Partitioning of dual-lipidated peptides into membrane microdomains: lipid sorting vs peptide aggregation

The lateral membrane organization and phase behavior of the lipid mixture DMPC(di-C(14))/DSPC(di-C(18))/cholesterol (0-33 mol %) with and without an incorporated fluorescence-labeled palmitoyl/farnesyl dual-lipidated peptide, BODIPY-Gly-Cys(Pal)-Met-Gly-Leu-Pro-Cys(Far)-OMe, which represents a membrane recognition model system for Ras proteins, was studied by two-photon excitation fluorescence microscopy. Measurements were performed on giant unilamellar vesicles (GUVs) over a large temperature range, ranging from 30 to 80 degrees C to cover different lipid phase states (all-gel, fluid/gel, liquid-ordered, all-fluid). At temperatures where the fluid-gel coexistence region of the pure binary phospholipid system occurs, large-scale concentration fluctuations appear. Incorporation of cholesterol levels up to 33 mol % leads to a significant increase of conformational order in the membrane system and a reduction of large domain structures. Adding the peptide leads to dramatic changes in the lateral organization of the membrane. With cholesterol present, a phase separation is induced by a lipid sorting mechanism owing to the high affinity of the lipidated peptide to a fluid, DMPC-rich environment. This phase separation leads to the formation of peptide-containing domains with high fluorescence intensity that become progressively smaller with decreasing temperature. As a result, the local concentration of the peptide increases steadily within the confines of the shrinking domains. At the lowest temperatures, where the acyl-chain order parameter of the membrane has already drastically increased and the membrane achieves a liquid-ordered character, an efficient lipid sorting mechanism is no longer supported and aggregation of the peptide into small clusters prevails. We can conclude that palmitoyl/farnesyl dual-lipidated peptides do not associate with liquid-ordered or gel-like domains in phase-separated bilayer membranes. In particular, the study shows the interesting ability of the peptide to induce formation of fluid microdomains at physiologically relevant cholesterol concentrations, and this effect very much depends on the concentration of fluid vs ordered lipid molecules.     

Model of the iron hydrogenase active site covalently linked to a ruthenium photosensitizer: synthesis and photophysical properties

A model of the iron hydrogenase active site with the structure [(mu-ADT)Fe2(CO)6] (ADT = azadithiolate (S-CH2-NR-CH2-S), (2: R = 4-bromophenyl, 3: R = 4-iodophenyl)) has been assembled and covalently linked to a [Ru(terpy)2]2+ photosensitizer. This trinuclear complex 1 represents one synthetic step toward the realization of our concept of light-driven proton reduction. A rigid phenylacetylene tether has been incorporated as the linking unit in 1 in order to prolong the lifetime of the otherwise short-lived [Ru(terpy)2]2+ excited state. The success of this strategy is demonstrated by comparison of the photophysical properties of 1 and of two related ruthenium complexes bearing acetylenic terpyridine ligands, with those of [Ru(terpy)2]2+. IR and electrochemical studies reveal that the nitrogen heteroatom of the ADT bridge has a marked influence on the electronic properties of the [Fe2(CO)6] core. Using the Rehm-Weller equation, the driving force for an electron transfer from the photoexcited *[Ru(terpy)2]2+ to the diiron site in 1 was calculated to be uphill by 0.59 eV. During the construction of the trinuclear complex 1, n-propylamine has been identified as a decarbonylation agent on the [(mu-ADT)Fe2(CO)6] portion of the supermolecule. Following this procedure, the first azadithiolate-bridged dinuclear iron complex coordinated by a phosphine ligand [(mu-ADT)Fe2(CO)5PPh3] (4, R = 4-bromophenyl) was synthesized.     

Substituted Ferrocenylboranes – Potential Ligand Precursors for ansa‐ Metallocenes,Constrained Geometry Complexes and ansa‐Diamido Complexes

