Kinetic analysis of genipin degradation in aqueous solution

Degradation of genipin (GP), a low toxicity natural protein crosslinking agent, in aqueous solution was monitored by HPLC at various pH levels. Degradation of GP was consistent with a mechanism consisting of a first order reaction with a reversible first step. Formation of the intermediate was slowest at more neutral pHs while formation of the irreversible product was correlated to increasing alkalinity. Degradation at all pHs was enhanced by the presence of phosphate ions. Degradation of GP most likely proceeds via the reversible opening of the dihydropyran ring by water followed by irreversible polymerization of the intermediate. Degraded solutions containing no detectable GP or intermediate, however, are still capable of crosslinking proteins.     

High-temperature degradation of polyacrylic acid in aqueous solution

Poly(acrylic acid) (PAA) was decarboxylated in aqueous solution as a function of pH and ionic strength in the temperature range 100–350°C. Degradation kinetics were first order with respect to acid functionality. The rate of decarboxylation at high pH (E_α = 51.1 kcal/mol) was much slower than that at low pH (E_α = 20.3 kcal/mol). At intermediate pH, the reactivity was found to depend on the degree of dissociation of PAA as a functions of ionic strength, pH, and temperature. No monomer was observed in the reaction product. © 1996 John Wiley & Sons, Inc.     

Radiation-induced degradation of 4-chloroaniline in aqueous solution

The radiation-induced decomposition of 4-chloroaniline (4-ClA) was studied under steady-state conditions using aqueous solutions saturated with air, pure oxygen, N₂O, argon and argon in the presence of t-Butanol. Using HPLC-method, the initial G-values of the substrate degradation as well as of a number of radiolytic products were determined. The formation of aminophenols, chlorophenols, aniline and phenol in addition to chloride, ammonia, formaldehyde and mixture of aldehydes as well as carboxylic acids was studied as a function of absorbed dose. Based on the experimental data, probable reaction mechanisms for the degradation of 4-ClA by γ-rays and the formation of the identified products are presented.     

Free radical-induced oxidative degradation of polyacrylamide in aqueous solution

The oxidative main chain degradation of polyacrylamide initiated by ^·OH radicals attacking the polymer in aqueous solution was studied. ^·OH radicals were produced by irradiating dilute polymer solutions with high energy radiation. A bimolecular process (combination of PO₂ radicals) was found to be the rate determining step in the series of consecutive reactions leading to main-chain rupture. This was revealed from results obtained in pulse radiolysis studies using the light scattering detection method. Under the given experimental conditions, the number of radical sites per initial macromolecule exceeded unity with the consequence that intramolecular reactions of PO₂ radicals dominated intermolecular combinations. From both pulse radiolysis and continuous irradiations it was inferred that only a small fraction (about 1%) of the attacking ^·OH radicals initiated main-chain scission.     

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.     

Photodegradation of a polyamidehydroxyurethane type polymer in aqueous solution. The role of some dyes in the degradation

The influence of some dyes on the photodegradation of a polyamidehydroxyurethane type polymer in aqueous solution has been studied. It has been found that, among the dyes used, only riboflavin sensitizes and accelerates the degradation of the polymer. It is proposed that under ultraviolet irradiation riboflavin undergoes photoreduction to lumichrome, which sensitizes the photodegradation of the polymer. It is also possible that the mechanism of photodegradation involves the participation of singlet oxygen.     

Squarate complexes of some lanthanide ions in aqueous solution

The squarate complexes of Eu³⁺, Tb³⁺ and Tm³⁺ in aqueous solutions of 0.05M, 0.075M and 0.1M ionic strength are studied using the solvent extraction method. Effects of changes in the ionic strength on the stability constants of the complexes formed are discussed.     

Solubility of some calcium-carboxylic ligand complexes in aqueous solution

Insoluble species were identified in the systems Ca(2+)-hemimellitate, Ca(2+)-1,2,3,4-butanetetracarboxylate and Ca(2+)-citrate, and their solubilities were determined in aqueous solution at T = 25 degrees C. Values of pK(s0) were obtained for the species CaLH (L = benzene-1,2,3-tricarboxylate or hemimellitate), Ca(2)L (L = 1,2,3,4-butanetetracarboxylate), CaLH and Ca(3)L(2) (L = citrate), together with their dependence on ionic strength. Solid compounds were also characterized by thermogravimetry. The complex formation in solution for the system Na(+) - and Ca(2+)-hemimellitate was studied too.     

Photo-induced reduction of flavin mononucleotide in aqueous solutions

The photo-induced reduction of flavin mononucleotide (FMN) in aqueous solutions is studied by absorption spectra measurement under aerobic and anaerobic conditions. Samples without exogenous reducing agent and with the exogenous reducing agents ethylene-diamine-tetraacetic acid (EDTA) and dithiothreitol (DTT) are investigated. Under anaerobic conditions the photo-induced reduction with and without reducing agents is irreversible. Under aerobic conditions the photo-reduction without added reducing agent is small compared to the photo-degradation, and the photo-reduction of FMN by the reducing agents is reversible (re-oxidation in the dark). During photo-excitation of FMN the dissolved oxygen is consumed by singlet oxygen formation and subsequent chemical reaction. After light switch-off slow re-oxidation (slow absorption recovery) occurs due to air in-diffusion from surface. EDTA degradation by FMN excitation leads to oxygen scavenging. The quantum efficiencies of photo-reduction under aerobic and anaerobic conditions are determined. The re-oxidation of reduced FMN under aerobic conditions and due to air injection is investigated.     

