Absolute Reaction Rate Research Articles

Removal of psychoactive pharmaceutical caffeine from water by electro-Fenton process using BDD anode: Effects of operating parameters on removal efficiency

Caffeine, as a typical representative of pharmaceutical pollution, was subjected to the removal from water by means of the electro-Fenton process. The study of a single-molecule solution was meant for better understanding of the influence of operating parameters on the removal rates and for finding their optimal values. The setup comprised a bench-scale reactor equipped with a boron-doped diamond anode and a 3D carbon felt cathode. Degradation and mineralization kinetics were monitored for different sets of two major operating parameters: current intensity (from 100 to 1500 mA) and Fe2+ concentration (from 0.1 to 0.5 mM). Experimental data revealed that the optimal catalyst concentration was 0.2 mM, regardless the applied current intensity. For experiments on degradation kinetics, the trend of increasing the reaction rate with an increasing current was valid up to 300 mA. In contrast, the mineralization rate increased up to 1500 mA. The absolute reaction rate constant between caffeine and hydroxyl radical was determined as (2.48 ± 0.01) × 109 M−1 s−1. A follow-up of aromatic compounds, carboxylic acids and inorganic ions, enabled composition of a plausible degradation pathway for caffeine degradation by hydroxyl radicals. An analysis of the operating parameters versus evolution of degradation and mineralization showed that even small concentrations of Fe2+ and low current intensities led to complete degradation and almost complete mineralization.

Application of the Eyring Equation in the Evaluation of Semi-Solid Forming-Induced Si Particle Refinement in the Hypereutectic Al-Si Alloys

On the basis of Eyring’s theory of absolute reaction rate, an approach to modeling Si particle refinement acceleration in the semi-solid forming of a hypereutectic Al-Si alloy has been developed. The acceleration variable data used in the present analysis were obtained from a semi-solid compression test using Al-25 mass pct Si alloy cylindrical specimens with a diameter of 15 mm and a height of 15 mm; the test conditions comprised a combination of compression displacements ∆h = 5, 10, and 12 mm; compression rates v = 5, 25, and 125 mm/min; and test temperatures T = 853 K and 863 K (580 °C and 590 °C). The coarse primary Si particle refinement depends on a complex interaction among variables, such as compression displacement, compression rate, and test temperature. The performance of Si particle refinement degraded under higher temperature, slower strain rates, and slower shear rates. The results of the Si particle size are suitably summarized by the Eyring equation as a function of the temperature and the shear rate. The baseline Si particle size and the baseline temperature of Si particle refinement, i.e., the reference temperature, were GN = 0.27 mm and TN = 866.4 K (593.4 °C), respectively. The calculated results using this equation correlated well with the observed results. An acceleration factor of Si particle refinement was successfully derived on the basis of this equation and indicated that operating at a higher shear rate and a temperature just above the melting point of eutectic Al-Si alloy are the optimum conditions for refining Si particles.

Trimerization Reaction Kinetics and Tg Depression of Polycyanurate under Nanoconfinement

Trimerization of a mixture containing a mono- and difunctional cyanate ester is investigated under the nanoporous confinement of silanized hydrophobic controlled pore glass using differential scanning calorimetry. The trimerization reaction of the nanoconfined monomer mixture is accelerated relative to the bulk by as much as 12 times in 8 nm pores, but this acceleration is less than half that observed for nanoconfinement of the individual monomers. The absolute reaction rate of the monomer mixture lies between those of the individual species, being slower than the monocyanate ester and faster than the dicyanate ester. The results are consistent with the hypothesis that the reaction acceleration is due to monomer ordering or layering at the pore surface, leading to a local concentration of reactive groups higher than in the bulk. In addition to the influence of nanoconfinement on trimerization kinetics, the molecular weight and glass transition temperature (Tg) of the polycyanurate formed in the nanopores are investigated. The molecular weight decreases approximately 20% for synthesis in the smallest 8 nm pores relative to the bulk value of 5200 g/mol. Upon extraction from the pores, the polymer Tg is 5–9 K higher than in the bulk. However, in the 8 nm diameter pores, a Tg depression of 44 K is observed relative to the value of the material after extraction from the pores. This depression lies between the values previously observed for the products of the individual cyanate esters which formed a low molecular weight trimer and a cross-linked polymer network. A secondary Tg, associated with a less mobile layer at the pore wall, is 26–40 K above the primary value. The implication is that the origin of confinement effects on reactivity and Tg differ, with changes in reactivity in this system arising from surface layering or ordering and Tg depressions arising from intrinsic size effects.

