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An atomic scale molecular dynamics simulation (100 ns) was carried out to reveal the conformational features of a cationic polyelectrolyte, i.e., hyperbranched polyethyleneimine (PEI), inside of water-in-oil microemulsion droplets stabilized by the anionic sodium dodecyl sulfate surfactant (SDS) layer. Simulations show that the polymer reorients very quickly and is localized at the headgroup region, i.e., the polymer nitrogens are close to SDS sulfur atoms. In spite of the availability of surface roughness caused by the polymer, we track a stable inverse micelle during the production run. In overall, the obtained parameters are well compared with experimental findings. (C) 2016 Elsevier B.V. All rights reserved.
Rotational Barriers of Substituted BIPHEP Ligands: A Comparative Experimental and Theoretical Study
(2016)
The interconversion barriers of 14 different 3,3- and 5,5-disubstituted tropos BIPHEP [2,2-bis(diphenylphosphino)-1,1-biphenyl] and BIPHEP(O) [2,2-bis(diphenylphosphoryl)-1,1-biphenyl] ligands were investigated by enantioselective dynamic high performance liquid chromatography (DHPLC) and DFT calculations using the B3LYP/6-31G* and M06-2X/6-31G* levels of theory. The experimentally determined enantiomerization barriers varied from 86.8 to 101.4 kJmol(-1) and were found to be in excellent agreement with the calculated data. The root-mean-square deviations are 7.3 kJmol(-1) for the B3LYP functional and 11.3 kJmol(-1) for the M06-2X method.
Cryogenic transmission electron microscopy (cryo-TEM) studies suggest that TTBC molecules self-assemble in aqueous solution to form single-walled tubes with a diameter of about 35 A. In order to reveal the arrangement and mutual orientations of the individual molecules in the tube, we combine information from crystal structure data of this dye with a calculation of linear absorbance and linear dichroism spectra and molecular dynamics simulations. We start with wrapping crystal planes in different directions to obtain tubes of suitable diameter. This set of tube models is evaluated by comparing the resulting optical spectra with experimental data. The tubes that can explain the spectra are investigated further by molecular dynamics simulations, including explicit solvent molecules. From the trajectories of the most stable tube models, the short-range ordering of the dye molecules is extracted and the optimization of the structure is iteratively completed. The final structural model is a tube of rings with 6-fold rotational symmetry, where neighboring rings are rotated by 30 and the-transition dipole moments of the chromophores form an angle of 74 with respect to the symmetry axis of the tube. This model is in agreement with cryo-TEM images and can explain the optical spectra, consisting of a sharp red-shifted J-band that is polarized parallel to to the symmetry axis of the tube and a broad blue-shifted H-band polarized perpendicular to this axis. The general structure of the homogeneous spectrum of this hybrid HJ-aggregate is described by an analytical model that explains the difference in redistribution of oscillator strength inside the vibrational manifolds of the J- and H-bands and the relative intensities and excitation energies of those bands. In addition to the-particular system investigated here, the present methodology can be expected to aid the structure prediction for a wide range of self-assembled dye aggregates.
A three dimensional biopolymer network structure with incorporated nano-porous calcium phosphate (CaP) balls was fabricated by using gelatin-chitosan (GC) polymer blend and GC stabilized olive/silicone oil Janus emulsions, respectively. The emulsions were freeze-dried, and the oil droplets were washed out in order to prepare porous scaffolds with larger surface area. The morphology, pore size, chemical composition, thermal and swelling behavior was studied by Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR) and micro-Differential Scanning Calorimetry (micro-DSC). Microscopic analysis confirmed that the pore size of the GC based sponges after freeze-drying may be drastically reduced by using Janus emulsions. Besides, the incorporation of nanoporous calcium phosphate balls is also lowering the pore size and enhancing thermal stability. (C) 2016 Elsevier B.V. All rights reserved.
Synthetic routes to different oligospirothioketal (OSTK) Forster resonance energy transfer (FRET) constructs are described and the photophysics of these constructs were explored in different solvents. The FRET efficiencies were determined from the experimental data and compared with theoretical values. The influence of the outstanding rigidity of the novel OSTK compounds on the FRET is discussed.
The enzymatic degradation of oligo(epsilon-caprolactone) (OCL) based films at the air-water interface is investigated by Langmuir monolayer degradation (LMD) experiments to elucidate the influence of the molecular architecture and of the chemical structure on the chain scission process. For that purpose, the interactions of 2D monolayers of two star-shaped poly(epsilon-caprolactone)s (PCLs) and three linear OCL based copolyesterurethanes (P(OCL-U)) with the lipase from Pseudomonas cepacia are evaluated in comparison to linear OCL. While the architecture of star-shaped PCL Langmuir layers slightly influences their degradability compared to OCL films, significantly retarded degradations are observed for P(OCL-U) films containing urethane junction units derived from 2, 2 (4), 4-trimethyl hexamethylene diisocyanate (TMDI), hexamethylene diisocyanate (HDI) or lysine ethyl ester diisocyanate (LDI). The enzymatic degradation of the OCL based 2D structures is related to the presence of hydrophilic groups within the macromolecules rather than to the packing density of the film or to the molecular weight. The results reveal that the LMD technique allows the parallel analysis of both the film/enzyme interactions and the degradation process on the molecular level. (C) 2016 Elsevier Ltd. All rights reserved.
A promising replacement for the radioactive sources commonly encountered in ion mobility spectrometers is a miniaturized, energy-efficient photoionization source that produce the reactant ions via soft X-radiation (2.8 keV). In order to successfully apply the photoionization source, it is imperative to know the spectrum of reactant ions and the subsequent ionization reactions leading to the detection of analytes. To that end, an ionization chamber based on the photoionization source that reproduces the ionization processes in the ion mobility spectrometer and facilitates efficient transfer of the product ions into a mass spectrometer was developed. Photoionization of pure gasses and gas mixtures containing air, N-2, CO2 and N2O and the dopant CH2Cl2 is discussed. The main product ions of photoionization are identified and compared with the spectrum of reactant ions formed by radioactive and corona discharge sources on the basis of literature data. The results suggest that photoionization by soft X-radiation in the negative mode is more selective than the other sources. In air, adduct ions of O-2 - with H2O and CO2 were exclusively detected. Traces of CO2 impact the formation of adduct ions of O-2 - and Cl -(upon addition of dopant) and are capable of suppressing them almost completely at high CO2 concentrations. Additionally, the ionization products of four alkyl nitrates (ethylene glycol dinitrate, nitroglycerin, erythritol tetranitrate and pentaerythritol tetranitrate) formed by atmospheric pressure chemical ionization induced by X-ray photoionization in different gasses (air, N-2 and N2O) and dopants (CH2Cl2, C2H5Br and CH3I) are investigated. The experimental studies are complemented by density functional theory calculations of the most important adduct ions of the alkyl nitrates (M) used for their spectrometric identification. In addition to the adduct ions [M + NO3](-) and [M + Cl](-), adduct ions such as [M + N2O2](-), [M + Br](-) and [M+ I](-) were detected, and their gas-phase structures and energetics are investigated by density functional theory calculations. Copyright (C) 2016 John Wiley & Sons, Ltd.
