Reaction Of HOBr Research Articles

The role of reactive N-bromo species and radical intermediates in hypobromous acid-induced protein oxidation

Activated eosinophils, and hypobromous acid (HOBr) generated by these cells, have been implicated in the tissue injury in asthma, allergic reactions, and some infections. Proteins are major targets for this oxidant, but limited information is available on the mechanisms of damage and intermediates formed. Reaction of HOBr with proteins is shown to result in the formation of bromamines and bromamides, from side-chain and backbone amines and amides, and 3-bromo- and 3,5-dibromo-Tyr, from Tyr residues; these materials account for ca. 70% of the oxidant consumed. Protein carbonyls, dityrosine, and 3,4-dihydroxyphenylalanine are also formed, though these are minor products (<5% of HOBr added). With BSA, extensive (selective and nonspecific) protein fragmentation and limited aggregation are also observed. The bromamines/bromamides are unstable and induce further oxidation and free radical formation as detected by EPR spin trapping. Evidence was obtained for the generation of nitrogen-centered radicals on side-chain and backbone amide groups of amino acids, peptides, and proteins. These radicals readily undergo rearrangement reactions to give carbon-centered radicals. With proteins, α-carbon (backbone) radicals are detected, which may play a role in protein fragmentation. A novel damage transfer pathway from Gln side-chain amide groups to backbone sites was also observed.

Uptake of hypobromous acid (HOBr) by aqueous sulfuric acid solutions: low-temperature solubility and reaction

Abstract. Hypobromous acid (HOBr) is a key species linking inorganic bromine to the chlorine and odd hydrogen chemical families. We have measured the solubility of HOBr in 45-70wt% sulfuric acid solutions representative of upper tropospheric and lower stratospheric aerosol composition. Over the temperature range 201-252 K, HOBr is quite soluble in sulfuric acid, with an effective Henry's law coefficient, H*=104-107mol L-1atm-1. H* is inversely dependent on temperature, with ΔH=-45.0±5.4 kJ mol-1 and ΔS=-101±24 J mol-1K-1 for 55-70wt% H2SO4 solutions. Our study includes temperatures which overlap both previous measurements of HOBr solubility. For uptake into 55-70wt% H2SO4, the solubility is described by log H*=(2349±280)/T-(5.27±1.24). At temperatures colder than ~213K, the solubility of HOBr in 45wt% H2SO4 is at least a factor of five larger than in 70wt% H2SO4, with log H*=(3665±270)/T-(10.63±1.23). The solubility of HOBr is comparable to that of HBr, indicating that upper tropospheric and lower stratospheric aerosols should contain equilibrium concentrations of HOBr which equal or exceed those of HBr. Upon uptake of HOBr into aqueous sulfuric acid in the presence of other brominated gases, particularly for 70wt% H2SO4 solution, our measurements demonstrate chemical reaction of HOBr followed by evolution of gaseous products including Br2O and Br2.

Is there a role of taurine bromamine in inflammation? Interactive effects with nitrite and hydrogen peroxide

The myeloperoxidase system of neutrophils generates chlorinating and brominating oxidants in vivo. The major haloamines of the system are taurine chloramine (TauCl) and taurine bromamine (TauBr). It has been demonstrated in vitro that TauCl exerts both antiinflammatory and anti-bacterial properties. Much less is known about TauBr. The present study was conducted to compare bactericidal and immunoregulatory capacity of TauBr with that of the major chlorinating oxidants: HOCl and TauCl. Moreover, the effect of nitrites and H(2)O(2) on TauBr activity was investigated. TauBr was prepared by reaction of HOBr with taurine. The reaction was monitored by UV absorption spectra. Bactericidal activity of TauBr, TauCl and HOCl was tested by incubation of E. coli with the compounds and determined by the pour-plate method. To test the anti-inflammatory activity the compounds were incubated with LPS and IFN-gamma stimulated murine peritoneal macrophages. The production of following mediators was measured: nitrites by Griess reaction; TNF-alpha, IL-6, IL-10, IL-12p40 using capture ELISA. In some experiments the compounds were incubated with either nitrites or H(2)O(2). In our experimental set-up TauBr and HOCl exerted strong bactericidal effects on E. coli (MBC = 110 microM and 8 microM, respectively), while TauCl (< 1000 microM) did not kill test bacteria. However, both, TauBr and TauCl, at noncytotoxic concentrations (< 300 microM) inhibited the cytokine and nitric oxide production by macrophages. H(2)O(2) completely abolished the biological activities of TauBr but not those of TauCl. Nitrites did not affect any activity of TauBr or TauCl while they diminished the HOCl(-) mediated bacterial killing. TauBr, despite very low concentration of Br(-) in body fluids, may support TauCl and HOCl in the regulation of inflammatory response and in killing of bacteria by neutrophils. However, TauBr activity in vivo will depend on the presence of H(2)O(2) and possible other mediators of inflammation which can compete with target molecules for TauBr.