Application of dhurrin for kinetics and thermodynamic characterization of linamarase (β-glucosidase) genetically engineered from Saccharomyces cerevisiae.

Recombinant Saccharomyces cerevisiae cells at the stationary phase of growth were recovered, homogenized and centrifuged to obtain crude extracts designated as GELIN 0 . Carboxy methyl cellulose, diethyl amino-ethyl-sephadex and diethyl amino-ethyl-cellulose were used to purify the crude extracts of GELIN 0 resulting in GELIN 1 , GELIN 2 and GELIN 3 , respectively. The ability of the enzyme extracts and a commercial native linamarase (CNLIN) to hydrolyse cyanogenic glucosides was challenged using dhurrin from sorghum as substrate. Precisely, the actions of commercial native linamarase (CNLIN) and the genetically engineered linamarase (β-glucosidase) from Saccharomyces cerevisiae on dhurrin as influenced by degree of its purification, pH (6.8 ) and temperature(30-45°C) were investigated and the data derived were applied for kinetics and thermodynamic characterization of the enzymes. Enzymic degradation kinetics of the dhurrin were evaluated using a 4 x 6 x 8 B/W design comprising of 4 enzyme types ( GELIN o , GELIN 1 GELIN 2 and GELIN 3 ,, 6 temperatures (30, 32, 35, 37, 40, 45 °C) and 8 time intervals( 0-70 min.). Data obtained from the residual HCN with time were fitted into zero, first and second order kinetics models to derive reaction rate constant (Kmin -1 ) values which were analyzed using the Arrhenius and absolute reaction rate models Thermodynamic parameters were obtained including; activation energies (E a ), frequency factor(K o ), enthalpy (ΔH ) and entropy (ΔS#) that characterized the reactions on dhurrin catalyzed by commercial native linamarase (CNLIN) and the genetically engineered linamarase (β-glucosidase) from Saccharomyces cerevisiae. The results showed that the best fitted order based on higher coefficient of linear regression (r 2 ) values > 0.998 and linearity of curves was the first order kinetics model and not either zero or second order models. Kmin -1 values ranged from GELIN O- GELIN 3 0.03-0.07 μmol/min while the derived D-values from K-values were in the range of 24-65 min. The frequency factors (K o ) increased with enzyme purity from GELIN 0 to GELIN 3 corresponding to K o (min -1 ) of 22.585 to 56.462. The energy of activation E a (KJ/mol)generated 60.0995 to 150.6900 corresponding to enzymes GELIN 0 to GELIN 3 followed the same pattern with frequency factor for breaking of bonds in dhurrin molecules. At pH 6.8 CNLIN showed no action on dhurrin. The high correlation coefficient values of (r 2 = 0.97 to 0.99) indicated the best fit of the Arrhenius and the absolute reaction rate models. The entropy change (ΔS) increased with enzyme purity from 0.588 J/mol.deg. to 1.4625Jmol degree. The enthalpy change KJ/mol followed the same pattern whereby increases influenced by enzyme purity ranged from 1892 KJ/mol to 13104KJ/mol. Keywords : kinetics, thermodynamic, characterization, dhurrin, genetically engineered β- glucosidase, Saccharomyces cerevisiae.

