Initial Reaction Sites Research Articles

Efficient Degradation of Carbendazim by Ferrate(VI) Oxidation under Near-Neutral Conditions

Carbendazim (CBZ), a widely used fungicide in agriculture, is frequently detected in aquatic environment and causes significant concerns because of its endocrine-disrupting activity. This study investigated the degradation kinetics of CBZ in ferrate (Fe(VI)) oxidation, the influence of water matrices, and the transformation pathways of CBZ. The second-order rate constant for the reaction between CBZ and Fe(VI) decreased from 88.0 M−1·s−1 to 1.6 M−1·s−1 as the solution pH increased from 6.2 to 10.0. The optimum reaction conditions were obtained through response surface methodology, which were pH = 7.8 and [Fe(VI)]/[CBZ] = 14.2 (in molarity), and 96.9% of CBZ could be removed under such conditions. Cu2+ and Fe3+ accelerated the degradation of CBZ by Fe(VI) oxidation; common cations and anions found in natural water had no significant effect, while the presence of humic acid also accelerated the degradation of CBZ. Based on the degradation products identified, degradation of CBZ in Fe(VI) oxidation proceeded via three pathways: namely, hydroxylation, removal of the methoxyl group, and cleavage of the C–N/C=N bond. The initial reaction site of CBZ oxidation by Fe(VI) was also supported by the atomic partial charge distribution on the CBZ molecule obtained from density functional theory (DFT) calculations. CBZ in natural water matrices was efficiently removed by Fe(VI) oxidation under near-neutral conditions, indicating that Fe(VI) oxidation could be a promising treatment option for benzimidazole fungicides.

Effectiveness and degradation pathways of bisphenol A (BPA) initiated by hydroxyl radicals and sulfate radicals in water: Initial reaction sites based on DFT prediction

Bisphenol A (BPA), one of the widely known endocrine-disrupting chemicals, can be effectively degraded by advanced oxidation processes in water because of the powerful reactive oxygen species. In this study, Fenton, UV/Fenton, and metal ion/peroxymonosulfate (PMS) processes were compared to investigate BPA degradation efficiency and pathways initiated by hydroxyl radicals and sulfate radicals. In contrast to the Fenton system, which only degraded 60% of BPA within 15 min, the UV/Fenton system could degrade greater than 80% of BPA, because more hydroxyl radicals (•OH) were generated under the reduction of Fe3+ to Fe2+. The optimized parameters of the UV/Fenton system were as follows: 8 μmol/L of Fe2+, 80 μmol/L of H2O2, and a pH value of 3.0. As for the metal ion/PMS system, the BPA degradation efficiency was closely associated with the applied metal ions, and the order was as follows: Co2+/PMS (∼100%) > Fe2+/PMS (∼80%) > Cu2+/PMS (∼79%). The degradation pathways of BPA were theoretically interpreted through density functional theory prediction and degradation products during various processes. Two major initial reaction sites (4C and 6C) for •OH initiated using the UV/Fenton system and one initial reaction site (4C) for sulfate radicals (SO4•−) using the metal ion/PMS system were recognized for BPA degradation processes. The degradation products by •OH showed a larger average molecular weight than those by SO4•−. These studies are instructive for the application of different advanced oxidation systems in the treatment process of BPA in wastewater.

Effectiveness and Degradation Paths of Bisphenol a (Bpa) Initiated by Hydroxyl Radicals and Sulfate Radicals in Water: Initial Reaction Sites Based on Dft Prediction

Effectiveness and Degradation Paths of Bisphenol a (Bpa) Initiated by Hydroxyl Radicals and Sulfate Radicals in Water: Initial Reaction Sites Based on Dft Prediction

Overall mechanism of JP-10 pyrolysis unraveled by large-scale reactive molecular dynamics simulation

