Competition Kinetics Method Research Articles

Thiol Oxidase Activity of Copper, Zinc Superoxide Dismutase Stimulates Bicarbonate-Dependent Peroxidase Activity via Formation of a Carbonate Radical

Here, we investigated the effect of bicarbonate anion (HCO3-) on the peroxidase activity stimulated by the thiol oxidase activity of copper, zinc superoxide dismutase (SOD1) using electron spin resonance (ESR) and optical techniques. Low temperature direct ESR revealed that cysteine (Cys) caused the reduction of copper(II) to copper(I) that was reoxidized by molecular oxygen to copper(II) at the active site of SOD1. The addition of HCO3- to aerobic incubations containing SOD1, Cys, and DTPA in phosphate buffer enhanced the peroxidase activity of SOD1, as measured by hydroxylation of cyclic nitrone spin traps, dichlorodihydrofluorescein oxidation to dichlorofluorescein, and oxidation of tyrosine to dityrosine. The addition of catalase inhibited the SOD1 peroxidase activity stimulated by the thiol oxidase actvity, implicating an intermediary role for H2O2 in SOD1/Cys/HCO3(-)-mediated oxidation and hydroxylation reactions. Using a competitive kinetic method, rate constants for the reaction between the oxidant formed in the SOD1/Cys/HCO3- system and selected inhibitors were measured. On the basis of these rate constants, we conclude that the thiol oxidase activity of SOD1 stimulates carbonate anion radical (CO3*-) formation in the presence of HCO3- and that the CO3*- formed in the SOD1/Cys/ HCO3- system is responsible for oxidation and hydroxylation reactions. Biological implications of this finding are discussed.

Hydroxyl free radical reactivity toward aqueous chlorinated phenols

Second-order kinetic constants (k(OH,S)) for the hydroxyl free radical attack on a series of nine chlorophenols (2-chlorophenol, 2,4-dichlorophenol, 2,5-dichlorophenol, 2,4,5-trichlorophenol, 2,4,6-trichlorophenol, 2,3,5,6-tetrachlorophenol, 2,3,4,5-tetrachlorophenol, 2,3,4,6-tetrachlorophenol, and pentachlorophenol) in aqueous solution were determined by means of the competitive kinetics method. Experimental values ranged from 3.5 x 10(09)M(-1)s(-1) for pentachlorophenol to 8.2 x 10(09)M(-1)s(-1) for 2-chlorophenol. A general trend of lower kinetic constant values with higher degree of chlorination was observed and tested with four different correlations using Hammett's sigma values, the number of chlorine substituents on the aromatic ring, and estimated diffusion coefficients. These correlations were statistically significant (alpha=0.01), although the regression coefficients were moderate (R(2)<0.6). Statistical analysis indicated that all correlations were equally valid. This report includes second-order kinetic constants not previously reported for six chlorophenols, and also provides the means to estimate constants for other chlorophenols for which no experimental data are available.

Studies on the spatial distribution of polymeric reagents in sonochemical reactions - application of competitive kinetics

Summary — Intense ultrasound may initiate chemical reactions in aqueous solutions. The reactivity is not uniform in the whole sonicated volume, but rather concentrated in the close vicinity of oscillating or collapsing gas bubbles formed by the action of ultrasound (cavitation bubbles). It has been shown that certain low-molecular-weight substrates, due to their partially hydrophobic properties, tend to accumulate at the surface of cavitation bubbles, thus being particularly susceptible to ultrasound-induced chemical reactions. In this paper, using an approach based on competition kinetics method, we demonstrate that this effect takes place also in the case of polymeric substrates. Relatively hydrophobic water-soluble polymer, poly(ethylene oxide), and its oligomer poly(ethylene glycol) accumulate in the close vicinity of the bubbles. Their local concentrations in these zones may be two orders of magnitude higher than the average concentration in solution. In contrast, such effect is observed neither for strongly hydrophilic polyelectrolyte chains exemplified by poly(acrylic acid), nor for dissociated sodium acetate used as a low-molecular-weight hydrophilic model. The ultrasound-induced processes employed in the competition kinetics study in this work were the reactions of substrates with hydroxyl radicals emerging from the cavitation bubbles. In order to provide quantitative comparison with a system of uniform reactivity distribution, the same reactions were studied using ionizing radiation for OH-radicals generation.

