Radiolysis of paracetamol in dilute aqueous solution

Using radiolytic experiments hydroxyl radical (main reactant in advanced oxidation processes) was shown to effectively destroy paracetamol molecules. The basic reaction is attachment to the ring. The hydroxy-cyclohexadienyl radical produced in the further reactions may transform to hydroxylated paracetamol derivatives or to quinone type molecules and acetamide. The initial efficiency of aromatic ring destruction in the absence of dissolved O₂ is c.a. 10%. The efficiency is 2–3 times higher in the presence of O₂ due to its reaction with intermediate hydroxy-cyclohexadienyl radical and the subsequent ring destruction reactions through peroxi radical. Upon irradiation the toxicity of solutions at low doses increases with the dose and then at higher doses it decreases. This is due to formation of compounds with higher toxicity than paracetamol (e.g. acetamide, hidroquinone). These products, however, are highly sensitive to irradiation and degrade easily.     

Dielectric relaxation behavior of SDS/β-CD organized self-assembly in dilute aqueous solution

Dielectric relaxation behavior of SDS/β-CD self-organized with mass concentrations from 1% to 7% was investigated. The phase microstructure of SDS/β-CD aqueous solution was confirmed by analyzing the dielectric parameters. The dielectric relaxation behavior was attributed to the interfacial polarization between vesicle and medium, and the relaxation distribution parameter can indicate the shape transition from vesicles to microtubules with increasing concentration. Dielectric relaxation provided a new method to study surfactant organized self-assembly.     

Vibrational and rotational relaxation of 1-hexyne in solution

The IR and isotropic Raman bandwidths of the ν(CH) and ν(CC) stretching modes of 1-hexyne have been measured in dilute solutions in n C₇H₁₆ and CCl₄ as a function of T. The deduced vibrational and rotational bandwidths are interpreted in terms of different models.     

Thermodynamic properties of the benzene-phenol dimer in dilute aqueous solution

Precise vapor pressure-solubility measurements have been obtained for dilute solutions of benzene and phenol in water at 15, 25, 35 and 45°C. All of the results are consistent with a mass action model that attributes deviations from ideal solution behavior to the formation of benzene dimers and hetero-dimers between benzene and phenol. The benzene-phenol dimer forms endothermically at 25°C, with a very large negative heat capacity, and a formation constant that reaches a maximum value of 0.66 l-mol^?1 at approximately 35°C. Thermodynamic properties of the benzene-phenol dimer are reported and compared with those of other aggregates that are believed to be stabilized primarily by hydrophobic interactions.     

Radiation induced degradation of ketoprofen in dilute aqueous solution

The intermediates and final products of ketoprofen degradation were investigated in 0.4 mmol dm^?3 solution by pulse radiolysis and gamma radiolysis. For observation of final products UV?vis spectrophotometry and HPLC separation with diode array detection were used, and for identification MS was used. The reactions of ^?OH lead to hydroxycyclohexadienyl type radical intermediates, in their further reactions hydroxylated derivatives of ketoprofen form as final products. The hydrated electron is scavenged by the carbonyl oxygen and the electron adduct protonates to ketyl radical ^?OH is more effective in decomposing ketoprofen than hydrated electron. Chemical oxygen demand and total organic carbon content measurements on irradiated aerated solutions showed that using irradiation technology ketoprofen can be mineralised. The initial toxicity of the solution monitored by the Daphnia magna test steadily decreases with irradiation. Using 5 kGy dose no toxicity of the solution was detected with this test.     

Conductometric studies of DyCl3 in dilute aqueous solution

The limiting conductivity of Dy³⁺(aq) has been determined for the first time by linear extrapolation of conductivity measured in dilute aqueous solutions of (DyCl₃+HCl) at 25°C as ^o(Dy³⁺, aq) = (62.9±0.7) S-cm²-eq^-1. A second set of conductivity measurements in dilute aqueous solutions of DyCl₃ has given evidence of very slight hydrolysis of the cation, with a first hydrolysis constant of 6 x 10^–8 mol-dm^–3 (pK=7.2±0.5) calculated by applying the Onsager-Kim law of electrolyte mixtures.     

Monte carlo simulation of ethane in dilute aqueous solution

A Monte Carlo simulation of a dilute aqueous solution of ethane both fixed and flexible conformation runs shows that energetically and entropically the eclipsed conformation of ethane is preferred to the staggered conformation in solution which is a reversal in the gas phase.     