This paper reports the overall reaction mechanism of JP-10 pyrolysis obtained in large-scale reactive molecular dynamics simulations employing the force field of ReaxFF CHO-2008. The C<5 products obtained from the simulations are basically consistent with what detected using varied experimental techniques reported in literature. Particularly, the product evolution tendency of methane, ethane, ethylene, propylene, acetylene, allene,1−butene, propyne, 1,3-butadiene, cyclopentadiene with temperature is in good agreement with the results of single-pulse shock tube experiment performed in this work. The simulation results indicate that JP-10 pyrolysis reactions can be divided into three stages on basis of the evolution of total radicals, namely, the initial ring-openning through CC bond homolysis in stage I, the initiation and growth of chain radicals through β-scission reactions as well as some of the chain propagation via CH bond scission in stage II, the chain propagation through CH bond cleavage and the chain termination reactions in stage III. The C5H7• and C3H5• radicals were found playing dominant role in the reaction propagation. The obtained initial reaction sites of JP-10 pyrolysis are ranked as: B3>B4>B2>B5>B1>B6>B7 that will not be significantly affected by temperature. The obtained aromatic hydrocarbons in simulations and the increasing C/H ratio with temperature and time during the three pyrolysis stages exhibit the coking tendency during JP-10 pyrolysis.

Degradation of sulfadimethoxine in phosphate buffer solution by UV alone, UV/PMS and UV/H2O2: Kinetics, degradation products, and reaction pathways

The presence of residual sulfonamide antibiotics such as sulfadimethoxine (SDM) in surface waters has become an emerging concern due to their adverse effects on the environment and human health. In this study, UV alone, UV/PMS and UV/H2O2 degradation processes were studied by comparing the degradation efficiency and reaction mechanisms for SDM. Moreover, we systematically studied various factors that influenced the removal of SDM by UV/PMS, including the pH (5.0, 7.0, and 9.0), oxidant doses, humic acid (HA) and bicarbonate (HCO3−). UV alone can highly degrade SDM, and the combination of PMS or H2O2 with UV radiation further facilitated the oxidation performance. The removal efficiency of SDM in the three degradation systems was recorded with the order of UV/PMS > UV/H2O2 > UV alone. The conditions of [SDM]0: [PMS]0 = 1:20, pH = 7.0, and T = 25 ± 2 ℃ cause a 100% removal of SDM (5 mg L−1) after 7.0 min of irradiation by a 300 W mercury vapor lamp. Degradation products of SDM were identified using an electrospray time-of-flight mass spectrometer. Their structures were further elucidated using MS/MS spectra. Three initial reaction sites of SDM were suggested, which were the direct photooxidation of the –NH2 group, hydroxylation of the –NH2 group and aniline ring via attack by SO4− and OH radicals. It was found that nitrated products were only produced in UV/PMS and UV/H2O2 systems. Ecological structure activity relationships (ECOSAR) analysis revealed that the degradation products of SDM during the three oxidation processes were not considered as toxic to three typical aquatic species. Thus, UV alone, UV/PMS and UV/H2O2 could be applied as an efficient technique for the elimination of SDM from water.

Photodegradation of polychlorinated diphenyl sulfides (PCDPSs) under simulated solar light irradiation: Kinetics, mechanism, and density functional theory calculations

The direct photolysis of 25 individual polychlorinated diphenyl sulfides (PCDPSs) substituted with 1–7 chlorine atoms was investigated using a 500-W Xe lamp. Photolysis of PCDPSs followed pseudo-first-order kinetics, with the higher chlorinated diphenyl sulfides generally degrading faster than the lower chlorinated congeners. A quantitative structure-activity relationship model to predict the photolysis rates of PCDPSs was developed using 16 fundamental quantum chemical descriptors. We found that the substitution pattern for chlorine atoms, the dipole moment, and ELUMO − EHOMO were major factors in the photolysis of PCPDSs. The reaction kinetics, products, and photodegradation pathways of 2,2′,3′,4,5-pentachlorodiphenyl sulfide (PeCDPS) suggest hydroxylation, direct photooxidation, the C–S bond cleavage reaction, and hydroxyl substitution were mainly involved in the photodegradation process, leading to the formation of 13 intermediates, detected by an electrospray time-of-flight mass spectrometer. The initial reaction sites of PCDPSs under photolysis were rationalized by density functional theory calculations. Anions (Cl−, SO42−, NO3−, and HCO3−) and Co2+ had no influence on the removal of PeCDPS, while Fe3+, Cu2+, and HA decreased the photolysis efficiency of PeCDPS. This report is the first to develop a logk quantitative structure–property relationships (QSPR) model of 25 PCDPSs and to describe mechanistic pathways for the photolysis of PeCDPS.

