Co-reporter:Peirong Chen, Abhishek Khetan, Fengkai Yang, Vadim Migunov, Philipp Weide, Sascha P. Stürmer, Penghu Guo, Kevin Kähler, Wei Xia, Joachim Mayer, Heinz Pitsch, Ulrich Simon, and Martin Muhler
ACS Catalysis February 3, 2017 Volume 7(Issue 2) pp:1197-1197
Publication Date(Web):December 21, 2016
DOI:10.1021/acscatal.6b02963
By doping the TiO2 support with nitrogen, strong metal–support interactions (SMSI) in Pd/TiO2 catalysts can be tailored to obtain high-performance supported Pd nanoparticles (NPs) in nitrobenzene (NB) hydrogenation catalysis. According to the comparative studies by X-ray diffraction, X-ray photoelectron spectroscopy (XPS), and diffuse reflectance CO FTIR (CO–DRIFTS), N-doping induced a structural promoting effect, which is beneficial for the dispersion of Pd species on TiO2. High-angle annular dark-field scanning transmission electron microscopy study of Pd on N-doped TiO2 confirmed a predominant presence of sub-2 nm Pd NPs, which are stable under the applied hydrogenation conditions. XPS and CO–DRIFTS revealed the formation of strongly coupled Pd–N species in Pd/TiO2 with N-doped TiO2 as support. Density functional theory (DFT) calculations over model systems with Pdn (n = 1, 5, or 10) clusters deposited on TiO2(101) surface were performed to verify and supplement the experimental observations. In hydrogenation catalysis using NB as a model molecule, Pd NPs on N-doped TiO2 outperformed those on N-free TiO2 in terms of both catalytic activity and stability, which can be attributed to the presence of highly dispersed Pd NPs providing more active sites, and to the formation of Pd–N species favoring the dissociative adsorption of the reactant NB and the easier desorption of the product aniline.Keywords: DFT calculations; hydrogenation; nitrogen doping; palladium nanoparticles; strong metal−support interactions; TiO2;
Co-reporter:J. Ruff, S. Hüwel, Marcelo J. Kogan, Ulrich Simon, Hans-Joachim Galla
Nanomedicine: Nanotechnology, Biology and Medicine 2017 Volume 13, Issue 5(Issue 5) pp:
Publication Date(Web):1 July 2017
DOI:10.1016/j.nano.2017.02.013
We studied the effect of gold nanoparticle (AuNP) size, surface charge, concentration and morphology on the integrity of the blood–brain barrier (BBB) in a well-established in vitro model set-up. We focused on the effect of peptide functionalized hollow gold nanospheres and gold nanorods, which selectively bind to amyloidogenic β-amyloid structures. These AuNP conjugates have already been successfully tested as photothermal absorbers for potential application in Alzheimer's disease (AD) therapy in an in vitro set-up, but may exhibit a low passage through the BBB due to their overall negative charge. Our results show that: (i) small (1.4 nm) AuNPs strongly affects the BBB integrity, (ii) negative surface charge impedes BBB passage, and (iii) this charge effect caused by the peptide is compensated by covalent coupling to a polyethylene glycol ligand stabilizing the particles in diluted manner.Gold nanoparticles (AuNP) of different size, surface charge, and morphology affect the integrity and thereby the complex electrical impedance of a model blood–brain barrier (BBB) in a different manner. Negative surface charge impedes BBB passage of the particles. This can be compensated by introducing polyethylene glycol ligands, which allows BBB transfer of peptides bound to the AuNP, which selectively can bind to amyloidogenic β-Amyloid structures.Download high-res image (47KB)Download full-size image
Co-reporter:Peirong Chen, Magdalena Jabłońska, Philipp Weide, Tobias Caumanns, Thomas Weirich, Martin Muhler, Ralf Moos, Regina Palkovits, and Ulrich Simon
ACS Catalysis 2016 Volume 6(Issue 11) pp:7696
