A Convenient,Large-Scale Preparation of a Differentially Protected α-Aminoglycine Suitable for the Synthesis of α-Aminoglycine-Containing Peptides

α-Boc-amino-Fmoc-glycine 6 was prepared in two steps from 9-fluorenyl-methylcarbamate 1, glyoxylic acid 3 and t-butyl carbamate 5. This compound is useful in Solid Phase Peptide Synthesis to prepare α-aminoglycine-containing peptides using Fmoc-strategy.     

Concise Synthesis of α-(Hydroxymethyl) Alkyl and Aryl Vinyl Ketones

2,4-Diketoesters 2 have first been reported as starting materials for the synthesis of a new class of α-hydroxymethyl-α,β-unsaturated ketones 3. Thus, under heterogeneous liquid–liquid medium in the presence of concentrated aqueous potassium carbonate as a base, both aliphatic and aromatic 2,4-dioxoalkanoates 2 react with aqueous formaldehyde to afford the corresponding ketones 3 in fair to good yields.     

Fabrication of p/n heterojunctions by electrochemical deposition of Cu2O onto TiO2 nanotubes

This work describes the TiO₂ nanotubes formation by anodic oxidation under different experimental conditions and the following attempts to optimize the electrochemical deposition of Cu₂O within the nanotubular structure. The as-formed Cu₂O/TiO₂ interface is a p/n junction that could be used in various light-assisted devices. The effect of the F^– concentration, the polarization duration and the post-thermal treatment on the TiO₂ nanotubes is recalled. Then the electrochemical deposition of cuprous oxide is investigated by cyclic voltammetry and the influence of the pH on the morphology and crystal structure is studied. Finally, potential pulses were applied to optimize the Cu₂O film morphology in order to improve the nanotubes covering.     

Chemistry of bridging phosphanes: PdI dimers bearing 2,5-dipyridylphosphole ligands

Two synthetic routes to Pd(I) dimers that feature a bridging 1-phenyl- and 1-cyclohexyl-2,5-di(2-pyridyl)phosphole ligand, 3 a and 3 b, respectively, are described. The first involves a conproportionation process between Pd(II) and Pd(0) complexes, while the second involves ligand displacement from a preformed Pd(I) dimer. Both routes are operable for 1-phenylphosphole 1 a, whereas the former failed with 1-cyclohexylphosphole 1 b. A mechanistic study revealed that the conproportionation pathway implies a reversible oxidative addition of the P-C(phenyl) bond of Pd(II)-coordinated 1 a to Pd(0) leading to a bimetallic Pd(II) complex 5. The structures of complexes 3 a and 3 b were studied by means of X-ray diffraction. The similarity of these solid-state structures suggests that the bridging mode of the P atom is due to mu-1kappaN:1,2kappaP:2kappaN coordination of ligands 1 a, b. The electrochemical behaviour and UV/Vis absorption properties of complexes 3 a, b are reported. Complex 3 a is inert towards CO, PPh(3) and 1,3-dipoles. It reacted with dimethylacetylene dicarboxylate to give complex 6 as a result of insertion of the alkyne into the Pd-Pd bond. X-ray diffraction studies of complexes 5 and 6 are also presented.     

Quasi-periodic harmonic balance method for rubbing self-induced vibrations in rotor–stator dynamics

A quasi-periodic harmonic balance method (HBM) coupled with a pseudo arc-length continuation algorithm is developed and used for the prediction of the steady-state dynamic behaviour of rotor–stator contact problems. Quasi-periodic phenomena generally involve two incommensurable fundamental frequencies, and at present, the HBM has been adapted to deal with cases where those frequencies are known. The problem here is to improve the procedure in order to be able to deal with cases where one of the two fundamental frequencies is a priori unknown, in order to be able to reproduce self-excited phenomena such as the so-called quasi-periodic partial rub. Considering the proposed developments, the unknown fundamental frequency is automatically determined during calculation and an automatic harmonic selection procedure gives both accuracy and performance improvements. The application is based on a Jeffcott rotor model, and results obtained are compared with traditional time-marching solutions. The modified quasi-periodic HBM appears one order of magnitude faster than transient simulations while providing very accurate results.     