Kinetics and Mechanisms of Bromine Chloride Reactions with Bromite and Chlorite Ions

Chloride ion catalyzes the reactions of HOBr with bromite and chlorite ions in phosphate buffer (p[H(+)] 5 to 7). Bromine chloride is generated in situ in small equilibrium concentrations by the addition of excess Cl(-) to HOBr. In the BrCl/ClO(2)(-) reaction, where ClO(2)(-) is in excess, a first-order rate of formation of ClO(2) is observed that depends on the HOBr concentration. The rate dependencies on ClO(2)(-), Cl(-), H(+), and buffer concentrations are determined. In the BrCl/BrO(2)(-) reaction where BrCl is in pre-equilibrium with the excess species, HOBr, the loss of absorbance due to BrO(2)(-) is followed. The dependencies on Cl(-), HOBr, H(+), and HPO(4)(2)(-) concentrations are determined for the BrCl/BrO(2)(-) reaction. In the proposed mechanisms, the BrCl/ClO(2)(-) and BrCl/BrO(2)(-) reactions proceed by Br(+) transfer to form steady-state levels of BrOClO and BrOBrO, respectively. The rate constant for the BrCl/ClO(2)(-) reaction [k(Cl)(2)]is 5.2 x 10(6) M(-1) s(-1) and for the BrCl/BrO(2)(-) reaction [k(Br)(2)]is 1.9 x 10(5) M(-1) s(-1). In the BrCl/ClO(2)(-) case, BrOClO reacts with ClO(2)(-) to form two ClO(2) radicals and Br(-). However, the hydrolysis of BrOBrO in the BrCl/BrO(2)(-) reaction leads to the formation of BrO(3)(-) and Br(-).

Organotrihalide Complexes: α-Nucleophiles and Effective Oxidizing Agents in Decomposition Reactions of Organophosphorus Compounds in Water and Surfactant Micelles

We have studied the nucleophilic and oxidative reactivity of the system HOBr/BrO−, in water and in the presence of different types of surfactants, relative to 4-nitrophenyldiethylphosphate, 4-nitrophenyl- 4´-toluenesulfonate (nucleophilic substitution), and 4-nitrophenol (oxidation). As the source of "active" bromine, we used organotrihalide complexes. The micellar effects of the surfactants in nucleophilic substitution reactions are adequately described within both a pseudophase distribution model and an ion-exchange model. Just transferring the reaction from water to micelles of a cationic surfactant leads to an increase in the observed rates of reaction of the BrO− ion with esters by up to a factor of 20-30 and an increase in the rate for reaction of HOBr with nitrophenol by up to a factor of 5, while the HOBr/BrO− system is one of the most effective systems in decomposition of organophosphorus compounds.

Mechanistic Investigations of the BZ Reaction with Oxalic Acid Substrate. I. The Oscillatory Parameter Region and Rate Constants Measured for the Reactions of HOBr, HBrO2, and Acidic BrO3- with Oxalic Acid

This paper is the first part of a study reinvestigating the mechanism of the Belousov−Zhabotinsky (BZ) reaction of oxalic acid, which is the simplest organic substrate for a BZ oscillator. New experiments are performed to find the oscillatory region in 1 M sulfuric acid at 20 °C. The removal rate of the end product bromine by an inert gas stream is a critical parameter here: oscillations can be observed only in a window of that parameter. The “rate constant” for the physical removal of bromine is measured as a function of the gas flow rate and reactor volume; furthermore, the rate constants of three component reactions important in this system are also determined. These are oxygen atom transfer reactions to the oxalic acid substrate from Br(I) (hypobromous acid), from Br(III) (bromous acid), and from Br(V) (acidic bromate) compounds. In these second-order reactions, the partial order of each oxybromine species is 1. The measured rate constants are kI = 17 ± 2 M-1 s-1, kIII = 4.2 ± 0.5 M-1 s-1, and kV = (...