The aggregation behavior of O-carboxymethylchitosan in dilute aqueous solution

O-Carboxymethylchitosan (OCMCS) is a kind of biocompatible derivatives of chitosan whose water solubility is strongly dependent on the degree of carboxymethylation. The OCMCS with 100 carboxymethyl groups and 75 amino groups per 100 anhydroglucosamine units of OCMCS was synthesized by the reaction of chitosan and monochloroacetic. When OCMCS was dissolved in water, its solution was neutral and OCMCS behaved like a weak polyanionic polyeclectrolyte because most of carboxylic groups were not dissociated in neutral aqueous solution. The aggregation behavior of OCMCS in aqueous solution was studied by surface tensiometry, steady-state fluorescence spectroscopy and viscometry. The critical aggregation concentration (cac) of OCMCS was determined to be between 0.042 mg/ml and 0.050 mg/ml. The possible aggregation mechanism of OCMCS in water was elucidated.     

Calculation of the nmr relaxation time of dilute 129 Xe gas

The spin-lattice relaxation time T₁ of ¹²⁹ Xe gas is calculated with the kinetic theory due to Chem and Snider. A Lennard-Jones (12,6) potential functions is employed as a model for the spherical potential while the transient spin-rotation interaction is assumed to be responsible for the relaxation of the nuclei. Cross sections for spin transitions on collisions are calculated either quantum mechanically or semiclassically depending on the relative energy. The temperature dependence of T₁ is determined in the range 200–450 K. The calculated value of T₁ at 298 K and 1 amagat is 2.8 x 0⁵ s while the value measured by Hund and Carr is (2.0 ± 0.2) x 10⁵s.     

Dielectric analysis on phase transition and micelle shape of polyoxyethylene trisiloxane surfactant in dilute aqueous solution

The cloudy Silwet L-77 aqueous solution on the concentration range from 0.5%to 50%was investigated by dielectric relaxation spectroscopy.The concentration dependence of phase microstructure was confirmed by means of analyzing the dielectric parameters of bulk solution.The relaxation behavior was assigned to the interfacial polarization between the micelle and the medium,and the relaxation distribution parameter was used to figure the shape transition from sphere to ellipsoid with the concentration increasing.The synchronous reduction of permittivity and conductivity indicated the formation of the lamellar phase. As compensation,the quantity of the surfactant liquid phase gradually decreased,whose shape constantly kept ellipsoidal.     

Conformation and hydration of sugars and related compounds in dilute aqueous solution

The effect of hydroxyl substitution on the nature of the hydration of an alkane chain has been studied by calorimetric techniques. Static permittivities (₀) of a range of monosaccharides and related compounds in aqueous solution have also been determined. The (₀) data, suitably processed, have provided information about the solute dipole moments. In conjunction with earlier results from volumetric, compressibility, and relaxation studies, the specific hydration model is further developed and the relationships between solute molecular conformations and solute-water interactions are discussed.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.     

An unusually slow self-assembly of inorganic ions in dilute aqueous solution

A combination of static and dynamic laser light-scattering techniques was used to monitor an unusual slow self-assembly of giant polyoxomolybdate-based molecules into vesicle structures in dilute aqueous solution. Contrary to the behavior of common inorganic ions, these giant molecules need months to reach an equilibrium state. The process is an endothermic process and roughly follows the rule of a first-order reaction. The possible reasons for such a slow solution process are also discussed.     

Ionizing radiation induced reactions of 2,6-dichloroaniline in dilute aqueous solution

In pulse radiolysis investigations the hydroxyl radical formed in water radiolysis reacts with 2,6-dichloroaniline in radical addition to the ring forming hydroxy-cyclohexadienyl radical and also in hydrogen atom abstraction from the amino group resulting in anilino radical. The hydroxy-cyclohexadienyl radical in the absence of dissolved O₂ partly transforms to anilino radical, when dissolved oxygen is present the radical transforms to peroxy radical. According to chemical oxygen demand measurements the reaction of one OH radical induces the incorporation of 0.6 O₂ into the products. It is a typical value for chlorine atom substituted aromatic molecules, and smaller than found for molecules without chlorine atom (1.0–2.0).     

