Radiation-chemical transformations of humic acid in aqueous solutions

The transformations of kinetically stable aqueous humic acid solutions saturated with Ar, N₂O, or air by the action of fast electrons at absorbed doses to 20 kGy were studied. In radiolytic and postradiation processes, humic acid was converted into insoluble compounds, whose precipitation accelerated with dose. The formation of insoluble compounds was enhanced in neutral and acidified solutions saturated with air and/or N₂O. As low-molecular-mass carboxylic acids that resulted from the radiolytic fragmentation of humic acid were accumulated in solution, the phase transformation weakened. The irradiated solutions were easy to purify by chemical coagulation.     

Peculiarities of phase transformations in aqueous isopropanol solutions

Peculiarities of phase transformations in aqueous isopropanol solutions are studied in the range from room temperature to −15°C. It is found that solution cooling results in the formation of macroaggregates with regular geometrical shapes, which are dispersed in the liquid phase and directedly move in the field of a temperature gradient. In aqueous isopropanol solutions with concentrations of 10–30 vol %, the aggregates are formed at temperatures of −10 to −15°C. The average aggregate size is several millimeters. Under the action of a temperature gradient, the aggregates move to the region of higher temperatures. At temperature gradients of 1–2 K/cm, the aggregate velocity is 1–2 mm/s. The characters of the motion and interaction of aggregates are very sensitive to the temperature distribution in a solution. After the aggregate motion ceases, crystallization of the liquid phase that initially is outside of the aggregates is observed.     

Equilibrium transformations of meso-methylated thiacarbocyanine in aqueous solutions

Equilibrium processes of dimerization and H*- and J-aggregation of 3,3′-di-(γ-sulfopropyl)-5,5′-dichloro-9-methylthiacarbocyanine (TCC) in aqueous solutions have been investigated, and the thermodynamic parameters of the processes have been calculated. At least seven equilibrium forms of TCC have been found in aqueous solution for the first time. The absorption bands of the dye have been attributed to various forms (M, D, H*, and J) with allowance for existence of stereoisomers. The aggregation numbers for J- and H*-aggregates have calculated from the dependence of the absorption spectra on the dye concentration in solutions. It has been shown that the TCC aggregates consisting of a large number of molecules are formed by the “block” mechanism via intermediate steps of the formation of dimers, J- or H*-tetramers, octamers, etc.     

Thermochemical transformations of hydrocarbonate ions in aqueous solutions

The influence of heat treatment on the reactivity index k ₁, pH value, and content of hydrocarbonate ions HCO₃⁻ in an aqueous solution was examined. The factors responsible for enhanced reactivity of thermally activated water were discussed.     

Nonaqueous and aqueous capillary electrophoresis of synthetic polymers

In this work, the use of capillary electrophoresis (CE) to analyze synthetic polymers is reviewed including works published till February 2004. The revised works have been classified depending on the CE mode (e.g., free solution capillary electrophoresis, capillary gel electrophoresis, etc.) and type of buffer (i.e., nonaqueous, aqueous and hydro-organic background electrolytes) employed to separate synthetic macromolecules. Advantages and drawbacks of these different separation procedures for polymer analysis are discussed. Also, physicochemical studies of complex polymer systems by CE are reviewed, including drug release studies, synthetic polyampholytes, dendrimers, fullerenes, carbon nanotubes and associative copolymers.     

Radiation-induced transformations of threonine and its derivatives in aqueous solutions

It was found that the presence of the α,β-aminoalcohol group in the molecules of the hydroxyl-containing amino acid threonine and its derivatives is responsible for their ability to undergo free-radical degradation with C-C bond cleavage. This degradation occurs by the fragmentation of the nitrogen- and carbon-centered radicals of the initial substances.     