Kinetic analysis of the reactions of hypobromous acid with protein components: implications for cellular damage and use of 3-bromotyrosine as a marker of oxidative stress.

Hypohalous acids (HOX, X = Cl, Br) are produced by activated neutrophils, monocytes, eosinophils, and possibly macrophages. These oxidants react readily with biological molecules, with amino acids and proteins being major targets. Elevated levels of halogenated Tyr residues have been detected in proteins isolated from patients with atherosclerosis, asthma, and cystic fibrosis, implicating the production of HOX in these diseases. The quantitative significance of these findings requires knowledge of the kinetics of reaction of HOX with protein targets, and such data have not been previously available for HOBr. In this study, rate constants for reaction of HOBr with protein components have been determined. The second-order rate constants (22 degrees C, pH 7.4) for reaction with protein sites vary by 8 orders of magnitude and decrease in the order Cys > Trp approximately Met approximately His approximately alpha-amino > disulfide > Lys approximately Tyr >> Arg > backbone amides > Gln/Asn. For most residues HOBr reacts 30-100 fold faster than HOCl, though Cys and Met residues are approximately 10-fold less reactive, and ring halogenation of Tyr is approximately 5000-fold faster. Thus, Tyr residues are more, and Cys and Met much less, important targets for HOBr than HOCl. Kinetic models have been developed to predict the targets of HOX attack on proteins and free amino acids. Overall, these results shed light on the mechanisms of cell damage induced by HOX and indicate, for example, that the 3-chloro-Tyr:3-bromo-Tyr ratio does not reflect the relative roles of HOCl and HOBr in disease processes.

Oxidation of chlorine(III) by hypobromous acid: kinetics and mechanism.

The kinetics and mechanism of the chlorine(III)-HOBr reaction were studied by the stopped-flow method under acidic conditions, pH 1.0-3.0, in 1.0 M NaClO(4) and at 25.0 degrees C. The overall redox process occurs in two consecutive steps via the formation of the BrClO(2) intermediate. The electron transfer reactions are coupled with bromine hydrolysis, the formation of the tribromide ion, and the protolytic equilibrium of chlorine(III). On the basis of simultaneous evaluation of the kinetic traces, the following rate constants were obtained for the redox steps: HClO(2) + HOBr right harpoon over left harpoon BrClO(2) + H(2)O, k(3) = (3.34 +/- 0.02) x 10(4) M(-1) s(-1), k(-3) = (3.5 +/- 1.3) x 10(3) s(-1); BrClO(2) + ClO(2)(-)<==>2ClO(2) + Br(-), k(4) = (2.9 +/- 1.0) x 10(7) M(-1) s(-1). The second step was practically irreversible under the conditions applied, and the value of k(-4) could not be determined. The equilibrium constant for the formation of BrClO(2), K(3) = 9.5 M(-1), was calculated from the kinetic results, and it was confirmed that this species is a very powerful oxidant. The redox potential was also estimated for the BrClO(2) + e(-) = Br(-) + ClO(2) reaction: epsilon(0) approximately 1.70 V.

Direct ab initio dynamics studies on the hydrogen-abstraction reactions of OH radicals with HOX (X = F, Cl, and Br).

The hydrogen abstract reactions of OH radicals with HOF (R1), HOCl (R2), and HOBr (R3) have been studied systematically by a dual-level direct-dynamics method. The geometries and frequencies of all the stationary points are optimized at the MP2/6-311+G(2d, 2p) level of theory. A hydrogen-bonded complex is located at the product channel for the OH + HOBr reaction. To improve the energetics information along the minimum energy path (MEP), single-point energy calculations are carried out at the CCSD(T)/6-311++G(3df, 3pd) level of theory. Interpolated single-point energy (ISPE) method is employed to correct the energy profiles for the three reactions. It is found that neither the barrier heights (DeltaE) nor the H-O bond dissociation energies [D(H-O)] exhibit any clear-cut linear correlations with the halogen electronegative. The decrease of DeltaE and D(H-O) for the three reactions are in order of HOF > HOBr > HOCl. Rate constants for each reaction are calculated by canonical variational transition-state theory (CVT) with a small-curvature tunneling correction (SCT) within 200-2000 K. The agreement of the rate constants with available experimental values for reactions R2 and R3 at 298 K is good. Our results show that the variational effect is small while the tunneling correction has an important contribution in the calculation of rate constants in the low-temperature range. Due to the lack of the kinetic data of these reactions, the present theoretical results are expected to be useful and reasonable to estimate the dynamical properties of these reactions over a wide temperature range where no experimental value is available.

