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Iron oxygenases generate elusive transient oxygen species to catalyze substrate oxygenation in a wide range of metabolic processes. Here we resolve the reaction sequence and structures of such intermediates for the archetypal non-heme Fe II and α-ketoglutarate-dependent dioxygenase TauD. Time-resolved Raman spectra of the initial species with 16 O 18 O oxygen unequivocally establish the Fe IV ═O structure. 1 H/ 2 H substitution reveals direct interaction between the oxo group and the C1 proton of substrate taurine. Two new transient species were resolved following Fe IV ═O; one is assigned to the ν FeO mode of an Fe III ─O(H) species, and a second is likely to arise from the vibration of a metal-coordinated oxygenated product, such as Fe II ─O─C 1 or Fe II ─OOCR. These results provide direct insight into the mechanism of substrate oxygenation and suggest an alternative to the hydroxyl radical rebinding paradigm.

The stoichiometry and the kinetics of oxidation of the cyanide complexes M(CN) n 4- (M = Fe(II), Ru(II), Os(II), Mo(IV), and W(IV)) by the peroxydisulfate ion, S 2 O 8 2-, and by the much more strongly oxidizing fluoroxysulfate ion, SO 4 F-, were studied in aqueous solutions containing Li + . Reactions of S 2 O8 2 - with M(CN) n 4 - are known to be strongly catalyzed by Li + and other alkali metal ions, and this applies also to the corresponding reactions of SO 4 F-. The primary reactions of S 2 O 8 2- and SO 4 F- have both been found to be one-electron processes in which the equally strong O-O and O-F bonds are broken. The primary reaction of S 2 O8 2 - consists of a single step yielding M(CN) n 3- , SO 4 -, and SO 4 2-, whereas the primary reaction of SO 4 F- comprises two parallel one-electron steps, one leading to M(CN) n 3 -, SO 4 -, and F- and the other yielding M(CN) n -1 2- , CN - , SO 4 - and F-. The relationship between the rate constants and the standard free energies of reaction for the Li + -catalyzed reactions of SO 4 F- and S 2 O 8 2- with M(CN) n 4- , and for the uncatalyzed reactions of S 2 O 8 2- with bipyridyl and phenanthroline complexes ML n 2+ (M = Fe(II), Ru(II), and Os(II)) studied previously, suggests that the intrinsic barrier for all three sets of reactions is similar, i.e., unaffected by the Li + catalysis, and that the electron transfer and the breakage of the O-O and O-F bonds are concerted processes.

CF3OH, an important and controversial by-product of atmospheric decomposition of CF3CFH2 (HFC-134a) and other hydrofluorocarbons, has been examined by photoionization mass spectrometry. The ionization onset is characterized by a broad Franck–Condon distribution, arising primarily from a substantial elongation of the C–O bond upon ionization. An upper limit to the adiabatic ionization potential (IP) of ⩽13.08±0.05 eV has been established. The appearance potentials (APs) of the first two fragments have been accurately determined by fitting with appropriate model functions as AP0(CF2OH+/CF3OH)⩽13.830±0.005 eV and AP0(CF3+/CF3OH)⩽13.996±0.005 eV. While the exact nature of the lowest-energy fragment (nominally CF2OH+) is not clear, the CF3+ fragment threshold leads unambiguously to ΔHf 298∘(CF3OH)⩾−217.2±0.9 kcal/mol and D298(CF3–OH)⩽115.2±0.3 kcal/mol. With previously derived ΔHf 298∘(CF3O)=−151.8−1.1+1.7 kcal/mol, this yields D298(CF3O–H)=117.5−1.4+1.9 kcal/mol, very close to, or only slightly weaker than th...

Our efforts to model the oxygen activation chemistry of nonheme iron enzymes have yielded transient intermediates with novel properties. These properties can be dramatically affected by the introduction of a 6-methyl substituent on the pendant pyridines of the tetradentate ligand TPA (TPA = tris(2-pyridylmethyl)amine). A series of Fe(TPA) complexes has thus been synthesized and characterized to provide the structural basis for these dramatic effects. The following complexes have been obtained: [Fe(L)(CH3CN)2](ClO4)2 (1, L = TPA; 2, L = 6-MeTPA; 3, L = 6-Me2TPA; 4, L = 6-Me3TPA) and [Fe(L)(acac)](ClO4)2 (5, L = TPA; 6, L = 5-Me3TPA; 7, L = 6-MeTPA). As indicated by 1H NMR and/or EPR, 1, 5, and 6 with no 6-methyl substituent are low spin, while complexes 2, 3, 4, and 7 with at least one 6-methyl substituent are all high spin, with higher redox potentials than their low-spin counterparts. The ligands with 6-methyl substituents thus favor a metal center with a larger ionic radius, i.e., FeII over FeIII and h...

In light of the recent controversy surrounding its heat of formation, CF2O was reexamined by photoionization mass spectrometry. In particular, the CO+ fragment ion yield curve from CF2O was interpreted in terms of a retarded CO++F2 process, and a more facile two‐step fragmentation to CO++2F. The former process produces a weak, slowly growing tail region without a clear onset, while the latter occurs at higher energy and causes a pronounced growth with a conspicuous onset, which was found to occur at ≤20.87+0.03/−0.07 eV at 0 K by fitting with a model curve that incorporates ‘‘fluctuations’’ associated with second‐generation fragments. This onset leads to ΔHf° 298(CF2O) ≥−149.1+1.4/−0.7 kcal/mol, and indicates that the older experimental values for this quantity are too low by at least 3–4 kcal/mol. While the F2 elimination is retarded by competition with lower energy processes, the two‐step process derives its strength from the FCO+ fragment, which assumes the role of a pseudoparent. Thus, the onset of CO...

