Evan H. Appelman

Millimeter‐Wave Spectrum and Structure of Hypofluorous Acid: HOF and DOF

The microwave spectra of two isotopic species of hypofluorous acid, HOF and DOF, have been investigated. The values of the A0, B0, and C0 rotational constants are 590 000, 26 758.00, and 25 512.51 MHz for HOF and 316 800, 25 591.25, and 23 587.75 MHz for DOF. The structural parameters calculated with these rotational constants are: r(O–H) = 0.964 ± 0.01 A, r(O–F) = 1.442 ± 0.001 A, and > HOF = 97.2° ± 0.6° Centrifugal distortion analysis in the symmetric top approximation gave DJ and DJK values of 0.0934 and 2.417 MHz for HOF and 0.0775 and 1.745 MHz for DOF, respectively. The P6 distortion term was not significant.

Insight into the mechanism of an iron dioxygenase by resolution of steps following the FeIV═O species

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 FeII and α-ketoglutarate-dependent dioxygenase TauD. Time-resolved Raman spectra of the initial species with 16O18O oxygen unequivocally establish the FeIV═O structure. 1H/2H substitution reveals direct interaction between the oxo group and the C1 proton of substrate taurine. Two new transient species were resolved following FeIV═O; one is assigned to the νFeO mode of an FeIII─O(H) species, and a second is likely to arise from the vibration of a metal-coordinated oxygenated product, such as FeII─O─C1 or FeII─OOCR. These results provide direct insight into the mechanism of substrate oxygenation and suggest an alternative to the hydroxyl radical rebinding paradigm.

The standard enthalpy of formation of peroxymonosulfate (HSO5−) and the standard electrode potential of the peroxymonosulfate-bisulfate couple

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: HSO5−>+2H++2e−=HSO4−+H2O 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.

Photoionization of ozone: Formation of O4+ and O5+

Ionization yields of O+, O2+, and O3+ have been studied as a function of wavelength in the photoionization of ozone from threshold to 600 A with the primary process being the production of O3+. The ratio O3+ : O2+ : O+ at 600 A is 1.00 : 0.36 : 0.05. The adiabatic ionization potential of O3+ is 990.32±0.3 A (12.519±0.004 eV). Steplike structure occurs near threshold, at wavelengths corresponding to vertical ionization potentials reported in photoelectron spectroscopy studies. A weak onset for O2+ production appears at 13.082 eV (947.7 A), followed by more intense O2+ production at 13.432 eV (932.2 A). The onset for O+ formation appears weakly at 15.21 eV, rising continuously with decreasing wavelength. The formation of O5+ via the ion–molecule reaction O3++O3→O5++O was also observed and measured as a function of wavelength. The O4+ ion was also detected. Pressure dependences and enthalpy considerations make the reaction O3++O2→O4++O a highly probable mechanism for O4+ formation.

Gas‐Phase Infrared Spectra of HOF and DOF

The infrared spectra of HOF and DOF in the gas phase have been studied. From the analysis of rotational subbands, the fundamental frequencies are determined to be 3578.5, 1354.8, and 889.0 cm−1 for HOF; and 2643.5, 1003.9, and 891.1 for DOF. The respective values of the constants (A″ − B″) and B″ are 18.37 and 0.86 cm−1 for HOF, and 9.79 and 0.81 cm−1 for DOF.

Photoionization mass spectrometric study of CH3OF

The vacuum ultraviolet photoionization mass spectrum of CH3OF displays a prominent parent ion peak, whose adiabatic onset is 11.340±0.008 eV, although much lower energy fragmentation processes (CH2O++HF, 8.0 eV; CH2OH++F, 9.3 eV) are possible. These lower energy processes have very low intensity. Two higher energy processes, to CH+3+OF and CH2O++H+F, are observed. Their thresholds are used to determine ΔH0f0 (CH3OF)≥−23.0±0.7 kcal/mol, or D0 (CH3O–F)≤47.4±1.2 kcal/mol. CH2OF+ is a significant fragment, whose appearance energy leads to ΔH0f0 (CH2OF+)≊215.1±0.8 kcal/mol.

Infrared spectrum of matrix-isolated HOF

Abstract The i.r. spectrum of molecular HOF was measured in dilute matrices obtained by codepositing pure HOF with N 2 at ca . 8°K. The fundamental frequencies observed are 886.0, 1359.0 and 3537.1 cm −1 . These results are compared with values obtained previously, and discrepancies are discussed.

ON THE HEAT OF FORMATION OF CARBONYL FLUORIDE, CF2O

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...

Photoionization of HOF with mass analysis

The ionization yields of HOF+, O+, and OH+ have been studied as a function of wavelength in the photoionization of HOF. The first ionization potential of HOF is 12.71±0.01 eV. The threshold for O+ formation, 14.34 eV, leads to Δ Hf00 (HOF)=−22.8± 1 kcal/mole. The threshold for OH+ formation, 15.07 eV, leads to a value for Δ Hf0 (HOF) in good agreement with the above result if one of two discrepant values for Δ Hf0 (HO+) is chosen. This choice implies that the ionization potential for OH is 12.9o±0.05 eV. The proton affinity of OF is 5.82 eV. Pronounced structure in the ionization yield curves is interpreted as vibrational autoionization in the region near threshold, and as electronic autoionization at higher photon energies.

Synthesis of radiofluorinated analogs of m-tyrosine as potential l-dopa tracers via direct reaction with acetylhypofluorite

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.