Recently we introduced iron trichloride as an environmentally benign and cost-efficient reagent for the synthesis of N-benzoylguanidines. This highly attractive synthetic approach grants access to a broad spectrum of N-benzoylguanidines under mild conditions in short reaction times. In this work we present an extended scope of Our methodology along with the results obtained from mechanistic studies via in situ IR spectroscopy in combination with LC (liquid chromatography)-MS analyses. On the basis of these new mechanistic insights we were able to optimize the synthetic protocol and to develop an alternative mechanistic proposal. In this context the symbiotic roles of iron trithloride and oxygen in the guanylation process are highlighted.
alpha-Methylene-gamma-butyrolactone and alpha-methylene-gamma-valerolactone undergo Pd-catalyzed Matsuda-Heck couplings with arene diazonium salts to alpha-benzyl butenolides or pentenolides, respectively, or to alpha-benzylidene lactones. The observed regioselectivity is strongly ring size dependent, with six-membered rings giving exclusively alpha-benzyl pentenolides, whereas the five-membered alpha-methylene lactone reacts to mixtures of regioisomers with a high proportion of (E)-alpha-benzylidene-gamma-butyrolactones. DFT calculations suggest that the reasons for these differences are not thermodynamic but kinetic in nature. The relative energies of the conformers of the Pd sigma-complexes resulting from insertion into the Pd-aryl bond were correlated with the dihedral angles between Pd and endo-beta-H. This correlation revealed that in the case of the six-membered lactone an energetically favorable conformer adopts a nearly synperiplanar Pd/endo-beta-H arrangement, whereas for the analogous Pd sigma-complex of the five-membered lactone the smallest Pd/endo-beta-H dihedral angle is observed for a conformer with a comparatively high potential energy. The optimized conditions for Matsuda-Heck arylations of exo-methylene lactones were eventually applied to the synthesis of the natural product anemarcoumarin A.
Using density functional theory (PBE functional), we show that the degree of surface hydroxylation increases in the MgO, CaO, SrO series, accompanied by an increase in water adsorption energy. Already for water coverage of two monolayers, structures with dissolved M2+. ions are considerably more stable than the intact, nondissolved surface. The dissolved ions above the surface form different patterns including ordered ones (e.g., an infinite stripe) that are preferred for MgO(001) and CaO(001) and disordered ones that are favored for SrO(001). Contrary to previous assignments, an analysis of calculated X-ray photoelectron spectra shows that O(1s) signals arising from OH and H2O groups might coincide in the experimental spectrum.
Multiblock copolymers named PCL-PIBMD consisting of crystallizable poly(epsilon-caprolactone) segments and crystallizable poly[oligo(3S-iso-butylmorpholine-2,5-dione)] segments coupled by trimethyl hexamethylene diisocyanate provide a versatile molecular architecture for achieving shape-memory effects (SMEs) in polymers. The mechanical properties as well as the SME performance of PCL-PIBMD can be tailored by the variation of physical parameters during programming such as deformation strain or applied temperature protocols. In this study, we explored the influence of applying different strain rates during programming on the resulting nanostructure of PCL-PIBMD. Programming was conducted at 50 degrees C by elongation to epsilon(m)=50% with strain rates of 1 or 10 or 50 mmmin(-1). The nanostructural changes were visualized by atomic force microscopy (AFM) measurements and investigated by in situ wide and small angle X-ray scattering experiments. With increasing the strain rate, a higher degree of orientation was observed in the amorphous domains. Simultaneously the strain-induced formation of new PIBMD crystals as well as the fragmentation of existing large PIBMD crystals occurred. The observed differences in shape fixity ratio and recovery stress of samples deformed with various strain rates can be attributed to their different nanostructures. The achieved findings can be relevant parameters for programming the shape-memory polymers with designed recovery forces. (c) 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 1935-1943
In the reconstruction and regeneration of bone tissue, a primary goal is to initiate bone growth and to stabilize the surrounding bone. In this regard, a potentially useful component in biomaterials for bone tissue engineering is strontium, which acts as cationic active agent, triggering certain intracellular pathways and acting as so called dual action bone agent which inhibits bone resorption while stimulating bone regeneration. In this study we established a novel processing for the foaming of a polymer (poly-epsilon-caprolactone) and simultaneous chemical reaction of a mixture of calcium and strontium hydroxides to the respective carbonates using supercritical carbon dioxide. The resultant porous composite scaffold was optimized in composition and strontium content and was characterized via different spectroscopic (infrared and Raman spectroscopy, energy dispersive X-ray spectroscopy), imaging (SEM, mu CT), mechanical testing and in vitro methods (fluorescence vital staining, MTT-assay). As a result, the composite scaffold showed good in vitro biocompatibility with partly open pore structure and the expected chemistry. First mechanical testing results indicate sufficient mechanical stability to support future in vivo applications. (C) 2016 Elsevier B.V. All rights reserved.
A convenient and general synthesis of 2-thiocarbohydrates via cerium ammonium nitrate oxidation of the thiocyanate ion is described. Radical addition to glycals proceeds with excellent regio- and good stereoselectivities in only one step, deprotection affords water-soluble 2-thio saccharides. Binding studies to Con A have been performed by isothermal titration calorimetry (ITC) and saturation transfer difference (STD) NMR spectroscopy. The 2-thiomannose derivative binds even stronger to Con A than the natural substrate, offering opportunities for new lectin or enzyme inhibitors.
Oligospirothioketal (OSTK) rods are presented as an adjustable scaffold for optical membrane probes. The OSTK rods are readily incorporated into lipid bilayers due to their hydrophobic backbones. Because of their high length-over-diameter aspect ratio, only a minimal disturbance of the lipid bilayer is caused. OSTK rods show outstanding rigidity and allow defined labeling with fluorescent dyes, yielding full control of the orientation between the dye and OSTK skeleton. This. allows the construction of novel Forster resonance energy transfer probes with highly defined relative orientations of the transition dipole moments of the donor and acceptor dyes and makes the class of OSTK probes a power-fill, flexible toolbox for optical biosensing applications. Data on steady-state and time-resolved fluorescence experiments investigating the incorporation of coumarin- and [1,3]-dioxolo[4,5-f][1,3]benzo-dioxole-labeled OSTKs in large unilamellar vesicles are presented as a show case.