The vanadium(V)-catalyzed oxidation of (1-hydroxyethylidene)bisphosphonic acid, CH 3 C(OH)(PO 3 H 2 ) 2 , by hydrogen peroxide in aqueous solution has been studied at temperatures between 50 and 80°C. In contrast to vanadium(V), six-valent Mo and W are without significant catalytic action, as is SeO 2 , while OsO 4 is only weakly catalytic. With excess substrate a limiting stoichiometry is reached in which ca. 4 mol H 2 O 2 are consumed per mol of substrate oxidized. With excess H 2 O 2 , the reaction competes with catalytic decomposition of the peroxide, and a substantial excess of peroxide is required to consume the substrate completely. The reaction is optimal near pH 1. At higher pH it becomes slower, while at lower pH the catalytic decomposition of H 2 O 2 comes to predominate. The principal reaction products are phosphoric and acetic acids and carbon dioxide, along with lesser quantities of CO and formic acid. The consumption of substrate in the presence of a large excess of H 2 O 2 follows first-order kinetics, but the apparent first-order rate constant shows a weak positive dependence on initial substrate concentration, which may be pH-related, and at high substrate concentration it shows a weak negative dependence on initial [H 2 O 2 ]. The principal reactant appears to be the diperoxovanadium(V) anion, OV(O 2 ) − 2 , but the apparent rate shows a greater-than-first-order dependence on catalyst concentration, suggesting a secondary reaction path involving a dimeric peroxovanadium species. A free-radical mechanism has been proposed in which one-electron reduction of the vanadium accompanies oxidation of the substrate to an intermediate alkoxyl radical species that can yield either acetic acid or CO 2 . This mechanism is supported by the observation that vanadium(V) itself oxidizes the substrate at a measurable rate.

Methylrhenium dioxide, CH3ReO2 (or MDO), is produced from methylrhenium trioxide, CH3ReO3 (or MTO), and hypophosphorous acid in acidic aqueous medium. Its mechanism is discussed in light of MTO's coordination ability and the inverse kinetic isotope effect (kie): H2P(O)OH, k = 0.028 L mol-1 s-1; D2P(O)OH, k = 0.039 L mol-1 s-1. The Re(V) complex, MDO, reduces perchlorate and other inorganic oxoanions (XOn-, where X = Cl, Br, or I and n = 4 or 3). The rate is controlled by the first oxygen abstraction from perchlorate to give chlorate, with a second-order rate constant at pH 0 and 25 °C of 7.3 L mol-1 s-1. Organic oxygen-donors such as sulfoxides and pyridine N-oxides oxidize MDO to MTO as do metal oxo complexes: VO2+(aq), VO2+(aq), HOMoO2+(aq), and MnO4-. The reaction between V2+(aq) with MTO and the reduction of VO2+ with MDO made it possible to determine the free energy for MDO/MTO. Oxygen-atom transfer from oxygen-donors to MDO involves nucleophilic attack of X−O on the electrophilic Re(V) center of M...

Peroxynitric acid, HOONO{sub 2}, can be prepared in aqueous solution by the reaction of nitrous acid with a greater-than-2-fold excess of hydrogen peroxide at or below 0{degrees}C. Under optimum conditions, concentrations in excess of 1.5 M can be obtained. In acid solution at room temperature, the compound has a ca. 30 min half-life for decomposition; in alkaline solution, decomposition is very rapid, yielding nitrite ion and oxygen. The aqueous acid is a potent oxidizing agent, reacting rapidly with I{sup {minus}}, Br{sup {minus}}, N{sub 3}{sup {minus}}, and VO{sup 2+}. Raman, UV, and {sup 15}N NMR spectra of the aqueous acid have been obtained. The Raman spectra reveal three new fundamental vibrations of the peroxynitric acid molecule, leaving only two that have yet to be positively identified. The UV spectrum shows a monotonic rise in absorbance between 290 and 230 nm; the {sup 15}N NMR resonance has a chemical shift of -28.3 ppm relative to dilute nitric acid.

The NMR spectra (35Cl, 79Br, 81Br, 127I and 17O) of the tetrahedral perhalate anions XO4− (X Cl, Br and I) were compared for the first time in acetonitrile solution, a medium in which the resonances are relatively sharp and in which no oxygen exchange occurs. Relaxation studies of the quadrupolar nuclei in these solutions at 24°C are reported and show that excellent spectra may be obtained at 0.1 M concentration; thus the observation of separate resonances for Cl 16O4− and Cl 18O 16O3− represents the first reported instance of a 35Cl secondary isotopic shift [1 Δ 35Cl(18.16O) = -0.090 ppm]. Enrichment with 17O of all three ions was carried out and the 1J(127I, 17O) coupling constant (489 Hz) has been observed for the first time. The chemical shifts and coupling constants are discussed, especially in connection with the anomalous properties of the perbromate ion. Halogen chemical shifts for BrO3F, IF7 and IF6+ AsF6− are reported for the first time.

