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Journal of Pharmaceutical Sciences May 2004The metal-catalyzed oxidation (MCO) of proteins represents an important pathway for protein degradation. Although many mechanistic details of MCO are currently unknown,...
The metal-catalyzed oxidation (MCO) of proteins represents an important pathway for protein degradation. Although many mechanistic details of MCO are currently unknown, such mechanistic information would greatly benefit formulation scientists in the rational design and analysis of protein formulations. Here, we describe the Fenton oxidation (by Fe(2+)/H(2)O(2)) of several Met-, Tyr-, and His containing model peptides, including one derivative containing a conformationally restricted norbornyl Met analogue (Nor), Nor-Gly-His-Met-NH(2). Our results will provide evidence for a metal-bound reactive oxygen species selectively oxidizing Met to Met sulfoxide, indicating a Met-specific oxidant and arguing against the involvement of freely diffusible hydroxyl radicals. The Fenton oxidation of Nor-Gly-His-Met-NH(2) yields a 2:1 preference for sulfoxide formation at the C-terminal Met versus the N-terminal Nor residue, respectively, while incubation of the peptide with H(2)O(2) alone results in a 1:1 ratio. These results are rationalized by the better access of the thioether side chain of the flexible C-terminal Met residue to the peptide-bound iron compared with the conformationally restricted Nor residue. It is commonly believed that Fenton oxidation reactions involve hydroxyl radicals, and that Met oxidation in proteins is predominantly controlled by the surface-accessibility of the respective Met residues. However, occasionally protein oxidation in formulations shows selectivities, which are not consistent with these paradigms. Our results demonstrate additional features of the Fenton reaction such as the formation of a metal-bound oxidant specific for Met (and not Tyr or His), which may assist formulation scientists in the rationalization of unexpected oxidation selectivities.
Topics: Binding Sites; Hydrogen Peroxide; Iron; Methionine; Oxidants; Oxidation-Reduction; Peptides
PubMed: 15067689
DOI: 10.1002/jps.20013 -
Journal of Hazardous Materials Jul 2023Ultraviolet (UV) irradiation is widely used for wastewater disinfection but suffers from low inactivation rates and can cause photoreactivation of microorganisms.... (Review)
Review
Ultraviolet (UV) irradiation is widely used for wastewater disinfection but suffers from low inactivation rates and can cause photoreactivation of microorganisms. Synergistic disinfection with UV and oxidants is promising for enhancing the inactivation performance. This review summarizes the inactivation effects on representative microorganisms by UV/hydrogen peroxide (HO), UV/ozone (O), UV/persulfate (PS), UV/chlorine, and UV/chlorine dioxide (ClO). UV synergistic processes perform better than UV or an oxidant alone. UV mainly attacks the DNA or RNA in microorganisms; the oxidants HO and O mainly attack the cell walls, cell membranes, and other external structures; and HOCl and ClO enter cells and oxidize proteins and enzymes. Free radicals can have strong oxidation effects on cell walls, cell membranes, proteins, enzymes, and even DNA. At similar UV doses, the inactivation rates of Escherichia coli with UV alone, UV/HO, UV/O, UV/PS (peroxydisulfate or peroxymonosulfate), and UV/chlorinated oxidant (chlorine, ClO, and NHCl) range from 2.03 to 3.84 log, 2.62-4.30 log, 4.02-6.08 log, 2.93-5.07 log, and 3.78-6.55 log, respectively. The E. coli inactivation rates are in the order of UV/O ≈ UV/Cl > UV/PS > UV/HO. This order is closely related to the redox potentials of the oxidants and quantum yields of the radicals. UV synergistic disinfection processes inhibit photoreactivation of E. coli in the order of UV/O > UV/PS > UV/HO. The activation mechanisms and formation pathways of free radicals with different UV-based synergistic processes are presented. In addition to generating HO·, O can reduce the turbidity and chroma of wastewater to increase UV penetration, which improves the disinfection performance of UV/O. This knowledge will be useful for further development of the UV-based synergistic disinfection processes.
Topics: Disinfection; Hydrogen Peroxide; Wastewater; Chlorine; Escherichia coli; Oxidants; Oxidation-Reduction; Chlorides; Ultraviolet Rays; Water Purification
PubMed: 37062094
DOI: 10.1016/j.jhazmat.2023.131393 -
Inorganic Chemistry Jul 2009In acidic aqueous solutions, nitrogen monoxide oxidizes monosulfonated triphenylphosphine, TPPMS(-), to the corresponding phosphine oxide. The NO-derived product is...
