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991.
al-Khalili A Thomas R Ehlerding A Hellberg F Geppert WD Zhaunerchyk V af Ugglas M Larsson M Uggerud E Vedde J Adlhart C Semaniak J Kamińska M Zubarev RA Kjeldsen F Andersson PU Osterdahl F Bednarska VA Paál A 《The Journal of chemical physics》2004,121(12):5700-5708
Dimethyl disulfide (DMDS) and N-methylacetamide are two first choice model systems that represent the disulfide bridge bonding and the peptide bonding in proteins. These molecules are therefore suitable for investigation of the mechanisms involved when proteins fragment under electron capture dissociation (ECD). The dissociative recombination cross sections for both protonated DMDS and protonated N-methylacetamide were determined at electron energies ranging from 0.001 to 0.3 eV. Also, the branching ratios at 0 eV center-of-mass collision energy were determined. The present results give support for the indirect mechanism of ECD, where free hydrogen atoms produced in the initial fragmentation step induce further decomposition. We suggest that both indirect and direct dissociations play a role in ECD. 相似文献
992.
Factors affecting the electrochemical and spectroelectrochemical properties of diruthenium(III,II) complexes containing four unsymmetrical bridging ligands are reported for seven related compounds which were isolated in one or two of the four possible isomeric forms. The investigated compounds are represented as Ru(2)(2-CH(3)ap)(4)Cl, Ru(2)(2,5-F(2)ap)(4)Cl, Ru(2)(2,6-F(2)ap)(4)Cl, and Ru(2)(2,4,6-F(3)ap)(4)Cl where 2-CH(3)ap, 2,5-F(2)ap, 2,6-F(2)ap, and 2,4,6-F(3)ap are, respectively, the 2-(2-methylanilino)pyridinate anion, the 2-(2,5-difluoroanilino)pyridinate anion, the 2-(2,6-difluoroanilino)pyridinate anion, and the 2-(2,4,6-trifluoroanilino)pyridinate anion. Ru(2)(2-CH(3)ap)(4)Cl and Ru(2)(2,5-F(2)ap)(4)Cl exist only in a (4,0) conformation while Ru(2)(2,4,6-F(3)ap)(4)Cl is present in both (3,1) and (4,0) isomeric forms. Ru(2)(2,6-F(2)ap)(4)Cl also exists in two isomeric forms, but only the (3,1) isomer was generated in sufficient quantities to be isolated and structurally characterized. This series of seven closely related metal-metal bonded complexes thus provides the first possibility to systematically examine how differences in position and number of the electron-donating or electron-withdrawing groups on the anionic bridging ligands might be related to the electronic properties and structural features of the compound as well as the type and number of geometric isomers which are formed. Each diruthenium derivative undergoes three one-electron transfers in CH(2)Cl(2) containing 0.1 M tetra-n-butylammonium perchlorate (TBAP). The first reduction and first oxidation products were characterized by thin-layer UV-vis spectroelectrochemistry, and the spectroscopic data, along with E(1/2) values, were then related via linear free energy relationships to the type of isomer and/or position of the electron-donating or electron-withdrawing substituents on the anionic ap bridge. The electrogenerated Ru(2)(6+) and Ru(2)(4+) forms of the compounds were assigned on the basis of electrochemical and UV-vis spectroscopic data as having the electronic configuration sigma(2)pi(4)delta(2)pi(2) and sigma(2)pi(4)delta(2)pi(3)delta, respectively, and seemed to be independent of the isomer type ((3,1) or (4,0)). The spectral and electrochemical properties of the compounds both vary substantially as a function of the isomer type, but this is not reflected in the structural features of the compounds which are within the range of what is seen for other Ru(2)(5+) species described in the literature. The Ru-Ru bond lengths of the four structurally characterized (4,0) isomers of the ap complexes range from 2.275 to 2.296 A while those of the three structurally characterized (3,1) isomers of ap derivatives fall in the range 2.284-2.286 A and show no significant difference among the three compounds. The Ru-Cl bond lengths of the (3,1) isomers do not vary significantly with the bridging ligand and range from 2.458 to 2.471 A whereas those of the (4,0) isomers range from 2.437 to 2.487 A and show larger variations among the compounds. The Ru-Ru-Cl bond angle is virtually independent of the bridging ligand in the case of the (4,0) isomers but decreases with the electron-withdrawing effect of the substituent in the case of the (3,1) isomers. 相似文献
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