Reactivity of OH radicals with chlorobenzoic acids—A pulse radiolysis and steady-state radiolysis study

The reactions of OH radicals with 2-, 3-, 4-chlorobenzoic acids (ClBzA) and chlorobenzene (ClBz), k(OH+substrates)=(4.5?6.2)×10⁹ dm³ mol^?1 s^?1, have been studied by pulse radiolysis in N₂O saturated solutions. The absorption maxima of the OH-adducts were in the range of 320?340 nm. Their decay was according to a second-order reaction, 2k=(1?9)×10⁸ dm³ mol^?1 s^?1. In the presence of N₂O/O₂ the formation of peroxyl radicals was detectable for 2-, 4-ClBzA and ClBz, k(OH-adduct+O₂)=(2?4)×10⁷ dm³ mol^?1 s^?1, while this reaction for 3-ClBzA was too slow to be registered. In the presence of N₂O the degradation rates induced by gamma radiation were very similar for all chlorobenzoic acids, yet the chloride formation was distinctly higher for 3-ClBzA. In the presence of oxygen the initial degradation of 2-and 4-ClBzA equaled the OH-radical concentration, whereas in case of 3-ClBzA only ～60% of OH led to degradation. The order for the efficiency of dehalogenation was 4->2->3-ClBzA. Several primary radiolytic products could be detected by HPLC. To evaluate the toxicity of final products a bacterial bioluminescence test was carried out.     

Alkyl methylphosphonic acids,the degradation products of organophosphorous CWA — preparation and direct quantitative GC-FID analysis

Seven alkyl methylphosphonic acids, products of hydrolytic degradation of organophosphorus chemical warfare agents, were obtained with a high purity (mostly above 98%), with the aim of being applyed as future certified reference materials. Ethyl (EMPA), isopropyl (IMPA), pinacolyl (PMPA), butyl (BUMPA), isobutyl (IBUMPA), cyclohexyl (CHMPA) and 2-ethylhexyl (EHMPA) monoesters of MPA were synthesized and characterized by MS EI, FTIR and NMR (¹H, ¹³C, ³¹P), TLC, as well as GC and GC-MS after derivatization. The conditions for a direct quantitative GC FID analysis on CP-FFAP CB column of non-derivatized alkyl methylphosphonic acids were developed. This is the first successful attempt of a directed GC analysis of free alkyl phosphonic acids. Their chemical purity was determined and limit of quantification (LOQ) values for some of them were evaluated for the GC-FID method.     

Pulse radiolysis study on gatifloxacin——A fluoroquinolone antibiotic

The reactions between gatifloxacin(GFX) and various one-electron oxidants,such as ˙OH,N3˙,Br2˙ˉ,and SO4˙ˉ,have been studied by pulse radiolysis techniques.The GFX radical anion formed in the reaction of GFX with eaqˉ could either be protonated or deprotonated,and the absorption of GFX radical anion was located at 390 nm.The transient species produced by the reaction of GFX with ˙OH radical shows a broad band in the 380?600 nm region with a shoulder,while the oxidation by N3˙,SO4˙ˉ,and Br2˙ˉ results in an absorption band with λmax = 370 nm.At neutral condition(pH 7),the rate constants of GFX reacting with ˙OH,N3˙,Br2˙ˉ,SO4˙ˉ and eaqˉ are estimated to be 1.0 × 1010,3.1 × 109,2.8 × 109,3.0 × 109,and 1.8 × 1010 dm3 mol?1 s?1,respectively.From the pH dependence on the formation of electron adducts and on the rate constant of GFX with eaqˉ,the pKa of GFX radical anion is estimated to be 5.5 and 9.3.     