Publication Date(Web):October 10, 2016
DOI:10.1021/acscatal.6b02496
With the help of a technique combining in situ electrical impedance spectroscopy and DRIFT spectroscopy, we observed directly the formation of ammonium ion (NH4+) intermediates resulting from the interaction of NO and NH3 on Fe-ZSM-5 catalysts for selective catalytic reduction by NH3 (NH3–SCR). The formed NH4+ intermediates, indicating the activation of NO in the presence of adsorbed NH3, were found to be strongly related to the NH3–SCR activity of Fe-ZSM-5 catalysts at low temperatures. These findings, which are not easily achievable by conventional methods, provide new and important perspectives to understand mechanistically the NH3–SCR reaction over Fe-zeolite catalysts.Keywords: ammonium ion intermediates; NH3−SCR mechanism; NO activation; proton transport; redox cycle
Co-reporter:J. Ruff, J. Steitz, A. Buchkremer, M. Noyong, H. Hartmann, A. Besmehn and U. Simon
Journal of Materials Chemistry A 2016 vol. 4(Issue 16) pp:2828-2841
Publication Date(Web):24 Mar 2016
DOI:10.1039/C6TB00674D
In this work the effect of multivalency on the stability of NIR-absorbing HAuNSs and AuNRs functionalized by mono-, bi- and tridentate polyethyleneglycol (PEG) thiol ligands is reported. Comparison of commercially-available monodentate and self-synthesized bi- and tridentate methoxy terminated thiol-polyethyleneglycol ligands having molecular weights of around 5000 Da shows the stability increase of HAuNSs and AuNRs for bi- and tridentate ligands, attributed to the multivalency of the ligands. The stability was explored according to three different aspects: (1) stability towards competition reactions with the strong binding ligand dithiothreitol, (2) resistance towards oxidative Au dissolution with potassium cyanide, and (3) colloidal stability, tested by the addition of NaCl. Our PEGylation approach leads to AuNRs where the CTAB concentration is below the detection limit of the performed analytical methods, which is vital for any clinical applications. Furthermore, we found strikingly high biocompatibility after PEGylation for both particle types whereby we observed no significant difference in cytotoxicity comparing the mono-, bi- and tridentate PEGylated species.
Co-reporter:Peirong Chen, Dieter Rauch, Philipp Weide, Simon Schönebaum, Thomas Simons, Martin Muhler, Ralf Moos and Ulrich Simon
Catalysis Science & Technology 2016 vol. 6(Issue 10) pp:3362-3366
Publication Date(Web):20 Apr 2016
DOI:10.1039/C6CY00452K
Proton transport studies revealed the different influence of Fe and Cu cations on the NH3–zeolite interaction and the NO–zeolite interaction in the presence of adsorbed NH3. At low temperatures, after NH3 saturation, Cu-ZSM-5 is more reactive than Fe-ZSM-5 for NO activation forming highly mobile NH4+ intermediates.
Co-reporter:Benjamin S. Gutrath;Frank Schiefer;Melanie Homberger;Ulli Englert;Mihaela-D. &x15e;erb;Wolfgang Bettray;Igor Beljakov;Velimir Meded;Wolfgang Wenzel
European Journal of Inorganic Chemistry 2016 Volume 2016( Issue 7) pp:975-981
Publication Date(Web):
DOI:10.1002/ejic.201501334
Abstract
We present a detailed structural discussion of [Au8(PPh3)8](NO3)2, crystallized as a CH2Cl2 solvate. Its structure is compared with closely related triphenylphosphine-stabilized gold clusters. Characterization by optical extinction spectroscopy, luminescence spectroscopy, voltammetry and DFT calculations was performed to determine the electronic HOMO–LUMO gap. Comparison of its characteristic energies with those of structurally related clusters revealed that the evolution of the HOMO–LUMO gap does not follow a simple scaling law but depends on specific structural features.