Resonance Raman spectra were measured selectively for the "607 nm" form, which had been assigned to a peroxy intermediate formed in the reaction of oxidized cytochrome c oxidase with hydrogen peroxide at ambient temperature. A single oxygen isotope-sensitive band was found at 803 cm-1 for the reaction with H2(16)O2 (at 769 cm-1 with H2(18)O2) upon excitation at 607 nm, the wavelength of the difference absorption maximum characteristic of the "peroxy" intermediate. Upon excitation at shorter wavelengths (down to 580 nm), the Raman spectrum simply became weaker without yielding any new features. When H2(16)O18O was used, two bands were observed at 803 and 769 cm-1 (within an accuracy of 0.5 cm-1), but with only half the intensity of those observed with H2(16)O2 or H2(18)O2, which ruled out the possibility that the 803 cm-1 band arose from the O-O or Fe-O2 stretching of the FeIII(O-O-) heme. Conversely, the 34-cm-1 downshift with 18O is in good agreement with the calculated 16O/18O shift (35 cm-1) expected for the diatomic Fe = 16O oscillator at 803 cm-1. This band exhibited an upshift by 1.3 cm-1 in 2H2O, similar to the case of compound II of horseradish peroxidase at neutral pH, and indicative of the presence of a hydrogen bond to the FeIV = O oxygen. The 803/769 cm-1 pair of resonance Raman bands were also observed upon blue excitation, as is the case for the bands found in the dioxygen cycle of this enzyme (Ogura, T., Takahashi, S., Hirota, S., Shinzawa-Itoh, K., Yoshikawa, S., Appelman, E. H., and Kitagawa, T. (1993) J. Am. Chem. Soc. 115, 8527-8536). This observation provides the first direct characterization of the 607 nm form of this enzyme in its reaction with H2O2.

A new oxygen-isotope-sensitive Raman band was found for oxyhemoglobin (HbO[sub 2]) and oxycytochrome c oxidase (CcO[center dot]O[sub 2]) in the frequency region lower than the Fe-O[sub 2] stretching mode ([nu][sub Fe-O2]). This band was located at 425 cm[sup [minus]1] for Hb[sup 16]O[sub 2] and shifted to 405 cm[sup [minus]1] with Hb[sup 18]O[sub 2] and to approximately 423 and approximately 407 cm[sup [minus]1] with Hb[sup 16]O[sup 18]O. The corresponding band appeared at 435 cm[sup [minus]1] for CcO[center dot][sup 16]O[sub 2] and shifted to 415 cm[sup [minus]1] with CcO[center dot][sup 18]O[sub 2]. Accordingly, the band has been assigned to the Fe-O-O bending mode (delta[sub FeOO]). However, the corresponding band could not be identified for oxymyoglobin (MbO[sub 2]). The Fe-O[sub 2] stretching mode ([nu][sub Fe-O2]) was observed at 568, 567, 544, and 544 cm[sup [minus]1] for Hb[sup 16]O[sub 2], Hb[sup 16]O[sup 18]O, Hb[sup 18]O[sup 16]O, and Hb[sup 18]O[sub 2], respectively, and the corresponding modes were observed at 571, 569, 547, and 545 cm[sup [minus]1] for MbO[sub 2] and 571, 567, 548, and 544 cm[sup [minus]1] for CcO[center dot]O[sub 2]. The [nu][sub Fe-O(2)] bandwidths of HbO[sub 2] and MbO[sub 2] were alike and 1.5 times broader than that of CcO-O[sub 2], suggesting that themore » Fe-O-O geometry is more nearly fixed in the latter. 44 refs., 6 figs., 1 tab.« less

Oxidation Reactions with HOF and Adducts of HOF and HF with Acetonitrile In acetonitrile solution HOF oxides CF3SSCF3 via CF3S(O)nSCF3 (n = 1, 2) to yield [CF3S(O)2]2O. Analogously, CF3Se(O)OH and CF3SeX (X = Cl, Br) are oxidized via CF3Se(VI) intermediates to provide finally [CF3Se(O)2]2O. With CH3CN at low temperatures HOF and HF form 1:1 adducts, whose structures have been elucidated by low-temperature X-ray structure analysis. Additional proof for the formation of CH3CN · HF in the liquid phase is provided.

Time-resolved resonance Raman (RR) spectra were observed for catalytic intermediates of bovine cytochrome c oxidase at room temperature by using an Artificial Cardiovascular System for Enzymatic Reactions and Raman/Absorption Simultaneous Measurement Device. The isotope-frequency-shift data using an asymmetrically labeled dioxygen, [sup 16]O[sup 18]O, established that the primary intermediate (compound A) is an end-on-type dioxygen adduct of cytochrome a[sub 3]. Higher resolution RR experiments revealed that the approximately 800-cm[sup [minus]1] band assigned previously to the Fe[sup TV]= O stretching mode of the subsequent intermediate (compound B) was actually composed of two bands that behaved differently upon deuteration. The 804/764-cm[sup [minus]1] pair for the [sup 16]O[sub 2]/[sup 18]O[sub 2] derivatives were insensitive to deuteration, and these bands became noticeably stronger at higher temperatures. The present experiments have conclusively established that the main pathway for dioxygen reduction by cytochrome c oxidase is Fe[sup II]-O[sub 2] [yields] Fe[sup III]-O-O-H [yields] Fe[sup IV]=O [yields] Fe[sup III]-OH and that their key bands for the [sup 16]O[sub 2]/[sup 18]O[sub 2] pair are at 571/544, 785/751, 804/764, and 450/425 cm[sup [minus]1], respectively. 79 refs., 8 figs., 3 tabs.

tert-Butyl hypofluorite ((CH[sub 3])[sub 3]COF) can be synthesized by the low-temperature reaction of elemental fluorine with tert-butyl alcohol dissolved in propionitrile or acetonitrile. The isolated compound, which melts around -94[degrees]C and has an extrapolated boiling point of about +40[degrees]C, has been characterized by mass, NMR, and IR spectrometry. The [sup 19]F NMR shift of +67 ppm lies between the corresponding shifts of HOF and CH[sub 3]OF and implies a rather high O-F bond energy. Although sterically crowded, tert-butyl hypofluorite adds to olefins to form [beta]-fluoro-tert-butoxy compounds. Addition is mainly in an anti mode, and the regioselectivity corresponds to the action of a hitherto unknown tert-butoxylium electrophile. Also formed are adducts containing F and CH[sub 2]CN, the latter deriving from the acetonitrile solvent. 19 refs., 1 tab.