Photocatalytic degradation of three amantadine antiviral drugs as well as their eco-toxicity evolution

Abstracts Advanced oxidation processes (AOPs) relying on in situ generated highly reactive OH are successfully applied to water purification. The absolute reaction rate constants for OH with three antiviral drugs were first reported through pulsed radiolysis experiments. Results found that OH reacted quickly with these substrates, with bimolecular reaction rate constants of 6.31 × 10 9 , 5.13 × 10 9 , and 7.05 × 10 9 M −1 s −1 for 1-amantadine, 2-amantadine, and rimantadine, respectively. The photocatalytic degradation kinetics of substrates were followed pseudo-first-order kinetics according to Langmuir–Hinshelwood model in TiO 2 suspensions, and the apparent rate constants were obtained as 0.076, 0.084, and 0.102 min −1 for three antiviral drugs, respectively. Scavenger experiments revealed that OH was the major reactive species involved in antiviral drugs degradation. To probe the photocatalytic degradation mechanism, the fate of nitrogen elements and the change of total organic carbon were also examined, and the data showed that all three drugs could be completely mineralized into CO 2 , H 2 O, and inorganic ions (NO 3 − and NH 4 + ) without generating any detectable products with enough degradation time. To further insight into the potential adverse effect of three antiviral drugs and their degradation products, the acute aquatic toxicity of degradation solutions were evaluated at three different trophic levels, and the toxicities first increased slightly and then decreased rapidly as the total organic carbon decreased.

Fluxome study of Pseudomonas fluorescens reveals major reorganisation of carbon flux through central metabolic pathways in response to inactivation of the anti-sigma factor MucA.

BackgroundThe bacterium Pseudomonas fluorescens switches to an alginate-producing phenotype when the pleiotropic anti-sigma factor MucA is inactivated. The inactivation is accompanied by an increased biomass yield on carbon sources when grown under nitrogen-limited chemostat conditions. A previous metabolome study showed significant changes in the intracellular metabolite concentrations, especially of the nucleotides, in mucA deletion mutants compared to the wild-type. In this study, the P. fluorescens SBW25 wild-type and an alginate non-producing mucA- ΔalgC double-knockout mutant are investigated through model-based 13C-metabolic flux analysis (13C-MFA) to explore the physiological consequences of MucA inactivation at the metabolic flux level. Intracellular metabolite extracts from three carbon labelling experiments using fructose as the sole carbon source are analysed for 13C-label incorporation in primary metabolites by gas and liquid chromatography tandem mass spectrometry.ResultsFrom mass isotopomer distribution datasets, absolute intracellular metabolic reaction rates for the wild type and the mutant are determined, revealing extensive reorganisation of carbon flux through central metabolic pathways in response to MucA inactivation. The carbon flux through the Entner-Doudoroff pathway was reduced in the mucA- ΔalgC mutant, while flux through the pentose phosphate pathway was increased. Our findings also indicated flexibility of the anaplerotic reactions through down-regulation of the pyruvate shunt in the mucA- ΔalgC mutant and up-regulation of the glyoxylate shunt.ConclusionsAbsolute metabolic fluxes and metabolite levels give detailed, integrated insight into the physiology of this industrially, medically and agriculturally important bacterial species and suggest that the most efficient way of using a mucA- mutant as a cell factory for alginate production would be to use non-growing conditions and nitrogen deprivation.Electronic supplementary materialThe online version of this article (doi:10.1186/s12918-015-0148-0) contains supplementary material, which is available to authorized users.

Evaluated kinetics of terminal and non-terminal addition of hydrogen atoms to 1-alkenes: a shock tube study of H + 1-butene.

