Rate Constants For Formation Research Articles

Kinetics and Mechanism of Alcohol Dehydration on γ-Al2O3: Effects of Carbon Chain Length and Substitution

Steady-state rates of ether formation from alcohols (1-propanol, 2-propanol, and isobutanol) on γ-Al2O3 at 488 K increase at low alcohol pressure (0.1–4.2 kPa) but asymptotically converge to different values, inversely proportional to water pressure, at high alcohol pressure (4.2–7.2 kPa). This observed inhibition of etherification rates for C2–C4 alcohols on γ-Al2O3 by water is mechanistically explained by the inhibiting effect of surface trimers composed of two alcohol molecules and one water molecule. Unimolecular dehydration of C3–C4 alcohols follows the same mechanism as that for ethanol and involves inhibition by dimers. Deuterated alcohols show a primary kinetic isotope effect for unimolecular dehydration, implicating cleavage of a C–H bond (such as the Cβ–H bond) in the rate-determining step for olefin formation on γ-Al2O3. Bimolecular dehydration does not show a kinetic isotope effect with deuterated alcohols, implying that C–O or Al–O bond cleavage is the rate-determining step for ether formation. The amount of adsorbed pyridine estimated by in situ titration to completely inhibit ether formation on γ-Al2O3 shows that the number of sites available for bimolecular dehydration reactions is the same for different alcohols, irrespective of the carbon chain length and substitution. 2-Propanol has the highest rate constant for unimolecular dehydration among studied alcohols, demonstrating that stability of the carbocation-like transition state is the primary factor in determining rates of unimolecular dehydration which concomitantly results in high selectivity to the olefin. 1-Propanol and isobutanol have olefin formation rate constants higher than that of ethanol, indicating that olefin formation is also affected by carbon chain length. Isobutanol has the lowest rate constant for bimolecular dehydration because of steric factors. These results implicate the formation and importance of di- and trimeric species in low-temperature dehydration reactions of alcohols and demonstrate the critical role of substitution and carbon chain length in determining selectivity in parallel unimolecular and bimolecular dehydration reactions.

Interactions between a series of pyrene end-labeled poly(ethylene oxide)s and sodium dodecyl sulfate in aqueous solution probed by fluorescence.

The interactions between a series of poly(ethylene oxide)s covalently labeled at both ends with pyrene pendants (PEO(X)-Py2, where X represents the number-average molecular weight of the PEO chains and equals 2K, 5K, 10K, and 16.5K) and an ionic surfactant, namely, sodium dodecyl sulfate (SDS), in water were investigated at a fixed pyrene concentration of 2.5 μM corresponding to polymer concentrations smaller than 21 mg/L and with an SDS concentration range between 5 × 10(-6) and 0.02 M, thus encompassing the 8 mM critical micelle concentration (CMC) of SDS in water. The steady-state fluorescence spectra showed that the I1/I3 ratio decreased from 1.73 ± 0.06 for SDS concentration smaller than 2 mM where pyrene was exposed to water to 1.43 ± 0.03 for SDS concentration greater than 6 mM where pyrene was incorporated inside SDS micelles. The ratio of excimer-to-monomer emission intensities (the IE/IM ratio) of all PEO(X)-Py2 samples remained constant at low SDS concentrations, then increased, passed through a maximum at the same SDS concentration of 4 mM before decreasing to a plateau value that is close to zero for PEO(10K)-Py2 and PEO(16.5K)-Py2 but nonzero for PEO(2K)-Py2 and PEO(5K)-Py2. The pyrene end groups of these two latter samples could not bridge two different micelles due to the short PEO chain, and excimer was formed by intramolecular diffusion inside the same SDS micelle. Time-resolved fluorescence decays of the pyrene monomer and excimer of the PEO(X)-Py2 samples were acquired at various SDS concentrations and globally fitted according to the "Model Free" analysis over the entire range of SDS concentration. The molar fractions of various excited pyrene species and the rate constant of pyrene excimer formation retrieved from the analysis of fluorescence decays were obtained as a function of SDS concentration. Interactions between SDS and PEO could not be detected by isothermal titration calorimetry, potentiometry with a surfactant selective electrode, and conductance measurements.

