Transport inefficiency in branched-out mesoscopic networks: an analog of the Braess paradox

We present evidence for a counterintuitive behavior of semiconductor mesoscopic networks that is the analog of the Braess paradox encountered in classical networks. A numerical simulation of quantum transport in a two-branch mesoscopic network reveals that adding a third branch can paradoxically induce transport inefficiency that manifests itself in a sizable conductance drop of the network. A scanning-probe experiment using a biased tip to modulate the transmission of one branch in the network reveals the occurrence of this paradox by mapping the conductance variation as a function of the tip voltage and position.     

Biosynthesis and Characterization of Pd and Pt Nanoparticles Using Piper betle L. Plant in a Photoreduction Method

An extremely rapid green approach that generates bulk quantities of nanocrystals of noble metals such as palladium (Pd) and platinum (Pt) nanoparticles (NPs) with a small sizes of 3.8 ± 0.2 and 2.1 ± 0.4 nm by using Piper betle L. (Piperaceae) leaf extract is described. The highly stable and monodispersed Pd and Pt NPs were obtained at 10 min of continuous sunlight exposure. The bio-reduced Pd and Pt NPs were further characterized by using UV–Visible spectroscopy, transmission electron microscopy, selected area electron diffraction, X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis and cyclic voltammetry measurements. The particles, although discrete, were predominately associated with the P. betle plant proteins, which makes them stable over long time periods. These synthesized biogenic Pd and Pt NPs were evaluated for their acute toxicity studies against aquatic organism, Daphnia magna.     

Nature of reactive O2 and slow CO2 evolution kinetics in CO oxidation by TiO2 supported Au cluster

Recent experiments on CO oxidation reaction using seven-atom Au clusters deposited on TiO2 surface correlate CO2 formation with oxygen associated with Au clusters. We perform first principles calculations using a seven-atom Au cluster supported on a reduced TiO2 surface to explore potential candidates for the form of reactive oxygen. These calculations suggest a thermodynamically favorable path for O2 diffusion along the surface Ti row, resulting in its dissociated state bound to Au cluster and TiO2 surface. CO can approach along the same path and react with the O2 so dissociated to form CO2. The origin of the slow kinetic evolution of products observed in experiments is also investigated and is attributed to the strong binding of CO2 simultaneously to the Au cluster and the surface.     

Exploiting Free‐Energy Minima to Design Novel EphA2 Protein–Protein Antagonists: From Simulation to Experiment and Return

The free‐energy surface (FES) of protein–ligand binding contains information useful for drug design. Here we show how to exploit a free‐energy minimum of a protein‐ligand complex identified by metadynamics simulations to design a new EphA2 antagonist with improved inhibitory potency.     

Causal loop diagrams as a de-escalation technique

Escalation of commitment, the tendency of decision makers to keep on investing in losing courses of action, has been shown to be a costly decision bias that affects many areas of decision making. Even though escalation is a widely studied phenomenon, there has been comparatively little research on how to avoid this bias. The present study focuses on de-escalation of commitment and proposes that causal loop diagrams (CLDs) can help to decrease escalating commitment to a failing course of action. By means of an experiment, this study shows that using a CLD decreases escalation tendencies.     

Effect of cellulase adsorption on the surface and interfacial properties of cellulose

The surface properties of several purified cellulose (Sigmacell 101, Sigmacell 20, Avicel pH 101, and Whatman CF 11) were characterised, before and after cellulase adsorption. The following techniques were used: thin-layer wicking (except for the cellulose Whatman), thermogravimetry, and differential scanning calorimetry (for all of the above celluloses). The results obtained from the calorimetric assays were consistent with those obtained from thin-layer wicking – Sigmacell 101, a more amorphous cellulose, was the least hydrophobic of the analysed celluloses, and had the highest specific heat of dehydration. The other celluloses showed less affinity for water molecules, as assessed by the two independent techniques. The adsorption of protein did not affect the amount of water adsorbed by Sigmacell 101. However, this water was more strongly adsorbed, since it had a higher specific heat of dehydration. The more crystalline celluloses adsorbed a greater amount of water, which was also more strongly bound after the treatment with cellulases. This effect was more significant for Whatman CF-11. Also, the more crystalline celluloses became slightly hydrophilic, following protein adsorption, as assessed by thin-layer wicking. However, this technique is not reliable when used with cellulase treated celluloses.     

