Palcernuine,the first [5/6/6/6]-cernuane-type alkaloid from Palhinhaea cernua f. sikkimensis

One novel(named palcernuine, 1) and five known cernuane-type(2–6) alkaloids were isolated from the whole plant of Palhinhaea cernua f. sikkimensis. The structure of 1, possessing an unprecedented [5/6/6/6]-tetracyclic ring system containing two nitrogen atoms, was established on the basis of spectroscopic methods, and its absolute configuration was determined by comparison of the experimental and calculated electronic circular dichroism(ECD) spectra. A plausible biosynthetic pathway to 1 is proposed.     

Molecular depth-profiling of polycarbonate with low-energy Cs+ ions

In this work, we explored the possibility of performing molecular depth-profiling by using very low-energy (about 200 eV) monoatomic Cs(+) ions. We show, for the first time, that this simple approach is successful on polymer layers of polycarbonate (PC). Under 200 eV Cs(+) irradiation of PC, a fast decrease of all characteristic negatively charged molecular ion signals is first observed but, rather surprisingly, these signals reach a minimum before rising again. A steady state is reached at which time most specific PC fragments are detected, some with even higher signal intensity (e.g. C(6)H(5)O(-)) than before irradiation. It is believed that the implanted Cs plays a major role in enhancing the negative ionisation of molecular fragments, leading to their easy detection for all the profile, although some material degradation obviously occurs. In the positive ion mode, all molecular fragments of the polymer disappear very rapidly, but clusters combining two Cs atoms and one molecular fragment (e.g. Cs(2)C(6)H(5)O(+)) are detected during the profile, proving that some molecular identification remains possible. In conclusion, this work presents a simple approach to molecular depth-profiling, complementary to cluster ion beam sputtering.     

Breaking of Ergodicity in Expanding Systems of Globally Coupled Piecewise Affine Circle Maps

To identify and to explain coupling-induced phase transitions in coupled map lattices (CML) has been a lingering enigma for about two decades. In numerical simulations, this phenomenon has always been observed preceded by a lowering of the Lyapunov dimension, suggesting that the transition might require changes of linear stability. Yet, recent proofs of co-existence of several phases in specially designed models work in the expanding regime where all Lyapunov exponents remain positive. In this paper, we consider a family of CML composed by piecewise expanding individual map, global interaction and finite number $N$ of sites, in the weak coupling regime where the CML is uniformly expanding. We show, mathematically for $N=3$ and numerically for $N\ge 3$ , that a transition in the asymptotic dynamics occurs as the coupling strength increases. The transition breaks the (Milnor) attractor into several chaotic pieces of positive Lebesgue measure, with distinct empiric averages. It goes along with various symmetry breaking, quantified by means of magnetization-type characteristics. Despite that it only addresses finite-dimensional systems, to some extend, this result reconciles the previous ones as it shows that loss of ergodicity/symmetry breaking can occur in basic CML, independently of any decay in the Lyapunov dimension.     

Cationic Gallium(III) Halide Complexes: A New Generation of π-Lewis Acids

Ga-neration X: Well-defined neutral and cationic gallium(III) halide complexes have been synthesized and evaluated in catalysis. Both the (NHC)GaX(3) /AgSbF(6) catalytic mixture and isolated (NHC)GaX(2) (+) species function as exquisite π-Lewis acids in typical GaX(3) -catalyzed reactions. The cationic complexes are more active than GaX(3) and yet more resistant to hydrolysis, which allows lower catalytic loadings and faster reactions.     

Targeting bacterial toxins

Protein toxins constitute the main virulence factors of several species of bacteria and have proven to be attractive targets for drug development. Lead candidates that target bacterial toxins range from small molecules to polymeric binders, and act at each of the multiple steps in the process of toxin-mediated pathogenicity. Despite recent and significant advances in the field, a rationally designed drug that targets toxins has yet to reach the market. This Review presents the state of the art in bacterial toxin targeted drug development with a critical consideration of achieved breakthroughs and withstanding challenges. The discussion focuses on A-B-type protein toxins secreted by four species of bacteria, namely Clostridium difficile (toxins A and B), Vibrio cholerae (cholera toxin), enterohemorrhagic Escherichia coli (Shiga toxin), and Bacillus anthracis (anthrax toxin), which are the causative agents of diseases for which treatments need to be improved.     

