@article{WessigMoellnitzKellingetal.2011, author = {Wessig, Pablo and M{\"o}llnitz, Kristian and Kelling, Alexandra and Schilde, Uwe}, title = {Crystal structure of 1r,2c,3c,4t,5t,6t-1,2,3,4,5,6-hexakis-trimethylsilanyloxy-cyclohexane, C24H60O6Si6}, series = {Zeitschrift f{\"u}r Kristallographie : international journal for structural, physical and chemical aspects of crystalline materials ; New crystal structures}, volume = {226}, journal = {Zeitschrift f{\"u}r Kristallographie : international journal for structural, physical and chemical aspects of crystalline materials ; New crystal structures}, number = {2}, publisher = {De Gruyter Oldenbourg}, address = {M{\"u}nchen}, issn = {1433-7266}, doi = {10.1524/ncrs.2011.0105}, pages = {228 -- 230}, year = {2011}, abstract = {C24H60O6Si6, triclinic, P (1) over bar (no. 2), a = 11.307(2) angstrom, b = 12.159(2) angstrom, = 16.576(2) angstrom, alpha = 109.47(1)degrees, beta = 94.64(1)degrees, gamma = 111.65(1)degrees, V = 1942.3 angstrom(3), Z = 2, R-gt(F) = 0.043, wR(ref)(F-2) = 0.118, T = 210 K.}, language = {en} } @article{DavidCoyEnriqueCucaSefkow2011, author = {David Coy, Ericsson and Enrique Cuca, Luis and Sefkow, Michael}, title = {Pd-NHC catalyzed biaryl coupling by direct C-H Activation-A Novel strategy for the synthesis of dibenzocyclooctane lignans}, series = {Synthetic communications : an international journal for rapid communication of synthetic organic chemistry}, volume = {41}, journal = {Synthetic communications : an international journal for rapid communication of synthetic organic chemistry}, number = {1}, publisher = {Taylor \& Francis Group}, address = {Philadelphia}, issn = {0039-7911}, doi = {10.1080/00397910903531755}, pages = {41 -- 51}, year = {2011}, abstract = {Cross-coupling reactions, such as Buchwald-Hartwig arylamination and direct intramolecular biaryl coupling by C-H activation, were carried out using various Palladium-N-heterocyclic carbenes (Pd-NHC) as catalysts. The yields were good to excellent. The latter strategy was adopted to transform two dibenzylbutane lignans, isolated from the leaves of Ocotea macrophylla (Lauraceae), into the corresponding dibenzocyclooctane lignans in good overall yields. Supplemental materials are available for this article. Go to the publisher's online edition of Synthetic Communications (R) to view the free supplemental file.}, language = {en} } @article{BresselPrevostAppavouetal.2011, author = {Bressel, Katharina and Prevost, Sylvain and Appavou, Marie-Sousai and Tiersch, Brigitte and Koetz, Joachim and Gradzielski, Michael}, title = {Phase behaviour and structure of zwitanionic mixtures of perfluorocarboxylates and tetradecyldimethylamine oxide-dependence on chain length of the perfluoro surfactant}, series = {Soft matter}, volume = {7}, journal = {Soft matter}, number = {23}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1744-683X}, doi = {10.1039/c1sm05618b}, pages = {11232 -- 11242}, year = {2011}, abstract = {Phase behaviour and the mesoscopic structure of zwitanionic surfactant mixtures based on the zwitterionic tetradecyldimethylamine oxide (TDMAO) and anionic lithium perfluoroalkyl carboxylates have been investigated for various chain lengths of the perfluoro surfactant with an emphasis on spontaneously forming vesicles. These mixtures were studied at a constant total concentration of 50 mM and characterised by means of dynamic light scattering (DLS), electric conductivity, small-angle neutron scattering (SANS), viscosity, and cryo-scanning electron microscopy (Cryo-SEM). No vesicles are formed for relatively short perfluoro surfactants. The extension of the vesicle phase becomes substantially larger with increasing chain length of the perfluoro surfactant, while at the same time the size of these vesicles increases. Head group interactions in these systems play a central role in the ability to form vesicles, as already protonating 10 mol\% of the TDMAO largely enhances the propensity for vesicle formation. The range of vesicle formation in the phase diagram is not only substantially enlarged but also extends to shorter perfluoro surfactants, where without protonation no vesicles would be formed. The size and polydispersity of the vesicles are related to the chain length of the perfluoro surfactant, the vesicles becoming smaller and more monodisperse with increasing perfluoro surfactant chain length. The ability of the mixed systems to form well-defined unilamellar vesicles accordingly can be controlled by the length of the alkyl chain of the perfluorinated surfactant and depends strongly on the charge conditions, which can be tuned easily by pH-variation.