Rate constants of reactions of bromine with phenols in aqueous solution

The kinetics of bromination of six ortho- and para-substituted phenols was investigated between pH 5 and pH 12 in aqueous solution. Kinetics was followed with a continuous-flow reactor previously validated by studying the fast reaction between chlorine and ammonia. The overall reaction rate between bromine and phenols is controlled by the reaction of HOBr with the phenoxide ion between pH 6 and pH 10. The reaction of HOBr with the undissociated phenols and the reaction of BrO − with the phenoxide ions become only significant for pH<6 and pH>10, respectively. The second-order rate constants for the reaction of HOBr with phenoxide ions vary between 1.4(±0.1)×10 3 and 2.1(±0.5)×10 8 M −1 s −1 for 2,4,6-trichlorophenol and 4-methylphenol, respectively. Hammett-type correlation was obtained for the reaction of HOBr with the phenoxide ions (log( k)=8.0−3.33× Σσ) and was compared with Hammett-type correlations of HOCl and HOI. The reaction rate of bromine with phenol-like organic compounds was estimated to be about 10 3-fold higher than with chlorine and 10 3-fold lower than with ozone in drinking water treatment conditions.

Reactions of HOBr + HCl + nH 2O and HOBr + HBr + nH 2O

The reactions of HOBr with HCl and HBr in the presence of n=0, 1, 2 and 3 water molecules are investigated by hybrid density functional theory methods in combination with canonical, variational transition state theory including tunneling corrections. Compared to the reactions of HOCl with HCl and HBr [J. Phys. Chem. A 106 (2002) 7850], we found that the barriers of the title reactions are significantly lower yielding much higher rate constants. Support of only two water molecules makes the reaction of HOBr with HBr barrierless. Under stratospheric conditions the reactions of HOBr with HBr are the most reactive ones.

Interaction of HOBr and HCl on ice surfaces in the temperature range 205–227 K

The uptake of HOBr on ice surfaces as well as the interaction of HOBr with HCl‐doped ice surfaces has been studied in a wall‐coated tubular flow reactor coupled to a quadrupole mass spectrometer. The uptake coefficient for HOBr on ice (γHOBr) was measured between 205 and 227 K and was independent of HOBr concentration over the range (2–22) × 1011 mol cm−3. A negative temperature dependence of γ was observed with γ = 0.003 ± 0.001 at 227 K increasing to γ = 0.040 ± 0.007 at 205 K. The reaction of HOBr + HCl on ice was studied over a temperature range of 205–227 K using an HCl concentration of (4.0–8.0) × 1011 mol cm−3 and an HOBr concentration of (2–22) × 1011 mol cm−3. On exposing HOBr to the HCl‐doped ice surface, BrCl was observed as a reaction product. Under conditions with the HCl concentration in excess of the HOBr concentration, the rate of the surface reaction was found to be diffusion controlled at all temperatures, with an approximate lower limit of the uptake coefficient for HOBr + HCl on ice of γ ≥ 0.1. Under conditions with the HOBr concentration in excess of the HCl concentration, a change in uptake behavior of HOBr on HCl‐doped ice was noted. Experimental evidence suggests that the reaction follows an Eley–Rideal‐type mechanism. The atmospheric implications of these results on the chemistry of the upper troposphere are discussed.

Kinetics and Product Yields in the Heterogeneous Reactions of HOBr with Ice Surfaces Containing NaBr and NaCl

The heterogeneous reactions of HOBr with ice surfaces formed by freezing sodium halide solutions were studied using a coated-wall, low-pressure flow tube coupled to a quadrupole mass spectrometer. Experiments were conducted at 233 and 248 K with films containing bromide, chloride, or a mixture of the two, and with HOBr gas-phase concentrations of about 1012 molecules/cm3. Gas−surface uptake coefficients and product yields are presented for a range of halide and hydrogen ion concentrations. Compared to analogous reactions with HOCl, HOBr reactions were slower than expected with a maximum uptake coefficient of approximately 0.01. At both 233 and 248 K, gas-phase Br2 was formed exclusively from bromide-only films and only BrCl was formed from chloride films. When both ions were present, BrCl was the sole gas-phase product observed at 233 K, while both gas-phase Br2 and BrCl were formed at 248 K. The relative yields of the gas-phase products depend on the temperature, composition, and acidity of halide-ice surfaces. A mechanism consistent with the observations involves initial formation of a HOBr·X- complex, where X- is either chloride or bromide, followed by reaction of the complex with a proton. For this reason, reaction probabilities for the formation of BrCl or Br2 were higher on acidified films than on films formed from pH-neutral solutions. The atmospheric implications of these results are discussed.

