The homogeneity range of lyonsite-type phase existing in the CrVO4 - Co3V2O8 system

In the work presented here, the way of obtaining the phase with general formula Co_3+1.5xCr_2–x(VO₄)₄ (0 ≤ × < 0.4) is demonstrated. A new phase is detected in CrVO₄ - Co₃V₂O₈ that is formed in one of the intersection of the ternary CoO - V₂O₅ - Cr₂O₃ system. Monophasic Co₃Cr₂(VO₄)₄ (Co_3+1.5xCr_2−x(VO₄)₄, where × = 0) was obtained from both a mixture comprising CrVO₄ and Co₃V₂O₈ as well as from the mixture of CoV₂O₆ with CoCr₂O₄. The Co_3+1.5xCr_2−x(VO₄)₄ is isotypic with the those demonstrating the lyonsite-type structure. The temperature of melting for the new compound was established using the DTA methods.      

Influence of the Electrode Material on the Electrochemical Behavior of Carbon Paste Electrodes Modified with Meldola Blue and Methylene Green Adsorbed on a Synthetic Zeolite

Carbon paste electrodes modified with a phenoxazine derivative, Meldola blue, and a phenothiazine derivative, methylene green, both strongly adsorbed on a synthetic zeolite were investigated using either glassy carbon powder (Sigradur K, SK) or single‐walled carbon nanotubes (SWCNT) as conductive electrode material. In the case of SWCNT based electrodes, the formal potential of both mediators was pH dependent, as expected for a redox process involving proton transfer. In contrast, the formal potential of both mediators of SK based modified electrodes was practically insensitive to pH. This behavior is discussed in terms of interactions existing in the heterogeneous system mediator‐zeolite‐electrode material.     

On regular coderivatives in parametric equilibria with non-unique multipliers

This paper deals with the computation of regular coderivatives of solution maps associated with a frequently arising class of generalized equations (GEs). The constraint sets are given by (not necessarily convex) inequalities, and we do not assume linear independence of gradients to active constraints. The achieved results enable us to state several versions of sharp necessary optimality conditions in optimization problems with equilibria governed by such GEs. The advantages are illustrated by means of examples.     

Di-ionizable p-tert-butylcalix[4]arene-1,2-crown-5 and -crown-6 compounds in the cone conformation: synthesis and alkaline earth metal cation extraction

Di-ionizable p-tert-butylcalix[4]arene-1,2-crown-5 and -crown-6 ethers in the cone conformation were prepared and their conformations and regioselectivities were verified by NMR spectroscopy. The metal ion-complexing properties of these ligands were evaluated by competitive solvent extractions of alkaline earth metal cations from water into chloroform. The ligands were found to be efficient extractants with selectivity for Ba(2+). The maximal loadings were 95-100% as calculated for formation of 1 : 1 ionized ligand-metal ion complexes. With the variation of proton-ionizable groups, which were oxyacetic acid moieties and N-(X)sulfonyl oxyacetamide units with X = methyl, phenyl, 4-nitrophenyl, and trifluoromethyl, "tunable" acidity was obtained.     

Perimeter Exploration of Linear Chains of Circles

Perimeter data, obtained from structured walks performed upon straight chains of circles and displayed in Richardson plots, reveal two distinct classes of discontinuities: textural and structural. Textural discontinuities contain information about the surface features of the profile, while structural discontinuities reveal the profile's overall shape. The origins of both types of discontinuities have easy explanations. The highly predictable behavior of the structural discontinuities serves as the basis of a newly proposed method of analysis for perimeter data. The number of structural discontinuities is equal to N, the number of circles in the chain; furthermore, the value of the step size $ \underline {\lambda} $ * associated with the first structural discontinuity is inversely related to N. These properties seem is be retained when the circles slightly intersect and also when the circles vary in diameter. Analysis of the structural discontinuities may provide a new method suitable for automated examination of chain-like agglomerate particles.     