}, language = {en} } @article{WeissBoettcherLaschewsky2011, author = {Weiss, Jan and B{\"o}ttcher, Christoph and Laschewsky, Andr{\´e}}, title = {Self-assembly of double thermoresponsive block copolymers end-capped with complementary trimethylsilyl groups}, series = {Soft matter}, volume = {7}, journal = {Soft matter}, number = {2}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1744-683X}, doi = {10.1039/c0sm00531b}, pages = {483 -- 492}, year = {2011}, abstract = {A set of double thermoresponsive diblock copolymers poly(N-n-propylacrylamide)-block-poly(N-ethylacrylamide) (PNPAM-b-PNEAM) was synthesised by sequential reversible addition-fragmentation chain transfer (RAFT) polymerisations. Using a twofold trimethylsilyl (TMS)-labeled RAFT-agent, the relative size of the two blocks was varied. While soluble as unimers below 15 degrees C, all copolymers exhibited thermally induced two-step self-assembly in water, due to distinct lower critical solution temperature (LCST) phase transitions of PNPAM (around 20 degrees C) and PNEAM (around 70 degrees C). Their temperature-dependent self-organisation in dilute aqueous solution was studied by turbidimetry, dynamic light scattering, transmission electron microscopy, and (1)H NMR spectroscopy. The copolymers show distinct, two-step self-organisation behaviour with respect to transition temperatures, aggregate type and size, which can be correlated to the relative lengths of the low and high LCST blocks. For polymers having short blocks with low LCST, the first thermal transition induces the formation of individual micelles. Further heating above the second thermal transition results reversibly either in a shrink of the micelle size or in aggregation of the micelles, with hydrodynamic diameters below 250 nm. In contrast in the case of polymers having a long block with low LCST, the first thermal transition already leads to clusters of micelles, while the second thermal transition makes the clusters shrink. Noteworthy, the twofold TMS-labeled end groups report not only on the molar masses of the polymers, but can simultaneously serve as NMR-probes for the self-assembly process. The signal of the TMS-aryl end group displays a reversible temperature dependent, two-step splitting that is indicative of the self-organisation of the block copolymers.}, language = {en} } @misc{KitaTokarczykJungingerBelegrinouetal.2011, author = {Kita-Tokarczyk, Katarzyna and Junginger, Mathias and Belegrinou, Serena and Taubert, Andreas}, title = {Amphiphilic polymers at interfaces}, series = {Advances in polymer science}, volume = {242}, journal = {Advances in polymer science}, number = {1}, editor = {Muller, AHE and Borisov, O}, publisher = {Springer}, address = {Berlin}, isbn = {978-3-642-22297-9}, issn = {0065-3195}, doi = {10.1007/12_2010_58}, pages = {151 -- 201}, year = {2011}, abstract = {Self-assembly phenomena in block copolymer systems are attracting considerable interest from the scientific community and industry alike. Particularly interesting is the behavior of amphiphilic copolymers, which can self-organize into nanoscale-sized objects such as micelles, vesicles, or tubes in solution, and which form well-defined assemblies at interfaces such as air-liquid, air-solid, or liquid-solid. Depending on the polymer chemistry and architecture, various types of organization at interfaces can be expected, and further exploited for applications in nanotechnology, electronics, and biomedical sciences. In this article, we discuss the formation and characterization of Langmuir monolayers from various amphiphilic block copolymers, including chargeable and thus pH-responsivematerials. Solid-supported polymer films are reviewed in the context of alteration of surface properties by ultrathin polymer layers and the possibilities for application in tissue engineering, sensors and biomaterials. Finally, we focus on how organic and polymer monolayers influence the growth of inorganic materials. This is a truly biomimetic approach since Nature uses soft interfaces to control the nucleation, growth, and morphology of biominerals such as calcium phosphate, calcium carbonate, and silica.