Kinetics of reactions of OH with organic carbonyl compounds in aqueous solution

The OH radical plays an important role in tropospheric chemistry. The OH radical is a very strong oxidant and its reactivity contributes to the atmospheric degradation of volatile organic compounds in aqueous solution. In this work the temperature dependencies of the rate constants for the reactions of OH with the following organic carbonyl compounds, (1) methyl ethyl ketone (MEK), (2) acetonylacetone, (3) isobutyraldehyde, (4) ethyl formate and (5) diacetyl are studied. By means of laser flash photolysis and applying a competition kinetics method the following Arrhenius expressions were obtained: The errors stated throughout this study are statistical errors for a confidence interval of 95%. Reaction mechanisms are discussed and Evans–Polanyi correlations are presented.

Redox behavior of transient species produced during pulse radiolysis of morpholine in aqueous solutions

Hydroxyl radical reactions with morpholine (MOR) in aqueous solution lead to the formation of both oxidizing and reducing radical species at alkaline (pH⩾9.8) and acidic/neutral (pH⩽7) solutions. Transient absorbance was generally quite weak. However, the absorbance of the species generated at pH 9.8 was more intense as compared to that obtained at pH 6.2. This may be due to p K a of the semi-oxidized species formed by H-abstraction from –CH 2– group beta to nitrogen, which was determined to be 7.8. The rate constants for OH radical reactions were determined by competition kinetics method using potassium thiocyanate (KCNS) as a reference solute and were found to be (1.0±0.05)×10 10 and (1.0±0.05)×10 9 dm 3 mol −1 s −1, respectively, at pH 9.8 and 6.2. Reactivity of the semi-oxidized species towards MV 2+ as well as ascorbic acid at both the pHs indicates the formation of two types of intermediates. The OH radical reaction appears to occur both at –NH– and –CH 2– sites. The rate constant for reaction of e aq − with MOR was determined from the decay of hydrated electron to be (2.0±0.4)×10 8 dm 3 mol −1 s −1 at pH 6.8 and <10 7 dm 3 mol −1 s −1 at pH 11.

Reaction of hydroxyl radicals with S-nitrosothiols: determination of rate constants and end product analysis

The reaction of the hydroxyl radical (.OH) with S-nitroso derivatives of cysteine, acetylcysteine and glutathione was studied at neutral and acidic pH. The second-order rate constants were determined by a competition kinetic method using a deoxyribose-thiobarbituric acid assay. The rate constants were diffusion controlled and were 2.27, 1.94 and 1.46 x 10(10) dm3 mol-1 s-1, for S-nitrosocysteine, S-nitrosoacetylcysteine and S-nitrosoglutathione respectively, at neutral pH. The major products of the degradation induced by .OH were found to be the corresponding disulfide (-S-S-) and nitrite (NO2-) at neutral pH as well as at pH 3. Simultaneous proton formation has also been observed. A plausible mechanism based on the formation of an intermediate thiol radical (RS.), as a result of electron transfer from the S-nitrosothiols (RSNOs) to .OH, is proposed for the formation of disulfide and nitrite at both pHs. The high rate constant values and the degradation of these compounds demonstrate the potential role of .OH in RSNO metabolism under physiological conditions.

Antioxidative Properties of Martynoside: Pulse Radiolysis and Laser Photolysis Study

Free radical reactions of Martynoside (MAR), a phenylpropanoid glycoside, with a variety of oxidants were studied in the aqueous solution by laser photolysis and pulse radiolysis techniques. The pKa value of MAR in aqueous solution was measured from the pH dependent changes of the UV absorption at 384 nm with value of pKa=9.2. The phenoxyl radical of MAR which exhibits maximum absorption at 360 nm was generated by one-electron transfer to N3• or Br2•-. Other important properties of phenoxyl radical such as extinction coefficient, formation and decay rate constants were also determined. The reaction rate constant of O2•- with MAR, k=8.5×104 dm3 · mol-1 · s-1, was measured by the method of competition kinetics. By measuring time-resolved luminescence emission at 1270 nm, the quenching rate constant of singlet oxygen by MAR was obtained to be 3.3×106 dm3 · mol-1 · s-1. Reduction potential of the MAR couple (MAR•/MAR), determined using rutin as reference compound, gave a value E=0.66 V vs. NHE. The antioxidative properties of MAR were compared with those of some well-known antioxidants.

