A system based on two designed peptides, namely the cationic peptide K, (KIAALKE) 3 , and its complementary anionic counterpart called peptide E, (EIAALEK) 3 , has been used as a minimal model for membrane fusion, inspired by SNARE proteins. Although the fact that docking of separate vesicle populations via the formation of a dimeric E/K coiled-coil complex can be rationalized, the reasons for the peptides promoting fusion of vesicles cannot be fully explained. Therefore it is of significant interest to determine how the peptides aid in overcoming energetic barriers during lipid rearrangements leading to fusion. In this study, investigations of the peptides' interactions with neutral PC/PE/cholesterol membranes by fluorescence spectroscopy show that tryptophan-labeled K* binds to the membrane (K K*~6 .2 10 3 M À1 ), whereas E* remains fully water-solvated. 15 N-NMR spectroscopy, depth-dependent fluorescence quenching, CD-spectroscopy experiments, and MD simulations indicate a helix orientation of K* parallel to the membrane surface. Solid-state 31 P-NMR of oriented lipid membranes was used to study the impact of peptide incorporation on lipid headgroup alignment. The membrane-immersed K* is found to locally alter the bilayer curvature, accompanied by a change of headgroup orientation relative to the membrane normal and of the lipid composition in the vicinity of the bound peptide. The NMR results were supported by molecular dynamics simulations, which showed that K reorganizes the membrane composition in its vicinity, induces positive membrane curvature, and enhances the lipid tail protrusion probability. These effects are known to be fusion relevant. The combined results support the hypothesis for a twofold role of K in the mechanism of membrane fusion: 1) to bring opposing membranes into close proximity via coiled-coil formation and 2) to destabilize both membranes thereby promoting fusion.
This work reports an aqueous dye‐sensitized photoelectrochemical cell (DSPEC) capable of oxidizing glycerol (an archetypical biobased compound) coupled with H2 production. We employed a mesoporous TiO2 photoanode sensitized with the high potential thienopyrroledione‐based dye AP11, encased in an acetonitrile‐based redox‐gel that protects the photoanode from degradation by aqueous electrolytes. The use of the gel creates a biphasic system with an interface at the organic (gel) electrode and aqueous anolyte. Embedded in the acetonitrile gel is 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO), acting as both a redox‐mediator and a catalyst for oxidative transformations. Upon oxidation of TEMPO by the photoexcited dye, the in situ generated TEMPO+ shuttles through the gel to the acetonitrile–aqueous interface, where it acts as an oxidant for the selective conversion of glycerol to glyceraldehyde. The introduction of the redox‐gel layer affords a 10‐fold increase in the conversion of glycerol compared to the purely aqueous system. Our redox‐gel protected photoanode yielded a stable photocurrent over 48 hours of continuous operation, demonstrating that this DSPEC is compatible with alkaline aqueous reactions.
This work reports ad ye-sensitized photoelectrochemical cell (DSPEC) that couples redox-mediated lightdriven oxidative organic transformations to reductive hydrogen (H 2)f ormation.T he DSPEC photoanodec onsists of am esoporousa nataseT iO 2 film on FTO (fluorine-doped tin oxide), sensitized with the thienopyrroledione-based dye AP11,w hileH 2 was formeda taFTO-Pt cathode. Irradiation of the dye-sensitizedp hotoanode transforms 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) to the oxidized TEMPO (TEMPO +), whicha cts as ac hemical oxidant for the conversion of benzyla lcohol. The TEMPO 0/ + couple,p reviously used as redoxm ediator in DSSC, mediates efficient electron transfer from the organic substrate to the photo-oxidized dye. AD SPEC photoreactorw as designed that allows in situ monitoring the reaction progress by infrared spectroscopy and gas chromatography.S ustained light-driven oxidation of benzyla lcoholt ob enzaldehydew ithin the DSPEC photoreactor,u sing of TEMPO as mediator,d emonstrated the efficiency of the device, with ap hotocurrent of 0.4 mA cm À2 ,a pproachingq uantitative Faradaic efficiency and exhibiting excellent device stability. Solar energy is an attractive CO 2-neutral energy source, providing % 4200 times the energy consumption estimated for 2035. [1, 2] Beyondw idely deployed silicon-based photovoltaic (PV) technology,d ye-sensitizeds olar cells (DSSCs) [3] present a low-cost alternative with improved performance in low/diffuse light conditions. DSSCs use molecular dyes, wide-bandg ap semiconductors and redox mediators to absorb light and separate charges affording efficienciest hat have surpassed 14 %. [4, 5] While the application of solar-to-electric energy conversion is increasing, long-term energy storageremains ac hallenge. Elec
In this study we examine two different strategies—a homo- and heterogeneous approach—of the light-driven oxidation of benzyl alcohol in dye-sensitized photoelectrochemical cells (DSPECs). The DSPEC consists of a mesoporous anatase...
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