Pulse radiolysis investigations on the reactions of primary radiolytic species of water with atropine

On pulse radiolysis of N₂O saturated aqueous solutions of atropine, an optical absorption band (_max at 320 nm,e=2.81·10³ dm³·mol^–1·cm^–1) was observed, which is assigned to the product of reaction of OH radicals with the solute. This absorption decayed following second order kinetics with a rate constant of 4.5·10⁸ dm³·mol^–1·s^–1. The rate constant for the reaction of OH radicals with atropine as estimated by following the build-up kinetics is 2.7·10⁹ dm³·mol^–1·s^–1. The H atoms also reacted with this compound to produce a transient absorption band behaving similarly to the one observed in the case of reaction with OH radicals. The transient species formed in both cases is assigned to a radical derived by H atom abstraction by H/OH radicals from the parent compound. This radical was unreactive towards 2-mercaptoethanol. e _aq ^– was found to react with atropine forming a transient band with _max at 310 nm (=3.55·10³ dm³·mol^–1). Its decay was also second order with a rate constant of 1.64·10⁹ dm³·mol^–1·s^–1. The bimolecular rate constant for the reaction of e _aq ^– with atropine as estimated from the decay of e _aq ^– absorption at 720 nm is 3.9·10⁹ dm³·mol^–1·s^–1. Specific one-electron oxidizing and reducing agents (such as Cl ₂ ^– , Tl²⁺, SO ₄ ^– and (CH₃)₂COH, CO ₂ ^– , respectively) failed to oxidize or reduce this compound in aqoues solutions. The radical anion of atropine formed by its reaction with e _aq ^– was found to reduce thionine and methyl viologen with bimolecular rate constant of 3.8·10⁹ and 3.2·10⁹ dm³·mol^–1·s^–1, respectively.     

Superoxide radical dismutation by copper proteins

The catalytic effects of human superoxide dismutase and bovine ceruloplasmin on superoxide radical dismutation were studied by pulse radiolysis at room temperature. The rate constants for the disappearance of superoxide radicals were found to be (8.1±1.2)·10⁵M^–1·s^–1 for spontaneous disproportionation, (9.8±1.5)·10⁶ M^–1·s^–1 in the presence of ceruloplasmin, and (2.1±0.3)·10⁹M^–1·s^–1 in the presence of superoxide dismutase.     

Ligand exchange reaction of Zn(II)-acetylacetonate complex with 5,10,15,20-tetraphenyl-21H,23H-porphinetetrasulfonic acid

Ligand exchange reaction of Zn(II)-acetylacetonate complex (Zn-acac₂) with 5,10,15,20-tetraphenyl-21H,23H-porphinetetrasulfonic acid (H₂TPPS) has been investigated spectrophotometrically and radiometrically. The exchange reaction was observed by spectral change from H₂TPPS to Zn-TPPS or activity of⁶⁵Zn(acac)₂ extracted into the chloroform phase. The 2nd order rate constants (k ₂) for the exchange reaction at 70 °C and at pH 7.8 were found to be 32.8±2.3 and 31.2±3.2 M^–1·s^–1 from the spectrometric and radiotracer experiments, respectively. For the direct complexation of Zn(II) with H₂TPPS, a similar 2nd order rate constant (k=32.4±4.7 M^–1·s^–1) was obtained as that in the ligand exchange reaction. The activation energies (E) for the exchange and the formation of Zn-TPPS were found to be 69.3±0.2 and 69.4±0.2 kJ·mol^–1, respectively, in the temperature range from 40 to 70 °C.     

Der Einfluß großer Salzkonzentrationen auf die Oxydationsreaktion von Fe(phen) 3 2+ mit Ce(IV) in Schwefelsäure

The influence of NaClO₄, NaCl and Na₂SO₄ on the oxidation of Fe(phen) ₃ ²⁺ by Ce(IV) was investigated by means of the stopped-flow method. At the concentrations range of NaClO₄ and NaCl 0.1–1.0M the rate constant values decrease from 1.03·10⁵ to 0.56·10⁵M^–1s^–1 and from 1.08·10⁵ to 0.81·10⁵M^–1s^–1 respectively.In varying concentrations of Na₂SO₄ solutions (0.05–0.35M) the rate constant values decrease from 1.05·10⁵M^–1s^–1 to 0.45·10⁵M^–1s^–1.Taking into account the negative salt effect the mechanism of the reaction progress is proposed.