The effect of the base in the fragmentation of nucleotide C4′ radicals

A series of 3′- O-diethylphosphoryl-4′-α-[(2-halophenylethylthio)carbonyl] substituted esters of thymidine, cytidine, adenosine and guanosine are prepared by total synthesis and used as C4′-radical precursors in a competition kinetic method using tributyltin hydride as the reductant. The pseudo-first order rate constants for the C4′-radicals so generated decrease in the order guansoine>cytidine>adenosine>thymidine with that for guanosine being too rapid for determination by the present competition kinetic method. A 119Sn NMR method is presented for estimation of the purity of tin hydride solutions.

Oxidation kinetics of phenolic and indolic compounds by ozone: applications to synthetic and real swine manure slurry

In this study, an oxidation model combining the mass transfer of ozone and ozonation kinetics was developed to predict the degradation of several phenolic and indolic compounds in a semi-batch reactor. The mass transfer and partition coefficients were calculated at various physical and chemical conditions. In addition, the reaction rate constants of ozone with phenolic and indolic compounds were also estimated independently using the method of competition kinetics and relative reaction-rate constants. Incorporating mass transfer and chemical reaction concepts, an oxidation model that considers side reactions between ozone and byproducts has been established using non-linear simultaneous differential equations. Thus, numerical computation is capable of simulating the degradation of phenolic and indolic compounds both in synthetic and real manure.

Reaction of the tamoxifen cation and the bis-(4-methoxyphenyl)methyl cation in aqueous solutions containing 2'-deoxyguanosine

The competition between 2'-deoxyguanosine (dG) and water has been quantitatively evaluated for the allylic carbocation derived from tamoxifen and for the stabilized diarylmethyl cation (bis-(4-methoxyphenyl)methyl). Both systems were examined by the competition kinetics method, in which the products were quantitatively analyzed after the SN1 solvolysis of the corresponding acetate esters in aqueous solutions containing the nucleoside. The principal product of the reaction of both cations with dG is the adduct at the NH2 group, a characteristic of delocalized carbocations. The tamoxifen cation was also examined by laser flash photolysis, with absolute rate constants for the reaction with dG and water being obtained and converted into rate constant ratios. The principal result of this study is that there is a three orders of magnitude difference in the reactivity of these cations towards the neutral form of dG and its conjugate base. Under acidic conditions where the reaction occurs with neutral dG, the guanine–water selectivity is low. Even at relatively high concentrations of dG, the majority of the product is alcohol derived from the water reaction. At pH 10 to 11, in contrast, dG is present as the anion and this is highly competitive. Yields of adduct as high as 90% can be attained. A consequence of the large difference in reactivities is that at neutral pH the majority of the reaction of the cation with dG is actually occurring via the small amount of conjugate base present. A further feature of the results is that the NH2 adduct is the predominant stable product from the anion. To explain the high rate constant for the reaction forming this product, a mechanism is proposed whereby one of the protons of the NH2 group is transferred to N1 as the N2-cation bond is forming.Key words: guanine, DNA adduct, carbocation, tamoxifen.

Advanced oxidation with ozone of 1,3,6‐naphthalenetrisulfonic acid in aqueous solution

AbstractThe kinetics of oxidation with ozone of 1,3,6‐naphthalenetrisulfonic acid was analysed by studying the influence of different experimental parameters such as the concentration of tert‐butyl alcohol (2‐methyl‐2‐propanol), initial concentration of the acid, pH, and temperature. The rate constant of the direct reaction at 25 °C was calculated (kD = 6.72 M−1s−1). The constant of the free radical reaction was determined with the competitive kinetics method, using sodium 4‐chlorobenzoate as reference compound, obtaining a value of kOH = 3.7 × 109 M−1s−1. It was demonstrated that even at very acid pH values, 80% of the 1,3,6‐naphthalenetrisulfonic acid was degraded by free radical reactions, so that the ozonation of this acid may be considered an advanced oxidation process.© 2002 Society of Chemical Industry

Radiation effect on poly ( p-sodium styrene sulphonate) of different degrees of polymerization in aqueous solution: pulse radiolysis and steady state study

