Application of quasi-equilibrated thermodesorption of hexane and cyclohexane for characterization of porosity of zeolites and ordered mesoporous silicas

Quasi equilibrated temperature programmed desorption and adsorption (QE-TPDA) of hexane and cyclohexane was applied for characterization of zeolites 5A, ZSM-5, 13X, Y, NaMOR and ordered mesoporous silicas MCM-41, MCM-41/TMB, SBA-15 and HMS. Similar QE-TPDA profiles of hexane and cyclohexane with a single desorption maximum were observed for the wide pore zeolites. No adsorption of cyclohexane for zeolite 5A and a single desorption maximum for ZSM-5 were found, while two-step desorption profiles of hexane were observed for these zeolites. Similar values of the adsorption enthalpy and entropy of hexane and cyclohexane were obtained by fitting the Langmuir model functions for the zeolites X and Y. For NaMOR and ZSM-5 larger differences in these parameters were found. A single desorption peak found at low temperatures in the QE-TPDA profiles of hexane and cyclohexane for the studied silicas was attributed to the multilayered adsorption on their mesopore surface. The adsorption isobars calculated from the thermodesorption profiles were fitted with the BET function. This way values of the specific surface area and the adsorption heat were calculated. Additionally values of the initial heat of adsorption were found by fitting the Henry’s law to the high-temperature sections of the linearized isobars. The largest deviations from the BET and Henry functions and the largest values of the adsorption heats found for SBA-15 indicated the greatest heterogeneity of the adsorption sites on its surface.     

The charging of the carbon nanotube/oligothiophene interphase as studied by in situ electron spin resonance/UV-Vis-NIR spectroelectrochemistry

A detailed in situ Electron Spin Resonance (ESR)/UV-Vis-NIR spectroelectrochemical study of the oligothiophene/single walled carbon nanotube (SWCNT) interphase is presented to provide an insight into the interaction of nanotubes with oligothiophenes. Used as electrode materials these composites are followed in situ with respect to the paramagnetic and diamagnetic states formed upon electrochemical charging. The variation of the oligomer chain length and the type, position and number of substituents at the oligomer is used to understand the structural influence on the formation of the charged states in the material upon electrochemical reaction. For β,β'-dihexylsexithiophene (β,β'-DHST)-SWCNT the enlarged current in the composite and a decreased radical cation concentration can be explained by the formation of π-dimers. By interaction with SWCNTs the π-dimerization of oligothiophenes and the formation of multi π-stack structures occur. For α,ω-dicyano-β,β'-dibutylquaterthiophene (DCNDBQT)-SWCNT a new paramagnetic structure of the oligomer is formed as an intermediate which undergoes follow-up reactions. Using different substituted oligothiophenes their interaction with nanotubes can be understood with respect to the structure of the oligomer.     

Synthetic studies on the solanacol ABC ring system by cation-initiated cascade cyclization: implications for strigolactone biosynthesis

We report a new method for constructing the ABC ring system of strigolactones, in a single step from a simple linear precursor by acid-catalyzed double cyclization. The reaction proceeds with a high degree of stereochemical control, which can be qualitatively rationalized using DFT calculations. Our concise synthetic approach offers a new model for thinking about the (as yet) unknown chemistry that is employed in the biosynthetic pathways leading to this class of plant hormones.     

Quantification of omega-3 fatty acids in dietary supplements and cooking products available on the polish market by thin-layer chromatography—densitometry

JPC – Journal of Planar Chromatography – Modern TLC - The effect of omega-3 fatty acids in the human body is multidirectional. They are used in cancer and cardiovascular disease...     

Diastereoselective lower rim (1S)-camphorsulfonylation as the shortest way to the inherently chiral calix[4]arene

[structure: see text]. A diastereomeric mixture of chiral 25-(1S)-camphorsulfonyloxy-26-isopropoxycalix[4]arene 2a (de 15%) and 25-isopropoxy-26-((1S)-10-camphorsulfonyl)calix[4]arene 2b has been obtained by asymmetrical lower rim (1S)-camphorsulfonylation of the monoisopropoxycalix[4]arene. Pure diastereomer 2a has been obtained by simple crystallization, and its absolute configuration has been determinated by X-ray analysis. Enantiomerically pure inherently chiral 5,11-dibromo-26-isopropoxycalix[4]arene 4 has been synthesized by the upper rim dibromination of the diastereomer 2a followed by hydrolytical removal of the auxiliary camphorsulfonyl group.     

Thermo-chemical properties of biomass from Posidonia oceanica

Posidonia oceanica (PO) is a marine plant endemic to the Mediterranean basin, forming extensive grasslands. Onshore residues represent a major environmental, economic, social and hygienic problem in all coastal zones of the Mediterranean basin due to the great disturbance they cause to bathers and beachfront populations. This work sought to evaluate the thermo-chemical properties of PO in pyrolysis and thermo-oxidative degradation processes. The investigations were carried out using a thermogravimetric analyser (TGA) coupled to a quadrupole mass spectrometer (MS) and an infrared spectrometer (FTIR). In addition, proximate, ultimate, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and biodegradability analyses were carried out on PO. The biodegradability analysis confirmed that residues of PO were a biodegradable material. Accordingly, the application of PO as a feedstock for combustion/co-combustion or biorefining is recommended.     

Synthesis and Use of 6-, 7-and 8-Membered P-Heterocycles

The synthesis of new families of P-heterocycles by reductive modifications, ring enlargement and Diels-Alder cycloaddition is described.