}, language = {en} } @article{AntoniouPashalidisGessneretal.2011, author = {Antoniou, Stella and Pashalidis, I. and Gessner, Andre and Kumke, Michael Uwe}, title = {The effect of humic acid on the formation and solubility of secondary solid phases (Nd(OH)CO3 and Sm(OH)CO3)}, series = {Radiochimica acta : international journal for chemical aspects of nuclear science and technology}, volume = {99}, journal = {Radiochimica acta : international journal for chemical aspects of nuclear science and technology}, number = {4}, publisher = {De Gruyter}, address = {Berlin}, issn = {0033-8230}, doi = {10.1524/ract.2011.1812}, pages = {217 -- 223}, year = {2011}, abstract = {The formation of secondary Ln(III) solid phases (e.g. Nd(OH)CO3 and Sm(OH)CO3) has been studied as a function of the humic acid (HA) concentration in 0.1 M NaClO4 aqueous solution and their solubility has been investigated in the neutral pH range (6.5-8) under normal atmospheric conditions. Nd(III) and Sm(III) were selected as analogues for trivalent lanthanide and actinide ions. The solid phases under investigation have been prepared by alkaline precipitation and characterized by TGA, ATR-FTIR, XRD, TRLFS, DR-UV-Vis and Raman spectroscopy, and solubility measurements. The spectroscopic data obtained indicate that Nd(OH)CO3 and Sm(OH)CO3 are stable and remain the solubility limiting solid phases even in the presence of increased HA concentration (0.5 g/L) in solution. Upon base addition in the Ln(III)-HA system decomplexation of the previously formed Ln(III)-humate complexes and precipitation of two distinct phases occurs, the inorganic (Ln(OH)CO3) and the organic phase (HA), which is adsorbed on the particle surface of the former. Nevertheless, HA affects the particle size of the solid phases. Increasing HA concentration results in decreasing crystallite size of the Nd(OH)CO3 and increasing crystallite size of the Sm(OH)CO3 solid phase, and affects inversely the solubility of the solid phases. However, this impact on the solid phase properties is expected to be of minor relevance regarding the chemical behavior and migration of trivalent lanthanides and actinides in the geosphere.}, language = {en} } @article{BullerLaschewskyLutzetal.2011, author = {Buller, Jens and Laschewsky, Andr{\´e} and Lutz, Jean-Francois and Wischerhoff, Erik}, title = {Tuning the lower critical solution temperature of thermoresponsive polymers by biospecific recognition}, series = {Polymer Chemistry}, volume = {2}, journal = {Polymer Chemistry}, number = {7}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1759-9954}, doi = {10.1039/c1py00001b}, pages = {1486 -- 1489}, year = {2011}, abstract = {A thermosensitive statistical copolymer based on oligo(ethylene glycol) methacrylates incorporating biotin was synthesized by free radical copolymerisation. The influence of added avidin on its thermoresponsive behaviour was investigated. The specific binding of avidin to the biotinylated copolymers provoked a marked increase of the lower critical solution temperature.