Catalytic effect of CTAB on the interaction of dipeptide glycyl-tyrosine (Gly-Tyr) with ninhydrin

The effect of cationic micelles of cetyltrimethylammonium bromide (CTAB) on the interaction of dipeptide glycyl-tyrosine (Gly-Tyr) with ninhydrin under varying conditions has been studied spectrophotometrically at 70 °C and pH 5.0. The reaction followed first- and fractional-order kinetics with respect to [Gly-Tyr] and [ninhydrin], respectively. Increase in total concentration of CTAB from 0 to 70 × 10⁻³ mol dm⁻³ resulted in an increase in the pseudo-first-order rate constant (k_ψ) by a factor of ca. 3. Quantitative kinetic analysis of k_ψ − [CTAB] data was performed on the basis of pseudo-phase model of the micelles (proposed by Menger and Portnoy and developed by Bunton) and Piszkiewicz model. A possible mechanism has been proposed and the kinetic data have been used to evaluate the micellar binding constants K_S (268 mol⁻¹ dm³ for Gly-Tyr) and K_N (64 mol⁻¹ dm³ for ninhydrin).     

Radiolytic degradation of 4-nitrophenol in aqueous solutions: Pulse and steady state radiolysis study

The radiation induced degradation of 4-nitrophenol (4-NP) has been studied by gamma irradiation, while the reactivity and spectral features of the short lived transients formed by reaction with primary transient radicals at different pHs has been investigated by pulse radiolysis technique. In steady state radiolysis a dose of 4.4 k Gy is able to degrade 98% of 1×10⁻⁴ mol dm⁻³ 4-NP. 4-NP has pK_a at 7.1, above which it is present in the anionic form. At pH 5.2, ^•OH and N₃^• radicals were found to react with 4-NP with rate constants of 4.1×10⁹ dm³ mol⁻¹ s⁻¹ and 2.8×10⁸ dm³ mol⁻¹ s⁻¹, respectively. Differences in the absorption spectra of species formed in the reactions of 4-NP with ^•OH and N₃^• radicals suggested that ^•OH radicals add to the aromatic ring of 4-NP along with electron transfer reaction, whereas N₃^• radicals undergo only electron transfer reaction. At pH 9.2, rate constants for the reaction of ^•OH radicals with 4-NP was found to be higher by a factor of 2 compared to that at pH 5.2. This has been assigned to the deprotonation of 4-NP at pH 9.2.     

Photocatalysis of 4-nitrophenol using zinc phthalocyanine complexes

Photodegradation of 4-nitrophenol (4-Np) in the presence of zinc tetrasulfophthalocyanine (ZnPcS₄), zinc octacarboxyphthalocyanine (ZnPc(COOH)₈) and a sulfonated ZnPc containing a mixture of differently sulfonated derivatives (ZnPcS_mix), as photocatalysts is reported. ZnPcS_mix is the most effective catalyst in terms of a high quantum yield for 4-Np degradation and the stability of the catalyst. However ZnPc(COOH)₈ degrades readily during the catalysis, but it has a higher quantum yield (Φ_4-Np) for 4-Np degradation than the rest of the complexes. The Φ_4-Np values were closely related to the singlet oxygen quantum yields Φ_Δ and hence aggregation. The rate constants for the reaction with 4-Np were k_r = 0.67 × 10⁶ mol⁻¹ dm³ s⁻¹ for ZnPcS_mix and 2.8 × 10⁸ mol⁻¹ dm³ s⁻¹ for ZnPc(COOH)₈.     