The gas-to-crystal-shift denotes the shift of electronic excitation energies, i.e., the difference between ground and excited state energies, for a molecule transferred from the gas to the bulk phase. The contributions to the gas-to-crystal-shift comprise electrostatic as well as inductive polarization and dispersive energy shifts of the molecular excitation energies due to interaction with environmental molecules. For the example of 3,4,9,10-perylene-tetracarboxylic-diimide (PTCDI) bulk, the contributions to the gas-to-crystal shift are investigated. In the present work, electrostatic interaction is calculated via Coulomb interaction of partial charges while inductive and dispersive interactions are obtained using respective sum over states expressions. The coupling of higher transition densities for the first 4500 excited states of PTCDI was computed using transition partial charges based on an atomistic model of PTCDI bulk obtained from molecular dynamics simulations. As a result it is concluded that for the investigated model system of a PTCDI crystal, the gas to crystal shift is dominated by dispersive interaction. Published by AIP Publishing.
Seven enzymes have been screened for the cleavage of aryl acetates. Phenyl and naphthyl acetates react with lipases and esterases, whereas the sterically demanding anthracene acetate gave a conversion only with porcine liver esterase and esterase 2 from Bacillus subtilis (BS2). These two enzymes have been employed on a preparative (0.5 mmol) scale and afforded cleavage products in 91 and 94% yields, even for anthracene acetate. Thus, this method is superior to chemical cleavage with catalytic amounts of sodium methoxide (Zemplen conditions), which gave only low conversions. Finally, regioselectivity has been achieved with an anthracene bisacetate, in which an ethyl group controls the cleavage of the first acetate. This indicates that steric interactions play a crucial role in the enzymatic cleavage of aryl acetates, which might be interesting for future applications or the development of enzyme inhibitors.
This paper focused on the synthesis of triangular nanoplatelets in the presence of a tubular network structure. The tubular network structure is formed by adding a strongly alternating polyampholyte, i.e., PalPhBisCarb, to a mixed vesicle system with a negatively charged bilayer containing phosphatidylcholin and AOT. Using the tubular network as a reducing agent in a one-step procedure, triangular and hexagonal nanoplatelets are formed. One can show that the nanoplatelet yield is enhanced by increasing the temperature and decreasing the reaction time. The platelet edge length can be decreased by heating the system up to 100 A degrees C. Due to specific interactions between PalPhBisCarb and the AOT/phospholipid bilayer, stacking and welding effects lead to the formation of ordered platelet structures. The reaction pathway to flat gold nanotriangles is discussed with regard to the twin plane growth model of gold nanoplates.
The optical properties of semiconductor nanocrystals (SC NCs) are largely controlled by their size and surface chemistry, i.e., the chemical composition and thickness of inorganic passivation shells and the chemical nature and number of surface ligands as well as the strength of their bonds to surface atoms. The latter is particularly important for CdTe NCs, which – together with alloyed CdxHg1−xTe – are the only SC NCs that can be prepared in water in high quality without the need for an additional inorganic passivation shell. Aiming at a better understanding of the role of stabilizing ligands for the control of the application-relevant fluorescence features of SC NCs, we assessed the influence of two of the most commonly used monodentate thiol ligands, thioglycolic acid (TGA) and mercaptopropionic acid (MPA), on the colloidal stability, photoluminescence (PL) quantum yield (QY), and PL decay behavior of a set of CdTe NC colloids. As an indirect measure for the strength of the coordinative bond of the ligands to SC NC surface atoms, the influence of the pH (pD) and the concentration on the PL properties of these colloids was examined in water and D2O and compared to the results from previous dilution studies with a set of thiol-capped Cd1−xHgxTe SC NCs in D2O. As a prerequisite for these studies, the number of surface ligands was determined photometrically at different steps of purification after SC NC synthesis with Ellman's test. Our results demonstrate ligand control of the pH-dependent PL of these SC NCs, with MPA-stabilized CdTe NCs being less prone to luminescence quenching than TGA-capped ones. For both types of CdTe colloids, ligand desorption is more pronounced in H2O compared to D2O, underlining also the role of hydrogen bonding and solvent molecules.
Surface-enhanced infrared absorption spectroscopy (SEIRA) is applied to study protein conformational changes. In general, the appropriate functionalization of metal surfaces with biomolecules remains a challenge if the conformation and activity of the biomolecule shall be preserved. Here we present a SEIRA study to monitor pH-induced conformational changes of poly-L lysine (PLL) covalently bound to a thin gold layer via self assembled monolayers (SAMs). We demonstrate that the composition of the SAM is crucial. A SAM of 11-mercaptoundecanonic acid (MUA) can link PLL to the gold layer, but pH-driven conformational transitions were hindered compared to poly-L lysine in solution. To address this problem, we devised a variety of SAMs, i.e., mixed SAMs of MUA with either octanethiol (OT) or 11-mercapto-1-undecanol (MUoL) and furthermore SAMs of MT(PEG)(4) and NHS-PEG(10k)-SH. These mixed SAMs modify the surface properties by changing the polarity and the morphology of the surface present to nearby PLL molecules. Our experiments reveal that mixed SAMs of MUA-MUoL and SAMs of NHS-PEG(10k)-SH-MT(PEG)(4) are suitable to monitor pH-driven conformational changes of immobilized PLL. These SAMs might be applicable for chemoselective protein immobilization in general.
Encapsulation of diagnostic and therapeutic compounds in transporters improves their delivery to the point of need. An even more efficient treatment of diseases can be achieved using carriers with targeting or protecting moieties. In the present work, we investigated micellar and liposomal nanocarriers modified with fluorescein, peptides, and polymers that are covalently bound to fatty acids or phospholipids to ensure a self-driven incorporation into the micelles or liposomes. First, we characterized the photophysics of the fluorescent probes in the absence and in the presence of nanocarriers. Changes in the fluorescence decay time, quantum yield, and intensity of a fluorescein-labeled fatty acid (fluorescein-labeled palmitic acid [fPA]) and a fluorescein-labeled lipopeptide (P2fA2) were found. By exploiting these changes, we investigated a lipopeptide (P2A2 as an uptake-mediating unit) in combination with different nanocarriers (micelles and liposomes) and determined the corresponding association constant K-ass values, which were found to be very high. In addition, the mobility of fPA was exploited using fluorescence correlation spectroscopy (FCS) and fluorescence depolarization (FD) experiments to characterize the nanocarriers. Cellular uptake experiments with mouse brain endothelial cells provided information on the uptake behavior of liposomes modified by uptake-mediating P2A2 and revealed differences in the uptake behavior between pH-sensitive and pH-insensitive liposomes.