Degradation kinetics and transformation products of chlorophene by aqueous permanganate

This paper evaluates the oxidation of an antibacterial agent, chlorophene (4-chloro-2-(phenylmethyl)phenol, CP), by permanganate (Mn(VII)) in water. Second-order rate constant (k) for the reaction between Mn(VII) and CP was measured as (2.05 ± 0.05) × 101 M−1 s−1 at pH 7.0 for an initial CP concentration of 20.0 μM and Mn(VII) concentration of 60.0 μM. The value of k decreased with increasing pH in the pH range of 5.0–7.0, and then increased with an increase in solution pH from 7.0 to 10.0. The presence of MnO2 and Fe3+ in water generally enhanced the removal of CP, while the effect of humic acid was not obvious. Fourteen oxidation products of CP were identified by an electrospray time-of-flight mass spectrometer, and direct oxidation, ring-opening, and decarboxylation were mainly observed in the reaction process. The initial reaction sites of CP by Mn(VII) oxidation were rationalized by density functional theory calculations. Toxicity changes of the reaction solutions were assessed by the luminescent bacteria P. phosphoreum, and the intermediate products posed a relatively low ecological risk during the degradation process. The efficient removal of CP in secondary clarifier effluent and river water demonstrated the potential application of this Mn(VII) oxidation method in water treatment.

Organic chemistry: Nickel steps towards selectivity.

Hydrocarbons called alkenes are isolated from petroleum as mixtures of isomers, often making it hard to use them as reagents for synthesis. A reaction involving a migrating nickel atom offers a possible solution. See Letter p.84 Functionalizing a specific position on a molecule other than the initial reaction site is a key challenge in synthetic chemistry. Several recent strategies for remote functionalization make use of complex transition-metal complexes to direct bond formation at distant sites. Here, Ruben Martin and colleagues use a cheap and abundant nickel catalyst that adds into a carbon–bromine bond, walks along a hydrocarbon chain and adds carbon dioxide at the terminal position, regardless of where it began. Through a two-step procedure that uses feedstock chemicals, a mixture of saturated hydrocarbons or alkenes can be transformed into a single carboxylic acid product. On carbonyl-containing substrates, the direction of chain migration can be controlled and inverted simply by raising the temperature by 30 degrees Celsius, which switches the reaction from kinetic to thermodynamic control.

Simulation of nucleation and growth of atomic layer deposition phosphorus for doping of advanced FinFETs

Simulations for the nucleation and growth of phosphorus films were carried out using density functional theory. The surface was represented by a Si9H12 truncated cluster surface model with 2 × 1-reconstructured (100) Si-OH terminations for the initial reaction sites. Chemistries included phosphorous halides (PF3, PCl3, and PBr3) and disilane (Si2H6). Atomic layer deposition (ALD) reaction sequences were illustrated with three-dimensional molecular models using sequential PF3 and Si2H6 reactions and featuring SiFH3 as a byproduct. Exothermic reaction pathways were developed for both nucleation and growth for a Si-OH surface. Energetically favorable reactions for the deposition of four phosphorus atoms including lateral P–P bonding were simulated. This paper suggests energetically favorable thermodynamic reactions for the growth of elemental phosphorus on (100) silicon. Phosphorus layers made by ALD are an option for doping advanced fin field-effect transistors (FinFETs). Phosphorus may be thermally diffuse...