Methyl hypofluorite (CH 3 OF) has been prepared by the reaction of elemental fluorine with methanol in acetonitrile or propionitrile at low temperature. It was removed from the reaction mixture in a stream of nitrogen and purified by fractional distillation. The compound is moderately long-lived, although the liquid has exploded upon rapid warming. The liquid compound has a freezing point of about −142°C, and vapor pressure measurements indicate a normal boiling point of −32.6±0.9°C and an enthalpy of vaporization of 23.37±0.26 kJ/mol. The infrared spectrum of the vapor is consistent with the molecule being isostructural with CH 3 OH and CF 3 OF. The compound has also been characterized by mass spectrometry and by 1 H, 19 F, and 13 C NMR spectrometries. This novel reagent adds across various double bonds to form the corresponding fluoro methoxy adducts, which are not easily accessible by other methods

Trifluoromethanesulfonyl hypofluorite (CF[sub 3]SO[sub 2]OF) has been synthesized by the reaction of fluorosulfuryl hypofluorite (FSO[sub 2]OF) with cesium trifluoromethanesulfonate. It is the first compound in which a sulfur atom is bonded both to carbon and to an O-F moiety. The compound has a melting point of -87 [plus minus] 2[degrees]C and an extrapolated boiling point of 0 [plus minus] 1[degrees]C. The [sup 19]F NMR spectrum of the compound in CFCl[sub 3] at -80[degrees]C shows a CF[sub 3] doublet at -71 ppm and a broad OF singlet at +238 ppm. From the latter can be deduced an O-F bond energy of about 145 kJ/mol, comparable to that of FSO[sub 2]OF. The compound hydrolyses in base to give a mixture of O[sub 2] and CF[sub 4], along with (presumably) sulfate and trifluoromethanesulfonate. It decomposes thermally in the presence of CsF to yield principally CF[sub 3]SO[sub 2]F and OF[sub 2] along with (presumably) cesium trifluoromethanesulfonate. 14 refs., 1 tab.

The strong oxidant produced by the reaction of elemental fluorine with acetonitrile containing ca. 10% water has been shown to be hypofluorous acid, HOF, which is stabilized by complexing to the solvent. The reaction represents a new and convenient method of preparing and handling HOF, a unique oxygenating reagent. The presence of acetonitrile results in subtle but significant changes in the chemical behavior of the HOF. Vibrational and NMR spectroscopic studies of the solutions resulting from this reaction, as well as of solutions prepared by dissolving neat HOF in dry acetonitrile, have shown that the complex is a 1:1 hydrogen-bridged entity, in which the HOF proton is most likely bonded to the nitrogen atom of the nitrile. The 19 F NMR data indicate that the complexation reaction has an equilibrium constant of ca. 3 at room temperature, and that the enthalpy of formation of the complex is −14.3 ± 0.5 kJ mol −1 . The success of this method of synthesizing hypofluorous acid is a consequence of the very slow reaction between HOF and low concentrations of water in acetonitrile. This reaction accelerates drastically as the water content increases. As the solution composition approaches 100% water, the rate constant appears to approach a limit of about 0.7 s −1 at 25 °C, which may be the actual rate of reaction of HOF with the water.

tert-Butyl hypofluorite ((CH[sub 3])[sub 3]COF) can be synthesized by the low-temperature reaction of elemental fluorine with tert-butyl alcohol dissolved in propionitrile or acetonitrile. The isolated compound, which melts around -94[degrees]C and has an extrapolated boiling point of about +40[degrees]C, has been characterized by mass, NMR, and IR spectrometry. The [sup 19]F NMR shift of +67 ppm lies between the corresponding shifts of HOF and CH[sub 3]OF and implies a rather high O-F bond energy. Although sterically crowded, tert-butyl hypofluorite adds to olefins to form [beta]-fluoro-tert-butoxy compounds. Addition is mainly in an anti mode, and the regioselectivity corresponds to the action of a hitherto unknown tert-butoxylium electrophile. Also formed are adducts containing F and CH[sub 2]CN, the latter deriving from the acetonitrile solvent. 19 refs., 1 tab.

The strong oxidant produced by the reaction of elemental fluorine with acetonitrile containing ca. 10% water has been shown to be hypofluorous acid, HOF, which is stabilized by complexing to the solvent. The reaction represents a new and convenient method of preparing and handling HOF, a unique oxygenating reagent. The presence of acetonitrile results in subtle but significant changes in the chemical behavior of the HOF. Vibrational and NMR spectroscopic studies of the solutions resulting from this reaction, as well as of solutions prepared by dissolving neat HOF in dry acetonitrile, have shown that the complex is a 1:1 hydrogen-bridged entity, in which the HOF proton is most likely bonded to the nitrogen atom of the nitrile. The 19 F NMR data indicate that the complexation reaction has an equilibrium constant of ca. 3 at room temperature, and that the enthalpy of formation of the complex is −14.3 ± 0.5 kJ mol −1 . The success of this method of synthesizing hypofluorous acid is a consequence of the very slow reaction between HOF and low concentrations of water in acetonitrile. This reaction accelerates drastically as the water content increases. As the solution composition approaches 100% water, the rate constant appears to approach a limit of about 0.7 s −1 at 25 °C, which may be the actual rate of reaction of HOF with the water.

