Konstantin Balashev

Spreading kinetics of dimyristoylphosphatidylcholine liposomes at the air/water interface below and above the main phase-transition temperature

The spreading kinetics of dimyristoylphosphatidylcholine liposomes at the air/water interface, below and above the main phase-transition temperature are studied by measuring the evolution of the surface pressure. The reorganization mechanism of the closed liposomal bilayers into a surface film is dependent on the state of the bilayer. The estimated values of the interfacial reorganization rate constant for liposomes in a liquid-crystal state are larger than those for liposomes in crystal-gel state. Atomic force microscopic imaging demonstrates the different morphology of the interfacial mesophases obtained.

Brassinosteroids regulate the thylakoid membrane architecture and the photosystem II function

Brassinosteroids (BRs) are plant steroid hormones known to positively affect photosynthesis. In this work we investigated the architecture and function of photosynthetic membranes in mature Arabidopsis rosettes of BR gain-of-function (overexpressing the BR receptor BR INSENSITIVE 1 (BRI1), BRI1OE) and loss-of-function (bri1-116 with inactive BRI1 receptor, and constitutive photomorphogenesis and dwarfism (cpd) deficient in BR biosynthesis) mutants. Data from atomic force microscopy, circular dichroism, fluorescence spectroscopy and polarographic determination of oxygen yields revealed major structural (enlarged thylakoids, smaller photosystem II supercomplexes) and functional (strongly inhibited oxygen evolution, reduced photosystem II quantum yield) changes in all the mutants with altered BR response compared to the wild type plants. The recorded thermal dependences showed severe thermal instability of the oxygen yields in the BR mutant plants. Our results suggest that an optimal BR level is required for the normal thylakoid structure and function.

Foam production--ratio between foaminess and rate of foam decay.

Foams are usually characterized by the foaminess of their surfactant solutions and the rate of foam decay. These two properties have been described many times separately in the literature. There is a certain correlation between them, which can vary depending on the type and the concentration of the surfactants, the method of foam generation, etc. We suggest with this work a new parameter unifying foaminess and rate of foam decay. The foam production is a parameter, which is a ratio between foaminess and rate of foam decay. It was shown an example how foaminess, rate of foam decay and foam production depends on C/CMC (C - surfactant concentration, CMC - critical micelle concentration) of aqueous solutions of sodium octylsulfate (SOS). In addition, it has been stressed that a number of scientific problems on transient foams can be solved by means of the approach pointed out by this study. An example, for which the foam production depends on the way of foam generation, is given. A new criterion for assessing the ability of the surfactants to stabilize foams has been suggested. Thus, the stronger surfactants do not always produce more stable transient foams than the weaker ones, as usually is assumed.

Polyzwitterionic copolymer nanoparticles loaded in situ with metoprolol tartrate: synthesis, morphology and drug release properties

Polyzwitterions belong to the “smart” polymers’ group because of their specific swelling properties which depend on pH and ionic strength of the aqueous media. Novel polyzwitterionic copolymer nanoparticles of vinyl acetate (VA) and 3-dimethyl(methacryloyloxyethyl)ammonium propane sulfonate (DMAPS) (p(VA-co-DMAPS)) with loaded in situ metoprolol tartrate were synthesized by emulsifier-free emulsion copolymerization in water. The influence of in situ addition of metoprolol tartrate on the emulsifier-free emulsion copolymerization mechanism was studied. It was suggested that the interactions between metoprolol tartrate and the copolymer nanoparticles are responsible for the creation of “bridge” connections between them and these bonds led to the formation of coagulum. To validate possible mechanisms of interaction between metoprolol tartrate and copolymer nanoparticles Differential Scanning Calorimetry was employed. Scanning Electron Microscopy, Atomic Force Microscopy, Dynamic Light Scattering and ζ-potential measurements were used to determine the average diameter, size distribution and ζ-potential of the copolymer nanoparticles. It was shown that the copolymer composition was an effective parameter for control of the release kinetics of in situ loaded metoprolol tartrate in copolymer nanoparticles.

The linker histone in Saccharomyces cerevisiae interacts with actin-related protein 4 and both regulate chromatin structure and cellular morphology.

Chromatin structure promotes important epigenetic mechanisms that regulate cellular fate by organizing, preserving and controlling the way by which the genetic information works. Our understanding of chromatin and its functions is sparse and not yet well defined. The uncertainty comes from the complexity of chromatin and is induced by the existence of a large number of nuclear proteins that influence it. The intricate interaction among all these structural and functional nuclear proteins has been under extensive study in the recent years. Here, we show that Saccharomyces cerevisiae linker histone physically interacts with Arp4p (actin-related protein 4) which is a key subunit of three chromatin modifying complexes - INO80, SWR1 and NuA4. A single - point mutation in the actin - fold domain of Arp4p together with the knock-out of the gene for the linker histone in S. cerevisiae severely abrogates cellular and nuclear morphology and leads to complete disorganizing of the higher levels of chromatin organization.

Low pH modulates the macroorganization and thermal stability of PSII supercomplexes in grana membranes.