Oxidation of microcystin-LR in water by ozone combined with UV radiation: The removal and degradation pathway

In this study, the performance of the combined UV/O3 process for the degradation of microcystin-LR (MC-LR) in water was investigated, and the possible degradation pathway of the toxin was elucidated according to reaction intermediates. Results demonstrated that the UV/O3 process was a more effective method for the removal and mineralization of MC-LR in water, compared with UV- and O3-alone processes. Increasing the solution pH (5–10) and dissolved organic carbon concentration (0–5.3mg/L) could inhibit the degradation of the toxin. Nine reaction intermediates of MC-LR were detected by LC/MS, and four initial reaction sites of the toxin were observed: the conjugated diene of Adda, the double bonds of Mdha and two free acid groups of MeAsp and Glu. The degradation pathways of the toxin during UV/O3 process involved isomerization, hydroxylation and oxidative cleavage of the Adda side chain, oxidation of Mdha and decarboxylation of MeAsp and Glu. The pathway of the oxidation and cleavage of Adda and Mdha could result from both HO and O3 oxidation, but the isomerization of Adda moiety and the decarboxylation of MeAsp and Glu mainly resulted from UV radiation. The yield trends of the intermediates indicated that the oxidation of Adda moiety was the dominant degradation pathway and that the combined UV/O3 process had a higher potential for the simultaneous degradation of MC-LR and its intermediates than the individual processes.

Photocatalytic and photoelectrocatalytic degradation and mineralization of small biological compounds amino acids at TiO2 photoanodes

Quantitative evaluation of photocatalytic (PC) and photoelectrocatalytic (PEC) degradation of small biological compounds like amino acids (AAs) were systematically investigated at illuminated nanoparticulate TiO2 photoanode using a thin-layer photoelectrochemical cell. Three model AAs like phenylalanine (Phe), tyrosine (Tyr) and tryptophan (Trp), were found to be photocatalytically and photoelectrocatalytically degradable. PEC degradation efficiency was much higher than that of PC method for all compounds investigated, and the superiority becomes more obvious at higher concentrations. Organic nitrogen atoms in AAs can be oxidized to either NH3/NH4+ or NO3–, or both, depending the chemical structures of AAs and degradation methods used. HPLC analysis found that, for a given AA except Phe, the hydrophilicity characteristics of intermediates are differed slightly between PC and PEC process. For a given method, similar hydrophilicity characteristics were obtained from all AAs investigated except Phe. Theoretically calculated results showed that initial reaction sites for all single-ringed AAs are likely to occur on the atoms within 6-membered ring structure, while for double-ringed AA, the initial reaction sites are likely to occur at 6-membered ring structure (PC) or at 5-membered ring structure (PEC). Both experimental and theoretical results demonstrated PEC reaction mechanisms differed remarkably from that of PC process.

Effects of pH on the speciation coefficients in models of bromide influence on the formation of trihalomethanes and haloacetic acids

This study investigated effects of pH, bromide and natural organic matter (NOM) level on yields and speciation of trihalomethanes (THMs) and haloacetic acids (HAAs) in chlorinated water. Experimental data were obtained using two water sources, one with a medium (DOC = 1.4 mg/L and SUVA = 2.60 L mg−1 m−1) and the other with higher (DOC = 7.7 mg/L and SUVA = 4.26 L mg−1 m−1) organic carbon level. The experiments employed the simulated distribution system (SDS) procedure at varying bromide concentrations and pH values of 7.0, 8.5 and 10. The speciation of THMs and dihalogenated HAAs (DHAAs) was interpreted based on the modelling of mixed halogenation yields via dimensionless ratios of bromination/chlorination reaction rates at each halogen incorporation node. The approach allowed precise modelling of the speciation of THMs and DHAAs at all examined pHs. In the case of DHAA, the dimensionless ratios of the bromination/chlorination reaction rates were not consistently affected by pH variations. For THMs, increase of pH caused the values of the dimensionless bromination/chlorination reaction rates to decrease in the case of halogenation of the initial reaction sites indicating a decreasing preference toward bromination at this reaction node. A similar trend was observed for the reactivity of dichlorinated reaction intermediate denoted as SCl2 whose formation precedes the release of CHCl3 and CHBrCl2. A similar but less consistent trend was observed for intermediate SBrCl whose halogenation yields both CHBrCl2 and CHBr2Cl. An opposite trend of increasing preference towards bromination at higher pHs was observed monobrominated intermediate SBr and in some extent dibrominated intermediate SBr2. These results help develop detailed DBP speciation models which needed to better understand the generation and potential health effects of THMs and HAAs at varying operating conditions and ultimately to adopt measure to minimize their levels in drinking water systems.