Methyl hypofluorite (CH 3 OF) has been prepared by the reaction of elemental fluorine with methanol in acetonitrile or propionitrile at low temperature. It was removed from the reaction mixture in a stream of nitrogen and purified by fractional distillation. The compound is moderately long-lived, although the liquid has exploded upon rapid warming. The liquid compound has a freezing point of about −142°C, and vapor pressure measurements indicate a normal boiling point of −32.6±0.9°C and an enthalpy of vaporization of 23.37±0.26 kJ/mol. The infrared spectrum of the vapor is consistent with the molecule being isostructural with CH 3 OH and CF 3 OF. The compound has also been characterized by mass spectrometry and by 1 H, 19 F, and 13 C NMR spectrometries. This novel reagent adds across various double bonds to form the corresponding fluoro methoxy adducts, which are not easily accessible by other methods

The direct electrophilic radiofluorination of m-tyrosine using [18F]acetylhypofluorite was investigated. Results showed that this reaction was both rapid and efficient with recovered decay corrected yield of 71% radiofluorinated m-tyrosines based on starting [18F]acetylhypofluorite. Specific activity of the product obtained in this study was 100-200 mCi/mmol although 1-5 Ci/mmol are easily achievable with our improved production of [18F]AcOF. Three positional isomers were found and identified by 19F-NMR to be 2-, 4-, 6-fluoro-m-tyrosine with a distribution of 36:11:52, respectively. This measured distribution allowed the assignment of the radio-HPLC peaks. Biological studies are currently underway in our laboratory using these fluoro-m-tyrosines to determine which isomer would be most suited for the evaluation of the dopamine system by positron tomography.

Ozone in the presence of hydrogen peroxide has been employed succesfully for the oxidative degradation of polycarboxylic and diphosphonic acid chelating agents present at the 0.1 M level in a neutral or weakly alkaline aqueous solution. The geminal diphosphonic acid complexants methanediphosphonic acid and (1-hydroxyethylidene)bisphosphonic acid have been successfully mineralized, as have the polycarboxylic acids ethylenediaminetetraacetic acid and tetrahydrofurantetracarboxylic acid.

Trifluoromethanesulfonyl hypofluorite (CF[sub 3]SO[sub 2]OF) has been synthesized by the reaction of fluorosulfuryl hypofluorite (FSO[sub 2]OF) with cesium trifluoromethanesulfonate. It is the first compound in which a sulfur atom is bonded both to carbon and to an O-F moiety. The compound has a melting point of -87 [plus minus] 2[degrees]C and an extrapolated boiling point of 0 [plus minus] 1[degrees]C. The [sup 19]F NMR spectrum of the compound in CFCl[sub 3] at -80[degrees]C shows a CF[sub 3] doublet at -71 ppm and a broad OF singlet at +238 ppm. From the latter can be deduced an O-F bond energy of about 145 kJ/mol, comparable to that of FSO[sub 2]OF. The compound hydrolyses in base to give a mixture of O[sub 2] and CF[sub 4], along with (presumably) sulfate and trifluoromethanesulfonate. It decomposes thermally in the presence of CsF to yield principally CF[sub 3]SO[sub 2]F and OF[sub 2] along with (presumably) cesium trifluoromethanesulfonate. 14 refs., 1 tab.

Resonance Raman spectroscopy has been applied to two distinct temporal species of indoleamine 2,3-dioxygenase during catalytic turnover. We have identified two oxygen-isotope-sensitive Raman modes ...

Six oxygen-associated vibrations were observed for reaction intermediates of bovine cytochrome c oxidase with O2 using time-resolved resonance Raman spectroscopy. The isotope shift of the Fe-O2 stretching frequency for an asymmetrically labeled dioxygen, 16O18O, has established that the primary intermediate of cytochrome a 3 is an end-on type dioxygen adduct of Fea3. The subsequent intermediates at about 0.1–1 ms following the initiation of reaction yielded Raman band pairs at 804/764, 785/751, and 356/342 cm−1 for 16O2/18O2 derivatives in H2O and, while these frequencies were the same between the H2O and D2O solutions, the final intermediate appearing at about 3 ms gave the Raman bands at 450/425 cm−1 in H2O and 443/417 cm−1 in D2O. The last bands are reasonably assigned to the Fe-OH(D) stretching mode. The extended measurements at lower temperatures and longer delay times have revealed that the 804/764 cm−1 pair appears before the 785/751 cm−1 pair and that the conversion from the former to the latter species is significantly delayed in D2O than in H2O, suggesting that this step of electron transfer is tightly coupled with proton pumping. The experiments using 16O18O have established that all the 804/764, 785/751, and 356/342 cm−1 bands arise from the Fe=O heme but definitely not from the Fe-O−-O− heme, whose presence has been long postulated. It is noted that the reaction intermediates of oxidized cytochrome c oxidase with hydrogen peroxide yield the same three sets of oxygen isotope-sensitive bands as those that have been seen for intermediates of dioxygen reduction, indicating the identity of intermediates.

Time-resolved resonance Raman (TR3) spectroscopy has been applied to cytochrome c oxidase (CcO) to elucidate the mechanism of dioxygen reduction. Six oxygen isotope-sensitive Raman bands have been identified in the TR3 spectra. The “607-nm species” defined by difference absorption spectrum, which is referenced against the oxidized enzyme, is demonstrated to have an Fe=O heme, although it has long been believed to have an Fe-O-O-X (X=H or CuB) heme. The one-electron reduction of this Fe=O intermediate, which yields the oxoferryl intermediate, is demonstrated to be coupled with proton transfer in the protein. The mechanism of dioxygen reduction by CcO is discussed on the basis of the structures of the reaction intermediates.