Electrochemistry of Azocrown Ethers in Langmuir-Blodgett Monolayers

Abstract

Monomolecular films of amphiphilic derivatives of crown ethers bearing an azo group in the macrocycle were prepared on surfaces of pure water and transferred onto electrodes using the Langmuir-Blodgett technique. The azocompounds studied were separated into Z and E stereoisomers. Monolayers of both isomers of azocrowns were transferred onto the surfaces of hydrophilic (thin mercury film electrode, TMFE) and hydrophobic (indium-tin oxide, ITO) electrodes. The electrode processes showed more reversible cyclic voltammetry profiles when mercury was used instead of ITO as the electrode substrate. This difference was ascribed to the different orientation of the molecules on the electrode surface.     

Phase equilibria up to the solidus line in the system Fe2O3−Fe8V10W16O85

Phase equilibria up to the solidus line in the system Fe₂O₃?Fe₈V₁₀W₁₆O₈₅ were determined by means of X-ray phase powder diffraction and differential thermal analysis. This system is one of the intersections of the three-component system Fe₂O₃?V₂O₅?WO₃. The studies revealed that this is not a real binary system, even in the solid state.     

Impact of Strong and Weak Lipid–Protein Interactions on the Structure of a Lipid Bilayer on a Gold Electrode Surface

A lipid bilayer deposited on an electrode surface can serve as a benchmark system to investigate lipid–protein interactions in the presence of physiological electric fields. Recoverin and myelin‐associated glycoprotein (MAG) are used to study the impact of strong and weak protein–lipid interactions on the structure of model lipid bilayers, respectively. The structural changes in lipid bilayers are followed using electrochemical polarization modulation infrared reflection–absorption spectroscopy (PM IRRAS). Recoverin contains a myristoyl group that anchors in the hydrophobic part of a cell membrane. Insertion of the protein into the 1,2‐dimyristoyl‐sn‐glycero‐3‐phosphatidylcholine (DMPC)–cholesterol lipid bilayer leads to an increase in the capacitance of the lipid film adsorbed on a gold electrode surface. The stability and kinetics of the electric‐field‐driven adsorption–desorption process are not affected by the interaction with protein. Upon interaction with recoverin, the hydrophobic hydrocarbon chains become less ordered. The polar head groups are separated from each other, which allows for recoverin association in the membrane. MAG is known to interact with glycolipids present on the surface of a cell membrane. Upon probing the interaction of the DMPC–cholesterol–glycolipid bilayer with MAG a slight decrease in the capacity of the adsorbed lipid film is observed. The stability of the lipid bilayer increases towards negative potentials. At the molecular scale this interaction results in minor changes in the structure of the lipid bilayer. MAG causes small ordering in the hydrocarbon chains region and an increase in the hydration of the polar head groups. Combining an electrochemical approach with a structure‐sensitive technique, such as PM IRRAS, is a powerful tool to follow small but significant changes in the structure of a supramolecular assembly.     

Effect of Pendant Group Length Upon Metal Ion Complexation in Acetonitrile by Di-Ionized Calix[4]Arenes Bearing Two Dansyl Fluorophores

A series of three di-ionizable calix[4]arenes with two pendant dansyl (1-dimethylaminonaphthalene-5-sulfonyl) groups linked to the lower rims was synthesized. Structures of the three ligands were identical except for the length of the spacers which connected the two dansyl groups to the calix[4]arene scaffold. Following conversion of the ligands into their di-ionized di(tetramethylammonium) salts, absorption and emission spectrophotometry were utilized to probe the influence of metal cation (Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Ag⁺, Cd²⁺, Co²⁺, Fe²⁺, Hg²⁺, Mn²⁺, Pb²⁺, Zn²⁺ and Fe³⁺) complexation in acetonitrile. Upon complexation with these metal cations, emission spectra underwent marked red shifts and quenching of the dansyl group fluorescence for the di-ionized ligand with the shortest spacer. A similar effect was noted for the di-ionized ligand with an intermediate spacer for all of the metal ions, except Ba²⁺. For the di-ionized ligand with the longest spacer, the metal cations showed different effects on the emission spectrum. Li⁺, Mg²⁺, Ca²⁺ and Ba²⁺ caused enhancement of emission intensity with a red shift. Other metal cations produce quenching with red shifts in the emission spectra. Transition metal cations interacted strongly with all three di-ionized ligands. In particular, Fe³⁺ and Hg²⁺ caused greater than 99% quenching of the dansyl fluorescence in the di-ionized ligands.