Oxalato-bridged dinuclear complexes of Cr(III) and Fe(III): synthesis, structure, and magnetism of [(C2H5)4N]4[MM'(ox)(NCS)8] with MM' = CrCr, FeFe, and CrFe

A new series of homo- and heterometallic oxalato-bridged dinuclear compounds of formulas [Et4N]4[MM'(ox)(NCS)8] ([Et4N]+ = [(C2H5)4N]+; ox = C2O4(2-)) with MM' = Cr(III)-Cr(III) (1), Fe(III)-Fe(III) (2), and Cr(III)-Fe(III) (3) is reported. They have been structurally characterized by infrared spectra and single-crystal X-ray diffraction. The three compounds are isostructural and crystallize in the orthorhombic space group Cmca with Z = 8, a = 16.561(8) A, b = 13.481(7) A, and c = 28.168(8) A for 1, a = 16.515(2) A, b = 13.531(1) A, and c = 28.289(4) A for 2, a = 16.664(7) A, b = 13.575(6) A, and c = 28.386(8) A for 3. The structure of 3 is made up of a discrete dinuclear anion [CrFe(ox)(NCS)8]4- and four disordered [Et4N]+ cations, each of them located on special positions. The anion, in a crystallographically imposed C2h symmetry, contains metal cations in distorted octahedral sites. The Cr(ox)Fe group, which is planar within 0.02 A, presents an intramolecular metal-metal distance of 5.43 A. Magnetic susceptibility measurements indicate antiferromagnetic pairwise interactions for 1 and 2 with J = -3.23 and -3.84 cm-1, respectively, and ferromagnetic Cr-Fe coupling with J = 1.10 cm-1 for 3 (J being the parameter of the exchange Hamiltonian H = -2JS1S2). The ESR spectra at different temperatures confirm the magnetic susceptibility data.     

Sur une nouvelle synthèse et les caractéristiques chimico-physiques du picolylidène-2-bis-(p-phénylsulfate de sodium) (DCI: «Picosulfate de sodium»)

The synthesis of 2-picolylidene-bis-(p-phenylsulfuric acid) disodium salt (I, DCI: ‘sodium picosulfate’) has been realized by two routes. I has been characterized by the usual analytical data and UV., IR. and PMR. spectral properties.     

Functionalized surface as template for in situ generation of two-dimensional metal nanoparticle assembly

Two-dimensional gold nanoparticle assemblies with an average nanoparticle size of 6 nm are generated on silicon and indium tin oxide (ITO)-coated glass surfaces, functionalized with polyethylenimine (PEI) silane monolayer. Contact angle measurements show increased hydrophilic character of the surface due to nanoparticle formation. X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) are used to monitor the chemical and structural development of these nanostructures, while UV–vis spectroscopy is used to follow the formation of the nanoparticle assemblies. This paper elucidates a simple route to in situ synthesis of surface immobilized gold nanoparticles under ambient conditions and also extends to the synthesis of other surface bound nanoparticles, like silver and platinum. Gold nanoparticle assemblies generated in this study are also catalytically active towards methanol oxidation reaction (MOR), which is relevant for direct methanol fuel cells (DMFCs).     

Design and synthesis of novel polycycles based on the 3H‐pyrrolo/6,7‐dihydropyrido[1,2‐a]indole scaffold as templates for pharmaceutical development

In the course of our work aimed at developing novel heterocycles of pharmaceutical interest, we designed and synthesized several polycyclic templates as potential substrates to be used in drug design. We obtained a set of condensed ring systems as versatile structural platforms to generate potential DNA‐interactive agents and/or reversible inhibitors of enzymes such as topoisomerases, poly(ADP‐ribose) polymerase‐1 (PARP‐1), telomerase, and, in particular, cyclin dependent kinases. Herein, we report the design, synthesis, structural investigation, and preliminary DNA‐binding affinity of these heteroaromatic systems. J. Heterocyclic Chem., (2011).