Fluorescent molecular probes for metal ions have a raft of potential applications in chemistry and biomedicine. We report the synthesis and photophysical characterisation of 1,8-disubstituted-cyclam/naphthalimide conjugates and their zinc complexes. An efficient synthesis of 1,8-bis-(2-azidoethyl)cyclam has been developed and used to prepare 1,8-disubstituted triazolyl-cyclam systems, in which the pendant group is connected to triazole C4. UV/Vis and fluorescence emission spectra, zinc binding experiments, fluorescence quantum yield and lifetime measurements and pH titrations of the resultant bis-naphthalimide ligand elucidate a complex pattern of photophysical behaviour. Important differences arise from the inclusion of two fluorophores in the one probe and from the variation of triazole substitution pattern (dye at C4 vs. N1). Introducing a second fluorophore greatly extends fluorescence lifetimes, whereas the altered substitution pattern at the cyclam amines exerts a major influence on fluorescence output and metal binding. Crystal structures of two key zinc complexes evidence variations in triazole coordination that mirror the solution-phase behaviour of these systems.
Quantum dynamics of H-2(+) excited by two-cycle laser pulses with laser carrier frequencies corresponding to the wavelengths lambda(1) = 800 and 200 nm (corresponding to the periods tau(1) = 2.667 and 0.667 fs, respectively) and being linearly polarized along the molecular axis have been studied by the numerical solution of the non-Born-Oppenheimer time-dependent Schrodinger equation within a three-dimensional (3D) model, including the internuclear distance R and electron coordinates z and rho. The amplitudes of the pulses have been chosen such that the energies of H-2(+) after the ends of the laser pulses, < E > approximate to-0.515 au, were close to the dissociation threshold of H-2(+). It is found that there exists a certain characteristic oscillation frequency omega(osc) = 0.2278 au (corresponding to the period tau(osc) = 0.667 fs and the wavelength lambda(osc) = 200 nm) that plays the role of a "carrier" frequency of temporally shaped oscillations of the expectation values <-partial derivative V/partial derivative z) emerging after the ends of the laser pulses, both at lambda(1) = 800 nm and at lambda(1) = 200 nm. Moreover, at lambda(1) = 200 nm, the expectation value < z > also demonstrates temporally shaped oscillations after the end of the laser pulse. In contrast, at lambda(1) = 800 nm, the characteristic oscillation frequency omega(osc) = 0.2278 au appears as the frequency of small-amplitude oscillations of the slowly varying expectation value < z > which makes, after the end of the pulse, an excursion with an amplitude of about 4.5 au along the z axis and returns back to < z > approximate to 0 afterward. It is found that the period of the temporally shaped post-field oscillations of <-partial derivative V/partial derivative z > and < z >, estimated as tau(shp) approximate to 30 fs, correlates with the nuclear motion. It is also shown that vibrational excitation of H-2(+) is accompanied by the formation of "hot" and "cold" vibrational ensembles along the R degree of freedom. Power spectra related to the electron motion in H-2(+) calculated for both the laser-driven z and optically passive rho degrees of freedom in the acceleration form proved to be very interesting. In particular, both odd and even harmonics can be observed.
We propose a new methodology for the first principles description of the electronic properties relevant for charge transport in organic molecular crystals. This methodology, which is based on the combination of a nonempirical, optimally tuned range separated hybrid functional with the polarizable continuum model, is applied to a series of eight representative molecular semiconductor crystals. We show that it provides ionization energies, electron affinities, and transport gaps in very good agreement with experimental values, as well as with the results of many-body perturbation theory-within the GW approximation at a fraction of the computational cost. Hence, this approach represents an easily applicable and computationally efficient tool to estimate the gas-to crystal phase shifts of the frontier-orbital quasiparticle energies in organic electronic materials.
Three-dimensional (3D) Bragg coherent x-ray diffractive imaging (CXDI) with a nanofocused beam was applied to quantitatively map the internal strain field of a single indium phosphide nanowire. The quantitative values of the strain were obtained by pre-characterization of the beam profile with transmission ptychography on a test sample. Our measurements revealed the 3D strain distribution in a region of 150 nm below the catalyst Au particle. We observed a slight gradient of the strain in the range of +/- 0.6% along the [111] growth direction of the nanowire. We also determined the spatial resolution in our measurements to be about 10 nm in the direction perpendicular to the facets of the nanowire. The CXDI measurements were compared with the finite element method simulations and show a good agreement with our experimental results. The proposed approach can become an effective tool for in operando studies of the nanowires.
In this work, three ligands produced from amino acids were synthesized and used to produce five bis- and PEPPSI-type palladium-NHC complexes using a novel synthesis route from sustainable starting materials. Three of these complexes were used as precatalysts in the aqueous-phase Suzuki-Miyaura coupling of various substrates displaying high activity. TEM and mercury poisoning experiments provide evidence for Pd-nanoparticle formation stabilized in water.
Arene diazonium salts undergo Matsuda-Heck reactions with vinylsulfonates and -sulfonamides to give styrylsulfonic acid derivatives in high to excellent yields and with high to excellent selectivities. By quantifying the evolution of nitrogen over time in a gas-meter apparatus, the reactivities of ethylvinylsulfonate and the benchmark olefin methyl acrylate were compared for an electron-rich and an -deficient arene diazonium salt. Tertiary sulfonamides react in Matsuda-Heck couplings with high conversions, but require long reaction times, which prevents the determination of kinetic data through the measurement of nitrogen evolution. Secondary sulfonamides were found to be unreactive. From these results, the following order of reactivity could be deduced: H2C=CHCO2Me > H2C=CHSO2OEt > H2C=CHSO2N(Me)Bn >> H2C=CHSO2NHBn. Through the Matsuda-Heck coupling of 5-indolyldiazonium salt and a tertiary vinylsulfonamide, the synthesis of the C-5-substituted indole part of the antimigraine drug naratriptan was accomplished in high yield.
Nowadays, the encapsulation of therapeutic compounds in so-called carrier systems is a very smart method to achieve protection as well as an improvement of their temporal and spatial distribution. After the successful transport to the point of care, the delivery has to be released under controlled conditions. To monitor the triggered release from the carrier, we investigated different fluorescent probes regarding their response to the pH-induced collapse of pH-sensitive liposomes (pHSLip), which occurs when the environmental pH falls below a critical value. Depending on the probe, the fluorescence decay time as well as fluorescence anisotropy can be used equally as key parameters for monitoring the collapse. Especially the application of a fluorescein labeled fatty acid (fPA) enabled the monitoring of the pHSLips collapse and the pH of its microenvironment simultaneously without interference. Varying the pH in the range of 3 < pH < 9, anisotropy data revealed the critical pH value at which the collapse of the pHSLips occurs. Complementary methods, e.g., fluorescence correlation spectroscopy and dynamic light scattering, supported the analysis based on the decay time and anisotropy. Additional experiments with varying incubation times yielded information on the kinetics of the liposomal collapse.