}, language = {en} } @article{ZehmLaschewskyHeunemannetal.2011, author = {Zehm, Daniel and Laschewsky, Andr{\´e} and Heunemann, Peggy and Gradzielski, Michael and Prevost, Sylvain and Liang, Hua and Rabe, J{\"u}rgen P. and Lutz, Jean-Francois}, title = {Synthesis and self-assembly of amphiphilic semi-brush and dual brush block copolymers in solution and on surfaces}, series = {Polymer Chemistry}, volume = {2}, journal = {Polymer Chemistry}, number = {1}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1759-9954}, doi = {10.1039/c0py00200c}, pages = {137 -- 147}, year = {2011}, abstract = {The combination of two techniques of controlled free radical polymerization, namely the reversible addition fragmentation chain transfer (RAFT) and the atom transfer radical polymerization (ATRP) techniques, together with the use of a macromonomer allowed the synthesis of symmetrical triblock copolymers, designed as amphiphilic dual brushes. One type of brush was made of poly(n-butyl acrylate) as soft hydrophobic block, i.e. characterized by a low glass transition temperature, while the other one was made of hydrophilic poly(ethylene glycol) (PEG). The new triblock polymers represent "giant surfactants" according to their molecular architecture. The hydrophobic and hydrophilic blocks microphase separate in the bulk. In aqueous solution, they aggregate into globular micellar aggregates, their size being determined by the length of the stretched polymer molecules. As determined by the combination of various scattering techniques for the dual brush copolymer, a rather compact structure is formed, which is dominated by the large hydrophobic poly(n-butyl acrylate) block. The aggregation number for the dual brush is about 10 times larger than for the "semi-brush" precursor copolymer, due to the packing requirements for the much bulkier hydrophobic core. On mica surfaces the triblock copolymers adsorb with worm-like backbones and stretched out side chains.}, language = {en} } @article{UtechtKlamrothSaalfrank2011, author = {Utecht, Manuel Martin and Klamroth, Tillmann and Saalfrank, Peter}, title = {Optical absorption and excitonic coupling in azobenzenes forming self-assembled monolayers a study based on density functional theory}, series = {Physical chemistry, chemical physics : a journal of European Chemical Societies}, volume = {13}, journal = {Physical chemistry, chemical physics : a journal of European Chemical Societies}, number = {48}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1463-9076}, doi = {10.1039/c1cp22793a}, pages = {21608 -- 21614}, year = {2011}, abstract = {Based on the analysis of optical absorption spectra, it has recently been speculated that the excitonic coupling between individual azobenzene-functionalized alkanethiols arranged in a self-assembled monolayer (SAM) on a gold surface could be strong enough to hinder collective trans-cis isomerization-on top of steric hindrance [Gahl et al., J. Am. Chem. Soc., 2010, 132, 1831]. Using models of SAMs of increasing complexity (dimer, linear N-mers, and two-dimensionally arranged N-mers) and density functional theory on the (TD-) B3LYP/6-31G* level, we determine optical absorption spectra, the nature and magnitude of excitonic couplings, and the corresponding spectral shifts. It is found that at inter-monomer distances of about 20 angstrom and above, TD-B3LYP excitation frequencies (and signal intensities) can be well described by the frequently used point-dipole approximation. Further, calculated blue shifts in optical absorption spectra account for the experimental observations made for azobenzene/gold SAMs, and hint to the fact that they can indeed be responsible for reduced switching probability in densely packed self-assembled structures.}, language = {en} } @article{KleinpeterKoch2011, author = {Kleinpeter, Erich and Koch, Andreas}, title = {Chelatoaromaticity-existing: yes or no? An answer given by spatial magnetic properties (through space NMR shieldings-TSNMRS)}, series = {Physical chemistry, chemical physics : a journal of European Chemical Societies}, volume = {13}, journal = {Physical chemistry, chemical physics : a journal of European Chemical Societies}, number = {46}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1463-9076}, doi = {10.1039/c1cp21942a}, pages = {20593 -- 20601}, year = {2011}, abstract = {The spatial magnetic properties (through space NMR shieldings-TSNMRS) of metal complexes (with ligands such as acetylacetone, 3-hydroxy-pyran(4) one) and "metallobenzenes" have been calculated by the GIAO perturbation method and visualized as Iso-Chemical-Shielding Surfaces (ICSS) of various sizes and directions. The TSNMRS values, thus obtained, can be successfully employed to quantify and visualize partial aromaticity of the metallocyclic ring by comparison with the spatial magnetic properties of the corresponding non-complexed ligands in comparable structural and electronic situations, and benzene, respectively. Because anisotropy/ring current effects in H-1 NMR spectra proved to be the molecular response property of TSNMRS, the results obtained concerning partial "chelatoaromaticity" are experimentally ensured.