Thermodynamic investigation of methyl salicylate/1-pentanol binary system in the temperature range from 278.15 K to 303.15 K

Densities (ρ), speeds of sound (u), isentropic compressibilities (k_s), refractive indices (n_D), and surface tensions (σ) of binary mixtures of methyl salicylate (MSL) with 1-pentanol (PEN) have been measured over the entire composition range at the temperatures of 278.15 K, 288.15 K, and 303.15 K. The excess molar volumes (V^E), excess surface tensions (σ^E), deviations in speed of sound (Δu), deviations in isentropic compressibility (Δk_s), and deviations in molar refraction (ΔR) have been calculated. The excess thermodynamic properties V^E, σ^E, Δu, Δk_s, and ΔR were fitted to the Redlich–Kister polynomial equation and the A_k coefficients as well as the standard deviations (d) between the calculated and experimental values have been derived. The surface tension (σ) values have been further used for the calculation of the surface entropy (S^S) and the surface enthalpy (H^S) per unit surface area. The lyophobicity (β) and the surface mole fraction $(x_2^{\text{S}})$ of the surfactant component PEN have been also derived using the extended Langmuir model. The results provide information on the molecular interactions between the unlike molecules that take place at the surface and the bulk.     

Ac polarography and faradaic impedance of strongly adsorbed electroactive species: Part IV. Experimental study of the faradaic impedance of the redox systems benzo(c)cinnoline-dihydrobenzo(c) cinnoline

The faradaic impedance of the surface redox system benzo(c)cinnoline-dihydrobenzo(c)-cinnoline is studied experimentally in aqueous medium between pH 5 and 13. The variations of the impedance components are in good accord with the theoretical predictions. A V-shaped curve is found for log k_s=f(pH) (k_s=rate constant of the surface electrochemical reaction). It is estimated that the determination of rate constant values up to 2×10⁴ s^?1 on a mercury electrode is possible by this method.     

Heterogeneous electron-transfer kinetics for some multiply bonded dirhenium complexes

Standard electrochemical rate constants k^ex_ob have been measured for the two sequential one-electron oxidations of triply-bonded dirhenium(II) complexes Re₂X₄(PR₃)₄, where X = Cl or Br, and PR₃ = a monodentate tertiary phosphine, and also for allied complexes in methylene chloride, acetonitrile, and N,N-dimethylformamide at platinum electrodes. The objective is to explore the possible dependence of k^ex_ob upon the known differences in the structural changes accompanying electron transfer. Although significant and even substantial variations in k^ex_ob were observed for closely related redox couples, the reactivity trends appear to be chiefly a consequence of differences in electrostatic work terms at the metal/solution interface. Comparisons are made with recent results for mononuclear organometallic redox couples.     

Steady-state and pulsed studies of the radiation-induced polymerization of methyl methacrylate

In order to quantify our fluorogenic molecular probe studies on the radiation-induced polymerization of methyl methacrylate (MMA), measurements have been made of the monomer conversion, C _M, and polymer molecular weight distribution as a function of dose for bulk MMA polymerized by steady-state (⁶⁰Co γ-rays) and nanosecond-pulsed (3 MeV electrons) radiation. In all cases, C _M was found to increase close to linearly with dose up to ca. 30%. Above this conversion, autoacceleration of polymerization (the gel or Trommsdorff effect) occurs in the γ-irradiated samples. From the low-conversion steady-state data, using dose-rates of 0.21 and 2.7 Gy/s, the parameter 〈k _p〉 ² G(R^.)/2〈k _t〉 = 0.011 and 0.015 lmol^-1 s^-1 (100 eV)^-1 respectively have been determined (with 〈k _p〉 and 〈k _t〉 the average rate coefficients for bimolecular propagation and termination respectively, and G(R^.) the yield of the chain-initiating free radicals per 100 eV (G = 1 (100 eV)^-1 0.1036 μ mol J^-1)). From the 5 Hz repetitive pulse data the value of 〈k _p〉 G(R^.) = 1700 lmol^-1 s^-1 (100 eV)^-1 has been determined. Taking 〈k _p〉 = 342 lmol^-1 s^-1 from the literature results in G(R^.) = 5.0 (100 eV)^-1 and 〈k _t〉 = 2.7 × 10⁷ lmol^-1 s^-1.     

