Arrhenius Pre-exponential Factor Research Articles

An unlocking/relocking barrier in conformational fluctuations of villin headpiece subdomain

A reversible structural unlocking reaction, in which the close-packed van der Waals interactions break cooperatively, has been found for the villin headpiece subdomain (HP35) using triplet-triplet-energy transfer to monitor conformational fluctuations from equilibrium. Unlocking is associated with an unfavorable enthalpy change (DeltaH(0) = 35 +/- 4 kJ/mol) which is nearly compensated in free energy by the entropy change (DeltaS(0) = 112 +/- 20 Jxmol(-1)xK(-1)). The unlocking reaction has a time constant of about 1 mus at 5 degrees C and is enthalpy-limited with an activation energy of 32 +/- 1 kJ/mol and a large Arrhenius preexponential factor of A = 7.5 x 10(11) s(-1). In the unlocked state a fast local conformational fluctuation with a time constant of 170 ns and a low activation barrier of 17 +/- 1 kJ/mol leads to unfolding of the C-terminal helix and to its undocking from the core. On a much slower time scale, global unfolding occurs from the unlocked state. These results suggest that native protein structures are locked into conformations with low amplitude motions. Large scale motions and global unfolding require an initial structural unlocking step leading to a state with properties of a dry molten globule. The experiments additionally yielded information on the dynamics of loop formation between different positions in unfolded HP35. Comparison of the results with dynamics in unstructured model peptides indicates slightly decelerated kinetics of local loop formation in the C-terminal region which points at residual, nonrandom structure. Dynamics of long-range loop formation, in contrast, are not influenced by residual structure, which argues against unfolded state properties as molecular origin for ultrafast folding of HP35.

How Do We Introduce the Arrhenius Pre-Exponential Factor (A) to Graduate Students?

A simple and easy understanding of Arrhenius pre-exponential factor (A) is described in this article for a graduate class-room lecture.

Kinetic correlations for H2 addition and elimination reaction mechanisms during silicon hydride pyrolysis

The mechanism of H(2) addition and elimination reactions in selected silicon hydrides (Si(x)H(y), x = 1-10, y = 4-20) was modeled using quantum chemical calculations, statistical thermodynamics, transition state theory and transition state group additivity. Rate coefficients for 25 H(2) addition reactions were calculated using G3//B3LYP. For nearly every reaction, the overall conversion exhibits two steps. In the addition direction, the reactants first meet to form an adduct which then converts into a saturated silicon hydride via homolytic H-H bond cleavage. Values for the single-event Arrhenius pre-exponential factor, Ã, and the activation energy, E(a), were calculated from the G3//B3LYP rate coefficients, and a group additivity scheme was developed to predict à and E(a). The values predicted by group additivity are more accurate than kinetic correlations currently used in the literature, which rely on representative à values and the Evans-Polanyi correlation. The factors that have the most pronounced effect on à and E(a) were investigated, and stabilization of the divalent silicon atom of the unsaturated silicon hydride with electron-donating substituents was found to influence kinetic parameters considerably. The rate coefficients for H(2) addition reactions were found to correlate reasonably well with the difference in energy between the highest occupied molecular orbital of H(2) (E(HOMO)) and the lowest unoccupied molecular orbital of the reactant silylene (E(LUMO)).

Synthesis, characterisation and computational studies on a novel one-dimensional arrangement of Schiff-base Mn3 single-molecule magnet

The syntheses, structures and magnetic properties are reported for three new manganese complexes containing the Schiff-base ((2-hydroxy-3-methoxyphenyl)methylene)isonicotinohydrazine (H(2)hmi) ligand. Complex [Mn(II)(H(2)hmi)(2)(MeOH)(2)Cl(2)] (1) was obtained from the reaction of H(2)hmi with MnCl(2) in a MeOH-MeCN mixture. Addition of triethylamine to the previous reaction mixture followed by diethyl ether diffusion yielded a dinuclear manganese [Mn(III)(2)(hmi)(2)(OMe)(2)](infinity).2MeCN.2OEt(2) (2) compound. Upon increasing the MnCl(2)/H(2)hmi ratio, the mixed valence complex [Mn(III)(2)Mn(II)(hmi)(2)(OMe)(2)Cl(2)](infinity).MeOH (3) was obtained. Dc and ac magnetic measurements were carried out on all three samples. The ac susceptibility and field dependence of the magnetisation measurements confirmed that complex 3 exhibits a single-molecule magnet behaviour with an effective energy barrier of 8.1 K and an Arrhenius pre-exponential factor of 3 x 10(-9) s.

