Photochemical Processes Involved in a Biopolymer Doped by Chromium(VI) during Hologram Recording

This paper is devoted to the study of the photochemical processes occurring during hologram formation in a biopolymer, agar doped by chromium(VI). The evolution of both the absorbing chromium species and the polymer allowed elucidating the reactions taking place during irradiation in conditions representative of hologram formation. As previously observed with dichromated poly(vinyl alcohol) (PVA), polymer containing hydroxyl groups as agar, irradiation of dichromated agar provoked a two step reduction of chromium species and the crosslinking of the host polymer. But agar has a rather complex chemical structure and the photoproducts formed along the polymeric chains throughout the photoredox process were different in agar and in PVA. The photostability of the matrix, that has been proven, coupled with the possibility to record good quality holograms, allowed us to propose dichromated agar as a new natural photosensitive biomaterial.     

Phosphorus Containing Tri-and Hexamacrocycles

Abstract

Multisite receptors containing more than two macrocyclic cavities. despite of the fact that their syntheses, most often, require sophisticated pathways, arc of very high interest since they may allow new insights into ion channel transfer, ion conduction.[1] We report here a method which combine simple reactions, high yields (80%), with easily prepared starting reagents[2], of two new polymacrocyclic system, a tri-(r) and an hexamacrocyck(II). They were obtained by a condensation reaction between 4-formylbenzo-15-crown-5 (3 or 6 quiv, respectively) and phosphouihydrazide (1 equiv.) or hexahydrazide (1 equiv.) in tetrahydrofuran.     

Global persistence of geometrical structures for the Boussinesq equation with no diffusion

Our main aim is to investigate the temperature patch problem for the two-dimensional incompressible Boussinesq system with partial viscosity: the initial temperature is the characteristic function of some simply connected domain with 𝒞^1,𝜀 Hölder regularity. Although recent results ensure that the 𝒞¹ regularity of the patch persists for all time, whether higher order regularity is preserved has remained an open question. In the present paper, we give a positive answer to that issue. We also study the higher dimensional case, after prescribing an additional smallness condition involving critical Lebesgue or weak-Lebesgue norms of the data, so as to get a global-in-time statement. All our results stem from general properties of persistence of geometrical structures (of independent interest), that we establish in the first part of the paper.     

On the Dimension of Posets with Cover Graphs of Treewidth 2

In 1977, Trotter and Moore proved that a poset has dimension at most 3 whenever its cover graph is a forest, or equivalently, has treewidth at most 1. On the other hand, a well-known construction of Kelly shows that there are posets of arbitrarily large dimension whose cover graphs have treewidth 3. In this paper we focus on the boundary case of treewidth 2. It was recently shown that the dimension is bounded if the cover graph is outerplanar (Felsner, Trotter, and Wiechert) or if it has pathwidth 2 (Biró, Keller, and Young). This can be interpreted as evidence that the dimension should be bounded more generally when the cover graph has treewidth 2. We show that it is indeed the case: Every such poset has dimension at most 1276.     

Engineering Hierarchical Nanostructures by Elastocapillary Self‐Assembly

Surfaces coated with nanoscale filaments such as silicon nanowires and carbon nanotubes are potentially compelling for high‐performance battery and capacitor electrodes, photovoltaics, electrical interconnects, substrates for engineered cell growth, dry adhesives, and other smart materials. However, many of these applications require a wet environment or involve wet processing during their synthesis. The capillary forces introduced by these wet environments can lead to undesirable aggregation of nanoscale filaments, but control of capillary forces can enable manipulation of the filaments into discrete aggregates and novel hierarchical structures. Recent studies suggest that the elastocapillary self‐assembly of nanofilaments can be a versatile and scalable means to build complex and robust surface architectures. To enable a wider understanding and use of elastocapillary self‐assembly as a fabrication technology, we give an overview of the underlying fundamentals and classify typical implementations and surface designs for nanowires, nanotubes, and nanopillars made from a wide variety of materials. Finally, we discuss exemplary applications and future opportunities to realize new engineered surfaces by the elastocapillary self‐assembly of nanofilaments.     

Effect of surface roughness and chemical composition on the wetting properties of silicon-based substrates

The article reports on the wetting properties of silicon-based materials as a function of their roughness and chemical composition. The investigated surfaces consist of hydrogen-terminated and chemically modified atomically flat crystalline silicon, porous silicon and silicon nanowires. The hydrogenated surfaces are functionalized with 1-octadecene or undecylenic acid under thermal conditions. The changes occurring upon surface functionalization are characterized using Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS) spectroscopy and water contact angle measurements. By increasing the surface roughness, the static water contact angle increases. The combination of high surface roughness with chemical functionalization with water repellent coating (1-octadecene) enables reaching superhydrophobicity (water contact angle greater than 150°) for silicon nanowires.     

Multicompartment micelles from silicone-based triphilic block copolymers

An amphiphilic linear ternary block copolymer was synthesised in three consecutive steps via reversible addition–fragmentation chain transfer polymerisation. Oligo(ethylene glycol) monomethyl ether acrylate was engaged as a hydrophilic building block, while benzyl acrylate and 3-tris(trimethylsiloxy)silyl propyl acrylate served as hydrophobic building blocks. The resulting “triphilic” copolymer consists thus of a hydrophilic (A) and two mutually incompatible “soft” hydrophobic blocks, namely, a lipophilic (B) and a silicone-based (C) block, with all blocks having glass transition temperatures well below 0 °C. The triphilic copolymer self-assembles into spherical multicompartment micellar aggregates in aqueous solution, where the two hydrophobic blocks undergo local phase separation into various ultrastructures as evidenced by cryogenic transmission electron microscopy. Thus, a silicone-based polymer block can replace the hitherto typically employed fluorocarbon-based hydrophobic blocks in triphilic block copolymers for inducing multicompartmentalisation.     

“Heteroglycals” As New Potential Glycosidase Inhibitors. Synthetic Approaches From D-Arabinose

Within the frame of an ongoing project on glycosidase inhibitors, we have been interested in the synthesis of “heteroglycals”, namely, glycal analogues with sulfur or nitrogen in the ring. Glycals² are well known for their applications in sugar chemistry in particular for glycosyl transfer.³ They are also known as glycosidase inhibitors through a slow chemical reaction with the enzyme. Recently exo-glycals emerged as a new class of glycals⁴ which showed interesting features as glycosidase inhibitors but also as precursors of glycomimetics such as C-glycosides.⁵ We have undertaken investigations on related heteroglycals: such compounds are of interest because they combine a planar geometry at the anomeric center and a possible charge site - both elements known to be important to mimic the transition state of the enzymatic glycoside hydrolysis process.⁶