Cadmium ion reduction at mercury electrode in aqueous KCl solution in presence of adsorbed polyvinyl alcohol

The influence of polyvinyl alcohol on the kinetics of cadmium ion reduction in 1M aqueous KCl solution at the dropping mercury electrode was investigated using the impedance method. It was found that small additions of PVA did not change the diffusion coefficient much, but affected only the rate of charge transfer process. The electroreduction of cadmium in the presence of PVA became less reversible. The standard rate constant dependence on coverage degree is described by the following equation: k_s=k_s0(1?ν)ⁿ, where n=2.     

On-line FFT faradaic admittance measurements application to A.C. cyclic voltammetry

A measurement approach is described and data are presented which demonstrate the ability to effect a.c. cyclic voltammetric measurements with the on-line digital FFT approach to faradaic admittance data acquisition. The equipment utilized enables complete faradaic admittance spectra to be obtained at an effective spectrum acquisition rate of 10 s^?1, so that the d.c. potential range encompassed by a typical cyclic wave can be encompassed with adequate resolution in the E_dc dimension in ≥6 s, approximately. The instrument features dynamic, computerized measurement and compensation of the non-faradaic ohmic resistance and double-layer capacitance contributions to the acquired total cell admittance. Measurements with quasi-reversible systems yield the expected faradaic admittance and phase angle responses over a quite generous bandwidth. Applications to mercury and platinum electrodes are illustrated.     

Polymer films on electrodes: Part XVIII. Determination of heterogeneous electron transfer kinetics at poly(vinylferrocene) and nafion/Ru(bpy)2+3 polymer-modified electrodes by convolution voltammetry

Convolution voltammetry was used to evaluate the rates of heterogeneous charge transfer to ferrocene groups in poly(vinylferrocene) and to Ru(bpy)²⁺₃ in Nafion-modified electrodes under semi-infinite conditions. This technique allows correction for uncompensated resistance and double layer capacitance, as well as detrmination of the diffusion coefficient, D, transfer coefficient, α, and half-wave potential, E_1/2, from a single cyclic voltammogram. Vinylferrocene in solution and a bound copolymer of vinylferrocene and styrene in a ratio of 58:42 were also examined. For the polymer films, the heterogeneous charge transfer rate constants, k°, are 10^?4 ≥ k° ≥ 10^?5 cm/s; these values are about two order of magnitude smaller than those for the similar species in homogeneous solution. The values of k°/D^1/2, however, are comparable to those in soluton; 10 > (k°/D^1/2) > 0.1 s^?1/2.     

The fluorescence of all-trans diphenyl polyenes

The temperature dependence of the fluorescence and fluorescence excitation spectra of all-trans diphenyl hexathene (DPH) and octatetraene (DPO) in six solvents confirms the S₁(¹A_g*) and S₂(¹B_u*) state assignment, and determines their energy difference ΔE. The S₁ fluorescence rate parameter k_F depends on ΔE, the solvent refractive index n, the S₂ (n = 1) fluorescence rate parameter k_F20 (2.23 × 10⁸ s^?1 for DPH, 2.33 × 10⁸ s^?1 for DPO), and the S₂-S₁ coupling matrix element V (745 cm^?1 for DPH, 500 cm^?1 for DPO). The S₁ fluorescence is induced by ¹B_u*-¹A_g* potential interaction (PI), via a b_u vibrational mode (≈ 900 cm^?1), and not by vibronic coupling. The main S₁ radiationless transition, rate parameter k_R, is thermally-activated internal rotation through an angle θ about the central ethylenic bond(s). The PI distorts the S₁ (θ) potential surface and thus influences k_R.     

Normalized potential sweep voltammetry: Part III. Elimination of the effect of uncompensated Resistance and the application to heterogeneous kinetics of rapid charge-transfer processes

Uncompensated resistance (R_u) has a distoring effect on normalized potential sweep voltammetry (NPSV) slopes. This provides a simple and effective method to determine R_f^o, the value of the potentiostat feedback resistance necessary for full compensation. If the NPSV range is divided into overlapping segment, 1 and 2, corresponding to I_N of 0.20–0.50 and 0.50–0.80 respectively, the slopes m₁ and m₂ differ significantly when R_f differs form R_f^o. The difference, m₁-m₂, is negative for R_f<R_f^o and positive for R_f>R_f^o. Fine tuning of the potentiostat R_f setting so that the average value of the difference is the theoretical value can be accomplished in a minimum of time. Under these conditions, m₁ and m₂, as well as m_T, the slope of the entire correlation have very nearly the same values. Linear equations were derived from theoretical data which allow heterogeneous rate constants to be obtained directly from NPSV slopes. The precision in the NPSV slopes was observed to be of the order of ±0.002 which implies that the method should give reliable rate constants as great as 10cm s^? at a voltage sweep rate of 100V s^?1. The method is demonstrated using the reduction of benzonitrile and perylene in N,N-dimethylformamide and acetonitrile as examples.     

