New functional polyamides derived from citric acid and L-lysine: Synthesis and characterization

New functional aliphatic polyamides bearing pendant carboxylic acid and tertiary alcohol groups have been synthesized by step-growth polymerization of protected citric acid in the diacyl chloride activated form and protected L-lysine using the interfacial method. It has been found that a secondary reaction occurs during polymerization and leads to the formation of intramolecular imide cycles. Cleavage of protecting groups and partial or total hydrolysis of imide functions were carried out stepwisely. Resulting structural changes are discussed on the basis of IR and ¹³C NMR data.     

Hintanhaltung der Harng?hrung

Ohne Zusammenfassung     

Self-assembly and hydrophobic clusters of amphiphilic polysaccharides

The objective of this work was to synthesize and characterize new polymeric surfactants deriving from natural polymers and designed for membrane protein solubilization. For this purpose, a set of hydrophobically-modified pullulans (HMCMPs) of moderate molar mass and differing in hydrophobic modification ratio, charge ratio and the nature of the hydrophobic chains introduced, were prepared. Their behaviour in aqueous dilute solutions was investigated by surface tension measurement and with a polarity probe, the Coomassie Brilliant Blue dye. Two distinct critical concentrations were evidenced, demonstrating the complex behaviour of HMCMPs. Amphiphilic pullulan derivatives may indeed establish hydrophobic associations in bulk solution while adsorbing at the air  water interface. The structural parameters of the polymers influence their aqueous behaviour. Self-assembly of HMCMPs occurs at smaller concentrations when the hydrophobic modification ratio or the alkyl hydrophobic chain length increases. It seems to be governed by the concentration of hydrophobic grafts, rather than by polymer concentration. Probably because of steric hindrance, 3-phenylpropyl grafts do not favour self-assembly, and lead to HMCMPs that preferentially adsorb at the air  water interface.     

Depth‐resolved micro‐Raman spectroscopy of tri‐layer PFSA membrane for PEM fuel cells: how to obtain reliable inner water contents

Raman depth‐profiling microspectroscopy is currently emerging as a fast and non‐invasive method for the local content measurement of water diffusing across the perfluorosulfonic acid polymer used as electrolyte in low‐temperature fuel cells. However, water depth profiles obtained thereby are affected by the gradual degradation of the Raman signal as the exciting radiation is focused deeper into the sample and, thus, usually exhibit artificial gradients. The appropriate way to rectify raw data, in order to measure reliable inner water contents, is discussed in the case of perfluorosulfonic acid membranes soaked in water. The method is tested on a tri‐layer material composed by stacked ionomers with different chemical composition, ionic exchange capacity and swelling. Comparison of Raman spectra of the different ionomers, obtained under strictly the same hydration and optical conditions, allows critical discussion of previously reported band assignments. It is shown that Raman bands arising from the polymer backbone and from the side chain can be readily discriminated. Reliable water concentration profiles can then be obtained from the ratio between the Raman signal of sorbed water and of the polymer phase. Comparison with depth profiles obtained by using the pure water signal as internal reference shows that quantitative measurement requires the careful choice of the adequate Raman bands for representing the ionomer occupation of the volume probed by the exciting radiation. Different to what usually performed, the ionomer Raman signal to be integrated for compensating optical losses should include both bands arising from the polymer backbone and side chains. Last, obtaining accurate water concentration profiles also needs the knowledge of the so‐called optical factor β, i.e. the ratio between the scattering cross sections of ionomer chemical groups and sorbed water, which has to be measured by independent Raman experiments. Copyright © 2012 John Wiley & Sons, Ltd.     

In situ μ-Raman spectroscopy study of an isolated micrometer-size pseudo-single crystal of β-H2NiO2 under electrochemical operation

The response of micrometric pseudo-single crystals of β-H₂NiO₂, deposited on an Au substrate and submitted to high rate charge/discharge cycling under controlled current conditions, is studied by in situ μ-Raman spectroscopy. The intensities of the Raman background and of the hydroxyl stretching band are used to probe in time the single-particle surface and bulk oxidation states respectively. Results, obtained in the absence of electrical binders and chemical dopants, substantiate previous electrochemical investigations suggesting that the occurrence of the nickel electrode activation process is related to the formation of a thin surface limiting layer hindering the active material capacity to store and deliver energy. The feasibility of in situ μ-Raman spectroscopy on nickel hydroxide single particles submitted to electrochemical operation is demonstrated for the first time.     