Radiation induced effects on poly ( p-sodium styrene sulphonate) (PSSS) of two molecular weights, namely 10 6 and 70,000 in aqueous solution have been investigated by steady state and pulse radiolysis (PR) techniques. The reactions of primary radicals of water radiolysis such as OH radical, e aq −, H atom, some oxidizing radicals like N 3 , Cl 2 − and SO 4 − and reducing species like CO 2 − with PSSS have been investigated. The results indicate that the reactivity of these species towards PSSS is a function of molecular weight of PSSS. The absorption spectra of transient species produced when dilute aqueous solutions of PSSS of different molecular weights are subjected to pulse radiolysis have been compared. Rate constants for the reaction of OH radical and H atom with PSSS have been evaluated both by competition kinetics method and by direct observation of build up of transient species. The results indicate that OH radical and H atom react with PSSS in different ways. Near neutral pH, the OH radical reacts with substituted pendant aromatic ring of the PSSS to form an adduct, with a rate constant of 5.5×10 8 and 1.1×10 9 dm 3 mol −1 s −1 for PSSS of molecular weights 10 6 and 70,000, respectively. H atom on the other hand abstracts H atom from the PSSS backbone as well as forms an adduct by reacting with aromatic ring. The rate constant values for reaction of aqueous electron with PSSS were found to be 5×10 7 dm 3 mol −1 s −1 ( M w=10 6) and 2.2×10 8 dm 3 mol −1 s −1 ( M w=70,000). The anion formed did not transfer electron to methyl viologen in the pH range of 6–10.5. The viscosity of the aqueous PSSS solution decreases with irradiation, up to doses of 1000 kGy indicating degradation of PSSS in this dose range. The PSSS of higher molecular weight is more prone to degradation. The chain scission is a function of dose rate, concentration of polymer and ambient of irradiation. At doses beyond ∼2500 kGy there is a sharp increase in viscosity of the PSSS solutions till the solutions set to a soft, sticky gel mass. The gelation dose ( D gel) is a function of molecular weight of the polymer and initial polymer concentration. In the presence of crosslinking agent like N, N-methylene bis acrylamide, the gelation was faster for PSSS of higher molecular weight. Gelation was most efficient for 20% (w/w) polymer concentration.

Photochemical production of hydroxyl radical from aqueous iron(III)-hydroxy complex: determination of its reaction rate constants with some substituted benzenes using deoxyribose-thiobartituric acid assay.

Hydroxyl radical (OH) production, mediated by UV light, from aqueous ferric perchlorate was investigated at low pH using a deoxyribose-thiobarbituric acid (-TBA) assay. The rate of production of OH was found to be dependent on the irradiation time. Addition of suitable substrates such as substituted benzenes can compete for the reaction of OH with deoxyribose, leading to a decreased yield of TBA chromogen formed from the deoxyribose-TBA assay. The second-order rate constants of the added substrates can be determined from such a simple competition kinetic method. The second-order rate constants for the reaction of OH with a number of substituted benzenes were determined using this method and the values were compared with the reported rate constants using pulse radiolysis technique. The values determined using the present method (1 to 8 x 10(9) dm3/mols) are in good agreement with those reported by use of the pulse radiolysis technique. It is proposed that the photoproduction of OH from aqueous ferric perchlorate coupled with deoxyribose-TBA assay is a simple and efficient method for determination of rate constants for the reaction of OH with a variety of substituted benzenes that are known to be organic water contaminants.

OZONATION KINETICS OF PHENOLIC COMPOUNDS PRESENT IN TABLE OLIVE WASTEWATERS: p-HYDROXYBENZOIC ACID, TYROSOL AND p-COUMARIC ACID

A kinetic study of the degradation by ozone of three phenolic compounds present in table olive wastewaters and other agroindustrial wastewaters has been performed by using a competition kinetic method. The selected phenolic compounds were: p-hydroxybenzoic acid, p-coumaric acid and tyrosol. The influence of the operating variables (temperature and pH) is established and the stoichiometric ratios for the individual direct reactions between ozone and each compound are determined. Once the reaction rate constants were evaluated, they have been correlated as a function of temperature and pH into kinetic expressions which are provided for every phenolic compound. The global process occurs in the fast and pseudo first order kinetic regime of absorption, a condition required by the competition model to be used.