Ring opening polymerization of ε‐caprolactone initiated by decamolybdate anion: Determination of kinetic and thermodynamic parameters by DSC and 1H‐NMR

AbstractThe aim of this work is the kinetic and thermodynamic study (by differential scanning calorimetry (DSC) and proton nuclear magnetic resonance (1H‐NMR)) of the polymerization of ε‐caprolactone initiated by ammonium decamolybdate. By means of isothermal kinetics, enthalpies of reaction in the range 150–160°C, as well as constant rates of polymerization (using an nth‐order kinetics function model), were determined. From an Arrhenius plot, activation energy (Ea = 85.3 kJ/mol) and preexponential factor (A = 1.78 × 108 min−1) were estimated. Using dynamic methods, crystallization and melting temperatures for the polymer obtained in situ were derived. Kinetic data for polymerization (obtained by 1H‐NMR) were fitted to 13 different model reaction functions. It was found that power law equations represent better the conversion versus time plots for this system. On the basis of experimental facts, a coordination‐insertion mechanism involving molybdenum(V) species is proposed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Exploring 1,2-Hydrogen Shift in Silicon Nanoparticles: Reaction Kinetics from Quantum Chemical Calculations and Derivation of Transition State Group Additivity Database

Accurate rate coefficients for 35 1,2-hydrogen shift reactions for hydrides containing up to 10 silicon atoms have been calculated using G3//B3LYP. The overall reactions exhibit two distinct barriers. Overcoming the first barrier results in the formation of a hydrogen-bridged intermediate species from a substituted silylene and is characterized by a low activation energy. Passing over the second barrier converts this stable intermediate into the double-bonded silene. Values for the single event Arrhenius pre-exponential factor, A, and the activation energy, E(a), were calculated from the G3//B3LYP rate coefficients, and a group additivity scheme was developed to predict A and E(a). The values predicted by group additivity are more accurate than structure/reactivity relationships currently used in the literature, which rely on a representative A value and the Evans-Polanyi correlation to predict E(a). The structural factors that have the most pronounced effect on A and E(a) were considered, and the presence of rings was shown to influence these values strongly.

Enzymatic H Transfers: Quantum Tunneling and Coupled Motion from Kinetic Isotope Effect Studies

AbstractMany hydrogen transfer processes exhibit nonclassical behavior due to inherent quantum mechanical properties of the hydrogen. Investigation of various enzymes under physiological conditions indicates that hydrogen transfer processes often show significant quantum mechanical behavior. Traditionally, this phenomenon was treated in terms of a tunneling correction to classical or semiclassical models. However, more recently, it has been observed that increasing numbers of enzymes yield data that cannot be rationalized by tunneling correction models. Observations such as large kinetic isotope effects (KIEs) with unusual temperature dependence, isotope effects on Arrhenius preexponential factors with values different from semiclassical predicted ranges, and small temperature‐independent KIEs for processes with significant energy of activation, could only be explained with full tunneling models for H transfer. Full tunneling models presume that the solvent or protein fluctuations generate a reactive configuration along the heavy‐atom coordinate, from which the hydrogen is transferred through quantum mechanical tunneling. These models are sometimes denoted as environmentally coupled tunneling (ECT) or Marcus‐like models, and they link protein dynamics to the catalyzed H transfer. Several enzymatic systems (dihydrofolate reductase, thymidylate synthase, and soybean lipoxygenase) are presented as case studies of proton, hydrogen, and hydride transfer.

Poly(ester amide)/clay nanocomposites prepared by in situ polymerization of the sodium salt of N‐chloroacetyl‐6‐aminohexanoic acid

