Helical self-assembly and co-assembly of fluorinated, preorganized discotics

The synthesis and self-assembly properties of a fluorinated C(3)-symmetrical 3,3'-bis(acylamino)-2,2'-bipyridine discotic (1) in the mesophase and in solution are described. First, 3,4,5-tris-(1H,1H,2H,2H,3H,3H-perfluoroundecyl-1-oxy)benzoyl chloride was coupled to mono-t-BOC protected 2,2'-bipyridine-3,3'-diamine to afford after deprotection the corresponding fluorinated aromatic amine on a multigram scale. Then, three-fold reaction of this amine with trimesyl chloride yielded the target C(3)-symmetrical fluorinated disc. The latter displayed columnar liquid crystallinity over a temperature range of more than 350 K in which helical rectangular and hexagonal columnar mesophases were detected by X-ray diffraction measurements. (1)H-NMR spectroscopy showed a preorganized structure due to strong intramolecular hydrogen bonding between the amide N-H's and bipyridine nitrogen atoms, even in the presence of a large excess of hexafluoroisopropanol. This preorganized structure allows the formation of helical self-assemblies in fluorinated solvents, as was established using UV-Vis spectroscopy. The fluorinated disc and two chiral hydrocarbon analogues (a C(3)-symmetrical and a desymmetrized disc) were mixed in a 1:10 v:v mixture of methoxynonafluorobutane (MNFB) and 1,1,2-trichloro-1,2,2-trifluoroethane (Freon 113). Importantly, the C(3)-symmetrical hydrocarbon disc dissolves only in the presence of fluorinated disc in the latter solvent mixture, proving a mutual interaction. CD spectroscopy performed on these mixtures points to a preference for alternating self-assemblies of fluorinated and chiral hydrocarbon discotics.     

Heterocycles via intramolecular platinum-catalyzed propargylic substitution

We report a Pt(II)-catalyzed cyclization of nucleophile-tethered propargylic acetates yielding substituted heterocycles containing multiple heteroatoms including morpholines, dioxanes and sulfamates with high cis-selectivity.     

A quantitative analysis of histone methylation and acetylation isoforms from their deuteroacetylated derivatives: application to a series of knockout mutants

The core histones, H2A, H2B, H3 and H4, undergo post‐translational modifications (PTMs) including lysine acetylation, methylation and ubiquitylation, arginine methylation and serine phosphorylation. Lysine residues may be mono‐, di‐ and trimethylated, the latter resulting in an addition of mass to the protein that differs from acetylation by only 0.03639 Da, but that can be distinguished either on high‐performance mass spectrometers with sufficient mass accuracy and mass resolution or via retention times. Here we describe the use of chemical derivatization to quantify methylated and acetylated histone isoforms by forming deuteroacetylated histone derivatives prior to tryptic digestion and bottom‐up liquid chromatography‐mass spectrometric analysis. The deuteroacetylation of unmodified or mono‐methylated lysine residues produces a chemically identical set of tryptic peptides when comparing the unmodified and modified versions of a protein, making it possible to directly quantify lysine acetylation. In this work, the deuteroacetylation technique is used to examine a single histone H3 peptide with methyl and acetyl modifications at different lysine residues and to quantify the relative abundance of each modification in different deacetylase and methylase knockout yeast strains. This application demonstrates the use of the deuteroacetylation technique to characterize modification ‘cross‐talk’ by correlating different PTMs on the same histone tail. Copyright © 2013 John Wiley & Sons, Ltd.     

Asymptotics for Ratios with Applications to Reinsurance

This paper provides an overview of results pertaining to moment convergence for certain ratios of random variables involving sums, order statistics and extreme terms in the sense of modulus. Most of the literature on this matter originates from Darling (1952) who gave a criterion for the convergence in probability to 1 of the ratio of the maximum to the sum in case of nonnegative random variables. Sophie A. Ladoucette is supported by the grant BDB-B/04/03 of the Catholic University of Leuven.     

Multistep deposition of Cu2Si(S,Se)3 and Cu2ZnSiSe4high band gap absorber materials for thin film solar cells

Cu₂ZnSi(S,Se)₄ and Cu₂Si(S,Se)₃ are potential materials to obtain cost effective high band gap absorbers for tandem thin film solar cell devices. A method to synthesize Cu₂SiS₃, Cu₂SiSe₃and Cu₂ZnSiSe₄thin film absorbers is proposed. This method is based on a multistep process, using sequential deposition and annealing processes. X‐ray diffraction analysis performed on the final thin films have confirmed the presence of the Cu₂Si(S,Se)₃ and Cu₂ZnSiSe₄phases. Scanning electron microscopy images revealed the formation of polycrystalline layers with grains size up to 1 µm. The band gap of the ternary Cu₂SiSe₃ and Cu₂SiS₃, and quaternary Cu₂ZnSiSe₄ based thin films as determined from optical and photoluminescence measurements are found to be close to their theoretical values. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Development of two diastereoselective routes towards trans-4-aminomethyl-piperidin-3-ol building blocks

Two diastereoselective, scaleable routes towards trans-3,4-disubstituted piperidines with a 4-hydroxymethyl-3-hydroxy or 4-aminomethyl-3-hydroxy substitution pattern are being described. In the first route, the 3,4-trans configuration was introduced regio- and diastereoselectively via a hydroboration/oxidation sequence starting from 4-hydroxymethylpyridine. In the second route, regioselective epoxide ring opening of N-benzyl-3,4-epoxy-piperidine was achieved with LiCN, in situ generated from acetocyanohydrin and LiNH₂. The regioselectivity of both the hydroboration and the epoxide ring opening was positively influenced by the presence of the basic piperidine nitrogen. Both routes have been optimized to be performed at large scale.