Odd random phase multisine EIS as a detection method for the onset of corrosion of coated steel

In this work, odd random phase multisine Electrochemical Impedance Spectroscopy (ORP-EIS) was used as a detection method for the onset of corrosion of coated steel. The possibility to use ORP-EIS as a rapid-screening test for corrosion was investigated. It is concluded that the detection of a non-linear behavior combined with a non-stationary behavior during the onset of corrosion can be used as a criterion in a rapid-screening test for corrosion of coated steel.     

Near UV Spectra of the Aniliniums: φCH+ 2CH2X, φNH+ (CH2Xa)CH2Xb and φNH+ (C2H4)2X. Long Range Interactions Involving φ and X

We have shown in preceding papers^(1–3), in a study of some specific anilinium ions such as φNH⁺ _3-n (CH₃)_n, φ₂NH⁺ ₂ and φ₃NH⁺, that varying the ammonium groups, or the medium, can lead to great changes in the intensity of the secondary transition of the chromophore^(1–4) because of a δ, π coupling involving the substituent ^(1–10) and φ. In the present work we should like to extend our experiments to more complex ions - since apart our own works the UV spectroscopy of the aniliniums is almost unknown - to study the sensitivity of the chromophore to long range interactions with X through space or through the bonds of the substituents^(11–16).     

The Dualistic Nature of -NH3 +, A weak π-Donating,Strong σ-Withdrawing Substituent. Effects on the Intensity of the UV Spectra of the Toluidinium Ions and Related Molecules

Abstract

Hyperconjugation is not restricted to alkyl groups^(1–4) and ammoniums interact with π systems through σ-π hyperconjugative coupling^(5–9). Their influence on the UV spectrum of the secondary transition of the benzene chromophore in anilinium ions has only been studied during the last years. Previously it was assumed without enough experimental support, that ammonium groups have no spectroscopic effects on a π chromophore (for example:^(10,11)). In fact, although it is a strong σ-electronwithdrawing substituent, an ammonium group is a π-donating one ^5–8). Its π-donating ability - contrary to what is observed in the corresponding alkyl groups where N is replaced by C - increases whenever the number of N⁺?C bonds increases, and ?N(CH³)³+ could be as much π-donating as the ?C(CH₃)₃ group for pseudo-free molecules⁽⁵⁾.     

Bis(2-sulfanylethyl)amino native peptide ligation

The reaction of a peptide featuring a bis(2-sulfanylethyl)amino (SEA) group on its C-terminus with a cysteinyl peptide in water at pH 7 and 37 °C leads to the chemoselective and regioselective formation of a native peptide bond. This method called SEA ligation enriches the native peptide ligation repertoire available to the peptide chemist. Preparation of an innovative solid support which allows the straightforward synthesis of peptide SEA fragments using standard Fmoc/tert-butyl solid phase peptide synthesis procedures is also described.     

Study of the affinity of thermographic additives for silver by time-of-flight static secondary ion mass spectrometry and surface-enhanced Raman spectroscopy on silver nanoparticles

Detection of the interactions between low molecular weight organic compounds and metals in the form of sols on a nanoscale is analytically challenging. This study aims to provide experimental evidence using a combination of UV-Vis absorption spectrometry, surface-enhanced Raman spectrometry (SERS), and static secondary ion mass spectrometry (S-SIMS). The field of application is thermography where silver images are formed via heat-catalyzed reactions. Several organic compounds called tone modifiers and stabilizers are used in thermographic materials for the optimization of the image quality. With exploitation of the strengths of each of the above-mentioned methods, an affinity ranking of several tone modifiers and a stabilizer was established on the basis of competitive adsorption experiments using different model systems. Specifically, silver sols, SERS probes, and sputter-coated silver substrates were exposed to systems with one or two additives. The UV-Vis results provided insight on the aggregation of silver nanoparticles in a hydrosol, which was necessary for the interpretation of the SERS data. Both SERS and S-SIMS measurements led to a similar ranking of the relative affinity of the additives in two components, which was largely consistent with empirical knowledge derived from macroscopic behavior.     

