Preparation and Structural and Electrochemical Characteristics of a Carbon-Containing Material Based on Aspen Bark Modified with Zinc and Iron Chlorides

Russian Journal of Applied Chemistry - The possibility of using aspen bark modified with zinc and iron chlorides for preparing highly porous materials with specific properties was examined. The...     

Novel zwitterionic reverse micelles for encapsulation of proteins in low-viscosity media

Large proteins remain inaccessible to structural NMR studies because of their unfavorable relaxation properties. Their solubilization in the aqueous core of reverse micelles, in a low-viscosity medium, represents a promising approach, provided that their native tertiary structure is maintained. However, the use of classical ionic surfactants may lead to protein unfolding, due to strong electrostatic interactions between the polar head groups and the protein charges. To design reverse micelles in which these interactions are weakened, a new zwitterionic surfactant molecule was synthesized and studied by high-resolution NMR spectroscopy, for which cytochrome C and 15N-labeled ubiquitin were used as guest candidates. At different ionization states, both proteins are encapsulated in the absence of salts or other additives, in a folded conformation similar to the native one.     

pH dependence of friction forces between silica surfaces in solutions

The pH dependence of the friction between a silica particle and a silica wafer was investigated using lateral force microscopy. Measurements were done in the range of 3.6 < or = pH < or = 10.6 and the effect of high loading force was also examined. It is found that the friction is independent of the pH of solutions and increases linearly with the applied load, when the pH is between 3.6 and 8.6. On the other hand, once the pH is above 9.0, the friction becomes extremely small and the dependence on the applied load becomes nonlinear. It is postulated that this transition is due to the development of a gel layer composed of polymer-like segments of silicilic acid anchored on the surface; at the lower applied load, this layer acts as a boundary lubricant between the surfaces, but, at the higher applied load, the entanglements of these segments and more direct contact between two solid surfaces leads to the increase of the friction. The effects found here are expected to play an important role in elucidating the basic mechanism of the planarization process of silica wafers.     

Effects of cleaning procedures of silica wafers on their friction characteristics

Silicon wafers with thermal silicon oxide layers were cleaned and hydrophilized by three different methods: (1) the remote chemical analysis (RCA) wet cleaning by use of ammonia and hydrogen peroxide mixture solutions, (2) water-vapor plasma cleaning, and (3) UV/ozone combined cleaning. All procedures were found to remove effectively organic contaminations on wafers and gave identical characteristics of the contact angle, the surface roughness and the normal force interactions, measured by atomic force microscopy (AFM). However, it is found that wafers cleaned by the RCA method have several times larger friction coefficients than those cleaned by the plasma and UV/ozone methods. The difference was explained by the atomic-scale topological difference induced during the RCA cleaning. This study reveals the lateral force microscopy as a very sensitive method to detect the microstructure of surfaces.     

Phosphine-catalyzed alpha-P-addition on activated alkynes: A new route to P-C-P backbones

n-Tributylphosphine was found to efficiently catalyze the alpha-P addition of H-phosphonates, H-phosphinates, and H-phosphine oxide pronucleophiles on alkynes bearing phosphane oxide activating moieties. The reaction leads to 2-aryl-1-vinyl-1,1-diphosphane dioxide derivatives in good yields affording a new route to P-C-P backbones. The products of this reaction are easily converted to biologically important 1,1-bis-phosphonates analogues.     

Nucleophilic reactivity of the peroxide anion in microemulsions of the “oil-in-water” type in the decomposition of phosphate and toluenesulfonate esters

The kinetics of the reaction of the 4-nitrophenyl esters of diethylphosphoric and 4-toluenesulfonic acids with HO^– and HOO^– anions in microemulsions of the “oil-in-water” type was studied. It was shown that the reactivity of the HOO^– anion depends on the nature of the detergent forming the microemulsion and decreases in the order cetyltrimethylammonium bromide > Triton X-100 > sodium dodecyl sulfate. It was established that concentration of the reagents on the surface of the microdrops leads to an increase of 2–3 orders of magnitude in the rate during the transition from aqueous solutions to the microemulsion.     

Kinetic regularities of micellar catalysis in the dephosphorylation with peroxide anion

The acid-base equilibrium of hydrogen peroxide in water solutions of cetyltrimethylammonium bromideand the reactivity of hydroxide and peroxide anions with respect to 4-nitrophenyl diethyl phosphate were investigated. In the micelles the acid ionization constant of the hydrogen peroxide increased three-fold. The application of the pseudophase distribution model under the conditions of competitive sorption of HO⁻ and HOO⁻ anions with the micelles of cetyltrimethylammonium bromide to the estimation of the main kinetic parameters of the micellar process was tested.     

Resonant CARS in I2 vapor

We discuss electronically enhanced CARS in gases and report the first experimental observation of this effect in I₂ vapor at 1 millibar.