Supersonic jet studies of solvation effects on the spectroscopy and photophysics of 4-diethylaminopyridine

We present the results of spectroscopic and photophysical investigations of 4-diethylaminopyridine (DEAP) and its 1 : 1 complexes with a number of protic solvents such as water and various alcohols of different acidity isolated under supersonic jet conditions. While a double resonance vibrational spectroscopic method was employed to investigate the size and geometrical structure of jet-cooled clusters, laser-induced fluorescence spectroscopy was used to examine the changes of photophysics induced by complexation of DEAP with solvent molecule(s). The results obtained from ab initio calculations enable the assignment of geometries and of the vibrational spectra of the clusters in the OH-stretch region. The comparison of the experimental and calculated vibrational spectra indicates that the solvent molecule is hydrogen-bonded to the pyridine nitrogen atom. Dual luminescence is observed only for the complexes with alcohols of relatively strong acidity.     

Influence of hybrid system of nanofillers on the functional properties of postconsumer PET‐G–based nanocomposites

In this article, postconsumer poly (ethylene glycol‐co‐1,4‐cyclohexanedimethanol terephthalate) (PET‐G) foils have been modified with three types of carbon nanofillers that differ in size and shape, ie, multiwalled carbon nanotubes (MWCNTs), graphene nanoplatelets (GNP), and nanosized carbon black (nCB), thus enabling the reusage of recyclate in receiving new functional materials. The series of polymer hybrid nanocomposites have been prepared via a two‐stage polycondensation process, be means of glycolysis of postconsumer PET‐G foil, followed by polycondensation in the presence of carbon nanofillers. The scanning electron microscopy revealed that nanoadditives were uniformly dispersed into the whole volume of polymer matrix. The results present the synergistic effect of hybrid system of nanofillers in improving tensile properties of PET‐G. It has been found that the incorporation of three types of carbon nanofillers has not affected the glass transition temperature of the polymer matrix. Moreover, the incorporation of carbon nanofillers, and the mixture of two, or even three of those, caused an improvement in thermal conductivity and thermal stability.     

Methods for determination of polybrominated diphenyl ethers in environmental samples - review

Polybrominated diphenyl ethers (PBDEs) are a group of persistent organic pollutants. They are used as flame retardants in plastics, paints, varnishes and textile materials. PBDEs pose great risk to the environment because of their high persistence and ability to get into the environment easily due to the lack of chemical bonds with the matrix of materials, to which they are added. Global research studies confirmed the occurrence of those compounds in the majority of elements of water and land environment. Analysis of PBDEs in environmental samples is one of the specific analytical methods of criteria that comprise low detection limits and high selectivity. The analysis of PBDEs in environmental samples is one of the specific analytical methods, in which the main criteria are low detection limits and high selectivity. In this article, a literature review of methods for environmental sample preparation and analysis of the PBDE content was presented. The article discusses the potential of modern extraction techniques such as: solid-phase microextraction, single-drop microextraction, dispersive liquid-liquid microextraction, microwave-assisted extraction, cloud point extraction, hollow fibre-liquid phase microextraction and others for the separation of PBDEs from environmental samples with a complex matrix. Among the methods for qualitative and quantitative determination of PBDEs, a particular focus was put on gas chromatography/mass spectrometry with various injection techniques and different types of sample ionisation.     

Thermogravimetry applied to characterization of fly ash-based MCM-41 mesoporous materials

The thermogravimetry (TG) was used for characterization of the fly ash (FA)-based MCM-41 mesoporous materials. MCM-41 mesoporous materials were synthesized using silica extracts from different FA. The synthesis of MCM-41 from FA was carried out by the hydrothermal method using the supernatants of coal FA (in the form of sodium silicate) and cationic cetyltrimethylammonium bromide (CTAB) surfactants as the structure-directing agents. On the basis of the data obtained from the TG analysis, thermal behaviour of FA-based MCM-41 mesoporous materials was assessed. This study has established the range of temperatures corresponding to the desorption of water, decomposition of the surfactant and condensation of silanol, thereby making the overall quality assessment of FA-based MCM-41 mesoporous materials.     

