Phosphavinylidene-Carbenoids [P]˭C(Li)X (X ˭ Br,Cl, F): Structure and Dynamics

Abstract

The extraordinary reactivity of carbenoids towards electrophilic as well as nucleophilic reagents awards them for a central importance in organic chemistry. Their unusual bonding situation has been the subject of several theoretical studies'. Having shown in previous reports' that phosphoranyl carbenoids are significantly stabilized by incorporation of the carbenoid center in delocalized n-systems, we succeeded in isolating the first stable bromo. chloro and fluoro-lithio carbenoids 21-c.     

Fragrance encapsulation in polymeric matrices by emulsion electrospinning

We present the successful application of emulsion electrospinning for the encapsulation of a model for highly volatile fragrances, namely (R)-(+)-limonene in a poly(vinyl alcohol) (PVA) fibrous matrix. The influence of the emulsion formulation and of its colloidal properties on the fiber morphology, as well as on the limonene encapsulation efficiency, is described. The release profile of the fragrance from the electrospun nanofibers over a fifteen days range shows that this type of nanofibrous matrices with a high fragrance loading capacity is of great potential for applications in various fields, such as cosmetics or food packaging.     

How to broaden the light reflection band in cholesteric liquid crystals? A new approach based on polymorphism

Cholesteric liquid crystals (CLCs) may selectively reflect light when the helicoidal pitch is of the order of the wavelength of the incident beam propagating along the helix axis. The reflection bandwidth is dependent on the birefringence and is limited to a few tens of nanometers, which is insufficient for applications such as white-on-black reflective displays. Recent studies have shown that CLC polymer networks with a pitch gradient induce a broadening of the reflection bandwidth over several hundreds of nanometers. Most related processes rely on photocrosslinking reactions with a UV-gradient in a mixture made of chiral and achiral monomers with different UV-reactivities. Here a new experimental route exploiting the polymorphism of the mixture is presented. The basic concept lies in a thermally-induced pitch variation simultaneously carried out with the UV-crosslinking reaction. The optical behaviour is investigated in parallel with the cross-sectional microstructure as observed by transmission electron microscopy.     

Characterization of glycosyl inositol phosphoryl ceramides from plants and fungi by mass spectrometry

Although glycosyl inositol phosphoryl ceramides (GIPCs) represent the most abundant class of sphingolipids in plants, they still remain poorly characterized in terms of structure and biodiversity. More than 50 years after their discovery, little is known about their subcellular distribution and their exact roles in membrane structure and biological functions. This review is focused on extraction and characterization methods of GIPCs occurring in plants and fungi. Global methods for characterizing ceramide moieties of GIPCs revealed the structures of long-chain bases (LCBs) and fatty acids (FAs): LCBs are dominated by tri-hydroxylated molecules such as monounsaturated and saturated phytosphingosine (t18:1 and t18:0, respectively) in plants and mainly phytosphingosine (t18:0 and t20:0) in fungi; FA are generally 14–26 carbon atoms long in plants and 16–26 carbon atoms long in fungi, these chains being often hydroxylated in position 2. Mass spectrometry plays a pivotal role in the assessment of GIPC diversity and the characterization of their structures. Indeed, it allowed to determine that the core structure of GIPC polar heads in plants is Hex(R1)-HexA-IPC, with R1 being a hydroxyl, an amine, or a N-acetylamine group, whereas the core structure in fungi is Man-IPC. Notably, information gained from tandem mass spectrometry spectra was most useful to describe the huge variety of structures encountered in plants and fungi and reveal GIPCs with yet uncharacterized polar head structures, such as hexose–inositol phosphoceramide in Chondracanthus acicularis and (hexuronic acid)₄–inositol phosphoceramide and hexose–(hexuronic acid)₃–inositol phosphoceramide in Ulva lactuca.