Tilted peptides: the history

Nature has selected peptide motifs for protein functions. It is clear that specific sequence motifs can identify families of enzymes. These sequence motifs are one dimensional signatures and nature has also developed two dimension motifs which cannot be read in the one dimension of sequence language but can be detected in the three dimensional properties of a secondary structure. One of such motifs is tilted peptides. They do not correspond to any consensus of sequence but correspond to a consensus motif where hydrophobicity balance is used as a functional device. In the nineteen eighties, the first tilted peptide was deciphered from the sequence of a virus fusion protein by molecular modelling. It was described as a protein fragment hydrophobic enough to insert into a membrane but too short to span it. The fragment exhibited an asymmetric distribution of hydrophobicity along the helix long axis and hence, was unable to lie parallel or perpendicular to a membrane surface but adopted an orientation in between. Hydrophobicity motif was a very new and very challenging concept and tilted peptides were rapidly found to be involved in several mechanisms of virus fusion. They were also found to be involved in protein secretion and future studies could establish their involvement in the destabilization of 3D protein structures and in the alpha to beta transconformations, which drive the generation of amyloid deposits.     

On the affinity regulation of the metal-ion-dependent adhesion sites in integrins

Density functional theory and a polarizable continuum model are used to (i) understand the affinity modulating mechanisms of the interaction between the metal-ion-dependent adhesion site (MIDAS) of a selected integrin, lymphocyte function-associated antigen-1 (LFA-1) and a ligand mimetic acetate molecule and to (ii) propose a new, promising family of inhibitors to block the interaction of the integrin with intercellular adhesion molecule-1 (ICAM-1). We quantify the effect of isolated factors, such as the metal coordination, the nature of the ligand or the cation present on the MIDAS, and the effect of the permittivity of the media. We show that the affinity for ligand decreases when metal coordination changes from the open conformation to the closed conformation. In addition, Mn2+ and Zn2+ showed to be good competitors for the octahedrically coordinated Mg2+ and yielded excellent affinity values, whereas Ca2+ in an octahedric environment would decrease the affinity for the ligand. Our affinity studies of the open MIDAS showed that nitronate-derived or carboxylic acid-containing ligands may represent new promising scaffolds of future inhibitors. Finally, we show that affinities are always highly favored by low-dielectric environments, which explains the propensity of MIDAS motifs to be surrounded by hydrophobic residues in integrins and highlights the importance of including hydrophobic groups in the inhibitors.     

Theoretical study of Cu(I)Y zeolite: structure and electronic properties

The structural and electronic properties of the accessible Cu(I) site of a faujasite-type zeolite have been studied, by use of large cluster models and a density functional theory-based methodology. We demonstrate that the local ideal C(3) symmetry of the Cu(I) site II is broken. The Cu(I) cation is bonded to the zeolite framework by one bond of about 2.26 A and two shorter ones of 2.07 A. We demonstrate that only one cation position exists at this site. This result is also confirmed by a molecular electrostatic potential analysis. We show that local properties at site II, as well as the global properties of the solid (frontier orbitals), do not depend on the Al and cation distribution and only slightly on the cocation nature. Taking into account the present results and well-known experimental data, we propose that specific catalytic behaviors are correlated with local response properties, such as the local acid strength or, in other reactions, specific local architecture or confinement.     

Complex Networks: from Graph Theory to Biology

The aim of this text is to show the central role played by networks in complex system science. A remarkable feature of network studies is to lie at the crossroads of different disciplines, from mathematics (graph theory, combinatorics, probability theory) to physics (statistical physics of networks) to computer science (network generating algorithms, combinatorial optimization) to biological issues (regulatory networks). New paradigms recently appeared, like that of ‘scale-free networks’ providing an alternative to the random graph model introduced long ago by Erdös and Renyi. With the notion of statistical ensemble and methods originally introduced for percolation networks, statistical physics is of high relevance to get a deep account of topological and statistical properties of a network. Then their consequences on the dynamics taking place in the network should be investigated. Impact of network theory is huge in all natural sciences, especially in biology with gene networks, metabolic networks, neural networks or food webs. I illustrate this brief overview with a recent work on the influence of network topology on the dynamics of coupled excitable units, and the insights it provides about network emerging features, robustness of network behaviors, and the notion of static or dynamic motif.