     

Kinetics and mechanism of distribution of Am(III) and Eu(III) between thenoyltrifluoroacetone-triphenylarsine oxide mixture in chloroform and aqueous nitrate medium

The kinetics of distribution of Am(III) and Eu(III) between thenoyltrifluoroacetone (HTTA) and triphenylarsine oxide (Ph₃AsO) mixture in chloroform and aqueous nitrate medium has been investigated using a stirred Lewis cell at ionic strength of 0.1M. The effect of the concentration of HTTA, Ph₃AsO, H⁺ and NO ₃ ^– on the rate of distribution of Am(III) and Eu(III) was studied. The results were interpreted by reaction mechanisms where the rate-determining steps are the parallel reactions of Am(OH)²⁺ or Eu(OH)²⁺ with one HTTA molecule and one Ph₃AsO molecule in the aqueous medium. The values at 25 °C of the rate constantk _HLL (HL=HTTA andL=Ph₃AsO) are 1.6±0.3·10⁶M^–2·s^–1 and 2.3±±0.3·10⁸M^–2·s^–1 for Am(III) and Eu(III), respectively.     

Formation and decay of phenoxyl radicals: Variation with pH and pulse dose

Phenoxyl type radicals were produced from tyrosine methyl ester (TME) using azide (N ₃ ^. ) radicals. The rate constant of formation increased from 2·10⁸ dm³·mol^–1·s^–1 at pH 7 to 4·10⁹ dm³·mol^–1·s^–1 at pH 11, whereas that of the decay, 2k=(6±1)·10⁸ dm³·mol^–1·s^–1, remained constant. The maximum yield of the radicals varied with pH and pulse dose consistently with the kinetic scheme, which involved a competition of the oxidation of TME by azide radicals with the natural decay of N ₃ ^. .     

Electron transfer at tetrahedral cobalt(II). Part 1. Kinetics of bromate ion reduction

Summary The bromate ion reduction by 12-tungstocobaltate(II) anion has been investigated. The reaction obeys the empirical rate law:-d[reductant]/dt=5(a+b[H⁺]²)[BrO ₃ ^– ][reductant]: where a=(2.49±0.18)×10^–4M^–1 s^–1, b=(4.65±0.20)×10^–5M^–3s^–1 at 24.5±0.1°C [H⁺]=0.05–1.50M and I=2.0M (NaClO₄). This rate law is interpreted in terms of parallel reactions of BrO ₃ ^– and H₂BrO ₃ ⁺ . On the basis of the observed anion catalysis, substitution intertness of the reductant and Marcus type linear free energy relations, the outer sphere mechanism is proposed for both pathways.     

Spectral and kinetic characteristics of the α-propionic acid methyl ester radical in cyclohexane and water

The -propionic acid methyl ester radical was produced in dissociative electron capture reaction of 2-chloropropionic acid methyl ester. The absorption maxima of the radical are at 310 and 300 nm in cyclohexane and water with extinction coefficients of 440±50 and 400±50 mol^–1 dm³ cm^–1. The second order decay rate parameter in water is (2.3±0.5)×10⁹ mol^–1 dm³ s^–1. The peroxy radicals have the characteristics: _max=265–270 nm, _max=700–900 mol^–1 dm³ and 2k=(7±2)·10⁸ mol^–1 dm³ s^–1.     

Spectrofluorimetric determination of clioquinol in pharmaceutical preparations

Summary The absorption spectrum of the nitrate radical (NO₃) in aqueous solution and the kinetic of the reactions with Cl^– and OH^– have been determined using laser-spectrometric techniques. The maximum absorption was found at 635 nm with a decadic absorption coefficient of =(530±110) l/mol·cm. At 298 K rate constants of k₁=(1.0±0.2)·10⁷ l/mol·s for the reaction with chloride and of k₂=(8.2±0.9)·10⁷ l/mol·s for the reaction with hydroxide were obtained.     