AbstractPreparation of nanocomposites of organo‐modified montmorillonites and the biodegradable poly(ester amide) derived from glycolic acid and 6‐aminohexanoic acid has been evaluated by the in situ polymerization technique. The reaction was based on the thermal polycondensation of sodium chloroacetylaminohexanoate, which has the formation of the sodium chloride salt as the driving force of the process. Polymerized samples were studied by means of X‐ray diffraction and transmission electron microscopy. The most dispersed structure was obtained by addition of C25A organoclay. Evaluation of thermal stability and crystallization behavior of these samples showed significant differences between the neat polymer and its nanocomposite with C25A. Isothermal and nonisothermal calorimetric analyses of the polymerization reaction revealed that the kinetics was highly influenced by the presence of the silicate particles. Crystallization of the polymer was observed to occur when the process was isothermally conducted at temperatures lower than 145 °C. In this case, dynamic FTIR spectra and WAXD profiles obtained with synchrotron radiation were essential to study the polymerization kinetics. Clay particles seemed to reduce chain mobility and the Arrhenius preexponential factor. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3616–3629, 2009

Catalytic Action of Atmospheric Water Vapor on the Thermal Decomposition of Synthetic Hydrozincite

The effect of atmospheric water vapor on the kinetic rate behavior of the thermal decomposition of zinc carbonate hydroxide, Zn5(CO3)2(OH)6, was investigated by means of TG-DTA under the controlled partial pressure of atmospheric water vapor, p(H2O). With increasing p(H2O) from 0.7 to 9.4 kPa, the reaction temperature at the restricted heating rate was reduced systematically accompanied by the change in the shape of TG curves. Through systematic kinetic analysis of the reaction at different p(H2O), the change in the kinetic behavior was characterized by the mutually dependent decreases in the apparent activation energy and the Arrhenius pre-exponential factor, where the catalytic action of atmospheric water vapor on the surface nucleation process was identified as the possible mechanistic origin.

Entropic effects in excited state CT reactions

The kinetics of the dual fluorescence of several derivatives of dimethylaminobenzonitrile (DMABN) has been compared using fs-fluorescence upconversion experiments. Variation of the size and twist angle of the donor (dialkylamino group) suggest a large amplitude solvent-viscosity controlled diffusional twisting motion towards larger twist angles as the rate limiting step.Large rate differences were observed for an ester group as acceptor. Temperature dependent studies indicate that these differences are not connected with different activation barriers but with changes in the Arrhenius preexponential factor. It is argued that conical intersections along the reaction path can bring about these entropy changes.

Reaction of Phenols with the 2,2-Diphenyl-1-picrylhydrazyl Radical. Kinetics and DFT Calculations Applied To Determine ArO-H Bond Dissociation Enthalpies and Reaction Mechanism

The formal H-atom abstraction by the 2,2-diphenyl-1-picrylhydrazyl (dpph(*)) radical from 27 phenols and two unsaturated hydrocarbons has been investigated by a combination of kinetic measurements in apolar solvents and density functional theory (DFT). The computed minimum energy structure of dpph(*) shows that the access to its divalent N is strongly hindered by an ortho H atom on each of the phenyl rings and by the o-NO(2) groups of the picryl ring. Remarkably small Arrhenius pre-exponential factors for the phenols [range (1.3-19) x 10(5) M(-1) s(-1)] are attributed to steric effects. Indeed, the entropy barrier accounts for up to ca. 70% of the free-energy barrier to reaction. Nevertheless, rate differences for different phenols are largely due to differences in the activation energy, E(a,1) (range 2 to 10 kcal/mol). In phenols, electronic effects of the substituents and intramolecular H-bonds have a large influence on the activation energies and on the ArO-H BDEs. There is a linear Evans-Polanyi relationship between E(a,1) and the ArO-H BDEs: E(a,1)/kcal x mol(-1) = 0.918 BDE(ArO-H)/kcal x mol(-1) - 70.273. The proportionality constant, 0.918, is large and implies a "late" or "product-like" transition state (TS), a conclusion that is congruent with the small deuterium kinetic isotope effects (range 1.3-3.3). This Evans-Polanyi relationship, though questionable on theoretical grounds, has profitably been used to estimate several ArO-H BDEs. Experimental ArO-H BDEs are generally in good agreement with the DFT calculations. Significant deviations between experimental and DFT calculated ArO-H BDEs were found, however, when an intramolecular H-bond to the O(*) center was present in the phenoxyl radical, e.g., in ortho semiquinone radicals. In these cases, the coupled cluster with single and double excitations correlated wave function technique with complete basis set extrapolation gave excellent results. The TSs for the reactions of dpph(*) with phenol, 3- and 4-methoxyphenol, and 1,4-cyclohexadiene were also computed. Surprisingly, these TS structures for the phenols show that the reactions cannot be described as occurring exclusively by either a HAT or a PCET mechanism, while with 1,4-cyclohexadiene the PCET character in the reaction coordinate is much better defined and shows a strong pi-pi stacking interaction between the incipient cyclohexadienyl radical and a phenyl ring of the dpph(*) radical.