Uptake and reaction of HOBr on frozen and dry NaCl/NaBr surfaces between 253 and 233 K

Abstract. The uptake and reaction of HOBr with frozen salt surfaces of variable NaCl / NaBr composition and temperature were investigated with a coated wall flow tube reactor coupled to a mass spectrometer for gas-phase analysis. HOBr is efficiently taken up onto the frozen surfaces at temperatures between 253 and 233 K where it reacts to form the di-halogens BrCl and Br2, which are subsequently released into the gas-phase. The uptake coefficient for HOBr reacting with a frozen, mixed salt surface of similar composition to sea-spray was &lt;approx&gt; 10-2. The relative concentration of BrCl and Br2 released to the gas-phase was found to be strongly dependent on the ratio of Cl- to Br - in the solution prior to freezing / drying. For a mixed salt surface of similar composition to sea-spray the major product at low conversion of surface reactants (i.e. Br - and Cl-) was Br2. Variation of the pH of the NaCl / NaBr solution used to prepare the frozen surfaces was found to have no significant influence on the results. The observations are explained in terms of initial formation of BrCl in a surface reaction of HOBr with Cl-, and conversion of BrCl to Br2 via reaction of surface Br -. Experiments on the uptake and reaction of BrCl with frozen NaCl / NaBr solutions served to confirm this hypothesis. The kinetics and products of the interactions of BrCl, Br2 and Cl2 with frozen salt surfaces were also investigated, and lower limits to the uptake coefficients of &gt; 0.034, &gt;0.025 and &gt;0.028 respectively, were obtained. The uptake and reaction of HOBr on dry salt surfaces was also investigated and the results closely resemble those obtained for frozen surfaces. During the course of this study the gas diffusion coefficients of HOBr in He and H2O were also measured as (273 ± 1) Torr cm2 s-1 and (51 ± 1) Torr cm2 s-1, respectively, at 255 K. The implications of these results for modelling the chemistry of the Arctic boundary layer in springtime are discussed.

An ab initio study of the hydrogen abstraction reaction of methane by bromine atoms and bromine monoxide radicals

The structures, vibrational spectra, and relative energetics for the transition states of the hydrogen abstraction reactions of methane by bromine (Br) atoms and bromine monoxide (BrO) radicals have been examined by using the quadratic configuration interaction method in conjunction with different basis sets. From the calculated energetics of the CH 4+Br→CH 3+HBr and CH 4+BrO→CH 3+HOBr reactions, we find that the energy barrier for the formation of HOBr is higher than that for the formation of HBr. The endothermicity of the CH 4+Br→CH 3+HBr reaction is 7.9 kcal mol −1 higher than that for the CH 4+BrO→CH 3+HOBr reaction.

On the Irreversible Destruction of Reduced Nicotinamide Nucleotides by Hypohalous Acids

