Pulse radiolysis study on one-electron oxidation of 1-naphthylamine-4-sulphonic acid in aqueous solutions

Reactions of 1-naphthylamine-1-sulphonic acid (NASA) with hydroxyl radicals and oneelectron oxidants such as N₃, Br₂ ^- and Cl₂ ^- radicals have been studied at various pHs using pulse radiolysis technique. Rate constants for the reaction of N₃ and Br₂ ^-. radicals with NASA at neutral pH were found to be 5 × 10⁹ and 4 × 10⁸ dm³ mol^-1 s^-1 respectively. These reactions led to the formation of a cation radical (semi-oxidized species). OH radical reaction with NASA (k = 7.2 × 10⁹ dm³ mol^-1 s^-1) at neutral pH gave a mixture of species, namely, a semi-oxidized species as well as an adduct species. Cl₂ ^-. radicals reacted with NASA rather slowly (k = 7 × 10⁷ dm³ mol^-1 s^-1) at pH 1 to give the semioxidised species. However, even at pH 1, OH radical reaction with NASA gave a mixture containing semi-oxidized as well as an adduct species. The OH-adduct species having _max at 340 nm decays at acidic pHs to give semi-oxidized species having _max at 370 nm. Electron adduct of NASA was found to be a strong reducing radical.     

ESR study of low-temperature radiolysis and photolysis of substitutedN′-furfurylidenebenzhydrazides

Low-temperature (77 K) γ- and UV irradiation of substitutedN′-furfurylidenebenzhydrazides produces paramagnetic particles in radiation-chemical yields of (0.05–0.5)/100 eV and quantum yields of 4·10⁻⁵–10⁻³, respectively. ESR study showed that hydrazyl radicals and HC·O and N·O₂ are the main products of radiolysis and photolysis, and the latter decay upon heating of the sample to 190 K, whereas the hydrazyl radicals survive up to 423 K. Further heating results in thermodestruction of the hydrazides, and the ESR spectrum exhibits only a singlet with splitting at 1 mT, which is characteristic of polyconjugated compounds. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2078–2082, November, 1999.     

An ESR and NMR study of the gamma radiolysis of a bisphenol-A based polycarbonate and a phthalic acid ester

A study of the γ-radiolysis of the commercial polymers U-polymer, UP (Unitake) and polycarbonate, PC, (Aldrich) has been undertaken using ESR spectroscopy. The G-value of radical formation at 77 K has been found to be 0.31±0.01 for UP and 0.5±0.02 for PC. By using thermal annealing and spectral subtraction, the paramagnetic species formed on irradiation has been assigned. The effect of radiation on the chemical structure of UP and PC has been investigated at ambient temperature and at 423 K. The NMR results show that a new phenol type chain end is formed in the polymers on exposure to γ-radiation. The G-value of formation of the new phenol ends was estimated to be 0.7 for PC (423 K) and 0.4 for UP (300 K). © 1998 John Wiley & Sons, Ltd.     

Reactions of H atoms and OH radicals with ascorbic acid: A pulse radiolysis Fourier transform ESR study

Using pulse radiolysis, free radicals of ascorbic acid were generated by reactions of the primary radicals H and OH in acidic and basic aqueous solutions. The formation and the decay of several radicals of ascorbic acid were detected by time resolved Fourier transform electron spin resonance within a time interval of 100 ns to 1 ms. The rate constant of addition of H atoms to ascorbic acid (1.3·10⁸ dm³· mol⁻¹·s⁻¹) was directly determined by the change of line width of the low field line of the H atom in the presence of ascorbic acid. The addition of OH radicals to ascorbic acid results in different radical structures, detected by highly resolved Fourier transform ESR spectra.     

Multi-frequency ESR study of the polycrystalline phenoxyl radical of alpha-(3,5-di-tert-butyl-4-hydroxyphenyl)-N-tert-butylnitrone in the diamagnetic matrix

Multifrequency (X-, Q-, and W-band) electron spin resonance (ESR) spectroscopy has been used to characterize the phenoxyl radical produced from alpha-(3,5-di-tert-butyl-4-hydroxyphenyl)-N-tert-butylnitrone, which is a new spin-trapping reagent. The X-band measurement did not resolve the powder-pattern ESR spectrum. Because of its higher resolution with g value, the Q-band ESR study revealed that the g factor has an axial-like symmetry and that the observed hyperfine structure in the Z-direction is caused by the nitrogen nucleus at the para-position. Furthermore, the results of the W-band ESR experiment more clearly distinguished the perpendicular components from the parallel component, resolving the perpendicular components into x and y components. The X-band powder spectrum was similar to the X-band ESR spectrum of the radical in a frozen solution of toluene. The computer simulation spectra performed using the obtained parameters fitted the experimental spectra well. A comparison of the amplitude of g( perpendicular)(gx, gy) with that of gz showed that the unpaired electron is delocalized over the pi-conjugated framework. Considering the hyperfine coupling constant, it was concluded that about 16% of the unpaired electron distributed over the nitrogen nucleus at the para-position. This study thus showed the significant potential of a multifrequency ESR approach to a powder sample radical in terms of its high resolution with g value.     