Synthesis of α-monoglycerides of aromatic acids

The synthesis of -monoglycerides of aromatic acids has been performed by the transesterification of the methyl esters of the corresponding acids with glycerol. The structures of the compounds obtained have been confirmed by their IR, UV, and¹H and¹³C NMR spectra.A. B. Bekturov Institute of Chemical Sciences, Academy of Sciences of the Republic of Kazakhstan, Almaty, fax (3272) 61 57 65. Translated from Khimiya Prirodnykh Soedineii, No. 4, pp. 452–457, July–August, 1999.     

γ-ray radiolysis of dihydroxyurea in nitric acid and its radiolytic products

Journal of Radioanalytical and Nuclear Chemistry - Dihydroxyurea (DHU) is a new salt-free reducing agent applied for the separation of Pu and Np from U in spent fuel reprocessing. This paper...     

Antitumor mechanism of VP-16: A pulse radiolysis study

The antitumor mechanism of etoposide (VP-16) is investigated using pulse radiolysis technology. The oxidizing mechanism of VP-16 is studied by sodium persulfate, and the reaction rate constant is 4.04× 109 L· mol-1 · s-1. The electron-transfer between VP-16 and tyrosine is observed and the reaction rate constant is 1.1 - 108 L · mol-1· s-1.     

Spectrometric study of a-methylene aromatic araminenone and aminoketone

Thirteen α-methylene aromatic araminenone and four α-methylene aromatic aminoketones were prepared by modified Mannich reaction. On the basis of isotopic labeling, a plausible way of cleavage was proposed for the formation of the M^＋- 17 fragment peak in the MS of the α-methylene aromatic araminenone and aminoketones. The characteristic chemical shift of the olefinic protons in ^1H NMR is also discussed.     

Effect of temperature on O⊘ reactions and equilibria: A pulse radiolysis study

The pK_a of the hydroxyl radical was measured over the 20–80°C temperature range. At 20°C, the pK_a was 11.84 and fell to 10.81 at 80°C. The dissociation constant for the ozonide anion (O⊘₃⇌O₂+O⊘) was found to be 5.5 × 10^-7 mol dm^-3 at 20°C and 46.2 × 10^-7 mol dm^-3 at 70°C. The rate constants and activation energies for the reaction of O⊘ and OH with 2-propanol, methanol and 3-hexene-1,6-dicarboxylate ions have also been measured.     

Thermal-catalytic degradation of polyethylene over silicoaluminophosphate molecular sieves—A thermogravimetric study

The present work is aimed at recycling plastic wastes economically and efficiently, for which pure high density polyethylene (HDPE) has been initially selected for the investigations. Thermogravimetric technique has been used to investigate, analyze and compare the thermal and catalytic degradation of HDPE. The catalytic degradation was investigated over the medium pore silicoaluminophosphate, SAPO-11 molecular sieve. The thermogravimetric evaluation was performed using 2–30 wt% catalyst, and the apparent activation energies for the thermal and catalytic polymer degradation were estimated using various iso-conversional methods. The apparent activation energy was found to be lower when SAPO-11 was used compared to the direct thermal degradation of HDPE. The activation energy and coke levels are comparable to the medium pore zeolite ZSM-5 and lower than the values obtained over large pore zeolites reported in literature.     

Spectrometric study ofα-methylene aromatic araminenone and aminoketone

Thirteenα-methylene aromatic araminenone and fourα-methylene aromatic aminoketones were prepared by modified Mannich reaction.On the basis of isotopic labeling,a plausible way of cleavage was proposed for the formation of the M~ -17 fragment peak in the MS of theα-methylene aromatic araminenone and aminoketones.The characteristic chemical shift of the olefinic protons in ~1H NMR is also discussed.     

