Molten salt synthesis of potassium and barium niobates

The interaction of powdered niobium oxide with molten potassium and barium nitrate salts containing KOH was studied. It was shown that KNbO₃ can be obtained with the use of binary mixtures of the KOH-KNO₃ system. The BaNb₂O₆ compound can be synthesized in melts of the KNO₃-Ba(NO₃)₂ system. The treatment of Nb₂O₅ with melts of the system KNO₃-Ba(NO₃)₂-KOH with various KOH percentages allowed us to obtain mixtures of Ba₅Nb₄O_15.33 with Nb₁₂O₂₉ or Ba₅Nb₄O_15.48 with K_0.8Ba_0.2NbO₃.     

Vibrational spectra of potassium hydrogen 3,4 furandicarboxylate and intramolecular H-bond

I.r. and Raman spectra of potassium hydrogen 3,4 furandicarboxylate are presented. An assignment of the band is proposed and the details of the hydrogen bond bonds are discussed by analogy with potassium hydrogen maleate. Anharmonic coupling between ν_as, OHO and ν_s OHO is found in the combination band at about 1000 cm⁻¹.     

Vibrational spectra of potassium hydrogen 2,3-furandicarboxylate and intramolecular H-bond

Infrared and Raman spectra of KHFur 2,3 and KDFur 2,3 are presented. An assignment of the bands is given which is in good agreement with previous results concerning acid salts possessing intramolecular hydrogen bonds. The ν_as OHO participation was observed at 670 and 520 cm⁻¹, absorption bands of medium intensity. The absence of a more pronounced broadening might be explained by assuming an anharmonic coupling between the ν_as OHO and the ν_s OHO modes, resulting in a combination band at 1000 cm⁻¹.     

The mechanism of photoinduced hydrogen transfer during photoreduction of carbonyl compounds

A model reaction of hydrogen transfer has been proposed that describes well the results of kinetic studies of the photoreduction of o- and p-quinones and fluorenone in the presence of para-substituted N,N-dimethylanilines and polyalkylbenzenes in various solvents.     

Action spectra for photoinduced inactivation of bacteriophage T7 sensitized by 8-methoxypsoralen and angelicin

The action spectrum (240-300 nm) for photoinactivation of unsensitized phage T7 and the action spectra (310-380 nm) for photoinactivation of phage T7 sensitized with 8-methoxypsoralen (8-MOP) and angelicin were measured by an automated method. For unsensitized phage T7 the action spectrum is in good agreement with the absorption spectrum. For sensitization with angelicin the action spectrum is similar to the absorption spectrum, but for sensitization with 8-MOP the spectra are different. The agreement between the T7 absorption and action spectra in the far-UV region is due to photodamage of DNA, leading to phage inactivation. The similarity in the action and absorption spectra in the near-UV region for sensitization with angelicin seems to be in accordance with the monofunctional photobinding of angelicin to DNA. The action spectrum for sensitization with 8-MOP has a maximum at about 320 nm and this suggests that, in addition to the monoadducts, the biadducts play a role in the inactivation of phage T7. Taking the number of bound furocoumarin molecules into consideration, the quantum efficiencies were estimated. Furocoumarin increases the quantum efficiency in the near-UV region and the values are similar to those obtained in far-UV light without psoralens.     

Hydrogen bonds in fluorosubstituted dicarboxylic acids: vibrational spectra and crystal structure of potassium hydrogen difluorofumarate and potassium hydrogen difluoromaleate

The crystal structures of potassium hydrogen difluoromaleate (KHDFM) and potassium hydrogen difluorofumarate (KHDFF) have been determined by single crystal X-ray methods. The hydrogen difluoromaleate ion has a closed ring structure with a short intramolecular hydrogen bond. The O· O distance is 2.415(1) Å The hydrogen difluorofumarate ions form infinite chains via short intermolecular hydrogen bonds.The O· ;O distance is 2.450(5) Å. In both compounds the hydrogen bonds are across crystallographic symmetry elements. The vibrational spectra of both compounds and their deuterated derivatives have been recorded and assigned. The IR spectrum of KHDFF is of Speakman's A₂ type. The spectra of KHDFM and potassium hydrogen maleate are very similar.     

