors: Paukku Y. , Hill G. 
Published: May 2011

AbstractA Quantitative structure–activity relationship study is performed on a set of organophosphorus compounds to reveal structural and quantum‐chemical features influencing the toxic effect. The properties derived from the topological analysis of the electron density have been used to model the toxicity data. A multiple linear regression analysis in conjunction with genetic algorithm is used in the study, followed by subsequent validation of the results. Obtained QSAR models are beneficial for virtual screening of toxicity for new compounds of interest. Because toxicity of organophosphorus compounds is dependent on conformational properties, a conformational search has been performed before optimization of geometries. All quantum‐chemical calculations are carried out at DFT/B3LYP level of theory with 6‐311++G(d,p) basis set. Frequency calculations are performed after full geometry optimization. Ab initio wave functions were obtained for further analysis and evaluation of quantum topological properties of target molecules. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012
A DFT study of the enantioselective reduction of oxime ethers promoted by chiral spiroborate esters
Authors: Qu Zhibo , Chen Xiaolan , Wei Donghui , Ke Diandian , Qu Lingbo , Yuan Jinwei , Bai Yunliang , Wang Fujun , Zhao Yufen 
Published: May 2011

AbstractMechanisms of borane reduction of the (E)‐acetophenone O‐methyl oxime catalyzed by the easily prepared and stable spiroborate ester 1, derived from diphenylvalinol has been reported for the first time using density functional theory. Two reaction pathways are investigated at the B3LYP/6‐31G(d,p) level of theory. The calculated results reveal that this reaction is accomplished via four steps. All the reactants, products, transition states, and intermediates have been optimized at the B3LYP/6‐31G (d,p) level. The analysis of these results reveals that one pathway is more energetically favorable than the other, and its associated product is in good agreement with the experimental result. The solvent effect has been further considered at the B3LYP/6‐31G(d,p) level in the solvent THF using the PCM model, and the results indicate that it has no great influence on the enantioselectivity of this reduction. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012
Are cluster ion analysis beams good choices for hydrogen depth profiling using time‐of‐flight secondary ion mass spectrometry?
Authors: Zhu Zihua , Shutthanandan Vaithiyalingam 
Published: May 2011

AbstractFor more than three decades, time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) has been used for elemental depth profiling. In recent years, cluster primary ion sources (principally, C60+, Bin+, and Aun+) have become widely available, and they can greatly enhance the signal intensity of molecular ions (10–1000 times). Understanding the performance of cluster ion analysis beams used in elemental depth profiling can greatly assist normal ToF‐SIMS users in choosing the optimal analysis beam for depth profiling work. Presently, however, the experimental data are lacking, and such choices are difficult to make. In this paper, hydrogen and deuterium depth profiling were studied using six different analysis beams—25 keV Bi+, Bi3+, Bi5+, 50 keV Bi32+, 10 keV C60+, and 20 keV C602+. The effort shows that cluster primary ions do enhance H− and D− yields, but the enhancement is only about 1.5–4.0 times when compared to atomic Bi+ ions. Because the currents of atomic ion analysis beams are much stronger than the currents of cluster ion analysis beams for most commercial ToF‐SIMS instruments, the atomic ion analysis beams can provide the strongest H− and D− signal intensities, and may be the best choices for hydrogen and deuterium depth profiling. In addition, two representative nuclides, 30Si and 18O, were also studied and yielded results similar to those of H− and D−. Copyright © 2011 John Wiley & Sons, Ltd.
Adhesion and friction studies of Au nanoparticle‐textured surfaces with colloidal tips
Authors: Zhang Xiaoliang , Lu Yongjuan , Zhong Xiaohua , Yi Gewen , Jia Junhong 
Published: May 2011