Single-pulse shock tube methods have been used to thermally generate hydrogen atoms and investigate the kinetics of their addition reactions with 1-butene at temperatures of 880 to 1120 K and pressures of 145 to 245 kPa. Rate parameters for the unimolecular decomposition of 1-butene are also reported. Addition of H atoms to the π bond of 1-butene results in displacement of either methyl or ethyl depending on whether addition occurs at the terminal or nonterminal position. Postshock monitoring of the initial alkene products has been used to determine the relative and absolute reaction rates. Absolute rate constants have been derived relative to the reference reaction of displacement of methyl from 1,3,5-trimethylbenzene (135TMB). With k(H + 135TMB → m-xylene + CH3) = 6.7 × 10(13) exp(-3255/T) cm(3) mol(-1) s(-1), we find the following: k(H + 1-butene → propene + CH3) = k10 = 3.93 × 10(13) exp(-1152 K/T) cm(3) mol(-1) s(-1), [880-1120 K; 145-245 kPa]; k(H + 1-butene → ethene + C2H5) = k11 = 3.44 × 10(13) exp(-1971 K/T) cm(3) mol(-1) s(-1), [971-1120 K; 145-245 kPa]; k10/k11 = 10((0.058±0.059)) exp [(818 ± 141) K/T), 971-1120 K. Uncertainties (2σ) in the absolute rate constants are about a factor of 1.5, while the relative rate constants should be accurate to within ±15%. The displacement rate constants are shown to be very close to the high pressure limiting rate constants for addition of H, and the present measurements are the first direct determination of the branching ratio for 1-olefins at high temperatures. At 1000 K, addition to the terminal site is favored over the nonterminal position by a factor of 2.59 ± 0.39, where the uncertainty is 2σ and includes possible systematic errors. Combining the present results with evaluated data from the literature pertaining to temperatures of <440 K leads us to recommend the following: k∞(H + 1-butene → 2-butyl) = 1.05 × 10(9)T(1.40) exp(-366/T) cm(3) mol(-1) s(-1), [220-2000 K]; k∞(H + 1-butene → 1-butyl) = 9.02 × 10(8)T(1.40) exp(-1162/T) cm(3) mol(-1) s(-1) [220-2000 K]. Analogous rate constants for other unbranched 1-olefins should be very similar. Despite this, a factor of three discrepancy in the branching ratio for terminal and nonterminal addition is noted when comparing the present values with recommendations from a recent model of the important H + propene reaction. This difference is suggested to be well outside of the possible experimental errors of the present study or the expected differences with 1-butene. There thus appear to be inconsistencies in the current model for propene. In particular the addition branching ratio from that model should not be used as a reference value in extrapolations to other systems via rate rules or automated mechanism generation techniques.

Conformations of disulfide-intact and -reduced lysozyme ions probed by proton-transfer reactions at various temperatures.

Proton-transfer reactions of disulfide-intact and -reduced lysozyme ions (7+ through 14+) to 2,6-dimethylpyridine were examined in the gas phase using tandem mass spectrometry with electrospray ionization. By changing temperature of a collision cell from 280 to 460 K, temperature dependence of reaction rate constants and branching fractions was measured. Absolute reaction rate constants for the protein ions of specific charge states were determined from intensities of parent and product ions in the mass spectra. Remarkable change was observed for the rate constants and distribution of product ions. The rate constants for disulfide-intact ions changed more drastically with change of charge states and temperature than those for disulfide-reduced ions. Observed branching fractions for parent and product ions were represented by calculated reaction rate constants with a scheme of sequential process. The reaction rate constants are closely related to conformation changes with change of temperature, which are profoundly influenced by amputation of disulfide bonds.

Viscosities of Binary Liquid Mixtures of Acetylene Tetrachloride with Benzene, Toluene, p-xylene, Acetone &amp; Cyclohexane at 303.15K