Oxidation of naringenin by gamma-radiation

The reaction of OH with naringenin (4′,5,7-trihydroxyflavanone) in the presence of air induced the formation of the hydroxylation product eriodictyol (3′,4′,5,7-tetrahydroxyflavanone). Its yield was dependent on pH. The initial degradation yield of naringenin was G_i(-Nar)=(2.5±0.2)×10⁻⁷ mol dm⁻³ J⁻¹. For the reaction with OH, a rate constant k (OH+naringenin)=(7.2±0.7)×10⁹ M⁻¹ s⁻¹ was determined. In the presence of N₂O and NaN₃/N₂O, no eriodyctiol was formed. Apigenin (4′,5,7-trihydroxyflavon) was detected as decay product of the naringenin phenoxyl radicals. In Ar-saturated solutions, naringenin exhibited a pronounced radiation resistance, G(-naringenin) ∼0.3×10⁻⁷ mol dm⁻³ J⁻¹.     

Reactivity of H atoms and hydrated electrons with chlorobenzoic acids

H radicals react with chlorobenzoic acids and chlorobenzene (k(H+substrates)=(0.7–1.5)×10⁹ dm³ mol⁻¹ s⁻¹) by addition to the benzene ring forming H adducts with characteristic absorption bands in the range of 310–360 nm. The rate constants for their second-order decay are 2k=(3.5–6)×10⁸ dm³ mol⁻¹ s⁻¹. By reduction with e_aq⁻ fragmentation and chloride release was established for 2- and 4-chlorobenzoic acid, for 3-chlorobenzoic acid the addition of electrons to the carboxylate group was observed by pulse radiolysis. By gamma radiolysis could be proved that these radical anions undergo intramolecular electron transfer and quantitave dechlorination. The efficiency in degradation was 4-chlorobenzoic acid>3-chlorobenzoic acid>2-chlorobenzoic acid. Benzoic acid was found as final product for all substrates.     

Synthesis of silver nanoparticles supported on silica aerogel using gamma radiolysis

Silver clusters on SiO₂ support have been synthesized using ⁶⁰Co gamma radiation. The irradiation of Ag⁺ in aqueous suspension of SiO₂ in the presence of 0.2 mol dm⁻³ isopropanol resulted in the formation of yellow suspension. The absorption spectrum showed a band at 408 nm corresponding to typical characteristic surface plasmon resonance of Ag nanoparticles. The effect of Ag⁺ concentration on the formation of Ag cluster indicated that the size of Ag clusters vary with Ag⁺ concentration, which was varied from 4×10⁻⁴ to 5×10⁻³ mol dm⁻³. The results showed that Ag clusters are stable in the pH range of 2–9 and start agglomerating in the alkaline region at pH above 9. The effect of radiation dose rate and ratio of Ag⁺/SiO₂ on the formation of Ag clusters have also been investigated. The prepared clusters have been characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM), which showed the particle size of Ag clusters to be in the range of 10–20 nm.     

Re-evaluation of the rate constant for the H atom reaction with tert-butanol in aqueous solution

The rate constant (k) of the H+tert-butanol reaction at pH∼1–2 was measured by the time profile of the absorbance build-up of the tert-butanol radical and by competitive reactions for H atoms between maleic acid and tert-butanol. The determined rate constant, k=(1.15±0.2)×10⁶ mol⁻¹ dm³ s⁻¹, is nearly an order of magnitude higher than the previously published rate constants.     

Reduction reactions of bovine serum albumin and lysozyme by CO- .2 radical in polyvinyl alcohol solution: a pulse radiolysis study

Pulse radiolytic reduction of bovine serum albumin (BSA) and lysozyme by CO^⨪₂ radical in presence of polyvinyl alcohol (PVA) has been studied. At pH 6.8 in presence of 2% (w/v) PVA, reduction of BSA and lysozyme (both at 1×10⁻⁴ mol dm⁻³) give an additional transient peak at 390 nm along with the usual 420 nm peak. The bimolecular rate constants for the reaction of CO^⨪₂ radical at pH 6.8±0.2 with BSA are 2.7×10⁸ and 7.13×10⁸ dm³ mol⁻¹ s⁻¹ at 420 nm and 390 nm respectively. The same for lysozyme are 3.2×10⁸ and 5.6×10⁸ dm³ mol⁻¹ s⁻¹ at 420 nm and 390 nm, respectively. Dimethyl disulfide also gives 390 nm and 420 nm peaks in this system upon reduction with CO^⨪₂ radical. The 390 nm peak is ascribed to the sulfenium radical (RSS(H)R). Studies on the variation of pH suggests the protonation of RSSR^⨪ radical (420 nm) to form RSS(H)R radical (390 nm) in this viscous media. The decay of RSS(H)R radical occurs via formation of RS radical and RS(H)S(H)R, the final product being RSH in both cases.     

