Andrea Lapi

The Herschel ATLAS

The Herschel ATLAS is the largest open-time key project that will be carried out on the Herschel Space Observatory. It will survey 570 deg2 of the extragalactic sky, 4 times larger than all the other Herschel extragalactic surveys combined, in five far-infrared and submillimeter bands. We describe the survey, the complementary multiwavelength data sets that will be combined with the Herschel data, and the six major science programs we are undertaking. Using new models based on a previous submillimeter survey of galaxies, we present predictions of the properties of the ATLAS sources in other wave bands.

X-ray Absorption Spectroscopy of Hemes and Hemeproteins in Solution: Multiple Scattering Analysis

A full quantitative analysis of Fe K-edge X-ray absorption spectra has been performed for hemes in two porphynato complexes, that is, iron(III) tetraphenylporphyrin chloride (Fe(III)TPPCl) and iron(III) tetraphenylporphyrin bis(imidazole) (Fe(III)TPP(Imid)2), in two protein complexes whose X-ray structure is known at atomic resolution (1.0 A), that is, ferrous deoxy-myoglobin (Fe(II)Mb) and ferric aquo-myoglobin (Fe(III)MbH2O), and in ferric cyano-myoglobin (Fe(III)MbCN), whose X-ray structure is known at lower resolution (1.4 A). The analysis has been performed via the multiple scattering approach, starting from a muffin tin approximation of the molecular potential. The Fe-heme structure has been obtained by analyzing independently the Extended X-ray Absorption Fine Structure (EXAFS) region and the X-ray Absorption Near Edge Structure (XANES) region. The EXAFS structural results are in full agreement with the crystallographic values of the models, with an accuracy of +/- 0.02 A for Fe-ligand distances, and +/-6 degrees for angular parameters. All the XANES features above the theoretical zero energy (in the lower rising edge) are well accounted for by single-channel calculations, for both Fe(II) and Fe(III) hemes, and the Fe-N p distance is determined with the same accuracy as EXAFS. XANES evaluations of Fe-5th and Fe-6th ligand distances are determined with 0.04-0.07 A accuracy; a small discrepancy with EXAFS (0.01 to 0.05 A beyond the statistical error), is found for protein compounds. Concerns from statistical correlation among parameters and multiple minima in the parameter space are discussed. As expected, the XANES accuracy is slightly lower than what was found for polarized XANES on Fe(III)MbCN single crystal (0.03-0.04 A), and states the actual state-of-the-art of XANES analysis when used to extract heme-normal parameters in a solution spectrum dominated by heme-plane scattering.

Epoxidation and hydroxylation reactions catalysed by β-Tetrahalogeno and β-octahalogeno manganese porphyrins

Abstract β-Tetrahalogenated manganese(III) porphyrins are more efficient catalysts than the β-octahalogenated ones in oxidations promoted by H 2 O 2 .

Epoxidation and hydroxylation reactions catalyzed by the manganese and iron complexes of 5,10,15,20-tetrakis(2,6-dimethoxyphenyl)porphyrin

Abstract Manganese(III) and iron(III) complexes of 5,10,15,20-tetrakis-(2,6-dimethoxyphenyl)porphyrin (H2TDMeOPP) were tested as catalysts in the epoxidation of alkenes and in the hydroxylation of adamantane with H2O2 (in the presence of imidazole) or PhIO as oxidants. The behavior of the two catalysts is compared with that of the corresponding manganese(III) and iron(III) complexes of 5,10,15,20-tetrakis-(2,6-dichlorophenyl)porphyrin and 5,10,15,20-tetraphenylporphyrin, and the observed differences ascribed to the electron donating effect of the methoxy groups.

N-demethylation of N,N-dimethylanilines by the benzotriazole N-oxyl radical: evidence for a two-step electron transfer-proton transfer mechanism.

The reaction of the benzotriazole N-oxyl radical (BTNO) with a series of 4-X-N,N-dimethylanilines (X = CN, CF(3), CO(2)CH(2)CH(3), CH(3), OC(6)H(5), OCH(3)) has been investigated in CH(3)CN. Product analysis shows that the radical, 4-X-C(6)H(4)N(CH(3))CH(2)(*), is first formed, which can lead to the N-demethylated product or the product of coupling with BTNO. Reaction rates were found to increase significantly by increasing the electron-donating power of the aryl substituents (rho(+) = -3.8). With electron-donating substituents (X = CH(3), OC(6)H(5), OCH(3)), no intermolecular deuterium kinetic isotope effect (DKIE) and a substantial intramolecular DKIE are observed. With electron-withdrawing substituents (X = CN, CF(3), CO(2)CH(2)CH(3)), substantial values of both intermolecular and intramolecular DKIEs are observed. These results can be interpreted on the basis of an electron-transfer mechanism from the N,N-dimethylanilines to the BTNO radical followed by deprotonation of the anilinium radical cation (ET-PT mechanism). By applying the Marcus equation to the kinetic data for X = CH(3), OC(6)H(5), OCH(3) (rate-determining ET), a reorganization energy for the ET reaction was determined (lambda(BTNO/DMA) = 32.1 kcal mol(-1)). From the self-exchange reorganization energy for the BTNO/BTNO(-) couple, a self-exchange reorganization energy value of 31.9 kcal mol(-1) was calculated for the DMA(*+)/DMA couple.