Hydrogen atom transfer reactions of a ruthenium imidazole complex: hydrogen tunneling and the applicability of the Marcus cross relation.

The reaction of Ru(II)(acac)2(py-imH) (Ru(II)imH) with TEMPO(*) (2,2,6,6-tetramethylpiperidine-1-oxyl radical) in MeCN quantitatively gives Ru(III)(acac)2(py-im) (Ru(III)im) and the hydroxylamine TEMPO-H by transfer of H(*) (H(+) + e(-)) (acac = 2,4-pentanedionato, py-imH = 2-(2'-pyridyl)imidazole). Kinetic measurements of this reaction by UV-vis stopped-flow techniques indicate a bimolecular rate constant k(3H) = 1400 +/- 100 M(-1) s(-1) at 298 K. The reaction proceeds via a concerted hydrogen atom transfer (HAT) mechanism, as shown by ruling out the stepwise pathways of initial proton or electron transfer due to their very unfavorable thermochemistry (Delta G(o)). Deuterium transfer from Ru(II)(acac)2(py-imD) (Ru(II)imD) to TEMPO(*) is surprisingly much slower at k(3D) = 60 +/- 7 M(-1) s(-1), with k(3H)/k(3D) = 23 +/- 3 at 298 K. Temperature-dependent measurements of this deuterium kinetic isotope effect (KIE) show a large difference between the apparent activation energies, E(a3D) - E(a3H) = 1.9 +/- 0.8 kcal mol(-1). The large k(3H)/k(3D) and DeltaE(a) values appear to be greater than the semiclassical limits and thus suggest a tunneling mechanism. The self-exchange HAT reaction between Ru(II)imH and Ru(III)im, measured by (1)H NMR line broadening, occurs with k(4H) = (3.2 +/- 0.3) x 10(5) M(-1) s(-1) at 298 K and k(4H)/k(4D) = 1.5 +/- 0.2. Despite the small KIE, tunneling is suggested by the ratio of Arrhenius pre-exponential factors, log(A(4H)/A(4D)) = -0.5 +/- 0.3. These data provide a test of the applicability of the Marcus cross relation for H and D transfers, over a range of temperatures, for a reaction that involves substantial tunneling. The cross relation calculates rate constants for Ru(II)imH(D) + TEMPO(*) that are greater than those observed: k(3H,calc)/k(3H) = 31 +/- 4 and k(3D,calc)/k(3D) = 140 +/- 20 at 298 K. In these rate constants and in the activation parameters, there is a better agreement with the Marcus cross relation for H than for D transfer, despite the greater prevalence of tunneling for H. The cross relation does not explicitly include tunneling, so close agreement should not be expected. In light of these results, the strengths and weaknesses of applying the cross relation to HAT reactions are discussed.

Thermal degradation of allicin in garlic extracts and its implication on the inhibition of the in-vitro growth of Helicobacter pylori.

Allicin, the main active principle related to Allium sativum chemistry, is considered to be responsible for the bacteriostatic properties of garlic. The work described here has demonstrated the direct implication of the allicin present in solvent-free garlic extracts obtained with ethanol (ethanolic garlic extract, EGE) and acetone (acetonic garlic extract, AGE) in the inhibition of the in-vitro growth of Helicobacter pylori (Hp), the bacterium responsible for serious gastric diseases such as ulcers and even gastric cancer. The evolution of allicin concentration as a function of time and temperature has been the subject of a kinetic study. The reaction order, activation energy, and preexponential factor (in accordance with Arrhenius theory) have been determined for the decomposition process of allicin in these organic media. First-order decomposition, an activation energy of 97.4 kJ/mol, and an Arrhenius preexponential factor of 8.9 x 10(10) s(-1) have been determined for allicin in EGE. For allicin in AGE the kinetic order determined was 1.5, the activation energy 184.5 kJ/mol, and the preexponential factor 3.1 x 10(24) s(-1) (mg/L)(-0.5). The presence or absence of allicin in these garlic products was found to be crucial for the inhibition of the in-vitro growth of Hp, as demonstrated by microbiological analysis for AGE. A relationship has been identified between the effectiveness and durability of the anti-Hp properties shown by AGE and the allicin content of these products. The bacteriostatic properties were active for up to 10 months if the samples were maintained at 6 degrees C.