A study by pulse radiolysis of the radiation-chemical transformation of aqueous solutions of hydrazine in the presence of oxygen

It is shown by pulse radiolysis that in aqueous solutions of hydrazine containing oxygen the radical N₂H₃ reduces oxygen to O₂ ^– at pH > 7 (k 3·10⁹ dm³· mole^–1·sec^–1), while this reaction does not occur for the protonated form N₂H₄ ⁺ at pH < 7 (k, 5·10⁶ dm³·mole^–1·sec^–1). The rate constants for the disappearance of O₂ ^– have been determined in the pH range from 4 to 12. Rate constants have been calculated for the reaction of O^– with N₂H₄ [k=(1.6 ±0.2)·10⁹ dm³·mole^–1·sec^–1] and of O₃with N₂H₄ [k=(1.2 ±0.2)·10⁶ dm³· mole^–1·sec^–1].Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 341–345, February, 1991.     

Kinetics and mechanism of ligand substitution of mono(polyamine)-nickel(II) complexes with 4-(2-pyridylazo)resorcinol

Summary The kinetics and mechanism of ligand substitution reactions of tetraethylenepentamine nickel(II), Ni (Teren), and triethylenetetraamine nickel(II), Ni(Trien), with 4-(2-pyridylazo)resorcinol (parH₂) have been studied spectrophotometrically at I=0.1 M (NaClO₄) at 25°C. In both systems two distinct reaction steps are observed. The rapid first step follows the rate law d[Ni(Polyamine)(ParH₂)]/dt=k₁ [Ni(Polyamine)] [ParH₂]. The formation of ternary complexes of Ni (Polyamine) with ParH₂ has been investigated under second order equal concentration conditions. The values of second order rate constants for the Trien and Teren reactions are (2.1±0.2)×10⁴ M^–1s^–1 and (7.8±0.6)×10³ M^–1s^–1 respectively at pH=9.0, I=0.1 M and 25°C.The rate law for the second step may be written as d[Ni(Par)₂]/dt=k₂[Ni(Polyamine)(ParH₂)]. Values of k₂ for the Trien and Teren systems are (2.5±0.1)×10^–4 s^–1 and (4.76±0.3)×10^–5 s^–1 respectively.     

Electromigration of carrier-free radionuclides

Dependences of La(III) overall ion mobilities on concentrations of ox^2– and tart^2– anions of oxalic and tartaric acid in aqueous solutions of 0.01 overall ionic strength and temperature 298.1 K were obtained by direct measurements of electromigration of carrierfree¹⁴⁰La-lanthanum(III). Concentration stability constants K_n and individual ion mobilities u _i ^o of oxalate and tartrate complexes of La(III) have been calculated for nitrate and perchlorate electrolytes, respectively: [La(ox)]⁺, lg K₁=5.63(9), u⁰[La(ox)]⁺=1.95(15)·10^–4 cm²·s^–1·V^–1; [la(ox)₂]^–, lg K₂=4.05(19) u⁰[La(ox)₂]^–=–1.76(20)·10^–4 cm²·s^–1·V^–1; [La(tart)]⁺, lg K₁=4.40(5), u⁰[La(tart)]⁺=+1.99(18)·10^–4 cm²·s^–1·V^–1.Results are compared with literature data. Additional, limiting individual La³⁺ ion mobility was calculated: =+6.9(1)·10^–4 cm²·s^–1·V^–1 for pure water at 298.1 K.     

An NMR study of proton exchange in the system p-nitrosophenol—p-quinone monooxime

The solvent used was dimethylformamide at neutral and alkaline pH. The equilibrium constants are determined by spectrophotometry. The rate of proton exchange has been measured as a function of temperature and concentration. The rate constants and activation energies have been measured; for uncatalyzed exchange k_n=(1.5±0.5) ·· 10³ M^–1 sec^–1, E=8±1 kcal/mole, while base-catalyzed exchange has k=(0.3±0.1) · 10⁶ M^–1 sec^–1 and E=6±1 kcal/mole.We are indebted to A. I. Brodskii for assistance in this work, and to V. I. Oshkaderov and L. A. Kichakova for recording the NMR spectra.     