New relation between ionic radii,bond length,and bond strength

Based on the table of the effective ionic radii of R. D. Shannon (Acta Crystallogr. Sect. A32, 751, 1976), the linear relation of the cationic radii on the coordination numberk has been observed:

$r_k=r_0+dk?\frac{0.0236\mathit{k}}{z},$

wherer₀ is the radius of free cation, z its valence, andd = 0.1177 - 0.0081 z - 0.0347 r₀ - 0.0050 zr₀. The analogous relation for O^2? anion has been found to ber′_k′ = r′₀ + a′k′ = 1.328 + 0.0118 k′. By addingr_k andr′_k′ corresponding to the same bond strength new dependence between bond lengthR and bond strengths has been established for cation-oxygen bonds:

$s=\frac{d\mathit{z}}{R?R_0},$

whereR₀ = r₀ + r′₀. The necessity to choose a standard state for ionic radii and for bond strength is pointed out and argued. Structures of simple oxides at room temperature and at normal pressure are chosen as standard state at which the sum of the strengths of bonds around the cation is assumed to be exactly equal to itsz.Standard radii of free ions r₀ are determined for about 230 ions and are listed. As in Shannon's table some ionic radii were found to be negative. Physical sense can be hardly attributed to this finding. To avoid the negative radii a new scale ofabsolute ionic radiiρ₀ is proposed, based on assumption thatρ₀(H¹⁺) = 0 instead ofr₀(H¹⁺) = ?h = ?0.499 (the size of the proton is known to be of the order of 10^?5A?, i.e., much less than the accuracy of determination of ionic radii). Consequentlyρ₀ for all cations is assumed to beρ₀ = r₀ + h and for anionsρ′₀ = r′₀ ? h (e.g.,ρ′₀(O^2?) = 0.829A?). Bond-length-bond-strength relationship expressed by the equation indicated above is rationalized in terms of the new proposedelectrostatic hover model of crystal structure. In this model ions are of constant size (r₀ orρ₀), they do not touch each other, but they are maintained at distancesL = R - R₀ by the electrostatic forces. This remains in agreement with the suggested (J. Zio´?kowski,J. Catal.84, 317, (1983)) linear relation between bond strength and bond energyE = Js which will be proved in the forthcoming paper (J. Zio´?kowski and L. Dziembaj,J. Solid State Chem.57, 291 (1985)).     

Thermodynamic interactions in binary mixtures of anisole with ethanol, propan-1-ol, propan-2-ol, butan-1-ol, pentan-1-ol, and 3-methylbutan-1-ol at T = (298.15, 303.15, and 308.15) K

In this paper, excess thermodynamic functions have been computed from the measured values of density, viscosity, and refractive index at T = (298.15, 303.15, and 308.15) K, ultrasonic velocity at T = 298.15 K over the entire mixture composition range of (anisole with ethanol, propan-1-ol, propan-2-ol, butan-1-ol, pentan-1-ol, or 3-methyl butan-1-ol). Excess molar volume, V^E has been calculated from densities, whereas deviations in viscosity, Δη, were computed from the measured viscosities. From ultrasonic velocities, isentropic compressibilities were calculated, from which deviations in isentropic compressibility, Δk_s have been computed. Lorenz-Lorentz mixture rule was used to compute molar refractivity, R from refractivity index data and from these data, deviations in molar refractivity, ΔR have been computed. Computed thermodynamic quantities have been fitted to Redlich and Kister polynomial equation to derive the coefficients and standard errors between experimental and predicted quantities. Intermolecular interactions between anisole and alkanols have been studied based on the computed excess thermodynamic quantities.     

Self-quenching and electronic energy transfer of triplet molecules. The benzaldehyde-biacetyl system in the vapor phase

The triplet-triplet energy transfer from benzaldehyde to biacetyl and the competing self-quenching between triplets and ground state molecules of benzaldehyde were investigated in the dilute vapor phase by monitoring the phosphorescence (T₁(nπ^*)S_o) decay of benzaldehyde. Following excitation into the S₁(nπ^*)S₀ absorption band, a triplet self-quenching rate constant of k_SQ=(2.4±0.1) × 10⁴ s^?1 Torr^?1, corresponding to a gas-kinetic cross section of σ_SQ=0.22 A², was measured. The collision-free lifetime of the benzaldehyde triplet was found to be 2.3 ± 0.4 ms. Substitution of the aldehydic proton by deuterium reduces k_SQ by a factor of two: complete deuteration of the molecule has no further effect. Under the same excitation conditions, the energy transfer rate to biacetyl is k_ET=(2.8 ± 0.1) × 10⁶ s^?1 Torr^?1, with σ_ET = 24 A². This process is not influenced by deuteration.     

