Electrochemical reduction of 4-methyl-4-(trichloromethyl)cyclohexa-2,5-dien-1-one

The properties of 4-methyl-4-(trichloromethyl)cyclohexa-2,5-dien-1-one which contains the trichloromethyl substituent at a quaternary carbon atom have been studied by cyclic voltammetry, rotating disk electrode voltammetry, and preparative electrolysis. Reductive dehalogenation involves initial two-electron reductive elimination of one of the geminal chlorine atoms followed by consecutive addition of proton, simultaneous elimination of the two residual halogen atoms to form carbene, and rearrangement of cyclohexadienone into the corresponding 4-methylcyclohepta-2,4,6-trien-1-one.     

Parametric excitation of shear waves in soft solids

One of the possible mechanisms that may underlie ultrasound-induced damage of soft solids is discussed. The model of three-wave interaction in a solid is used to consider shear wave generation by a longitudinal sound wave in a solid with a small shear modulus. Numerical estimates are obtained for the excitation threshold of the shear wave in biological tissues. Since the wavelength of ultrasound-generated shear waves is small, the shear stresses may be sufficient to destroy the structure of biological tissue. Results of model experiments are presented.     

Corrosion–Electrochemical Behavior of Chromium Deposits Obtained from Sulfuric Acid Solutions Containing Oxalates

The corrosion–electrochemical behavior of chromium electrodeposits, which are formed in sulfuric acid solutions of Cr(III) containing oxalates, is studied by taking steady-state polarization measurements in a 0.5 M H₂SO₄ solution. No region of the metal's active dissolution is observed for such coatings, and the open-circuit potential is localized in the passivity region, i.e. it is substantially displaced in the positive direction as compared with that for metallurgic chromium or the coatings deposited from standard chromium-plating electrolytes. According to XPS data, the surface layer of the passive metal a few nanometers thick includes oxide compounds of chromium and also carbides formed during the coating electrodeposition. Specific features of the corrosion–electrochemical behavior of the deposits are attributed to the presence of carbide compounds of chromium in them, with the compounds playing the role of a cathodic alloying agent.     

Progress and problems in the application of focused ultrasound for blood-brain barrier disruption

Advances in neuroscience have resulted in the development of new diagnostic and therapeutic agents for potential use in the central nervous system (CNS). However, the ability to deliver the majority of these agents to the brain is limited by the blood-brain barrier (BBB), a specialized structure of the blood vessel wall that hampers transport and diffusion from the blood to the brain. Many CNS disorders could be treated with drugs, enzymes, genes, or large-molecule biotechnological products such as recombinant proteins, if they could cross the BBB. This article reviews the problems of the BBB presence in treating the vast majority of CNS diseases and the efforts to circumvent the BBB through the design of new drugs and the development of more sophisticated delivery methods. Recent advances in the development of noninvasive, targeted drug delivery by MRI-guided ultrasound-induced BBB disruption are also summarized.     

A TEM and XRD study of the SbNbSe3 misfit layer structures

Two new misfit layer structures have been synthesized within the Sb-Nb-Se system. Powder X-ray diffraction and electron microscopy techniques (electron diffraction, HREM, XEDS) have been used to determine the nature of their structure. According to TEM and XEDS data (for more than 15 crystals studied) both phases are monolayer type, i.e. (SbSe)1+delta (NbSe2). Electron microscopy reveals a composite modulated structure that consists of the periodical intergrowth of a pseudotetragonal SbSe layer, denominated as Q, and a pseudohexagonal layer NbSe2, denominated as H. Both layers fit along b, stack along c and do not fit along a (misfit) giving rise to an incommensurate modulation along this direction. The two phases differ in the symmetry of the Q layers being in one case orthorhombic (for delta = 0.17) and monoclinic in the other (for delta = 0.19). After the characterization of the sample by electron microscopy the unit cells of the basic layers could be refined for both phases by powder X-ray diffraction: aQ = 5.824(2) A, bQ = 5.962(5) A, cQ = 23.927(6) A, alpha = 90 degrees, beta = 90 degrees and gamma = 90 degrees and aH = 3.415(5) A, bH = 5.962(6) A,, cH = 11.962(1) A, alpha = 90 degrees, beta = 90 degrees and gamma = 90 degrees for the orthorhombic phase; aQ = 5.844(2) A, bQ = 5.981(1) A, cQ = 23.919(5) A, alpha = 90 degrees, beta = 90 degrees and gamma = 96.00(3)degrees and aH = 3.439(1) A, bH = 5.994(2) A, cH = 11.956(3) A, alpha = 90 degrees, beta = 90 degrees and gamma = 90 degrees for the monoclinic phase. The phase with the monoclinic Q-sublattice often appears as twinned crystals. The more abundant crystals are disordered intergrowths of both monolayer phases.     