Viscosities which are accurate to ± 0.01mP, have been measured for binary liquid mixtures of acetylene tetrachloride (CHCl2CHCl2, hereafter abbreviated simply as ATC) with benzene, toluene, p-xylene, acetone and cyclohexane at 303.15 ±0.01K. The values of the quantity Δη, which refer to the deviations of the experimental values of the dynamic viscosities of the mixtures from the mole fraction mixture law values, have been found to be negative for the systems ATC-benzene, ATC-toluene, ATC-p-xylene and ATC-cyclohexane. For ATC-acetone, Δη has been found to be negative at low mole fractions of ATC and positive at high mole fractions. Also the values of the parameter d have been calculated from the equation ln η = x1 ln η1+x2 ln η2 +x1 x2 d, where η1 &amp; η2 refer to the dynamic viscosities of the two pure liquids 1 and 2 whose mole fractions in the mixtures are x1 &amp; x2 respectively. The values of d indicate the existence of specific interaction of ATC with benzene, toluene, p-xylene and acetone. The viscosity data have been analysed in the light of absolute reaction rate and free volume theories of liquid viscosity.

Correlation of thermal and spectral properties of chromium(III) picolinate complex and kinetic study of its thermal degradation

Chromium(III) picolinate complex, namely [Cr(pic)3]·H2O, was prepared and characterized by the methods of the elemental analysis, infrared spectroscopy, X-ray diffraction, and thermal analysis (TG/DTG, DTA). The correlation of the thermal and spectral properties of the complex with its structure is discussed in the study. The correlation of the spectral data with the structure leads to the accord, and coherence was found between thermal properties and structure of the complex for both steps of the thermal decomposition (dehydration and pyrolysis of organic ligand). Activation parameters were evaluated using the theory of absolute reaction rate.

Observation of the isotope effect in sub-kelvin reactions

Quantum phenomena in the translational motion of reactants, which are usually negligible at room temperature, can dominate reaction dynamics at low temperatures. In such cold conditions, even the weak centrifugal force is enough to create a potential barrier that keeps reactants separated. However, reactions may still proceed through tunnelling because, at low temperatures, wave-like properties become important. At certain de Broglie wavelengths, the colliding particles can become trapped in long-lived metastable scattering states, leading to sharp increases in the total reaction rate. Here, we show that these metastable states are responsible for a dramatic, order-of-magnitude-strong, quantum kinetic isotope effect by measuring the absolute Penning ionization reaction rates between hydrogen isotopologues and metastable helium down to 0.01 K. We demonstrate that measurements of a single isotope are insufficient to constrain ab initio calculations, making the kinetic isotope effect in the cold regime necessary to remove ambiguity among possible potential energy surfaces.

VOLUMETRIC PROPERTIES AND VISCOSITIES OF ACETIC ACID WITH ETHYLENE GLYCOL AND DIETHYLENE GLYCOL AT TEMPERATURES FROM 303.15 TO 323.15 K

Densities and viscosities of the binary mixtures of acetic acid with ethylene glycol and diethylene glycol were measured over the entire range of composition at five temperatures T = 303.15, 308.15, 313.15, 318.15, and 323.15 K. The excess molar volumes and viscosity deviations were calculated and fitted to the Redlich-Kister type polynomial equation. The viscosity data reported herein were used to examine the modeling capabilities of viscosity equations based on Eyring's absolute reaction rate theory and excess Gibbs free energy functions, namely, the Eyring-Van Laar, the Eyring-Scatchard and Hamer, and the Eyring-UNIQUAC equations. Some one-parameter models such as the Fang and He equation and the Grunberg and Nissan equation were also tested.

Modeling alumina atomic layer deposition reaction kinetics during the trimethylaluminum exposure

A model describing the reaction kinetics and surface species dynamics for trimethylaluminum (TMA) half-reactions of alumina atomic layer deposition (ALD) is presented. The model is based on reaction energetics data taken from published quantum chemical computational studies; these data are used to determine kinetic parameters using statistical thermodynamics and absolute reaction rate theory. Four TMA half-reactions were modeled to account for TMA adsorption and subsequent reaction on a range of growth surfaces spanning bare to fully hydroxylated states. By coupling the reaction rate models with surface species conservation equations, we create a dynamic model useful for examining the relative rates of completing surface reactions. Numerical simulations performed with the model reveal that it is a combination of TMA adsorption on hydroxylated and bare surface oxygen sites that produces Al adsorption rates comparable with those found for saturating ALD growth of alumina.