Kinetic size-exclusion chromatography with mass spectrometry detection: an approach for solution-based label-free kinetic analysis of protein-small molecule interactions.

Studying the kinetics of reversible protein-small molecule binding is a major challenge. The available approaches require that either the small molecule or the protein be modified by labeling or immobilization on a surface. Not only can such modifications be difficult to do but also they can drastically affect the kinetic parameters of the interaction. To solve this problem, we present kinetic size-exclusion chromatography with mass spectrometry detection (KSEC-MS), a solution-based label-free approach. KSEC-MS utilizes the ability of size-exclusion chromatography (SEC) to separate any small molecule from any protein-small molecule complex without immobilization and the ability of mass spectrometry (MS) to detect a small molecule without a label. The rate constants of complex formation and dissociation are deconvoluted from the temporal pattern of small molecule elution measured with MS at the exit from the SEC column. This work describes the concept of KSEC-MS and proves it in principle by measuring the rate constants of interaction between carbonic anhydrase and acetazolamide.

Kinetics of Aminocarbyne Formation on Pt(111)

The kinetics of aminocarbyne (CNH2) formation from coadsorbed CN and H on Pt(111) was studied in the temperature range of 220 to 235 K by monitoring the time-dependent increase in the δ(NH2) mode of CNH2 at 1566 cm–1 with reflection absorption infrared spectroscopy (RAIRS). The surface was exposed using a directed-gas doser to 0.05 L of HCN, which immediately dissociates in the temperature range studied to deposit CN and H on the surface. A peak observed at 3348 cm–1 is assigned to the CNH intermediate. A simple model with rate constants for CNH formation, CNH decomposition, and CNH2 formation was used to analyze the experimental time-dependent coverages of CNH2. A modified model in which hydrogen was assumed to diffuse rapidly over the surface to occupy all available sites as the reaction proceeded was also used to obtain the three rate constants. From the temperature dependence of these rate constants and fits to Arrhenius plots, activation energies of 0.26, 0.22, and 0.41 eV for CNH formation, CNH diss...

Molecular Catalysis of H2 Evolution: Diagnosing Heterolytic versus Homolytic Pathways

Molecular catalysis of H2 production from the electrochemical reduction of acids by transition-metal complexes is one of the key issues of modern energy challenges. The question of whether it proceeds heterolytically (through reaction of an initially formed metal hydride with the acid) or homolytically (through symmetrical coupling of two molecules of hydride) has to date received inconclusive answers for a quite simple reason: the theoretical bases for criteria allowing the distinction between homolytic and heterolytic pathways in nondestructive methods such as cyclic voltammetry have been lacking heretofore. They are provided here, allowing the distinction between the two pathways. The theoretical predictions and the diagnosing strategy are illustrated by catalysis of the reduction of phenol, acetic acid, and protonated triethylamine by electrogenerated iron(0) tetraphenylporphyrin. Rather than being an intrinsic property of the catalytic system, the occurrence of either a heterolytic or a homolytic pathway results from their competition as a function of the concentrations of acid and catalyst and the rate constants for hydride formation and H2 evolution by hydride protonation or dimerization.

Influence of ligand lipophilicity on the NO-donating ability of the binuclear tetranitrosyl iron complexes in an erythrocyte suspension