ESR study of the diacetylene polymer 4BCMU

Electron Spin Resonance (ESR) measurements of the polydiacetylene 4BCMU in the solid-state indicate the presence of a thermally activated paramagnetic center with g ≈ 2.002 and first-derivative peak-to-peak linewidth of ≈ 17G. An abrupt and irreversible decrease in ESR signal intensity is observed at ca. 400 K, and appears to be associated with the solid-state planar-nonplanar conformational transformation manifested by an irreversible color change from metallic brown to red.     

Computer-assisted study of the complexation of quinizarin-2-sulphonic acid with iron(III)

A detailed spectrophotometric study of the complexation of iron(III) with quinizarin-2-sulphonic acid (Q) in 0.1M perchloric acid solution is reported. There is evidence that more than one complex exists in the solution. Analyses of the data were made by a PITMAP-type procedure, and comparison of the results from considering several models of solution composition show the preferred model to be that for two complexes with Fe:Q ratios 1:1 and 4:3. Stability constants and calculated spectra for the species are reported. It is suggested that the ligand is bis-chelating in the polynuclear species.     

Ionic species in irradiated poly(methyl methacrylate). A pulse radiolysis and ESR study

Poly(methyl methacrylate) free of initiators was synthesized by γ-irradiation and cast into transparent films. The samples were investigated by ns pulse radiolysis at various temperatures, and by ESR spectroscopy after γ irradiation at 77°K. Short-lived transients with optical absorptions at 440 and 725 nm were observed. The 440 nm absorption has been ascribed to the cation and the 725 nm absorption (εG = 3000 M^?1 cm^?1 (100 eV)^?1, τ_1/2 = 190 ns at ?13°C, E_a = 6.5 kcal/mol) to the anion. These assignments are based on ESR data of samples of poly(methyl methacrylate) and pivalic acid methyl ester deuterated at the ester deuterated at the ester and α-methyl groups, respectively, and subjected to thermal annealing and photobleaching. The anion decomposes on photobleaching by loss of the ester ·CH₃ radical, and the cation is proposed to decay by loss of the ·CH₃ radical from the α-methyl group. The thermal decay of the anion is discussed.     

ESR study of ascorbic acid irradiated with gamma-rays

The interest in application of high-energy ionizing radiation for stenlization of pharmaceutical products and foodstuffs has led a number of workers to investigate the radiation sensitivity of vitamins. Aside from its use as a vitamin, ascorbic acid (AA) or some derivatives are employed as antioxidants in foodstuffs. The effects of ionizing radiation on AA in simple solutions and in mixture of naturally occurring compounds have been extensively reported in the literature. However, the effects of ionizing radiation on solid AA were reported in few works which described rather dosimetric features of AA No reports, except one, are available describing the characteristic features of the radiolytic intermediates produced after irradiation of polycrystalline AA. Irradiation studies performed on single crystal of AA has led us to reinvestigate our previous work on the radiolytic intermediates produced in irradiated polycrystalline AA. Three radical species, rather than two, having different characteristics were decided contributing to the formation of experimental electron spin resonance (ESR) spectrum of γ-irradiated polycrystalline AA. Spectral parameters of these species were calculated after exhaustive spectrum simulation calculations based on data derived from experimental microwave saturation and dose-response studies.     

In-situ spectroelectrochemical evidences for the copolymerization of o-toluidine with diphenylamine-4-sulphonic acid by UV-visible spectroscopy.

In-situ spectroelectrochemical studies on the copolymerization of o-toluidine (OT) with diphenylamine-4-sulfonic acid (DPASA) were carried out on ITO electrode in 0.5 M H2SO4 for different feed ratios of OT and DPASA. The early stages of copolymerization of OT with DPASA have been identified through spectroelectrochemical techniques. The results revealed the formation of a head-to-tail dimer type of intermediate at the initial stages of copolymerization. This N-phenyl-paraphenylene diamine (PPD) type of intermediate was assigned to have a peak at 550 nm in UV-visible spectra and confirmed via derivative cyclic voltabsorptogram (DCVA). Constant potential electropolymerization results also supported the formation of intermediate with an absorption maximum at 550 nm.     