AbstractSurface roughness plays an important role in affecting the adhesive force and friction force in microelectromechanical systems (MEMS)/nanoelectromechanical systems (NEMS). One effective approach of reducing adhesion and friction of contacting interfaces is to create textured surface, which is especially beneficial for MEMS'/NEMS' production yield and product reliability. In this article, we present a convenient method to fabricate the nano‐textured surfaces by self‐assembling Au nanoparticles (NPs) on the silicon (100) surfaces. The nanoparticle‐textured surfaces (NPTS) with different packing density and texture height were prepared by controlling the assembling time and the size of Au NPs. The morphologies and chemical states of NPTS were characterized by atomic force microscope (AFM), field emission scanning electron microscope, and XPS. The adhesion and friction on the NPTS were studied by AFM with colloidal tip. The results show that the nano‐textured surfaces have effectively reduced adhesive force and friction force compared with the 3‐aminopropyl trimethoxysilane self‐assembled monolayer surfaces. The lowered adhesion and friction were attributed to the reduced real area of contact between NPTS and colloidal tip. The adhesion and friction of the NPTS are varying with the texture packing density and dependent on both the texture height and asperities spacing, which are related to the size and coverage ratio of NPs on surfaces. Copyright © 2011 John Wiley & Sons, Ltd.
Laser surface treatment of high‐speed steel: presence of TiC particles at the surface
Authors: Abdul Aleem B. J. , Hashmi M. S. J. , Yilbas B. S. 
Published: May 2011

AbstractLaser treatment of a high‐speed steel surface is carried out and metallurgical and morphological changes in the laser‐treated layer are examined using SEM, EDS and XRD. A carbon film of 50 µm thickness and containing 5% TiC particles is formed at the workpiece surface prior to the laser treatment process. The carbon film formed at the surface enhances the absorption of laser irradiation and retains TiC particles at the workpiece surface. The residual stress formed at the laser‐treated surface is determined using the XRD technique while the indentation tests are carried out to measure microhardness and fracture toughness of the resulting surface. It is found that ε‐Fe3N, and ε‐Fe3 (N,C) compounds are formed at the laser‐treated surface, which are attributed to the presence of carbon film and high‐pressure nitrogen‐assisting gas. The fracture toughness of the laser‐treated surface reduces because of the increased hardness and dense layer formed at the surface vicinity. Copyright © 2011 John Wiley & Sons, Ltd.
Value creation and value capture with frictions
Authors: Chatain Olivier , Zemsky Peter 
Published: May 2011

AbstractWe use a formal value‐based model to study how frictions—incomplete linkages in the industry value chain that keep some parties from meeting and transacting—affect value creation and value capture. Frictions arise from search and switching costs and moderate the intensity of industry rivalry and the efficiency of the market. We find that firms with a competitive advantage prefer industries with less, but not zero, frictions. We show that rivalry interacts nontrivially with other competitive forces to affect industry attractiveness. Firm heterogeneity emerges naturally when we introduce resource development. Heterogeneity falls with frictions, but the sustainability of competitive advantage increases. Overall, we show that introducing frictions makes value‐based models very effective at integrating analyses at the industry, firm, and resource levels. Copyright © 2011 John Wiley & Sons, Ltd.
Flexible Carbon Nanotube–Cu2O Hybrid Electrodes for Li‐Ion Batteries
Authors: Goyal Anubha , Reddy Arava L. M. , Ajayan Pulickel M. 
Published: May 2011

AbstractThis study demonstrates the formation of a flexible and free‐standing carbon nanotube–copper oxide–poly(vinylidene fluoride) (CNT–Cu2O–PVDF) nanocomposite and its application as an electrode‐separator material for Li‐ion batteries. Binder‐free hybrid electrodes are obtained by conformally coating CNTs with Cu2O via electrodeposition and then embedding the resulting architecture into a porous poly(vinylidene fluoride‐hexafluoropropylene) PVDF‐HFP–SiO2 polymer electrolyte membrane. The synergistic presence of high‐capacity transition metal oxides and conductive CNTs results in twice the reversible areal capacity of 2.3 mAh cm−2 as compared to 1.2 mAh cm−2 for pure CNTs.
Fatigue Failure and Molecular Machine Design
Authors: Hess Henry , Dumont Emmanuel L. P. 
Published: May 2011