Ionic dissociation of ionene polymers in aqueous solutions

The degree of ionic dissociation of aliphatic ionene polymers, 3,3-, 4,4-, 6,6-, and 8,8-ionene bromide in salt-free aqueous solutions at infinite dilution was obtained by emf measurements with a bromide ion electrode. The results show that the longer the methylene chain between neighboring charges on the polymer backbone, the greater is the degree of dissociation, as Manning's theory predicts. The distance between the neighboring charges on the polymer backbone was calculated by using Manning's equation. The distance was compared with that calculated geometrically on the basis of the contour length of the molecule according to Manning's definition. The former distance was much smaller than the latter. The former distance was then compared with the length calculated from Eyring's equation for the end-to-end distance of a freely rotating methylene chain. In this case, good agreement was obtained.     

Photochemical transformations of sphingosine and serinol in aqueous and ethanol solutions

It has been established that the main products of the direct photolysis of C15-sphingosine and serinol are 2-tridecenal and glycolaldehyde, which are formed as a result of C–C bond cleavage in the parent compounds. It has been shown that the addition of hydrogen peroxide and acetone to the test solutions extended the range of the photolysis products due to the occurrence of deamination processes. The set of the experimental data has made it possible to propose mechanisms for the photochemical reactions of C15- sphingosine and serinol fragmentation, which occur through the steps of the formation of N- and C-centered radicals.     

Structural and optical characteristics of CdxZn1−x S nanoparticles stabilized in aqueous solutions of polymers

The structural and optical characteristics of Cd_xZn_1−xS nanoparticles, produced in aqueous solutions of sodium polyphosphate, polyvinyl alcohol, and gelatin, were studied. It was shown that the stoichiometric ratio of Cd(II) and Zn(II) in the nanoparticles can differ from that in the initial mixture. It was established that the main factors determining the final size of the Cd_xZn_1−xS nanoparticles are the nature and concentration of the polymer, the ratio of the initial concentrations of the reagents, and the temperature and duration of the post-synthesis treatment of the colloids. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 42, No. 3, pp. 168–172, May–June, 2006.     

DNA interaction with synthetic polymers in solution

DNA complexes with cationic polymers (polyvinylamine (PVA), polyallylamine (PAA), polydimethylaminoethylmethacrylate (PDMAEM), poly-(N,N,N-trimethylammonio)ethyl methacrylate chloride (PTMAEM), poly-l-lysine (PLL)) were investigated. It was shown that volume and persistent length of DNA do not change essentially at low cationic polymer concentration in a solution. DNA packaging in 0.005 M NaCl was observed at charge ratio N/P ≈ 1. Secondary DNA structure in complexes was not disrupted, and DNA was protected from protonation. The comparison between DNA packaging in complexes with polycations and DNA condensation induced by trivalent ions was made.     

Simulation of radiation-chemical transformations in aqueous nitric oxide and nitrite solutions

A kinetic model of radiation-chemical transformations of nitrogen oxide and nitrites in aqueous solutions is proposed. It includes the previously developed reaction scheme for water and H₂, H₂O₂, and O₂ solutions complemented by the reactions of water radiolysis products with NO and NO₂⁻. It has been shown that the model describes well experimental data on the decomposition of the compounds and the buildup of products depending on the absorbed dose in aqueous solutions at different pH values.     

Simulation of the radiation-chemical transformations of acetic acid in aqueous solutions

A general model for the radiolysis of acetic acid and its aqueous solutions is proposed. The model adequately describes experimental data on the degradation of the acid and the formation of gases (H₂, CO₂, and CH₄) in aqueous solutions at various pH values.     

An investigation of the segmental flexibility of spin labelled synthetic macromolecules in solutions

Within the framework of a model, which takes into account fast anisotropic rotation of the spin label and slow diffusion motion of the polymer chain segment, the ESR spectra of 1% solutions of spin labelled poly(4-vinylpyridine) have been analysed. It has been shown that the model describes the observed spectra satisfactorily. The rotational correlation times for the segment together with its effective dimensions (～ 12 monomer units) have been calculated. The dependence of segment correlation time on temperature is described by the Arrhenius equation with E = 4 kcal/mol. τ_o = 2·10^?13 sec.     