}, language = {en} } @article{TiseanuParvulescuBoutonnetetal.2011, author = {Tiseanu, Carmen and Parvulescu, Vasile I. and Boutonnet, Magali and Cojocaru, Bogdan and Primus, Philipp A. and Teodorescu, Cristian M. and Solans, Conchita and Sanchez Dominguez, Margarita}, title = {Surface versus volume effects in luminescent ceria nanocrystals synthesized by an oil-in-water microemulsion method}, series = {Physical chemistry, chemical physics : a journal of European Chemical Societies}, volume = {13}, journal = {Physical chemistry, chemical physics : a journal of European Chemical Societies}, number = {38}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1463-9076}, doi = {10.1039/c1cp21135h}, pages = {17135 -- 17145}, year = {2011}, abstract = {Pure and europium (Eu3+) doped cerium dioxide (CeO2) nanocrystals have been synthesized by a novel oil-in-water microemulsion reaction method under soft conditions. In-situ X-ray diffraction and RAMAN spectroscopy, high-resolution transmission electron microscopy, UV/Vis diffuse-reflectance and Fourier transform infrared spectroscopy as well as time-resolved photoluminescence spectroscopy were used to characterize the nanaocrystals. The as-synthesized powders are nanocrystalline and have a narrow size distribution centered on 3 nm and high surface area of similar to 250 m(2) g(-1). Only a small fraction of the europium ions substitutes for the bulk, cubic Ce4+ sites in the europium-doped ceria nanocrystals. Upon calcination up to 1000 degrees C, a remarkable high surface area of similar to 120 m(2) g (-1) is preserved whereas an enrichment of the surface Ce4+ relative to Ce3+ ions and relative strong europium emission with a lifetime of similar to 1.8 ms and FWHM as narrow as 10 cm(-1) are measured. Under excitation into the UV and visible spectral range, the europium doped ceria nanocrystals display a variable emission spanning the orange-red wavelengths. The tunable emission is explained by the heterogeneous distribution of the europium dopants within the ceria nanocrystals coupled with the progressive diffusion of the europium ions from the surface to the inner ceria sites and the selective participation of the ceria host to the emission sensitization. Effects of the bulk-doping and impregnation with europium on the ceria host structure and optical properties are also discussed.}, language = {en} } @article{ThielKlamrothStrauchetal.2011, author = {Thiel, Kerstin and Klamroth, Tillmann and Strauch, Peter and Taubert, Andreas}, title = {On the interaction of ascorbic acid and the tetrachlorocuprate ion [CuCl4](2-) in CuCl nanoplatelet formation from an ionic liquid precursor (ILP)}, series = {Physical chemistry, chemical physics : a journal of European Chemical Societies}, volume = {13}, journal = {Physical chemistry, chemical physics : a journal of European Chemical Societies}, number = {30}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1463-9076}, doi = {10.1039/c1cp20648f}, pages = {13537 -- 13543}, year = {2011}, abstract = {The formation of CuCl nanoplatelets from the ionic liquid precursor (ILP) butylpyridinium tetrachlorocuprate [C4Py](2)[CuCl4] using ascorbic acid as a reducing agent was investigated. In particular, electron paramagnetic resonance (EPR) spectroscopy was used to evaluate the interaction between ascorbic acid and the Cu(II) ion before reduction to Cu(I). EPR spectroscopy suggests that the [CuCl4](2-) ion in the neat IL is a distorted tetrahedron, consistent with DFT calculations. Addition of ascorbic acid leads to the removal of one chloride from the [CuCl4](2-) anion, as shown by DFT and the loss of symmetry by EPR. DFT furthermore suggests that the most stable adduct is formed when only one hydroxyl group of the ascorbic acid coordinates to the Cu(II) ion.