Mechanism in the reaction of cytochrome c oxidase with organic hydroperoxides: an ESR spin-trapping investigation.

Organic hydroperoxides are of great utility in probing the reaction mechanism and the toxicological consequences of lipid peroxidation. In the present study, ESR spin-trapping was employed to investigate the peroxidation of mitochondrial cytochrome c oxidase (CcO) with t-butyl hydroperoxide (t-BuOOH) and cumene hydroperoxide (CumOOH). The spin trap 5,5-dimethyl-1-pyrroline N-oxide (DMPO) was used to detect the radical species formed from the reaction of CcO with t-BuOOH. The presence of t-BuOOH-derived alkoxyl radical (t-BuO*) as the primary radical indicates reductive scission of the O-O bond by CcO. The ESR signal of DMPO/*Ot-Bu can be partially abolished by cyanide, implying that the reductive cleavage involved the haem a(3)Cu(B) binuclear site of CcO. A nitroso spin trap, 2-methyl-2-nitrosopropane (MNP), was used to detect and identify radical species from the reaction of CcO with CumOOH. In addition to the t-BuOOH-derived methyl, hydroxylmethyl and tertiary carbon-centred radicals, a protein-derived radical was detected. The intensity of the ESR signal from the protein radical increased with the CumOOH concentration at low CumOOH/CcO ratios, with maximal intensity at a ratio of 100 mol of CumOOH/mol of CcO. The immobilized protein radical adduct of MNP was stable and persistent after dialysis; it was also resistant to proteolytic digestion, suggesting that it was formed in the transmembrane region, a region that is not accessible to proteases. Its signal was greatly enhanced when CcO cysteine residues were chemically modified by N-ethylmaleimide, when the tryptophan residues in CcO were oxidized by N-bromosuccimide, and when tyrosine residues on the surface of CcO were iodinated, showing that a radical equilibrium was established among the cysteine, tryptophan and tyrosine residues of the protein-centred radical. Pre-treatment of CcO with cyanide prevented detectable MNP adduct formation, confirming that the haem a(3)-Cu(B) binuclear centre was the initial reaction site. When the CcO was pre-treated with 10 mM (100 equivalents) of CumOOH, the enzyme activity decreased by more than 20%. This inhibition was persistent after dialysis, suggesting that the detected protein-centred radical was, in part, involved in the irreversible inactivation by CumOOH. Visible spectroscopic analysis revealed that the haem a of CcO was not affected during the reaction. However, the addition of pyridine to the reaction mixture under alkaline conditions resulted in the destruction of the haem centre of CcO, suggesting that its protein matrix rather than its haem a is the target of oxidative damage by the organic hydroperoxide.