Non-covalently lactose imprinted polymers and recognition of saccharides in aqueous solutions

The aim of this work was to prepare lactose imprinted polymer and study of its selectivity for the recognition of different mono- and disaccharides. A series of molecularly imprinted polymers (MIPs) against lactose were synthesized and their binding properties were compared with a Blank non-imprinted polymer. Methacrylamide (MAAM) and ethylene glycol dimethacrylate were used as functional monomer and cross-linker, respectively. Dimethylsulfoxide was also applied as polymerization solvent. Different lactose:MAAM ratios were applied and optimized MIP was selected in a conventional batch adsorption study. The dissociation constant and maximum binding sites of polymer were determined using the Scatchard analysis. The selectivity of MIP for different mono- and disaccharides was also evaluated. The results indicated that the shape of cavity and orientation of functional monomers in binding sites and the spatial arrangement of hydroxyl groups in saccharide structure were responsible for the selectivity of lactose imprinted polymer.     

Synthesis of polymers in aqueous solutions: Polyaddition of bis(oxazolines) with dithiol in aqueous solutions

Polyaddition of bis(4-mercaptophenyl) sulfide ( BMPS ) with m-phenylenebis(2-oxazoline) ( MPBO ) proceeded very smoothly in the mixtures of aprotic ploar solvents such as N-methyl-2-pyrrolidone ( NMP ) with water to produce the corresponding poly(amide–sulfide) with high molecular weights at 90°C under nitrogen. The reaction of BMPS with MPBO , p-phenylenebis(2-oxazoline), and 1,4-butylenebis(2-oxazoline) was also examined in water under the same conditions, and it was found that the reaction proceeds successfully to give the corresponding poly(amide–sulfide)s with high molecular weights. These results mean that water along as well as the mixed solvents of aprotic polar solvents such as NMP with water can be uses as suitable reaction media for the polyaddition of bis(oxazolines) with dithiol to synthesize poly(amide—sulfide)s with high molecular weights. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2711–2717, 1997     

Adiabatic compressibility and solvation of drag reducing polymers in aqueous solutions

Adiabatic compressibilities of aqueous solutions of some drag reducing polymers have been evaluated from ultrasonic velocity and density measurements. The solvation numbers of the repeat units of the polymers have been further evaluated by using Passynsky equation. It is observed that the solvation number increases with the shear stability of drag reducing polymers in turbulent flow.     

Structural aspects of aqueous tetraalkylammonium salt solutions

Various thermodynamic and spectroscopic investigations on aqueous tetraalkylammonium salt solutions are reviewed from a structural viewpoint. At present, it is not yet clear what kind of water structure is formed around the alkyl groups of the large cations. However, the importance of cosphere overlap and ion-ion interaction (cation-anion, cation-cation, cation-anion-cation, etc.) in determining the solution properties are emerging more clearly. In this regard, model calculations based on the approach of Friedman and his coworkers are expected to be of considerable value.This paper was presented at the symposium, The Physical Chemistry of Aqueous Systems, held at the University of Pittsburgh, Pittsburgh, Pennsylvania, June 12–14, 1972, in honor of the 70th birthday of Professor H. S. Frank.     

Conformational characteristics of polyethylene glycol macromolecules in aqueous solutions according to refractometry data

The aqueous solutions of polyethylene glycols with molecular masses of 600, 1000, 1500, 3000, 6000, and 20000 were studied by refractometry. The conformational polarizabilities, mean-square distances between the ends of the macromolecular chain, segment lengths, and the number of Kuhn segments in a macromolecule were determined using the Lorentz-Lorentz equation. The polarizability of a hydrated macro-molecule was represented as the sum of polarizabilities of the nonhydrated macromolecule with retained conformation and polarizabilities of the water molecules involved in hydration of macromolecules. The size of macromolecules stabilized starting from a certain concentration. It was concluded that the initial concentration of stabilization shifts toward low concentrations as the molecular mass of polyethylene glycol increases. The dependence of the mean-square distance between the ends of the macromolecular chain on the number of Kuhn segments was expressed as the exponential function with index 0.3.