Protonation of the lumen-exposed residues of some photosynthetic complexes in the grana membranes occurs under conditions of high light intensity and triggers a major photoprotection mechanism known as energy dependent nonphotochemical quenching. We have studied the role of protonation in the structural reorganization and thermal stability of isolated grana membranes. The macroorganization of granal membrane fragments in protonated and partly deprotonated state has been mapped by means of atomic force microscopy. The protonation of the photosynthetic complexes has been found to induce large-scale structural remodeling of grana membranes-formation of extensive domains of the major light-harvesting complex of photosystem II and clustering of trimmed photosystem II supercomplexes, thinning of the membrane, and reduction of its size. These events are accompanied by pronounced thermal destabilization of the photosynthetic complexes, as evidenced by circular dichroism spectroscopy and differential scanning calorimetry. Our data reveal a detailed nanoscopic picture of the initial steps of nonphotochemical quenching.

Savinase proteolysis of insulin Langmuir monolayers studied by surface pressure and surface potential measurements accompanied by atomic force microscopy (AFM) imaging

The mechanism of the enzymatic action of Savinase on an insulin substrate organized in a monolayer at the air-water interface was studied. We followed two steps experimental approach classical surface pressure and surface potential measurements in combination with atomic force microscopy imaging. Utilizing the barostat surface balance, the hydrolysis kinetic was followed by measuring simultaneously the decrease in the surface area and the change of the surface potential versus time. The decrease in the surface area is a result of the random scission of the peptide bonds of polypeptide chain, progressively appearance of amino acid residues, and their solubilization in the aqueous subphase. The interpretation of the surface potential data was based on the contribution of the dipole moments of the intact and broken peptide groups which remain at the interface during the proteolysis. An appropriate kinetic model for the Savinase action was applied, and the global kinetic constant was obtained. The application of the AFM revealed the state of the insulin monolayers before and after the Savinase action. The comparison of the topography of the films and the roughness analysis showed that insulin Langmuir-Blodgett (LB) films transferred before the enzyme action were flat, while at the end of hydrolysis, roughness of films has increased and the appearance of 3D structures was observed.

Sterically stabilized liposomes as a platform for salinomycin metal coordination compounds: physicochemical characterization and in vitro evaluation

Sterically stabilized DPPC:CHOL:DSPE-PEG-2000 liposomal formulations of the lipophilic complexes of salinomycin with Na(I), K(I), Mn(II), Co(II), and Ni(II) ions were prepared by film-hydration method at different drug-to-DPPC molar ratios. For the K(I) and Na(I) complexes, optimal loading was established at a drug-to-DPPC molar ratio of 0.5:1, whereas for the Me(II) complexes, it was encountered at 0.1:1. DLS revealed uniform LUV populations (130–160 nm) with monomodal size distribution, further corroborated by AFM. Free and entrapped salinomycinates exhibited cytotoxicity in three human tumor cell lines, whereby the liposomal agents were superior vs. free complexes. DNA-fragmentation and flow cytometric assays showed that the cytotoxicity of free and liposomal salinomycinates is mediated by the induction of apoptosis and G 1 arrest. The ability of the carriers to retain the bio-activity of the entrapped cargo gives us reason to conclude that the presented DPPC:CHOL:DSPE- PEG-2000 liposomes are suitable platforms for the salinomycin complexes, needing further evaluation and optimization.

Effects of Ca2+ ions on bestrophin-1 surface films

Human bestrophin-1 (hBest1) is a transmembrane calcium-activated chloride channel protein - member of the bestrophin family of anion channels, predominantly expressed in the membrane of retinal pigment epithelium (RPE) cells. Mutations in the protein cause ocular diseases, named Bestrophinopathies. Here, we present the first Fourier transform infrared (FTIR) study of the secondary structure elements of hBest1, π/A isotherms and hysteresis, Brewster angle microscopy (BAM) and atomic force microscopy (AFM) visualization of the aggregation state of protein molecules dispersed as Langmuir and Langmuir-Blodgett films. The secondary structure of hBest1 consists predominantly of 310-helices (27.2%), α-helixes (16.3%), β-turns and loops (32.2%). AFM images of hBest1 suggest approximate lateral dimensions of 100×160Å and 75Å height. Binding of calcium ions (Ca2+) induces conformational changes in the protein secondary structure leading to assembly of protein molecules and changes in molecular and macro-organization of hBest1 in monolayers. These data provide basic information needed in pursuit of molecular mechanisms underlying retinal and other pathologies linked to this protein.

Microstructural investigations of carbon foams derived from modified coal-tar pitch

This work reports the microstructural evaluation of carbon foams derived from coal-tar pitch precursors treated with H2SO4 and HNO3 and finally annealed at 1000°C and 2000°C. Our experimental investigations combine scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM) imaging, X-ray photoelectron spectroscopy (XPS) and micro-spot near-edge X-ray absorption fine structure (μ-NEXAFS) spectroscopy. This set of complementary techniques provides detailed structural and chemical information of the surface and the bulk of the carbon foams. The high-resolution microscopy data indicate the formation of carbonaceous amorphous microspheres (average diameters of 0.28±0.01μm) embedded in the partially graphitized carbon foam matrix at 1000°C. The microspheres are enriched with sp-bonded species and their microstructural characteristics depend on the reagent (nitric vs. sulfuric acid) used for pitch treatment. A complete chemical transformation of the microspheres at temperatures >1000°C occurs and at 2000°C they are spectroscopically identical with the bulk material (sp(2)- and sp(3)-hybridised forms of carbon). The microstructure-property relationship is exemplified by the compressive strength measurements. These results allow a better description of coal-tar pitch-derived carbon foams at the atomic level, and may account for a better understanding of the processes during graphitization step.