Cavity ring‐down spectroscopic study of the kinetics of the reactions of FCO radicals with O2 and NO at 295 K

Cavity ring‐down UV absorption spectroscopy was used to study the kinetics of the recombination reaction of FCO radicals and the reactions with O₂ and NO in 4.0–15.5 Torr total pressure of N₂ diluent at 295 K. k(FCO + FCO) is (1.8 ± 0.3) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹. The pressure dependence of the reactions with O₂ and NO in air at 295 K is described using a broadening factor of Fc = 0.6 and the following low (k₀) and high (k_∞) pressure limit rate constants: k₀(FCO + O₂) = (8.6 ± 0.4) × 10⁻³¹ cm⁶ molecule⁻¹ s⁻¹, k_∞(FCO + O₂) = (1.2 ± 0.2) × 10⁻¹² cm³ molecule⁻¹ s⁻¹, k₀(FCO + NO) = (2.4 ± 0.2) × 10⁻³⁰ cm⁶ molecule⁻¹ s⁻¹, and k_∞ (FCO + NO) = (1.0 ± 0.2) × 10⁻¹² cm³ molecule⁻¹ s⁻¹. The uncertainties are two standard deviations. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 130–135, 2001     

Cyclic voltammetry of FAD adsorbed on graphite,glassy carbon,platinum and gold electrodes

The electrochemical properties of FAD adsorbed on graphite were studied with cyclic voltammetry. A film with a surface coverage of up to 2×10^?8 mol cm^?2 was formed after 4 h. The film-covered electrodes were stable for long times and they were investigated in buffers without any FAD. A single well-behaved wave was observed, k⁰≌1 s^?1. The pH dependence of E_1/2 was studied. On glassy carbon, platinum and gold much less FAD was adsorbed and it was removed with one rinse.     

Free radical inactivation of trypsin

Reactivities of free radical oxidants, ^.OH, Br^-·₂ and Cl₃COO^. and a reductant, CO^-·₂, with trypsin and reactive protein components were determined by pulse radiolysis of aqueous solutions at pH 7, 20°C. Highly reactive free radicals, ^.OH, Br^-·₂ and CO^-·₂, react with trypsin at diffusion controlled rates, k(^.OH + trypsin) = 8.2 × 10¹⁰ M^-1 s^-1, k(Br^-·₂ + trypsin) = 2.55 × 10⁹ M^-1 s^-1 and k(CO^-·₂ + trypsin) = 2.6 × 10⁹ M^-1 s^-1. Moderately reactive trichloroperoxy radical, k(Cl₃COO^. + trypsin) = 3 × 10⁸ M^-1 s^-1, preferentially oxidizes histidine residues. The efficiency of inactivation of trypsin by free radicals is inversely proportional to their reactivity. The yields of inactivation of trypsin by ^.OH, Br^-·₂ and CO^-·₂ are low, G(inactivation) = 0.6-0.8, which corresponds to ∾ 10% of the initially produced radicals. In contrast, Cl₃COO^. inactivates trypsin with ∾ 50% efficiency, i.e. G(inactivation) = 3.2.     

The kinetics and mechanisms of gas phase elimination of primary,secondary, and tertiary 2‐hydroxyalkylbenzenes

