Oriented confined water induced by cationic lipids

We report on attenuated total reflection Fourier-transform infrared (ATR FTIR) spectroscopic measurements on oriented lipid multilayers of N,N-dimethyl-N,N-dioctadecyl-ammonium halides (DODAX, X = F, Cl, Br, I). The main goal of this study is the investigation of the structure and spectroscopic properties of water absorbed to these model membranes. Intensities of the water stretch absorptions were used to determine the amount of bound water. At high water activity, DODAF membranes bind ~11 water molecules/lipid while DODAC and DODAB adsorb 1-2 water/lipid and DODAI was hydrophobic. By adjustment of DODAF hydration to ~2 water molecules, stretching absorptions from water of the first hydration shell were accessible for the fluoride, chloride, and bromide analogs. The polarized measurements demonstrate highly confined and oriented water with infrared (IR) order parameters ranging from 0.2 to -0.4. Resolved IR water band components are attributed to different hydrogen-bonded populations. Complementary molecular dynamics simulations of DODAB strongly support the existence of differently hydrogen-bonded and oriented water within DODAB multilayers. A combination of both techniques was used for an assignment of water stretch band components to structures. The described cationic lipid systems are a prototype for a bottom-up approach to understand the IR spectroscopy of structured water at biological interfaces since they permit a defined increase of hydrophilic water-anionic interactions leading to extended water networks at membranes.     

Enhanced CO2 Adsorption over Polymeric Amines Supported on Heteroatom‐Incorporated SBA‐15 Silica: Impact of Heteroatom Type and Loading on Sorbent Structure and Adsorption Performance

Silica supported amine materials are promising compositions that can be used to effectively remove CO₂ from large stationary sources, such as flue gas generated from coal‐fired power plants (ca. 10 % CO₂) and potentially from ambient air (ca. 400 ppm CO₂). The CO₂ adsorption characteristics of prototypical poly(ethyleneimine)–silica composite adsorbents can be significantly enhanced by altering the acid/base properties of the silica support by heteroatom incorporation into the silica matrix. In this study, an array of poly(ethyleneimine)‐impregnated mesoporous silica SBA‐15 materials containing heteroatoms (Al, Ti, Zr, and Ce) in their silica matrices are prepared and examined in adsorption experiments under conditions simulating flue gas (10 % CO₂ in Ar) and ambient air (400 ppm CO₂ in Ar) to assess the effects of heteroatom incorporation on the CO₂ adsorption properties. The structure of the composite adsorbents, including local information concerning the state of the incorporated heteroatoms and the overall surface properties of the silicate supports, are investigated in detail to draw a relationship between the adsorbent structure and CO₂ adsorption/desorption performance. The CO₂ adsorption/desorption kinetics are assessed by thermogravimetric analysis and in situ FT‐IR measurements. These combined results, coupled with data on adsorbent regenerability, demonstrate a stabilizing effect of the heteroatoms on the poly(ethyleneimine), enhancing adsorbent capacity, adsorption kinetics, regenerability, and stability of the supported aminopolymers over continued cycling. It is suggested that the CO₂ adsorption performance of silica–aminopolymer composites may be further enhanced in the future by more precisely tuning the acid/base properties of the support.     

Free energy landscapes for homogeneous nucleation of ice for a monatomic water model

We simulate the homogeneous nucleation of ice from supercooled liquid water at 220 K in the isobaric-isothermal ensemble using the MW monatomic water potential. Monte Carlo simulations using umbrella sampling are performed in order to determine the nucleation free energy barrier. We find the Gibbs energy profile to be relatively consistent with that predicted by classical nucleation theory; the free energy barrier to nucleation was determined to be ~18 k(B)T and the critical nucleus comprised ~85 ice particles. Growth from the supercooled liquid gives clusters that are predominantly cubic, whilst starting with a pre-formed subcritical nucleus of cubic or hexagonal ice results in the growth of predominantly that phase of ice only.     

Calciate-mediated intermolecular hydroamination of diphenylbutadiyne with secondary anilines

Calciate-mediated intermolecular hydroamination of diphenylbutadiyne with N-phenyl and N-isopropyl-substituted anilines yields E- and Z-isomers of the corresponding 1-anilino-1,4-diphenylbut-1-ene-3-yne. In the case of HNPh(2) solely heterobimetallic K(2)Ca(NPh(2))(4) is able to effectively catalyze this hydroamination reaction in tetrahydrofuran at elevated temperatures.     

Fluidity modulation of phospholipid bilayers by electrolyte ions: insights from fluorescence microscopy and microslit electrokinetic experiments

Fluidity and charging of supported bilayer lipid membranes (sBLMs) prepared from 1,2-dioleoyl-sn-glycero-3-phosphatidylcholine (DOPC) were studied by fluorescence recovery after photobleaching (FRAP) and microslit electrokinetic measurements at varying pH and ionic composition of the electrolyte. Measurements in neutral electrolytes (KCl, NaCl) revealed a strong correlation between the membrane fluidity and the membrane charging due to unsymmetrical water ion adsorption (OH(-) ? H(3)O(+)). The membrane fluidity significantly decreased below the isoelectric point of 3.9, suggesting a phase transition in the bilayer. The interactions of both chaotropic anions and strongly kosmotropic cations with the zwitterionic lipids were found to be related with nearly unhindered lipid mobility in the acidic pH range. While for the chaotropic anions the observed effect correlates with the increased negative net charge at low pH, no correlation was found between the changes in the membrane fluidity and charge in the presence of kosmotropic cations. We discuss the observed phenomena with respect to the interaction of the electrolyte ions with the lipid headgroup and the influence of this process on the headgroup orientation and hydration as well as on the lipid packaging.     

Biosupramolecular nanowires from chlorophyll dyes with exceptional charge-transport properties

Conductive tubes: Self-assembled nanotubes of a bacteriochlorophyll derivative are reminiscent of natural chlorosomal light-harvesting assemblies. After deposition on a substrate that consists of a non-conductive silicon oxide surface (see picture, brown) and contacting the chlorin nanowires to a conductive polymer (yellow), they show exceptional charge-transport properties.     

Novel approach to biscarbazole alkaloids via Ullmann coupling - synthesis of murrastifoline-A and bismurrayafoline-A

Unprecedented Ullmann couplings of murrayafoline-A with either 6-bromo- or 4-bromocarbazole derivatives provide highly efficient synthetic routes to the biscarbazole alkaloids murrastifoline-A (6 steps, 66% overall yield) and bismurrayafoline-A (6 steps, 28% overall yield).     

Trace metal impurities in catalysis

Metal-catalysed transformations are a powerful tool in organic chemistry and the enormous progress, which has been made in the last few decades, was one more time honoured by the Nobel Prize in Chemistry in 2010. Many metal-containing compounds have been applied in carbon-carbon and carbon-heteroatom bond formations. However, not every component originally claimed as catalyst turned out to be the active ingredient in the end. Sometimes trace metal impurities were the actual catalytic species. In this tutorial review, we will highlight recent findings in transition metal-catalysed cross-coupling reactions and detail several reports from the past, which illustrate that "trace metal catalysis" is not a newly discovered phenomenon.