One electron oxidation of Ni(II)-iminodiacetate by carbonate radical

Reactions of carbonate radical (CO₃ ^–), generated by photolysis or by radiolysis of a carbonate solution with nickel(II)-iminodiacetate (Ni(II)IDA) were studied at pH 10.5 and ionic strength (I)==0.2 mol·dm^–3. The stable product arising from the ligand degradation in the complex is mainly glyxalic acid. Time-resolved spectroscopy and transient kinetics were studied using flash photolysis. From the kinetic data it was suggested that the carbonate radical initially reacts with Ni(III)IDA with a rate constant (2.4±0.4)·10⁶ dm³·mol^–1·s^–1 to form a Ni(II)IDA species which, however, undergoes a first-order transformation (k=2.7·10²·s^–1) to give a radical intermediate of the type Ni(II)RNHCHCO ₂ ^– ) which rapidly forms an adduct containing a Ni–C bond. This adduct decays very slowly to give rise to glyoxalic acid. From a consideration of equilibrium between Ni(II)IDA and Ni(III)IDA, the one electron reduction potential for the Ni(III)IDA/Ni(II)IDA couple was determined to be 1.467 V.     

Complex formation followed by internal electron transfer: The reaction between cysteine and iron(III)

Summary A kinetic study of the anaerobic oxidation of cysteine (H₂ L) by iron(III) has been performed over thepH-range 2.5 to 12 by use of a stopped-flow high speed spectrophotometric method. Reaction is always preceded by complex formation. Three such reactive complex species have been characterized spectrophotometrically: FeL ⁺ (_max=614 nm, =2 820 M^–1cm^–1); Fe(OH)L (_max=503 nm; shoulder at 575 nm, =1 640 M^–1cm^–1); Fe(OH)L ₂ ^2– (_max=545 nm; shoulder at 445 nm, =3 175 M^–1 cm^–1). Formation constants have been evaluated from the kinetic data: Fe³⁺+L ^2– FeL ⁺: logK ₁ ^M =13.70±0.05; Fe(OH)²⁺+L ^2– Fe(OH)L: logK ₁ ^MOH =10.75±0.02; Fe(OH)L+L ^2– Fe(OH)L ₂ ^2– ; logK ₂ ^MOH =4.76±0.02. Furthermore the hydrolysis constant for iron(III) was also obtained: Fe(OH)²⁺+H⁺ Fe _aq ³⁺ : logK ^FeOH=2.82±0.02). Formation of the mono-cysteine complexes, FeL ⁺ and Fe(OH)L, is via initial reaction of Fe(OH)²⁺ with H₂ L (k=1.14·10⁴M^–1s^–1), the final product depending on thepH. FeL ⁺ (blue) formed at lowpH decomposes following protonation with a second-order rate constant of 1.08·10⁵M^–1s^–1. Fe(OH)L (purple) decomposes with an apparent third order rate constant ofk=3.52·10⁹M^–2s^–1 via 2 Fe(OH)L+H⁺ products, which implies that the actual (bimolecular) reaction involves initial dimer formation. Finally, Fe(OH)L ₂ ^2– (purple) is remarkably stable and requires the presence of Fe(OH)L for electron transfer. A rate constant of 8.36·10³M^–1s^–1 for the reaction between Fe(OH)L and Fe(OH)L ₂ ^2– is evaluated.Dedicated to Prof. Dr. mult. Viktor Gutmann on the occasion of his 70th birthday     

Kinetics and mechanism of the reaction between bis 4-(2-pyridylazo) resorcinol ferrate(II) complex and cyanide ion

Summary Cyanide ion reacts with [Fe(Par)₂]^2–,i.e. Par=4-(2-pyridylazo)resorcinol to form a 113 mixed cyanocomplex. The reaction has been studied spectrophotometrically at 720 nm _max, pH=11.5±0.02, and I=0.1 M (NaClO₄) at 25±0.1°C. The order with respect to cyanide varies from one to two at high and low cyanide concentrations respectively. The rate constants for respective reactions are k₁=(6.1±0.3)×10^–2 M^–1 s^–1, k₂=(12.6±1.0) M^–2 s^–1. The reverse reaction does not occur at a measurable rate even in presence of a large excess of Par. These observations suggest that [Fe(Par)₂]^2– forms a mixed [FePar(CN)₃]^3– complex in presence of an excess of cyanide ion. The activation parameters for the reaction have been calculated and used to support a three step mechanism consistent with these results. The effect of ionic strength tends further support to the mechanism.     