Recent photo- and radiation chemical studies of sulfur radical cations

The chemistry of sulfur radical cations has continued to attract considerable interest in recent years, not only for its practical and theoretical aspects but also for its important biological implications (1). Photoand radiation chemical studies are among the most convenient methods for the analysis of the reactivity and properties of these species. In the present review, the most recent pulse and γ -radiolysis results and laser and steady-state photolysis investigations of sulfur radical cations collected in the last decade are reported, with a special attention focussed on their fragmentation reactions. We have also discussed the photooxygenations of organic sulfides involving radical cations as reactive intermediates and on the role of sulfur radical cations in biochemical oxidation processes of amino acids and peptides. In the last few years, a considerable increase in our knowledge about sulfide radical cations has been derived from photoand radiation chemical studies.

Isotope-effect profiles in the oxidative N-demethylation of N,N-dimethylanilines catalysed by lignin peroxidase and a chemical model

Lignin peroxidase catalyses the oxidative N-demethylation of ring-substituted N,N-dimethylanilines by an electron-transfer mechanism whereby an anilinium radical cation is formed which is then deprotonated by the enzyme. Information on the nature of the basic centre which deprotonates the radical cation has been obtained by determining the KDIE profile (plot of kH/kD vs. the pKa of the aniline radical cations) for a number of ring-substituted N,N-bis(dideuteriomethyl)anilines. From the bell-shaped curve it has been estimated that the pKa of the proton-abstracting base is about 7. Interestingly, almost the same value has been obtained when the same type of study has been carried out using a water-soluble model compound: 5,10,15,20-tetraphenyl-21H,23H-porphine-p,p′,p′′,p′′′-tetrasulfonic acid iron(III) chloride. This is a strong indication that the radical cation is deprotonated by the same species in the enzymatic and in the chemical reactions. It is suggested that this species is the reduced iron-oxo complex.

Vaporization of the prototypical ionic liquid BMImNTf2 under equilibrium conditions: a multitechnique study

The vaporization behaviour and thermodynamics of the ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethyl)sulfonylimide (BMImNTf2) were studied by combining the Knudsen Effusion Mass Loss (KEML) and Knudsen Effusion Mass Spectrometry (KEMS) techniques. KEML studies were carried out in a large temperature range (398-567) K by using effusion orifices with 0.3, 1, and 3 mm diameters. The vapor pressures so measured revealed no kinetically hindered vaporization effects and provided second-law vaporization enthalpies at the mean experimental temperatures in close agreement with literature. By exploiting the large temperature range covered, the heat capacity change associated with vaporization was estimated, resulting in a value of -66.8 J K(-1) mol(-1), much lower than that predicted from calorimetric measurements on the liquid phase and theoretical calculations on the gas phase. The conversion of the high temperature vaporization enthalpy to 298 K was discussed and the value Δ(l)(g)H(m)(298 K) = (128.6 ± 1.3) kJ mol(-1) assessed on the basis of data from literature and present work. Vapor pressure data were also processed by the third-law procedure using different estimations for the auxiliary thermal functions, and a Δ(l)(g)H(m)(298 K) consistent with the assessed value was obtained, although the overall agreement is sensitive to the accuracy of heat capacity data. KEMS measurements were carried out in the lower temperature range (393-467) K and showed that the largely prevailing ion species is BMIm(+), supporting the common view of BMImNTf2 vaporizing as individual, neutral ion pairs also under equilibrium conditions. By monitoring the mass spectrometric signal of this ion as a function of temperature, a second-law Δ(l)(g)H(m)(298 K) of 129.4 ± 7.3 kJ mol(-1) was obtained, well consistent with KEML and literature results. Finally, by combining KEML and KEMS measurements, the electron impact ionization cross section of BMIm(+) was estimated.

Formation of quinones in the iron porphyrin catalyzed oxidation of benzene and alkylbenzenes by magnesium monoperoxyphthalate

Abstract Biomimetic oxidation of unactivated arenes with magnesium monoperoxyphthalate and a fluorinated iron porphyrin as catalyst lead mainly to p-quinones without involving phenols as reaction intermediates.

Stereochemistry of the C-S Bond Cleavage in cis-2-Methylcyclopentyl Phenyl Sulfoxide Radical Cation

The TiO(2) photocatalyzed oxidation of cis-2-methylcyclopentyl phenyl sulfoxide in the presence of Ag(2)SO(4) in MeCN/H(2)O leads to the formation of 1-methylcyclopentanol, 1-methylcyclopentyl acetamide, and phenyl benzenethiosulfonate as the main reaction products. It is suggested that the C-S heterolysis in the radical cation is an unimolecular process leading to an ion radical pair. Fast 1,2-hydride shift in the secondary carbocation leads to 1-methylcyclopentyl carbocation that forms the observed products by reaction with H(2)O and MeCN. Attack of H(2)O on the ion radical pair may also occur, but as a minor route (<3%), with formation of trans-2-methylcyclopentanol.