Alsmaphorazines C–E,indole alkaloids from Alstonia pneumatophora

Three novel indole alkaloids, alsmaphorazines C (1)–E (3), were isolated from the leaves of Alstonia pneumatophora (Apocynaceae) and their structures were determined on the basis of the 2D NMR and MS spectral analyses. The absolute configurations of 1 and 3 were elucidated by applying a modified Mosher’s method and CD spectral analysis. These alkaloids possessed novel ring skeletons containing an octahydropyrrolo[2,3-b]pyrrole unit.     

Phorone A and Isophorbasone A, Sesterterpenoids Isolated from the Marine Sponge Phorbas sp

A chemical investigation of a Korean marine sponge, Phorbas sp., yielded unprecedented sesterterpenoids phorone A (1) and isophorbasone A (2) along with ansellone B (3) and phorbasone A acetate (4). Their complete structures were elucidated by the combination of spectroscopic data and chemical manipulation. Phorone A (1) and isophorbasone A (2) have the new "phorane"(5) and "isophorbasane"(6) sesterterpenoid carbon skeletons, respectively. Ansellone B (3) and phorbasone A acetate (4) exhibited potent inhibitory activity on nitric oxide production in RAW 264.7 LPS-activated mouse macrophage cells with IC(50) values of 4.5 and 2.8 μM, respectively.     

Nuclear spin conversion to probe the methyl rotation effect on hydrogen-bond and vibrational dynamics

A noteworthy example of a molecule with coupled large-amplitude motions is provided by acetylacetone (methyl group torsions and intramolecular hydrogen bonds). The molecule was trapped in solid parahydrogen to investigate the complex proton tunneling processes. Nuclear spin conversion in methyl groups is observed and, combined with IR spectra, documents the coupling between high frequency modes and large amplitude motions.     

Evaluation of chemical durability,thermal properties and structure characteristics of Nb–Sr-phosphate glasses by Raman and NMR spectroscopy

Thermal properties, water durability and structure of Nb₂O₅–SrO–P₂O₅ glasses containing 0–25 mol% Nb₂O₅ and 35–60 mol% SrO were explored aiming to develop high refractive index optical glasses. Structure studied using Raman and NMR spectra reveals that by increasing Nb₂O₅ content, niobium plays the role as intermediate. Nb⁵⁺ tends to break P–O–P and O–P–O bonds forming [NbO₆] structure. Thus fractions of Q³ and Q² decrease, while Q¹ fraction increases. Furthermore the Q⁰ fraction replaces the lessened Q³ fraction. As P₂O₅ content is reduced to 30 mol%, partial [NbO₆]_octa turns into [NbO₄]_tetra and partial (Nb–O)_short-octa becomes (Nb–O)_short-tetra bond to stabilize the glass structure. Glass-transition and softening-temperatures of the glasses increase by increasing SrO and Nb₂O₅ contents. Thermal expansion coefficient increases by increasing SrO while decreases with Nb₂O₅ content. Water durability is enhanced as increasing Nb₂O₅ and SrO contents. Properties of the glasses correlate well with the worked out structure.     

α-Synuclein induces both positive mean curvature and negative Gaussian curvature in membranes

Using a combination of X-ray scattering, fluorescence correlation spectroscopy, coarse-grained molecular dynamics (MD) simulations and potential of mean force calculations, we have explored the membrane remodeling effects of monomeric α-synuclein (αS). Our initial findings from multiple approaches are that αS (1) causes a significant thinning of the bilayer and (2) stabilizes positive mean curvature, such that the maximum principle curvature matches that of synaptic vesicles, αS-induced tubules, and the synthetic lipid vesicles to which the protein binds most tightly. This suggests that αS binding to synaptic vesicles likely stabilizes their intrinsic curvature. We then show that αS induces local negative Gaussian curvature, an effect that occurs in regions of αS shown previously via NMR and corroborated by MD simulation to have significant conformational flexibility. The induction of negative Gaussian curvature, which has implications for all curvature-sensing and curvature-generating amphipathic α-helices, supports a hypothesis that connects helix insertion to fusion and fission of vesicles, processes that have recently been linked to αS function. Then, in an effort to explain these biophysical properties of αS, we promote an intrinsic curvature-field model that recasts long-range protein-protein interactions in terms of the interactions between the local curvature fields generated by lipid-protein complexes.     

