Carane amino alcohols as organocatalysts in asymmetric aldol reaction of isatin with acetone

Carane-derived β-amino alcohols with amino and hydroxy groups at positions 3 and 4 differing in their mutual arrangement and configuration were synthesized. Their application as organocatalysts in the asymmetric aldol reaction of isatin with acetone allowed one to obtain adducts with up to 84% enantiomeric excess.     

Checking of applicability of conditions for reaching the limiting-current mode to flow-by porous electrodes

For the flow-by porous electrodes, which differ in thickness, specific surface area, solution flow rate, and a ratio between the phase conductivities, the conditions providing the limiting-current mode over the entire electrode surface at nearly 100% current efficiency are determined using the method of successive refinement of total current and profile of its distribution along the solution flow. The used values of electrode thickness L are compared with available estimates for the limiting thickness of porous electrode L _lim derived for the ideal limiting-current mode and calculated using real values of the width of the limiting-current plateau of overall polarization curve, solution conductivity, and the diffusion limiting current in the zone of solution input into the electrode. It is found that these values are close to each other in all cases. The largest error of estimation of L _lim does not exceed 10% indicating that it can be used for preliminary estimation of the conditions for reaching the limiting-current mode for the flow porous electrodes of this type.     

Electrochemical oxidation of thrombin on carbon screen printed electrodes

The electrochemical oxidation of thrombin on the surface of carbon screen printed electrodes was studied. The electrochemical activity of thrombin was predicted, using bioinformation analysis, based on the data about the electrochemical properties of amino acids. The number of potentially electroactive amino acid residues, namely, tyrosine (Tyr), tryptophan (Trp), cysteine (Cys), histidine (His), methionine (Met), and cystine (Cys-Cys) located on the protein surface and orientated by their electroactive groups toward the electrode surface, i.e., accessible for electrochemical oxidation was calculated. The theoretical data were confirmed experimentally by cyclic and square-wave voltammetry. The available data on the protein structure allowed us to attribute the recorded electrochemical signals of thrombin oxidation to certain types of amino acid residue: the oxidation peak with a potential maximum at 0.7–0.8 V (vs. Ag/AgCl) was attributed to the oxidation of the Trp and Tyr residues; the wave in the range 1.0–1.2 V, to the oxidation of His; and the wave at 1.2–1.5 V, to the oxidation of Met and Cys-Cys. The electroanalysis based on the oxidation peak of the Tyr and Trp amino acid residues allowed to detect thrombin up to the concentration of 10^–7 M. The suggested strategy for predicting the electrochemical activity can be used for investigating the properties of many other proteins and peptides and serve as a basis for their quantitative determination when developing various sensor and biosensor devices.     

The synthesis,structure, and electrochemical properties of Li<Subscript>2</Subscript>FeSiO<Subscript>4</Subscript>-based lithium-accumulating electrode material

Different approaches to synthesis of Li₂FeSiO₄-based electrode materials for lithium intercalation, using low-cost and abundant Li-, Si-, and Fe-containing parent substances, are discussed. XRD, SEM, and a laser-diffraction analyzer of particle size were used for structure and morphology characterization of the composite electrode materials. Li₂FeSiO₄ was shown to be the main lithium-accumulating crystalline phase; minor LiFeO₂ and Li₂SiO₃ admixtures are also present. The material microparticles’ average size was shown to vary from tenths of micrometer to 1 μm. Larger objects sized ca. 2–4 μm are the microparticles’ agglomerates. The material electrochemical properties were studied by dc chronopotentiometry (galvanostatic charging–discharging) and cyclic voltammetry with potential linear sweeping. The initial reversible cycled capacity of the best samples is 170 mA h/g. The anodic and cathodic processes manifest obvious hysteresis caused by the presence of several different lithium ion energy states in the material; the transition between the states is kinetically hindered. The dependences of the specific capacity and its stability under cycling on the current load and the conductive carbon component content in the composite were elucidated.     

Transport properties of metacomposites in eutectic MAO<Subscript>4</Subscript>–V<Subscript>2</Subscript>O<Subscript>5</Subscript> systems (M = Ca,Sr; A = W,Mo)

Metal molybdates MMoO₄ (M = Ca, Sr) and their composites with vanadium oxide V₂O₅ were synthesized. An X-ray diffraction analysis confirmed that the obtained molybdates were single-phase, and the heterogeneous systems were two-phase. The temperature dependences of the total conductivity of the composites were studied. The ion transport numbers in the {CaMoO₄ · xV₂O₅} composites (x = 1–30 mol %) were studied by the EMF method. The conductivity of the composites at x ≤ 5 mol % was shown to be ionic. The conductivity of the composites was described using the mixing equation.     