Hydrothermal saccharification of cotton cellulose in dilute aqueous formic acid solution

Cotton cellulose subjected to a dilute aqueous formic acid solution, at acid concentrations up to 1% (w/w), under hydrothermal conditions in a semi-batch reactor was converted into glucose and oligomers with lower degrees of polymerizations (DP). After heating at 250 °C for 60 min in 0.1% (w/w) aqueous formic acid solution, yields of glucose and total sugar with DP = 1 to 9 were 36.6 and 83.8% (100 × gC/gC of initial cotton sample), respectively, and 5-hydroxymethylfurfural was almost as low as 1%. The yields of glucose and oligomers were significantly improved by adding the acid. The reaction was represented by first-order reaction kinetics with regard to (1 ?C x) where x is the conversion based on the total sugar or glucose yield. At 250 °C, the differences in the rate constants (k ? k _water) were proportional to the square root of formic acid concentration.     

Adsorption of n-butanol from dilute aqueous solution with grafted calixarenes

Materials were synthesized for the recovery of n-butanol from dilute aqueous solutions, as may be useful for applications in biofuel-water separations. These materials are composed of hydrophobic, cavity-containing calixarenes covalently bound directly to porous, hydrophilic silica supports through a Si linker atom rather than a flexible organic linker, as is common, at surface coverages of up to ～0.25 calixarenes/nm(2) (～250 μmol calix/g matl). The calixarene ring size, upper rim groups, bridging group (calixarene vs thiacalixarene), and surface density were varied. The materials were characterized by NMR, UV-vis, and TGA. The absolute butanol uptake reached ～0.16 mmol butanol per gram of material at equilibrium concentrations below 0.12 M and increased monotonically with the calixarene surface density. The background adsorption onto the silica surface was small at high calixarene loading. At 298 K, the free energy of adsorption in the calixarene cavities became more favorable by 3 kJ/mol as the surface area of the hydrophobic calixarene upper rim groups increased from H to methyl to tert-butyl, consistent with adsorption driven by van der Waals interactions. A thiacalix[4]arene-SiO(2) material, containing polarizable sulfur bridges and a larger, more conformationally mobile calixarene structure, had slightly stronger adsorption still. All materials except this thiacalixarene exhibited fully reversible adsorption into solution. As a representative material, the adsorption of n-butanol from aqueous solution at a tert-butylcalix[4]arene site was accompanied by a negligible enthalpy change but a small, favorable entropy change of +50 ± 20 J/mol/K, indicating that adsorption is driven by desolvation. Butanol desorbed from tert-butylcalix[4]arene materials at ～150 °C into the gas phase, well within the range of stability of calixarenes (<300 °C), indicating that these materials have promise as regenerable adsorbents.     

UV radiation effects on flavocytochrome b2 in dilute aqueous solution

A dilute aqueous solution of flavocytochrome b2 when exposed to inactivating doses of UV radiation at 280 nm underwent reversible loss in activity both under aerated and deaerated conditions. The active site as well as the substrate binding sites were found to be modified in the irradiated enzyme. Irradiation of the enzyme in the UV-C range resulted in partial unfolding of the polypeptide framework. Destruction and/or modification of both tryptophan and tyrosine residues as well as heme moieties took place. Preliminary laser flash photolysis studies suggest that the initial photo-ionization takes place with tryptophan and tyrosine residues with the formation of excited states and radicals, and then rapid transfer of electrons takes place to histidyl and cystinyl sites which might have eventually been altered in the process.     

Hydrodynamic behavior of high molar mass linear polyglycidol in dilute aqueous solution

Six high molar mass polyglycidol samples were obtained by fractionation of polyglycidol synthesized by means of cationic polymerization of ethoxyethyl glycidyl ether followed by cleavage of the protective groups. The fractions covering the molar mass range from 0.1 to 2.4 x 10(6) were studied by dynamic and static light scattering. The weight-average molar masses (Mw), second virial coefficients (A2), radii of gyration (Rg), diffusion coefficients (D0), hydrodynamic radii (Rh), and dynamic virial coefficients (kDphi) were determined for the single coil in dilute aqueous solution at 25 degrees C, and scaling equations were established. It was found that polyglycidol in water does not exhibit the expected asymptotic good solvent behavior. The scaling exponents for A2, D0, and Rh are even closer to those for polymer coils in marginal solvents than to the expected ones in the excluded-volume region. The values of the interpenetration parameter, psi, and kDphi are far from reaching limiting values even for the fractions of the highest molar masses. The scaling exponent for Rg as well as the Rg/Rh ratio, which was found to increase with increasing molar mass, imply elongated coil conformation in the high molar mass region.