2‐Phenylethanol, racemic 1‐phenyl‐2‐propanol, and 2‐methyl‐1‐phenyl‐2‐propanol have been pyrolyzed in a static system over the temperature range 449.3–490.6°C and pressure range 65–198 torr. The decomposition reactions of these alcohols in seasoned vessels are homogeneous, unimolecular, and follow a first‐order rate law. The Arrhenius equations for the overall decomposition and partial rates of products formation were found as follows: for 2‐phenylethanol, overall rate log k₁(s⁻¹)=12.43−228.1 kJ mol⁻¹ (2.303 RT)⁻¹, toluene formation log k₁(s⁻¹)=12.97−249.2 kJ mol⁻¹ (2.303 RT)⁻¹, styrene formation log k₁(s⁻¹)=12.40−229.2 kJ mol⁻¹(2.303 RT)⁻¹, ethylbenzene formation log k₁(s⁻¹)=12.96−253.2 kJ mol⁻¹(2.303 RT)⁻¹; for 1‐phenyl‐2‐propanol, overall rate log k₁(s⁻¹)=13.03−233.5 kJ mol⁻¹(2.303 RT)⁻¹, toluene formation log k₁(s⁻¹)=13.04−240.1 kJ mol⁻¹(2.303 RT)⁻¹, unsaturated hydrocarbons+indene formation log k₁(s⁻¹)=12.19−224.3 kJ mol⁻¹(2.303 RT)⁻¹; for 2‐methyl‐1‐phenyl‐2‐propanol, overall rate log k₁(s⁻¹)=12.68−222.1 kJ mol⁻¹(2.303 RT)⁻¹, toluene formation log k₁(s⁻¹)=12.65−222.9 kJ mol⁻¹(2.303 RT)⁻¹, phenylpropenes formation log k₁(s⁻¹)=12.27−226.2 kJ mol⁻¹(2.303 RT)⁻¹. The overall decomposition rates of the 2‐hydroxyalkylbenzenes show a small but significant increase from primary to tertiary alcohol reactant. Two competitive eliminations are shown by each of the substrates: the dehydration process tends to decrease in relative importance from the primary to the tertiary alcohol substrate, while toluene formation increases. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 401–407, 1999     

Abfangreaktionen kurzlebiger radikale XVIII. Kinetische und CIDNP-studien der photoreaktion von distannanen mit alkylhalogeniden und der thermischen reaktion mit diacylperoxiden

A longlived triplet state is shown by ¹¹⁹Sn CIDNP for distannanes R₆Sn₂ upon irradiation (E_T = 300 kJ), which may be split into 2 radicals R₃Sn·(k_a), but also into R₅Sn₂· + R· (k_b. With R = Me, k_a is more important, but with R = Et, Bu, k_a ≈ k_b. Compounds R₆Sn₂ are cleaved by R· into R₄Sn + R₃Sn·, the effectivity being increased in the series t-Bu < i-Pr << Pr < Et < Me ≈ Ph. For Me₆Sn₂ and Me·, k = 0.85 X 10⁴ l mol^?1 sec^?1 at 23°C. The distannane Et₅Sn₂Br is attacked by Me· predominantly, by Pr· and Bu· exclusively at the halogenated Sn atom. Diacetyl peroxide reacts quickly with R₆Sn₂ via a nonradical mechanism yielding MeCOOSnR₃, as does dibenzoyl peroxide analogously but more slowly. In both cases a free-radical reaction is superposed (¹³C CIDNP) giving R₄Sn, CO₂, and RCOOSnR₃. It is stopped by t-BuBr, but increased markedly at higher temperatures.     

Flash photolysis of SiBr4: the UV spectrum of SiBr2

In the flash photolysis of SiBr₄ both the absorption and the emission spectra corresponding to the B̃²Σ−X̃²Π transition of SiBr have been observed. A broad, structureless absorption band has also been detected in the 340–400 nm region which could be assigned to the hitherto unreported à ¹B₁−x̃ ¹A₁ transition of SiBr₂. The decay of both absorption spectra followed first-order kinetics yielding the pseudo-first-order rate constants: k(SiBr)=2.6 × 10⁴s⁻¹ and k(SiBr₂) = 8.9 × 10³⁻¹. Assuming that the principal reactions consuming these intermediates are SiBr+SiBr₄→Si₂Br₅ and SiBr₂+SiBr₄→ Si₂Br₆, the second-order rate constants have the values k(SiBr)= 9.7×10⁹ M⁻¹s⁻¹ and k(SiBr₂)= 3.3×10⁸M⁻¹s⁻¹.     

Theoretical analysis of the influence of the adosorption process on the voltammetric curves in the case of a second order adsorption step followed by a first order charge transfer reaction: Part II. Comparison between linear potential sweep voltammetry and steady state cyclic voltammetry

The voltammetric curves for a 2-step sequential reaction involving a 2nd order adsorption process (such as the catalytic mechanism met in the anodic oxidation of hydrogen) are investigated theoretically by computer calculations. Steady state cyclic voltammetry (s.s.c.v.) is particularly treated by repeating forward and backward sweeps as many times as necessary to reach the steady state. For both l.p.s.v. and s.s.c.v., the usual characteristic features are considered, i.e. E_M, θ_M, i_M as a function of sweep rate υ, especially in the range of υ, where the computed data fit the results derived from analytical solution (quasi-reversible charge transfer, and irreversible charge transfer). In s.s.c.v., indications are given to obtain the kinetic parameters (k₁, k₂, α) from experimental plots.