Sergey A. Prikhod’ko

Influence of C2-Methylation of Imidazolium Based Ionic Liquids on Photoinduced Spin Dynamics of the Dissolved ZnTPP Studied by Time-Resolved EPR

Abstract Unusual physical properties of ionic liquids (ILs) can be implemented in many different applications and are very sensitive to the structure of IL. In this work we investigate the spin dynamics of probe molecule Zn tetraphenylporphyrin (ZnTPP) dissolved in a series of ILs using time-resolved electron paramagnetic resonance (TR EPR). We compare the TR EPR characteristics in C2-methylated imidazolium-based ILs [bmmim]BF4 and [bmmim]PF6 and in their C2-protonated analogs [bmim]BF4 and [bmim]PF6 to assess the influence of C2-methylation. The corresponding TR EPR signatures are drastically different in the two types of ILs. The analysis of experimental data allows assumptions that the ZnTPP molecule is distorted in C2-methylated ILs, contrary to other organic media and C2-protonated analogs. The mobility of ZnTPP in C2-methylated ILs is smaller compared to that in C2-protonated analogs, implying different microenvironment formed around dissolved ZnTPP.

Structural Anomalies in Ionic Liquids near the Glass Transition Revealed by Pulse EPR

Unusual physical and chemical properties of ionic liquids (ILs) open up prospects for various applications. We report the first observation of density/rigidity heterogeneities in a series of ILs near the glass transition temperature ( Tg) by means of pulse electron paramagnetic resonance (EPR). Unprecedented suppression of molecular mobility is evidenced near the glass transition, which is assigned to unusual structural rearrangements of ILs on the nanometer scale. Indeed, pulse and continuous wave EPR clearly indicate the occurrence of heterogeneities near Tg, which exist in a rather broad temperature range of ∼50 K. The two types of local environments are evidenced, being drastically different by their stiffness. The more rigid one suppresses molecular mobility, whereas the softer one instead promotes diffusive molecular rotation. Such properties of ILs near Tg are of general importance; moreover, the observed density/rigidity heterogeneities controlled by temperature might be considered as a new type of tunable reaction nanoenvironment.

Pulse EPR of Triarylmethyl Probes: A New Approach for the Investigation of Molecular Motions in Soft Matter

Triarylmethyl (TAM) radicals have become widely used free radicals in the past few years. Their electron spins have long relaxation times and narrow electron paramagnetic resonance (EPR) lines, which make them an important class of probes and tags in biological applications and materials science. In this work, we propose a new approach to characterize librations by means of TAM radicals. The temperature dependence of motional parameter ⟨α2⟩τc, where ⟨α2⟩ is the mean-squared amplitude of librations and τc is their characteristic time, is obtained by comparison of the 1/ Tm phase-relaxation rates at X- and Q-band EPR frequencies. We study three soft matrixes, viz., glassy trehalose and two ionic liquids, using TAMs with optimized relaxation properties OX063D and a dodeca- n-butyl homologue of Finland trityl (DBT). The motional parameters ⟨α2⟩τc obtained using TAMs are in excellent agreement with those obtained by means of nitroxide radicals. At the same time, the new TAM-based approach has (1) greater sensitivity due to the narrower EPR spectrum and (2) greater measuring accuracy and broader temperature range due to longer relaxation times. The developed approach may be fruitfully implemented to probe low-temperature molecular motions of TAM-labeled biopolymers, membrane systems, polymers, molecules in glassy media, and ionic liquids.

Liquid Phase Pentanol Guerbet-Markovnikov Condensation Over VIII Group Metals

Liquid phase pentanol condensation in solutions of nonpolar hydrocarbons as well as in solventfree conditions was studied in the presence of platinum group metals (platinum, palladium, iridium, ruthenium, and rhodium) supported on mesoporous carbon support Sibunit as well as on metal oxides – alumina, zirconia and ceria. This reaction was carried out in a batch mode in the temperature range 140-200 °C, under nitrogen pressure 1 – 10 bar in the presence of catalysts and a base – NaOH. It was shown that pentanol condensation mainly resulted in formation of the target product 2-propylheptanol (Guerbet alcohol), whereas pentanal, 2-propyl-2-heptenal, 2-propyl-1-heptanal, 2-propyl-1-heptenol were observed in minor quantities. The effect of metals as catalysts and reaction conditions on pentanol conversion and selectivity to 2-propylheptanol was studied. The reaction temperature increase not only as expected accelerates the reaction rate but in addition improves selectivity to 2-propylheptanol. Conversion of pentanol increased in the row Ir/CeO2 << Rh/Al2O3 < Pd/ZrO2 < Ru/C < Ir/C < Pd/C < Pt/C < Pt/Al2O3. Selectivity to 2-propylheptanol was elevated over metallic catalysts in the sequence Ir/CeO2 << Ir/C < Ru/C < Rh/Al2O3 ~ Pd/C ~ Pt/C ~ Pd/ZrO2 ~ Pt/Al2O3 being substantially influenced by temperature increase. The highest yield of 2-propylheptanol under comparable conditions was demonstrated for Pd/C, Pt/C и Pt/Al2O3 catalysts.

Synthesis and Structural Features of Nanostructured Cuprous Chloride with High Catalytic Activity

A method for nanostructured cuprous chloride preparation by reductive thermolysis of a CuCl2⋅2H2O and Cu(OH)2 mixture in glycerol has been developed. The resultant CuCl was characterized with infrared spectroscopy, X-ray photoelectron spectroscopy, EXAFS spectroscopy, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The prepared samples of CuCl demonstrated high catalytic activity in the “direct synthesis” of triethoxysilane.