}, language = {en} } @article{DodooSteitzLaschewskyetal.2011, author = {Dodoo, S. and Steitz, R. and Laschewsky, Andr{\´e} and von Klitzing, Regine}, title = {Effect of ionic strength and type of ions on the structure of water swollen polyelectrolyte multilayers}, series = {Physical chemistry, chemical physics : a journal of European Chemical Societies}, volume = {13}, journal = {Physical chemistry, chemical physics : a journal of European Chemical Societies}, number = {21}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1463-9076}, doi = {10.1039/c0cp01357a}, pages = {10318 -- 10325}, year = {2011}, abstract = {This study addresses the effect of ionic strength and type of ions on the structure and water content of polyelectrolyte multilayers. Polyelectrolyte multilayers of poly(sodium-4-styrene sulfonate) (PSS) and poly(diallyl dimethyl ammonium chloride) (PDADMAC) prepared at different NaF, NaCl and NaBr concentrations have been investigated by neutron reflectometry against vacuum, H2O and D2O. Both thickness and water content of the multilayers increase with increasing ionic strength and increasing ion size. Two types of water were identified, "void water" which fills the voids of the multilayers and does not contribute to swelling but to a change in scattering length density and "swelling water" which directly contributes to swelling of the multilayers. The amount of void water decreases with increasing salt concentration and anion radius while the amount of swelling water increases with salt concentration and anion radius. This is interpreted as a denser structure in the dry state and larger ability to swell in water (sponge) for multilayers prepared from high ionic strengths and/or salt solution of large anions. No exchange of hydration water or replacement of H by D was detected even after eight hours incubation time in water of opposing isotopic composition.}, language = {en} } @article{FuechselKlamrothMonturetetal.2011, author = {F{\"u}chsel, Gernot and Klamroth, Tillmann and Monturet, Serge and Saalfrank, Peter}, title = {Dissipative dynamics within the electronic friction approach the femtosecond laser desorption of H-2/D-2 from Ru(0001)}, series = {Physical chemistry, chemical physics : a journal of European Chemical Societies}, volume = {13}, journal = {Physical chemistry, chemical physics : a journal of European Chemical Societies}, number = {19}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1463-9076}, doi = {10.1039/c0cp02086a}, pages = {8659 -- 8670}, year = {2011}, abstract = {An electronic friction approach based on Langevin dynamics is used to describe the multidimensional (six-dimensional) dynamics of femtosecond laser induced desorption of H-2 and D-2 from a H(D)-covered Ru(0001) surface. The paper extends previous reduced-dimensional models, using a similar approach. In the present treatment forces and frictional coefficients are calculated from periodic density functional theory (DFT) and essentially parameter-free, while the action of femtosecond laser pulses on the metal surface is treated by using the two-temperature model. Our calculations shed light on the performance and validity of various adiabatic, non-adiabatic, and Arrhenius/Kramers type kinetic models to describe hot-electron mediated photoreactions at metal surfaces. The multidimensional frictional dynamics are able to reproduce and explain known experimental facts, such as strong isotope effects, scaling of properties with laser fluence, and non-equipartitioning of vibrational, rotational, and translational energies of desorbing species. Further, detailed predictions regarding translations are made, and the question for the controllability of photoreactions at surfaces with the help of vibrational preexcitation is addressed.