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- ItemTowards on-site testing of Phytophthora species(Cambridge : RSC Publ., 2014) Schwenkbier, Lydia; Pollok, Sibyll; König, Stephan; Urban, Matthias; Werres, Sabine; Cialla-May, Dana; Weber, Karina; Popp, JürgenRapid detection and accurate identification of plant pathogens in the field is an ongoing challenge. In this study, we report for the first time on the development of a helicase-dependent isothermal amplification (HDA) in combination with on-chip hybridization for the detection of selected Phytophthora species. The HDA approach allows efficient amplification of the yeast GTP-binding protein (Ypt1) target gene region at one constant temperature in a miniaturized heating device. The assay's specificity was determined by on-chip DNA hybridization and subsequent silver nanoparticle deposition. The silver deposits serve as stable endpoint signals that enable the visual as well as the electrical readout. Our promising results point to the direction of a near future on-site application of the combined techniques for a reliable detection of Phytophthora species.
- ItemHydrogen bonding in a mixture of protic ionic liquids: A molecular dynamics simulation study(Cambridge : RSC Publ., 2015) Paschek, Dietmar; Golub, Benjamin; Ludwig, RalfWe report results of molecular dynamics (MD) simulations characterising the hydrogen bonding in mixtures of two different protic ionic liquids sharing the same cation: triethylammonium-methylsulfonate (TEAMS) and triethylammonium-triflate (TEATF). The triethylammonium-cation acts as a hydrogen-bond donor, being able to donate a single hydrogen-bond. Both, the methylsulfonate- and the triflate-anions can act as hydrogen-bond acceptors, which can accept multiple hydrogen bonds via their respective SO3-groups. In addition, replacing a methyl-group in the methylsulfonate by a trifluoromethyl-group in the triflate significantly weakens the strength of a hydrogen bond from an adjacent triethylammonium cation to the oxygen-site in the SO3-group of the anion. Our MD simulations show that these subtle differences in hydrogen bond strength significantly affect the formation of differently-sized hydrogen-bonded aggregates in these mixtures as a function of the mixture-composition. Moreover, the reported hydrogen-bonded cluster sizes can be predicted and explained by a simple combinatorial lattice model, based on the approximate coordination number of the ions, and using statistical weights that mostly account for the fact that each anion can only accept three hydrogen bonds.
- ItemIn situ spectroelectrochemical and theoretical study on the oxidation of a 4H-imidazole-ruthenium dye adsorbed on nanocrystalline TiO2 thin film electrodes(Cambridge : RSC Publ., 2015) Zhang, Ying; Kupfer, Stephan; Zedler, Linda; Schindler, Julian; Bocklitz, Thomas; Guthmuller, Julien; Rau, Sven; Dietzek, BenjaminTerpyridine 4H-imidazole-ruthenium(II) complexes are considered promising candidates for use as sensitizers in dye sensitized solar cells (DSSCs) by displaying broad absorption in the visible range, where the dominant absorption features are due to metal-to-ligand charge transfer (MLCT) transitions. The ruthenium(III) intermediates resulting from photoinduced MLCT transitions are essential intermediates in the photoredox-cycle of the DSSC. However, their photophysics is much less studied compared to the ruthenium(II) parent systems. To this end, the structural alterations accompanying one-electron oxidation of the RuIm dye series (including a non-carboxylic RuIm precursor, and, carboxylic RuImCOO in solution and anchored to a nanocrystalline TiO2 film) are investigated via in situ experimental and theoretical UV-Vis absorption and resonance Raman (RR) spectroelectrochemistry. The excellent agreement between the experimental and the TDDFT spectra derived in this work allows for an in-depth assignment of UV-Vis and RR spectral features of the dyes. A concordant pronounced wavelength dependence with respect to the charge transfer character has been observed for the model system RuIm, and both RuImCOO in solution and attached on the TiO2 surface. Excitation at long wavelengths leads to the population of ligand-to-metal charge transfer states, i.e. photoreduction of the central ruthenium(III) ion, while high-energy excitation features an intra-ligand charge transfer state localized on the 4H-imidazole moiety. Therefore, these 4H-imidazole ruthenium complexes investigated here are potential multi-photoelectron donors. One electron is donated from MLCT states, and additionally, the 4H-imidazole ligand reveals electron-donating character with a significant contribution to the excited states of the ruthenium(III) complexes upon blue-light irradiation.
