Platinum(II) 1,10-phenanthroline complexes of acetylides containing redox-active groups.

The new diimine ligand 3,8-di-n-pentyl-4,7-di(phenylethynyl)-1,10-phenanthroline (1) was used for the synthesis of a range of Pt(II) complexes, viz.[Pt(1)Cl2], [Pt(1)(C triple bond C-Ph)2], [Pt(1)(C triple bond C-Fc)2] and [Pt(1)(C triple bond C-p-C6H4-C triple bond C-Fc)2](Fc = ferrocenyl). Crystal structure analyses were performed for [Pt(1)Cl2] and [Pt(1)(C triple bond C-Ph)2] and revealed that the di(acetylide)pi-tweezer of the latter binds a molecule of chloroform through C-H...pi hydrogen bonds. The redox and optical properties of 1 and its complexes were investigated by (spectro-)electrochemistry, UV-Vis and luminescence spectroscopy, and an energy level diagram was derived for [Pt(1)(C triple bond C-Fc)2] and related compounds on the basis of the data collected. The ferrocenyl-substituted Pt(II) complexes are donor-sensitiser assemblies. Intramolecular quenching of the photoexcited Pt(II) diimine unit leads to very short luminescence lifetimes for [Pt(1)(C triple bond C-p-C(6)H(4)-C triple bond C-Fc)2](2 ns) and [Pt(1)(C triple bond C-Fc)2](0.3 ns), as opposed to [Pt(1)(C triple bond C-Ph)2](0.7 micros). Excimer formation has been observed for [Pt(1)(C triple bond C-Ph)(2)] at room temperature in dichloromethane and at low temperatures in frozen glassy dichloromethane and 2-methyltetrahydrofuran solution, but not in the solid state.

Static and time-resolved fluorescence investigations of tryptophan analogues--a solvent study.

The fluorescence properties of tryptophan, polytryptophan and seven of its analogues (7-azatryptophan, 5-hydroxytryptophan, 5-methoxytryptophan, 5-fluorotryptophan, 5-methyltryptophan, 5-bromotryptophan, and 6-fluorotryptophan) are studied using two novel fluorescence spectroscopic techniques for a wide range of solvent polarities. Two-dimensional mapping of all emission and all fluorescence spectra using excitation-emission spectroscopy (EES) has been used to determine quantum yields, positions of emission maxima, full widths at half maximum (FWHMs) as well as Stokes' shifts. Additionally, fluorescence lifetimes obtained from time-resolved experiments using a picosecond laser system are presented and compared with the data acquired from the static setup. This systematic study of the fluorescence characteristics is a prerequisite to assess the potential of these analogues to act as structure-conserving substitutes for tryptophan in protein fluorescence experiments. The potential of these analogues, to act as probes for the local environment, and allow estimation of the polarity in the vicinity of the fluorophore and its exposure to the solvent, is discussed.

Ferrocenyl-functionalised terpyridines and their transition-metal complexes: syntheses, structures and spectroscopic and electrochemical properties.

Terpyridine ligands of the type Fc'-X-tpy (Fc'=ferrocenyl or octamethylferrocenyl, X=rigid spacer, tpy'=4'-substituted 2,2':6',2''-terpyridine) were prepared, crystallographically characterised and used for the synthesis of di- and trinuclear bis(terpyridine) complexes of RuII, FeII and ZnII. Donor-sensitiser dyads and triads based on RuII were thoroughly investigated by (spectro)electrochemistry, UV/Vis, transient absorption and luminescence spectroscopy, and an energy level scheme was derived on the basis of the data collected. Intramolecular quenching of the photoexcited RuII complexes by the redox-active Fc' groups can occur reductively and by energy transfer. Both the redox potential of the donor Fc' and the nature of the spacer X have a decisive influence on excited-state lifetimes and emission properties of the complexes. Some of the compounds show room-temperature luminescence, which is unprecedented for ferrocenyl-functionalised compounds of this kind.

Reaction mechanism of plant 2-Cys peroxiredoxin. Role of the C terminus and the quaternary structure.

Barley 2-cysteine peroxiredoxin (2-Cys Prx) was analyzed for peroxide reduction, quaternary structure, thylakoid attachment, and function as well as in vivo occurrence of the inactivated form, with emphasis on the role of specific amino acid residues. Data presented show the following. 1) 2-Cys Prx has a broad substrate specificity and reduces even complex lipid peroxides such as phosphatidylcholine dilineoyl hydroperoxide, although at low rates. 2) 2-Cys Prx partly becomes irreversibly oxidized by peroxide substrates during the catalytic cycle in a concentration-dependent manner, particularly by bulky hydroperoxides. 3) Using dithiothreitol and thioredoxin (Trx) as reductants, amino acids were identified that are important for peroxide reduction (Cys64, Arg140, and Arg163), regeneration by Trx (Cys185), and conformation changes from dimer to oligomer (Thr66, Trp99, and Trp189). 4) Oligomerization decreased the rate of Trx-dependent peroxide detoxification. 5) Comparison of PrxWT, W99L, and W189L using static and time-resolved LIF techniques demonstrated the contributions of the tryptophan residues and yielded information about their local environment. Data indicated protein dynamics in the catalytic site and the carboxyl terminus during the reduction-oxidation cycle. 6) Reduced and inactivated barley 2-Cys Prx oligomerized and attached to the thylakoid membrane in isolated chloroplasts. The in vivo relevance of inactivation was shown in leaves subjected to cold and wilting stress and during senescence. Based on these results, it is hypothesized that in addition to its function in peroxide detoxification, 2-Cys Prx may play a role as a structural redox sensor in chloroplasts.