Influence of the chemical structure of water-soluble cryptophanes on their overall chiroptical and binding properties

The synthesis and the chiroptical properties of the two enantiomers of the hexacarboxylic acid cryptophane-A derivative, 1, are described in this article. The chiroptical and binding properties of 1 toward achiral and chiral guests have been investigated in water under basic conditions by polarimetry, electronic circular dichroism (ECD), vibrational circular dichroism (VCD), and (1)H NMR spectroscopy. These experiments reveal that the (1)H NMR spectra of 1 are very sensitive to the nature of the guest trapped in its cavity whereas ECD and VCD spectra remain unchanged. We also show that the two enantiomers of 1 are able to distinguish between the two enantiomers of a series of small chiral epoxides. The enantiodiscrimination increases with the size of the chiral guest whereas the corresponding binding constants decrease. In contrast to what was observed for other water-soluble cryptophanes, the molecular recognition process is found independent of the nature of the counterions surrounding host 1, shedding light on the importance of the chemical structure of cryptophanes on their binding and chiroptical properties.     

QoS commitment between vertically integrated autonomous systems

Vertically integrated autonomous systems bargain to provide quality of service guarantees and revenue sharing. Depending on the perceived quality of service and access price, consumers determine whether they subscribe to the access provider’s service. Four types of contracts are compared: (i) best effort, (ii) bilateral bargaining, (iii) cascade negotiations and (iv) grand coalition cooperation; the impact of the consumers’ QoS sensitivity parameter and power relation are tested for each contract. Assuming that the consumers’ quality of service sensitivity parameter is unknown and might evolve dynamically due to error judgement, word-of-mouth effect or competition pressure, a learning algorithm is detailed and implemented by each integrated autonomous systems under asymmetrical information. Its convergence and the influence of bias introduction by the most informed autonomous system is analyzed.     

SiO2纳米颗粒单层膜流变特性的双Wilhelmy片法研究

本文采用两个互相垂直的Wilhelmy片对不同润湿性的SiO₂纳米颗粒单层膜的表面压和黏弹性进行了研究, 并利用Brewster角显微镜(BAM)对单层膜的形貌演变进行了观测. 实验发现, 当水面完全被颗粒覆盖时, 单层膜的表面压具有明显的各向异性, 中等润湿性(34%SiOH)的颗粒膜其表面压各向异性最大. 压缩模量E和剪切模量G均在中等润湿性时出现最大值. 这些结果表明, 单层膜的流变性能与泡沫的稳定性密切相关. 疏水性最强(20%SiOH)的颗粒膜具 关键词： 纳米颗粒 单层膜 表面压 流变     

What is the mechanism of soap film entrainment?

Classical Frankel's law describes the formation of soap films and their evolution upon pulling, a model situation of film dynamics in foams (formation, rheology, and destabilization). With the purpose of relating film pulling to foam dynamics, we have built a new setup able to give an instantaneous measurement of film thickness, thus allowing us to determine film thickness profile during pulling. We found that only the lower part of the film is of uniform thickness and follows Frankel's law, provided the entrainment velocity is small. We show that this is due to confinement effects: there is not enough surfactant in the bulk to fully cover the newly created surfaces which results in immobile film surfaces. At large velocities, surfaces become mobile and then Frankel's law breaks down, leading to a faster drainage and thus to a nonstationary thickness at the bottom of the film. These findings should help in understanding the large dispersion of previous experimental data reported during the last 40 years and clarifying the pulling phenomenon of thin liquid films.     

Dynamic surface tension of aqueous solutions of ionic surfactants: role of electrostatics

The adsorption kinetics of the cationic surfactant dodecyltrimethylammonium bromide at the air-water interface has been studied by the maximum bubble pressure method at concentrations below the critical micellar concentration. At short times, the adsorption is diffusion-limited. At longer times, the surface tension shows an intermediate plateau and can no longer be accounted for by a diffusion-limited process. Instead, adsorption appears kinetically controlled and slowed down by an adsorption barrier. A Poisson-Boltzmann theory for the electrostatic repulsion from the surface does not fully account for the observed potential barrier. The possibility of a surface phase transition is expected from the fitted isotherms but has not been observed by Brewster angle microscopy.     