Infrared transmission,attenuated total reflectance,and Raman spectra of potassium hydrogen succinate

The nature of the broad and strong absorption culminating near 950 m⁻¹ and of the bands in the 1600–1700 cm⁻¹ region is discussed with respect to polarized transmission, ATR, and Raman data obtained with single crystals of potassium hydrogen (and deuterium) succinate. The former absorption seems to be due to the B_u type OHO stretching combined with multiphononic components arising from transitions between the ν OHO and σ OHO branches for k ≠ 0. These appear to activate also the CO modes not allowed in the harmonic approximation for the C_2h factor group. Assignments for other bands are also given.     

Mechanism of the formation of hydrogen tetroxide and peroxide via low-temperature interaction between hydrogen atoms and molecular oxygen

A mechanism and kinetic model for the synthesis of peroxide radical condensate via the low-temperature interaction of hydrogen atoms with O₂ molecules is proposed. The main components of the reaction, hydrogen tetroxide H₂O₄ and hydrogen peroxide H₂O₂, are formed in a low-temperature liquid layer formed near the cold surface during synthesis. Molecules of H₂O₄ and H₂O₂ are stabilized by transitioning to the solid phase. The dependences of the \(N_{O_2 } /N_{H_2 O_2 }\) ratio on the ratio of concentrations of H and O₂ in the gas phase, calculated on the basis of the model, are consistent with the experimental data.     

Effects of photoinduced membrane rigidification on the lysosomal permeability to potassium ions

Mechanism for the photoinduced increase in the lysosomal K+ permeability is still unknown. In this study, we investigated the effect of photodamage-induced membrane rigidification on the lysosomal K+ permeability by measuring the membrane potential with bis(3-propyl-5-oxoisoxazol-4-yl)pentamethine oxonol and by monitoring proton leakage with p-nitrophenol. Membrane fluidity was measured by the steady-state fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene. Methylene blue-mediated photodamage to lysosomes decreased their membrane fluidity and increased their K+ permeability. The photoinduced increase in the K+ permeability can be reversed by fluidizing the rigidified lysosomal membranes with benzyl alcohol. The results suggest that the membrane rigidification induced by photodamage may increase lysosomal K+ permeability. This conclusion is supported by the observation that rigidifying lysosomal membranes by the treatment with membrane rigidifier cholesteryl hemisuccinate also enhanced the lysosomal K+ permeability.     

Determination of hydrogen peroxide by photoinduced fluorogenic reactions

4-Hydroxyproline, 8-hydroxyquinoline, 4-hydroxyquinoline-2-carboxylic acid and 4-hydroxyphenylacetic acid (HPA) react with H₂O₂ when irradiated with UV light to yield fluorescent products. Sub-micromolar detection limits of H₂O₂ are possible with HPA. The fluorescent product is the same as that formed in the peroxidase enzyme-mediated H₂O₂ oxidation of HPA. Several compounds that participate in the photomediated reaction do not react in the enzyme-mediated system. A mechanism for the photomediated reaction involving an aryloxy radical derived from the substrate is suggested. Although the limits of detection for H₂O₂ do not equal the best achievable with the enzyme-mediated systems, the simplicity of a single-step reaction and an ability to “photodevelop” the product offer a range of novel analytical possibilities.     

Reactivity of photoinduced hole centers on anatase and activation of molecular oxygen

The centers (g₁=1,999; g₂=1.984 and g₃=1.979) assigned to the stabilization of photoinduced O^– holes on coordinatively unsaturated Ti⁴⁺ ions, not interacting with CO up to 250 K, are shown to be the activation centers of the molecular oxygen as an complex (g₁=2.046; g₂=2.008) for CO oxidation even at 87 K with the formation of CO ₃ ^– (g=2.0285, g=2.005).

---

, (g₁=1,999; g₂=1,984; g₃=1,979), O^– Ti⁴⁺, CO 250° K (g₁=2,046; g₂=2,008) CO 87°K CO ₃ ^– (g=2,0285) g=2,0055).

     

Pathways of spontaneous and photoinduced hydrogen tunnelling in organic crystals

Optical excitation at liquid helium temperature of pentacene molecules embedded in benzoic acid crystals gives rise to defects in the environment of pentacene. By deuteration of the acid proton of the matrix and/or selective deuteration of the pentacene molecules, it has been proven that these defects are due to the displacement of acid protons of the matrix and are produced by reversible proton transfer between the benzoic acid host and the pentacene guest. The defect sites are unstable and decay with lifetimes ranging from subseconds to hours. Different defect sites also interconvert spontaneously in the dark or after absorption of a second photon.     