We present new optical and resonance Raman spectroscopic data that characterize the first intermediate as a diiron(III) peroxo species. The time-resolved optical and freeze-quench resonance Raman spectroscopic experiments strongly support assignment of the first intermediate, variously designated P or L, in the MMO hydroxylase reaction cycle as a symmetrical diiron(III) peroxo species. 32 refs., 2 figs.

In this paper we shall discuss a new and convenient method for the preparation of hypofluorous acid, HOF, and we shall describe the synthesis and characterization of the hitherto unknown methyl hypofluorite, CH 3 OF. The archetypal hypofluorite HOF is known to have remarkable oxygenating properties. Its investigation and application have been inhibited, however, by the difficulty of its synthesis, which has heretofore involved passage of elemental fluorine over ice in a complex recirculating system, and by the fact that the neat material can be explosively unstable. It has recently been found that passage of fluorine through acetonitrile containing 5–20% water generates strongly oxidizing solutions, and we have subsequently shown that these solutions contain HOF. Characterization of the solutions by NMR and molecular spectrometry indicates that a 1:1 hydrogen-bonded complex between the HOF and acetonitrile is present. The complex appears to be significantly more stable than neat HOF, and this interaction therefore serves as a means of “taming” hypofluorous acid and making the compound more accessible to researchers interested in working with it. Methyl hypofluorite has widely been assumed to be unmakeable because of the ease with which it could decompose to HF and formaldehyde. In fact, the compound can be readily prepared by fluorination of a cooled solution of methanol in acetonitrile or propionitrile, and even by fluorination of neat methanol at Dry Ice temperature. The extremely volatile compound (m.p. −142 °C, b.p. −33 °C) can be distilled from the reaction mixture, and it has been isolated and characterized by mass, NMR, and infrared spectrometry. Photoionization mass spectrometric measurements of fragment thresholds yield values of ca. −94 and 196 kJ/mol respectively for the enthalpy of formation of CH 3 OF and the dissociation energy of its oxygen-fluorine bond. This makes the oxygen-fluorine bond in CH 3 OF very slightly weaker than that in HOF, but stronger than that in any other known hypofluorite. Neat liquid CH 3 OF can decompose explosively, but the compound is well-behaved and relatively long-lived in the gas phase and as a solution in acetonitrile or propionitrile. It adds the elements of CH 3 O and F to olefins; with unsymmetrical olefins the addition takes place in the direction of electrophilic methoxylation rather than electrophilic fluorination.

The enthalpy of reaction of pure KHSO5·H2O with HI(aq) has been determined calorimetrically. This result has been combined with auxiliary enthalpy-of-solution measurements to yield the standard molar enthalpy of formation: ΔfHmo(KHSO5·H2O, cr, 298.15 K) = −(1359.88±0.57) kJ·mol−1. The standard molar enthalpies of solution in water of KHSO5·H2O and KHSO5 have also been measured: ΔslnHmo(KHSO5·H2O, cr, 298.15 K) = (46.24±0.34) kJ·mol−1, ΔslnHmo(KHSO5, cr, 298.15 K) = (33.68±0.24) kJ·mol−1. From these results, ΔfHmo(HSO5−, aq) with standard molality mo = 1 mol·kg−1, has been calculated to be −(775.64±0.68) kJ·mol−1. The standard potential for the aqueous half-reaction: HSO5− + 2H+ + 2e− = HSO4− + H2O, is estimated to be (1.85±0.03) V. Also reported are ΔfHmo(KHSO5, cr, 298.15 K) = −(1061.49±0.71) kJ·mol−1; the molar enthalpy of dehydration at 298.15 K for the reaction: KHSO5·H2O(cr) = KHSO5(cr) + H2O(l), ΔfHmo = (12.56±0.42) kJ·mol−1; and the equilibrium H2O(g) vapor pressure at 298.15 K for the dehydration reaction: KHSO5·H2O(cr) = KHSO5(cr) + H2O(g), p p o = (7.1±1.0) × 10 −3 . Taking po = 101325 Pa, the vapor pressure is (720±100) Pa.

X-ray absorption near edge structure (XANES) spectra of gaseous Kr, solid Kr and solid KrF2 have been obtained and compared to differentiate between continuum resonances near the edge and bound state transitions. By comparing experimental and ab initio (MSW-Xα) calculated spectra the influence of environment as well as molecular bonding on XANES is demonstrated.

Alkaline solutions of seven-valent neptunium in water enriched in oxygen-17 show a /sup 17/O NMR resonance about 1470 ppM downfield from the solvent resonance. Measurement of relative areas indicates that the Np(VII) oxygen resonance contains about four oxygen atoms per Np atom. This result is interpreted in terms of the six-coordinated Np(VII) anion NpO/sub 4/(OH)/sub 2//sup 3/minus//, in which four oxygen atoms are present in a square plane around the Np and are responsible for the observed resonance. The two hydroxyl groups are located further from the Np at the vertices of a tetragonal bipyramid and presumably exchange too rapidly with solvent oxygen for their /sup 17/O resonance to be seen. The Np(VII) oxygen resonance has a line width that increases with temperature and is around 400 Hz at 25/degree/C. The temperature dependence of the line width can be accounted for by a process of oxygen exchange between the Np(VII) species and the solvent, with a pseudo-first-order rate constant of about 10/sup 3/s/sup /minus/1/ at 25/degree/C. No Np(VI) oxygen resonance was observed in alkaline solution, probably because the Np(VI) oxygens exchange too rapidly with the solvent. 21 references, 2 tables.