Co-reporter:Thomas Simons, Peirong Chen, Dieter Rauch, Ralf Moos, Ulrich Simon
Sensors and Actuators B: Chemical 2016 Volume 224() pp:492-499
Publication Date(Web):1 March 2016
DOI:10.1016/j.snb.2015.10.069
•In situ measurements by simultaneous DRIFTS and impedance spectroscopy.•Correlation of the change in proton conductivity with differently adsorbed NH3 species in zeolites.•Assessment of the loading and SCR conversion of NH3 within zeolite catalysts in situ by impedance spectroscopy.In order to meet the legislative emission requirements for NOx-containing exhaust gases, SCR catalysts, in particular zeolites, are used. To improve catalysts and the catalytic processes, an in-depth understanding of the reaction mechanisms is required as well as an analysis of the physicochemical properties of the SCR catalysts, preferably in real-time. Here, we introduce a setup combining impedance spectroscopy and infrared spectroscopy in diffuse reflection mode for in situ measurements on zeolites under SCR-related conditions. This setup allows for the first time to simultaneously monitor both, the proton conductivity of zeolites and the vibration modes of the molecules involved in the catalytic conversion of NO by NH3. We studied both, pure and Fe-promoted H-form zeolites, as sensors and model catalysts at the same time, and found out that weakly bound NH3 is dominating the proton conductivity of both zeolites in a temperature range below the desorption temperature of NH3. When a part of the weakly bound NH3 is consumed by the SCR reaction, proton conductivity and thus the sensing effect gets dominated by strongly bound NH3. This allows applying impedance spectroscopy to assess the degree of NH3 loading and the state of the SCR conversion process in zeolite catalyst.
Co-reporter:Anne Buchkremer ; Malte J. Linn ; Jan U. Timper ; Thomas Eckert ; Joachim Mayer ; Walter Richtering ; Gero von Plessen
The Journal of Physical Chemistry C 2014 Volume 118(Issue 13) pp:7174-7184
Publication Date(Web):March 4, 2014
DOI:10.1021/jp412283q
Spatially defined networks of 15 nm-sized DNA-functionalized gold nanoparticles (DNA–AuNPs) were studied using dynamic light scattering (DLS), small-angle X-ray scattering (SAXS), as well as optical extinction spectroscopy (OES). We use a combination of these techniques with Monte Carlo simulations of pair-distance distribution function (PDDF) curves and generalized Mie theory simulations as well as in situ-transmission electron microscopy (in situ-TEM) to analyze the internal structure of the finite-size assemblies. The DLS data show that monodisperse, spherical networks with hydrodynamic radii of ca. 30 nm are found for reaction mixtures of complementarily functionalized DNA–AuNPs between 1:15 and 1:20. Different interparticle distances within these assemblies are identified and quantified. By controlling the network morphology through selection of the reaction mixture, center-shell geometries are obtained. The number of shell-AuNPs surrounding each center-AuNP is determined from the SAXS data and Monte Carlo simulations. This number is quantified to be ca. 10, with the exact number depending on the linking DNA double strand. The optical spectra of the networks are found to be consistent with the structural properties. The structural information gained here enables a quantitative description of optical and other physical properties, which is expected to prove useful for the construction and application of such systems, for example, in drug release, gene regulation, or external-stimuli-responsive materials.