- ItemDifferences in single and aggregated nanoparticle plasmon spectroscopy(Cambridge : RSC Publ., 2014) Singh, Pushkar; Deckert-Gaudig, Tanja; Schneidewind, Henrik; Kirsch, Konstantin; van Schrojenstein Lantman, Evelien M.; Weckhuysen, Bert M.; Deckert, VolkerVibrational spectroscopy usually provides structural information averaged over many molecules. We report a larger peak position variation and reproducibly smaller FWHM of TERS spectra compared to SERS spectra indicating that the number of molecules excited in a TERS experiment is extremely low. Thus, orientational averaging effects are suppressed and micro ensembles are investigated. This is shown for a thiophenol molecule adsorbed on Au nanoplates and nanoparticles.
- ItemThe effect of dispersion forces on the interaction energies and far infrared spectra of protic ionic liquids(Cambridge : RSC Publ., 2015) Ludwig, RalfWe could show by means of dispersion-corrected DFT calculations that the interaction energy in protic ionic liquids can be dissected into Coulomb interaction, hydrogen bonding and dispersion interaction. The H-bond energy as well as the dispersion energy can be quantified to be 50 kJ mol−1 each representing ten percent of the overall interaction energy. The dispersion interaction could be dissected into two portions. One third could be related to the dispersion interaction within an ion-pair enhancing the H-bond strength, two thirds stem from dispersion interaction between the ion-pairs. This distribution of dispersion interaction is reflected in the far infrared (FIR) spectra. The H-bond band is shifted weaker than the low frequency band where the latter indicates diffuse cation–anion interaction and H-bond bending motions. Finally, we can dissect the different types of interaction energies indicating their characteristic influence on vibrational modes in the FIR.
- ItemHole injection dynamics from two structurally related Ru-bipyridine complexes into NiOx is determined by the substitution pattern of the ligands(Cambridge : RSC Publ., 2015) Bräutigam, Maximilian; Kübel, Joachim; Schulz, Martin; Vos, Johannes G.; Dietzek, BenjaminThe dyes bis[2,2′-bipyridine][4,4′-dicarboxy-2,2′-bipyridine]ruthenium(II) dihexafluorophosphate, [Ru(bpy)2dcb](PF6)2 (Ru1), and tris[4,4′-bis(ethylcarboxy)-2,2′-bipyridine]ruthenium(II) dihexafluorophosphate, [Ru(dceb)3](PF6)2 (Ru2), attached to NiOx nanoparticle films were investigated using transient absorption and luminescence spectroscopy. In acetonitrile solution the dyes reveal very similar physical and chemical properties, i.e. both dyes exhibit comparable ground state and long-lived, broad excited state absorption. However, when immobilized onto a NiOx surface the photophysical properties of the two dyes differ significantly. For Ru1 luminescence is observed, which decays within 18 ns and ultrafast transient absorption measurements do not show qualitative differences from the photophysics of Ru1 in solution. In contrast to this the luminescence of photoexcited Ru2 on NiOx is efficiently quenched and the ultrafast transient absorption spectra reveal the formation of oxidized nickel centres overlaid by the absorption of the reduced dye Ru2 with a characteristic time-constant of 18 ps. These findings are attributed to the different localization of the initially photoexcited state in Ru1 and Ru2. Due to the inductive effect (−I) of the carboxylic groups, the lowest energy excited state in Ru1 is localized on the dicarboxy-bipyridine ligand, which is bound to the NiOx surface. In Ru2, on the other hand, the initially populated excited state is localized on the ester-substituted ligands, which are not bound to the semiconductor surface. Hence, the excess charge density that is abstracted from the Ru-ion in the metal-to-ligand charge-transfer transition is shifted away from the NiOx surface, which ultimately facilitates hole transfer into the semiconductor.
- ItemEnergy transfer and formation of long-lived 3MLCT states in multimetallic complexes with extended highly conjugated bis-terpyridyl ligands(Cambridge : RSC Publ., 2015) Wächtler, Maria; Kübel, Joachim; Barthelmes, Kevin; Winter, Andreas; Schmiedel, Alexander; Pascher, Torbjörn; Lambert, Christoph; Schubert, Ulrich S.; Dietzek, BenjaminMultimetallic complexes with extended and highly conjugated bis-2,2′:6′,2′′-terpyridyl bridging ligands, which present building blocks for coordination polymers, are investigated with respect to their ability to act as light-harvesting antennae. The investigated species combine Ru(II)- with Os(II)- and Fe(II)-terpyridyl chromophores, the latter acting as energy sinks. Due to the extended conjugated system the ligands are able to prolong the lifetime of the 3MLCT states compared to unsubstituted terpyridyl species by delocalization and energetic stabilization of the 3MLCT states. This concept is applied for the first time to Fe(II) terpyridyl species and results in an exceptionally long lifetime of 23 ps for the Fe(II) 3MLCT state. While partial energy (>80%) transfer is observed between the Ru(II) and Fe(II) centers with a time-constant of 15 ps, excitation energy is transferred completely from the Ru(II) to the Os(II) center within the first 200 fs after excitation.
