Faraday Trans Research Articles

On the hydrolysis of iodine in alkaline solution: A radiation chemical study

A reaction set has been constructed that describes the radiolysis of N 2O-saturated aqueous solutions of iodide ion. The kinetics and mechanism of the hydrolysis of iodine has been reassessed from conductivity measurements at pH 9.5–11.1 using pulse radiolysis (present work) and previously published data on the yields of I 2+I 3 −, HOI+IO − and IO 3 − produced by the γ-radiolysis of unbuffered solutions [Buxton, G.V., Sellers, R.M., 1985. Radiation induced redox reactions of iodine species in aqueous solutions J. Chem. Soc., Faraday Trans. I 81, 449–471]. The conductivity data are consistent with a value of k 5 ( I 2 + OH - ) = 1 × 1 0 10 dm 3 mol - 1 s - 1 and with the other hydrolysis parameters having values in the following ranges: k - 8 ( HOI + I - ) = ( 0.3 - 3 ) × 1 0 9 dm 3 mol - 1 s - 1 , K 5 ( I 2 + OH - ⇌ I 2 OH - ) = 5 – 50 dm 3 mol - 1 , K 8 ( I 2 OH - ⇌ HOI + I - ) = 8.3 – 0.83 mol dm - 3 , based on K 5 K 8=41.5. The values of K 5 obtained here are much smaller than the literature values of ca. 1.6×10 4 dm 3 mol −1 [Lengyel, I., Epstein, I.R., Kustin, K., 1993. Kinetics of iodine hydrolysis. Inorg. Chem. 32, 5880–5882]. The γ-radiolysis results are well described by these hydrolysis parameters.

Absence of clustering of phosphatidylinositol-(4,5)-bisphosphate in fluid phosphatidylcholine

Phosphatidylinositol-(4,5)-bisphosphate [PI(4,5)P(2)] plays a key role in the modulation of actin polymerization and vesicle trafficking. These processes seem to depend on the enrichment of PI(4,5)P(2) in plasma membrane domains. Here, we show that PI(4,5)P(2) does not form domains when in a fluid phosphatidylcholine matrix in the pH range of 4.8-8.4. This finding is at variance with the spontaneous segregation of PI(4,5)P(2) to domains as a mechanism for the compartmentalization of PI(4,5)P(2) in the plasma membrane. Water/bilayer partition of PI(4,5)P(2) is also shown to be dependent on the protonation state of the lipid.

Connection between parameters of the Murrell–Sorbie and Fayyazuddin potentials

A connection between the Murrell–Sorbie and the Fayyazuddin potential energy functions were established by obtaining conversion matrices that convert the former's parameters into the latter and vice versa. This was attained by rearranging the Fayyazuddin potential into another, but equivalent, form comparable to the Murrell–Sorbie function with the aid of series expansion. A list of 71 sets of Fayyazuddin diatomic parameters were generated by applying one of the conversion matrices on the Huxley–Murrell data [J. Chem. Soc. Faraday Trans. II 79, 323 (1983)]. Verification of the developed conversion matrices was performed by plotting the Murrell–Sorbie and the Fayyazuddin functions using the Huxley–Murrell data and the converted data, respectively. Potential energy plots of typical (OSi) and extreme (FO, BeS and HH) diatomic parameters exhibit very good agreement between the two potential functions considered, thereby confirming the conversion matrices’ validity. Slight discrepancies of the plotted diatomic energy curves further suggest the comparative suitability of the Fayyazuddin potential for curve-fitting harder, rather than softer, bonds.

Primary Electroviscous Effect in a Dilute Suspension of Charged Mercury Drops

The standard theory of the primary electroviscous effect in a dilute suspension of charged spherical rigid particles in an electrolyte solution (Watterson, I. G.; White, L. R. J. Chem. Soc., Faraday Trans. 2 1981, 77, 1115) is extended to cover the case of a dilute suspension of charged mercury drops of viscosity eta(d). A general expression for the effective viscosity or the electroviscous coefficient p of the suspension is derived. This expression tends to that for the case of rigid particles in the limit of eta(d) --> infinity. We also derive an approximate analytical viscosity expressions applicable to mercury drops carrying low zeta potentials at arbitrary kappaa (where kappa is the Debye-Hückel parameter and a is the drop radius) and to mercury drops as well as rigid spheres with arbitrary zeta potentials at large kappaa. It is shown that the large-kappaa expression of p for rigid particles predicts a maximum when plotted as a function of zeta potential. This result for rigid particles agrees with the exact numerical results of Watterson and White. It is also shown that in the limit of high zeta potential the effective viscosity of a suspension of mercury drops tends to that of uncharged rigid spheres given by Einstein's formula (Einstein, A. Ann. Phys. 1906, 19, 289), whereas in the opposite limit of low zeta potential the effective viscosity approaches that of a suspension of uncharged liquid drops derived by Taylor (Taylor, G. I. Proc. R. Soc. London, Ser. A 1932, 138, 41).