Oxidation of HMG‐CoA Reductase Inhibitors by tert‐Butoxyl and 1,1‐Diphenyl‐2‐picrylhydrazyl Radicals: Model Reactions for Predicting Oxidatively Sensitive Compounds During Preformulation

Hydrogen atom abstraction rate constants for the reaction of tert‐butoxyl and 1,1‐diphenyl‐2‐picrylhydrazyl (DPPH) radical with the HMG‐CoA reductase inhibitors lovastatin, simvastatin, and statins I–IV were measured. This series of diene‐containing drugs is known to be prone to oxidation. The tert‐butoxyl radical was generated by the thermolysis of di‐tert‐butylperoxyoxalate at 40 °C. A competitive kinetic method was used to determine the relative rate of hydrogen atom abstraction by tert‐butoxyl radical to β‐scission. The absolute rate constants were calculated using the experimentally determined product ratios of t‐butanol to acetone and the known rate of β‐scission of tert‐butoxyl radical. The rate constants for the reaction with DPPH radical were measured spectrophotometrically by monitoring the loss of DPPH radical as a function of substrate concentration. The rate constants correlate well with the structure of the molecules studied. These kinetic techniques allow for oxidatively sensitive compounds to be identified early in the drug development cycle. The tert‐butoxyl radical, a strong hydrogen atom abstractor, is representative of the hydroxyl ( · OH) and alkoxyl ( · OR) radicals; in contrast the DPPH radical, a much weaker radical, is a good kinetic model for hydroperoxyl ( · OOH) and peroxyl ( · OOR) radicals. These kinetic methods can be used to quantitatively assess the lability of drug candidates towards reaction with oxygen‐centered radicals at an early stage of development and facilitate the design of inhibiting strategies. © 2000 Wiley‐Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 89:1518–1524, 2000

Pesticide hydroxyl radical rate constants: Measurements and estimates of their importance in aquatic environments

Pesticide degradation by hydroxyl radicals produced in natural water is often cited as an important dissipation mechanism, yet its significance is rarely assessed with other dissipation processes occurring simultaneously in the aquatic environment. The computer model Exposure Analysis Modeling System (EXAMS) is useful for this purpose because it incorporates other dissipation processes and allows the assessment of their dynamics under different environmental conditions. Rate constants of reaction with photochemically generated hydroxyl radicals were measured for the herbicides sulfometuron, bensulfuron methyl, chlorsulfuron, triclopyr, dicamba, molinate, thiobencarb, 2,4-D, mecoprop, and oxadiazon, for the insecticides chlorpyrifos and imidacloprid, and for the fungicide chlorothalonil by competition kinetic methods and were used as the input value for second-order rate oxidation rate constant (KOX) in EXAMS. Hydroxyl radical degradation was estimated to be most significant in shallow water, where sunlight is less attenuated; however, in relatively clear water, it still could contribute to degradation at greater depths for compounds slowly degraded by other mechanisms. For carbaryl at shallow depths, degradation by hydroxyl radicals was predicted to contribute to less than 1% of the degradation profile at pH 8 to as much as 15% of the profile at pH 6. As unique degradation products may be generated by indirect photolysis mechanisms, it should be possible to use EXAMS to estimate when such products may occur for a particular chemical and environmental situation.

Oxidative degradation of triazine derivatives in aqueous medium: a radiation and photochemical study.

Pulse and steady state radiolysis techniques have been used to determine the bimolecular rate constants and to investigate the spectral nature of the intermediates and the degradation induced by hydroxyl radicals ((*)OH) with 1,3,5-triazine (T), 2,4, 6-trimethoxy-1,3,5-triazine (TMT), and 2,4-dioxohexahydro-1,3, 5-triazine (DHT) in aqueous medium. A competitive kinetic method with KSCN as the (*)OH scavenger was used to determine the rate constants for the reaction of (*)OH with T, TMT, and DHT. The bimolecular rate constants are 3.4 x 10(9), 2.06 x 10(8), and 1.61 x 10(9) dm(3) mol(-)(1) s(-)(1) respectively, for T, TMT, and DHT at pH approximately 6. The transient absorption spectra obtained from the reaction of (*)OH with T, TMT, and DHT have single absorption maxima at 320, 300, and 300 nm, respectively, and were found to undergo a second-order decay. The formation of TOH(*) [C(6)OH-N(5)-yl radical], TMTOH(*) [N(5)OH-C(6)-yl radical], and DHT(*) [C(6)-yl radical] is proposed from the initial attack of (*)OH with T, TMT, and DHT, respectively. A complete degradation of TMT (10(-3) mol dm(-3)) was obtained after absorbed doses of 5 kGy in N(2)O-saturated solutions and 16 kGy in aerated solutions. A similar degradation pattern was obtained with DHT in N(2)O-saturated solutions. Complete degradation was observed with an absorbed dose of 7 kGy. On the basis of the results from both pulse and steady state radiolysis, a possible reaction mechanism involving (*)OH-mediated oxidative degradation is proposed. A complete photodecomposition of DHT was also observed in the presence of ferric perchlorate using ultraviolet light at low pH. Photoinduced electron transfer between Fe(III) and DHT in the Fe(III)-DHT complex and subsequent formation of DHT(*) are proposed to be the major processes that lead to the complete degradation of DHT at pH 3.