A thermodynamic study of reactions of amino acids with crown ethers in nonaqueous media as examples of guest—host molecular complex formation

Our findings and the literature data on the effect of binary aqueous organic solvents on the enthalpy and entropy of molecular complexation reactions of 18-crown-6 with glycine, D, L-alanine, and L-phenylalanine and on the stability of the resulting complexes were reviewed. The relationships between the thermodynamic parameters of the complexation reactions and the reactant solvation were analyzed to reveal the key factors that are crucial for the stability of the complexes and the increasing exothermicity of the processes under study in water—ethanol, water—DMSO, and water—acetone. The changes in the stability of 18-crown-6 complexes with amino acids were assumed to be predicted from the Gibbs energy changes in the transsolvation of the amino acids. This criterion was proposed as a basic thermodynamic parameter for estimating the changes in the stability of 18-crown-6 complexes with peptides and ammoniumtype cations (structurally related to amino acids) when the composition of the binary aqueous organic solvent is varied.     

Effect of nitrous acid on γ-ray radiolysis and radiolytic products of N,N-dimethylhydroxylamine

Journal of Radioanalytical and Nuclear Chemistry - N, N-dimethylhydroxylamine (DMHA) is a new salt-free reductant used in spent fuel reprocessing, this paper reports the effect of HNO2 on...     

π-Complex formation and collapse in electrophilic halogenation of aromatic substrates

Kinetic evidence is offered in support of π-complex formation and slow conversion to σ-complex during the electrophilic molecular chlorination reaction of six aromatic hydrocarbons.     

Degradation of aliphatic and aliphatic–aromatic co-polyesters by depolymerases from Roseateles depolymerans strain TB-87 and analysis of degradation products by LC-MS

The degradation activities of bacterium, Roseateles depolymerans TB-87 and its depolymerases Est-H and Est-L against aliphatic as well as aliphatic–aromatic co-polyesters, were investigated. Strain TB-87 and its enzymes exhibited an ability to degrade aliphatic and aliphatic–aromatic co-polyesters. Monomers produced as a result of degradation of aliphatic polyesters [poly(butylene succinate) (PBS), poly(butylene succinate-co-adipate) (PBSA)] as well as aliphatic–aromatic co-polyester [poly(butylene succinate/terephthalate/isophthalate)-co-(lactate) (PBSTIL) by depolymerases Est-H and Est-L were investigated by liquid chromatography mass-spectrometry (LC-MS). Some common monomers like succinic acid and 1,4-butanediol were detected besides adipic acid and terephthalic/isophthalic acids as degradation products from PBSA and PBSTIL, respectively, whereas lactic acid was not detected. The succinic acid monomer was detected prior to adipic acid as a result of degradation of PBSA. The enzymes depolymerized PBS also into respective monomers. The analysis of PBSTIL degradation products revealed that enzymes easily degraded aliphatic segments as compared to aromatic segments and resulted in production of succinic acid prior to terephthalic and isophthalic acid. On the basis of these results, we speculate that both the enzymes Est-H and Est-L, attacked succinic acid segments (BS) first instead of adipic acid (BA) and terephthalic/isophthalic acid (BT or BI) segments of PBSA and PBSTIL, respectively. It is concluded from the results that R. depolymerans strain TB-87 can depolymerize aliphatic as well as aliphatic–aromatic co-polyesters; therefore, its enzymes can be applied in the process of biochemical monomer recycling.     

Radiolysis of halogenated aromatic compounds in aqueous solutions—I conductometric pulse radiolysis and steady-state studies of the reaction of eaq−

The reaction of e_aq⁻ with halogenated aromatic compounds (fluoro-, chloro-, bromobenzene, and 2-, 3-, 4-chloro-aniline) was studied by conductometric pulse radiolysis and under steady-state conditions. It was established that in the pH range from 4 to 10 all e_aq⁻ are reacting with the compound in question by quantitative splitting of the halide anion (X⁻). Considering certain experimental factors G(X⁻)=2.7 was obtained by both methods for all investigated substances. This fact is in disagreement with previous observations on various halogenated compounds. However, it can be explained taking all possible reactions for each system into account.     