Co-reporter:Ninet Babajani ; Corinna Kaulen ; Melanie Homberger ; Max Mennicken ; Rainer Waser ; Ulrich Simon ;Silvia Karthäuser
The Journal of Physical Chemistry C 2014 Volume 118(Issue 46) pp:27142-27149
Publication Date(Web):October 27, 2014
DOI:10.1021/jp5085179
Forming reliable and reproducible molecule–nanoelectrode contacts is one of the key issues for the implementation of nanoparticles as functional units into nanoscale devices. Utilizing heterometallic electrodes and Janus-type nanoparticles equipped with molecules allowing selective binding to a distinct electrode material represents a promising approach to achieve this goal. Here, the directed immobilization of individual Janus-type gold nanoparticles (AuNP) between heterometallic electrodes leading to the formation of asymmetric contacts in a highly controllable way is presented. The Janus-AuNP are stabilized by two types of ligands with different terminal groups on opposite hemispheres. The heterometallic nanoelectrode gaps are formed by electron beam lithography in combination with a self-alignment procedure and are adjusted to the size of the Janus-AuNP. Thus, by choosing adequate molecular end group/metal combinations, the immobilization direction of the Janus-AuNP is highly controllable. These results demonstrate the striking potential of this approach for the building-up of novel nanoscale organic/inorganic hybrid architectures.
Co-reporter:Corinna Kaulen, Melanie Homberger, Svenja Bourone, Ninet Babajani, Silvia Karthäuser, Astrid Besmehn, and Ulrich Simon
Langmuir 2014 Volume 30(Issue 2) pp:574-583
Publication Date(Web):2017-2-22
DOI:10.1021/la404110y
Integration of molecule-capped gold nanoparticles (AuNP) into nanoelectronic devices requires detailed knowledge about the AuNP–electrode interface. Here, we report the pH-dependent adsorption of amine or carboxylic acid-terminated gold nanoparticles on platinum or gold/palladium (30% Pd) alloy, respectively. We synthesized amine-terminated AuNP, applying a new solid phase supported approach, as well as AuNP exhibiting carboxylic acid as terminal groups. The pH-induced agglomeration of the synthesized AuNP was investigated by UV–vis, DLS, and ζ-potential measurements. Depending on the pH and the ionic strength of the AuNP solution a preferential adsorption on the different metals occurred. Thereby, we demonstrate that by choosing the appropriate functional group and adjusting the pH as well as the ionic strength a directed binding can be achieved, which is an essential prerequisite for applications of these particles in nanoelectronics. These findings will pave the way for a controlled designing of the interface between molecule-capped AuNP and metallic electrodes for applications in nanoelectronics.
Co-reporter:Clemens J. Belle, Günter E. Wesch, Stefan Neumeier, M. Janeth Lozano-Rodríguez, Andreas C. Scheinost, Ulrich Simon
Sensors and Actuators B: Chemical 2014 192() pp: 60-69
Publication Date(Web):
DOI:10.1016/j.snb.2013.10.094
Co-reporter:Annika Leifert, Yu Pan-Bartnek, Ulrich Simon and Willi Jahnen-Dechent
Nanoscale 2013 vol. 5(Issue 14) pp:6224-6242
Publication Date(Web):08 May 2013
DOI:10.1039/C3NR00916E
Gold nanoparticles (AuNPs) are widely used as contrast agents in electron microscopy as well as for diagnostic tests. Due to their unique optical and electrical properties and their small size, there is also a growing field of potential applications in medical fields of imaging and therapy, for example as drug carriers or as active compounds in thermotherapy. Besides their intrinsic optical properties, facile surface decoration with (bio)functional ligands renders AuNPs ideally suited for many industrial and medical applications. However, novel AuNPs may have toxicological profiles differing from bulk and therefore a thorough analysis of the quantitative structure–activity relationship (QSAR) is required. Several mechanisms are proposed that cause adverse effects of nanoparticles in biological systems. Catalytic generation of reactive species due to the large and chemically active surface area of nanomaterials is well established. Because nanoparticles approach the size of biological molecules and subcellular structures, they may overcome natural barriers by active or passive uptake. Ultrasmall AuNPs with sizes of 2 nm or less may even behave as molecular ligands. These types of potential interactions would imply a size and ligand-dependent behaviour of any nanomaterial towards biological systems. Thus, to fully understand their QSAR, AuNPs bioactivity should be analysed in biological systems of increasing complexity ranging from cell culture to whole animal studies.
