On the core-hole photoelectron satellites in N2 and CO

A theoretical study is given of core-level photoelectron satellites with special emphasis on the π?π* satellites in N₂ and CO. The discussion is based on an analysis of the properly constructed zeroth-order manifold of satellite states, and provides simple explanations for both bound state and photoelectron continuum aspects of core-level ionization. Similar to the frozen core static exchange approximation for the single core-hole states, we derive one-particle scattering potentials for the satellite states.     

Perfluoroalkyl-substituted triazapentadienes and their metal complexes

Triazapentadienides, C(3)F(7)-C(=NR)-N=C(NHR)-C(3)F(7), result from the reaction of primary amines RNH(2) with the fluorinated imine C(3)F(7)-CF=N-C(4)F(9). The aniline derivative (R = Ph) is a weak monoprotic acid in dmso. Its conjugate base exhibits an extensive coordination chemistry. It acts as a bidentate ligand toward the molecular fragments Pd(C(3)H(5)), Rh(c-C(8)H(12)), Ir(c-C(8)H(12)), and Rh(CO)(2). The chelates [C(3)F(7)-C(NPh)-N-C(NPh)-C(3)F(7)](2)M, M = Mg, Mn, Fe, Co, Ni, Cu, Zn, and Pd, were prepared. In the crystallographically characterized Co complex, the metal is 3d(7), S = (3)/(2) and tetrahedrally coordinated. Spin densities at carbon in the C(6)H(5) and C(3)F(7) groups were estimated from the (1)H and (19)F contact shifts. Spin delocalization onto phenyl sp(2) carbons is approximately 10 times greater than onto the fluorinated sp(3) carbons.     

Synthesis of (2R, 3R)-epigallocatechin-3-O-(4-hydroxybenzoate), a novel catechin from Cistus salvifolius, and evaluation of its proteasome inhibitory activities

The total and semi syntheses of (2R,3R)-epigallocatechin-3-O-(4-hydroxybenzoate), a novel catechin from Cistus salvifolius, were accomplished. The proteasome inhibition and cytotoxic activities of the synthetic compound and its acetyl derivative were studied and compared with (2R,3R)-epigallocatechin-3-gallate (EGCG), the active component from green tea.     

Fischer Carbene Complexes as Chemical Multitalents: The Incredible Range of Products from Carbenepentacarbonylmetal alpha,beta-Unsaturated Complexes

The metal carbene complexes, discovered by E. O. Fischer at the start of the 1960s and carrying his name, have since proved themselves to be irreplaceable building blocks for organic synthesis. In particular, since the discovery of the D?tz reaction, a formal cycloaddition of Fischer alpha,beta-unsaturated carbene complexes to alkynes with CO insertion, this area of chemistry has become increasingly interesting to organic chemists. In spite of the considerable diversity of reactions performed with these complexes, proper selection of substrates and careful adjustment of the reaction conditions have allowed, in most cases the perfectly selective preparation of individual compounds of this enormous range of products. The spectrum of new successes begins with the conventional Diels-Alder reaction of alkynylcarbene complexes and the formal regioselective [3+2] cycloaddition of alkenylcarbene complexes to alkynes. It extends much further, however, from cascade reactions with the formation of oligofunctional and oligocyclic products of impressive molecular complexity to complex, formal [3+6] cocyclizations in which six bonds are formed in a single operational step. Beyond doubt, the methodological arsenal of preparative organic chemistry cannot be imagined any more without the valuable transformations of the Fischer carbene complexes; it only remains to be seen whether one or other of the numerous new types of cocyclization products of these complexes can establish itself as a lead structure in the search for biologically active compounds.     

Separations of aldehydes by means of ion-exchange chromatography on bisulfite columns

Mixtures of carbonyl compounds were chromatographed on Dowex-I columns in the bisulfite form. Sodium bisulfite solutions of increasing concentrations were used as eluants. The studied compounds, including acetaldehyde, formaldehyde, 5-hydroxymethylfurfural, furfural and vanillin, were separated completely from each other. The eluate was also analysed quantitatively.     