Inativação de pseudomonas aeruginosa em resíduos de serviços de saúde por microondas

Resíduos de serviços de saúde da cidade de Ribeirão Preto - SP, previamente esterilizados em autoclave, foram inoculados com microrganismos da espécie P. aeruginosa na forma vegetativa para o processamento com microondas em escala de laboratório. Analisou-se a influência do tempo de exposição à radiação (25, 30, 35 e 40 min.) e da potência por unidade de massa de resíduo (60, 80 e 100 W/kg) no percentual de inativação dos microrganismos para a umidade de entrada do resíduo de 50% em base úmida. Os resultados experimentais foram ajustados com base na cinética de primeira ordem para determinação da energia de ativação (no intervalo de 13,9 a 14,1 kJ/mol) e do fator pré-exponencial da lei de Ahrrenius (10,7 min-1) pelo método dos mínimos quadrados. As equações propostas permitiram obter por simulação a constante cinética e estimar o tempo de processamento necessário para fornecer diferentes níveis de inativação. Por exemplo, o tempo de exposição à radiação de 117 min foi requerido para se obter o nível de inativação 6.Log 10 para os resíduos processados à 100 W/kg e à temperatura de 100ºC.

Two stages catalytic pyrolysis of olive oil waste

A study of the pyrolysis of a waste from the extraction of olive oil has been carried out. The work objective was to characterize the char, tar and gaseous phases generated in the process for their possible utilization in energy generation. On the other hand, the influence of a set of variables has been studied, including the efficacy of the dolomite as catalyst. Finally, as previous step to the design of industrial installations, a kinetic study of the process (catalyzed and uncatalyzed), based in the generation of the principal gases, has been carried out. In the uncatalyzed process only the influence of temperature (400–900 °C) was studied. In the catalytic process, the influence of temperature (500–800 °C) and mass of catalyst (0–100 g) was studied. Also, the dolomite effectiveness as catalyst was evaluated. For this motive, consecutive experiments, without reactivating dolomite, were carried out (0–6 runs), and the yields of solids, liquids and gases were determined. An increase in reaction temperature leads to a decrease in char and tar yield and to an increase in the gas phase yield. When the catalyst is present and when the mass of the same is increased, an important decrease in the tar yield and a high increase in the gas phase yield are produced. This increment in the yield of gases is very significant in the case of hydrogen. In addition, the catalyst is very stable. Your activity remains constant during six consecutive pyrolysis experiments, without need to carry out the reactivation of the same. In the kinetic study carried out, it has been considered that the gases are formed through parallel independent first-order reactions, with different activation energy. For uncatalyzed experiments, the experimental data, once adjusted to the model, provided activation energies of 77.8, 38.6, 70.5 and 16.9 kJ mol − 1 and the Arrhenius pre-exponential factors of 210.1, 9.9, 775.3 and 0.43 min − 1 for H 2, CO, CH 4, and CO 2, respectively. For catalyzed experiments (following the same sequence) the activation energies were 15.6, 16.5, 12.7 and 23.3 kJ mol − 1 and the Arrhenius pre-exponential factors 3.8, 1.4, 4.3 and 3.5 min − 1 .

Kinetic Model for the Thermal Degradation of Poly(Methylphenylsiloxane)

The kinetics of the thermal degradation of polymethylphenylsiloxane (PMPS) were investigated by dynamic thermogravimetric analysis. The thermal degradation of PMPS has two processes: “unzipped degradation” and “rearranged degradation”. The corresponding kinetic parameters of the two stages were determined using the Kissinger and Friedman methods respectively. The results showed that the value of the activation energy (E) obtained from the Friedman method was in good agreement with that obtained by the Kissinger method. For “unzipped degradation”, E was 164.2 kJ/mol and 168.2 kJ/mol, and for “rearranged degradation”, E was 228.6 kJ/mol and 232.0 kJ/mol. The Arrhenius pre-exponential factor (A) and reaction order (n) for the two stages were also discussed. A kinetic model was built by using the obtained kinetic parameters, and the results obtained by the model were in good agreement with the measured value.