The kinetics of nitric oxide release by representatives of a new class of synthetic nitric oxide donors, binuclear tetranitrosyl iron complexes (B-TNIC) with a structure of [Fe2(SR)2(NO)4], where R is pyrimidin-2-yl, 1-methylimidazol-2-yl, benzothiazol-2-yl, cysteamine, and penicillamine, was studied under the conditions simulating the blood vessel internal environment, when an erythrocyte suspension was used as a natural trap of nitric oxide. The apparent firstorder rate constants for intraerythrocyte methemoglobin formation were determined on the basis of the kinetic data. The NO-donating ability of B-TNIC was estimated from the values of these rate constants. It is assumed that the rate for the hydrolytic decomposition of B-TNIC decreases in the presence of erythrocytes due to binding of the complexes with the cell surface, leading to the restriction of their contact with an aqueous medium. Nitric oxide donating by the complex bearing penicillamine as a ligand is stoichiometric and independent of the presence of erythrocytes. This can be due to high hydrophilicity of this complex determined from the criterion of partition coefficient in an octanol-water system. This evidently provides a high level of solvation of the complex in an aqueous medium that prevents its binding with the erythrocyte surface.

Analysis of factors affecting luminescence decays: Concentration distribution of excited molecules in the reaction cell

An explicit method for calculating the spatial distribution of excited species in the reaction cell is presented. This method is used to analyze the relation between experimental conditions (excitation wavelength, ground state concentration, and laser intensity) and the observed luminescence decays (and the corresponding reaction kinetics) in both transient emission and transient absorption pulse laser photolysis experiments. Subsequently, the analysis was applied to the experimental conditions of previously extensively studied pyrene excimer formation in cyclohexane (J.B. Birks, Photophysics of Aromatic Molecules, Wiley-Interscience, London, 1970) and significantly different data were obtained in the redesigned experiment; the excimer formation and decay rate constants at 23.5°C were found to be (4.77±0.04)×109M−1s−1 and (2.07±0.01)×107s−1, respectively. Most importantly, the excimer dissociation into a singlet excited pyrene and ground state pyrene was found to be negligible, which is an important result that crucially affects the data processing in many previous and current applications of excimer formation.

Pharmacokinetic and pharmacogenomic modelling of the CYP3A activity marker 4β-hydroxycholesterol during efavirenz treatment and efavirenz/rifampicin co-treatment.

To assess the effect of the major efavirenz metabolizing enzyme (CYP2B6) genotype and the effects of rifampicin co-treatment on induction of CYP3A by efavirenz. Two study arms (arm 1, n = 41 and arm 2, n = 21) were recruited into this study. In arm 1, cholesterol and 4β-hydroxycholesterol were measured in HIV treatment-naive patients at baseline and then at 4 and 16 weeks after initiation of efavirenz-based antiretroviral therapy. In arm 2, cholesterol and 4β-hydroxycholesterol were measured among patients taking efavirenz during rifampicin-based tuberculosis (TB) treatment (efavirenz/rifampicin) just before completion of TB treatment and then serially following completion of TB treatment (efavirenz alone). Non-linear mixed-effect modelling was performed. A one-compartment, enzyme turnover model described 4β-hydroxycholesterol kinetics adequately. Efavirenz treatment in arm 1 resulted in 1.74 (relative standard error = 15%), 3.3 (relative standard error = 33.1%) and 4.0 (relative standard error = 37.1%) average fold induction of CYP3A for extensive (CYP2B6*1/*1), intermediate (CYP2B6*1/*6) and slow (CYP2B6*6/*6) efavirenz metabolizers, respectively. The rate constant of 4β-hydroxycholesterol formation [mean (95% CI)] just before completion of TB treatment [efavirenz/rifampicin co-treatment, 7.40 × 10(-7) h(-1) (5.5 × 10(-7)-1.0 × 10(-6))] was significantly higher than that calculated 8 weeks after completion [efavirenz alone, 4.50 × 10(-7) h(-1) (4.40 × 10(-7)-4.52 × 10(-7))]. The CYP3A induction dropped to 62% of its maximum by week 8 of completion. Our results indicate that efavirenz induction of CYP3A is influenced by CYP2B6 genetic polymorphisms and that efavirenz/rifampicin co-treatment results in higher induction than efavirenz alone.