Characterization of phospholipid bilayer formation on a thin film of porous SiO2 by reflective interferometric Fourier transform spectroscopy (RIFTS)

Classical methods for characterizing supported artificial phospholipid bilayers include imaging techniques such as atomic force microscopy and fluorescence microscopy. The use in the past decade of surface-sensitive methods such as surface plasmon resonance and ellipsometry, and acoustic sensors such as the quartz crystal microbalance, coupled to the imaging methods, have expanded our understanding of the formation mechanisms of phospholipid bilayers. In the present work, reflective interferometric Fourier transform spectrocopy (RIFTS) is employed to monitor the formation of a planar phospholipid bilayer on an oxidized mesoporous Si (pSiO(2)) thin film. The pSiO(2) substrates are prepared as thin films (3 μm thick) with pore dimensions of a few nanometers in diameter by the electrochemical etching of crystalline silicon, and they are passivated with a thin thermal oxide layer. A thin film of mica is used as a control. Interferometric optical measurements are used to quantify the behavior of the phospholipids at the internal (pores) and external surfaces of the substrates. The optical measurements indicate that vesicles initially adsorb to the pSiO(2) surface as a monolayer, followed by vesicle fusion and conversion to a surface-adsorbed lipid bilayer. The timescale of the process is consistent with prior measurements of vesicle fusion onto mica surfaces. Reflectance spectra calculated using a simple double-layer Fabry-Perot interference model verify the experimental results. The method provides a simple, real-time, nondestructive approach to characterizing the growth and evolution of lipid vesicle layers on the surface of an optical thin film.     

Halogenation in Fungi: What Do We Know and What Remains to Be Discovered?

In nature, living organisms produce a wide variety of specialized metabolites to perform many biological functions. Among these specialized metabolites, some carry halogen atoms on their structure, which can modify their chemical characteristics. Research into this type of molecule has focused on how organisms incorporate these atoms into specialized metabolites. Several families of enzymes have been described gathering metalloenzymes, flavoproteins, or S-adenosyl-L-methionine (SAM) enzymes that can incorporate these atoms into different types of chemical structures. However, even though the first halogenation enzyme was discovered in a fungus, this clade is still lagging behind other clades such as bacteria, where many enzymes have been discovered. This review will therefore focus on all halogenation enzymes that have been described in fungi and their associated metabolites by searching for proteins available in databases, but also by using all the available fungal genomes. In the second part of the review, the chemical diversity of halogenated molecules found in fungi will be discussed. This will allow the highlighting of halogenation mechanisms that are still unknown today, therefore, highlighting potentially new unknown halogenation enzymes.     

Lattice Boltzmann Simulations of Blood Flow: Non-Newtonian Rheology and Clotting Processes

The numerical simulation of thrombosis in stented aneurysms is an important issue to estimate the efficiency of a stent. In this paper, we consider a Lattice Boltzmann (LB) approach to bloodflow modeling and we implement a non-Newtonian correction in order to reproduce more realistic flow profiles. We obtain a good agreement between simulations and Casson’s model of blood rheology in a simple geometry. Finally we discuss how, by using a passive scalar suspension model with aggregation on top of the LB dynamics, we can describe the clotting processes in the aneurysm     

Functionalization of Testosterone at Position 7α and Synthesis of 7α-(3-Methoxypropyl)-4-androsten-17β-ol-3-one

An efficient transformation of the terminal alkene function of 7α-allyltestosterone is reported along with the stereospecific synthesis of 7α-(3-methoxypropyl)-4-androsten-17β-ol-3-one.