Marine bifunctional sphingolipids from the sponge Oceanapia ramsayi

During the course of our continuing studies on marine natural lipid products,two known sphingolipids have been isolated for the first time from a specimen of the marine sponge Oceanapia ramsayi collected at Itampolo on the west coast of Madagascar in the Indian Ocean. The structures were elucidated using NMR data and by comparison with literature data. The occurrence of these sphingolipids within other Oceanapia spp. is discussed.     

Layer-by-layer assembled composite films of side-functionalized poly(3-hexylthiophene) and CdSe nanocrystals: electrochemical, spectroelectrochemical and photovoltaic properties

Regioregular poly(3-hexylthiophene) containing one diaminopyrimidine side group per ten repeat units (P3HT-co-P3(ODAP)HT) can form molecular composites with 1-(6-mercaptohexyl)thymine capped CdSe nanocrystals (CdSe(MHT)) via hydrogen bonds directed molecular recognition. Here we report complementary spectroscopic, electrochemical and spectroelectrochemical investigations of both the functionalized poly(thiophene) and its composite with the nanocrystals, the latter being fabricated using the layer-by-layer (LbL) deposition technique. UV-Vis-NIR and Raman spectroelectrochemical investigations unequivocally show that the onset of the first anodic peak in the cyclic voltammogram of the copolymer can be attributed to the oxidation of the pi-conjugated backbone in the polymer chains. For this reason, it is possible to determine the width and the position of its band gap (corresponding to the pi-pi* transition) by UV-Vis spectroscopy combined with cyclic voltammetry. These studies show that the polymer exhibits a slightly larger band gap with the HOMO level insignificantly lower in energy (by 0.03 eV) as compared to the case of regioregular poly(3-hexylthiophene) of comparable degree of polymerization. Hydrogen bond interactions of the polymer with CdSe(MHT) in the molecular composite result in a hypsochromic shift of the band corresponding to the pi-pi* transition from 504 nm to 488 nm. This can be taken as a spectroscopic manifestation of the conformational changes induced by shortening of the conjugation length. The observed spectral modifications are consistent with electrochemically determined lowering of the polymer HOMO level (from -4.91 eV in the pure polymer to -4.99 eV in the composite). Cyclic voltammetry studies supported by spectroelectrochemistry also show that the redox stability of CdSe(MHT) in the molecular composite with P3HT-co-P3(ODAP)HT is lower than that determined for stearate-capped nanocrystals. Their irreversible oxidation starts at E = +0.7 V vs. Ag/0.1 M Ag(+)i.e. at potentials by ca. 0.3 V lower than the oxidation of stearate stabilized CdSe nanocrystals of the same size. We show that-despite these modifications-the alignment of the HOMO and LUMO levels of the composite components remains appropriate for its use in hybrid solar cells, which is demonstrated by the photovoltaic effect observed for the LbL-processed composite sandwiched between two electrodes.     

Determination of the electron's solvation site on D2O/Cu(111) using Xe overlayers and femtosecond photoelectron spectroscopy

We investigate the binding site of solvated electrons in amorphous D(2)O clusters and D(2)O wetting layers adsorbed on Cu(111) by means of two-photon photoelectron (2PPE) spectroscopy. On the basis of different interactions of bulk- or surface-bound solvated electrons with rare gas atoms, titration experiments using Xe overlayers reveal the location of the electron solvation sites. In the case of flat clusters with a height of 2-4 bilayers adsorbed on Cu(111), solvated electrons are found to reside at the ice-vacuum interface, whereas a bulk character is found for solvated electrons in wetting layers. Furthermore, time-resolved experiments are performed to determine the origin of the transition between these different solvation sites with increasing D(2)O coverage. We employ an empirical model calculation to analyse the rate of electron transfer back to the substrate and the energetic stabilization of the solvated electrons, which allows further insight into the binding site for clusters. We find that the solvated electrons reside at the edges of the clusters. Therefore, we attribute the transition from surface- to bulk-solvation to the coalescence of the clusters to a closed ice film occurring at a nominal coverage of 2-3 BL, while the distance of the binding sites to the metal-ice interface is maintained.     

How the surrounding water changes the electronic and magnetic properties of DNA

We study the influence of humidity on the transport and magnetic properties of DNA within the quantum chemistry methods. Strong influence of water molecules on these properties, observed in this study, opens up opportunities for application of DNA in molecular electronics. Interaction of the nucleobases with water molecules leads to breaking of some of the pi bonds and appearance of unbound pi electrons. These unbound electrons contribute significantly to the charge transfer at room temperature by up to 10(3) times, but at low temperature the efficiency of charge transfer is determined by the spin interaction of two unbound electrons located on the intrastrand nucleobases. The charge exchange between the nucleobases is allowed only when the spins of unbound electrons are antiparallel. Therefore, the conductance of DNA molecule can be controlled by a magnetic field. That effect has potentials for applications in developing nanoscale spintronic devices based on the DNA molecule, where efficiency of spin interaction will be determined by the DNA sequence.     

