DFT studies on tautomeric preferences of 1-(pyridin-2-yl)-4-(quinolin-2-yl)butane-2,3-dione in the gas phase and in solution

Density functional theory (DFT) calculations show that in vacuum such α-diketone as 1-(pyridin-2-yl)-4-(quinolin-2-yl)butane-2,3-dione is much less stable than its enolimine–enaminone ((1Z,3Z)-3-hydroxy-4-(pyridin-2-yl)-1-(quinolin-2(1H)-ylidene)but-3-en-2-one) and dienaminone tautomers ((1Z,3Z)-1-(pyridin-2-yl)-4-(quinolin-2-yl)buta-1,3-diene-2,3-diol). Other its tautomers (multiple basic and acidic centers in their molecules enable multiple proton transfer to take place) are even more labile. Strength of the intramolecular hydrogen bonds and aromatic character of the (quasi)rings [proved by the Harmonic Oscillator Model of Aromaticity (HOMA) index] in their molecules were found to be responsible for the observed tautomeric preferences. Polar and basic solvent disfavors and favors the enolimine and enaminone tautomers, respectively.     

Naringenin Schiff base: antioxidant activity,acid–base profile,and interactions with DNA

A Schiff base derived from naringenin (NTSC) and its complex with Cu(II) ([Cu(H₃L)(OAc)]·H₂O, Cu(II)–NTSC) have been synthesized and characterized by physicochemical and spectroscopic methods. EPR studies confirmed that nitrogen, oxygen, and sulfur are the donor atoms bound to Cu(II) in the complex. The geometry of the complex has been modelled using DFT methods. Furthermore, naringenin and NTSC were used for the formation of Cu(II) complexes in solution, for comparison of biological activities. Antioxidant studies confirmed better radical scavenging activity of both NTSC and its Cu(II) complex compared to naringenin. The interaction of these compounds with calf thymus DNA was monitored by UV–Vis spectroscopy.     

Applying Mechanochemistry for Bottom‐Up Synthesis and Host–Guest Surface Modification of Semiconducting Nanocrystals: A Case of Water‐Soluble β‐Cyclodextrin‐Coated Zinc Oxide

Mechanochemistry has recently emerged as an environmentally friendly solventless synthesis method enabling a variety of transformations including those impracticable in solution. However, its application in the synthesis of well‐defined nanomaterials remains very limited. Here, we report a new bottom‐up mechanochemical strategy to rapid mild‐conditions synthesis of organic ligand‐coated ZnO nanocrystals (NCs) and their further host–guest modification with β‐cyclodextrin (β‐CD) leading to water‐soluble amide‐β‐CD‐coated ZnO NCs. The transformations can be achieved by either one‐pot sequential or one‐step three‐component process. The developed bottom‐up methodology is based on employing oxo‐zinc benzamidate, [Zn₄(μ₄‐O)(NHOCPh)₆], as a predesigned molecular precursor undergoing mild solid‐state transformation to ZnO NCs in the presence of water in a rapid, clean and sustainable process.     

Dehydrogenation of ethylbenzene with nitrous oxide in the presence of mesoporous silica materials modified with transition metal oxides

The novel mesoporous templated silicas (MCM-48, SBA-15, MCF, and MSU) were used as supports for transition metal (Cu, Cr, or Fe) oxides. The catalysts were synthesized using the incipient wetness impregnation, and characterized by low-temperature N2 sorption, DRIFT, photoacoustic IR spectroscopy, UV-vis diffuse reflectance spectroscopy, and temperature-programmed desorption of ammonia. It was shown that the preparation method used results in different distributions and dimensions of the transition metal oxide clusters on the inert support surface. The prepared catalysts were tested in the reaction of oxidative dehydrogenation of ethylbenzene in the presence of nitrous oxide. The iron-containing catalysts showed the highest catalytic activity. The presence of isolated Fe3+ was found to be the most important factor influencing the ethylbenzene conversion. The undesirable effect of the increase in selectivity toward CO2 was observed for the samples with the highest concentrations of acidic surface sites.     

Thermal, pressure and light switchable spin-crossover materials

This article reviews the most relevant chemical and structural aspects that influence the spin-crossover phenomenon (SCO). Special attention is focussed on the recent development of SCO coordination polymers. The different approaches currently being explored in order to achieve multifunctionality in SCO materials are discussed.     

Isotachophoretic determination of carboxylic acids in biodegradation samples

In the current study a method of isotachophoretic separation of selected carboxylic acids was developed. The method was used for the determination of carboxylated oligo(ethylene glycol)s and their degradation products in biodegradation tests of PEG 250 DA [a mixture of dicarboxylated oligo(ethylene glycol)s]. Two tests were performed in the studies: the Organization for Economic Cooperation and Development (OECD) screening test and the river water die-away test. Both the biodegradation tests proved relatively fast biodegradation of the studied compounds. In the OECD screening test the biodegradation was faster than in the river water die-away test which can be ascribed to a higher concentration of bacteria in the biodegradation liquor. The minimal sample pretreatment and relatively low cost of analysis by the isotachophoretic method used here make it a good alternative to existing methods of carboxylic acids analysis.     

Photostability and the yield of triplet state generation of bacteriochlorophyll c and bacteriopheophytin c in solution

The paper deals with some fast and slow processes of excitation energy deactivation in bacteriochlorophyll c and bacteriopheophytin c. The experiments were carried out in the air, and in oxygen or nitrogen atmosphere at different temperatures. The parameters such as fluorescence yield, the yield of triplet state generation and photostability were estimated. On the basis of these parameters an attempt was made to preliminary select the pigments best suited for medical applications. It seems that the photosensitive and highly fluorescent bacteriochlorophyll c could be used as a fluorescence probe for diagnosis, whereas its derivative without the magnesium ion is better suited for the photochemical reactions occurring during therapeutic treatment.