Chiral [MnIIMnIII3M'] (M' = NaI, CaII, MnII) and [MnIIMnIII6NaI2] clusters built from an enantiomerically pure Schiff base: synthetic, chiroptical and magnetic properties

From the reaction of manganese halides with the chiral Schiff bases obtained by condensation of o-vanillin and (R)- or (S)-phenylglycinol, 11 complexes based on pentanuclear cages with trigonal bipyramidal [MnIIMnIII3M'] (M'=NaI, CaII, MnII) or enneanuclear [MnIIMnIII6NaI2] cores were synthesized. Structural, supramolecular chirality, and optical properties were explored. The magnetic properties of related systems were reviewed, and the magnetic response of the new systems was rationalized to the bond parameters

Trinuclear Complexes Derived from R/S Schiff Bases - Chiral Single-Molecule Magnets

The employment of enantiomerically pure Schiff bases in manganese chemistry is revealed to be an excellent method to obtain chiral single-molecule magnets and has allowed the characterization of several pairs of enantiomers, for which the magnetic properties were investigated. The reported systems consist of Mn-III-Mn-II-Mn-III linear trimers or Mn-3(III) cations in a triangular arrangement including the first example of a mu(3)-Cl bridge in an isolated manganese triangle

Syntheses, structures, chiroptical and magnetic properties of chiral clusters built from Schiff bases: a novel [MnIIMnIII6NaI2] core

Chiral clusters with MnIIMnIII3NaI and the new MnIIMnIII6NaI2 cores have been synthesised employing enantiomerically pure Schiff bases and halide ligands. The new compounds have been characterized by electronic circular dichroism (ECD) and magnetic susceptibility

From Mesocates to Helicates: Structural, Magnetic and Chiro-Optical Studies on Nickel(II) Supramolecular Assemblies Derived from Tetradentate Schiff Bases

The systematic reactions of a family of tetradentate pyridyl/imine and quinolyl/imine racemic or enantiopure Schiff bases with Ni(NO3)(2) or Ni(ClO4)(2) in the presence of sodium azide yielded, as a function of the starting racemic, chiral or achiral base, a set of chiral, meso or achiral complexes. In all cases, the compounds consist of two Ni-II cations linked by a double azido bridge in its end-on coordination mode. All the dimers exhibit a mesocate supramolecular structure and one of them, the unprecedented mix of helicate and mesocate in 2:1 ratio. The transition from mesocate to helicate conformation has been reached by tuning the flexibility of the central spacers of the Schiff bases and the size of the substituents. Electronic circular dichroism (ECD) studies have been performed for two pairs of enantiomers and interpreted by means of DFT calculations. Susceptibility measurements show a ferromagnetic coupling between the Ni-II cations mediated by the end-on azido bridges

The Expanding Universe of Prion Diseases

Prions cause fatal and transmissible neurodegenerative disease. These etiological infectious agents are formed in greater part from a misfolded cell-surface protein called PrP(C). Several mammalian species are affected by the diseases, and in the case of “mad cow disease” (BSE) the agent has a tropism for humans, with negative consequences for agribusiness and public health. Unfortunately, the known universe of prion diseases is expanding. At least four novel prion diseases—including human diseases variant Creutzfeldt-Jakob disease (vCJD) and sporadic fatal insomnia (sFI), bovine amyloidotic spongiform encephalopathy (BASE), and Nor98 of sheep—have been identified in the last ten years, and chronic wasting disease (CWD) of North American deer (Odocoileus Specis) and Rocky Mountain elk (Cervus elaphus nelsoni) is undergoing a dramatic spread across North America. While amplification (BSE) and dissemination (CWD, commercial sourcing of cervids from the wild and movement of farmed elk) can be attributed to human activity, the origins of emergent prion diseases cannot always be laid at the door of humankind. Instead, the continued appearance of new outbreaks in the form of “sporadic” disease may be an inevitable outcome in a situation where the replicating pathogen is host-encoded

Circularly polarized luminescence on dinuclear Tb(III) and Eu(III) complexes with (S-) and (R-) 2-phenylpropionate