}, language = {en} } @article{BartlettJankunasGoswamietal.2011, author = {Bartlett, Nate C. -M. and Jankunas, Justin and Goswami, Tapas and Zare, Richard N. and Bouakline, Foudhil and Althorpe, Stuart C.}, title = {Differential cross sections for H + D-2 -> HD(v '=2, j '=0,3,6,9) + D at center-of-mass collision energies of 1.25, 1.61, and 1.97 eV}, series = {Physical chemistry, chemical physics : a journal of European Chemical Societies}, volume = {13}, journal = {Physical chemistry, chemical physics : a journal of European Chemical Societies}, number = {18}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1463-9076}, doi = {10.1039/c0cp02460k}, pages = {8175 -- 8179}, year = {2011}, abstract = {We have measured differential cross sections (DCSs) for the reaction H + D-2 -> HD- (v' = 2, j' = 0,3,6,9) + D at center-of-mass collision energies E-coll of 1.25, 1.61, and 1.97 eV using the photoloc technique. The DCSs show a strong dependence on the product rotational quantum number. For the HD(v' = 2, j' = 0) product, the DCS is bimodal but becomes oscillatory as the collision energy is increased. For the other product states, they are dominated by a single peak, which shifts from back to sideward scattering as j' increases, and they are in general less sensitive to changes in the collision energy. The experimental results are compared to quantum mechanical calculations and show good, but not fully quantitative agreement.}, language = {en} } @article{HorschUrbaschWeitzeletal.2011, author = {Horsch, Philipp and Urbasch, Gunter and Weitzel, Karl-Michael and Kroener, Dominik}, title = {Circular dichroism in ion yields employing femtosecond laser ionization-the role of laser pulse duration}, series = {Physical chemistry, chemical physics : a journal of European Chemical Societies}, volume = {13}, journal = {Physical chemistry, chemical physics : a journal of European Chemical Societies}, number = {6}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1463-9076}, doi = {10.1039/c0cp01903h}, pages = {2378 -- 2386}, year = {2011}, abstract = {The circular dichroism (CD) induced by femtosecond laser pulse excitation of 3-methylcyclopentanone has been investigated by means of experiment and theory as a function of the laser pulse duration. In the experiment the CD in ion yields is measured by femtosecond laser ionization via a one-photon resonant excited state. In the theoretical part the CD is calculated by solving laser driven quantum electron dynamics for the same resonant excitation based on ab initio electronic structure calculations employing a complete description of the electric field-electric dipole and magnetic field-magnetic dipole interactions. Both the experimentally measured CD in ion yields and the calculated CD in excited state populations exhibit a marked increase of the CD for pulse duration increasing from 50 fs to about 200 fs. Beyond 200 fs pulse duration the CD levels off. The combination of experimental and theoretical evidences indicates that the CD decreases with increasing laser intensity connected to the increased coupling between the excited states.}, language = {en} } @article{WessigMatthesPick2011, author = {Wessig, Pablo and Matthes, Annika and Pick, Charlotte}, title = {The photo-dehydro-Diels-Alder (PDDA) reaction}, series = {Organic \& biomolecular chemistry : an international journal of synthetic, physical and biomolecular organic chemistry}, volume = {9}, journal = {Organic \& biomolecular chemistry : an international journal of synthetic, physical and biomolecular organic chemistry}, number = {22}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1477-0520}, doi = {10.1039/c1ob06066j}, pages = {7599 -- 7605}, year = {2011}, abstract = {The photo-dehydro-Diels-Alder (PDDA) reaction is a valuable extension of the classical Diels-Alder (DA) reaction. The PDDA reaction differs from the DA reaction by the replacement of one of the C-C-double bonds of the diene moiety by a C-C triple bond and by the photochemical triggering of the reaction. This entails that, in contrast to the DA reaction, the PDDA reaction proceeds according to a multistage mechanism with biradicals and cycloallenes as intermediates. The PDDA reaction provides access to a considerable variety of compound classes. For example, 1-phenylnaphthlenes, 1,1'-binaphthyls, N-heterocyclic biaryls, and naphthalenophanes could be obtained by this reaction.