A simple method of electrochemical lithium intercalation within graphite from a propylene carbonate-based solution

Electrochemical lithium intercalation within graphite from 1 mol dm^− 3 solution of LiClO₄ in propylene carbonate (PC) was investigated at 25 and − 15 °C. Lithium ions were intercalated into and de-intercalated from graphite reversibly at − 15 °C despite the use of pure PC as the solvent. However, ceaseless solvent decomposition and intense exfoliation of graphene layers occurred at 25 °C. The results of the Raman spectroscopic analysis indicated that the interaction between PC molecules and lithium ions became weaker at − 15 °C by chemical exchange effects, which suggested that the thermodynamic stability of the solvated lithium ions was an important factor that determined the formation of a solid electrolyte interface (SEI) in PC-based solutions. Charge–discharge analysis revealed that the nature of the SEI formed at − 15 °C in 1 mol dm^− 3 of LiClO₄ in PC was significantly different from that formed at 25 °C in 1 mol dm^− 3 of LiClO₄ in PC containing vinylene carbonate, 3.27 mol kg^− 1 of LiClO₄ in PC, and 1 mol dm^− 3 of LiClO₄ in ethylene carbonate.     

Thermochemistry of some barium compounds

The molar enthalpies of reaction of metallic barium with 0.047 mol·dm⁻³ HClO₄ as well as the molar enthalpies of dissolution of BaCl₂ in 1.01 mol·dm⁻³ HCl and in water have been measured at T=298.15 K in a sealed swinging calorimeter with an isothermal jacket. From these results the standard molar enthalpy of formation of the barium ion in an aqueous solution at infinite dilution, as well as the enthalpies of formation of barium chloride and barium perchlorate, are calculated to be: Δ_fH⁰_m(Ba²⁺,aq)=−(535.83±1.25) kJ · mol⁻¹; Δ_fH⁰_m(BaCl₂,cr)=−(855.66±1.28) kJ · mol⁻¹; and Δ_fH⁰_m(BaClO₄,cr)=−(796.26±1.35) kJ · mol⁻¹. The results obtained are discussed and compared with previous experimental values.     

Radiation-induced degradation of aqueous 2,3-dihydroxynaphthalene

The degradation of aqueous 2,3-dihydroxynaphthaline (2,3-DHN) under the influence of γ-ray was investigated under various experimental conditions. Using 2.5×10⁻⁵ mol L⁻¹ 2,3-DHN in aerated media (pH=6–6.8) an initial degradation yield, G_i-(2,3-DHN)=0.32 was obtained, whereas in solutions saturated with N₂O the yield come to G_i-(2,3-DHN)=0.50.In airfree media the substrate decomposition was negligible. Possible reaction mechanisms are presented.Further, the rate constant, k(OH+2,3-DHN)=2.14×10¹⁰ L mol⁻¹ s⁻¹ was determined by competition reactions with PNDA.     

Decomposition of 14C containing organic molecules released from radioactive waste by gamma-radiolysis under repository conditions

Decomposition of ¹⁴C containing organic molecules into an inorganic compound has been investigated by γ-ray irradiation experiments under simulated repository conditions for radioactive waste. Lower molecular weight organic acids, alcohols, and aldehydes leached from metallic waste are reacted with OH radicals to give carbonic acid. A decomposition efficiency that expresses consumption of OH radicals by decomposition reaction of organic molecules is proposed. Decomposition efficiency increases with increasing concentration of organic molecules (1×10⁻⁶–1×10⁻³ mol dm⁻³) and is not dependent on dose rate (10–1000 Gy h⁻¹). Observed dependence indicates that decomposition efficiency is determined by reaction probability of OH radicals with organic molecules.     