Hydrophobic attraction forces in asymmetric aqueous films between hydrophobized mica/bare mica surfaces

The water-structure-based, quasi-thermodynamic theory published several years ago of hydrophobic interaction forces in symmetric aqueous films [J.C. Eriksson, S. Ljunggren, P.M. Claesson, J. Chem. Soc., Faraday Trans. 2 (85) (1989) 163] has been generalized to encompass asymmetric films between, e.g. a hydrophobized mica surface and a bare mica surface. The interaction pressures derived on this basis are in good agreement with the experimental data recorded by Claesson et al. [P.M. Claesson, P.C. Herder, C.E. Blom, B.W. Ninham, J. Colloid Interface Sci. 118 (1987) 68]. Hence, additional support is gathered for the original claim that the hydrophobic attraction is related with hydrogen-bond-dependent cluster formation processes in water contacted with a hydrophobic solid surface.

Temperature dependence of the mean autodetachment lifetime of the p‐benzoquinone molecular radical anion

Experimental data previously published from this laboratory (Asfandiarov NL, Pshenichnyuk SA, Fokin AI, Nafikova EP. Chem. Phys. 2004; 298: 263), on the temperature dependence of the mean autodetachment lifetime of the p-benzoquinone molecular radical anion, were analyzed in the framework of a simple statistical model. This model is a simplification of the well-known semiempirical approach elaborated by Christophorou et al. (Christophorou LG, Hadjiantoniou A, Carter JG. J. Chem. Soc., Faraday Trans. II 1973; 69: 1722). Evaluation of the vibrational energy storage of the target molecule and anion was made in a quantum approximation following a published procedure (Matejcik S, Märk TD, Spanel P, Smith D, Jaffke T, Illenberger E. J. Chem. Phys. 1994; 102: 2516). The results obtained are in reasonable agreement with the experimental data.

A Multiphase Model for the Early Stages of the Hydration of Retarded Oilwell Cement

Cement is used in the oil industry to line oil wells. The major com- ponents of oilwell cement are tricalcium silicate (C3S), dicalcium silicate (C2S), tricalcium aluminate (C3A) and calcium sulphate (CaSO4). With the exception of C2S, each of these plays an important role in the initial thickening of cement slurry. It is important to control the time that it takes for a slurry to thicken, and this is achieved by the addition of chemical retarders, which delay the onset of thickening. In this paper, the action of a retarder whose efiects are flrstly, to form a com- plex with calcium ions, and secondly, to inhibit the growth of ettringite crystals is investigated. Ettringite is a product of the hydration of C3A and the subsequent reaction of the products with calcium sulphate. A modifled version of a model for the hydration of C3S previously investigated by Salhan, Billingham and King (J. Eng. Math. 45 (2003) 367), along with the chemical kinetic scheme for the action of a retarder on ettringite proposed by Billingham and Coveney (J. Chem. Soc. Faraday Trans. 89 (1993) 3021) is used. The model distinguishes between liquid and solid phases, and treats water, which is signiflcantly depleted by the formation of ettringite, as one of the chemical constituents. It is found that both of the chemical actions of the retarder contribute to slowing the initial reaction rate, and that the sudden crystallization of ettringite as the efiect of the retarder is overcome, investigated by Billingham and Coveney, occurs in successive layers around the surface of the cement grain.

Approximate expression for the electrophoretic mobility of a spherical colloidal particle in a solution of general electrolytes

An approximate analytic expression is derived for the electrophoretic mobility of a charged spherical colloidal particle in a solution of general electrolytes on the basis of an approximation method by [Ohshima et al., J. Chem. Soc. Faraday Trans. 2, 79 (1983) 1613]. This expression, which takes into account the relaxation effects, is applicable for all values of zeta potential at large κa ( κa ≥ ca. 30), where κ is the Debye–Hückel parameter and a is the radius of the particle core.

Correlation among parameters of the extended-Rydberg potential energy function

This paper reports a remarkable correlation among parameters of extended-Rydberg potential function by recasting the Morse potential in the form of extended-Rydberg function via the application of infinite series expansion to the exponential terms of the Morse function. By using linear regression, a reasonable band that encompasses 90% of the diatomic combination given by Huxley and Murrell [J. Chem. Soc. Faraday Trans. II 79 (1983) 323] is furnished in a plotted characteristic map.

