Kazimierz Czarnecki

Resonance Raman Spectra of Native and Mesoheme-reconstituted Horseradish Peroxidase and Their Catalytic Intermediates

Resonance Raman studies of native and mesoheme-reconstituted horseradish peroxidase and their catalytic intermediates, known as Compounds I and II, have been conducted using both near UV (∼350 nm) and visible (406.7 nm) excitation. Careful power studies indicate that the authentic Compound I spectra are obtainable using near UV excitation, but that use of visible excitation results in contamination of the Compound I spectrum with the spectrum of a Compound II-like photoproduct. Using H218O2, the ν(Fe=O) stretching modes for both systems are unambiguously identified, for the first time, at ∼790 cm−1. The authentic Compound I spectra are indicative of an 2A1u-like ground state for both the native and the mesoheme-reconstituted proteins. Finally, the possible biological implications of such information are briefly discussed.

Doming modes and dynamics of model heme compounds

Synchrotron far-IR spectroscopy and density-functional calculations are used to characterize the low-frequency dynamics of model heme FeCO compounds. The “doming” vibrational mode in which the iron atom moves out of the porphyrin plane while the periphery of this ring moves in the opposite direction determines the reactivity of oxygen with this type of molecule in biological systems. Calculations of frequencies and absorption intensities and the measured pressure dependence of vibrational modes in the model compounds are used to identify the doming and related normal modes.

Visible and resonance Raman spectra of low valent iron porphyrins

The resonance Raman spectrum of Fe(TPP)2− was obtained after the three-electron electrochemical reduction of Fe(TPP)(Cl). The coulometric reduction was carried out in the presence of bis(triphenylphosphoanylidine)ammonium chloride in DMF in order to avoid the formation of iron–σ-alkyl complexes. The resonance Raman spectrum of the intermediate oxidation states (Fe(TPP) and Fe(TPP)−) were consistent with previous work. The spectrum of the three-electron product, Fe(TPP)2−, obtained at 442 nm, was qualitatively similar to the two-electron reduced product, Fe(TPP)−, with an intense ν2 band at 1537 cm−1. The high frequency bands generally decreased in energy, contrary to the expectations based on the X-ray crystallographic core size. In particular, the ν2 and ν10 bands decreased by 18 and 22 cm−1. A small increase was observed for the ν4 band (+4 cm−1). While these changes were not consistent with the measured core size, they were in agreement with other porphyrin π-anion radicals such as Zn(TPP)− and VO(OEP)−. Based on the resonance Raman spectra, Fe(TPP)2− can be formulated as an iron(I) π-radical anion. Significant backbonding between the dπ-orbitals of the iron to the eg* orbital of the porphyrin, though, is probably occurring. As a result, the complex is probably not a pure π-anion radicals.

In situ study of the photodegradation of carbofuran deposited on TiO2 film under UV light, using ATR-FTIR coupled to HS-MCR-ALS.

The in situ study of the photodegradation of carbofuran deposited on a TiO2 catalyst film under UV light was carried out using the ATR-FTIR technique. The data were analyzed using a Hard-Soft Multivariate Curve Resolution-Alternating Least Squares (HS-MCR-ALS) methodology. Using S-MCR-ALS, four factors were deduced from the evolving factor analysis of the data, and their concentrations and spectra were determined. These results were used to draw qualitative and quantitative analyses of the major products of carbofuran photodegradation. The results of this analysis were in good agreement with GC-MS results and with reported mechanisms. Hard-MCR-ALS was then used to refine the spectra and concentrations, using a multistep kinetic model. The rate constant for the first step in the photodegradation of carbofuran was found to be 2.9 × 10(-3) min(-1). The higher magnitude of the correlation (96.87%), the explained variance (99.87%) and LOF (3.01), are good indicators of the reliability of the outcome of this approach. This method has been shown to be an efficient approach to study in situ photodegradation of pesticides on a solid surface.