The one electron reduction of Hg2+ by 1-hydroxyalkyl radicals in aqueous solution: a pulse radiolysis study

The rate constants for the reduction of the divalent mercury ion Hg²⁺ by alcohol radicals, which are produced in acidic aqueous solutions containing methanol, ethanol or 2-propanol, are determined by optical absorption measurements to be 7.0×10⁸, 3.8×10⁸ or 3.1×10⁸ dm³ mol⁻¹ s⁻¹, respectively.     

Thermodynamic properties of two zinc borates: 3ZnO·3B2O3·3.5H2O and 6ZnO·5B2O3·3H2O

Two pure zinc borates with microporous structure 3ZnO·3B₂O₃·3.5H₂O and 6ZnO·5B₂O₃·3H₂O have been synthesized and characterized by XRD, FT-IR, TG techniques and chemical analysis. The molar enthalpies of solution of 3ZnO·3B₂O₃·3.5H₂O(s) and 6ZnO·5B₂O₃·3H₂O(s) in 1 mol · dm⁻³ HCl(aq) were measured by microcalorimeter at T = 298.15 K, respectively. The molar enthalpies of solution of ZnO(s) in the mixture solvent of 2.00 cm³ of 1 mol · dm⁻³ HCl(aq) in which 5.30 mg of H₃BO₃ were added were also measured. With the incorporation of the previously determined enthalpy of solution of H₃BO₃(s) in 1 mol · dm⁻³ HCl(aq), together with the use of the standard molar enthalpies of formation for ZnO(s), H₃BO₃(s), and H₂O(l), the standard molar enthalpies of formation of −(6115.3 ± 5.0) kJ · mol⁻¹ for 3ZnO·3B₂O₃·3.5H₂O and −(9606.6 ± 8.5) kJ · mol⁻¹ for 6ZnO·5B₂O₃·3H₂O at T = 298.15 K were obtained on the basis of the appropriate thermochemical cycles.     

Effect of hydrolysis on the diffusion of ferric sulphate in aqueous solutions at T = 298.15 K

Diffusion coefficients of the Fe₂(SO₄)₃)/water system at T = 298.15 K and at concentrations between 0.050 mol · dm⁻³ and 0.200 mol · dm⁻³ have been measured, using a conductimetric cell and an automatic apparatus to follow diffusion. The cell uses an open-ended capillary method. A conductimetric technique is used to follow the diffusion process by measuring the resistance of a solution inside the capillaries at recorded times. These data are discussed on the basis of the Onsager–Fuoss model. The diffusion of Fe₂(SO₄)₃ is clearly affected by the Fe (III) hydrolysis. These data permit us to have a better understanding of the structure of such systems and the thermodynamic behaviour of ferric sulphate in different media.     

Diffusion coefficients of bolaform alkane-1,n-bis(trimethylammonium bromide) surfactants

Mutual diffusion coefficients of alkane-1,n-bis(trimethylammonium bromide), C_nMe₆Br₂ (n = 8, 10, 12), surfactants have been measured using the Taylor dispersion technique, at T = 298.15 K, at concentrations from (0.000 to 0.0380) mol · dm⁻³. The dependence of mutual diffusion coefficients on the concentration has been discussed in the framework of Onsager–Fuoss and Pikal models. On the basis of this discussion, it is suggested that these surfactants behave as associated electrolytes. From limiting mutual diffusion coefficient values, extrapolated from experimental values for c → 0, limiting ionic conductance, tracer diffusion coefficients, and hydration radii of alkane-1,n-bistrymethyl ammonium ions have been estimated. For the case of dodecane-1,12-bis(trimethylammonium bromide), no aggregation has been noticed up to 0.04 mol · dm⁻³.     