Approximate Analytic Expression for the Dynamic Electrophoretic Mobility of a Spherical Colloidal Particle in an Oscillating Electric Field

An approximate analytic expression is derived for the dynamic electrophoretic mobility of a spherical charged colloidal particle in an electrolyte solution in an applied oscillating electric field. This expression, which takes into account the relaxation effects, is applicable for all values of zeta potential at large kappa a (kappa a > or = ca. 30) and omega/2pi < or = ca. 10 MHz, where kappa is the Debye-Hückel parameter, a is the particle radius, and omega is the frequency of the electric field. It is shown that the obtained mobility expression is in excellent agreement with the exact numerical results of Mangelsdorf and White (J. Chem. Soc., Faraday Trans. 1992, 88, 3567).

Probing Pd–carbon interaction in Pd/C catalysts by EXAFS

The Pd/C catalyst prepared by PdCl 2 impregnation was examined with extended X-ray absorption fine structure (EXAFS) analysis. The model of precursor anchoring by surface oxygen groups is not supported by EXAFS. A Pd–C interaction at around 3.6 Å can be included in the fitting of the fresh catalyst. This Pd–C interaction remained after the fresh PdCl 2/C was washed and reduced by NaBH 4. However, a further hydrogen treatment at 338 K removed this Pd–C interaction and Pd sintering was indicated with increasing hydrogen treatment temperature. This Pd–C interaction was originally proposed [B.L. Mojet, M.S. Hoogenraad, A.J. van Dillen, J.W. Geus, D.C. Koningsberger, J. Chem. Soc., Faraday Trans. 93 (1997) 4271] for Pd(NH 3) 4Cl 2/C and was also found in the Pd/C prepared by Pd(NO 3) 2 impregnation in this study. This suggests a similar Pd–C interaction while preparing Pd/C catalyst from cationic, anionic and neutral Pd species.

The infrared spectrum of the AsD radical in its X3Σ − state, recorded by laser magnetic resonance

The infrared spectrum of the AsD radical in the X 3Σ − ground state has been recorded using CO laser magnetic resonance. The radical was formed by the reaction between D atoms and arsenic powder. Low- N transitions in the fundamental band and in the (2–1) and (3–2) hot bands have been detected. Hyperfine structure from the 75As nucleus ( I = 3/2) is seen on many of the resonances. These measurements have been combined with information from previous measurements of rotational transitions at sub-millimeter wavelengths [H. Fujiwara, K. Kobayashi, H. Ozeki, S. Saito, A.I. Jaman, J. Chem. Soc. Faraday Trans. 93 (1997) 1045–1051] to determine an extended and improved set of molecular parameters for 75AsD. Comparison is made with corresponding parameter values for AsH.

Radical entry in emulsion polymerization: Propagation at latex particles/water interfaces

In emulsion polymerization, complete entry of an initiator-derived, surface-active radical may involve its adsorption onto latex particles/water interfaces and subsequently its propagation with one more monomer molecule therein. However, all publications to date have defined this propagation step as a three-dimensional bulk reaction between a surface-active entry radical and a monomer molecule. This is incorrect conceptually. It is proposed that the rate of the propagation of surface-active entry radicals with monomer at latex particles/water interfaces be expressed as − d [ M Z ⋅ ] w / l / d t = k I A [ M ] P [ M Z ⋅ ] aq . In this equation, A is the interfacial area between water and latex particles; [ M ] P and [ M Z ⋅ ] aq are the mean concentrations of monomer in the particle phase and entry radicals in the aqueous phase, respectively; k I is the radical propagation constant at the interfaces, and may be estimated via transition state theory. For seeded styrene polymerization by Hawkett et al. (J. Chem. Soc. Faraday Trans. 1 76 (1980) 1323), k I ≈ ∼ 4.2 × 10 −9 k p ( mol −1 dm 4 s −1 ) is estimated. Here k p is the propagation rate coefficient in bulk polymerization. This alternative approach should be useful for one to simulate radical entry rate in emulsion polymerization where the propagation step may be rate-determining, such as under monomer-starved conditions.