Thiol–Yne Click Reactions on Alkynyl–Dopamine‐Modified Reduced Graphene Oxide

The large‐scale preparation of graphene is of great importance due to its potential applications in various fields. We report herein a simple method for the simultaneous exfoliation and reduction of graphene oxide (GO) to reduced GO (rGO) by using alkynyl‐terminated dopamine as the reducing agent. The reaction was performed under mild conditions to yield rGO functionalized with the dopamine derivative. The chemical reactivity of the alkynyl function was demonstrated by post‐functionalization with two thiolated precursors, namely 6‐(ferrocenyl)hexanethiol and 1H,1H,2H,2H‐perfluorodecanethiol. X‐ray photoelectron spectroscopy, UV/Vis spectrophotometry, Raman spectroscopy, conductivity measurements, and cyclic voltammetry were used to characterize the resulting surfaces.     

An Improved Synthesis and NMR Spectra of Benzylated Glycals

Abstract

Benzylated glycals, unlike their acylated congeners which easily undergo allylic rearrangement, are frequently employed as reactive enol ether type substrates in a variety of electrophilic addition reactions.^1–4 Although these compounds are considered to be readily available substrates, reported procedures for their syntheses involve some steps of limited efficiency, chromatographic separations or costly reagents,^5–7 and experimental requirements not amenable for large scale preparations. In view of the recent applications of benzylated glycals to syntheses of O-glycosides,^1,2 C-glycosyl compounds,³ and β-lactams,⁴ we have undertaken a study aimed at efficient one step benzylation procedures applicable to pyranoid 1-enitols as well as to their acylated derivatives. This goal was eventually achieved by employing a catalytic phase transfer alkylation system with     

Hydro­gen‐bonding patterns in two structural isomers of 3,6‐bis(2‐chloro­phenyl)‐1,4‐di­hydro‐1,2,4,5‐tetrazine

Two structural isomers, 3,6‐bis(2‐chloro­phenyl)‐1,4‐di­hydro‐1,2,4,5‐tetrazine, (I), and 3,5‐bis(2‐chloro­phenyl)‐4‐amino‐1H‐1,2,4‐triazole, (II), both C₁₄H₁₀Cl₂N₄, form chain‐like structures in the solid state, stabilized by N—H⋯N and N—H⋯Cl hydrogen bonds. A contribution from weak interactions to the strong hydrogen‐bond network is observed in both structures. The secondary graph sets for intermolecular hydrogen bonds [(11) for (I) and (12) for (II)] indicate the similarity between the networks.     

A new recyclable Pd catalyst supported on vertically aligned carbon nanotubes for microwaves-assisted Heck reactions

Palladium supported on vertically aligned multi-walled carbon nanotubes (Pd/VA-CNTs) is used as catalyst for the C-C coupling reactions of p-iodonitrobenzene with styrene and ethyl acrylate under microwaves irradiation. Pd/VA-CNTs catalyst exhibits higher activity compared to Pd supported on activated charcoal, under the same reaction conditions. Due to the microwaves irradiation, the kinetics of the reaction is strongly accelerated compared to that obtained with a traditional heating mode. The macroscopic form of aligned CNTs support allows an easy recovery of the catalyst, avoiding a costly post-reaction filtration. In addition, the interaction between the active phase and the support leads to the negligible leaching of palladium during recycling tests. The observed results indicate that Pd/CNTs is a recyclable and stable heterogeneous catalytic system.     

Imino- and aminomethylphenylboronic acids: stabilizing effect of hydrogen bonds

ortho-Iminomethylphenylboronic acids were synthesized from the reaction of 2-formyl–phenylboronic acid with primary aromatic amines. Reduction of these compounds yielded the corresponding aminomethylphenylboronic acids. For both types of the compounds, the crystal structure was determined by single crystal X-ray diffraction method. Hydrogen-bonded dimers with an additional intramolecular B–O–H…N hydrogen bond have been observed. Calculations at MP2/6–31+G** level proved that the most stable form is that with the above-mentioned intramolecular hydrogen bond while the form with dative N→B bond is less favoured. Since the calculated energy difference is small, the competition between possible forms was analyzed in terms of substituent effect stabilization energy (SESE). In the case of p-iminomethylphenylboronic acid, both hydroxyl groups are engaged in intermolecular O–H…O interactions resulting in a supramolecular ribbon motif.