Co-reporter:Sandra Gilles, André Tuchscherer, Heinrich Lang, Ulrich Simon
Journal of Colloid and Interface Science 2013 Volume 406() pp:256-262
Publication Date(Web):15 September 2013
DOI:10.1016/j.jcis.2013.05.047
•Silver dots are fabricated by dip-pen nanolithography.•Silver(I) carboxylate in diethylene glycol is used as precursor ink.•Parameters such as substrate functionalization and ink composition are investigated.•Structure sizes range from ∼20 μm to ∼2 μm.•Metallic conductivity of generated structures is proven.Direct fabrication of micro- and nanoscale metallic structures is advantageous for many applications. Here, we use dip-pen lithography with silver(I) carboxylate [AgO2C(CH2OCH2)3H] in diethylene glycol as precursor ink for the generation of conducting metal structures. After annealing the written dots, solid silver structures are generated. We investigate the influence of several parameters such as substrate functionalization and ink composition on the pattern formation. We found that a substrate coating with perfluorinated silane is necessary, if diethylene glycol will be used as ink carrier. By variation in ink concentration and ink carrier composition, structures with diameters ranging from ∼20 μm to ∼2 μm and with metal fractions ranging from ∼5% to ∼80% were fabricated. After gold enhancement of the written patterns, resistivities in the range of 4 × 10−5 Ωm on the structures were determined. The ink system introduced here appears promising for the direct fabrication of various metal or metal oxide patterns.Graphical abstract
Co-reporter:Benjamin S. Gutrath;Ulli Englert;Yutian Wang
European Journal of Inorganic Chemistry 2013 Volume 2013( Issue 12) pp:2002-2006
Publication Date(Web):
DOI:10.1002/ejic.201300148
Abstract
Because of quantum-size effects, molecular gold clusters are promising materials for applications in nanoscience and nanotechnology. Owing to the feasible synthesis of Au11 species out of [Au(PPh3)Cl], this material is the subject of many investigations, although its full crystal structure including the ligand shell remained unknown. We have been able to obtain the solid-state structure at atomic resolution, even for the cocrystallized solvent molecules: The composition of the red crystals corresponds to [Au11(PPh3)7Cl3]·CH2Cl2·1.5{(CH3CH2)2O}. The gold atoms in the cluster subtend a core of almost C3v symmetry derived from a centered icosahedron, which is present in most Au11 species. The mean Au–Au distance amounts to 2.8076 Å and the mean Au–Cl distance to 2.3730 Å; both are in good agreement with comparable data in structurally characterized gold clusters. The mean core diameter, measured between the centers of the gold atoms of opposite sides of the cluster, is about 4.9 Å, and the overall van der Waals diameter can be estimated to 19.8 Å. The optical absorbance of [Au11(PPh3)7Cl3] in solution reveals characteristic peaks at 318 and 406 nm and a shoulder between 450 and 550 nm. The peak at 406 nm and the shoulder can also be resolved for the solid. The energy of the first optically active electron transition of ca. 2.0 eV is very close to the theoretically derived data of the HOMO–LUMO gap. In accordance with the literature, only one singlet in the 31P{1H} NMR spectrum is found at δ = 52 ppm, even at –80 °C.