Picosecond pulse radiolysis study of highly concentrated nitric acid solutions: formation mechanism of NO3• radical

The formation of nitrate radical, NO(3)(?), is observed for the first time directly by picosecond pulse radiolysis of highly concentrated nitric acid solutions. The experimental yield of NO(3)(-) ionization is deduced from the pulse-probe transient absorption measurements in the visible region where this radical absorbs. On the basis of the value of the extinction coefficient of nitrate radical at 640 nm equal to 1300 M cm(-1), the experimental yield of NO(3)(?) at 20 ps is found to be around 0.36 × 10(-7), 1.33 × 10(-7), and 2.85 × 10(-7) mol J(-1) for 1, 3.5, and 7 M nitric acid solutions, respectively. Relative to the dose absorbed by nitric acid by the direct effect, we find an unexpected high formation yield of the nitrate radical within the electron pulse. Therefore, we suggest that the trapping of the positive hole, H(2)O(?+), by NO(3)(-) also contributes to the formation of NO(3)(?) within the electron pulse. Moreover, after the pulse and within 4 ns, the beginning of the reaction of OH(?) radical with undissociated nitric acid is observed for the most concentrated nitric acid solution.     

Gamma radiolytic degradation of fluoranthene and monitoring of radiolytic products using GC–MS and HPLC

Removal of priority pollutant fluoranthene in methanol by gamma-irradiation under varied conditions has been optimized. The influence of applied dose and dose rate on the degradation of fluoranthene under nitrogen has been investigated. The preliminary radiolytic degradation efficiency has been monitored by spectrophotometry. HPLC and GC–MS have been used to study the nature of degradation pattern. It is found that four main degradation products are formed and detected by HPLC. Different reversed phase columns have been used for the separation of degraded products under optimum chromatographic conditions. For 2 kGy dose ⩾80% fluoranthene has been degraded at dose rate 200 Gy/h. However, a dose of 370 Gy/h was more effective and it produces for less degradation products. Radiolytic degraded fluoranthene was also analyzed to detect various degradation products using GC–MS. It was proposed that major products were hydrocarbons and methoxy group containing organic compounds after comparing their mass spectra with the installed NIST mass spectral library.     

LC–MS/MS and NMR characterization of forced degradation products of mirabegron

A rapid, precise, and reliable liquid chromatography tandem mass spectrometry (LC–MS/MS) method has been developed for the characterization of stressed degradation products of mirabegron. It is used in the treatment of overactive bladder and administered to treat urinary symptoms such as urgency or frequency and incontinence. It also works by relaxing the muscles around bladder.

Mirabegron was subjected to hydrolysis (acidic, alkaline, and neutral) and peroxidation, as per ICH-specified conditions. The drug showed degradation under stress conditions. However, it was stable to neutral conditions. A total of seven degradation products were observed and the chromatographic separation of the drug and its degradation products was achieved on X-TerraRP-8 (250 mm × 4.6 mm, i.d., 5 µm) column using 0.01 M ammonium acetate as mobile phase-A and 60:40 ratio of acetonitrile (ACN):water as mobile phase-B. The degradation products were characterized by LC–MS/MS and its fragmentation pathways were proposed. Probable possible structures were drawn based on parent and daughter molecular ions. One peroxide degradant impurity was isolated using preparative LC and characterized using liquid chromatography–mass spectrometry and NMR data.     

Laser flash photolysis and pulse radiolysis study on chemical activity of VP-16 and podophyllotoxin

Time-resolved laser flash photolysis and pulse radiolysis have been used to study the chemical activity of podophyllotoxin(PPT) and etoposide(VP-16). The mechanism of photoioniza-tion of etoposide and podophyllotoxin has been confirmed and illustrated. It is demonstrated that VP-16 and PPT in aqueous solution can be photoionized at 248 nm to give hydrated electron and neutral radical resulting from rapid deprotonation of radical cation of VP-16 and PPT. The quantum yield for the photoionization of VP-16 and PPT with single-photo is 0.21 and 0.61, respectively. In addition, they can react with hydrated electron, hydrogen radical and hydroxyl radical. This will give chemists some advice on synthesizing new derivatives of podophyllotoxin in cancer treatment.