The crystal structure of CsBrO4 was determined by single-crystal X-ray diffraction and found to be different from the structures of the lighter alkali perbromates. Cesium perbromate crystallizes in the tetragonal space group I41/a, with unit cell constants of a = 5.751(4)A and c = 14.821(12)A. Full-matrix least-squares analyses indicate that tetrahedral perbromate ions are situated in the lattice so that all corresponding tetrahedral faces are parallel. The observed BrO distance is 1.591(6) A. The Cs+ ions reside in twelve coordinate positions with CsO distances of 3.146(7), 3.383(9), and 3.389(9) A. This unique stucture causes CsBrO4 crystals to have noticeable plasticity.

The infrared spectrum of the hypofluorous acid molecule, HOF, trapped in different solid matrices at low temperatures shows that the vibrational fundamentals {nu}{sub 1} and {nu}{sub 2} are perturbed to extents that vary with the basicity of the adjacent molecule, D, and the appearance of absorptions attributable to librational motions of the D{hor ellipsis}H-OF unit implies the formation of specific hydrogen-bonded complexes in some cases. As the matrix concentration of HOF increases, aggregation occurs to give (HOF){sub 2} and higher multimers. Exposure of HOF isolated in an Ar matrix to broad-band ultraviolet radiation results in photodissociation with the formation of two products thought to be O{hor ellipsis}(HF){sub 2} and O{sub 2}{hor ellipsis}(HF){sub 2} in proportions dependent on the concentration of HOF. Photolysis of HOF trapped in a reactive matrix results in oxygenation of the matrix molecules, X, and complexation of the product XO by HF; e.g. X = N{sub 2}, CO, O{sub 2}, or CH{sub 4}. The CO, O{sub 2}, or CH{sub 4} matrices also yield on photolysis small but significant amounts of FCO{sup {sm bullet}}, O{sub 2}F{sup {sm bullet}}, or CH{sub 3}{hor ellipsis}HF, respectively, products that signal the intervention of fluorine atoms. Photolysis of an Ar matrix including HOFmore » together with a potential substrate, Y, at concentrations > 1% results exclusively in oxygenation, and not fluorination, to give YO (Y = PF{sub 3}, AsF{sub 3}, or H{sub 2}O). The results are discussed in relation to the mechanisms likely to govern the matrix photochemistry of HOF.« less

This paper examines the reactions of F/sub 2/ and HOF with aqueous perchloric acid solutions containing various complexes of trivalent chromium. In no case is the chromium itself oxidized. The complex CrF/sup 2 +/ is unreactive toward either oxidant. CrClO/sub 3//sup 2 +/, CrNO/sup 2 +/, CrCl/sup 2 +/, and CrBr/sup 2 +/ show increasing reactivity, with the formation of Cr/sup 3 +/ as the principal product. In the case of CrBr/sup 2 +/ and CrCL/sup 2 +/ there is evidence that F/sub 2/ can react with the substrate directly, as well as via the intermediate formation of HOF. This direct reaction produces some CrF/sup 2 +/ in addition to Cr/sup 3 +/. Azidochromium(III), CrN/sub 3//sup 2 +/, is the most reactive of the complexes studied. It reacts directly with F/sub 2/ to form a mixture of Cr/sup 3 +/ and CrF/sup 2 +/; it reacts with HOF to form CrNO/sup 2 +/. Reaction mechanisms that can account for these observations are discussed.

The rubidium salt of the recently identified fluoroxysulfate anion, FOSO/sub 3//sup -/, has been characterized by single-crystal X-ray diffraction. RbFOSO/sub 3/ crystallizes in the centrosymmetric triclinic space group, Pl, with unit cell constants a = 5.503 (2) A, b = 5.623 (1) A, c = 7.603 (3) A, ..cap alpha.. = 100.64 (2)/sup 0/, ..beta.. = 106.72 (2)/sup 0/, ..gamma.. = 93.22 (2)/sup 0/, and Z = 2. The X-ray data refine to an R/sub F/ = 0.067 for 664 reflections with F/sup 2/ > sigmaF/sup 2/. The fluoroxysulfate anion has distorted tetrahedral coordination with each central sulfur atom bound to four oxygens. The S-O bond distances are 1.435 (8), 1.426 (8), 1.441 (7), and 1.652 (9) A. The O-F bond distance is 1.412 (10) A, and the S-O-F bond angle is 107.8 (6)/sup 0/. Each Rb/sup +/ cation is coordinated to nine oxygen atoms and two fluorine atoms.

The fluoroxysulfate ion, SO/sub 4/F/sup -/, substitutes fluorine on aromatic compounds in acetonitrile solution at room temperature. However, benzyl fluoride is the principal product from toluene. Other products are also formed, particularly in the case of the less reactive aromatic substrates. Product distributions and relative reactivities are interpreted in terms of an initial electrophilic attack that can be followed by free-radical side reactions.

The standard enthalpy of formation at 298.15 K of the aqueous peroxymonosulfate ion, HSO5−, has been determined by reduction of the ion in aqueous HI. The value obtained is ΔHfo(HSO5−, aq) = −(798.4 ± 2.5) kJ·mol−1. This enthalpy was combined with an estimated entropy for the aqueous ion to yield a standard electrode potential of (1.82 ± 0.03) V for the aqueous half-reaction: HSO 5 −> +2 H + +2 e − = HSO 4 − + H 2 O This potential is substantially greater than that derived from electrochemical measurements and implies that HSO5− is a considerably more powerful oxidant than has been generally recognized.

