Pentacyanoiron(II) as an Electron Donor Group for Nonlinear Optics: Medium-Responsive Properties and Comparisons with Related Pentaammineruthenium(II) Complexes

In this article, we describe a series of complex salts in which electron-rich {Fe^(II)(CN)_5}^(3-) centers are coordinated to pyridyl ligands with electron-accepting N-methyl/aryl-pyridinium substituents. These compounds have been characterized by using various techniques including electronic absorption spectroscopy and cyclic voltammetry. Molecular quadratic nonlinear optical (NLO) responses have been determined by using hyper-Rayleigh scattering (HRS) at 1064 nm, and also via Stark (electroabsorption) spectroscopic studies on the intense, visible d → π* metal-to-ligand charge-transfer (MLCT) bands. The relatively large static first hyperpolarizabilities, β_0, increase markedly on moving from aqueous to methanol solutions, accompanied by large red-shifts in the MLCT transitions. Acidification of aqueous solutions allows reversible switching of the linear and NLO properties, as shown via both HRS and Stark experiments. Time-dependent density functional theory and finite field calculations using a polarizable continuum model yield relatively good agreement with the experimental results and confirm the large decrease in β0 on protonation. The Stark-derived β0 values are generally larger for related {Ru^(II)(NH_3)_5}^(2+) complexes than for their {Fe^(II)(CN)_5}^(3-) analogues, consistent with the HRS data in water. However, the HRS data in methanol show that the stronger solvatochromism of the Fe^(II) complexes causes their NLO responses to surpass those of their Ru^(II) counterparts upon changing the solvent medium

Habitable Zones in the Universe

Habitability varies dramatically with location and time in the universe. This was recognized centuries ago, but it was only in the last few decades that astronomers began to systematize the study of habitability. The introduction of the concept of the habitable zone was key to progress in this area. The habitable zone concept was first applied to the space around a star, now called the Circumstellar Habitable Zone. Recently, other, vastly broader, habitable zones have been proposed. We review the historical development of the concept of habitable zones and the present state of the research. We also suggest ways to make progress on each of the habitable zones and to unify them into a single concept encompassing the entire universe.Comment: 71 pages, 3 figures, 1 table; to be published in Origins of Life and Evolution of Biospheres; table slightly revise

Protein Folding Activity of the Ribosome is involved in Yeast Prion Propagation.

6AP and GA are potent inhibitors of yeast and mammalian prions and also specific inhibitors of PFAR, the protein-folding activity borne by domain V of the large rRNA of the large subunit of the ribosome. We therefore explored the link between PFAR and yeast prion [PSI(+)] using both PFAR-enriched mutants and site-directed methylation. We demonstrate that PFAR is involved in propagation and de novo formation of [PSI(+)]. PFAR and the yeast heat-shock protein Hsp104 partially compensate each other for [PSI(+)] propagation. Our data also provide insight into new functions for the ribosome in basal thermotolerance and heat-shocked protein refolding. PFAR is thus an evolutionarily conserved cell component implicated in the prion life cycle, and we propose that it could be a potential therapeutic target for human protein misfolding diseases

Homogeneous Catalyst with Gold: Efficient Hydration of Phenylacetylene in Aqueous Media.

6 pages, 2 figures, 5 tables.A variety of gold(I) complexes containing the water-soluble phosphine ligands TPPMS, TPPDS, and TPPTS (mono-, di-, and tri-sulfonated triphenylphosphine, respectively) were tested as catalysts for the hydration of phenylacetylene in aqueous media. The gold(I) alkynyl complexes [AuCCR(TPPTS)] (where R = tBu and 3-thiophenyl) give the highest ever reported turnover frequencies (1000 and 1060 h-1, respectively) for the hydration of phenylacetylene under optimum conditions (0.1 mol % catalyst loading, 10 mol % H2SO4, 1 h reflux in 5:1 MeOH/H2O). The hydration of phenylacetylene can also be carried out using only water and reaction medium, which allows recycling of the gold catalyst without significant drop of activity for at least three cycles. DFT calculations were used to compare relative energies of possible intermediates involved in the catalytic cycle.We thank the Ministerio de Ciencia y Tecnología Spain for financial support (CTQ2005-08099-C03- 01) and for research grants to L.A.J. (SB2001-0191), S.S. (BES2003-2259), and F.M. (SB2003-0235).Peer reviewe