Characterization of polyvinyl resins used as binding media in paintings by pyrolysis–silylation–gas chromatography–mass spectrometry

Polyvinyl resins, in particular poly(vinyl acetate) emulsions (PVA), are widely used in contemporary paintings as binding media, because of the optimum mechanical and optical properties these polymers confer on the paint layers. A study has been carried out to chemically characterize samples of PVA resins prepared as coating films from commercial products currently available from fine arts suppliers. For this purpose, a new method has been based on "on-line" silylation-pyrolysis using hexamethyldisilazane as derivatisation reagent in pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS). This proposed procedure leads to unambiguous identification of this type of binder and improves conventional direct Py-GC-MS. PVA media used in three contemporary paintings from a private collection and from the Museum of Fine Arts of Málaga (Spain) have been successfully identified with this procedure. As a second step of this work, a study devoted to the characterization of changes in the chemical composition of the PVA commercial products studied has been carried out. Effects induced in the specimens by three different types of artificial accelerated ageing process--thermal, UV light, and in an SO(2)-polluted chamber--were compared.     

Species as a Relationship

The fact that humans have a special relationship to each other insofar as they belong in the same species is often taken to be a morally relevant difference between humans and other animals, one which justifies a greater moral status for all humans, regardless of their individual capacities. I give some reasons why this kind of relationship is not an appropriate ground for differential treatment of humans and nonhumans. I then argue that even if relationships do matter morally species membership cannot justify a difference in moral status. This has important implications because it removes one barrier to giving animals greater moral status.

The first heterometallic Cu(II)/Cr(III) complex with an open-chain Schiff-base ligand self-assembled from copper powder,Reineckes salt,ethylendiamine and acetone

A novel supramolecular assembly [{Cu(enac)}₂Cr(NCS)₄(NH₃)₂][Cr(NCS)₄(NH₃)₂]₃ · 4(CH₃)₂CO (enac = 4,6,6-trimethyl-3,7-diazanon-3-ene-1,9-diamine), the first example of a Cu/Cr heterometallic compound containing a Schiff-base ligand such as enac, and an anion of Reineckes salt, Cr(NCS)₄(NH₃)₂⁻, as a building block, was obtained by the self-assembly reaction of copper powder and Reineckes salt in an acetone/methanol (1:4) solution of ethylenediamine in the open air. An X-ray study shows that the complex includes a trinuclear Cu₂Cr cation, constructed from two Cu(enac)²⁺ moieties and a trans-[Cr(NCS)₄(NH₃)₂]⁻ block as a two-linking bridging ligand. The metal–metal separations within the cation are Cu?Cr = 6.393(31) Å and Cu?Cu = 12.786(63) Å. The supramolecular architecture of the complex involves two types of H-bonded chains, the first chain is generated by trinuclear cations [{Cu(enac)}₂Cr(NCS)₄(NH₃)₂]²⁺, [Cr(NCS)₄(NH₃)₂]⁻ anions and (CH₃)₂CO molecules, while the second by crystallographically different anions of Reineckes salt and (CH₃)₂CO. Variable-temperature (1.8–300 K) magnetic susceptibilities show a slight change of the μ_B value at low temperature, indicative of weak antiferromagnetic interactions (J_CuCr = −0.9 cm⁻¹) between the paramagnetic centers.     

Crystal structure and magnetic properties of the 1D bimetallic thiocyanate bridged compound: {(CuL1)[Co(NCS)4]}(L1 = N-rac-5,12-Me2-[14]-4,11-dieneN4)

The synthesis, crystal structure and magnetic properties are reported for the new bimetallic compound {(CuL₁)[Co(NCS)₄]} where L₁ = N-rac-5,12-dimethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene. The complex forms a one-dimensional zig-zag coordination polymer along the crystallographic c axis, with Co(II) and Cu(II) ions connected via thiocyanate bridges. The Co(II) centre in the [Co(NCS)₄] fragment approximates a distorted tetrahedral symmetry. The Cu(II) geometry is a distorted tetragonal bipyramid with the apical position occupied by the bridging thiocyanate ligand and the basal ones by the four nitrogen atoms from the macrocyclic ring. The polymer chain nearest Cu(1)?Co(1) distances are 6.4152(9) and 6.0988(9) Å and the nearest Cu(1)?Co(1) interchain distances are 6.8609(9), 6.9628(9) and 6.0336(10) Å. The magnetization measurements for the examined compound have been carried out over the range 1.8–300 K. This data suggest ferromagnetic interactions through the thiocyanate bridge.