Low-temperature and solution-calorimetric investigations of Cs 3 CrO 4 have yielded the following thermodynamic properties at T = 298.15 K: S °=(296.2±1.5)JK -1 mol -1 , C ° p =(179.9±0.5)JK -1 mol -1 ,-{ G °( T - H °(0)}=(169.0±0.8)JK -1 mol -1 ,{ H °(T)- H °(0)}=(37.912±0.114)kJ mol -1 and δ H ° f =-(1543.13±2.66)kJ mol -1 An unusual feature of the solution calorimetry was the use of aqueous xenon trioxide, XeO 3 (aq). as oxidant. High-temperature drop calorimetry revealed a solid-to-solid (β-to-γ) transition at 774 K with ΔH tr = 1.8 kJ mol −1 and ΔS tr = 2.3 J K −1 mol −1 . Below the transition temperature. the enthalpy increment as a function of temperature is best represented by { H °(T)- H °(298.15K)}/J mol -1 =-46804.3+135.625( T K )+6.633544×10 -2 ( T K ) 2 +1.777146×10 -5 ( T K ) 3 ,and, above the transition, by { H °(T)- H °(298.15K)}/J mol -1 =-38654.8+155.722( T K )+4.35257×10 -2 ( T K ) 2 A table of thermodynamic functions to 1000 K is given.

Resonance Raman spectra of the complex of Fe/sup III/-ethylenediaminetetraacetate with hydrogen peroxide have been obtained in the region of the peroxidic O-O stretching vibration that occurs at 815 cm/sup /minus/1/ in frozen solution. When the complex was prepared from nearly neat, mixed-isotope hydrogen peroxide, H/sub 2//sup 16/O/sup 18/O, a single O-O vibration was observed at 794 cm/sup /minus/1/. This observation establishes that the two oxygen atoms of the bound peroxide are equivalent and that the peroxide is ligated in an /eta//sup 2/ side-on configuration in this mononuclear complex. The absence of any shift in /nu/(O-O) when the complex was prepared in D/sub 2/O solvent provides further support for the side-on Fe(O-O) geometry and rules out the alternative /eta//sup 1/ end-on Fe-OOH configuration. In contrast, /nu/(O-O) of free hydrogen peroxide in the frozen state occurs at 877 cm/sup /minus/1/ in H/sub 2/O and 879 cm/sup /minus/1/ in D/sub 2/O. The 2-cm/sup /minus/1/ upshift in D/sub 2/O is similar to that observed previously with oxyhemerythrin and appears to be characteristic of a hydrogen-bonded or protonated peroxide species. 37 references, 4 figures, 1 table.

Aqueous SO/sub 4/F/sup -/ decomposes to form O/sub 2/, H/sub 2/O/sub 2/, and HSO/sub 5//sup -/. At 15/sup 0/C in 0.01 M HC1O/sub 4/ the first-order rate constant k = 3.6 x 10/sup -4/s/sup -1/, ..delta..H/sup + +/ = 16.8 +- 0.4 kcal/mol, and ..delta..S/sup + +/ = -15.7 +- 1.5 cal/(mol deg). The H/sub 2/O/sub 2/ and O/sub 2/ products both contain one oxygen atom from solvent and one from the fluoroxysulfate. The HSO/sub 5//sup -/ product also contains an atom of solvent oxygen in its terminal peroxide position. A mechanism is proposed in which the rate-determining steps are the interaction of SO/sub 4/F/sup -/ with water fo form HSO/sub 5//sup -/ and H/sub 2/O/sub 2/. The H/sub 2/O/sub 2/ probably interacts further with SO/sub 4/F/sup -/ by means of a free-radical chain reaction to produce O/sub 2/. Fluorosulfate ion, SO/sub 3/F/sup -/, appears to be formed only in the oxygen-transfer step that produces H/sub 2/O/sub 2/. Chlorite ion is rapidly oxidized to C1O/sub 2/ by SO/sub 4/F/sup -/ in accordance with the rate law -d(SO/sub 4/F/sup -/)/dt = k/sub ClO/sub 2//sup -//(ClO/sub 2//sup -/)(SO/sub 4/F/sup -/). In acid solution at 14.7/sup 0/C, k/sub ClO/sub 2//sup -// = 1.8more » x 10/sup 4/ L/(mol s), ..delta..H/sup + +/ = 7.3 +- 0.6 kcal/mol, and ..delta..S/sup + +/ = -14 +- 2 cal/(mol deg). The oxidation of Co(NH/sub 3/)/sub 5/ClO/sub 2//sup 2 +/ by SO/sub 4/F/sup -/ produces ClO/sub 2/ and a mixture of Co(NH/sub 3/)/sub 5/F/sup 2 +/ and Co(NH/sub 3/)/sub 5/H/sub 2/O/sup 3 +/. The oxidation of Cr/sup 2 +/ by SO/sub 4/F/sup -/ produces 42 to 47% Cr/sup 3 +/ and 41 to 45% CrF/sup 2 +/, the balance consisting of polynuclear Cr(III) species. The oxidation of I/sup -/ to I/sub 2/ by SO/sub 4/F/sup -/ consumes no acid and hence does not produce SO/sub 3/F/sup -/. These rapid reactions may be interpreted in terms of mechanisms involving either 1- or 2-equiv oxidation in the rate-determining steps. Oxygen transfer does not appear to be significant, but fluorine transfer is obviously involved at least in the oxidation of Cr/sup 2 +/ and Co(NH/sub 3/)/sub 5/ClO/sub 2//sup 2 +/.« less