Co-reporter:Dipl.-Chem. Benjamin S. Gutrath;Dr. Iris M. Oppel;Dr. Oliver Presly;Dipl.-Phys. Igor Beljakov;Dr. Velimir Meded; Wolfgang Wenzel;Dr. Ulrich Simon
Angewandte Chemie International Edition 2013 Volume 52( Issue 12) pp:3529-3532
Publication Date(Web):
DOI:10.1002/anie.201208681
Co-reporter:Annika Leifert;Yu Pan;Anne Kinkeldey;Frank Schiefer;Julia Setzler;Olaf Scheel;Hera Lichtenbeld;Günter Schmid;Wolfgang Wenzel;Willi Jahnen-Dechent
PNAS 2013 110 (20 ) pp:8004-8009
Publication Date(Web):2013-05-14
DOI:10.1073/pnas.1220143110
Understanding the mechanism of toxicity of nanomaterials remains a challenge with respect to both mechanisms involved and
product regulation. Here we show toxicity of ultrasmall gold nanoparticles (AuNPs). Depending on the ligand chemistry, 1.4-nm-diameter
AuNPs failed electrophysiology-based safety testing using human embryonic kidney cell line 293 cells expressing human ether-á-go-go-Related
gene (hERG), a Food and Drug Administration-established drug safety test. In patch-clamp experiments, phosphine-stabilized AuNPs irreversibly
blocked hERG channels, whereas thiol-stabilized AuNPs of similar size had no effect in vitro, and neither particle blocked
the channel in vivo. We conclude that safety regulations may need to be reevaluated and adapted to reflect the fact that the
binding modality of surface functional groups becomes a relevant parameter for the design of nanoscale bioactive compounds.
Co-reporter:Dipl.-Chem. Benjamin S. Gutrath;Dr. Iris M. Oppel;Dr. Oliver Presly;Dipl.-Phys. Igor Beljakov;Dr. Velimir Meded; Wolfgang Wenzel;Dr. Ulrich Simon
Angewandte Chemie 2013 Volume 125( Issue 12) pp:3614-3617
Publication Date(Web):
DOI:10.1002/ange.201208681
Co-reporter:Dipl.-Chem. Jan Timper;Dr. Katrin Gutsmiedl;Dr. Christian Wirges;Dipl.-Chem. Janine Broda;Dr. Michael Noyong;Dr. Joachim Mayer;Dr. Thomas Carell;Dr. Ulrich Simon
Angewandte Chemie 2012 Volume 124( Issue 30) pp:7705-7708
Publication Date(Web):
DOI:10.1002/ange.201202401
Co-reporter:Dipl.-Chem. Stefan Koch;Dr. Ravi K. Joshi;Dr. Michael Noyong;Dipl.-Chem. Jan Timper;Dr. Jörg J. Schneider;Dr. Ulrich Simon
Chemistry - A European Journal 2012 Volume 18( Issue 37) pp:11614-11620
Publication Date(Web):
DOI:10.1002/chem.201201170
Abstract
The formation of stochastically oriented carbon-nanotube networks on top of an array of free-standing chromium-capped silicon nanopillars is reported. The combination of nanosphere lithography and chemical vapor deposition enables the construction of nanostructures that exhibit a hierarchical sequence of structural sizes. Metallic chromium serves as an etching mask for Si-pillar formation and as a nucleation site for the formation of carbon nanotubes through the chemical vapor deposition of ethene, ethanol, and methane, respectively, thereby bridging individual pillars from top to top. Iron and cobalt were applied onto the chromium caps as catalysts for CNT growth and the influence of different carbon sources and different gas-flow rates were investigated. The carbon nanotubes were structurally characterized and their DC electrical properties were studied by in situ local- and ex situ macroscopic measurements, both of which reveal their semiconductor properties. This process demonstrates how carbon nanotubes can be integrated into Si-based semiconductors and, thus, this process may be used to form high-surface-area sensors or new porous catalyst supports with enhanced gas-permeation properties.
Co-reporter:Dipl.-Chem. Jan Timper;Dr. Katrin Gutsmiedl;Dr. Christian Wirges;Dipl.-Chem. Janine Broda;Dr. Michael Noyong;Dr. Joachim Mayer;Dr. Thomas Carell;Dr. Ulrich Simon
Angewandte Chemie International Edition 2012 Volume 51( Issue 30) pp:7586-7588
Publication Date(Web):
DOI:10.1002/anie.201202401
Co-reporter:Patrick A. Schaal, Astrid Besmehn, Eva Maynicke, Michael Noyong, Bernd Beschoten, and Ulrich Simon
Langmuir 2012 Volume 28(Issue 5) pp:2448-2454
Publication Date(Web):December 28, 2011
DOI:10.1021/la204393h
We report the formation of thiol nanopatterns on SAM covered silicon wafers by converting sulfonic acid head groups via e-beam lithography. These thiol groups act as binding sites for gold nanoparticles, which can be enhanced to form electrically conducting nanostructures. This approach serves as a proof-of-concept for the combination of top-down and bottom-up processes for the generation of electrical devices on silicon.