Concentrating orange juice through CO2 clathrate hydrate technology

A novel separation process was developed for orange juice concentration via CO2 hydrate formation. The CO2 hydrate equilibrium conditions were measured by an isochoric pressure search method. The effects of feed pressure, temperature, juice volume, and stirring speed on dehydration ratio were investigated. The dehydration ratio increased with increasing the feed pressure; the maximum dehydration ratio of 57.2% was reached at feed pressure of 4.10MPa; dehydration ratio maintained around 45.8% in the temperature range of 274.8–279.8K; the optimum orange juice volume is 80mL. The CO2 hydrate formation rate constants increased from 0.67×10−8 to 1.91×10−8mol2/(sJ) in relation to the feed pressure increasing from 1.96 to 4.10MPa. The results demonstrated that removal of water by formation of CO2 hydrate is an efficient technology for orange juice concentration.

Restriction enzyme Ecl18kI-induced DNA looping dynamics by single-molecule FRET.

Many type II restriction endonucleases require binding of two copies of a recognition site for efficient DNA cleavage. Simultaneous interaction of the enzyme with two DNA sites results in DNA loop formation. It was demonstrated with the tethered particle motion technique that such looping is a dynamic process where a DNA loop is repeatedly formed and disrupted. Here we use a better and in the context of protein-induced DNA looping virtually unexploited strategy of single-molecule Förster resonance energy transfer of surface immobilized biomolecules to quantitatively study the dynamics of Ecl18kI endonuclease-induced DNA looping and determine the rate constants of loop formation and disruption. We show that two DNA-bound Ecl18kI dimers efficiently form a bridging tetramer looping out intervening DNA with a rate that is only a few orders of magnitude lower than the diffusion limited rate. On the other hand, the existence of Ecl18kI tetramer is only transient, and the loop is rapidly disrupted within about 1 s.

Formation of monochloropropane-1,2-diol and its esters in biscuits during baking.

The formation of free monochloropropane-1,2-diol (3-MCPD and 2-MCPD) and its esters (bound-MCPD) was investigated in biscuits baked with various time and temperature combinations. The effect of salt as a source of chloride on the formation of these processing contaminants was also determined. Kinetic examination of the data indicated that an increasing baking temperature led to an increase in the reaction rate constants for 3-MCPD, 2-MCPD, and bound-MCPD. The activation energies of formation of 3-MCPD and 2-MCPD were found to be 29 kJ mol(-1). Eliminating salt from the recipe decreased 3-MCPD and 2-MCPD formation rate constants in biscuits by 57.5 and 85.4%, respectively. In addition, there was no formation of bound-MCPD in biscuits during baking without salt. Therefore, lowering the thermal load or limiting the chloride concentration should be considered a means of reducing or eliminating the formation of these contaminants in biscuits. Different refined oils were also used in the recipe to test their effect on the occurrence of free MCPD and its esters in biscuits. Besides the baking process, the results also confirmed the role of refined oil in the final concentration of these contaminants in biscuits.

Mechanistic and kinetic study on the ozonolysis of 2,4-hexadienedial

The formation and unimolecular reactions of primary ozonides and carbonyl oxides arising from the O3-initiated reactions of 2,4-hexadienedial (HDE) have been investigated using the density functional theory and ab initio method. The activation energies of O3 cycloaddition to the >C=C C=O bonds of HDE for the formation primary ozonides (POZ1 and POZ2) are 4.79 and 21.37 kcal mol−1, respectively, implying that the initial O3 to the >C=C C=C C=O bonds of HDE more difficult than to >C=C C=O bond of formaldehyde. The largest rate constants of OH formation and dioxirane formation in the unimolecular reactions of carbonyl oxides are 6.13 × 10−4 and 7.93 × 10−1 s−1 at 300 K, respectively. The dioxirane is main product in the unimolecular reaction of the carbonyl oxides arising from the O3-initiated reaction of HDE.

