Mandelalides A-D, cytotoxic macrolides from a new Lissoclinum species of South African tunicate

Mandelalides A-D are variously glycosylated, unusual polyketide macrolides isolated from a new species of Lissoclinum ascidian collected from South Africa, Algoa Bay near Port Elizabeth and the surrounding Nelson Mandela Metropole. Their planar structures were elucidated on submilligram samples by comprehensive analysis of 1D and 2D NMR data, supported by mass spectrometry. The assignment of relative configuration was accomplished by consideration of homonuclear and heteronuclear coupling constants in tandem with ROESY data. The absolute configuration was assigned for mandelalide A after chiral GC-MS analysis of the hydrolyzed monosaccharide (2-O-methyl-α-L-rhamnose) and consideration of ROESY correlations between the monosaccharide and aglycone in the intact natural product. The resultant absolute configuration of the mandelalide A macrolide was extrapolated to propose the absolute configurations of mandelalides B-D. Remarkably, mandelalide B contained the C-4' epimeric 2-O-methyl-6-dehydro-α-L-talose. Mandelalides A and B showed potent cytotoxicity to human NCI-H460 lung cancer cells (IC(50), 12 and 44 nM, respectively) and mouse Neuro-2A neuroblastoma cells (IC(50), 29 and 84 nM, respectively).     

Crystallisation of polypropylene matrix in composites filled with wooden parts of rapeseed straw

Nucleation ability of native and modified rapeseed straw during the polypropylene crystallization from the melt was investigated by the DSC method. Composites were made from isotactic polypropylene and lignocellulosic material using extrusion and injection moulding techniques. They were obtained using polypropylenes differing with respect to melt flow rates and different varieties of rapeseed straw. Chemical modification was carried out in two stages: through mercerisation and treatment with acetic acid anhydride. In the course of investigations, it was found that both native and modified rapeseed straw acted as an active nucleant of polypropylene crystallisation characterised by low values of MFR indices. It was found that for polypropylenes with high MFR values, the values of crystallization temperatures and crystallization half-time in composites were identical when compared with non-filled polymers. The investigations demonstrated that there were insignificant differences among composites containing straw from different varieties of rapeseed. The analysis of crystallization temperatures confirmed that rapeseed straw modification failed to change this parameter of the crystallization process. A similar tendency was observed in the case of changes of the half-time crystallization process. Moreover, the analysis of the crystallization temperature and crystallization half-time showed that the presence in composites of lignified rapeseed straw particles played an important role in the crystallization conditions.     

Anisotropic nanoparticles of precise microstructure polyolefins

Nanoparticles of precisely branched polyethylenes possess a distinct oblate shape resulting from a crystalline lamella in the particle as revealed by SAXS and TEM, and display controllable and well-behaved thermal behaviour.     

Stability of Frustration-Free Hamiltonians

We prove stability of the spectral gap for gapped, frustration-free Hamiltonians under general, quasi-local perturbations. We present a necessary and sufficient condition for stability, which we call Local Topological Quantum Order and show that this condition implies an area law for the entanglement entropy of the groundstate subspace. This result extends previous work by Bravyi et al. on the stability of topological quantum order for Hamiltonians composed of commuting projections with a common zero-energy subspace. We conclude with a list of open problems relevant to spectral gaps and topological quantum order.     

Application of BDD thin film electrode for electrochemical decomposition of heterogeneous aromatic compounds

The aim of the presented study is to investigate the applicability of electrochemical oxidation of aromatic compounds containing heteroatoms, e.g. waste from production of pesticides or pharmaceutics, at a borondoped diamond (BDD) electrode. The BDD electrodes were synthesized by microwave plasma enhanced chemical vapour deposition (MW PE CVD). Investigation of the electrode surface by optical microscopy and scanning electron microscopy (SEM) confirmed that the synthesized layer was continuous and formed a densely packed grain structure with an average roughness of less than 0:5 ??m. The influence of important electrochemical parameters: current density, kind of reactor, pH or mixing operation, on the efficiency of the oxidation was investigated. The fouling of electrode??s surface caused by the deposition of organic material was observed during CV and galvanostatic experiments. At low current density the oxidation rate constant k was low, but the current efficiency was relatively high. The BDD can be used successfully to remove heterogeneous aromatic compounds existing either as molecules or cations. During 4 h of electrolysis 95% of aromatic compounds were electrochemically decomposed to mineral forms. It was observed that the influence of the initial pH on mineralization was marginal.     

Lefschetz periodic point free self-maps of compact manifolds

Let f be a self-map of a compact connected manifold M. We characterize Lefschetz periodic point free continuous self-maps of M for several classes of manifolds and generalize the results of Guirao and Llibre [J.L.G. Guirao, J. Llibre, On the Lefschetz periodic point free continuous self-maps on connected compact manifolds, Topology Appl. 158 (16) (2011) 2165–2169].     

Isochroman derivatives and their tendency to crystallize in chiral space groups

In methyl [5‐methoxy‐4‐(4‐methoxy­phenyl)­isochroman‐3‐yl]­acetate, C₂₀H₂₂O₅, (I), and methyl [4‐(2,5‐di­methoxy­phenyl)‐8‐methoxy­isochroman‐3‐yl]­acetate, C₂₁H₂₄O₆, (II), the heterocyclic rings adopt half‐chair conformations. The substituents at the 3‐ and 4‐positions are in a trans configuration in both (I) and (II), being in an axial conformation in (I) and in an equatorial conformation in (II). The crystal structure of (I) is stabilized by weak C—H⋯O hydrogen bonding, leading to the formation of an infinite three‐dimensional network. Compound (II) crystallizes in a chiral space group. This feature, which was also found in previously investigated isochroman derivatives, is related to the arrangement of substituents attached to the isochroman moiety.     

Mass spectrometric study of amino acid–triethylborane chelates

Abstract  Synthesis of chelates from selected l-amino acids and triethylborane, and the mass spectra of the chelates, are described. Conditions for forming dimers between the chelates and the sodium ion are discussed, and structures are proposed for the dimers. Graphical abstract        

(+)-Usnic Acid as a Promising Candidate for a Safe and Stable Topical Photoprotective Agent

The study aimed to examine whether usnic acid—a lichen compound with UV-absorbing properties—can be considered as a prospective photoprotective agent in cosmetic products. Moreover, a comparison of two usnic acid enantiomers was performed to preselect the more effective compound. To meet this aim, an in vitro model was created, comprising the determination of skin-penetrating properties via skin-PAMPA assay, safety assessment to normal human skin cells (keratinocytes, melanocytes, fibroblasts), and examination of photostability and photoprotective properties. Both enantiomers revealed comparable good skin-penetrating properties. Left-handed usnic acid was slightly more toxic to keratinocytes (IC₅₀ 80.82 and 40.12 µg/mL, after 48 and 72 h, respectively) than its right-handed counterpart. The latter enantiomer, in a cosmetic formulation, was characterized by good photoprotective properties and photostability, comparable to the UV filter octocrylene. Perhaps most interestingly, (+)-usnic acid combined with octocrylene in one formulation revealed enhanced photoprotection and photostability. Thus, the strategy can be considered for the potential use of (+)-usnic acid as a UV filter in cosmetic products. Moreover, the proposed model may be useful for the evaluation of candidates for UV filters.