The analysis of volatile siloxanes in waste activated sludge

The increasing presence of siloxanes in waste activated sludge (WAS) considerably hampers the energy use of the biogas obtained during the anaerobic digestion of the sludge when concentrations exceed critical limits. To prevent the occurrence of unacceptable operating conditions, it is hence necessary to have a reliable analysis method for determining the siloxane content of the sludge. This paper describes and validates such a method, consisting of the extraction of the siloxanes using n-hexane and a subsequent analysis of the extract using GC-FID. The validation procedure confirms the excellent recovery and repeatability of the proposed method.     

Synthesis of bis-8-hydroxyquinolines via an imination or a Suzuki-Miyaura coupling approach

Bis-8-hydroxyquinolines represent an important yet underexplored class of potential ligands for the preparation of various coordination polymers, which can be used in a plethora of applications. In this work, the synthesis of two types of bis-8-hydroxyquinolines, prepared via either an imination or a Suzuki-Miyaura coupling approach, as well as their analysis is discussed. Imination was pursued through the condensation of quinolinecarbaldehydes with diamines or aminoquinolines with dialdehydes, and the Suzuki-Miyaura coupling reactions were evaluated using a bromoquinoline substrate and diboronic acids.     

Hydrogen-Bond-Assisted Diels–Alder Kinetics or Self-Healing in Reversible Polymer Networks? A Combined Experimental and Theoretical Study

Diels–Alder (DA) cycloadditions in reversible polymer networks are important for designing sustainable materials with self-healing properties. In this study, the DA kinetics of hydroxyl-substituted bis- and tetrafunctional furans with bis- and tris-functional maleimides, both containing ether-functionalized spacers, is investigated by modelling two equilibria representing the endo and exo cycloadduct formation. Concretely, the potential catalysis of the DA reaction through hydrogen bonding between hydroxyl of the furans and carbonyl of the maleimides or ether of the spacers is experimentally and theoretically scrutinized. Initial reaction rates and forward DA rate constants are determined by microcalorimetry at 20 °C for a model series of reversible networks, extended with (i) a hydroxyl-free network and hydroxyl-free linear or branched systems, and (ii) polypropylene glycol additives, increasing the hydroxyl concentration. A computational density-functional theory study is carried out on the endo and exo cycloadditions of furan and maleimide derivatives, representative for the experimental ones, in the absence and presence of ethylene glycol as additive. Additionally, an ester-substituted furan was investigated as a hydroxyl-free system for comparison. Experiment and theory indicate that the catalytic effect of H-bonding is absent or very limited. While increased concentration of H-bonding could in theory catalyze the DA reaction, the experimental results rule out this supposition.     

Selection of crude Solidago virgaurea L. ssp. extracts based on two fast and efficient chromatographic methods (high-performance thin-layer chromatography or high-performance liquid chromatography) for the quantification of total saponins

JPC – Journal of Planar Chromatography – Modern TLC - A previous study on Solidago virgaurea extracts showed an inhibiting activity of Candida albicans yeast—hyphal transition due...     

Synthesis and Reactivity of a Bio‐inspired Dithiolene Ligand and its Mo Oxo Complex

An original synthesis of the fused pyranoquinoxaline dithiolene ligand qpdt^2? is discussed in detail. The most intriguing step is the introduction of the dithiolene moiety by Pd‐catalyzed carbon–sulfur coupling. The corresponding Mo^IVO complex (Bu₄N)₂[MoO(qpdt)₂] ( 2 ) underwent reversible protonation in a strongly acidic medium and remained stable under anaerobic conditions. Besides, 2 was found to be very sensitive towards oxygen, as upon oxidation it formed a planar dithiin derivative. Moreover, the qpdt^2? ligand in the presence of [MoCl₄(tBuNC)₂] formed a tetracyclic structure. The products resulting from the unique reactivity of qpdt^2? were characterized by X‐ray diffraction, mass spectrometry, NMR spectroscopy, UV/Vis spectroscopy, and electrochemistry. Plausible mechanisms for the formation of these products are also proposed.     

Solid‐State Hierarchical Cyclodextrin‐Based Supramolecular Polymer Constructed by Primary,Secondary, and Tertiary Azido Interactions

The crystallization of a di‐azido‐α‐cyclodextrin revealed a polymeric self‐assembly involving a variety of azido‐type interactions. The crystal arrangement relies on the cooperativity of a primary azido inclusion, a secondary azido–azido interaction involving an unprecedented distribution of canonical forms, and a tertiary azido–groove interaction. The second azido group brings in a major contribution to the supramolecular structure illustrating the benefit of a difunctionalization for the generation of hierarchy.