In acidic aqueous solutions, nitrogen monoxide oxidizes monosulfonated triphenylphosphine, TPPMS(-), to the corresponding phosphine oxide. The NO-derived product is N(2)O. This chemistry parallels that reported for the reaction of NO with the unsubstituted triphenylphosphine in nonpolar organic solvents, but the rate constant measured in this work, 5.14 x 10(6) M(-2) s(-1), is greater by several orders of magnitude. This makes TPPMS(-) a useful analytical reagent for NO in aqueous solution. The increased rate constant in the present work appears to be a medium effect, and unrelated to the introduction of a single sulfonate group in the phosphine. The reaction between nitrous acid and TPPMS(-) has a 2:1 [TPPMS(-)]/[HNO(2)] stoichiometry and generates NH(2)OH quantitatively. The rate law, rate = 4k(d)[HNO(2)](2)[TPPMS(-)], identifies the second-order self-reaction of HNO(2) as the rate-limiting step that generates the active oxidant(s) for the fast subsequent reaction with TPPMS(-). It appears that the active oxidant is N(2)O(3), although the oxides NO and NO(2) derived from it may be also involved. Bimolecular self-reaction of HNO(2) also precedes the oxidations of ABTS(2-) and TMPD. Competing with this path are the acid-catalyzed oxidations of both reagents via NO(+).
Topics: Nitric Oxide; Nitrous Acid; Oxidation-Reduction; Phosphines; Spectrum Analysis; Water
PubMed: 19545139
DOI: 10.1021/ic900688g -
Environmental Science and Pollution... Sep 2017In this study, the effects of pre-oxidants permanganate (PM), persulfate (PS), hydrogen peroxide (PO), and ozone (OZ)) and/or adsorption on pseudoboemite-chitosan shell...
In this study, the effects of pre-oxidants permanganate (PM), persulfate (PS), hydrogen peroxide (PO), and ozone (OZ)) and/or adsorption on pseudoboemite-chitosan shell magnetic nanoparticles (ACMNs) on haloacetonitrile (HAN) and trichloronitromethane (TCNM) formation from aspartic acid (Asp; positive charge) and/or histidine (His; negative charge) were compared. Asp and His apparently do not interact in aqueous solution during chlorination. Asp and/or His can undergo partially oxidation by PM, but are recalcitrant to direct oxidation by PS and PO. Pre-oxidation with OZ decreases the formation of HANs but increases the formation of TCNM. ACMN prefers to adsorb Asp over His in the competitive sorption of coexisting Asp and His because of attractive electrostatic interactions. The rank order for the effect of the pre-oxidants and ACMN adsorption on dichloroacetonitrile and trichloroacetonitrile formation is OZ and ACMN adsorption > PM and ACMN adsorption > PS and ACMN adsorption > PO and ACMN adsorption; that for the effect of the pre-oxidants and ACMN adsorption on TCNM formation is PM and ACMN adsorption > PS and ACMN adsorption > PO and ACMN adsorption > OZ and ACMN adsorption. The favored adsorption of Asp over His by ACMN is weakened by pre-oxidation.
Topics: Acetonitriles; Adsorption; Halogenation; Hydrocarbons, Chlorinated; Hydrogen Peroxide; Manganese Compounds; Oxidants; Oxidation-Reduction; Oxides; Ozone; Water Pollutants, Chemical; Water Purification
PubMed: 28776295
DOI: 10.1007/s11356-017-9843-2 -
Journal of Pharmaceutical Sciences Dec 2009Recent oxidation events on monoclonal antibody candidates prompted us to investigate the mechanism of oxidation of Met, Trp, and His residues and to search for suitable...
Recent oxidation events on monoclonal antibody candidates prompted us to investigate the mechanism of oxidation of Met, Trp, and His residues and to search for suitable stabilizers. By using parathyroid hormone (1-34), PTH, as a model protein and various oxidants, aided by liquid chromatography, peptide mapping, and mass spectrometry, we identified and quantified the oxidation of these vulnerable residues. Whereas H(2)O(2) and t-butyl hydroperoxide (t-BHP) primarily oxidized the two Met residues, 2,2'-azobis(2-amidinopropane) dihydrochloride (AAPH), and H(2)O(2) + Fe(II) oxidized Met and Trp residues, with AAPH more capable of generating oxidized Trp species than the latter. H(2)O(2) + Fe(III) generated results comparable to those with H(2)O(2) + Fe(II), except that there was a lesser amount of hydroxylated Phe. Oxidation of the His residue in PTH occurred when copper was used instead of iron. AAPH, a free-radical generator, produced alkylperoxides, which simulated the oxidizing species from degraded polysorbate, commonly found in protein formulations. It is prudent to screen stabilizers by using H(2)O(2), H(2)O(2) + Fe(II), and AAPH because these agents represent potential assaults from the H(2)O(2) commonly present in degraded polysorbate, the residue of aseptic agents and the metal from stainless steel surfaces, and alkylperoxides from degraded polysorbate, respectively. Free Met protected the Met residues in PTH from oxidation by H(2)O(2) and H(2)O(2) + Fe(II). Mannitol and EDTA were effective against H(2)O(2) + Fe(II). Free Trp protected only the Trp residue in PTH from oxidation by AAPH, the combination of Trp and Met was effective against all three oxidant conditions. By using AAPH to generate oxidant, Trolox (6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid) and pyridoxine were also found to exhibit good free-radical scavenging activity and thus protected Trp in PTH against oxidation.