A new method for measuring carbonate radical reactivity toward pesticides

AbstractThe carbonate radical is produced from the scavenging of the hydroxyl radical by carbonate/bicarbonate and is strongly electrophilic toward electron‐rich compounds such as aromatic amine and sulfur‐containing compounds. Carbonate radical reactivity (CO3⋅−) was measured by setting up a competition between a chemical of known reactivity and a compound with unknown reactivity toward CO3⋅−. The carbonate radical was produced using a novel method whereby KOONO (potassium peroxonitrite) was dissolved into 0.01 NaHCO3 solution initially producing a HO⋅, which was rapidly scavenged by HCO3⋅−, yielding CO3⋅− CO3⋅− production was monitored using a stopped‐flow spectrometer at the absorption band for CO3⋅− of 600 nm. Results using this competition kinetic method indicated the second‐order rate constants for substituted anilines corresponded to reference values with a relative error less than 10%. Using σpara+ values, the rate constants of substituted anilines at pH 9.0 correlated well (R2 = 0.98) with the Hammett equation yielding ρ = −0.89. To measure the reactivity of pesticides toward the carbonate radical, p‐nitroaniline (PNA) was selected as the standard competitor. Of the nine pesticides tested, fenthion was the most reactive, followed by phorate, with rate constants above 107/M/s. Fluometuron and atrazine were of intermediate reactivity, and methyl parathion was one of the least reactive.

Evaluation of reactivity of pesticides with ozone in water using the energies of frontier molecular orbitals

The rate constants of ozone with four groups of pesticides (4 phenolic-, 8 organonitrogen-, 8 phenoxyalkylacitic-, and 4 heterocyclic N-pesticides) were determined under controlled conditions at a pH of 7.5, ionic strength of ca 10 −3 M, and 100 μM NaHCO 3. The rate constant for BPMC was first determined from a pseudo-first order reaction model, the rate constants for the other pesticides were then obtained by a competition kinetic method using BPMC as the first reference compound. The rate constants were found to vary widely according to the pesticides. The highest rate constant was 27,600 M −1 s −1 for PCP and the lowest was 61.8 M −1 s −1 for cyanazine. In order to quantify the effects of structure on the reactivity of pesticide with ozone, for each group of pesticides the rate constants were correlated with the energies of the highest occupied molecular orbital ( ϵ HOMO). The logarithm of the rate constants was found to linearly increase with the increase of the ϵ HOMO values except for the phenoxyalkylacitic group. When all examined pesticides were included in the correlation analysis, the rate constants gave a statistically unsatisfactory correlation with a coefficient of 0.92, but showed a similar trend of increasing reactivity with increasing ϵ HOMO values of pesticides. The results of the correlation analysis suggested that the reactivity of pesticides with ozone follows the frontier orbital theory and can be estimated by ϵ HOMO. The rate constants for the phenoxyalkylacitic group could be estimated accurately by a two-parameter QSAR model based on absolute electronegativity and ϵ HOMO.

Measurement of select radical processes in hydrocarbon pyrolysis

Methods for the measurement of absolute and relative rates of reactions of organic free radicals related to hydrocarbon pyrolysis in the condensed phase are illustrated. Examples are provided of methods for the determination of absolute rate expressions. The absolute rate expressions are employed in competition kinetic experiments that measure the ratio of an unknown rate constant to the known basis rate constant, yielding the desired competing reaction rate. Examples of use of the absolute and competition kinetic methods to measure rates of select free radical reactions of interest to hydrocarbon pyrolysis are illustrated. Methods for the measurement of absolute rate expressions for reactions of organic free radicals that will be covered include kinetic laserflash optical spectroscopy (KLS), kinetic electron spin resonance spectroscopy (KESR), and kinetic laserflash time resolved infrared spectroscopy (TRIR).