Formation of DNA‐Copolymer Fibrils Through an Amyloid‐Like Nucleation Polymerization Mechanism

Conjugation of a hydrophobic poly(2‐oxazoline) bearing tertiary amide groups along its backbone with a short single stranded nucleotide sequence results in an amphiphilic comb/graft copolymer, which organizes in fibrils upon direct dissolution in water. Supported by circular dichroism, atomic force microscopy, transmission electron microscopy, and scattering data, fibrils are formed through inter‐ and intramolecular hydrogen bonding between hydrogen accepting amide groups along the polymer backbone and hydrogen donating nucleic acid grafts leading to the formation of hollow tubes.

     

Oligosilanylated Silocanes

A number of mono- and dioligosilanylated silocanes were prepared. Compounds included silocanes with 1-methyl-1-tris(trimethylsilyl)silyl, 1,1-bis[tris(trimethylsilyl)silyl], and 1,1-bis[tris(trimethylsilyl)germyl] substitution pattern as well as two examples where the silocane silicon atom is part of a cyclosilane or oxacyclosilane ring. The mono-tris(trimethylsilyl)silylated compound could be converted to the respective silocanylbis(trimethylsilyl)silanides by reaction with KO^tBu and in similar reactions the cyclosilanes were transformed to oligosilane-1,3-diides. However, the reaction of the 1,1-bis[tris(trimethylsilyl)silylated] silocane with two equivalents of KO^tBu leads to the replacement of one tris(trimethylsilyl)silyl unit with a tert-butoxy substituent followed by silanide formation via KO^tBu attack at one of the SiMe₃ units of remaining tris(trimethylsilyl)silyl group. For none of the silylated silocanes, signs of hypercoordinative interaction between the nitrogen and silicon silocane atoms were detected either in the solid state. by single crystal XRD analysis, nor in solution by ²⁹Si-NMR spectroscopy. This was further confirmed by cyclic voltammetry and a DFT study, which demonstrated that the N-Si distance in silocanes is not only dependent on the energy of a potential N-Si interaction, but also on steric factors and through-space interactions of the neighboring groups at Si and N, imposing the orientation of the p_z(N) orbital relative to the N-Si-X axis.     

Dielectric Spectroscopy Analysis of Liquid Crystals Recovered from End-of-Life Liquid Crystal Displays

In the present work, the dielectric properties of recycled liquid crystals (LCs) (non-purified, purified, and doped with diamond nanoparticles at 0.05, 0.1, and 0.2 wt%) were investigated. The studied LC mixtures were obtained from industrial recycling of end-of-life LC displays presenting mainly nematic phases. Dielectric measurements were carried out at room temperature on a frequency range from 0.1 to 10⁶ Hz using an impedance analyzer. The amplitude of the oscillating voltage was fixed at 1 V using cells with homogeneous and homeotropic alignments. Results show that the dielectric anisotropy of all purified samples presents positive values and decreases after the addition of diamond nanoparticles to the LC mixtures. DC conductivity values were obtained by applying the universal law of dielectric response proposed by Jonscher. In addition, conductivity of the doped LC mixtures is lower than that of the undoped and non-purified LC.     

Line tension at fluid membrane domain boundaries measured by micropipette aspiration

Line tension is a determinant of fluid phase domain formation kinetics and morphology in lipid bilayer membranes, which are models for biological membrane heterogeneity. We describe the first direct measurement of this line tension by micropipette aspiration. Our data are analyzed with a model that does not rely on independently measured (and composition dependent) secondary parameters, such as bending stiffness or membrane viscosities. Line tension is strongly composition dependent and decreases towards a critical consolute point in a quasiternary room temperature phase diagram.     

Porphyrins and Polyoxometalate Scaffolds

Polyoxometalates (POMs) can act as unique reservoirs for multiple electron transfers. As POMs display only weak absorption in the visible spectrum, they can be associated with chromophores such as porphyrins and porphyrin antennae. In this Minireview, the research dedicated to the combination of porphyrins and polyoxometalates is put in context and the state of the art identifying the challenges addressed in the optimization of hybrid materials for applications is detailed.