Novel biomimetic iron-catalysts for environmentally benign epoxidations of olefins

A new selective and easily manageable epoxidation method is presented using an inexpensive and efficient FeCl₃·6H₂O and imidazole derivatives as catalysts. Aqueous hydrogen peroxide as an environmentally benign oxidant is utilized. This novel Fe/imidazole system gives moderate to excellent yields toward aromatic mono-, di-, and tri-substituted olefins.     

Fragmentation of doubly-protonated peptide ion populations labeled by H/D exchange with CD(3)OD

Doubly-protonated bradykinin (RPPGFSPFR) and an angiotensin III analogue (RVYIFPF) were subjected to hydrogen/deuterium (H/D) exchange with CD(3)OD in a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer. A bimodal distribution of deuterium incorporation was present for bradykinin after H/D exchange for 90 s at a CD(3)OD pressure of 4 x 10(-7) Torr, indicating the existence of at least two distinct populations. Bradykinin ion populations corresponding to 0-2 and 5-11 deuteriums (i.e., D(0), D(1), D(2), D(5), D(6), D(7), D(8), D(9), D(10), and D(11)) were each monoisotopically selected and fragmented via sustained off-resonance irradiation (SORI) collision-induced dissociation (CID). The D(0)-D(2) ion populations, which correspond to the slower exchanging population, consistently require lower SORI amplitude to achieve a similar precursor ion survival yield as the faster-reacting (D(5)-D(11)) populations. These results demonstrate that conformation/protonation motif has an effect on fragmentation efficiency for bradykinin. Also, the partitioning of the deuterium atoms into fragment ions suggests that the C-terminal arginine residue exchanges more rapidly than the N-terminal arginine. Total deuterium incorporation in the b(1)/y(8) and b(2)/y(7) ion pairs matches very closely the theoretical values for all ion populations studied, indicating that the ions of a complementary pair are likely formed during the same fragmentation event, or that no scrambling occurs upon SORI. Deuterium incorporation into the y(1)/a(8) pseudo-ion pair does not closely match the expected theoretical values. The other peptide, doubly-protonated RVYIFPF, has a trimodal distribution of deuterium incorporation upon H/D exchange with CD(3)OD at a pressure of 1 x 10(-7) Torr for 600 s, indicating at least three distinct ion populations. After 90 s of H/D exchange where at least two distinct populations are detected, the D(0)-D(7) ion populations were monoisotopically selected and fragmented via SORI-CID over a range of SORI amplitudes. The precursor ion survival yield as a function of SORI amplitude falls into two distinct behaviors corresponding to slower- and faster-reacting ion populations. The slower-reacting population requires larger SORI amplitudes to achieve the same precursor ion survival yield as the faster exchanging population. Total deuterium incorporation into the y(2)/b(5) ion pairs matches closely the theoretical values over all ion populations and SORI amplitudes studied. This result indicates the y(2) and b(5) ions are likely formed by the same mechanism over the SORI amplitudes studied.     

Mechanisms of exchange modulation in trimethylenemethane-type biradicals: the roles of conformation and spin density

The molecular structures and magnetic properties of six dinitroxide biradicals are described. Five of the dinitroxides are trimethylenemethane-type (TMM-type) biradicals; that is, the intramolecular exchange parameter, J, is modulated by a carbon-carbon double bond. However, the efficacy of the carbon-carbon double bond as an exchange coupler is determined by the molecular conformation. Our results show that the exchange parameters correlate with phenyl-ring torsion angles (phi) via a simple Karplus-Conroy-type relation: J = 44 cos(2) phi - 17. Comparison of these results to those obtained for our isostructural series of bis(semiquinone) biradicals shows that both the magnitude of J and the resistance of ferromagnetic J to bond torsions is proportional to the spin density adjacent to the exchange coupler.