Validation of absolute axial neutron flux distribution calculations with MCNP with 197Au(n,γ)198Au reaction rate distribution measurements at the JSI TRIGA Mark II reactor

The calculation of axial neutron flux distributions with the MCNP code at the JSI TRIGA Mark II reactor has been validated with experimental measurements of the 197Au(n,γ)198Au reaction rate. The calculated absolute reaction rate values, scaled according to the reactor power and corrected for the flux redistribution effect, are in good agreement with the experimental results. The effect of different cross-section libraries on the calculations has been investigated and shown to be minor.

Free radical destruction of haloacetamides in aqueous solution

Haloacetamides are disinfection byproducts (DBPs) formed through chlorine/chloramine disinfection processes in drinking waters and have been recently highlighted in the US national Reconnaissance Survey. These species occur at low concentrations, but have been determined to have high cytotoxicity and mutagenicity and therefore may represent a human health hazard. Advanced oxidation/reduction processes (AO/RPs) which utilize free radical reactions are new alternatives to degrade these species. This study reports the absolute bimolecular reaction rate constants for 12 haloacetamides with •OH radical and hydrated electron. The •OH radical reaction rates varied from 5.18 × 107 to 1.14 × 1010 M−1 s−1, and hydrated electron reaction rates varied from 5.00 × 109 to 3.64 × 1010 M−1 s−1. Results obtained using an ion chromatograph indicated that ARPs are suitable for dehaloliazation of haloacetamides. These data are required for both evaluating AO/RPs for the destruction of these compounds and for studies of their fate and transport in surface waters where radical chemistry may be important in assessing their lifetime.

Dynamic Modeling for the Design and Cyclic Operation of an Atomic Layer Deposition (ALD) Reactor

A laboratory-scale atomic layer deposition (ALD) reactor system model is derived for alumina deposition using trimethylaluminum and water as precursors. Model components describing the precursor thermophysical properties, reactor-scale gas-phase dynamics and surface reaction kinetics derived from absolute reaction rate theory are integrated to simulate the complete reactor system. Limit-cycle solutions defining continuous cyclic ALD reactor operation are computed with a fixed point algorithm based on collocation discretization in time, resulting in an unambiguous definition of film growth-per-cycle (gpc). A key finding of this study is that unintended chemical vapor deposition conditions can mask regions of operation that would otherwise correspond to ideal saturating ALD operation. The use of the simulator for assisting in process design decisions is presented.

Proton transfer and complex formation of angiotensin I ions with gaseous molecules at various temperature

Proton transfer reactions of angiotensin I ions for +2 charge state, [M+2H]2+, to primary, secondary and aromatic amines were examined in the gas phase. Absolute reaction rate constants for proton transfer were determined from intensities of parent and product ions in the mass spectra. Temperature dependence of the reaction rate constants was measured. Remarkable change was observed for distribution of product ions and reaction rate constants. Proton transfer reaction was enhanced or reduced by complex formation of [M+2H]2+ with gaseous molecules. The results relate to conformation changes of [M+2H]2+ with change of temperature, which are induced by complex formation and or by thermal collision with He. Proton transfer reactions of angiotensin I ions for +3 charge state, [M+3H]3+, were also studied. The reaction rates did not depend on temperature so definitely.

Local Composition Based Maxwell–Stefan Diffusivity Model for Binary Liquid Systems

A new model for predicting Maxwell–Stefan diffusivity of binary mixture is developed based on the local composition concept and Eyring’s Absolute reaction rate theory. The proposed model, extended from the Vignes equation, can predict the mutual diffusion coefficient based on the diffusivities at infinite dilution and the local volume fractions calculated by Wilson model. Diffusivities of nine binary systems are used to compare the proposed model with three available models. The diffusivities of five systems among the nine are measured experimentally in the present work with digital holographic interferometry. The comparison showed that this model was superior to the Vignes model for all systems and competed well with the other models.