We dissect the sources of error leading to inaccuracies in the description of the geometry and optical excitation energies of pi-conjugated polymers. While the ground-state bond length alternation is shown to be badly reproduced by standard functionals, the recently adapted functionals PBEh* and omega PBE* as well as the double hybrid functional XYGJ-OS manage to replicate results obtained at the CCSD(T) level. By analysis of the bond length alternation in the excited state, a sensitive dependence of the exciton localization on the long-range behavior of the functional and the amount of Hartree-Fock exchange present is shown. Introducing thermal disorder through molecular dynamics simulations allows the consideration of a range of thermally accessible configurations of each oligomer, including trans to cis rotations, which break the conjugation of the backbone. Thermal disorder has a considerable effect when combined with functionals that overestimate the delocalization of the excitation, such as B3LYP. For functionals with a larger amount of exact exchange such as our PBEh* and omega PBE*, however, the effect is small, as excitations are often localized enough to fit between twists in the chain.
The authors report on the fabrication of a thermoresponsive biosensor for the amperometric detection of glucose. Screen printed electrodes with heatable gold working electrodes were modified by a thermoresponsive statistical copolymer [polymer I: poly(omega-ethoxytriethylenglycol methacrylate-omega-3-(N,N-dimethyl-N-2-methacryloyloxyethyl ammonio) propanesulfonate-co-omega-butoxydiethylenglycol methacrylate-co-2-(4-benzoyl-phenoxy)ethyl methacrylate)] with a lower critical solution temperature of around 28 degrees C in aqueous solution via electrochemically induced codeposition with a pH-responsive redox-polymer [polymer II: poly(glycidyl methacrylate-co-allyl methacrylate-co-poly(ethylene glycol) methacrylate-co-butyl acrylate-co-2-(dimethylamino) ethyl methacrylate)-[Os(bpy)(2)(4-(((2-(2-(2-aminoethoxy) ethoxy) ethyl) amino) methyl)-N,N-dimethylpicolinamide)](2+)] and pyrroloquinoline quinone-soluble glucose dehydrogenase acting as biological recognition element. Polymer II bears covalently bound Os-complexes that act as redox mediators for shuttling electrons between the enzyme and the electrode surface. Polymer I acts as a temperature triggered immobilization matrix. Probing the catalytic current as a function of the working electrode temperature shows that the activity of the biosensor is dramatically reduced above the phase transition temperature of polymer I. Thus, the local modulation of the temperature at the interphase between the electrode and the bioactive layer allows switching the biosensor from an on-to an off-state without heating of the surrounding analyte solution. (C) 2015 American Vacuum Society.
Janus emulsions, formed by mixing two oil components (i.e., olive oil (OO) and silicone oil (SiO)) with water in the presence of two surface active biopolymers, i.e., gelatin and chitosan, are investigated in more detail. The stability of Janus droplets formed strongly depends on the polymer components used. The mixture of both biopolymers represents an extraordinary effect which can be related to the complex formation of gelatin and chitosan. Taken into account that under the given pH conditions, in the acidic pH range between 4 and 6, below the isoelectric point of gelatin, both polymers are polycations, one can conclude that non-Coulombic interactions are of relevance for the enhanced surface activity of the complexes. Dynamic interfacial tension (gamma) measurements by using the drop profile analysis tensiometry (PAT) indicate a strong adsorption of the polymer complexes at the olive oil/water interface in contrast to the silicone/water interface. In a first step, the polymer complexes are adsorbed at the interface, and in a second step, a more rigid skin-like polymer layer is formed. This first example of a polymer-stabilized Janus emulsion opens new perspectives for the application, e.g., in food emulsions or for making scaffold materials.
Metal-containing ionic liquids (ILs) are of interest for a variety of technical applications, e.g., particle synthesis and materials with magnetic or thermochromic properties. In this paper we report the synthesis of, and two structures for, some new tetrabromidocuprates(II) with several "onium" cations in comparison to the results of electron paramagnetic resonance (EPR) spectroscopic analyses. The sterically demanding cations were used to separate the paramagnetic Cu(II) ions for EPR measurements. The EPR hyperfine structure in the spectra of these new compounds is not resolved, due to the line broadening resulting from magnetic exchange between the still-incomplete separated paramagnetic Cu(II) centres. For the majority of compounds, the principal g values (g|| and g(perpendicular to)) of the tensors could be determined and information on the structural changes in the [CuBr4](2-) anions can be obtained. The complexes have high potential, e.g., as ionic liquids, as precursors for the synthesis of copper bromide particles, as catalytically active or paramagnetic ionic liquids.
The performance of non-empirically tuned long-range corrected hybrid functionals for the prediction of vertical ionization potentials (IPs) and electron affinities (EAs) is assessed for a set of 24 organic acceptor molecules. Basis set extrapolated coupled cluster singles, doubles, and perturbative triples [CCSD(T)] calculations serve as a reference for this study. Compared to standard exchange-correlation functionals, tuned long-range corrected hybrid functionals produce highly reliable results for vertical IPs and EAs, yielding mean absolute errors on par with computationally more demanding GW calculations. In particular, it is demonstrated that long-range corrected hybrid functionals serve as ideal starting points for non-self-consistent GW calculations.
The performance of different GW methods is assessed for a set of 24 organic acceptors. Errors are evaluated with respect to coupled cluster singles, doubles, and perturbative triples [CCSD(T)] reference data for the vertical ionization potentials (IPs) and electron affinities (EAs), extrapolated to the complete basis set limit. Additional comparisons are made to experimental data, where available. We consider fully self-consistent GW (scGW), partial self-consistency in the Green’s function (scGW0), non-self-consistent G0W0 based on several mean-field starting points, and a “beyond GW” second-order screened exchange (SOSEX) correction to G0W0. We also describe the implementation of the self-consistent Coulomb hole with screened exchange method (COHSEX), which serves as one of the mean-field starting points. The best performers overall are G0W0+SOSEX and G0W0 based on an IP-tuned long-range corrected hybrid functional with the former being more accurate for EAs and the latter for IPs. Both provide a balanced treatment of localized vs delocalized states and valence spectra in good agreement with photoemission spectroscopy (PES) experiments.
