Naturally occurring organic acids for organocatalytic synthesis of pyrroles via Paal–Knorr reaction

Research on Chemical Intermediates - In this study, common naturally occurring organic acids, namely oxalic, malonic, succinic, tartaric and citric acid (as safe, inexpensive, and biodegradable...     

Experimental study onp-wave neutron strength functions for light nuclei

Broad energy distributions in fast neutron beams have been achieved by appropriate filtering of the²³⁶U fission radiation provided from the RENT converter facility at the FRM research reactor. Transmission measurements in such beams result in average cross sections to which resonance reactions and shape elastic scattering contribute. We used a silicon (124.5 cm) filtered beam with a median energy of 143 keV (width 20 keV) and beams with 1.3 MeV (0.55 to 3 MeV) and 2.1 MeV (1 to 5.5 MeV) obtained through different filter combinations of lead and polyethylene. The relative high energies and the broad spectra made it possible to determine experimentally the contributions ofs- andp-wave resonance reactions to the average cross section even for light nuclei. Using the three different beams we determined the average cross sections for the elements in the mass regionA=9 to 65. Analysing the measured cross sections by means of theR matrix formalism provided a complete set ofp-wave strength functions and distant level parameters. Moreover, single particle shell effects in the cross sections were observed. In conclusion we obtained informations on the 2P and the 3S size resonances and about the validity of the optical model for neutron reactions with light nuclei.     

New complexes of Ni(II) and Cu(II) with tridentate ONO Schiff base ligand: synthesis,crystal structures,electrochemical and theoretical investigation

In this research, we prepared a new series of the Cu(II) (1) and Ni(II) (2) metal complexes of a tridentate Schiff base ligand, (E)-2-(5-bromo-2-hydroxybenzylideneamino) phenol (H₂L). These complexes were characterized by elemental analysis, FT-IR, UV–Vis, and ¹H-NMR spectroscopy. The crystal structures of (1) and (2) were determined by X-ray diffraction studies. The single crystal X-ray diffraction analyses revealed that copper(II) cation is five-coordinated and the coordination polyhedron is a slightly distorted square pyramid. Nickel(II), on the other hand, is four-coordinated, and has a regular, square planar geometry. Further discussed were the electrochemical reduction of these complexes. We also analyzed the nature of the metal–ligand bond in the complexes through NBO and EDA analysis. Besides, vibrational sample magnetometer (VSM) revealed complex (1) was ferromagnetic.     

Practical and efficient synthesis of tetrahydrobenzo[<Emphasis Type="Italic">b</Emphasis>]pyran using caffeine supported on silica as an ionic liquid solid acid catalyst

The new catalyst silica-caffeine hydrogen sulfate [SiO₂-caff.]HSO₄ was conveniently prepared from commercially available 3-chloropropyltriethoxysilane via immobilization on silica followed by reaction with caffeine. The catalyst prepared was then characterized by the FT-IR spectroscopy, TGA, EDX, and SEM techniques. It was found that this heterogeneous catalyst was a highly efficient one for the synthesis of tetrahydrobenzo[b]pyrans in good-to-high yields, and could be recovered by a simple filtration of the reaction solution and reused for five consecutive runs. The attractive features of this method are simple procedure, clean reaction, easy work-up, use of a reusable catalyst, and performing a multi-component reaction.     

Discrimination of Shirazi thyme from thymus species and antioxidant activity prediction using chemometrics and FT-IR spectroscopy

Local names are not reliable sources for identification of plants, because they differ significantly from one region to another. Apart from confusing nomenclature, the similar appearance and fragrance of Shirazi thyme and Thymus species cause misidentification. In order to prevent the adverse events in relation to the use of improper herbal products, easy-to-use quality control (QC) methodology was developed to classify these culinary plants. Fourier transform infrared (FT-IR) fingerprinting technique was applied for classification of these plants on the basis of their biochemical compositions. Powerful PLS-DA classification model with classification accuracy of 100% was obtained. For the first time in the present study, it was revealed that Shirazi thyme samples have higher antioxidant activity [average IC₅₀ of 37.03 (µg/ml)] compared to different Thymus species [average IC₅₀ of 148.35 (µg/ml)]. FT-IR fingerprint profiles were also used to construct a predictive model for antioxidant activity of the plants based on a reliable PLSR model. The developed PLSR model revealed that IR wavenumbers of 1000–1200, 1700, and 3200–3500 cm^?1 are important for antioxidant activity prediction of the analyzed plants. The applied approach has the potential for being used in QC programs not only for fraud mitigation and detection, but also for estimation of antioxidant activity of the culinary plants.     

Effect of surface modification with various thiol compounds on colloidal stability of gold nanoparticles

Gold nanoparticles (AuNPs) are attractive materials due to their special optical and electronic properties. However, they tend to aggregate particularly in the presence of thiol‐containing compounds. In this study, to investigate the effect of surface conjugation with thiol‐containing compounds on colloidal stability, thiol compounds with various structures as modifying agents were used. To this end, AuNPs were synthesized and stabilized by trisodium citrate in aqueous solution, and then modified with thiol‐containing compounds, namely cysteamine hydrochloride (MEA, containing primary amine groups), 2‐mercaptoethanol (BME, containing hydroxyl groups), 1‐dodecanthiol (LCA, containing long‐chain alkyl groups) and thioglycolic acid (TGA, containing carboxylic acid groups). We studied the effect of thiol ligands on solution stability of colloidal AuNPs and on the formation of aggregates originating from the modification process using UV–visible spectroscopy, dynamic light scattering, field emission scanning electron microscopy and transmission electron microscopy. Results showed that surface modification with MEA, BME and LCA led to the formation of aggregates. However, conjugation with TGA showed a concentration‐dependent behaviour: surface modification with low concentration resulted in the formation of aggregates whereas that with high concentration of TGA did not disturb the colloidal stability of AuNPs. Finally, the effect of surface modification on temperature increase of solutions originating from infrared light irradiation was studied, where the temperature increase depends on the surface‐modifying compound.