A laser flash photolysis study of amino acids and dipeptides using 4-nitroquinoline 1-oxide as a photosensitizer: The pH dependence

The pH effects on the photochemical reaction of amino acids and related dipeptides with 4-nitroquinoline 1-oxide (4NQO) as a photosensitizer have been investigated by laser flash photolysis. The obtained kinetic parameters show that the electron transfer from Tryptophan (Trp), Tyrosine (Tyr) as well as dipeptides containing Trp and/or Tyr residue to triplet 4NQO (T4NQO) are efficient, but inefficient from methionine (Met) and dipeptides containing neither Trp nor Tyr. The result was supported by the calculated values of the free energy change from measured oxidation potentials for the electron transfer. It was demonstrated that Trp and Tyr residues are initial reaction sites with T4NQO, while Tyr/O⋅ radical may be final species for Trp-Tyr dipeptide. In acidic aqueous solutions, the self-quenching rate constants of T4NQO and the rate constants of electron transfer from amino acids to T4NQO decrease with decreasing pH. In alkaline solutions, amino acids are easily oxidized by 4NQO under irradiation of laser pulse, and no transient absorption signal was observed.

Hyperthermal atomic oxygen beam-induced etching of HOPG (0001) studied by X-ray photoelectron spectroscopy and scanning tunneling microscopy

The basal planes of highly oriented pyrolytic graphite (HOPG) surfaces were exposed to atomic oxygen (AO) beam with a translational energy of approximately 5eV at room temperature. The characterization of the surfaces was carried out using X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM). The XPS spectra of the hyperthermal AO-exposed surfaces indicated that the oxygen coverage reached the saturated value of 0.94 with the AO fluence of approximately 4×1017 atomscm−2. The initial reaction site of the AO on the defect-free HOPG (0001) surface was observed as a protrusion in the STM images. In contrast, a hillock-like structure was formed at the AO-exposed HOPG (0001) surfaces at high AO fluences. The density of protrusions, observed in the initial AO/HOPG reaction, increased in proportion to the AO fluence. The reaction yield of hyperthermal AO with the defect-free HOPG (0001) surface was estimated to be 1.0×10−3. This value is two orders lower than that determined in the flight experiment aboard the space shuttle where the same chemical reaction was expected. The discrepancy was explained by the high reaction yield of the oxygen-covered prism planes of HOPG presented at the hillock surfaces.

Reactions of the Lithium Salts of the Tribenzylidenemethane Dianion, Diphenylacetone Dianion, and Related Compounds

Potentially synthetically useful reactions of the dilithium salts of the title dianions have been investigated. Electrophilic quenching with a variety of reagents usually leads to the expected products in good yield. Quenching the diphenylacetone dianion with 1 equiv of trimethylchlorosilane, however, gives a good yield of 1,3-diphenylallene obtained by formal elimination of a trimethylsiloxy anion from an intermediate monoquenched monoanion salt. NMR studies, however, do not reveal the intermediacy of the 1,3-diphenyl-2-(trimethylsiloxy)allyl anion but rather suggest that the initial reaction site is at carbon, rather than oxygen. Oxidation of the dianions leads either to ring closure or dimerization for the tribenzylidenemethane dianion and to dimerization for the diphenylacetone dianion. The dimerization reactions are stereospecific, both with respect to the two new stereocenters produced and for the double bonds of the bis-silyl enol ether products if the dimeric bis-enolate dianion products are quenc...

Cross-linking of DNA induced by chloroethylnitrosourea is presented by O6-methylguanine-DNA methyltransferase.

The DNA repair enzyme O6-methylguanine-DNA methyltransferase has been used as a reagent to analyse the initial reaction sites of alkylating agents such as chloroethylnitrosourea that cross-link DNA. The transferase can be employed for this purpose because it removes substituted ethyl groups from DNA, as shown by its ability to act on O6-hydroxyethylguanine residues in DNA. The enzyme counteracts the formation of interstrand cross-links induced by bis-chloroethylnitrosourea, but not those induced by nitrogen mustard. Once formed, chloroethylnitrosourea-induced cross-links are not broken by the enzyme. In agreement with deductions from experiments with living cells, it is concluded that chloroethylnitrosourea act by forming reactive monoadducts at the O6 position of guanine and/or the O4 position of thymine, which subsequently generate -CH2CH2- bridges to the complementary DNA strand. A new method for quantitating interstrand cross-links in DNA has been employed.