- ItemA comprehensive comparison of dye-sensitized NiO photocathodes for solar energy conversion(Cambridge : RSC Publ., 2015) Wood, Christopher J.; Summers, Gareth H.; Clark, Charlotte A.; Kaeffer, Nicolas; Braeutigam, Maximilian; Carbone, Lea Roberta; D'Amario, Luca; Fan, Ke; Farré, Yoann; Narbey, Stéphanie; Oswald, Frédéric; Stevens, Lee A.; Parmenter, Christopher D.J.; Fay, Michael W.; La Torre, Alessandro; Snape, Colin E.; Dietzek, Benjamin; Dini, Danilo; Hammarström, Leif; Pellegrin, Yann; Odobel, Fabrice; Sun, Licheng; Artero, Vincent; Gibson, Elizabeth A.We investigated a range of different mesoporous NiO electrodes prepared by different research groups and private firms in Europe to determine the parameters which influence good quality photoelectrochemical devices. This benchmarking study aims to solve some of the discrepancies in the literature regarding the performance of p-DSCs due to differences in the quality of the device fabrication. The information obtained will lay the foundation for future photocatalytic systems based on sensitized NiO so that new dyes and catalysts can be tested with a standardized material. The textural and electrochemical properties of the semiconducting material are key to the performance of photocathodes. We found that both commercial and non-commercial NiO gave promising solar cell and water-splitting devices. The NiO samples which had the two highest solar cell efficiency (0.145% and 0.089%) also gave the best overall theoretical H2 conversion.
- ItemSpectroscopic evidence of 'jumping and pecking' of cholinium and H-bond enhanced cation-cation interaction in ionic liquids(Cambridge : RSC Publ., 2015) Knorr, Anne; Fumino, Koichi; Bonsa, Anne-Marie; Ludwig, RalfThe subtle energy-balance between Coulomb-interaction, hydrogen bonding and dispersion forces governs the unique properties of ionic liquids. To measure weak interactions is still a challenge. This is in particular true in the condensed phase wherein a melange of different strong and directional types of interactions is present and cannot be detected separately. For the ionic liquids (2-hydroxyethyl)-trimethylammonium (cholinium) bis(trifluoro-methylsulfonyl)amide and N,N,N-trimethyl-N-propylammonium bis(trifluoromethylsulfonyl)amide which differ only in the 2-hydroxyethyl and the propyl groups of the cations, we could directly observe distinct vibrational signatures of hydrogen bonding between the cation and the anion indicated by ‘jumping and pecking’ motions of cholinium. The assignment could be confirmed by isotopic substitution H/D at the hydroxyl group of cholinium. For the first time we could also find direct spectroscopic evidence for H-bonding between like-charged ions. The repulsive Coulomb interaction between the cations is overcome by cooperative hydrogen bonding between the 2-hydroxyethyl functional groups of cholinium. This H-bond network is reflected in the properties of protic ionic liquids (PILs) such as viscosities and conductivities.
- ItemPost deposition annealing of epitaxial Ce1-xPrxO2-δ films grown on Si(111)(Cambridge : RSC Publ., 2015) Wilkens, H.; Spieß, W.; Zoellner, M.H.; Niu, G.; Schroeder, T.; Wollschläger, J.In this work the structural and morphological changes of Ce1−xPrxO2−δ (x = 0.20, 0.35 and 0.75) films grown on Si(111) due to post deposition annealing are investigated by low energy electron diffraction combined with a spot profile analysis. The surface of the oxide films exhibit mosaics with large terraces separated by monoatomic steps. It is shown that the Ce/Pr ratio and post deposition annealing temperature can be used to tune the mosaic spread, terrace size and step height of the grains. The morphological changes are accompanied by a phase transition from a fluorite type lattice to a bixbyite structure. Furthermore, at high PDA temperatures a silicate formation via a polycrystalline intermediate state is observed.