Degradation of the reduced pyridine nucleotides NMNH and NADH by HOCl involves two distinct stages: a fast reaction, k = 4.2 × 105 M−1 s−1, leads to generation of stable pyridine products (Py/Cl) with a strong absorption band at 275 nm (ϵ = 12.4 × 103 M−1 cm−1 in the case of NMNH); secondarily, a subsequent reaction of HOCl, k = 3.9 × 103 M−1 s−1, leads to a complete loss of the aromatic absorption band of the pyridine ring. HOBr and HOI(I2) react similarly. Apparent rate constants of the primary reactions of HOX species with NMNH at pH 7.2 increase in the order HOCl (3 × 105 M−1 s−1) < HOBr(∼4 × 106 M−1 s−1) < HOI(I2)(∼6.5 × 107 M−1 s−1). HOBr reacts fast also with the primary product Py/Br, k ∼ 9 × 105 M−1 s−1, while the reactions of HOI and I2 with Py/I are slower, ∼1.4 × 103 M−1 s−1 and >6 × 103 M−1 s−1, respectively. Halogenation of the amide group of NMN+ by HOX species is many orders of magnitude slower than oxidation of NMNH. Taurine inhibits HOCl-induced oxidation of NADH, but HOBr-induced oxidation is not inhibited because the taurine monobromamine rapidly oxidizes NADH, and oxidation by HOI(I2) is not inhibited because taurine is inert toward HOI(I2). Also sulfur compounds (GSH, GSSG, and methionine) are less efficient in protecting NADH against oxidation by HOBr and HOI(I2) than against oxidation by HOCl. The results suggest that reactions of HOBr and HOI(I2) in a cellular environment are much more selectively directed toward irreversible oxidation of NADH than reactions of HOCl. It is noteworthy that the rather inert N-chloramines react with iodide to generate HOI(I2), i.e., the most reactive and selective oxidant of reduced pyridine nucleotides. NMR investigations show that the primary stable products of the reaction between NMNH and HOCl are various isomeric chlorohydrins originating from a nonstereospecific electrophilic addition of HOCl to the C5C6 double bond of the pyridine ring. The primary products (Py/X) of NMNH all exhibit similar absorption bands around 275 nm and are hence likely to result from analogous addition of HOX to the C5C6 bond of the pyridine ring. Since the Py/X species are stable and inert toward endogeneous reductants like ascorbate and GSH, they may generally be useful markers for assessing the contribution of hypohalous acids to inflammatory injury.

Heterogeneous Interaction and Reaction of HOBr on Ice Films

The uptake coefficient γ of HOBr on the ice surface from 190 to 239 K has been investigated in a flow reactor interfaced with a differentially pumped quadrupole mass spectrometer. γ of HOBr on ice is in the range 0.11−7 × 10-3 at 190−218 K and is in the range 2 × 10-3 to 6 × 10-4 at 223−239 K. The desorption temperature Td of HOBr on the ice film was determined. Td increases with the HOBr exposure. The Monte Carlo simulation was used to shed light on the nature of the desorption and gas−surface interactions. This study extends our investigations to the reaction probability of the HOBr + HCl reaction. The reaction probability ranges from 0.05 to 0.23 at 190 K and 0.004 to 0.19 at 222 K as a function of PHCl, which varies from 1.3 × 10-7 to 8.8 × 10-6 Torr and 4.2 × 10-7 to 1.5 × 10-5 Torr, respectively. Kinetic analysis indicates that the heterogeneous reaction of HOBr + HCl follows the Langmuir−Hinshelwood type.

A Myeloperoxidase-Specific Assay Based upon Bromide-Dependent Chemiluminescence of Luminol

Measurement of myeloperoxidase (MPO; EC 1.11.1.7) activity is often used as a marker of neutrophil infiltration into tissues. However, most enzymatic assays for MPO are susceptible to interference from other peroxidases (including eosinophil peroxidase, EPX) and hemoproteins (such as hemoglobin and myoglobin) present in the tissues. In this report, we describe a bromide-dependent chemiluminescence (Br-CL) assay that uses luminol as a chemiluminescence probe. The assay can distinguish between MPO and nonspecific peroxidase reactions. The MPO-specific reaction is believed to proceed in two steps: (i) the enzymatic generation of hypobromous acid (HOBr) from KBr and H2O2 at pH 5 and (ii) the spontaneous reaction of HOBr and H2O2 with luminol to give a Br-CL signal. The assay is sufficiently sensitive to allow detection of MPO in <100 human neutrophils. Other peroxidases and hemoproteins do not interfere with the Br-CL signal. Although EPX can also oxidize bromide to generate HOBr, activities of MPO and EPX can be distinguished at different pHs. As a demonstration of the utility of the Br-CL assay, MPO activity was measured in murine tumors known to be infiltrated with neutrophils. A statistically significant correlation was seen between MPO activity and histological neutrophil counts in the tumors (r = 0.69, P < 0.01, n = 14). The assay should have wide application for measuring the neutrophil content of tissues.