Use of Cr(phen)33+ as luminescence probe to study the binding constants of phenols to micelles of SDS

Steady-state and time resolved luminescence quenching measurements of (²T/²E)Cr(phen)₃³⁺ were used to investigate the association of phenols to sodium dodecyl sulfate (SDS) micelles. Steady-state results show the quenching process occurs in the micellar pseudo phase. Scatchard plots indicate that the process is a partition between aqueous and micelles. The k₊ and k₋ rate constant have been evaluated from time resolved data and the binding constants were obtained. The trend found in the K's were 4-H-Ph < 2,6-diMe-Ph < 4-Br-Ph. We concluded that it is possible to use *Cr(phen)₃³⁺ as a luminescent probe to determine association parameters for quenchers to micelles of SDS.     

Reactions of the HO2 radical with OH,H, Fe2+ and Cu2+ at elevated temperatures

The temperature dependence of the rate constant for the reactions of HO₂ with OH, H, Fe²⁺ and Cu²⁺ has been determined using pulse radiolysis technique. The following rate constants, k (dm³ mol⁻¹ s⁻¹) at 20°C and activation energies, E_a (kJ mol⁻¹) have been found. The reaction with OH was studied in the temperature range 20–296°C (k=7.0×10⁹, E_a=7.4) and the reaction with H in the temperature range 5–149°C (k=8.5×10⁹, E_a=17.5). The reaction with Fe²⁺ was studied in the temperature range 16–118°C (k=7.9×10⁵, E_a=36.8) and the reaction with Cu²⁺ in the temperature range 17–211°C (k=1.1×10⁸, E_a=14.9).     

High-energy ionising radiation initiated decomposition of acetovanillone

Hydroxyl radical, hydrated electron and hydrogen atom intermediates of water radiolysis react with acetovanillone with rate coefficients of (1.05±0.1)×10¹⁰, (3.5±0.5)×10⁹ and (1.7±0.2)×10¹⁰mol^?1 dm³ s^?1. Hydroxyl radical and hydrogen atom attach to the ring forming cyclohexadienyl type radicals. The hydroxyl–cyclohexadienyl radical formed in hydroxyl radical reaction in dissolved oxygen free solution partly transforms to phenoxyl radical. In the presence of O₂ phenoxyl radical formation and ring destruction are observed. Hydrated electron in O₂ free solution attaches to the carbonyl oxygen and undergoes protonation yielding benzyl type radical. In air saturated 0.5 mmol dm^?3 solution using 15 kGy dose most part of acetovanillone is degraded, for complete mineralisation five times higher dose is required. The experiments clearly show that acetovanillone can be efficiently removed from water by applying irradiation technology.     

Speeds of sound in {(1 − x)CH4 + xN2} with x = (0.10001, 0.19999, and 0.5422) at temperatures between 170 K and 400 K and pressures up to 30 MPa

The speed of sound in {(1 − x)CH₄ + xN₂} has been measured with a spherical acoustic resonator. Two mixtures with x = (0.10001 and 0.19999) were studied along isotherms at temperatures between 220 K and 400 K with pressures up to 20 MPa; a few additional measurements at p = (25 and 30) MPa are also reported. A third mixture with x = 0.5422 was studied along pseudo-isochores at amount-of-substance densities between 0.2 mol · dm⁻³ and 5 mol · dm⁻³. Corrections for molecular vibrational relaxation are discussed in detail and relaxation times are reported. The overall uncertainty of the measured speeds of sound is estimated to be not worse than ±0.02%, except for those measurements in the mixture with x = 0.5422 that lie along the pseduo-isochore at the highest amount-of-substance density. The results have been compared with the predictions of several equations of state used for natural gas systems.