The reaction of Ln(NO3)(2)center dot 6H(2)O (Ln = Tb and Eu) with (S)-(+)-2-phenylpropionic acid (S-HL) and 1,10-phenanthroline (phen) in EtOH/H2O allows the isolation of the dinuclear chiral compounds of the formula [Ln(2)(S-L)(6)(phen)(2)]center dot 2.5 center dot S-HL in which Ln = Tb (S-1), Ln = Eu (S-2). The same synthesis by using (R)-(-)-2-phenylpropionic acid (R-HL) instead of (S)-(+)-2-phenylpropionic acid allows the isolation of the enantiomeric compounds with the formula [Ln(2)(R-L)(6)(phen)(2)]center dot 2 center dot 5 center dot R-HL where Ln = Tb (R-1), Ln = Eu (R-2). All compounds show sensitized luminescence. The luminescence study, including the circularly polarized luminescence spectra of the four compounds, is reported. The magnetic behavior of S-1 and S-2 is also reported

Chiral Dinuclear Ln(III) Complexes Derived from S- and R-2-(6-methoxy-2-naphthyl)propionate. Optical and Magnetic Properties.

The reaction of LnCl3·6H2O with (S)-(+)-2-(6-methoxy-2-naphthyl)propionic acid (S-HL), best known as naproxen, and 1,10-phenanthroline (phen) in EtOH allows the isolation of dinuclear chiral compounds S-1-4 of the formula [Ln2(S-L)6(phen)2]·3DMF·H2O [Ln(III) = Eu (1), Gd (2), Tb (3) and Dy (4)]. The use of the R-enantiomeric species of the HL ligand led to complexes R-1-4 with the formula [Ln2(R-L)6(phen)2]·3DMF·H2O. Compounds R- and S-1, 3 and 4 show strong sensitized metal-centred luminescence in the visible region. Moreover, Dy(III) complexes R- and S-4 display field-induced singlemolecule magnet (SMM) behaviour. For chiral and emissive compounds circularly polarized luminescence (CPL) measurements have also been performed

On Quantum Effects in Soft Leptogenesis

It has been recently shown that quantum Boltzman equations may be relevant for leptogenesis. Quantum effects, which lead to a time-dependent CP asymmetry, have been shown to be particularly important for resonant leptogenesis when the asymmetry is generated by the decay of two nearly degenerate states. In this work we investigate the impact of the use of quantum Boltzman equations in the framework ``soft leptogenesis'' in which supersymmetry soft-breaking terms give a small mass splitting between the CP-even and CP-odd right-handed sneutrino states of a single generation and provide the CP-violating phase to generate the lepton asymmetry.Comment: 15 pages, 4 figures. Replacement to match published versio

Probing oscillations into sterile neutrinos with cosmology, astrophysics and experiments

We perform a thorough analysis of oscillation signals generated by one extra sterile neutrino, extending previous analyses done in simple limiting cases and including the effects of established oscillations among active neutrinos. We consider the following probes: solar, atmospheric, reactor and beam neutrinos, Big-Bang Nucleosynthesis (helium-4, deuterium), Cosmic Microwave Background, Large Scale Structure, supernovae, neutrinos from other astrophysical sources. We find no evidence for a sterile neutrino in present data, identify the still allowed regions, and study which future experiments can best probe them: sub-MeV solar experiments, more precise studies of CMB or BBN, future supernova explosions, etc. We discuss how the LSND hint is strongly disfavoured by the constraints of (standard) cosmology.Comment: 50 pages, many (14) figures. The text is divided into "results" and "technical details" sections. Final updated versio

Ruling out four-neutrino oscillation interpretations of the LSND anomaly?

Prompted by recent solar and atmospheric data, we re-analyze the four-neutrino description of current global neutrino oscillation data, including the LSND evidence for oscillations. The higher degree of rejection for non-active solar and atmospheric oscillation solutions implied by the SNO neutral current result as well as by the latest 1489-day Super-K atmospheric neutrino data allows us to rule out (2+2) oscillation schemes proposed to reconcile LSND with the rest of current neutrino oscillation data. Using an improved goodness of fit (gof) method especially sensitive to the combination of data sets we obtain a gof of only 1.6 times 10^{-6} for (2+2) schemes. Further, we re-evaluate the status of (3+1) oscillations using two different analyses of the LSND data sample. We find that also (3+1) schemes are strongly disfavoured by the data. Depending on the LSND analysis we obtain a gof of 5.6 times 10^{-3} or 7.6 times 10^{-5}. This leads to the conclusion that all four-neutrino descriptions of the LSND anomaly, both in (2+2) as well as (3+1) realizations, are highly disfavoured. Our analysis brings the LSND hint to a more puzzling status.Comment: 21 pages, 7 figure