Q-Band Loop-Gap Resonator for EPR Applications with Broadband-Shaped Pulses

Recently, Q-band-pulsed electron paramagnetic resonance spectroscopy has strongly advanced its performance by the introduction of high-power microwave amplifiers and the use of shaped pulses. For such applications, the resonator Q value has to be low enough to achieve sufficient bandwidth for short microwave pulses and to reduce the ring-down time after the pulses. However, a low Q value reduces the detection sensitivity as well as the conversion efficiency of the microwave input power to the magnetic field strength at the sample position. Therefore, the resonator Q value has to be optimized for a given microwave input power and specific application. We designed a three-loop/two-gap resonator using CST Microwave Studio for such applications, and tested its performance in comparison with a standard Bruker D2 Q-band microwave resonator by accomplishing broadband SIFTER experiments on a nitroxide model compound.     

Fluorometric Detection of Adenosine Triphosphate with 3-Hydroxy-4′-(dimethylamino)flavone in Aqueous Solutions

An effect of appearance of new band in the excitation spectra of 3-hydroxy-4′-(dimethylamino)flavone (FME probe) in presence of adenosine triphosphate (ATP) is described. Considerable shift of new band up to the red and increase of fluorescence intensity points to the formation of FME-ATP associate, in which FME molecule undergoes to a strong electrostatic stabilization by tetra-charged ATP anion. It is shown the FME anion formation is possible under influence of ATP in the studied conditions. The dynamics of the observed effect is studied in mitochondria. The registered phenomenon allows the quantitative evaluation of ATP concentration in the range of 10⁻³–10⁻⁵ M. In contrast to ATP, other nucleoside phosphates do not give a new band in the excitation spectra of FME probe. This implies the possibility of the in vivo determination of the ATP concentration.     

Electrical performance of hgInTe surface-barrier photodiodes

Surface-barrier photodiodes prepared by the vacuum deposition of a semi-transparent gold layer on Hg₃In₂Te₆ single-crystal substrates are studied. I-V characteristics taken at temperatures between 278 and 323 K and the photosensitivity spectrum recorded in the range 0.6–1.8 µm, which is of great importance for fiber-optics communication, are given. Charge transfer mechanisms are treated in terms of generation-recombination processes in the space-charge region of the diode.     

Synthesis of 1-(R-Phenyl)-5-(R-Methyl)-1H-1,2,3-triazole-4-carboxylic Acids by One-Pot Tandem Reaction

Substituted 1H-1,2,3-triazole-4-carboxylic acids were synthesized by a three-component reaction of arylazides, ethyl 4-chloro-3-oxobutanoate, and either O- or S-nucleophiles in the presence of a base catalyst. The reaction most probably proceeded as a [3 + 2] cyclocondensation reaction between arylazide and ethyl 4-chloro-3-oxobutanoate with the further nucleophilic substitution of chlorine in the chloromethyl group. Reaction optimization was performed to carry out the reaction with an O-nucleophile. Conditions were found under which diethyl 2,5-dihydroxyterephthalate (the product of self-condensation of two molecules of ethyl 4-chloro-3-oxobutanoate with the further oxidation by azide) was obtained.     

The effect of hydrogen bonding interactions between 2-[4-(dimethylamino)phenyl]-3-hydroxy-4H-chromene-4-one in the ground and excited states and dimethylsulfoxide or methanol on electronic absorption and emission transitions

The surface state of optically pure polydisperse TiO₂ (anatase and rutile) was determined by infra-red (IR) spectroscopy analysis in the temperature range of 100–453 K. Anatase A300 spectrum, contrary to rutile R300 one, has a broad three-component absorption band with peaks at 1048, 1137 and 1222 cm⁻¹ in the spectral range of δ(Ti–O–H) deformation vibrations. For rutile R300 we observed a very weak band at 1047 cm⁻¹, and for the thermal treated rutile R900 these bands were not appeared at all. The analysis of temperature dependencies for the mentioned absorption bands revealed the spectral shift of 1222 cm⁻¹ band towards the high frequencies, when the temperature increased, but the spectral parameters of 1137 and 1048 cm⁻¹ bands remained the same. The temperature of 1222 cm⁻¹ band maximum shift was 373–393 K and correlated with DSC data. Obtained results allowed to assign 1222 cm⁻¹ band to the deformation vibrations of OH-groups, bounded to the surface adsorbed water molecules by weak hydrogen bonds (5 kcal/mol). During the temperature growth these molecules desorbed, which also resulted in the intensity decreasing of stretching OH-groups vibration IR-bands at 3420 cm⁻¹. The destruction and desorption of surface water complexes led to Ti–O–H bond strengthening. IR bands at 1137 and 1048 cm⁻¹ were attributed to the stronger bounded adsorbed water molecules, which are also characterized with stretching OH-groups vibration bands at 3200 cm⁻¹. These surface structure were additionally stabilized by hydrogen bonds with the neighbouring TiO₂ lattice anions and other OH-groups, and desorbed at higher temperatures.     

Reaction of metals with benzenediazonium tetrafluoroborate in aprotic solvents

The reaction of metals and glassy carbon with benzenediazonium tetrafluoroborate (BDFB) in aprotic solvents has been studied. During contact of Pt, Au, Ag, Pd, or V with glassy carbon in concentrated diazonium salt solution no change of color was observed. For Al, Ca, Cr, Cu, Fe, Ga, In, Mg, Li, Na, or Zn the process was accompanied by a rapid solution color change, rapid N₂ release and the loss of metal sample mass. The copper metal ionization-dissolution was studied by ultraviolet and visible absorption spectroscopy, along with gravimetric and volumetric measurements. A dissolution mechanism was proposed based on kinetic, infrared, and X-ray diffraction data. The 432 nm absorption band appearing after Cu-BDFB reaction indicates formation of the mixed complex [Cu(N₂C₆H₅·(N≡C-CH₃)₃]⁺ where the copper atom is covalently bonded to the azophenyl radical and coordinated to acetonitrile (ACN). This complex is thermodynamically unstable and decomposes slowly to a colorless crystalline and a black amorphous phase. The crystalline phase was identified as [Cu(NC-CH₃)₄]BF₄. The amorphous phase is a mixture of products formed by azophenyl and phenyl radical condensation.      

Influence of Freezing and Low Molecular Weight Cryoprotectants on Microsomal Membrane Structure: A Study by Multiparametric Fluorescent Probe

The influence of low molecular weight cryoprotectants (CPs) such as glycerol (GL), 1,2-propanediol (PD) and dimethylsulfoxide (DMSO) on the structure of rat liver microsomal membranes on the stages of equilibration and upon freezing up to −196°C was studied using a multiparametric fluorescent probe of flavonol nature. It was estimated that the studied CPs have individual concentration ranges defining low amplitude of their action on biomembranes. An exceeding of these ranges strongly increases the violation of membrane native structure already at the stage of incubation with CPs, strengthening it during the freezing procedure. According to the perturbation effect on microsomal membranes the studied CPs can be arranged in a sequence: DMSO > PD > GL.