Photo-induced degradation reactions of some alkyl- and aryl-carbonyl derivatives of manganese,molybdenum and tungsten

Photo-induced degradation of CH₃Mn(CO)₅ in pentane solution results in the formation of Mn₂(CO)₁₀, methane and carbon monoxide. Both CH₃D and CH₄ are formed when CH₃Mn(CO)₅ is photolyzed in C₆D₆. Photolysis of C₆H₅CH₂Mn(CO)₅ in pentane solution produces Mn₂(CO)₁₀, toluene and bibenzyl. Analogous photodegradation of C₆H₅Mn(CO)₅ in pentane solution yields Mn₂(CO)₁₀, benzene and carbon monoxide, but not biphenyl. The thermally unstable complex C₂H₅Mn(CO)₅ was studied by photolyzing it in solution at ?40°C. GC analysis indicates that both ethylene and ethane are formed, and that the mole ratio of these products is dependent on the initial concentration of C₂H₅Mn(CO)₅. These results are consistent with a β-hydrogen elimination mechanism for this reaction. Photolysis of CpMo(CO)₃CH₂C₆H₅ in pentane solution produces [CpMo(CO)₃]₂ and toluene, whereas photolysis of CpW(CO)₃CH₂C₆H₅ affords [CpW(CO)₃]₂, CpW(CO)₂(η³-benzyl), toluene, and a small amount (2%) of bibenzyl. When CpM(CO)₂(η₃-benzyl) (M = Mo, W) complexes are subjected to photolysis under similar conditions, the only identifiable product is toluene. CpW(CO)₃C₆H₅ degrades photochemically in pentane solution to form [CpW(CO)₃)₂ and benzene, together with a small amount (6%) of biphenyl.     

Oxidative degradation of formic acid in aqueous solution upon dielectric-barrier discharge treatment

The kinetics of degradation of formic acid in an aqueous solution during its dielectric-barrier discharge treatment in oxygen was studied. It was shown that, the lower the initial concentration and the longer the time of contact of the solution and the gas with the discharge zone, the higher the degree of conversion of the acid, which can reach 99%. It was found that the main degradation products (～94% on carbon basis) are formaldehyde (～24%) and carbon dioxide (～70%).     

水溶液中苯乙酮及其降解产物的紫外光光解

在紫外光作用下,水中苯乙酮(10^-^4mol.dm^-^3,pH=6)能发生直接光降解,生成邻羟基和间羟基苯乙酮等中间产物,并且这些产物又可进一步光解生成二羟基苯乙酮。在相同条件下,它们的相对光降解速率大小为:苯乙酮>间羟基苯乙酮>对羟基苯乙酮>邻羟基苯乙酮。     

The radiation-induced degradation of a diazo dye in aqueous solution,II

The effect of -radiation on the color intensity of aerated, deaerated and oxygenated aqueous solutions of a diazo dye (Helion Red 8B) has been investigated. The decoloration yields of Helion Red 8B neutral aqueous solution, G(-Dye), for the nitrogen-, oxygen- and aerated-saturated solutions were found to be 0.77, 0.46 and 0.36 in the respective early stage. The rate constant for the reaction of the OH radical with the HR8B dye, obtained from competition kinetics using ethanol, was found to be 1.3·10¹⁰ M^–1·s^–1. In aerated solutions (pH 3), the G(-Dye) decreased markedly upon the addition of a very small amount of ethanol. Suggestions are made for possible use of the dye as a radiation dosimeter in the dose range of 0.1 to 2 kGy.     

Photocatalytic degradation of betamethasone sodium phosphate in aqueous solution using ZnO nanopowder

The photocatalytic degradation of betamethasone sodium phosphate has been investigated in aqueous phase by using ultraviolet (UV) light and ZnO nanopowder. The effect of catalyst loading, irradiation time, pH, addition of oxidizers, effect of alcohol and anion presence on the reaction rate was ascertained and optimum conditions for maximum degradation were determined. The photocatalytic degradation of betamethasone sodium phosphate was strongly influenced by these parameters. The optimum amount of the photocatalyst used is 0.44 g/L. The efficiency of betamethasone sodium phosphate increases with the photo-degradation increase of the irradiation time.     

Theoretical calculation of the pKa values of some drugs in aqueous solution

In this work, calculations of pK_a values have been performed on benzoic acid and its para‐substituted derivatives and some drugs by using Gaussian 98 software package. Gas‐phase energies were calculated with HF/6‐31 G** and B3LYP/6‐31 G** levels of theory. Free energies of solvation have been computed using the polarizable continuum model (PCM), conductor‐like PCM (CPCM), and the integral equation formalism‐PCM at the same levels which have been used for geometry determination in the gas‐phase. The results that show the calculated pK_a values using the B3LYP are better than those using the corresponding HF. In comparison to the other models, the results obtained indicate that the PCM model is a suitable solvation model for calculating pK_a values. For the investigated compounds, a good agreement between the experimental and the calculated pK_a values was also observed. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Spectrophotometric determination of ionization constants of some organic compounds in aqueous solution

Ionization constants of some phenols and anilines in aqueous solution with a ionic strength of 0.01 were measured at 25°C by spectrophotometric method. The set of substrates was selected on the basis of the results of preliminary calculations of ionization constants in terms of an elemental linear empirical approach with account taken of the lack of the corresponding consistent published data.