Expanding Lipidome Coverage Using LC-MS/MS Data-Dependent Acquisition with Automated Exclusion List Generation

Untargeted omics analyses aim to comprehensively characterize biomolecules within a biological system. Changes in the presence or quantity of these biomolecules can indicate important biological perturbations, such as those caused by disease. With current technological advancements, the entire genome can now be sequenced; however, in the burgeoning fields of lipidomics, only a subset of lipids can be identified. The recent emergence of high resolution tandem mass spectrometry (HR-MS/MS), in combination with ultra-high performance liquid chromatography, has resulted in an increased coverage of the lipidome. Nevertheless, identifications from MS/MS are generally limited by the number of precursors that can be selected for fragmentation during chromatographic elution. Therefore, we developed the software IE-Omics to automate iterative exclusion (IE), where selected precursors using data-dependent topN analyses are excluded in sequential injections. In each sequential injection, unique precursors are fragmented until HR-MS/MS spectra of all ions above a user-defined intensity threshold are acquired. IE-Omics was applied to lipidomic analyses in Red Cross plasma and substantia nigra tissue. Coverage of the lipidome was drastically improved using IE. When applying IE-Omics to Red Cross plasma and substantia nigra lipid extracts in positive ion mode, 69% and 40% more molecular identifications were obtained, respectively. In addition, applying IE-Omics to a lipidomics workflow increased the coverage of trace species, including odd-chained and short-chained diacylglycerides and oxidized lipid species. By increasing the coverage of the lipidome, applying IE to a lipidomics workflow increases the probability of finding biomarkers and provides additional information for determining etiology of disease.

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Extinction coefficients of gold nanoparticles and their dimers. Dependence of optical factor on particle size

The generalized Mie theory has been employed to calculate extinction coefficients κ for isolated gold nanoparticles of different sizes (4–80 nm) and their dimers (κ₂) at the maximum of the short-wave plasmon resonance band. It has been found that the value of κ₂ essentially depends on both interparticle distance s and particle sizes R. According to the character of variations in the κ₂(s) dependence, three ranges of the distances are distinguished, i.e., large, intermediate, and small. In the first range, the κ₂ values slightly differ from doubled κ values. Nevertheless a tendency toward an increase in κ₂ is distinctly seen as the particles approach each other, and, within some range of s values and for particles with radii R < 15 nm, κ₂ is higher than 2κ. For dimers of larger particles, κ₂ < 2κ, with its value gradually decreasing with a reduction in the s value. The behavior changes when the particle sizes are of about 50 nm. In the range of small interparticle distances, κ₂ values slightly vary with the distance between the particles somewhat decreasing or oscillating with a small amplitude about some mean value. In this range, as the sizes of the gold particles grow, the extinction coefficients of dimers increasingly deviate from the sum of the extinction coefficients of the particles composing the dimers. For 20–80 nm nanoparticles, the size-dependence plotted for the extinction efficiency of dimers in logarithmic coordinates within the range of small interparticle distances is described by a straight line, the slope of which (1.036 ± 0.039) appears to be somewhat smaller than the slope of a corresponding line for individual gold particles (1.274 ± 0.014). The ratio between κ₂ and κ predetermines the character of variations in the optical factor as depending on the particle size and the interparticle distance and governs the behavior of the sol turbidity at the stage of nanoparticle dimerization.     

Micellization theory based on the law of mass action with a variable aggregation number

Variations in the aggregation number of spherical micelles are considered within the micellization theory based on the law of mass action. The mechanism of micellization in a polydisperse aggregated system and the transition to a monodisperse model are explained. A relation between aggregation numbers and chemical potentials of molecules or ions is determined using the curve for equilibrium distribution of aggregates over the aggregation numbers. It is shown that the aggregation numbers of nonionic surfactants unambiguously grow with concentration; however, such a conclusion cannot be drawn for ionic surfactants. For the explicit concentration dependence of the aggregation number, two versions of an analog of the Langmuir equation are proposed to be used, i.e., versions comprising the total surfactant concentration and the concentration of monomers. Comparison with experimental data is carried out by the example of conventional surfactants, namely, sodium dodecyl sulfate and hexadecyltrimethylammonium bromide.