Viscoelastic properties of 1,2-,1,4- and 1,2-1,4-diblock butadiene polymers

The use of polar modifiers to produce novel structures of butadiene polymers is well documented in the literature [Antkowiak TA, Oberster AE, Halasa AF, Tate DP. J Polym Sci 1972;10:1319; Langer AW. Polym Prep Am Sco Polym Div. 1966;7:132; Hay JN, McCabe JF, Robb JC. Polym Prep Am Chem Faraday Trans 1972;1:681; Halasa AF, Mochel VD, Frankel G. Polym Prep Am Chem Sco, Div Polym Chem 1980;21(1):13; Halasa AF, Schulz DN, Tate DP, Mochel VD. Adv Organomet Chem 1980;8:55 [1–5]]. Manipulating microstructures of 1,3-butadiene to produce diblock co-polymers has been reported by one of us [Halasa AF. Rubber Chem Technol 1981;54:627 [6]]. The discovery of polar modifier di-piperdinoethane to produce pure (100%) atactic 1,2-polubutadiene [Halasa AF, Lohr DF, Hall JE. J Polym Sci Polym Chem Ed 1981;19 [7]] provided scientists with a new tool to structurally engineer various block co-polymers of butadiene and styrene and study their structural and viscoelastic properties [Cohen RE, Torradas JM. MS Thesis, MIT, May 1980, PhD Thesis, MIT January, 1982 [8]].

Direct Measurement of Nitric Oxide and Oxygen Partitioning into Liposomes and Low Density Lipoprotein

Nitric oxide (*NO) has been proposed to play a relevant role in modulating oxidative reactions in lipophilic media like biomembranes and lipoproteins. Two factors that will regulate *NO reactivity in the lipid milieu are its diffusion and solubility, but there is no data concerning the actual diffusion (D) and partition coefficients (KP) of *NO in biologically relevant hydrophobic phases. Herein, a "equilibrium-shift" method was designed to directly determine the *NO and O2 partition coefficients in liposomes and low density lipoprotein (LDL) relative to water. It was found that *NO partitions 4.4- and 3.4-fold in liposomes and LDL, respectively, whereas O2 behaves similarly with values of 3.9 and 2.9, respectively. In addition, actual diffusion coefficients in these hydrophobic phases were determined using fluorescence quenching and found that *NO diffuses approximately 2 times slower than O2 in the core of LDL and 12 times slower than in buffer (DNOLDL=3.9 x 10(-6) cm2 s(-1),DO2LDL=7.0 x 10(-6) cm2 s(-1),DNObuffer=DO2buffer=4.5 x 10(-5) cm2 s(-1)). The influence of *NO and O2 partitioning and diffusion in membranes and lipoproteins on *NO reaction with lipid radicals and auto-oxidation is discussed. Particularly, the 3-4-fold increase in O2 and *NO concentration within biological hydrophobic phases provides quantitative support for the idea of an accelerated auto-oxidation of *NO in lipid-containing structures, turning them into sites of enhanced local production of oxidant and nitrosating species.

Analysis of the population of continuum states in wave packet propagation calculations

We present a ‘virtual detector’ method which allows the extraction of the momentum distributions in continuum states from time-dependent wave packet propagation studies with explicitly time-dependent Hamiltonians. It is based on the approach developed by Balint-Kurti et al (1990 J. Chem. Soc. Faraday Trans. 86 1741) for quantum chemistry applications and consists in measuring a signal in the asymptotic region. In that sense, it is close to the semiclassical method proposed recently in this journal (Feuerstein and Thumm 2003 J. Phys. B: At. Mol. Opt. Phys. 36 707). The advantage of the present approach is that it is based on a rigorous quantum mechanical treatment, robust, easy to handle and requires a much smaller grid size. The method is illustrated with the 3D example of electron detachment from the H− ion colliding with a free-electron metal surface.

Photophysics on Surfaces: Determination of Absolute Fluorescence Quantum Yields from Reflectance Spectra

A method for the calculation of absolute fluorescence quantum yields for dyes attached to solid particles based on reflectance measurements is reported. The same procedure allows calculation of true reflectance spectra (free of fluorescence) for highly fluorescent materials as well. Samples ofcresyl violet were immobilized by adsorption on microgranular cellulose in the concentration range 4.5 x 10(-9) to 3.8 x 10(-6) mol g(-1). Diffuse and total reflectance spectra were recorded with and without insertion of an optical absorption filter between the output of the integrating sphere of a reflectance spectrometer and the photodetector in order to block fluorescence partially. From these data, the relative emission spectrum of the dye, the filter transmission spectrum, and the detector sensitivity, true reflectances and absolute fluorescence quantum yields were recovered. Observed fluorescence quantum yields, affected by dye aggregation and inner filter effects, were concentration and wavelength dependent, ranging approximately between 0.1 and 0.6. The analysis of remission function spectra showed that dye aggregation is negligible up to a concentration of 1.41 x 10(-7) mol g(-1). Fluorescence data were corrected for reemission and reabsorption using a suitable model [Lagorio, M. G.; Dicelio, L. E.; Litter, M. I.; San Roman, E. J. Chem. Soc., Faraday Trans. 1998, 94, 419]. Application of this model to samples showing no aggregation yielded a wavelength-independent true fluorescence quantum yield of 0.60 +/- 0.05, similar to values found in solution. The usage of cresyl violet as a reference for the evaluation of fluorescence quantum yields for weakly fluorescing samples in the solid phase is discussed.

