Radiation-induced polymerization in dilute aqueous solutions of cyanides

It has been found that the addition polymerization of cyanides (HCN and NH₄CN) takes place in dilute, O₂-free irradiated aqueous solutions, in addition to the abundant formation of various smaller molecules. A polymer with a molecular mass of 16,000 amu was found. Its abundance increases with initial cyanide concentration and absorbed dose and can be up to 31% of the total amount of radiolytic products. HPLC data also indicate the presence of two more products at 22,000 amu and 10,000 amu, which are less abundant by one order of magnitude. The same molecular masses appear throughout the examined range of cyanide concentration (0.001–0.2 mol dm^–3) and absorbed dose (2–200 kGy). They remain also at large doses (up to 1250 kGy) after a complete destruction of cyanide.     

Hydration of nucleic bases in dilute aqueous solutions. Apparent molar adiabatic and isothermal compressibilities, apparent molar volumes and their temperature slopes at 25 degrees C

The concentration increment of the ultrasound velocity has been measured with an accuracy of +/- 0.03 cm/s in dilute aqueous solutions of a variety of nucleic bases and their derivatives in the concentration range 0.5-1.5 mg/g H2O at temperatures of 15-35 degrees C. A new method for the precise measurement of ultrasound velocity in small volumes of liquids has been used. The values of the apparent molar adiabatic compressibilities plus the corresponding temperature slopes, apparent molar volumes with their temperature slopes, and apparent molar isothermal compressibilities at infinite dilution have been obtained. The regularities describing the signs of these values and their dependence on the chemical structure of the solute have been revealed. It is shown that these regularities can be described as a consequence of partial 'normalization' of some of the properties of water around the bases, namely, weaker structural contribution to compressibility, less negative temperature slope of compressibility and less negative structural contribution to the coefficient of thermal expansion of water.     

The role of water in the thermodynamics of dilute aqueous solutions

Water plays a role in the thermodynamics of dilute aqueous solutions that is unusual in two ways. First, knowledge of hydration equilibrium constants of species is not required in calculations of thermodynamic properties of biochemical reactants and reactions at specified pH. Second, since solvent provides an essentially infinite source of oxygen atoms in a reaction system where water is a reactant, oxygen atoms are not conserved in the reaction system in dilute aqueous solutions. This is related to the fact that H₂O is omitted in equilibrium expressions for dilute aqueous solutions. Calculations of the standard transformed Gibbs energies of formation of total carbon dioxide and total ammonia at specified pH are discussed, and the average bindings of hydrogen ions by these reactants are calculated by differentiation. Since both of these reactants are involved in the urease reaction, the apparent equilibrium constants and changes in the numbers of hydrogen ions bound are calculated for this reaction as functions of pH.     

Investigation of uranium recovery from dilute aqueous solutions using silk fibroin

The uranium uptake ability of silk fibroin was investigated. High ability to uptake uranium from nonsaline water containing 2.500 mg of uranium was observed with the silk fibroin tested. The uranium uptake was very rapid and was dependent on pH, uranium concentration, temperature, and retention time. Almost all uranium taken up is easily eluted with 1 mol/L CH₃COONH₄. This biomatrix, therefore appears to have potential for use in a commercial process for uranium recovery from uranium-containing waste water.     

On the temperature-induced coil to globule transition of poly-N-isopropylacrylamide in dilute aqueous solutions

Poly-N-isopropylacrylamide (PNIPAM) is a chemical isomer of poly-leucine, having the polar peptide group in the side-chain rather than in the backbone. It has been demonstrated experimentally that PNIPAM dissolved in aqueous solution undergoes a collapse transition from coil to globule on increasing temperature above the θ-point. By a careful reviewing of existing experimental data, we emphasize that such coil to globule collapse has to be considered an intramolecular first-order transition, analogous to the cold renaturation of small globular proteins. The main theoretical approaches to the coil to globule collapse in homopolymers are discussed briefly, and a critical comparison between the existing models is performed. We point out that, as a general result, the coil to globule collapse is expected to be a first-order transition for rigid and semi-rigid macromolecules. Finally, taking advantage of the analogy between the coil to globule collapse of PNIPAM and the cold renaturation of small globular proteins, we try to clarify some important and intriguing aspects of protein thermodynamics. This leads to the conclusion that the amphiphilic nature of polypeptide chain plays the fundamental role for the existence of two temperature-induced conformational transitions.     

Separation of dilute aqueous butanol and acetone solutions by pervaporation through liquid membranes

A simultaneous extraction-stripping process is proposed for separating volatile products from fermentation broths, it is based on pervaporation through a liquid membrane supported with a hydrophobic porous membrane. The liquid membrane prepared with oleyl alcohol was selected as the most suitable for separating volatile products resulting from acetone-butanol fermentation. The separation performance and stability of the oleyl alcohol liquid membrane were investigated by using dilute aqueous butanol and acetone solutions. The oleyl alcohol liquid membrane was found to be superior by far in both selectivity and permeability of butanol to the better known silicone rubber membrane in its high selectivity for alcohols. Using the oleyl alcohol liquid membrane, the dilute aqueous butanol solutions of around 4 g/L obtained in acetone-butanol fermentation could be concentrated up to 100 times. The stability of this liquid membrane was also quite good as long as the surface tension of the feed solution was less than the critical surface tension of the support membrane. No change in the separation performance was found after the continuous usage in a long period of 100 h.     