Observation of Species of Intermediate Oxidation Degrees, Formed during Anodic Dissolution of Chromium, by the Rotating Ring–Disk Electrode Method

The possibilities and limitations of the RRDE method in recording and identifying intermediate and target products of chromium dissolution in sulfuric acid solutions of pH 0.3–2 are analyzed on the basis of own and literature data. From the experimental data, partial currents of chromium dissolution to Cr(II) ions in the region of active dissolution of chromium and its transition into a passive state are computed. The Cr(III) ions can be discovered through the reaction of their reduction on an Hg(Au) ring electrode only at pH 1.8. The current efficiency of reactions that lead to the formation of Cr(II) and Cr(III) ions near the anodic-dissolution peak is other than 100%. Assumptions as to the causes of this effect are made. In the solutions studied, Cr(VI) ions are recorded with a 100-% current efficiency on a gold ring electrode in a transpassive region of the chromium disk potentials.     

Composition of Chemisorption Layers Forming on a Chromium Electrode in Sulfuric Acid Solutions of Formaldehyde and Formic,Oxalic, and Glyoxylic Acids

Surface layers that form on a chromium electrode after its contact with sulfuric acid solutions of formaldehyde, formic, oxalic, and glyoxylic acids at an open-circuit potential and in conditions of cathodic polarization at a potential of ?1.05 ± 0.10 V (NHE) are examined by an x-ray photoelectron spectroscopy method. The structure of the Cls line, which characterizes the binding energy of electrons of that level with the nucleus in products of interaction of said organic compounds with metal, is analyzed in detail. It is established that chemisorption products include substances with reduced oxygen-containing functional groups and hydrocarbon fragments. The degree of carbonation of chemisorption products, whose appearance is probably connected with electrocatalytic reduction and processes of polymerization of organic substances, is given an estimate.     

Elucidation of the chemical state of phosphorus and boron in crystallographically amorphous nickel electroplates

Using the valence-to-core version of X-ray emission spectroscopy (valence-to-core XES) together with X-ray diffraction analysis, the structure and the composition of nickel coatings deposited from solutions containing hypophosphite ions or dimethylaminoborane (DMAB) are studied. The diffraction patterns of prepared deposits are characterized by the presence of a wide “halo”. Annealing of crystallographically amorphous deposits at temperatures of 500°C and higher transforms these haloes into the spectra corresponding to metal nickel and its phosphides or borides present in the crystallized deposits. A result of fundamental importance obtained in the simultaneously conducted examination of the same deposits by the valence-to-core XES method is that both the binding energy and the intensities of Kβ satellite spectral lines of annealed samples remain unchanged as compared with original samples. Based on this comparison, it is concluded that phosphide and boride nickel compounds were already formed in the course of electrodeposition, whereas the thermal treatment of deposits (crystallization) leads only to aggregation of the metal and metal-metalloid nanoparticles.     

Reduction of Triple-Charged Chromium Ions on Indium Cathode in Alkaline Sulfate Solutions

The problem of how the surface coverage of an indium electrode with chromium adatoms formed during the discharge of Cr(III) ions affects electrolytic evolution of hydrogen in alkaline solutions is studied using linear and cyclic voltametry. The method used permits stating that, in alkalinized media, the chromium deposition abruptly decelerates due to the formation of a hydroxide film on the electrode surface. Based on the results obtained, it is assumed that this film consists of mixed Cr(III)- and Cr(II)-containing hydroxo compounds (of the chromite type) and coadsorbed Cr_n clusters formed in the course of electrolysis.