Ordered equilibrium structures of soft particles in thin layers

Considering a system of gaussian particles confined between two hard, parallel plates, we investigate at T = 0, ordered equilibrium configurations that the system forms as the distance D between the plates gradually increases. Using a very sensitive and reliable optimization technique that is based on ideas of genetic algorithms, we are able to identify the emerging sequences of the energetically most favorable structures. Although the resulting phase diagram is rather complex, its essential features can be reduced to the discussion of two archetypes of structural transitions: (i) a continuous transformation at a fixed number of layers, leading from a square to a centered rectangular and then to a hexagonal lattice; (ii) a discontinuous transition, transforming a hexagonal to a square lattice via complex intermediate structures, i.e., the so-called buckling transition, which is encountered as the system forms a new layer. Detailed Monte Carlo simulations are able to confirm the theoretical predictions on a semiquantitative level but are not able to grasp the tiny energetic differences between competing structures.     

Etude des fragmentations en spectrographie de masse de dithiolannes-1,3 substitués en 2 par des groupements insaturés

The mass spectra of the title compounds always show an intense molecular ion. Some fissions involve loss of the ethylenic group, while others are related to cleavage of the dithiolane ring, eventually followed by recyclizations involving the ethylenic chain, due to which resonance structures can be written. If a phenyl group is present in the ethylenic chain, the spectra are modified due to the formation of the very stable benzothiopyrylium ion.     

Etude en RMN de l'Association des Sels de Lanthanides avec des Phénols; Application à la Détermination de Structure de Polyphénols Naturels

Interaction of lanthanide salts with phenols in DMSO solution was investigated as a tool for ¹H NMR structure determination in the field of naturally-occurring polyphenolic compounds. Intermolecular competition experiments evidenced reactivity differences with respect to the nature and position of substituents. Empirical rules of reactivity are suggested from which variations observed in the PMR chemical shifts on addition of lanthanide salts to natural polyphenols (flavones, xanthones) were rationalized.     

Transferts Protoniques de Sels d'Ammonium Substitues—VIII: Sels de Pyridinium 4-Substitues

The deprotonation rate 1/τ of the title compounds, [4 – R – Py H]⁺, where R = NH₂, t-Bu, Me, Cl, Br or CN, is measured using the coalescence of the pyridinic α-protons, in a mixture CF₃COOH/H₂O/HClO₄ of variable acidity Ho, at 38°C. 1/τ is a linear function k/ho of the acidity 1/ho. k is approximately proportional to the water content and independent of the salt concentration, which seems to be evidence for an exchange with an intermediate pyridine hydrate, according to: . After a preliminary ionisation step: k values, like K_A, fit a Hammett relationship (ρ = 5,05), except for R ? NH₂, and are very sensitive to the nature of R (k = 3,44 × 10² for R = NH₂ and k = 3,14 × 10⁸ M^?1 s^?1 for R ? CN), while k_H values (10¹⁰ s^?1) are not.     

Rapid synthesis of imidazo[4,5-b]pyridine containing polycyclics by means of palladium-catalyzed amidation of 2-chloro-3-nitropyridine

Regioselective nucleophilic substitution of 2-chloro 3-nitropyridine with heterocyclic amides under Pd-catalyzed reaction conditions as described by Buchwald yielded imidazo [4,5-b] pyridine-containing polycyclics as novel scaffolds.     

Line intensity measurements of methane’s \nu _3-band using a cw-OPO

We report on absolute line strength measurements of P(1), R(0) and R(1) singlet lines in the \(3.3\,\upmu\hbox {m}\,\nu _{3}\) (C–H stretching) band of methane \(^{12}\hbox {CH}_4\) at reference temperature \(T=296\)  K. Line strength measurements are performed at low pressure \((P \le 1\hbox { Torr})\) using direct absorption spectroscopy technique based on a widely tunable continuous-wave singly resonant optical parametric oscillator. The \(1\sigma \) overall accuracy in line strength determinations ranges between 7 and 8 % mostly limited by pressure and frequency measurements. A comparison with previous reported values is made. Our results show good agreement with the HITRAN 2012 database.     

Synthesis of New Benzylic Di-, Tri-, and Tetraphosphonic Acids as Potential Chelating Agents

Abstract

New di-, tri-, and tetraphosphonic acids were synthesized starting from four o-hydroxymethyl phenol derivatives and obtained in three steps in good overall yield. The phosphonic acids were isolated and purified using semi-preparative C₁₈ HPLC column. The new compounds were characterized using different spectroscopic methods (¹H, ¹³C, and ³¹P NMR; ESI MS; and MSⁿ, IR).

GRAPHICAL ABSTRACT     

Novel Syntheses of Heterocycles with N-(1-Haloalkyl)azinium Halides. Part V. Preparation of N-Substituted 1,4-Dihydropyridines

Thirty N-substituted Hantzsch 1,4-dihydropyridines were prepared under mild and neutral conditions from N-substituted enaminocarbonyl derivatives and aldehydes activated under the form of N-(1-chloroalkyl)pyridinium chlorides by means of thionyl chloride and pyridine. The scope of the method is discussed.     

From the onset of damage to rupture: construction of responses with damage localization for a general class of gradient damage models

We propose a construction method of non-homogeneous solutions for the traction problem of an elastic damaging bar. This bar has a softening behavior that obeys a gradient damaged model. The method is applicable for a wide range of brittle materials. For sufficiently long bars, we show that localization arises on sets whose length is proportional to the material internal length and with a profile that is also a material characteristic. From its onset until the rupture, the damage profile is obtained either in a closed form or after a simple numerical integration depending on the model. Thus, the proposed method provides definitions for the critical stress and fracture energy that can be compared with experimental results. We finally discuss some features of the global behavior of the bar such as the possibility of a snapback at the onset of damage. We point out the sensitivity of the responses to the parameters of the damage law. All these theoretical considerations are illustrated by numerical examples.