Topics: Amino Acid Sequence; Chromatography, High Pressure Liquid; Edetic Acid; Free Radical Scavengers; Histidine; Hydrogen Peroxide; Hydrolysis; Hydroxylation; Indicators and Reagents; Mannitol; Methionine; Molecular Sequence Data; Oxidants; Oxidation-Reduction; Oxidative Stress; Parathyroid Hormone; Peptide Mapping; Sucrose; Trypsin; Tryptophan
PubMed: 19455640
DOI: 10.1002/jps.21746 -
Environmental Research Sep 2023In this study, the relative residual UV absorbance (UV) and/or electron donating capacity (EDC) was investigated as a surrogate parameter to evaluate the abatement of...
In this study, the relative residual UV absorbance (UV) and/or electron donating capacity (EDC) was investigated as a surrogate parameter to evaluate the abatement of micropollutants during the Fe(II)/PMS and Mn(II)/NTA/PMS processes. In the Fe(II)/PMS process, due to the generation of SO and •OH at acidic pH, UV and EDC abatement was greater at pH 5. In the Mn(II)/NTA/PMS process, UV abatement was greater at pH 7 and 9, while EDC abatement was greater at pH 5 and 7. This was attributed to the fact that MnO was formed at alkaline pH to remove UV by coagulation, and manganese intermediates (Mn(V)) were formed at acidic pH to remove EDC via electron transfer. Due to the strong oxidation capacity of SO, •OH and Mn(V), the abatement of micropollutants increased with increasing dosages of oxidant in different waters in both processes. In the Fe(II)/PMS and Mn(II)/NTA/PMS processes, except for nitrobenzene (∼23% and 40%, respectively), the removal of other micropollutants was greater than 70% when the oxidant dosages were greater in different waters. The linear relationship between the relative residual UV, EDC and the removal of micropollutants was established in different waters, showing a one-phase or two-phase linear relationship. The differences of the slopes for one-phase linear correlation in the Fe(II)/PMS process (micropollutant-UV: 0.36-2.89, micropollutant-EDC: 0.26-1.75) were less than that in the Mn(II)/NTA/PMS process (micropollutant-UV: 0.40-13.16, micropollutant-EDC: 0.51-8.39). Overall, these results suggest that the relative residual UV and EDC could truly reflect the removal of micropollutants during the Fe(II)/PMS and Mn(II)/NTA/PMS processes.
Topics: Electrons; Manganese Compounds; Water Pollutants, Chemical; Oxides; Oxidation-Reduction; Oxidants; Ferrous Compounds
PubMed: 37276973
DOI: 10.1016/j.envres.2023.116253 -
Environmental Science & Technology Feb 2003Permanganate injection is increasingly applied for in situ destruction of chlorinated ethenes in groundwater. This laboratory and field study demonstrates the roles that...
Permanganate injection is increasingly applied for in situ destruction of chlorinated ethenes in groundwater. This laboratory and field study demonstrates the roles that carbon isotope analysis can play in the assessment of oxidation of trichloroethene (TCE) by permanganate. In laboratory experiments a strong carbon isotope fractionation was observed during oxidation of TCE with similar isotopic enrichment factors (-25.1 to -26.8 per thousand) for initial KMnO4 concentrations between 67 and 1,250 mg/L. At the field site, a single permanganate injection episode was conducted in a sandy aquifer contaminated with TCE as dense nonaqueous liquid (DNAPL). After injection, enriched delta13C values of up to +204% and elevated Cl- concentrations were observed at distances of up to 4 m from the injection point. Farther away, the Cl- increased without any change in delta13C of TCE suggesting that Cl- was not produced locally but migrated to the sampling point Except for the closest sampling location to the injection point, the delta13C rebounded to the initial 613C again, likely due to dissolution of DNAPL Isotope mass balance calculations made it possible to identify zones where TCE oxidation continued to occur during the rebound phase. The study indicates that delta13C values can be used to assess the dynamics between TCE oxidation and dissolution and to locate zones of oxidation of chlorinated ethenes that cannot be identified from the Cl- distribution alone.