A wide range of potential ligand precursors and related compounds have been synthesized from ferrocenyldibromoborane and ferrocenylenebis(dibromoborane) via salt elimination reactions. These comprise ligand precursors suitable for the preparation of (i) ansa‐metallocenes such as [FcB(η¹‐C₅H₅)₂] ( 2 ), [FcB(1‐C₉H₇)₂] ( 3 ), [FcB(3‐C₉H₇)₂] ( 4 ) and [1,1′‐fc{B(3‐C₉H₇)₂}₂] ( 11 ), (ii) constrained geometry complexes such as [FcB(1‐C₉H₇)N(H)Ph] ( 7 ) and [FcB(3‐C₉H₇)N(H)Ph] ( 8 ), (iii) ansa‐diamido complexes such as [FcB(N(H)Ph)₂] ( 9 ) as well as (iv) the related compounds [FcB(Br)N(H)tBu] ( 5 ), [FcB(Br)N(H)Ph] ( 6 ), [1,1′‐fc{B(Br)N(SiMe₃)₂}₂] ( 12 ) and [1,1′‐fc{B(Br)NiPr₂}₂] ( 13 ) (Fc = ferrocenyl, fc = ferrocenylene, C₅H₅ = cyclopentadienyl, C₉H₇ = indenyl). All new compounds have been characterised by multinuclear NMR spectroscopic techniques and in the case of 7 and 12 by X‐ray diffraction methods.     

Comparison of Different Di‐tert‐butyldimethyl‐Silylated Cyclodextrins as Chiral Stationary Phases in Capillary Gas Chromatography

Separation factors and thermodynamic data for the separation of various chiral analytes on different di‐O‐tert‐butyldimethyl‐silylated cyclodextrin derivatives are collected and described. Modifying the substitution pattern of the tert‐butyldimethylsilyl group in position 2 and 3 or changing from β‐ to γ‐cyclodextrin significantly affects the separation properties of the cyclodextrin derivatives.     

Factors that determine the protein resistance of oligoether self-assembled monolayers --internal hydrophilicity,terminal hydrophilicity,and lateral packing density

Protein resistance of oligoether self-assembled monolayers (SAMs) on gold and silver surfaces has been investigated systematically to elucidate structural factors that determine whether a SAM will be able to resist protein adsorption. Oligo(ethylene glycol) (OEG)-, oligo(propylene glycol)-, and oligo(trimethylene glycol)-terminated alkanethiols with different chain lengths and alkyl termination were synthesized as monolayer constituents. The packing density and chemical composition of the SAMs were examined by XPS spectroscopy; the terminal hydrophilicity was characterized by contact angle measurements. IRRAS spectroscopy gave information about the chain conformation of specific monolayers; the amount of adsorbed protein as compared to alkanethiol monolayers was determined by ellipsometry. We found several factors that in combination or by themselves suppress the protein resistance of oligoether monolayers. Monolayers with a hydrophobic interior, such as those containing oligo(propylene glycol), show no protein resistance. The lateral compression of oligo(ethylene glycol) monolayers on silver generates more highly ordered monolayers and may cause decreased protein resistance, but does not necessarily lead to an all-trans chain conformation of the OEG moieties. Water contact angles higher than 70 degrees on gold or 65 degrees on silver reduce full protein resistance. We conclude that both internal and terminal hydrophilicity favor the protein resistance of an oligoether monolayer. It is suggested that the penetration of water molecules in the interior of the SAM is a necessary prerequisite for protein resistance. We discuss and summarize the various factors which are critical for the functionality of "inert" organic films.     

A Survey of Aluminum Speciation in the Forest-Well Drainage Water from the Rhode River Watershed

In the Chesapeake Bay Region, acidic atmospheric deposition has deleterious effects on watershed and freshwater ecosystems. One of the associated effects is the disappearance of fish from the streams.     

Dynamical Gibbs–Non-Gibbs Transitions in Lattice Widom–Rowlinson Models with Hard-Core and Soft-Core Interactions

Journal of Statistical Physics - We consider the Widom–Rowlinson model on the lattice $${\mathbb {Z}}^d$$ in two versions, comparing the cases of a hard-core repulsion and of a soft-core...     

Pulse magnetoelectrolysis

We present a novel technique consisting in the combination of pulse plating and magnetoelectrolysis. This technique is applied to copper electrolysis between two vertical copper-electrodes. The modulation of the current inside an inhomogeneous magnetic field generates a modulated Lorentz force driving an oscillating convection studied using particle image velocimetry. The resulting changes in the concentration boundary layers are analysed by means of a Mach-Zehnder interferometer.     

The fundamental group of period domains over finite fields

We determine the fundamental group of period domains over finite fields. This answers a question of M. Rapoport raised in [M. Rapoport, Period domains over finite and local fields, in: Proc. Sympos. Pure Math., vol. 62, part 1, 1997, pp. 361-381].