Wide-Temperature-Range Kinetics of the Reactions of Cu with Cl2 and N2O and of CuCl with Cl2

The reactions Cu + Cl2 → CuCl + Cl (1), CuCl + Cl2 → CuCl2 + Cl (2), and Cu + N2O → CuO + N2 (3) have been studied using a high-temperature fast-flow reactor (HTFFR). The metallic species were the limiting reactants. Cu atoms were generated by vaporization, and CuCl, by reaction 1. Their concentrations were monitored by LIF. The following k(T) expressions in cm3 molecule-1 s-1 were obtained: k1(305−1140 K) = 3.9 × 10-10 exp(−355 K/T), k2(980−1150 K) = 3.1 × 10-11 exp(−4765 K/T), and k3(530−950 K) = 3.8 × 10-10 exp(−5441 K/T). The Arrhenius parameters of k1 are similar to other exothermic metal atom−Cl2 reactions. The activation energy of reaction 2 is rather large, which is attributed to the closed-shell electron structure of CuCl. Reaction 3 had been measured earlier in a pseudostatic photochemistry reactor (Narayan, A. S.; Futerko, P. M.; Fontijn, A. J. Phys. Chem. 1992, 96, 290) and in a different type of fast-flow reactor (Vinckier, C.; Verhaeghe, T.; Vanhees, I. J. Chem. Soc., Faraday Trans. 1994, 90, 2003). A comparison of these two studies showed mild disagreement. However, a critical evaluation of the three data sets confirms the validity of our previous recommendation: k3(470−1340 K) = 3.04 × 10-20(T/K)2.97 exp(−3087 K/T).

Corrected equations for membrane transport characterization by manometric techniques

Equations for characterization of membrane permeability and diffusivity via pressure decay measurements in closed and open systems for three different configurations are discussed in terms of time lag and general transient solutions. The solutions presented correct errors in the earlier work of Nguyen et al. [J. Chem. Soc., Faraday Trans. 88 (1992) 3553].

Rheological implications of completely monotone fading memory

In the constitutive equation modeling of a (linear) viscoelastic material, the “fading memory” of the relaxation modulus G(t) is a fundamental concept that dates back to Boltzmann [Ann. Phys. Chem. 7, 624 (1876)]. There have been various proposals that range from the experimental and pragmatic to the theoretical about how fading memory should be defined. However, if, as is common in the rheological literature, one assumes that G(t) has the following relaxation spectrum representation: G(t)=∫0∞ exp(−t/τ)[H(τ)/τ]dτ, t > 0, then it follows automatically that G(t) is a completely monotone function. Such functions have quite deep mathematical properties, that, in a rheological context, spawn interesting and novel implications. For example, because the set of completely monotone functions is closed under positive linear combinations and products, it follows that the dynamics of a linear viscoelastic material, under appropriate stress–strain stimuli, will involve a simultaneous mixture of different molecular interactions. In fact, it has been established experimentally, for both binary and polydisperse polymeric systems, that the dynamics can simultaneously involve a number of different molecular interactions such as the Rouse, double reptation and/or diffusion, [W. Thimm et al., J. Rheol., 44, 429 (2000); F. Leonardi et al., J. Rheol. 44, 675 (2000)]. The properties of completely monotone functions either yield new insight into modeling of the dynamics of real polymers, or they call into question some of the key assumptions on which the current modeling is based, such as the linearity of the Boltzmann model of viscoelasticity and/or the relaxation spectrum representation for the relaxation modulus G(t). If the validity of the relaxation spectrum representation is accepted, the resulting mathematical properties that follow from the complete monotonicity of G(t) allows one to place the classical relaxation model of Doi and Edwards [M. Doi and S. F. Edwards, J. Chem. Soc., Faraday Trans. 2 74, 1789 (1978)], as a linear combination of exp(−t/τ*) relaxation processes, each with a characteristic relaxation time τ*, on a more general and rigorous footing.