The effect of sodium cation concentration on the electrochemical reduction of copper(I) thiosulfate complexes

The electrochemical behavior of copper(I) thiosulfate complexes from aqueous solutions containing different amounts of sodium perchlorate NaClO4 is studied by the methods of hydrodynamic voltammetry and potentiometry with a Na+-selective electrode. The electrochemical reaction orders p with respect to Na+ cations are determined from the dependences of exchange currents and direct reaction currents at fixed potential on the equilibrium concentration of Na+ cations. The reaction order p is close to 1 in the Na+ concentration range of 0.06–0.12 M and drops to zero for \(c_{Na^ + } \) > 0.12 M. The ion pair (IP) {Na[Cu(S2O3)2]}2− the formation of which precedes the electron transfer reaction is the electrochemically active species for the reduction of copper(I) thiosulfate complexes. The stability constant of IP is determined (K = 27.0 ± 2.4) as well as the rate constants of IP formation and decomposition.

Entry of Cell-Penetrating Peptide Transportan 10 into a Single Vesicle by Translocating Across Lipid Membrane and Its Induced Pores

The cell-penetrating peptide, transportan 10 (TP10), can translocate across the plasma membrane of living cells and thus can be used for the intracellular delivery of biological cargo such as proteins. However, the mechanisms underlying its translocation and the delivery of large cargo remain unclear. In this report we investigated the entry of TP10 into a single giant unilamellar vesicle (GUV) and the TP10-induced leakage of fluorescent probes using the single GUV method. GUVs of 20% dioleoylphosphatidylglycerol (DOPG)/80% dioleoylphosphatidylcholine (DOPC) were prepared, and they contained a water-soluble fluorescent dye, Alexa Fluor 647 hydrazide (AF647), and smaller vesicles composed of 20% DOPG/80% DOPC. The interaction of carboxyfluorescein (CF)-labeled TP10 (CF-TP10) with these loaded GUVs was investigated using confocal microscopy. The fluorescence intensity of the GUV membrane increased with time to a saturated value, then the fluorescence intensity due to the membranes of the smaller vesicles inside the GUV increased prior to leakage of AF647. This result indicates that CF-TP10 entered the GUV from the outside by translocating across the lipid membrane before CF-TP10-induced pore formation. The rate constant of TP10-induced pore formation in lipid membranes increased with an increase in TP10 concentration. Large molecules such as Texas Red Dextran 40,000, and vesicles with a diameter of 1-2 μm, permeated through the TP10-induced pores or local rupture in the lipid membrane. These results provide the first direct experimental evidence that TP10 can deliver large cargo through lipid membranes, without the need for special transport mechanisms such as those found in cells.

Deprotonation Kinetics of 1-Methylguanine After One-Electron Oxidation

Among the four natural DNA bases, guanine (G) is the most sensitive to oxidation due to its lowest oxidation potential. When G base is oxidized to guanine cation radical (G(+center dot)), it will deprotonate from both the imino proton N-1-H and the amino proton N-2-H. According to the pKa values for N-1-H and N-2-H deprotonation, the main deprotonation site in G base is N-1-H which would interfere with the N-2-H deprotonation, making the kinetics of N-2-H deprotonation difficult to be measured. Herein, the N-2-H deprotonation kinetics is investigated using 1-methylguanosine (mG), where N-1-H is substituted by methyl group to avoid the N-1-H deprotonation and N-9-H is substituted by ribose to ensure enough solubility of methylguanine in water, by nanosecond transient absorption (ns-TA) spectroscopy. By 355 nm photolysis of Na2S2O8, the highly oxidizing radical SO4-center dot is generated, which will oxidize mG to mG(+center dot) instantaneously. The time-resolved absorption spectra obtained for reaction of mG with SO4-center dot exhibits transient absorptions for mG(N-2-H)(center dot) featured by absorption band at 600 nm, indicating that the mG(+center dot) deprotonation product is mG(N-2-H)(center dot) and the deprotonation site is therefore validated to be N-2-H. The mG concentration dependence of mG(N-2-H)(center dot) formation rate constant is assessed through changing the mG concentration from 0.25 mmol.L-1 to 5 mmol.L-1. The concentration dependence experiment reveals that the rate-limiting step to form mG(N-2-H)(center dot) is the bimolecular reaction of mG with SO4-center dot when mG concentration is lower than 2 mmol.L-1 and the bimolecular reaction rate constant to form mG(+center dot) is (3.7 +/- 0.1)x10(9) L.mol(-1).s(-1); when mG concentration is above 2 mmol.L-1, the rate-limiting step to form mG(N-2-H)(center dot) is the first-order mG(+center dot) deprotonation and the N-2-H deprotonation rate constant is (7.1 +/- 0.2) x 10(6) s(-1). Furthermore, the N-2-H deprotonation rate constant is measured at different temperatures varying from 278 K to 298 K. According to Arrhenius equation, the activation energy barrier for the N-2-H deprotonation is determined to be 19.9 +/- 1.0 kJ.mol(-1). These results can provide valuable kinetic information on the oxidative damage of DNA.