Co-reporter:Monika Fischler and Ulrich Simon
Journal of Materials Chemistry A 2009 vol. 19(Issue 11) pp:1518-1523
Publication Date(Web):06 Jan 2009
DOI:10.1039/B812225C
The connection between metal nanoparticles and biomolecular systems has been intensively studied in recent decades as this field promises a vast variety of new applications. In this context DNA has been widely used in combination with nanoparticles for the generation of complex nanoarchitectures. Herein we would like to highlight some recent advances in gold nanoparticle–DNA research that demonstrate distinct functionality and open the prospect of a broad range of innovative applications in nanoelectronics, medicine, sensors, and various other areas related to material science.
Co-reporter:Monika Fischler, Alla Sologubenko, Joachim Mayer, Guido Clever, Glenn Burley, Johannes Gierlich, Thomas Carell and Ulrich Simon
Chemical Communications 2008 (Issue 2) pp:169-171
Publication Date(Web):29 Nov 2007
DOI:10.1039/B715602B
We present a new type of azide-functionalized gold nanoparticle and their coupling to an alkyne-modified DNA duplex using the copper(I)-catalyzed Huisgen cycloaddition (‘click chemistry’), resulting in a chain-like assembly of nanoparticles on the DNA template.
Co-reporter:Katrin G. Witten, Jan C. Bretschneider, Thomas Eckert, Walter Richtering and Ulrich Simon
Physical Chemistry Chemical Physics 2008 vol. 10(Issue 14) pp:1870-1875
Publication Date(Web):22 Feb 2008
DOI:10.1039/B719762D
The DNA mediated assembly of complementary DNA-functionalized gold nanoparticles (DNA–AuNP) was investigated by means of UV/Vis-spectroscopy and Dynamic Light Scattering (DLS). The melting temperature of the aggregates was determined to be Tm = 31 °C. Characterization of the assembly at 20 °C, 25 °C and 30 °C showed a decrease of the initial assembly growth rate with increasing temperature. The correlation of the wavelengths at the absorbance maxima λmax and the hydrodynamic radii Rh of the AuNP assemblies proved the dependence of the optical properties on the assembly size while at higher assembly temperature (30 °C) a larger redshift of λmax with increasing Rh was observed than at lower temperatures. This tendency might give information about the dependence of the internal structure of the DNA–AuNP assemblies on assembly temperature. It is assumed that at higher temperatures more compact assemblies are built than at lower temperatures of 20 °C and 25 °C. To the best of our knowledge, this is the first systematic time-resolved in situ investigation of DNA-mediated AuNP assembly by UV/Vis-spectroscopy and DLS.