A series of meso monosubstituted metalloporphyrins were synthesized to assess the structural chemistry of porphyrins with only one substituent. The structures of four nickel(II) and zinc(II) complexes with either alkyl or aryl residues indicate primarily planar macrocycles. This gives rise to a different type of pi-interactions in the crystal and the formation of dimeric, trimeric or tetrameric porphyrin units that function as building blocks for the overall crystal structure. Notably, some structures exhibit a unique edge-on packing of porphyrins, while the molecules of (5-n-butylporphyrinato)nickel(II) forms an unusual bilayer type structure where rows of two porphyrin macrocycles are separated by the alkyl residues arranged in a head-to-head fashion. This adds to the canon of intermolecular porphyrin packing arrangements and is of relevance for the preparation of ordered nanoscopic porphyrin devices. (C) 2015 Elsevier Ltd. All rights reserved.
Polyplexes between Salmon DNA and non-modified hyperbranched poly(ethyleneimines) of varying molar mass, i.e., PEI(5 k) with 5000 g/mol and PEI(25 k) with 25,000 g/mol, and modified PEI(5 k) with maltose units (PEI-Mal) were investigated in dependence on the molar N/P ratio by using dynamic light scattering (DLS), zeta potential measurements, micro differential scanning calorimetry (mu-DSC), scanning-transmission electron microscopy (STEM), and cryo-scanning electron microscopy (cryo-SEM). A reloading of the polyplexes can be observed by adding the unmodified PEI samples of different molar mass. In excess of PEI a morphological transition from core-shell particles (at N/P 8) to loosely packed onion-like polyplexes (at N/P 40) is observed. The shift of the DSC melting peak from 88 degrees C to 76 degrees C indicates a destabilization of the DNA double helix due to the complexation with the unmodified PEI. Experiments with the maltose-modified PEI show a reloading already at a lower N/P ratio. Due to the presence of the sugar units in the periphery of the polycation electrostatic interactions between DNA become weaker, but cooperative H-bonding forces are reinforced. The resulting less-toxic, more compact polyplexes in excess of the PEI-Mal with two melting points and well distributed DNA segments are of special interest for extended gene delivery experiments. (C) 2015 Elsevier B.V. All rights reserved.
Total protein concentration (TPC) is a key parameter in many biochemical experiments and its quantification is often necessary for isolation, separation, and analysis of proteins. A sensitive and rapid nanobead-based TPC quantification assay based on Forster Resonance Energy Transfer (FRET) has been developed. A new, highly luminescent Tb(III) complex has been synthesised and applied as donor in this FRET assay with an organic dye (Cy5) as acceptor. FRET-induced changes in luminescence have been investigated both at donor and acceptor emission wavelength using time-resolved luminescence spectroscopy with time-gated detection. In the assay, the Tb(III) complex and fine-tuned polyglycidyl methacrylate (PGMA) nanobeads ensure that an improvement in sensitivity and background reduction is achieved. Using 40 nm large PGMA nanobeads loaded with the Tb(III) complex, it is possible to determine TPC down to 50 ng mL(-1) in just 10 minutes. Through specific assay components the sensitivity has been improved when compared to existing nanobead-based assays and to currently known commercial methods. Additionally, the assay is relatively insensitive to the presence of contaminants, such as non-ionic detergents commonly found in biological samples. Due to no need for any centrifugal steps, this mix-and-measure bioassay can easily be implemented into routine TPC quantification protocols in biochemical laboratories.
The aim of this study was to develop a one-step synthesis of gold nanotriangles (NTs) in the presence of mixed phospholipid vesicles followed by a separation process to isolate purified NTs. Negatively charged vesicles containing AOT and phospholipids, in the absence and presence of additional reducing agents (polyampholytes, polyanions or low molecular weight compounds), were used as a template phase to form anisotropic gold nanoparticles. Upon addition of the gold chloride solution, the nucleation process is initiated and both types of particles, i.e., isotropic spherical and anisotropic gold nanotriangles, are formed simultaneously. As it was not possible to produce monodisperse nanotriangles with such a one-step procedure, the anisotropic nanoparticles needed to be separated from the spherical ones. Therefore, a new type of separation procedure using combined polyelectrolyte/micelle depletion flocculation was successfully applied. As a result of the different purification steps, a green colored aqueous dispersion was obtained containing highly purified, well-defined negatively charged flat nanocrystals with a platelet thickness of 10 nm and an edge length of about 175 nm. The NTs produce promising results in surface-enhanced Raman scattering.
The fruit of Aristotelia chilensis is considered a "super fruit" due to its high concentration of polyphenols displaying exceptional antioxidant capacities ORAC. From maqui berries have been reported several anthocyanins and glycosylated flavonoids, those benefits increase the attention to restudy the plant. From the leaves of A. chilensis several indole alkaloids have been reported, we in addition to aristoteline, aristone, aristoquinoline and 3-fromylindole report the spectroscopic elucidation of 8-oxo-9-dehydromakomakine (1), hobartine (2) and a new alkaloid named 8-oxohobartine (3). Compound 1 to 3 did not show bactericidal activity against E. coli and S. aureus till 200 mu g.
On the basis of the clinical studies in patients with coronary artery disease (CAD) presenting an increased percentage of activated platelets, we hypothesized that hemocompatibility testing utilizing platelets from healthy individuals may result in an underestimation of the materials' thrombogenicity. Therefore, we investigated the interaction of polymer-based biomaterials with platelets from CAD patients in comparison to platelets from apparently healthy individuals. In vitro static thrombogenicity tests revealed that adherent platelet densities and total platelet covered areas were significantly increased for the low (polydimethylsiloxane, PDMS) and medium (Collagen) thrombogenic surfaces in the CAD group compared to the healthy subjects group. The area per single platelet—indicating the spreading and activation of the platelets—was markedly increased on PDMS treated with PRP from CAD subjects. This could not be observed for collagen or polytetrafluoroethylene (PTFE). For the latter material, platelet adhesion and surface coverage did not differ between the two groups. Irrespective of the substrate, the variability of these parameters was increased for CAD patients compared to healthy subjects. This indicates a higher reactivity of platelets from CAD patients compared to the healthy individuals. Our results revealed, for the first time, that utilizing platelets from apparently healthy donors bears the risk of underestimating the thrombogenicity of polymer-based biomaterials.