Topics: Chlorine Compounds; Ethylenes; Isotopes; Manganese Compounds; Oxidants; Oxidation-Reduction; Oxides
PubMed: 12636282
DOI: 10.1021/es020073d -
Critical Care Medicine Apr 2000The free radical nitric oxide (NO) has emerged in recent years as a fundamental signaling molecule for the maintenance of homeostasis, as well as a potent cytotoxic... (Review)
Review
The free radical nitric oxide (NO) has emerged in recent years as a fundamental signaling molecule for the maintenance of homeostasis, as well as a potent cytotoxic effector involved in the pathogenesis of a wide range of human diseases. Although this paradoxical fate has generated confusion, separating the biological actions of NO on the basis of its physiologic chemistry provides a conceptual framework which helps to distinguish between the beneficial and toxic consequences of NO, and to envision potential therapeutic strategies for the future. Under normal conditions, NO produced in low concentration acts as a messenger and cytoprotective (antioxidant) factor, via direct interactions with transition metals and other free radicals. Alternatively, when the circumstances allow the formation of substantial amounts of NO and modify the cellular microenvironment (formation of the superoxide radical), the chemistry of NO will turn into indirect effects consecutive to the formation of dinitrogen trioxide and peroxynitrite. These "reactive nitrogen species" will, in turn, mediate both oxidative and nitrosative stresses, which form the basis of the cytotoxicity generally attributed to NO, relevant to the pathophysiology of inflammation, circulatory shock, and ischemia-reperfusion injury.
Topics: Drug Interactions; Free Radical Scavengers; Homeostasis; Humans; Nitrates; Nitric Oxide; Nitrosation; Oxidants; Signal Transduction
PubMed: 10807315
DOI: 10.1097/00003246-200004001-00005 -
Waste Management (New York, N.Y.) 2003The polycyclic aromatic hydrocarbons (PAH) that contaminate soils at many industrial and government sites are resistant to natural biotic and abiotic degradation...
The polycyclic aromatic hydrocarbons (PAH) that contaminate soils at many industrial and government sites are resistant to natural biotic and abiotic degradation processes. The recalcitrant nature of these compounds may require aggressive chemical treatment to effectively remediate these sites. This study was conducted to assess the viability of permanganate oxidative treatment as a method to reduce PAH concentration in contaminated soils. Study results demonstrated a reduction in soil sorbed concentration for a mixture of six PAHs that included anthracene, benzo(a)pyrene, chrysene, fluoranthene, phenanthrene, and pyrene by potassium permanganate (KMnO4) oxidative treatment. The greatest reduction in soil concentration was observed for benzo(a)pyrene, pyrene, phenanthrene, and anthracene at 72.1, 64.2, 56.2, and 53.8%, respectively, in 30 min at a KMnO4 concentration of 160 mM. Minimal reductions in fluoranthene and chrysene concentration were observed at 13.4 and 7.8%, respectively, under the same conditions. A relative chemical reactivity order of benzo(a)pyrene>pyrene>phenanthrene>anthracene>fluoranthene>chrysene towards permanganate ion was observed. Aromatic sextet theory was applied to the degradation results to explain the highly variable and compound-specific chemical reactivity order.
Topics: Manganese Compounds; Oxidants; Oxidation-Reduction; Oxides; Polycyclic Aromatic Hydrocarbons; Soil Pollutants
PubMed: 14522192
DOI: 10.1016/S0956-053X(02)00119-8 -
Environmental Science & Technology Aug 2008Several groups of popular antibacterial agents (i.e., phenols, fluoroquinolones, aromatic N-oxides, and tetracyclines) were demonstrated in earlier studies to be highly...
Several groups of popular antibacterial agents (i.e., phenols, fluoroquinolones, aromatic N-oxides, and tetracyclines) were demonstrated in earlier studies to be highly susceptible to oxidation by manganese oxides, a common oxidant in soils. However, because of the high complexity, the reaction kinetics were not fully characterized. A mechanism-based kinetic model has now been developed to successfully describe the entire range of kinetic data for a total of 21 compounds of varying structural characteristics (with R2 > 0.93). The model characterizes the reaction kinetics by two independent parameters, the reaction rate constant (k) and total reactive surface sites (S(rxn)). The model fitting indicates that the reaction kinetics of antibacterials with MnO2 are controlled by either the rate of surface precursor complex formation (for tetracyclines) or by the rate of electron transfer within the precursor complex (for phenols, fluoroquinolones, and aromatic N-oxides). The effect of reactant concentration, pH, and cosolutes on the reaction kinetics was evaluated and correlated to kand S(rxn). All the trends are consistent with the proposed rate-limiting steps. This new model improves the ability to quantitatively evaluate the kinetics of oxidative transformation of organic contaminants by manganese oxides in well-defined systems.
Topics: Anti-Bacterial Agents; Cyclic N-Oxides; Electron Transport; Fluoroquinolones; Hydrogen-Ion Concentration; Kinetics; Manganese Compounds; Models, Chemical; Oxidants; Oxidation-Reduction; Oxides; Phenols; Soil Pollutants; Tetracyclines
PubMed: 18754474
DOI: 10.1021/es703143g