Anti- and pro-oxidant effects of ascorbate on iron-mediated oxidative damage to bovine serum albumin: [formula omitted] Ben-Zhan Zhu and Balz Frei. Linus Pauling Institute, Oregon State University, Corvallis, OR 97331

Degradation of the reduced pyridine nucleotides NMNH and NADH by HOCl involves two distinct stages: a fast reaction, k = 4.2 × 105 M−1 s−1, leads to generation of stable pyridine products (Py/Cl) with a strong absorption band at 275 nm (ϵ = 12.4 × 103 M−1 cm−1 in the case of NMNH); secondarily, a subsequent reaction of HOCl, k = 3.9 × 103 M−1 s−1, leads to a complete loss of the aromatic absorption band of the pyridine ring. HOBr and HOI(I2) react similarly. Apparent rate constants of the primary reactions of HOX species with NMNH at pH 7.2 increase in the order HOCl (3 × 105 M−1 s−1) < HOBr(∼4 × 106 M−1 s−1) < HOI(I2)(∼6.5 × 107 M−1 s−1). HOBr reacts fast also with the primary product Py/Br, k ∼ 9 × 105 M−1 s−1, while the reactions of HOI and I2 with Py/I are slower, ∼1.4 × 103 M−1 s−1 and >6 × 103 M−1 s−1, respectively. Halogenation of the amide group of NMN+ by HOX species is many orders of magnitude slower than oxidation of NMNH. Taurine inhibits HOCl-induced oxidation of NADH, but HOBr-induced oxidation is not inhibited because the taurine monobromamine rapidly oxidizes NADH, and oxidation by HOI(I2) is not inhibited because taurine is inert toward HOI(I2). Also sulfur compounds (GSH, GSSG, and methionine) are less efficient in protecting NADH against oxidation by HOBr and HOI(I2) than against oxidation by HOCl. The results suggest that reactions of HOBr and HOI(I2) in a cellular environment are much more selectively directed toward irreversible oxidation of NADH than reactions of HOCl. It is noteworthy that the rather inert N-chloramines react with iodide to generate HOI(I2), i.e., the most reactive and selective oxidant of reduced pyridine nucleotides. NMR investigations show that the primary stable products of the reaction between NMNH and HOCl are various isomeric chlorohydrins originating from a nonstereospecific electrophilic addition of HOCl to the C5C6 double bond of the pyridine ring. The primary products (Py/X) of NMNH all exhibit similar absorption bands around 275 nm and are hence likely to result from analogous addition of HOX to the C5C6 bond of the pyridine ring. Since the Py/X species are stable and inert toward endogeneous reductants like ascorbate and GSH, they may generally be useful markers for assessing the contribution of hypohalous acids to inflammatory injury.

Heterogeneous Kinetics of the Uptake of HOBr on Solid Alkali Metal Halides at Ambient Temperature

Bromine contg. compds. are thought to play an important role in the O3 destruction in various regions of the atm. Recent studies of atm. Br chem. suggest that HOBr is one of the important Br compds. The rapid photolysis of HOBr in daytime releases Br atoms and OH radicals, which causes ozone destruction. In this study, the reactivity of HOBr with solid alkali metal halides is reported which affords insights into the importance of heterogeneous reactions of HOBr with salt, which in the atm. act as substrate particles for the reactions. The heterogeneous reactions of HOBr with solid cryst. NaCl [HOBr(g) + NaCl(s) -> BrCl(g) + NaOH(s)] and KBr [HOBr(g) + KBr(s) -> Br2(g) + KOH(s)] substrates at ambient temp. have been investigated using a Teflon coated Knudsen cell reactor. Powder, grain, and spray-deposited salt substrates were used for the measurement of the HOBr reactivity. The obsd. uptake probability depends on the total external surface area of the salt substrates. For NaCl substrates, Br2 and BrCl are obsd. as products; for KBr substrates, Br2 is obsd. as the sole product. In both cases, a dependence of the initial uptake probability g0 on HOBr flow rate has been obsd. The initial uptake is large at low flow rate and 10 times smaller at high flow rate. Values of g0 ? (6.5 +- 2.5) * 10-3 for NaCl and g0 ? 0.18 +- 0.04 for KBr are obtained under our exptl. conditions of limiting low flow rates akin to atm. conditions. The prodn. of Br2 is obsd. even for HOBr interacting on solid NaNO3, a non-halogen contg. substrate. The yield measurements imply that a HOBr self-reaction occurs on salt surfaces according to 2HOBr -> Br2 + H2O + 1/2O2. The decrease in Br2 yield with increasing HOBr flow rate from 100 to 50% indicates that a competition between the heterogeneous reaction of HOBr with NaCl or KBr and the self-reaction of HOBr takes place on the solid salt surface under lab. exptl. conditions. The decrease of g0 with time indicates that approx. 5-10% of the Br atoms on a KBr surface interact with HOBr.