Complementary to the well-established zwitterionic monomer 3-((3-methacrylamidopropyl) dimethylammonio) propane-1-sulfonate (SPP), the closely related monomers 2-hydroxy-3-((3-methacrylamidopropyl) dimethylammonio) propane-1-sulfonate (SHPP) and 4-((3-methacrylamidopropyl) dimethylammonio)butane- 1-sulfonate (SBP) were synthesised and polymerised by reversible addition-fragmentation chain transfer (RAFT) polymerisation, using a fluorophore labeled RAFT agent. The polyzwitterions of systematically varied molar masses were characterised with respect to their solubility in water and aqueous salt solutions. Both poly(sulfobetaine)s show thermoresponsive behaviour in water, exhibiting phase separation at low temperatures and upper critical solution temperatures (UCST). For both polySHPP and polySBP, cloud points depend notably on the molar mass, and are much higher in D2O than in H2O. Also, the cloud points are effectively modulated by the addition of salts. The individual effects can be in parts correlated to the Hofmeister series for the anions studied. Still, they depend in a complex way on the concentration and the nature of the added electrolytes, on the one hand, and on the detailed nature of the spacer group separating the anionic and the cationic charges of the betaine moiety, on the other hand. As anticipated, the cloud points of polySBP are much higher than the ones of the analogous polySPP of identical molar mass. Surprisingly, the cloud points of polySHPP are also somewhat higher than the ones of their polySPP analogues, despite the additional hydrophilic hydroxyl group present in the spacer separating the ammonium and the sulfonate moieties. These findings point to a complicated interplay of the various hydrophilic components in polyzwitterions with respect to their overall hydrophilicity. Thus, the spacer group in the betaine moiety proves to be an effective additional molecular design parameter, apparently small variations of which strongly influence the phase behaviour of the polyzwitterions in specific aqueous environments.
Allyl, dimethylallyl, crotyl, and prenyl ethers of various aromatic ortho-hydroxy carbonyl compounds undergo a tandem sequence of Claisen rearrangement, carbonyl olefination, and cyclization upon microwave irradiation in the presence of a stabilized ylide. The products are multiply substituted 6- or 8-allylated or prenylated coumarins (2H-chromen-2-ones).
Catalytic amounts of a weak base are sufficient to induce the decomposition of anthracene endoperoxides to anthraquinone. The mechanism has been elucidated by isolation of intermediates in combination with DFT calculations. The whole process is suitable for the convenient generation of hydrogen peroxide under very mild conditions.
The ground-state classical path approximation is utilized to compute molecular absorption spectra in a mixed quantum-classical frame. To improve the description for high-frequency vibrational satellites, related quantum correction factors are introduced. The improved method is demonstrated for the Q(y),and Q(x)-bands of pheophorbide a. (C) 2015 Elsevier B.V. All rights reserved.
BACKGROUND: Thrombogenicity is one of the main parameters tested in vitro to evaluate the hemocompatibility of artificial surfaces. While the influence of the temperature on platelet aggregation has been addressed by several studies, the temperature influence on the adherence of platelets to body foreign surfaces as an important aspect of biomedical device handling has not yet been explored. Therefore, we analyzed the influence of two typically applied incubation-temperatures (22 degrees C and 37 degrees C) on the adhesion of platelets to biomaterials. MATERIAL AND METHODS: Thrombogenicity of three different polymers - medical grade poly(dimethyl siloxane) (PDMS), polytetrafluoroethylene (PTFE) and polyethylene terephthalate (PET) - were studied in an in vitro static test. Platelet adhesion was studied with stringently characterized blood from apparently healthy subjects. Collection of whole blood and preparation of platelet rich plasma (PRP) was carried out at room temperature (22 degrees C). PRP was incubated with the polymers either at 22 degrees C or 37 degrees C. Surface adherent platelets were fixed, fluorescently labelled and assessed by an image-based approach. RESULTS AND DISCUSSION: Differences in the density of adherent platelets after incubation at 22 degrees C and 37 degrees C occurred on PDMS and PET. Similar levels of adherent platelets were observed on the very thrombogenic PTFE. The covered surface areas per single platelet were analyzed to measure the state of platelet activation and revealed no differences between the two incubation temperatures for any of the analyzed polymers. Irrespective of the observed differences between the low and medium thrombogenic PDMS and PET and the higher variability at 22 degrees C, the thrombogenicity of the three investigated polymers was evaluated being comparable at both incubation temperatures.
The synthesis and photophysical properties of two new FRET pairs based on coumarin as a donor and DBD dye as an acceptor are described. The introduction of a bromo atom dramatically increases the two-photon excitation (2PE) cross section providing a 2PE-FRET system, which is also suitable for 2PE-FLIM.
The optical properties of semiconductor nanocrystals (SC NCs) are largely controlled by their size and surface chemistry, i.e., the chemical composition and thickness of inorganic passivation shells and the chemical nature and number of surface ligands as well as the strength of their bonds to surface atoms. The latter is particularly important for CdTe NCs, which – together with alloyed CdxHg1−xTe – are the only SC NCs that can be prepared in water in high quality without the need for an additional inorganic passivation shell. Aiming at a better understanding of the role of stabilizing ligands for the control of the application-relevant fluorescence features of SC NCs, we assessed the influence of two of the most commonly used monodentate thiol ligands, thioglycolic acid (TGA) and mercaptopropionic acid (MPA), on the colloidal stability, photoluminescence (PL) quantum yield (QY), and PL decay behavior of a set of CdTe NC colloids. As an indirect measure for the strength of the coordinative bond of the ligands to SC NC surface atoms, the influence of the pH (pD) and the concentration on the PL properties of these colloids was examined in water and D2O and compared to the results from previous dilution studies with a set of thiol-capped Cd1−xHgxTe SC NCs in D2O. As a prerequisite for these studies, the number of surface ligands was determined photometrically at different steps of purification after SC NC synthesis with Ellman's test. Our results demonstrate ligand control of the pH-dependent PL of these SC NCs, with MPA-stabilized CdTe NCs being less prone to luminescence quenching than TGA-capped ones. For both types of CdTe colloids, ligand desorption is more pronounced in H2O compared to D2O, underlining also the role of hydrogen bonding and solvent molecules.
Diese Arbeit befasst sich mit der Herstellung und Charakterisierung von thermoresponsiven Filmen auf Goldelektroden durch Fixierung eines bereits synthetisierten thermoresponsiven Polymers. Als Basis für die Entwicklung der responsiven Grenzfläche dienten drei unterschiedliche Copolymere (Polymere I, II und III) aus der Gruppe der thermisch schaltbaren Poly(oligo(ethylenglykol)methacrylate).
Die turbidimetrischen Messungen der Copolymere in Lösungen haben gezeigt, dass der Trübungspunkt vom pH-Wert, der Gegenwart von Salzen sowie von der Ionenstärke der Lösung abhängig ist. Nach der Charakterisierung der Polymere in Lösung wurden Experimente der kovalenten Kopplung der Polymere I bis III an die Oberfläche der Gold-Elektroden durchgeführt. Während bei Polymeren I und II die Ankopplung auf einer Amidverbrückung basierte, wurde bei Polymer III als alternative Methode zur Immobilisierung eine photoinduzierte Anbindung unter gleichzeitiger Vernetzung gewählt. Der Nachweis der erfolgreichen Ankopplung erfolgte bei allen Polymeren elektrochemisch mittels Cyclovoltammetrie und Impedanzspektroskopie in K3/4[Fe(CN)6]-Lösungen. Wie die Ellipsometrie-Messungen zeigten, waren die erhaltenen Polymer-Filme unterschiedlich dick. Die Ankopplung über Amidverbrückung lieferte dünne Filme (10 – 15 nm), während der photovernetzte Film deutlich dicker war (70-80 nm) und die darunter liegende Oberfläche relativ gut isolierte.