}, language = {en} } @article{SchmidtHoelter2011, author = {Schmidt, Bernd and H{\"o}lter, Frank}, title = {Suzuki-Miyaura cross coupling reactions with Phenoldiazonium salts}, series = {Organic \& biomolecular chemistry : an international journal of synthetic, physical and biomolecular organic chemistry}, volume = {9}, journal = {Organic \& biomolecular chemistry : an international journal of synthetic, physical and biomolecular organic chemistry}, number = {13}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1477-0520}, doi = {10.1039/c1ob05256j}, pages = {4914 -- 4920}, year = {2011}, abstract = {The Suzuki-Miyaura coupling of phenol diazonium salts and aryl trifluoroborates yields 4-hydroxybiaryls in a protecting group-free synthesis.}, language = {en} } @article{MantionGrafFloreaetal.2011, author = {Mantion, Alexandre and Graf, Philipp and Florea, Ileana and Haase, Andrea and Thuenemann, Andreas F. and Masic, Admir and Ersen, Ovidiu and Rabu, Pierre and Meier, Wolfgang P. and Luch, Andreas and Taubert, Andreas}, title = {Biomimetic synthesis of chiral erbium-doped silver/peptide/silica core-shell nanoparticles (ESPN)}, series = {Nanoscale}, volume = {3}, journal = {Nanoscale}, number = {12}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {2040-3364}, doi = {10.1039/c1nr10930h}, pages = {5168 -- 5179}, year = {2011}, abstract = {Peptide-modified silver nanoparticles have been coated with an erbium-doped silica layer using a method inspired by silica biomineralization. Electron microscopy and small-angle X-ray scattering confirm the presence of an Ag/peptide core and silica shell. The erbium is present as small Er(2)O(3) particles in and on the silica shell. Raman, IR, UV-Vis, and circular dichroism spectroscopies show that the peptide is still present after shell formation and the nanoparticles conserve a chiral plasmon resonance. Magnetic measurements find a paramagnetic behavior. In vitro tests using a macrophage cell line model show that the resulting multicomponent nanoparticles have a low toxicity for macrophages, even on partial dissolution of the silica shell.}, language = {en} } @article{XieWhiteWeberetal.2011, author = {Xie, Zai-Lai and White, Robin J. and Weber, Jens and Taubert, Andreas and Titirici, Magdalena M.}, title = {Hierarchical porous carbonaceous materials via ionothermal carbonization of carbohydrates}, series = {Journal of materials chemistry}, volume = {21}, journal = {Journal of materials chemistry}, number = {20}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {0959-9428}, doi = {10.1039/c1jm00013f}, pages = {7434 -- 7442}, year = {2011}, abstract = {We report on the ionothermal synthesis of porous carbon materials from a variety of carbohydrate precursors (i.e. D-glucose, D-fructose, D-xylose, and starch) using 1-butyl-3-methylimidazolium tetrachloroferrate(III), [Bmim][FeCl(4)] as a reusable solvent and catalyst. The carbon materials derived from these different carbohydrates are similar in terms of particle size and chemical composition, possessing relatively high surface areas from 44 to 155 m(2) g(-1) after ionothermal processing, which can be significantly increased to > 350 m(2) g(-1) by further thermal treatment (e. g. post-carbonization at 750 degrees C). CO(2) and N(2) sorption analysis, combined with Hg intrusion porosimetry, reveals a promising hierarchical pore structuring to these carbon materials. The ionic liquid [Bmim][FeCl(4)] has a triple role: it acts as both a soft template to generate the characterized pore structuring, solvent and as a catalyst resulting in enhanced ionothermal carbon yields. Importantly from a process point of view, the ionic liquid can be successfully recovered and reused. The current work shows that ionothermal synthesis has the potential to be an effective, low cost, and green reusable synthetic route towards sustainable porous carbon materials.}, language = {en} }