Monitoring of the microstructure of ion‐irradiated nuclear ceramics by in situ Raman spectroscopy

Raman spectroscopy is an efficient technique for studying the evolution of microstructure of materials under irradiation. For that purpose, a Raman spectrometer has been recently installed at the JANNUS‐Saclay platform. In this paper, we describe the new setup for in situ experiments. These in situ experiments allowed following the microstructural evolution of different materials (SiC, ZrO₂ and B₄C) as a function of ion fluence on a single sample (either single crystal or polycrystalline ceramics) under the same irradiation conditions. Our results show that Raman spectroscopy is a versatile non‐contact technique for studying on‐line crystalline phase changes or amorphization of irradiated iono‐covalent solids. A detailed analysis of Raman spectra is provided for the three materials (SiC, ZrO₂ and B₄C) investigated in this study, revealing quite different behaviors upon irradiation. Basically, Raman spectroscopy gives insight on these evolutions at the level of bonds given by specific phonon modes, in good agreement with Rutherford backscattering channeling (RBS/C), X‐ray diffraction (XRD) or transmission electron microscopy (TEM) data, which provide information at a long‐range scale. Copyright © 2015 John Wiley & Sons, Ltd.     

Activite optique de polyamines tertiaires du type poly[thio-(N-R1-N-R2 aminomethyl)-1 ethylene]

Ultra-violet, ORD and CD spectra of (?)poly[thio1-(N-N-diethylaminomethyl) ethylene] (Ia) prepared by stereoelective polymerization of racemic N-N-diethyl-N-(thiirane-2-ylmethyl) amine using ZnEt₂-(—) 3-3-dimethyl-1,2 butanediol as initiator system, of (+)poly[thio1-(N-N-diethyl aminomethyl) ethylene] obtained from a partially resolved enantiomer using ZnEt₂-CH₃OH as initiator system, of poly[thio1-(N-methyl-N-sec-butyl aminomethyl) ethylene] and of poly[thio1-(N-methyl-N-(1-phenylethyl) aminomethyl) ethylene] in organic solvents (tertiary amine form) and in water (hydrochloride form) are described. Observed Cotton effects are associated with electronic transitions of chromophores by comparison with model molecules: N-methyl2-aminobutane, ethyl-thio-2-methylbutane and polypropylene sulfide. For polyamine (Ia), their contributions to optical rotatory powers in the visible are evaluated after decomposition of corresponding CD curves in Gaussian partial Cotton effects. The effects of other optically active electronic transitions located below 180 nm are deduced by difference. Influence of positions of chromophores with regard to chiral centers and of the protonation of nitrogen atoms on observed Cotton effects are discussed.     

A routine method for the determination of plutonium in urine with a low detection limit

A radiochemical method for the determination of plutonium in urine is described. The steps involved are a) co-precipitation of plutonium, b) wet ashing, c) hydrolysis, d) extraction from 2M HNO₃ into capillary polypropylene columns coated with tri-n-octyl phosphineoxide 0.5M in toluene, and e) back-extraction of plutonium from the organic phase, f) electroplating onto stainless steel disks and spectrometry, since plutonium is extracted together with small amounts of uranium naturally occurring in urine. High quality deposits for spectrometry are obtained because iron interference is eliminated before back-extraction. The radiochemical recovery of²³⁹Pu is 55.6±7.5% and the detection limit is 1.0 mBq per liter of urine.     

A geometric mechanism of diffusion: Rigorous verification in a priori unstable Hamiltonian systems

In this paper we consider a representative a priori unstable Hamiltonian system with 2+1/2 degrees of freedom and we apply the geometric mechanism for diffusion introduced in [A. Delshams, R. de la Llave, T.M. Seara, A geometric mechanism for diffusion in Hamiltonian systems overcoming the large gap problem: heuristics and rigorous verification on a model, Mem. Amer. Math. Soc. 179 (844) (2006), viii + 141 pp.], and generalized in [A. Delshams, G. Huguet, Geography of resonances and Arnold diffusion in a priori unstable Hamiltonian systems, Nonlinearity 22 (8) (2009) 1997-2077]. We provide explicit, concrete and easily verifiable conditions for the existence of diffusing orbits.The simplification of the hypotheses allows us to perform the straightforward computations along the proof and present the geometric mechanism of diffusion in an easily understandable way. In particular, we fully describe the construction of the scattering map and the combination of two types of dynamics on a normally hyperbolic invariant manifold.