AbstractSophisticated molecular machines have evolved in nature, and the first synthetic molecular machines have been demonstrated. With our increasing understanding of individual operating cycles, the question of how operation can be sustained over many cycles comes to the forefront. In the design of macroscale machines, performance and lifetime are opposing goals. Similarly, the natural evolution of biological nanomachines, such as myosin motor proteins, is likely constrained by lifetime requirements. Rather than bond rupture at high forces, bond fatigue under repeated small stresses may limit the mechanical performance of molecular machines. Here, the effect of cyclic stresses using single and double bonds as simple examples are discussed. Additionally, it is demonstrated that an increase in lifetime requires a reduction in mechanical load and that molecular engineering design features, such as polyvalent bonds capable of rebinding, can extend the bond lifetime dramatically. A universal scaling law for the force output of motors is extrapolated to the molecular scale to estimate the design space for molecular machines.
Ordered, Mesoporous Metal Phosphonate Materials with Microporous Crystalline Walls for Selective Separation Techniques
Authors: Ma Tian‐Yi , Li Hui , Tang An‐Na , Yuan Zhong‐Yong 
Published: May 2011

AbstractOrdered, hexagonal, mesoporous metal (Ti, Zr, V, Al)‐phosphonate materials with microporous crystalline walls are synthesized through a microwave‐assisted procedure by using triblock copolymer F127 as the template. Corresponding metal chlorides and ethylene diamine tetra(methylene phosphonic acid) are chosen as the inorganic precursors and the coupling molecule, respectively. X‐ray diffractometry, transmission electron microscopy, N2 sorption, and thermogravimetry measurements confirm that the obtained metal phosphonates possess a hierarchically porous structure with pore sizes of 7.1–7.5 nm and 1.3–1.7 nm for mesopores and micropores, respectively, and the metal phosphonate materials are thermally stable up to around 450 °C with the pore structure and hybrid framework well preserved. Magic angle spinning NMR, Fourier‐transform infrared spectroscopy, and X‐ray photoelectron spectroscopy analyses indicate that the phosphonate groups are homogenously incorporated into the hybrid framework of the obtained materials. For the first time, the mesoporous hybrid materials are employed as the stationary phase in open tubular capillary electrochromatography technique for the separation of various substances including acidic, basic, and neutral compounds. These materials show good selectivity and reproducibility for this application.
Requirement of α7 nicotinic acetylcholine receptors for amyloid beta protein‐induced depression of hippocampal long‐term potentiation in CA1 region of rats in vivo
Authors: Li Shao‐Feng , Wu Mei‐Na , Wang Xiao‐Hui , Yuan Li , Yang Dong , Qi Jin‐Shun 
Published: May 2011

AbstractThe high density of senile plaques with amyloid beta protein (Aβ) and the loss of cholinergic neurons in the brain are the dominated pathological characteristics of Alzheimer's disease (AD). However, the active center of Aβ, especially the cholinergic mechanism underlying the Aβ neurotoxicity, is mostly unknown. This study examined the effects of different Aβ fragments on hippocampal long‐term potentiation (LTP) and investigated its probable α7 nicotinic acetylcholine receptors (nAChRs) mechanism. The results show that: (1) intracerebroventicular injection of Aβ25–35 or Aβ31–35 significantly and similarly suppressed hippocampal LTP in CA1 region in rats; (2) choline, a selective α7 nAChR agonist, did not affect the LTP induction but enhanced LTP suppression induced by Aβ31–35; and (3) methyllycaconitine, a specific α7 nAChR antagonist, slightly suppressed hippocamal LTP but effectively prevented against Aβ31–35‐induced LTP depression in the presence of Aβ31–35. These results indicate that: (1) the amino acid sequence 31–35 of the Aβ peptide might be a shorter active sequence in the full length molecule; (2) α7 nAChRs are required for the Aβ‐induced suppression of hippocampal LTP. Thus, this study not only provides a new insight into the mechanism by which Aβ impairs synaptic plasticity but also strongly suggests that sequence 31–35 in Aβ molecule and α7 nAChRs in the brain might be potential therapeutic targets for the treatment of AD. Synapse 2011. © 2011 Wiley‐Liss, Inc.
Striatal dopamine D1 and D2 receptors: Widespread influences on methamphetamine‐induced dopamine and serotonin neurotoxicity
Authors: Gross Noah B. , Duncker Patrick C. , Marshall John F. 
Published: May 2011