Elektrochemische Temperaturexperimente an Polymer-modifizierten Oberflächen in Lösungen in Gegenwart von K3/4[Fe(CN)6] zeigten, dass auch die immobilisierten Polymere I bis III responsives Temperaturverhalten zeigen. Bei Elektroden mit den immobilisierten Polymeren I und II ist der Temperaturverlauf der Parameterwerte diskontinuierlich – ab einem kritischen Punkt (37 °C für Polymer I und 45 °C für Polymer II) wird zunächst langsame Zunahme der Peakströme wird deutlich schneller. Das Temperaturverhalten von Polymer III ist dagegen bis 50 °C kontinuierlich, der Peakstrom sinkt hier durchgehend.
Weiterhin wurde mit den auf Polymeren II und III basierten Elektroden deren Anwendung als responsive Matrix für Bioerkennungsreaktionen untersucht. Es wurde die Ankopplung von kleinen Biorezeptoren, TAG-Peptiden, an Polymer II- und Polymer III-modifizierten Elektroden durchgeführt. Das hydrophile FLAG-TAG-Peptid verändert das Temperaturverhalten des Polymer II-Films unwesentlich, da es die Hydrophilie des Netzwerkes nicht beeinflusst. Weiterhin wurde der Effekt der Ankopplung der ANTI-FLAG-TAG-Antikörper an FLAG-TAG-modifizierte Polymer II-Filme untersucht. Es konnte gezeigt werden, dass die Antikörper spezifisch an FLAG-TAG-modifiziertes Polymer II binden. Es wurde keine unspezifische Anbindung von ANTI-FLAG-TAG an Polymer II beobachtet. Die Temperaturexperimente haben gezeigt, dass die thermische Restrukturierung des Polymer II-FLAG-TAG-Filmes auch nach der Antikörper-Ankopplung noch stattfindet. Der Einfluss der ANTI-FLAG-TAG-Ankopplung ist gering, da der Unterschied in der Hydrophilie zwischen Polymer II und FLAG-TAG bzw. ANTI-FLAG-TAG zu gering ist.
Für die Untersuchungen mit Polymer III-Elektroden wurde neben dem hydrophilen FLAG-TAG-Peptid das deutlich hydrophobere HA-TAG-Peptid ausgewählt. Wie im Falle der Polymer II Elektrode beeinflusst das gekoppelte FLAG-TAG-Peptid das Temperaturverhalten des Polymer III-Netzwerkes nur geringfügig. Die gemessenen Stromwerte sind geringer als bei der Polymer III-Elektrode. Das Temperaturverhalten der FLAG-TAG-Elektrode ähnelt dem der reinen Polymer III-Elektrode – die Stromwerte sinken kontinuierlich bis die Temperatur von ca. 40 °C erreicht ist, bei der ein Plateau beobachtet wird. Offensichtlich verändert FLAG-TAG auch in diesem Fall nicht wesentlich die Hydrophilie des Polymer III-Netzwerkes. Das an Polymer III-Elektroden gekoppelte hydrophobe HA-TAG-Peptid beeinflusst dagegen im starken Maße den Quellzustand des Netzwerkes. Die Ströme für die HA-TAG-Elektroden sind deutlich geringer als die für die FLAG-TAG-Polymer III-Elektroden, was auf geringeren Wassergehalt und dickeren Film zurückzuführen ist. Bereits ab 30 °C erfolgt der Anstieg von Stromwerten, der bei Polymer III- bzw. bei Polymer III-FLAG-TAG-Elektroden nicht beobachtet werden kann. Das gekoppelte hydrophobe HA-TAG-Peptid verdrängt Wasser aus dem Polymer III-Netzwerk, was in der Stauchung des Films bereits bei Raumtemperatur resultiert. Dies führt dazu, dass der Film im Laufe des Temperaturanstieges kaum noch komprimiert. Die Stromwerte steigen in diesem Fall entsprechend des Anstiegs der temperaturabhängigen Diffusion des Redoxpaares. Diese Untersuchungen zeigen, dass das HA-TAG-Peptid als Ankermolekül deutlich besser für eine potentielle Verwendung der Polymer III-Filme für sensorische Zwecke geeignet ist, da es sich deutlich in der Hydrophilie von Polymer III unterscheidet.
In this contribution, we study using first principles the co-adsorption and catalytic behaviors of CO and O2 on a single gold atom deposited at defective magnesium oxide surfaces. Using cluster models and point charge embedding within a density functional theory framework, we simulate the CO oxidation reaction for Au1 on differently charged oxygen vacancies of MgO(001) to rationalize its experimentally observed lack of catalytic activity. Our results show that: (1) co-adsorption is weakly supported at F0 and F2+ defects but not at F1+ sites, (2) electron redistribution from the F0 vacancy via the Au1 cluster to the adsorbed molecular oxygen weakens the O2 bond, as required for a sustainable catalytic cycle, (3) a metastable carbonate intermediate can form on defects of the F0 type, (4) only a small activation barrier exists for the highly favorable dissociation of CO2 from F0, and (5) the moderate adsorption energy of the gold atom on the F0 defect cannot prevent insertion of molecular oxygen inside the defect. Due to the lack of protection of the color centers, the surface becomes invariably repaired by the surrounding oxygen and the catalytic cycle is irreversibly broken in the first oxidation step.
The aim of this study was to develop a one-step synthesis of gold nanotriangles (NTs) in the presence of mixed phospholipid vesicles followed by a separation process to isolate purified NTs. Negatively charged vesicles containing AOT and phospholipids, in the absence and presence of additional reducing agents (polyampholytes, polyanions or low molecular weight compounds), were used as a template phase to form anisotropic gold nanoparticles. Upon addition of the gold chloride solution, the nucleation process is initiated and both types of particles, i.e., isotropic spherical and anisotropic gold nanotriangles, are formed simultaneously. As it was not possible to produce monodisperse nanotriangles with such a one-step procedure, the anisotropic nanoparticles needed to be separated from the spherical ones. Therefore, a new type of separation procedure using combined polyelectrolyte/micelle depletion flocculation was successfully applied. As a result of the different purification steps, a green colored aqueous dispersion was obtained containing highly purified, well-defined negatively charged flat nanocrystals with a platelet thickness of 10 nm and an edge length of about 175 nm. The NTs produce promising results in surface-enhanced Raman scattering.