Highly Stereoselective Aldol Reactions by Memory of Chirality: Synthesis of Quaternary β-Hydroxy α-Amino Acids

We describe here an asymmetric aldol reaction based on the principle of Memory of Chirality. From α-amino acids such as leucine and methionine, we have synthesized in two steps quaternary α-amino acid derivatives with high diastereoselectivity and enantioselectivity, using the chirality of the initial α-amino acid as the only chirality source. Furthermore, we were able to determine the relative and absolute configurations of the aldol products thanks to crystallographic structures and thus showed that the relative configuration depended on the aldehyde employed. We proposed a stereoselectivity explanation and obtained also quaternary β-hydroxy α-amino acids after acidic hydrolysis.     

A new constrained edit distance between quotiented ordered trees

In this paper we propose a dynamic programming algorithm to compare two quotiented ordered trees using a constrained edit distance. An ordered tree is a tree in which the left-to-right order among siblings is significant. A quotiented ordered tree is an ordered tree T with an equivalence relation on vertices and such that, when the equivalence classes are collapsed to super-nodes, the graph so obtained is an ordered tree as well. Based on an algorithm proposed by Zhang and Shasha [K. Zhang, D. Shasha, Simple fast algorithms for the editing distance between trees and related problems, SIAM Journal on Computing 18 (6) (1989) 1245–1262] and introducing new notations, we describe a tree edit distance between quotiented ordered trees preserving equivalence relations on vertices during computation which works in polynomial time. Its application to RNA secondary structures comparison is finally presented.     

Synthesis and crystal structure of IM-6, a new open framework cobalt-gallium phosphate with ten- and twelve-membered pore openings

A new three-dimensional microporous cobalt-gallium phosphate, named IM-6, has been synthesized under solvothermal conditions with an N-substituted piperazine as organic template. The structure was solved by single-crystal X-ray diffraction (triclinic, P(-)1, a=9.848(20), b=12.470(32), c=12.603(28)A, alpha=63.47(16) degrees, beta=74.56(16) degrees, gamma=76.03(17) degrees). IM-6 exhibits a new framework topology. The inorganic framework is built up of MO(4) (M=Co, Ga) and PO(4) tetrahedra. It displays a two-dimensional interconnected channel system running along the [0(-)11] and [100] directions and delimited by ten- and twelve-membered ring openings, respectively.     

Dualité dans l’espace des caractères virtuels tempérés d’un groupe réductif <Emphasis Type="Italic">p</Emphasis>-adique

Résumé We define an involution on the set of tempered virtual characters of a connected reductive p-adic group. This involution commutes with character of parabolic induction and with truncation. It also preserves the irreducible characters up to sign and the elliptic inner product.     

Time-Resolved Spectroscopy and High-Efficiency Light-Driven Hydrogen Evolution of a {Mo3S4}-Containing Polyoxometalate-Based System

Polyoxothiometalate ions (ThioPOM) are active hydrogen-evolution reaction (HER) catalysts based on modular assembly built from electrophilic clusters {MoS_x} and vacant polyoxotungstates. Herein, the dumbbell-like anion [{(PW₁₁O₃₉)Mo₃S₄(H₂O)₃(OH)}₂]⁸⁻ exhibits very high light-driven HER activity, while the active cores {Mo₃S₄} do not contain any exposed disulfido ligands, which were suspected to be the origin of the HER activity. Moreover, in the catalyst architecture, the two central {Mo₃S₄} cores are sandwiched by two {PW₁₁O₃₉}⁷⁻ subunits that act as oxidant-resistant protecting groups and behave as electron-collecting units. A detailed photophysical study was carried out confirming the reductive quenching mechanism of the photosensitizer [Ir(ppy)₂(dtbbpy)]⁺ by the sacrificial donor triethanolamine (TEOA) and highlighting the very high rate constant of the electron transfer from the reduced photosensitizer to the ThioPOM catalyst. Such results provide new insights into the field of molecular catalytic systems able to promote high HER activity.