Thiolate chemistry: a powerful and versatile synthetic tool for immobilization/functionalization of oligothiophenes on a gold surface

The synthesis and characterization of a series of quaterthiophenes (4Ts) with thiolate groups protected with 2-cyanoethyl (CNE), 2-trimethylsilylethyl (TMSE), and acetyl (Ac) groups are described. Sequential cleavage of these different protecting groups allows for the preparation of 4Ts derivatized with ferrocene and/or alkanethiol chains. The electrochemical behavior of these compounds has been analyzed in solution by cyclic voltammetry (CV). A ferrocene-derivatized dithiol 4T 14 and a dithiol 4T 15 with two TMSE-protected thiolate groups have been immobilized on a gold surface as monolayers that have been characterized by CV, ellipsometry, contact-angle measurement, and X-ray photoelectron spectroscopy (XPS). The results show that molecules 14 and 15 are doubly grafted with a horizontal orientation of the conjugated system relative to the surface. Furthermore, application of the deprotection/alkylation sequence of the remaining protected thiolate groups on a monolayer of 15 allows for efficient post-functionalization.     

Mechanical unfolding of the beet western yellow virus -1 frameshift signal

Using mechanical unfolding by optical tweezers (OT) and steered molecular dynamics (SMD) simulations, we have demonstrated the critical role of Mg(2+) ions for the resistance of the Beet Western Yellow Virus (BWYV) pseudoknot (PK) to unfolding. The two techniques were found to be complementary, providing information at different levels of molecular scale. Findings from the OT experiments indicated a critical role of stem 1 for unfolding of the PK, which was confirmed in the SMD simulations. The unfolding pathways of wild type and mutant appeared to depend upon pH and nucleotide sequence. SMD simulations support the notion that the stability of stem 1 is critical for -1 frameshifting. The all-atom scale nature of the SMD enabled clarification of the precise role of two Mg(2+) ions, Mg45 and Mg52, as identified in the BWYV X-ray crystallography structure, in -1 frameshifting. On the basis of simulations with "partially" and "fully" hydrated Mg(2+) ions, two possible mechanisms of stabilizing stem 1 are proposed. In both these cases Mg(2+) ions play a critical role in stabilizing stem 1, either by directly forming a salt bridge between the strands of stem 1 or by stabilizing parallel orientation of the strands in stem 1, respectively. These findings explain the unexpected drop in frameshifting efficiency to null levels of the C8U mutant in a manner consistent with experimental observations.     

Anthranilamides with quinoline and β-carboline scaffolds: design,synthesis, and biological activity

Molecular Diversity - In the present study, we report the design and synthesis of novel amide-type hybrid molecules based on anthranilic acid and quinoline or β-carboline heterocyclic...     

The periodic capacitated arc routing problem with irregular services

The aim of this paper is to introduce the periodic capacitated arc routing problem with irregular services. Some applications can be found in road maintenance operations and road network surveillance. The problem consists of determining a set of routes to cover a given network over a time horizon. The roads must be serviced a number of times in sub-periods over the time horizon, according to a hierarchy of arc classes. We present a mathematical model and a heuristic solution approach.     

A comparison of noise models in a hybrid reference spectrum and principal components analysis algorithm for Raman spectroscopy

Raman spectroscopy exploits the Raman scattering effect to analyze chemical compounds with the use of laser light. Raman spectra are most commonly analyzed using the ordinary least squares (LS) method. However, LS is known to be sensitive to variability in the spectra of the analyte and background materials. In a previous paper, we addressed this problem by proposing a novel algorithm that models expected variations in the analyte as well as background signals. The method was called the hybrid LS and principal component analysis (HLP) algorithm and used an unweighted Gaussian distribution to model the noise in the measured spectra. In this paper, we show that the noise in fact follows a Poisson distribution and improve the noise model of our hybrid algorithm accordingly. We also approximate the Poisson noise model by a weighted Gaussian noise model, which enables the use of a more efficient solver algorithm. To reflect the generalization of the noise model, we from hereon call the method the hybrid reference spectrum and principal components analysis (HRP) algorithm. We compare the performance of LS and HRP with the unweighted Gaussian (HRP‐G), Poisson (HRP‐P), and weighted Gaussian (HRP‐WG) noise models. Our experiments use both simulated data and experimental data acquired from a serial dilution of Raman‐enhanced gold‐silica nanoparticles placed on an excised pig colon. When the only signal variability was zero‐mean random noise (as examined using simulated data), HRP‐P consistently outperformed HRP‐G and HRP‐WG, with the latter coming in as a close second. Note that in this scenario, LS and HRP‐G were equivalent. In the presence of random noise as well as variations in the mean component spectra, the three HRP algorithms significantly outperformed LS, but performed similarly among themselves. This indicates that, in the presence of significant variations in the mean component spectra, modeling such variations is more important than optimizing the noise model. It also suggests that for real data, HRP‐WG provides a desirable trade‐off between noise model accuracy and computational speed. Copyright © 2013 John Wiley & Sons, Ltd.