Theoretical Study of Hydrogen Abstraction and Sulfur Insertion in the Reaction H2S + S

The reaction of H2S + S has been characterized at the multireference configuration interaction level with the geometries optimized using the aug-cc-pVTZ basis set and the single-point energy calculated using the aug-cc-pV(Q+d)Z basis set. As in the analogous reaction of H2 + S, the presence of an intersystem crossing enables products (SH + SH) to be formed on the singlet surface through S insertion, which bypasses the triplet barrier (19.1 kJ mol-1 relative to SH + SH) of the H abstraction route. This provides theoretical evidence for SH + SH formation without barrier beyond endothermicity at sufficiently low temperatures. The H abstraction route, however, is expected to be competitive at higher temperatures due to a much higher Arrhenius pre-exponential factor (6.9 x 10(14) cm3 mol-1 s-1 derived from TST calculation) than that of S insertion channel (3.7 x 10(13) cm3 mol-1 s-1, derived by a least-squares fit to the measurements). With a slightly higher transition-state barrier than that of the H abstraction channel, the production of S2 + H2 is less favored due to proceeding via intersystem crossing and insertion. While the formation of HSS + H is energetically unfavorable relative to SH + SH, recombination channels producing H2SS or the more stable HSSH are expected to occur under collisional stabilization conditions at high pressures.

Effects of reduction on the denaturation kinetics of human hair

Although human hair as an alpha-keratinous fiber exhibits a complex morphology, it can be considered as a nano-structured filament/matrix composite for the context of thermal analysis. Using differential scanning calorimetry (DSC) in water, the denaturation performance of the alpha-helical protein fraction and the effects of reductive treatments were studied. The results are viewed in the context of a previous study for oxidative treatments. It was found that the course of the denaturation process remains generally unperturbed by the treatment, following an irreversible, one-step, first-order process. Arrhenius activation energies and pre-exponential factors were determined from the DSC-curves by applying the principles of the Friedman-method. Comparing activation energy values between reductive and oxidative processes shows the differences of the effects on the components of the composite. In contrast, the values of the rate constant at the denaturation temperature, though showing differences in their trends with cumulative treatments, are very similar. This further emphasizes the theory that the viscosity of the matrix affects strict kinetic control over the denaturation of the alpha-helical segments. Once the viscosity of the matrix has decreased enough for the denaturation process to occur, this follows a path that is largely independent of the temperature range and of the chemical pre-history.

Thermal degradation kinetics and solid state, temperature dependent, electrical conductivity of charge-transfer complex of phenothiazine with chloranil and picric acid

Temperature dependent electrical conductivity and thermal degradation kinetics of charge-transfer (C-T) complexes of phenothiazine (PTZ) with p-chloranil (CHL) and picric acid (PA), are reported. These C-T complexes exhibited semiconducting behaviour. The activation energies for PTZ-CHL and PTZ-PA complexes are calculated based on their electrical conductivities measured over the temperature ranges 30–110°C and 30–90°C, respectively. And these energies for PTZ-CHL and PTZ-PA are 0·54 eV and 0·75 eV, respectively. The complexes are analysed for the kinetic parameters like the activation energy for decomposition and the Arrhenius pre-exponential factors in their pyrolysis region using Broido’s, Coats-Redfern as well as Horowitz-Metzger methods. Using standard equations, thermodynamic parameters such as enthalpy, entropy and free energies, are calculated.

Thermal ZnO dissociation in a rapid aerosol reactor as part of a solar hydrogen production cycle

An experimental investigation of the thermal dissociation of ZnO particles in aerosol flow was conducted. A cooling lance and quench tube were used to sharpen residence time determination and limit product recombination. Experiments were performed at temperatures between 1873 and 2023 K and residence times between 1.11 and 1.78 s. Product particles were distributed between the walls of the quench tube, a gravity collection vessel, and a downstream HEPA filter. Chemical analysis showed material in gravity vessel was largely unreacted. Physical and chemical analysis of particles collected in the quench tube and filter indicated conversion to Zn with some recombination. Arrhenius pre-exponential factors were measured between 2.23 × 10 9 and 1.67 × 10 10 s - 1 . These parameters gave rates three orders of magnitude faster than stationary configurations. The net conversions after recombination had a maximum value of 18%, with a mean value of 8%. Product particle sizes ranged between 5 and 70 nm, a size whose surface area was expected to increase the rate of the Zn hydrolysis step of the cycle.