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Electrospray ionization in combination with Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry are used to explore the gas-phase oxygen-atom transfer chemistry, characterize and reactivities of meso-tetrakis(pentafluorophenyl)porphyrin (TPFPP) chromium complexes, as well as some other tetradentate macrocyclic ligands. The TPFPP are excellent systems to examine the effects of spin-state change on oxygen-atom transfer due to doublet nature of the [d.sup.1] [Cr.sup.V] species and quartet ground states feature of [Cr.sup.III] complexes with high-lying doublet excited states.

An oxo iron(IV) porphyrin radical cation intermediate, functional model of Compound I, is produced as a bare species. The gas-phase reactivity of this intermediate with amines including N,N-dimethylanilines is examined in order to understand the Compound I-like reactivity of high-valent oxo iron intermediates in a solvent free environment.

A one-step enzymatic reaction for improving the collision-induced dissociation (CID)-based tandem mass spectrometry (MS/MS) analysis of phosphorylated peptides in an ion trap is presented. Carboxypeptidase-B (CBP-B) was used to selectively remove C-terminal arginine or lysine residues from phosphorylated tryptic/Lys-C peptides prior to their MS/MS analysis by CID with a Paul-type ion trap. Removal of this basic C-terminal residue served to limit the extent of gas-phase neutral loss of phosphoric acid (HPO), favoring the formation of diagnostic b and y ions as determined by an increase in both the number and relative intensities of the sequence-specific product ions. Such differential fragmentation is particularly valuable when the HPO elimination is so predominant that localizing the phosphorylation site on the peptide sequence is hindered. Improvement in the quality of tandem mass spectral data generated by CID upon CBP-B treatment resulted in greater confidence both in assignment of the phosphopeptide primary sequence and for pinpointing the site of phosphorylation. Higher Mascot ion scores were also generated, combined with lower expectation values and higher delta scores for improved confidence in site assignment; Ascore values also improved. These results are rationalized in accordance with the accepted mechanisms for the elimination of HPO upon low energy CID and insights into the factors dictating the observed dissociation pathways are presented. We anticipate this approach will be of utility in the MS analysis of phosphorylated peptides, especially when alternative electron-driven fragmentation techniques are not available. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Model ferris heme nitrosyl complexes, [Fe(TPP)(NO)]+ and [Fe(TPFPP)(NO)]+, where TPP is the dianion of 5,10,15,20-tetrakis-phenyl-porphyrin and TPFPP is the dianion of 5,10,15,20-tetnlis-pentafluorophenyl-porphyrin, have been obtained as isolated spedes by the gas phase reaction of NO with [FeIII(TPP)]+ and [FeIII (TPFPP)]+ ions delivered in the gas phase by electrospray ionization, respectively. The so-formed nitrosyl complexes have been characterized by vibrational spectroscopy also exploiting 15N-isotope substitution in the NO ligand. The characteristic NO stretching frequency is observed at 1825 and 1859 cm-1 for [FeIII(TPP)(NO)]+ and [FeIII(TPFPP)(NO)]+ ions, respectively, providing reference values for genuine five-coordinate FeIII(NO) porphyrin complexes differing only for the presence of either phenyl or pentafluorophenyl substituents on the meso positions of the porphyrin ligand. The vibrational assignment is aided by hybrid density functional theory (DFT) calculations ofgeometry and electronic stnlcture and frequency analysis which dearly support a singlet spin electronic state fur both [Fe(TPP)(NO)]+ and [Fe(TPFPP)(NO)]+ complexes. Both TD-DFT and CASSCF calculations suggest that the singlet ground state is best described as FeII(NO+) and that the open-shell AFC bonding scheme contribute for a high-energy excited state. The kinetics of the NO addition reaction in the gas phase are faster for [FeIII(TPFPP)]+ ions bya relatively small factor, though highly reliable because of a direct comparative evaluation. The study was aimed at gaining vibrational and reactivity data on five-coordinate FeIII(NO) porphynis complexes, typically transient species in solution, ultimately to provide insights into the nature of the Fe(NO) interaction in heme proteins. [ABSTRACT FROM AUTHOR]