Kinetics of DNA duplex formation: A-tracts versus AT-tracts.

The hybridisation and melting of DNA strands are critical steps in many biological processes, but still a deeper understanding of the kinetics is lacking. This is evident from the absence of a clear correlation between rate constants for duplex formation and the number of bases in the strand or the sequence. Here we have probed differences between formation times of A-tracts and AT-tracts by studying complementary model strands mainly comprised of adenine (A) and thymine (T) in stopped-flow (SF) experiments. These strands are relevant as DNA replication begins in regions with a large number of AT base pairs. Interpretation of our results is aided by secondary-structure modelling where both the fractions of the different types of structures and the number of paired bases in the lowest-energy ones are determined. The model is based on calculation of free energies using fixed values for enthalpies and entropies associated with base pairing and a stochastic sampling of the possible structures. We find that the strand length affects rates: the activation energy for the formation of short (16-base pairs) A-tracts is larger than that for longer ones (20-base pairs). Activation energies for the formation of AT-tracts are an order of magnitude larger, and larger for shorter strands than for long ones. These higher activation energies are in agreement with the fact that the fraction of unpaired bases in the constituent AT-tract strands is less than in those which comprise the A-tracts. That the pre-structures of the single strands significantly affect rates is also used to rationalise the results obtained for two pairs of complementary 12-mer strands that have the same bases but in a different sequence; we report here similar activation energies as reported earlier and that these are strongly sequence dependent. Finally, we demonstrate that SF can be coupled with the measurement of circular dichroism (CD) in the vacuum ultraviolet (VUV) region, taking advantage of a synchrotron radiation facility, and that CD is useful to probe geometrical structures in the VUV where the absorption by DNA is high. Though this work is preliminary, our initial results suggest that the strands align prior to the formation of base pairs.

Lattice Oxygen Activity in Pr- and La-Doped CeO2for Low-Temperature Soot Oxidation

Effects of Pr- and La-doped CeO2 on desorption of active lattice oxygen to soot oxidation were studied. Thermogravimetric analysis under N2 flow indicated that, despite the decrease in reducible Ce content, the amount of oxygen deficiency increases with increasing La content (x) to 15 mol % in Ce0.80–xPr0.20LaxO2. In inert atmosphere, the introduction of oxygen vacancies by doping La increased the available lattice oxygen for desorption. In the oxygen isotopic exchange, under 18O2 flow, desorption of oxygen molecules containing lattice oxygen atom (16O) was favored because of Pr and La doping in CeO2. These dopants increase the exchange rate constant between gas-phase and lattice oxygen atoms. The apparent activation energy, derived from an Arrhenius plot, for CeO2, Ce0.80Pr0.20O2, and Ce0.65 Pr0.20La0.15O2 were 311, 230, and 135 kJ/mol, respectively. The values indicated that Pr and La doping causes facile oxygen exchange between the gas phase and the solid. The comparison of the rate constants for 16O18O formation under 18O2 flow and 18O2/16O2 mixture flow showed that lattice oxygen predominantly contributes to the exchange reaction. Surface exchange coefficient (k) and diffusion coefficient (D) were obtained by secondary ion mass spectrometry (SIMS) depth analysis of the oxides after diffusion annealing in 18O2. The values of both k and D increase by doping Pr and La, and the surface exchange coefficient value, k, especially increases significantly. Hence, Pr and La doping enhances the oxygen exchange with lattice oxygen, and so high soot oxidation activity at low temperature could be related to the increased contribution of lattice oxygen.

