Single flexible hydrophobic polyelectrolyte molecules adsorbed on solid substrate: transition between a stretched chain, necklace-like conformation and a globule

Single flexible polyelectrolyte molecules of poly(2-vinylpyridine) undergo conformational transition from a stretched wormlike coil to a necklace-like globule, and to a compact globule depending on pH and ionic strength in aqueous solution in good agreement with recent theoretical reports. AFM investigations allow the visualization of details of the chain conformation on mica and the extraction of quantitative statistics of molecular dimensions.     

Luminescent determination of automobile petrol in hexane solutions

The work deals with the problem of determination of automobile petrol of various octane numbers and petroleum contamination of some objects on the basis of analysis of photoluminescence spectra of automobile petrol samples. For this purpose steady state luminescence properties of samples of automobile petrol of different types being in sale were measured. Samples of automobile petrol diluted in hexane were prepared and their luminescence spectra were measured at room and liquid nitrogen temperatures of samples. We constructed concentration dependences of luminescence intensity of both wide band luminescence of liquid solutions obtained at room temperature and peak intensities of luminescence lines of quasi linear spectra of solutions frozen at 77 K. Possibility to use luminescence method for analysis of petrol pollutions on some objects is illustrated by results of investigation of pine-wood pieces contaminated by automobile petrol.     

Influence of Calixarenes on Chromatographic Separation of Benzene or Uracil Derivatives

The addition of calix[4]arenes to MeCN/H₂O or MeOH/MeCN/THF/H₂O mobile phases improves LC separation of benzene or uracil derivatives on Separon SGX C18 or Separon SGX NH₂ supports. Structure of the calixarenes and their host–guest supramolecular complexes with the analytes are discussed in context of the LC separation.     

Nonlinear oscillations of circular membranes of a low-frequency acoustic radiator

We study the features of oscillations of an acoustic radiator in the form of a rigid cylinder with elastic circular membranes fixed at the cylinder ends. For different membrane models and different vibration modes, the spectra of linear and nonlinear free and forced oscillations are found. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 51, No. 3, pp. 199–215, March 2008.     

Driving forces of the solute self-organization in an evaporating liquid microdroplet

A method is proposed for preparing solid phases of desired morphologies from microscopic droplets on solid substrates with a GMS 417 Arrayer, which is commonly used for biochip production. The initial droplet of an aqueous solution is about 100 pl (about 100 μm in diameter), and the evaporation time is about 0.5 s. Such small solution volumes are first considered from the viewpoint of the solute self-organization. Aqueous solutions of inorganic molecular and ionic substances, organic dyes, and latex colloid particles in the evaporating droplets are experimentally studied. Various substrates and solute concentrations are used. The morphology of the solid phase formed on the substrate after water evaporation is analyzed with the use of computer simulation of dynamics of the latex particles within the evaporating microdroplet. Elucidating the self-organization mechanisms will facilitate producing of the desired morphology of the solid phase, which can find an application in nanotechnology.     

Preparation of polymer composites on the base of polyurethanes and natural polysaccharides

A series of composites based on segmented polyurethanes (PU) as polymer matrices and natural polysaccharides – cellulose and starch – as fillers have been synthesized. Using IR method and Differential Scanning Calorimetry the peculiarities of the structure of composites and their behavior in the buffer solutions in conditions imitating natural soil environment have been investigated.     

Stable Carbenes as Structural Components of Partially Saturated Sulfur-Containing Heterocycles

Recently, an unusual elongation of the C-S bond was observed experimentally for some sulfur-containing heterocycles. Using a superior ab initio (SCS-MP2/cc-pVTZ) level of theory, we showed that the phenomenon can be explained by a contribution of a donor–acceptor adduct of a carbene with an unsaturated ligand. One may achieve further elongation of the C-S bond, eventually turning it to a coordinate one, by increasing the stability of each part of the system as, e.g., in the utmost case of spiro adducts with Arduengo carbenes. The effect of carbene stability was quantified by employing the isodesmic reactions of carbene exchange.     

Novel,Monomeric Cyanine Dyes as Reporters for DNA Helicase Activity

The dimeric cyanine dyes, YOYO-1 and TOTO-1, are widely used as DNA probes because of their excellent fluorescent properties. They have a higher fluorescence quantum yield than ethidium homodimer, DAPI and Hoechst dyes and bind to double-stranded DNA with high affinity. However, these dyes are limited by heterogeneous staining at high dye loading, photocleavage of DNA under extended illumination, nicking of DNA, and inhibition of the activity of DNA binding enzymes. To overcome these limitations, seven novel cyanine dyes (Cyan-2, DC-21, DM, DM-1, DMB-2OH, SH-0367, SH1015-OH) were synthesized and tested for fluorescence emission, resistance to displacement by Mg²⁺, and the ability to function as reporters for DNA unwinding. Results show that Cyan-2, DM-1, SH-0367 and SH1015-OH formed highly fluorescent complexes with dsDNA. Of these, only Cyan-2 and DM-1 exhibited a large fluorescence enhancement in buffers, and were resistant to displacement by Mg²⁺. The potential of these two dyes to function as reporter molecules was evaluated using continuous fluorescence, DNA helicase assays. The rate of DNA unwinding was not significantly affected by either of these two dyes. Therefore, Cyan-2 and DM-1 form the basis for the synthesis of novel cyanine dyes with the potential to overcome the limitations of YOYO-1 and TOTO-1.