C2-Symmetric hemiaminal ethers and diamines: new ligands for copper-catalyzed desymmetrization of meso-1,2-diols and asymmetric Henry reactions

The synthesis of novel, enantiomerically pure C₂-symmetrical hemiaminal ethers and diamines containing piperazine core is presented. The key steps of the synthesis involve the dimerization of an in situ generated α-amino aldehyde into the corresponding cyclic bis-hemiaminal, followed by dehydration in the presence of a base to give a 7-oxa-2,5-diaza-bicyclo[2.2.1]heptane derivative, which can be regarded as a bicyclic bis-hemiaminal inner ether. These compounds represent a new class of molecule, with a structure unambiguously established for the first time. Finally, sodium triacetoxy-borohydride reduction gave the corresponding diamines. Both classes of compounds, new diamines and hemiaminal ethers, were shown to be good ligands for the copper(II)-catalyzed desymmetrization of meso-diols (up to 87% ee) and Henry reactions (up to 84% ee).     

A limit theorem for random sums modulo 1

Residues of partial sums in a class of dependent random variables, including functionals of uniformly recurrent Markov chains, are in the domain of attraction of the uniform distribution. These types of limit theorems arise for example in the multiplication of floating-point numbers.     

Densitometric Quantification of Monogalactosyldiacylglycerol (MGDG) and Digalactosyldiacylglycerol (DGDG) in Extracts of Fresh Samples of Erigeron canadensis Collected at Different Stages of Growth

JPC – Journal of Planar Chromatography – Modern TLC - Erigeron canadensis is an annual plant of the Asteraceae family, widely distributed in rural and urban areas of Poland and other...     

Two derivatives of (N‐phenylthioureidoalkyl)phosphonates

The structures of di­phenyl [3‐methyl‐1‐(3‐phenyl­thio­ureido)­butyl]­phosphonate and di­phenyl [2‐methyl‐1‐(3‐phenyl­thio­ureido)­butyl]­phosphonate, both C₂₄H₂₇N₂O₃PS, are reported. In both compounds, the thio­urea moiety adopts a syn–syn conformation (i.e. the S—C—N—C torsion angles are synperi­planar), which enables N—H⋯O hydrogen bonds to be formed between centrosymmetrically related mol­ecules. The geometries around the P atoms can be described as distorted tetrahedral. Some of the functional groups in each structure are disordered. The bulk of the different alkyl substituents between the amide and phosphonate groups influences the molecular conformation and crystal packing. Although the structures of these compounds and two related derivatives appear to be similar, they are not isostructural.     

Cavitation and cavity-free deformation of filled crystalline polymer systems

Main mechanisms of tough response of polymers are described. In heterogeneous polymer systems due to mechanical misfit between heterogeneities and the matrix a high negative pressure (tri-axial stress) is generated. The excessive negative pressure is the main reason of material cavitation. Cavitation appears to be another mechanism of tough response of the material to loading. Cavitation is a massive phenomenon in crystalline polymers and in all filled polymers. Cavitation itself does not consume much energy but allows for further toughening by activating other mechanisms. Examples of polypropylene filled with chalk modified by liquid, rubber and mineral filled polypropylene and syndiotactic polypropylene filled with chalk are described. Modes of deformation with significant compressive component of stress prevents for cavitation. Materials deformed in a cavity-free manner show much higher strength. It is pointed out that high polymer crystal anisotropy is necessary for the formation of a network of easy crystallographic slip in the unusual toughening of highly filled polymers observed recently. An example of syndiotactic polypropylene filled with submicro-chalk particles is presented.     

Analysis of Fragmentation Pathways of Peptide Modified with Quaternary Ammonium and Phosphonium Group as Ionization Enhancers

Peptide modification by a quaternary ammonium group containing a permanent positive charge is a promising method of increasing the ionization efficiency of the analyzed compounds, making ultra-sensitive detection even at the attomolar level possible. Charge-derivatized peptides may undergo both charge remote (ChR) and charge-directed (ChD) fragmentation. A series of model peptide conjugates derivatized with N,N,N-triethyloammonium (TEA), 1-azoniabicyclo[2.2.2]octane (ABCO), 2,4,6-triphenylopyridinium (TPP) and tris(2,4,6-trimetoxyphenylo)phosphonium (TMPP) groups were analyzed by their fragmentation pathways both in collision-induced dissociation (CID) and electron-capture dissociation (ECD) mode. The effect of the fixed-charge tag type and peptide sequence on the fragmentation pathways was investigated. We found that the aspartic acid effect plays a crucial role in the CID fragmentation of TPP and TEA peptide conjugates whereas it was not resolved for the peptides derivatized with the phosphonium group. ECD spectra are mostly dominated by c_n ions. ECD fragmentation of TMPP-modified peptides results in the formation of intense fragments derived from this fixed-charge tag, which may serve as reporter ion.     

Investigating the Crystallization Process of Boron-Bearing Silicate-Phosphate Glasses by Thermal and Spectroscopic Methods

Glasses and devitrificates from the SiO₂–B₂O₃–P₂O₅–K₂O–CaO–MgO system with constant contents of SiO₂ and P₂O₅ network formers, modified by the addition of B₂O₃, were analyzed. All materials were synthesized by the traditional melt-quenching technique. The glass stability (GS) parameters (K_rg, ∆T, K_W, K_H) were determined. The effect of the addition of B₂O₃ on the GS, liquation phenomenon, crystallization process, and the type of crystallizing phases were examined using SEM-EDS, DSC, XRD, and Raman spectroscopy imaging methods. It was observed that the addition of B₂O₃ increased the tendency of the glass to crystallize. Both phosphates (e.g., Ca₉MgK(PO₄)₇, Mg₃Ca₃(PO₄)₄), and silicates (e.g., K₂Mg₅(Si₁₂O₃₀), CaMg(Si₂O₆), MgSiO₃) crystallized in the studied system. The Raman spectrum for the orthophosphate Mg₃Ca₃(PO₄)₄ stanfieldite type was obtained. Boron ions were introduced into the structures of crystalline compounds at high crystallization temperatures. The type of crystallizing phases was found to be related to the phenomenon of liquation, and the order of their occurrence was dependent on the Gibbs free enthalpy.     

Novel evidence on the chemistry of β-Lactone anionic polymerization

The mechanistic aspects of the β-lactones anionic polymerization initiated by both classical initiators, i.e. alkali metal alkoxides, and non-traditional ones, such as supramolecular complexes of alkali metals and alkali metal naphthalenes, are discussed in this paper.