Radiation chemical studies of nickel-glycine reaction with carbonate radical

Carbonate radical shows moderate reactivity (k₂=1.8·10⁶ M^–1 s^–1) with nickelglycine complex. As an oxidizing free radical, it may attack the ligand to form Ni(II) coordinated glycine radical or oxidize the metal center to form a Ni(III) glycine transient. Continuous -irradiation of the complex-bicarbonate mixture yields glyoxalic acid (G=1.7) as the major product. The reaction involves an attack of the ligand and precludes the oxidation of metal center.     

The antioxidant reactivity of sorbitylfurfural towards potential harmful radicals,studied by radiation chemistry techniques

Ionising radiations, employed in a broad range of dose-rate, together with a complex non-linear computation of reaction mechanisms, allow the determination of boundary values of rate constants concerning sorbitylfurfural (SF) reactivity towards a wide series of oxidant and/or virtually harmful radicals. SF reacts with some radicals (H, SO₄^-˙, CO₃^-˙, Br₂^-˙, CH₃˙), produced with both pulse and stationary radiolysis in neutral aqueous solution, having electrophilic and/or oxidative behaviour. The rate constants range from diffusional (k = (7-9) × 10⁹ M^-1 s^-1) to relatively low values (k = 2 × 10⁵ M^-1 s^-1). The possibility to observe these reactions, by means of radiolytical techniques, is heavily influenced by dose-rate. A relation between the radical E⁰_NHE and their reactivity with SF is hinted.     

Kinetic investigation of sulfur(IV) oxidation by peroxo compounds R-OOH in aqueous solution

Summary Normal and rapid-scan stopped-flow spectrophotometry in the range of 260–300 nm was used to study the kinetics of sulfur(IV) oxidation by peroxo compounds R-OOH (such as hydrogen peroxide, R=H; peroxonitrous acid, R=NO; peroxoacetic acid, R=Ac; peroxomonosulfuric acid, R=SO ₃ ^– ) in the pH range 2–6 in buffered aqueous solution at an ionic strength of 0.5 M (NaClO₄) or 1.0 M (R=NO; Na₂SO₄). The kinetics follow a three-term rate law, rate=(k_H[H]+k_HX[HX]+k_p)[HSO ₃ ^– ][ROOH] ([H] = proton activity; HX = buffer acid = chloroacetic acid, formic acid, acetic acid, H₂PO ₄ ^– ). Ionic strength effects (I=0.05–0.5 M) and anion effects (Cl^–, ClO ₄ ^– , SO ₄ ^2– ) were not observed. In addition to proton-catalysis (k_H[H]) and general acid catalysis (k_HX[HX]), the rate constant k_p characterizes, most probably, a water induced reaction channel with k_p=k_HOH[H₂O]. It is found that k_Hf(R) with k_H(mean)=2.1·10⁷ M^–2 s^–1 at 298 K. The rate constant k_HX ranges from 0.85·10⁶ M^–2 s^–1 (HX=ClCH₂–COOH; R=NO; 293 K) to 0.47·10⁴ M^–2 s^–1 (HX=H₂PO ₄ ^– ; R=H; 298 K) and the rate constant k_p covers the range 0.2·M^–1 s^–1 (R=H) to 4.0·10⁴ M^–1 s^–1 (R=NO). LFE relationships can be established for both k_HX, correlating with the pK_a of HX, and k_p, correlating with the pK_a of the peroxo compounds R-OOH. These relationships imply interesting aspects concerning the mechanism of sulfur(IV) oxidation and the possible role of peroxonitrous acid in atmospheric chemistry. A UV-spectrum of the unstable peroxo acid ON-OOH is presented.     

Pulsed Corona Discharge-Induced Reactions of Acetophenone in Water

The reactions of acetophenone in water by pulsed corona discharges have been investigated to provide fundamental information concerning the reactions of acetophenone in water. Experimental results indicated that photolysis of acetophenone did not involve a hydroxyl radical mechanism and the majority flux of hydroxyl radicals originated from the dissociation of gas-phase oxygen in the plasma channels. The rate constants for photolysis and pyrolysis were determined to be 1.5×10^–7 M-s^–1, 2.2×10^–4 s^–1, respectively. The rate constant for the oxidative reactions was measured as 1.2×10^–7 M-s^–1. Results from this study support the proposal that acetophenone degradation reaction proceed through the oxidative reaction pathway, where molecular oxygen accelerates acetophenone degradation, photolysis, and pyrolysis pathways.