Kinetics of catalyst-free thermal and photo-oxidation of cumene

Kinetics of thermal and photo-oxidation of cumene in the absence of catalyst was studied using high-pressure differential scanning calorimetry and low-pressure photocalorimetry. Kinetics of oxidation was followed by cumene hydroperoxide (CHP), acetophenone, and phenol formation. The amount of CHP formed was deduced from the total heat of reaction of thermal degradation of CHP at 453 K and using a new gas chromatographic method. CHP solution in cumene oxidized at 453 K and 680 psi of oxygen reproducibly with the heat of reaction linearly dependent on peroxide concentration in cumene. It was confirmed that cumene thermal oxidation was slow at <453 K, but at ≥453 K could occur explosively. Autocatalysis by CHP during thermo-oxidation was confirmed. Apparent activation energy of the photo-oxidation of cumene was found to be E a = 22.3 kJ mol−1. The value corresponds to radical chain process of the cumene autoxidation. Under assumption of pseudo-first order reaction, the rate constant of CHP formation was found to change from k CHP ≈ 0.76 s−1 during the first 4 h of photo-oxidation to k CHP ≈ 0.2 s−1 at the later stages at 2.0 W cm−2 of UV exposure dose. It was established that the initial presence of the CHP in cumene does not change the photo-oxidation kinetics, but shifts the kinetic curve to earlier time. Finite difference method was employed to numerically model kinetics of cumene oxidation. The result indicated higher than expected thermal and photo-stability of both, cumene and CHP.

Clustering Chlorine Reactivity of Haloacetic Acid Precursors in Inland Lakes

Dissolved organic matter (DOM) represents the major pool of organic precursors for harmful disinfection byproducts, such as haloacetic acids (HAAs), formed during drinking water chlorination, but much of it remains molecularly uncharacterized. Knowledge of model precursors is thus a prerequisite for understanding the more complex whole water DOM. The utility of HAA formation potential data from model DOM precursors, however, is limited due to the lack of comparability to water samples. In this study, the formation kinetics of dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA), the two predominant HAA species, were delineated upon chlorination of seventeen model DOM precursors and sixty-eight inland lake water samples collected from the Upper Midwest region of the United States. Of particular interest was the finding that the DCAA and TCAA formation rate constants could be grouped into four statistically distinct clusters reflecting the core structural features of model DOM precursors (i.e., non-β-diketone aliphatics, β-diketone aliphatics, non-β-diketone phenolics, and β-diketone phenolics). A comparative approach built upon hierarchical cluster analysis was developed to gain further insight into the chlorine reactivity patterns of HAA precursors in inland lake waters as defined by the relative proximity to four model precursor clusters. This work highlights the potential for implementing an integrated kinetic-clustering approach to constrain the chlorine reactivity of DOM in source waters.

Amino acid salts for CO2 capture at flue gas temperatures

The amino acid salt potassium taurate has potential for use as a high-temperature absorbent for post-combustion CO2 capture, because of its low volatility and high absorption rate. In this study, the densities and viscosities of 2–6M taurate solution were determined over the temperature range of 293–353K. We found that the CO2 solubility of taurate solutions, measured using a stirred-cell reactor, is comparable to that of alkanolamines at high temperatures. The absorption rate of CO2 into CO2-free and CO2-loaded taurate solutions was determined using a wetted-wall column. The KG of 4M taurate at 353K is similar in magnitude to the KG of 7m monoethanolamine (MEA) at 313K. We also found that the KG of taurate decreased with increased CO2 loading, although the KG values of taurate solutions are still comparable to CO2-loaded 7m MEA solution. The reaction rate constant of taurate carbamate formation in this work agrees well with published values.