Water formation on Pd(111) by reaction of oxygen with atomic and molecular hydrogen

In this work we have studied the steady-state reaction of molecular and atomic hydrogen with oxygen on a Pd(111) surface at a low total pressure (<10(-7) mbar) and at sample temperatures ranging from 100 to 1100 K. Characteristic features of the water formation rate Phi(pH2; pO2; TPd) are presented and discussed, including effects that are due to the use of gas-phase atomic hydrogen for exposure. Optimum impingement ratios (OIR) for hydrogen and oxygen for water formation and their dependence on the sample temperature have been determined. The occurring shift in the OIR could be ascribed to the temperature dependence of the sticking coefficients for hydrogen (SH2) and oxygen (SO2) on Pd(111). Using gas-phase atomic hydrogen for water formation leads to an increase of the OIR, suggesting that hydrogen abstraction via hot-atom reactions competes with H2O formation. The velocity distributions of the desorbing water molecules formed on the Pd(111) surface have been measured by time-of-flight spectroscopy under various conditions, using either gas-phase H atoms or molecular H2 as reactants. In all cases, the desorbing water flux could be represented by a Maxwellian distribution corresponding to the surface temperature, thus giving direct evidence for a Langmuir-Hinshelwood mechanism for water formation on Pd(111).     

Time-resolved EPR spectra of the triplet excited states of diaminoacridine guests in polar potassium hydrogen phthalate single crystals

Mixed crystals of potassium hydrogen phthalate containing 3,6-diaminoacridine were photoexcited with visible light and the resulting triplet excited states were analyzed by time resolved EPR spectroscopy. Spectra from discrete growth sectors were compared with powders and polycrystalline glasses prepared at various pHs. The data yield the predominant protonation state and orientation of the triplets in each of a pair of growth sectors bounding the positive and negative ends of the polar crystal.     

Magnetic field control of photoinduced silver nanoparticle formation

The micellar photoreduction of benzophenone in the presence of Ag+ leads to very rapid and efficient formation of silver nanoperticles. External magnetic fields can be used to control the rate of formation and properties of silver nanoparticles generated by reaction of ketyl radicals formed in the photoreduction of benzophenone in surfactant micelles. The effect is attributed to Zeeman splitting of the triplet sublevels of the confined radical pair that causes a reduction in the rate of geminate processes and increases the availability of ketyl radicals (through escape processes) for metal ion reduction.     

On the mechanism of vanillin formation in the catalytic oxidation of lignin with oxygen

The influence of catalyst (CuSO₄ solution), pH and temperature on the vanillin formation and oxygen consumption in oxidation of lignin in alkaline media have been studied. It was shown that the main role of catalyst in the lignin oxidation is to change the selectivity of hydroperoxide fragmentation rather than to accelerate oxidation.     

On the radical mechanism for photoinduced nucleation of alkane vapors

The addition of 10^?5 — 2 Torr of NO, a radical scavenger, is found to significantly quench the rate of photonucleation of nonane by NO₂ or CH₃I in a diffusion cloud chamber. This confirms a recently proposed radical mechanism for the photoinduced nucleation of these systems. The photonucleation rate of nonane induced by o-tolualdehyde (a system whose mechanism is not known) is similarly quenched by the addition of small amounts of NO, suggesting a radical mechanism. A mechanism for this system, based upon the formation of nonane radicals (resulting from hydrogen abstraction from nonane by the carbonyl molecules in the n,π* singlet or triplet state) followed by further reaction of the radicals to form low vapor pressure species, is discussed. Acetone, a system known to dissociate into radicals, is found to photoinduce nucleation of nonane when excited to the lowest singlet or triplet excited states. This adds further support to the proposed radical mechanism and suggests that acetone dissociates in its lowest singlet as well as its lowest triplet state. A theoretical model is outlined in which the production of large involatile alkanes (dimers and higher polymers) are formed from an initially produced nonane radical. These results are combined with binary nucleation theory in order to calculate the effect of these species on the rate of nucleation. These calculations indicate that low concentrations of these involatile species can indeed induce nucleation. The ability of small, photochemically produced polymers to induce nucleation is also examined and the time dependent space distribution of polymers (e.g., vinyl polymers) generated by chain transfer from a single free radical is derived. The small polymers formed in this process are analogous to the species formed in the photoinduced nucleation of alkane vapors.