Radical scavenging reactions of chlorogenic acid: A pulse radiolysis study

At near neutral pH (approx. 5.5), the OH-adduct of chlorogenic acid (CGA), formed on pulse radiolysis of N₂O-saturated aqueous CGA solutions (λ _max = 400 and 450 nm) with k = 9 × 10⁹ dm³ mol⁻¹ s⁻¹, rapidly eliminates water (k = 1 × 10³ s⁻¹) to give a resonance-stabilized phenoxyl type of radical. Oxygen rapidly adds to the OH-adduct of CGA (pH 5.5) to form a peroxyl type of radical (k = 6 × 10⁷ dm³ mol⁻¹ s⁻¹). At pH 10.5, where both the hydroxyl groups of CGA are deprotonated, the rate of reaction of · OH radicals with CGA was essentially the same as at pH 5.5, although there was a marked shift in the absorption maximum to approx. 500 nm. The CGA phenoxyl radical formed with more specific one-electron oxidants, viz., Br ₂ ^·− and N ₃ ^· radicals show an absorption maximum at 385 and 500 nm, k ranging from 1–5.5 × 10⁹ dm³ mol⁻¹ s⁻¹. Reactions of other one-electron oxidants, viz., NO ₂ ^· , NO^· and CCl₃OO^· radicals, are also discussed. Repair rates of thymidine, cytidine and guanosine radicals generated pulse radiolytically at pH 9.5 by CGA are in the range of (0.7–3) × 10⁹ dm³ mol⁻¹ s⁻¹.     

Radiotracer method for the study of the radiolysis of aqueous solutions of pyruvic acid

The purpose of this work is to study the radiolytic behavior of aqueous solutions of¹⁴C-pyruvic acid (oxygen-free). Several parameters were varied such as radiation dose, pH, etc. Gas chromatography, mass spectrometry and high performance liquid chromatography were used extensively for the analysis of radiolytic products. The more abundant product was dimethyltartaric acid. Other products identified were acetic, lactic, succinic, malonic and tricarballylic acids, acetaldehyde, carbon dioxide, and hydrogen. The yields of these products were influenced by the irradiation dose, concentration of the target compound and pH of the solution.     

2,4-Bis(4-nitrobenzazo)resorcinol-6-sulphonic acid as a new acid-base indicator

2,4-Bis(4-nitrobenzazo)resorcinol-6-sulphonic acid is suggested as a new visual acid-base indicator, which because of its colour sharpness and other qualities is useful in titrations of weak acids. There are two colour transitions, one from yellow to red at pH 6.8-8.2, the other from red to blue-violet at 10.5-13.0. The corresponding dissociation constants are pK(1) 7.64, and pK(2) 11.64.     

Structures of the divalent metal complexes with benzene-1,2-dioxydiacetic acid

The divalent calcium, manganese, zinc, cobalt, magnesium and nickel complexes of benzene-1,2-dioxydiacetic acid (BDDAH₂) have been prepared and their structures determined by X-ray diffraction. Complexes [Ca(BDDA)(H₂O)₂]_n·nH₂O and [Mn(BDDA) (H₂O₂]_n·nH₂O are isomorphous and isostructural. There is a pentagonal bipyramidal seven-coordination about each metal, involving four oxygens of the BDDA ligand, two axial waters and a fifth bridging car☐yl oxygen giving a polymer structure. In contrast, [Zn(BDDA)(H₂O)₃]·3.5H₂O (and the cobalt and magnesium isomorphs) is discretely monomeric with the bridging position of the Ca/Mn structure replaced by a water. The nickel complex with formula [Ni(BDDAH)₂(H₂O)₄]·H₂O is monomeric and six-coordinate, bonded through only one car☐yl group of each of two trans-related BDDAH ligands.     

Mass spectrometric study of the radiolysis of di-(2-ethylhexyl)phosphoric acid

A mass spectrometric study on DEHPA was carried out and compared with radiolysis data on DEHPA for γ-irradiation in the liquid phase. The mass spectra of DEHPA show an extremely low intensity of parent ion and the presence of double rearrangement ions of (RO)P(OH) ₃ ⁺ and P(OH) ₄ ⁺ , where R is the 2-ethylhexyl group. The appearance potentials of the principal ions in the mass spectrum were determined and the dissociation processes of DEHPA in the phase discussed. The fragment ions show good agreement with the results in the liquid phase where the mono-ester, orthophosphoric acid, octane and heptane were formed by the dealkylation, however, the peak intensities of some fragment ions in the mass spectrum differ from the radiolytic yields of the corresponding products. These differences imply the significant role of neutralization and recombination reactions in the liquid phase radiolysis.     

Oxidation of cinnamic acid derivatives: A pulse radiolysis and theoretical study

We introduce an algorithm to solve the secular equation that arises in the time independent multimode expansion of the quadratic vibronic coupling problem in parallel. The implementation can handle expansions of arbitrary length, with the open-ended character of the algorithm achieved through the use of fine grained parallelism to partition the trial vectors. The characteristics of the algorithm are discussed and its utility is illustrated by determining a model photoelectron spectrum of the ethoxy radical (C₂H₅O) using a vibronic expansion involving more than 1 billion vibronic basis states. This calculation also represents the first determination of a photoelectron spectrum obtained using a diabatic Hamiltonian obtained with a recently introduced ab initio surface reshaping procedure.