Starch-based gel electrolyte thin films derived from native sago (Metroxylon sagu) starch

Starch-based gel electrolyte (SbGE) thin films were prepared by mixing native sago starch with different amounts of glycerol, and subsequently doped with various types of ionic salts. SbGE thin films showed substantially enhanced mechanical properties and ionic conductivity through incorporating optimal composition of native sago starch, glycerol, and ionic salts. A maximum room temperature ionic conductivity of the order of 10^?3 S cm^?1 was achieved for optimized SbGE thin film consisting of 80 wt% of native sago starch and 20 wt% of glycerol, and doped with 8 wt% of LiCl. SbGE thin films were characterized by Fourier transformed infrared spectrometry, scanning electron microscopy, and electrochemical impedance spectroscopy. Due to their favorable mechanical properties, high ionic conductivity at room temperature, ease of preparation, environmentally benign, and cheap, SbGE thin films show high potential utility as gel electrolyte materials for the fabrication of solid-state electrochemical devices.     

Metal–organic frameworks: a novel SERS substrate

We report the direct observation of surface‐enhanced Raman scattering (SERS) effect using metal–organic frameworks (MOFs) as substrates. Without the aid of any metal colloids or enhancing agents, the SERS signals of methyl orange (MO) adsorbed in MOFs were observed and even remained active if the organic linkers in MOFs were completely removed by high temperature and O₂ plasma treatments. It implies that the SERS active site is at the metal oxide clusters. The ultraviolet‐visible spectra of MO, MOFs, and MO–MOF complexes show that absorption peaks are far from laser excitation line. Thus, conventional resonance enhancement effect should be ruled out, and charge‐transfer mechanism is the most likely scenario responsible for the observed SERS effect. Density functional theory (DFT) was used to interpret the chemical enhancement mechanism and the adsorption orientation‐dependent SERS spectra in our observation. The preferred adsorption orientations calculated by DFT method are consistent with the observed SERS results. Copyright © 2013 John Wiley & Sons, Ltd.     

Revolving hollow fiber–liquid phase microextraction coupled to GC/MS using electron ionization for quantification of five aromatic hydrocarbon isomers

A dynamic liquid phase microextraction method using a revolving hollow fiber was demonstrated for coupling to GC/MS [using EI (electronic ionization) and selected ion monitor (SIM)] as a concentrating probe for rapid analysis and quantitative determination of five aromatic hydrocarbon isomers (cumene; propylbenzene; 2‐ethyltoluene; 1,2,3‐trimethylbenzene; and 1,2,4‐trimethylbenzene) from biological matrices (human urine and human plasma). This technique was named as revolving hollow fiber–liquid phase microextraction (RHF–LPME). The optimized parameters of RHF–LPME coupled to GC/MS experiments were extraction solvent, toluene; extraction time, 2 min; sample agitation rate, 700 rpm; salt concentration, 0%; rotating speed for motor driving rotator, 250 rpm; and the rotator was operated in a reversed direction with the stirrer. The linear range of calibration curve of RHF–LPME was from 0.002 to 0.4 μg/mL with R² > 0.9916 and the RSD values were from 4.5 to 5.2%. Additionally, comparing to single drop microextraction (SDME), this method offers better limits of detection (LODs) and EF (enrichment factor). This approach exhibits many advantages including simplicity, rapid detection with high reproducibility and high extraction efficiency, easy to operate and fast to reach equilibrium for analyzing biological samples. This approach has the potential to be widely used because it only requires simple devices to perform all extraction processes. We believe that this technique can be a powerful tool for GC/MS analysis of biological samples and clinical applications in the near future.     

Syntheses,Photophysics, and Application of Iridium(III) Phosphorescent Emitters for Highly Efficient,Long‐Life Organic Light‐Emitting Diodes

Long live the OLED! Rational design and synthesis of Ir^III complexes bearing two cyclometalated ligands (C N) and one 2‐(diphenylphosphino)phenolate chelate (P O) as well as the corresponding Ir^III derivatives with only one (C N) ligand and two P O chelates are reported. According to the observed photophysical data, a P O ligand is found to be able to fine‐tune the light‐emitting electronic transition of these complexes.