A study of dilute aqueous solutions of humic acids by scanning microcalorimetry

It has been found by reversed-phase chromatography that humic acids obtained from vermicomposts of different duration of vermicomposting consist of a hydrophilic and a hydrophobic fractions, the hydrophobic fraction having a substantially lower content of charged, probably carboxylic, groups. A change in the sign of the temperature dependence of the heat capacity of dilute aqueous solutions of humic acids at ∼58°C has been found by differential scanning microcalorimetry, which indicates an increase in the hydration of hydrophobic groups. A jump-wise increase in heat capacity in the temperature range from 86 to 90°C was also found, which is perhaps due to hydration of hydrophobic groups in the interior of “micelles“, because of “devitrification” of the hydrophobic nucleus of micelle-like structures. It was shown that increasing the duration of vermicomposting leads to an increase in the relative content of the hydrophobic fraction of humic acids and in the cooperativity of the thermodynamic transition, which manifests itself as the jump of heat capacity, which probably results from the increase in the “micelle” size.     

Ruthenium red complexation with ionic polysaccharides in dilute aqueous solutions: chirooptical evidence of stereospecific interaction.

This paper presents optical and chirooptical data on the interaction of the microscopy-staining agent ruthenium red with carboxylated polysaccharides in dilute aqueous solution. The polysaccharides used are both natural (alginate and pectate) and semisynthetic (C6-oxidized cellulose and C6-oxidized amylose). A preliminary discussion of the molecular structure and conformational features which control the interaction is presented.     

Selective recovery of uranium and thorium ions from dilute aqueous solutions by animal biopolymers

Selective actinide ion recovery from dilute, aqueous, multication waste streams is an important problem. The recovery of uranium (U) and thorium (Th) by various animal biopolymers was examined. Of four species of biopolymers tested, a high uptake of uranium and thorium was found in hen eggshell membrane (ESM) and silk proteins, with the maximum uranium and thorium recovery exceeding 98% and 79%, respectively. The uptake of U and Th was significantly affected by the pH of the solution. The optimum pH values were 6 and 3 for the uptake of U and Th, respectively. The effect of temperature differed with the metal. The uptake of U decreased with increasing temperature (30–50°C), whereas the Th uptake increased with increasing temperature. Selective recovery of U and Th from dilute aqueous binary and multimetal solutions was also examined. ESM and silk proteins tested were effective and selective for removing each metal by controlling the pH and temperature of the solution. In multimetal systems, the order of sorption of ESM proteins was preferential: U > Cu > Cd > Mn > Pb > Th > Ni > Co > Zn at pH 6 and Th > U > Cu > Pb > Cd > Mn > Co > Ni = Zn at pH 3. These biopolymers appear to have potential for use in a commercial process for actinide recovery from actinide-containing wastewater.     

Studies on human serum high density lipoproteins. Self-association of apolipoprotein A-I in aqueous solutions.

Human serum apolipoprotein A-I (apo-A-I), the major protein component of the human serum high density lipoproteins, was studied in aqueous solutions of differing ionic strength and pH by the techniques of sedimentation equilibrium ultracentrifugation and frontal analysis gel chromatography. The ultracentrifugal studies indicate the apo-A-I is a self-associating system that is dependent upon protein concentration, but relatively independent of the nature of the medium. The apparent weight average molecular weights obtained from solutions of initial apo-A-I concentration between 0.2 and 0.9 mg/ml were in the range of 3.0 to 16.7 x 10(4) (monomer molecular weight = 28,014). Of the several models of self-associated examined, that which gave the best theoretical fit was for the monomer-dimertetramer-octamer model. The self-association of apo-A-I in aqueous solutions was further documented by frontal analysis gel chromatography, which not only corroborated the ultracentrifugal results, but also indicated that the multiple species of apo-A-I in solution attain equilibrium rather rapidly. Besides having intrinsic importance, these results indicate that the solution properties of apo-A-I must be established before ligand binding studies are conducted and interpreted.     

Water activity, pH and density of aqueous amino acids solutions

The water activity, pH and density of some aqueous amino acid solutions were determined at 25 degrees C in three different types of solvents. Previous published experimental data on water activity and solubility of amino acids in aqueous solutions were used together with data from this work to test the applicability of a group contribution model. The activity coefficients were estimated by the UNIFAC-Larsen model combined with the Debye-Hückel equation, taking also into account the partial dissociation phenomena of species in solution. Interaction energies between the charged species Na(+) and Cl(-) and the specific groups of amino acids (COOH and NH(2)) were adjusted using experimental solubility data.