Arrhenius And Absolute Reaction Rate Models for Thermodynamic Characterization of Linamarase (Β-Glucosidase) using Linamarin Substrate

Thermodynamic characterization of linamarase (β-glucosidase)influenced by linamarin substrate purification, pH and temperature were investigated. In the study, recombinant Saccharomyces cerevisiae cells at the stationary phase of growth were recovered, homogenized and centrifuged to obtain crude extracts designated as GELIN0. Carboxy methyl cellulose, diethyl amino-ethyl-sephadex and diethyl amino-ethyl-cellulose were used to purify the crude extracts resulting in GELIN1, GELIN2 and GELIN3, respectively. Commercial native linamarase (CNLIN) was purchased and used as control. The ability of the GELIN extracts(β-glucosidase) and the commercial native linamarase (CNLIN) to hydrolyse cyanogenic glucosides was challenged using linamarin extracted from cassava as substrates. Degradation of linamarin was evaluated at optimum pH 6.8 using a 4 × 6 × 8 between and within factorial design comprising of 4 enzyme types (GELIN0, GELIN1, GELIN2 and GELIN3), and 6 temperatures (25, 27, 29, 31, 33, 35 oC, respectively) and 8 time intervals (0, 10, 20, 30, 40, 50, 60 and 70 min.). Data obtained from residual hydrocyanic acid with time were fitted with zero, first and second order kinetics, respectively, to determine the best fit order (based on r2 and linearity). Arrhenius and absolute reaction rate models were applied to obtain activation energies (Ea), frequency factor (K0) and enthalpy (ΔH#), entropy (ΔS#), respectively, that characterized the reactions. The results indicated that the degradation of linamarin by GELIN at the optimum pH 6.8 was best described by first order kinetics, Arrhenius and absolute reaction rate models showing high coefficient of linear regression (r2&gt;0.996) with reaction rate constant increasing from 0.0252 -0.0923 min-1 with enzyme purification ranging for GELIN0 – GELIN3. Frequency factor (Ko), Ea, ΔH# and ΔS# values decreased with enzyme purification. Activation energy (Ea) values for the degradation of linamarin (GELIN0 – GELIN3) ranged from 60.9 to 91.7 kJ/mol. Enthalpy values varied from 58 to 89 kJ/mol while ΔS# values varied from -92.8 to 4.1 J/mol. deg.) indicating spontaneous and irreversible degradation reactions which suggest a possible use of the purified linamarase (β-glucosidase) in detoxification process for foods containing linamarin.Keywords: purified linamarase, rate models, linamarin, Saccharomyces cerevisiae, cassava

Radiation chemistry of salicylic and methyl substituted salicylic acids: Models for the radiation chemistry of pharmaceutical compounds

Salicylic acid and its derivatives are components of many medications and moieties found in numerous pharmaceutical compounds. They have been used as models for various pharmaceutical compounds in pharmacological studies, for the treatment of pharmaceuticals and personal care products (PPCPs), and, reactions with natural organic matter (NOM). In this study, the radiation chemistry of benzoic acid, salicylic acid and four methyl substituted salicylic acids (MSA) is reported. The absolute bimolecular reaction rate constants for hydroxyl radical reaction with benzoic and salicylic acids as well as 3-methyl-, 4-methyl-, 5-methyl-, and 6-methyl-salicylic acid were determined (5.86±0.54)×109, (1.07±0.07)×1010, (7.48±0.17)×109, (7.31±0.29)×109, (5.47±0.25)×109, (6.94±0.10)×109 (M−1s−1), respectively. The hydrated electron reaction rate constants were measured (3.02±0.10)×109, (8.98±0.27)×109, (5.39±0.21)×109, (4.33±0.17)×109, (4.72±0.15)×109, (1.42±0.02)×109 (M−1s−1), respectively. The transient absorption spectra for the six model compounds were examined and their role as model compounds for the radiation chemistry of pharmaceuticals investigated.