The chemical nature of osmium tetroxide fixation and staining of membranes by X-ray photoelectron spectroscopy

X-ray photoelectron spectroscopy was used to determine the oxidation states of osmium compounds present in erythrocyte ghost preparations and related systems treated with osmium tetroxide. Osmium tetroxide and cholesterol, codeposited at −100 ° C, began to react at −70 ° C, and Os(VI) was formed. Similarly, Os(VI) was detected for the known cholesterol-osmate ester prepared and purified chemically. However, osmium tetroxide applied in phosphate buffer (pH 7.2) gave rise to large proportions of Os(IV) and Os(III) species in addition to Os(VI) compounds. Egg phosphatidylcholine likewise produced a mixture of Os(VI), Os(IV), and Os(III), but dipalmitoyl phosphatidylcholine failed to give significant amounts of osmium containing products under identical conditions. Glutaraldehyde gave a mixture of compounds with the same osmium oxidation states when allowed to react with aqueous osmium tetroxide. Unfixed and glutaraldehyde-fixed erythrocyte ghosts also produced mixtures of Os(VI), Os(IV) and Os(III) under conditions identical to those of normal tissue processing. Additionally, the mixture of adducts initially formed by treatment with osmium tetroxide was further reduced by dehydration of the tissue with ethanol, resulting in a final mixture which was 50–60% Os(III). The results support a scheme for the reaction of osmium tetroxide with tissues in which the initial reaction site is the double bonds of unsaturated lipids to form Os(VI) derivatives. Subsequent hydrolysis and further reduction yield complexes of Os(IV) and Os(III). A mixture of these three states is present in membrane specimens during microscopic observation. Os(VI) and Os(IV) could be present as osmate esters and osmium dioxide, respectively; Os(III) could be present as an oxo- or amino complex(es). The photoelectron spectrum of intact erythrocyte ghosts can be synthesized from the spectra of phospholipid and cholesterol only, suggesting the predominance of the reaction with lipids in the fixation process.

Reaction of Nitrogen Dioxide With Blood and Lung Components

Electron spin resonance studies of the effects of nitrogen dioxide and cigarette smoke upon blood and lung tissue components were performed. In vivo exposure of small animals to NO 2 and cigarette smoke has been interpreted in terms of pollutant reaction with the heme moiety of hemoglobin. Results imply that the pollutants have migrated through the erythrocyte membrane. So as to understand the effects of these pollutants upon the membranes themselves, various model systems have been studied, particularly the interaction of nitrogen dioxide with unsaturated lipids. Three stable free radicals have been characterized as products of these reactions; and a short-lived initial free radical was observed, the structure of which provides evidence as to the initial reaction site and mechanism.

Identification of initial reaction sites in the dinitrophenylation of bovine pancreatic ribonuclease A

The principal products formed in the initial stages of the dinitrophenylation of bovine pancreatic ribonuclease A are 41-DNP-ribonuclease, 1-DNP-ribonuclease, 1,41-bis-DNP-ribonuclease and 7,41-bis-DNP-ribonuclease. These proteins may be separated by chromatography over columns of IRC-50. The location of the substituent in 41-DNP-ribonuclease A was demonstrated: ( a) by comparative chromatography of tryptic hydrolysates of the performic acid-oxidized protein and oxidized ribonuclease A, and ( b) by isolation of the peptide CySO 3H-ϵ-DNP-Lys-Pro-Val-Asn-Thr-Phe from a hydrolysate prepared by the successive action of trypsin and chymotrypsin on the oxidized protein. Identification of 1-DNP-ribonuclease was made by isolation of the peptide α-DNP-Lys-Glu-Thr from a combined tryptic and chymotryptic hydrolysate of the oxidized enzyme. Identification of 1,41-bis-DNP-ribonuclease and 7,41-bis-DNP-ribonuclease were made by the same approach. Substitution at position 7 was established by isolation of the peptides ϵ-DNP-Lys-Phe and ϵ-DNP-Lys-Phe-Glu-Arg.