AbstractMethamphetamine (mAMPH) is an addictive psychostimulant drug that releases monoamines through nonexocytotic mechanisms. In animals, binge mAMPH dosing regimens deplete markers for monoamine nerve terminals, for example, dopamine and serotonin transporters (DAT and SERT), in striatum and cerebral cortex. Although the precise mechanism of mAMPH‐induced damage to monoaminergic nerve terminals is uncertain, both dopamine D1 and D2 receptors are known to be important. Systemic administration of dopamine D1 or D2 receptor antagonists to rodents prevents mAMPH‐induced damage to striatal dopamine nerve terminals. Because these studies employed systemic antagonist administration, the specific brain regions involved remain to be elucidated. The present study examined the contribution of dopamine D1 and D2 receptors in striatum to mAMPH‐induced DAT and SERT neurotoxicities. In this experiment, either the dopamine D1 antagonist, SCH23390, or the dopamine D2 receptor antagonist, sulpiride, was intrastriatally infused during a binge mAMPH regimen. Striatal DAT and cortical, hippocampal, and amygdalar SERT were assessed as markers of mAMPH‐induced neurotoxicity 1 week following binge mAMPH administration. Blockade of striatal dopamine D1 or D2 receptors during an otherwise neurotoxic binge mAMPH regimen produced widespread protection against mAMPH‐induced striatal DAT loss and cortical, hippocampal, and amygdalar SERT loss. This study demonstrates that (1) dopamine D1 and D2 receptors in striatum, like nigral D1 receptors, are needed for mAMPH‐induced striatal DAT reductions, (2) these same receptors are needed for mAMPH‐induced SERT loss, and (3) these widespread influences of striatal dopamine receptor antagonists are likely attributable to circuits connecting basal ganglia to thalamus and cortex. Synapse, 2011. © 2011 Wiley‐Liss, Inc.
Inhibition of the serotonin transporter induces microglial activation and downregulation of dopaminergic neurons in the substantia nigra
Authors: Macgillivray L. , Reynolds K.B. , Sickand M. , Rosebush P.I. , Mazurek M.F. 
Published: May 2011

AbstractDrugs that selectively inhibit the serotonin transporter (SERT) are widely used in the treatment of depression and anxiety disorders. These agents are associated with a range of extrapyramidal syndromes such as akathisia, dystonia, dyskinesia and parkinsonism, suggesting an effect on dopaminergic transmission. We studied the time course of changes in dopaminergic neurons in the substantia nigra (SN) after initiation of two different SERT inhibitors, citalopram and fluoxetine. In the first experiment, groups of Sprague‐Dawley rats received daily meals of rice pudding either alone (N = 9) or mixed with citalopram 5 mg/kg/day (N = 27). Rats were sacrificed after 24 h, 7 days or 28 days of treatment. Sections of SN were processed for tyrosine hydroxylase (TH) immunohistochemistry. Citalopram induced a significant decrease in TH‐positive cell counts at 24 h (44%), 7 days (38%) and 28 days (33%). No significant differences among the citalopram treatment groups were observed in the SN. To determine whether these changes would occur with other SERT inhibitors, we conducted a second experiment, this time with a 28 day course of fluoxetine. As was observed with citalopram, fluoxetine induced a significant 21% reduction of TH cell counts in the SN. Immunoblot analysis showed that fluoxetine also induced a 45% reduction of striatal TH. To investigate a possible role for the innate immune system in mediating these changes, we also studied the microglial marker OX42 after administration of fluoxetine and noted a significant 63% increase in the SN of fluoxtine‐treated animals. These results indicate that SERT inhibition can activate microglia and alter the regulation of TH, the rate limiting enzyme for dopamine biosynthesis. These changes may play a role in mediating the extrapyramidal side effects associated with SERT inhibitors. Synapse, 2011. © 2011 Wiley‐Liss, Inc.