Oxygen Reduction on Ag(100) in Alkaline Solutions—A Theoretical Study

Silver is much more reactive to oxygen than gold; nevertheless, in alkaline solutions, the rates of oxygen reduction on both metals are similar. To explain this phenomenon, the first, rate‐determining step of oxygen reduction on Ag(100) is determined by a combination of DFT, molecular dynamics, and electrocatalysis theory. In vacuum, oxygen is adsorbed on Ag(100), but in the electrochemical environment, the adsorption energy is offset by the loss of hydration energy as the molecule approaches the surface. As a result, the first electron transfer should take place in an outer‐sphere mode. Previously, the same mechanism for oxygen reduction on Au(100) has been predicted, and these calculations have been repeated by using a more advanced version of the electrocatalysis theory discussed herein to confirm previous conclusions. The theoretical results compare well with experimental data.     

Synthesis and cytotoxic activity of usnic acid cyanoethyl derivatives

Cyanoethyl derivatives of usnic acid (natural lichen metabolite) were prepared. The reaction proceeded as a C-alkylation process via addition of two acrylonitrile molecules. Cytotoxic effect of the synthesized derivatives on the blood tumor cell lines was studied.     

Preparative separation of methoxy derivatives of psoralen using supercritical-fluid chromatography

A method of separation of a mixture of three methoxy derivatives of psoralen—bergapten, xanthotoxin, and isopimpinellin—has been developed. The performed screening allows it to be concluded that it is appropriate to separate them by normal-phase supercritical-fluid chromatography (SCF). Analysis of mechanisms of separation of methoxypsoralens (MOPs) showed that, on all silica gel-based sorbents with immobilized polar groups, except for 2-ethylpyridine and pentafluorophenyl sorbents, absorption occurs by the same retention mechanism. A possible explanation for the observed regularities of elution of the related MOPs has been suggested. In the case of pentafluorphenyl sorbent, π-electronic intermolecular interactions play a key role in separation. Presumably the same effect is responsible for the particular order of elution observed when the 2-ethypyridine sorbent was used.     

Optical transitions of holes in uniaxially compressed germanium

Spontaneous emission and photoconductivity of germanium with gallium impurity are studied for determining the energy spectrum of hole states in this material in which radiation can be induced as a result of transitions of holes between these states. Holes were excited by electric field pulses with a strength up to 12 kV/cm at T = 4.2 K under uniaxial compression of samples up to 12 kbar. It has been found that hole emission spectra for transitions between resonant and local states of the impurity have a structure identical to the photoconductivity and absorption spectra. Transitions from resonance states, which are associated with the heavy hole subband, have not been detected. It has been found that in an electric field lower than 100 V/cm, a compressed crystal emits as a result of transitions of heavy holes. In a strong electric field (1–3 kV/cm), emission is observed in the energy range up to 140 meV, and transitions with emission of TA and LO phonons appear in such a field. The emission spectra under pressures of 0 and 12 kbar differ insignificantly. Hence, it follows that the contributions from heavy and light holes in a strong electric field are indistinguishable.     

Ionization energy and energy gap structure of MoSI molecular wires: Kelvin probe, ultraviolet photoelectron spectroscopy, and cyclic voltammetry measurements

The work function W of Mo(6)S(3)I(6) molecular nanowires is determined by Kelvin probe (KP) measurements, UV photoelectron spectroscopy (UPS), and cyclic voltammetry (CV). The values obtained by all three methods agree well, giving W = 4.8 ± 0.1 eV. CV measurements also give a gap between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of E(g) = 1.2 ± 0.1 eV, in agreement with recent optical measurements, but in disagreement with theoretical calculations, which predict the material to be a metal. The electronic structure of Mo(6)S(3)I(6) suggests use of the material in applications such as bulk heterostructure photovoltaics and transparent electrodes and for molecular electronics devices.     

Features of the behavior of 5-substituted N(3)-acyl-4,6-diaryl-3,4-dihydropyrimidin-2(1H)-ones under electron ionization

Mass spectra of 5-substituted N(3)-acyl-4,6-diaryl-3,4-dihydropyrimidin-2(1H)-ones are studied. The features of the dissociative ionization of their molecular ions, which occurs with ketene elimination from the acyl group, are revealed. The subsequent fragmentation of fragment ions proceeds according to the rules established for pyrimidin-2(1H)-one derivatives.     

Synthetic transformations of sesquiterpene lactones. IV.* Synthesis and transformations of <Emphasis Type="Italic">gem</Emphasis>-dichlorocyclopropyl-substituted isoalantolactone derivatives

Chloro-containing compounds, the ratio of which depended on the reaction time, were formed via reaction of isoalantolactone and CHCl₃ through the action of a phase-transfer catalyst. 4,15-(2,2-Dichlorocycloprop1-yl)isoalantolactone exhibited high activity and selectivity in the Heck reaction with arylhalides. Data for the cytotoxicity of the synthesized chloro-derivatives of isoalantolactone in CEM-13, MT-4, and U-937 cell tumor models were obtained. The doses of the most active compounds inhibiting the viability of tumor cells by 50 % (CCID₅₀) were 3.2–11.1 1 M.     

Plant coumarins. IX.* Phenolic compounds of <Emphasis Type="Italic">Ferulopsis hystrix</Emphasis> growing in Mongolia. Cytotoxic activity of 8,9-dihydrofurocoumarins

It was shown that plants of the genus Ferulopsis are valuable sources of coumarins. Nine angular 8-substituted and 8,9-disubstituted 8,9-dihydrofurocoumarins were isolated. The cytotoxicity of these compounds was studied on models of human CEM-13, MT-4, and U-937 tumor cells. X-ray structure data were obtained for peucenidin.     

Nonlinear conductivity of quasi-one-dimensional layered compound TiS3

The crystal structure and transport properties of TiS₃ whiskers in the plane of layers (ab) have been studied. Maxima of the logarithmic derivative of resistance, dln R/d(1/T), are observed at 17, 60 and 120 K both along and across the chains. Strong nonlinearity of the current–voltage characteristics has been revealed in both directions. Nonlinear conductivity along the chains is observed up to T=60 K, while in the transverse direction it is observed up to T=130 K. The results indicate possible phase transitions of electrons to collective states, probably, charge density waves.