Co-reporter:Fei Wen;Ulli Englert;Benjamin Gutrath
European Journal of Inorganic Chemistry 2008 Volume 2008( Issue 1) pp:106-111
Publication Date(Web):
DOI:10.1002/ejic.200700534
Abstract
The single-crystal structure of [Au9(PPh3)8](NO3)3 was resolved for the first time with atomic resolution. The cluster has crystallographic D2 and approximate molecular D2h skeletal symmetry derived from an icosahedron. Voltammetry of the Au9 clusters in CH2Cl2 reveals a 1.78-eV energy gap between the first one-electron oxidation peak and the first reduction peak. The UV/Vis and luminescence properties of Au9 clusters were also investigated. The cluster solid shows two broad emission peaks at 579 nm and 853 nm, respectively, at room temperature. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
Co-reporter:Dorota Sendor;Boniface P. T. Fokwa;Richard Dronskowski
European Journal of Inorganic Chemistry 2008 Volume 2008( Issue 3) pp:369-372
Publication Date(Web):
DOI:10.1002/ejic.200701099
Abstract
Large single-crystals of the cetineite-type phases (Rb;Se), (Sr;Se) and (Ba;Se) have been synthesized by hydrothermal reactions and single-crystal X-ray analyses with atomic resolution together with the electrical and optical measurements confirm a trend in the optical gap related to the chemical composition. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
Co-reporter:Luz Rodríguez-González, Enrique Rodríguez-Castellón, Antonio Jiménez-López, Ulrich Simon
Solid State Ionics 2008 Volume 179(35–36) pp:1968-1973
Publication Date(Web):30 October 2008
DOI:10.1016/j.ssi.2008.06.007
We compare the characteristic features obtained in TPD and in impedance measurements on the desorption of ammonia from zeolite H-ZSM-5. We show that the ammonia desorption peaks observed by TPD correspond to characteristic changes in the proton transport mechanism. While at low temperature an almost temperature independent Grotthus-like proton conductivity in the presence of ammonia is observed, the on-set of the low temperature desorption peak in TPD coincides with a change in the transport mechanism to a vehicle-mediated transport of protons. Furthermore, at higher temperature, the desorption of ammonia from the Brønsted acid sites, as indicated by the high temperature peak in TPD, causes again a characteristic change in the temperature dependent conductivity, reflected by a decreasing conductivity with increasing temperature in an intermitted range, which then turns over again to simply activated proton hopping.
Co-reporter:Stefan Neumeier, Thomas Echterhof, Ralf Bölling, Herbert Pfeifer, Ulrich Simon
Sensors and Actuators B: Chemical 2008 Volume 134(Issue 1) pp:171-174
Publication Date(Web):28 August 2008
DOI:10.1016/j.snb.2008.04.022
We present a humidity sensor based on H-ZSM-5 type zeolite that is suitable to detect traces of humidity (∼10–110 ppmV) under harsh conditions, e.g. reducing atmosphere (H2) and high temperature (up to 600 °C). By means of complex impedance spectroscopy (IS) we show that the zeolite sensor responds linearly towards minimal changes in humidity. Therefore this result indicates that the zeolite sensor is capable to detect traces of humidity in processes where high temperatures in a hydrogen environment are required.
Co-reporter:Sangaraju Shanmugam Dr.
Chemistry - A European Journal 2008 Volume 14( Issue 29) pp:8776-8779
Publication Date(Web):
DOI:10.1002/chem.200801263
Co-reporter:M. Siemons;A. Leifert;U. Simon
Advanced Functional Materials 2007 Volume 17(Issue 13) pp:
Publication Date(Web):26 JUL 2007
DOI:10.1002/adfm.200600454
Nanoparticulate perovskite-type LnBO3 (Ln = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu; B = Cr, Fe) oxides are prepared by polyol-mediated synthesis. X-ray diffraction is used to confirm the structure of the materials, and scanning electron microscopy is applied to image the sample morphology. The powders are used for the preparation of suspensions that are deposited as thick films on comb-type Pt electrodes on alumina substrates. Electrical characterization is performed by using high-throughput impedance spectroscopy. The materials exhibit p-type semiconductor behavior, and their sensitivity towards H2, CO, NO, NO2, and propylene in a temperature range from 200 to 500 °C is analyzed. In addition, the time-resolved response of the LnFeO3 materials is investigated. A correlation between the Ln–O binding energy and the sensing properties is observed.
Co-reporter:S. Rodríquez-Llamazares, P. Jara, N. Yutronic, M. Noyong, J. Bretschneider, U. Simon
Journal of Colloid and Interface Science 2007 Volume 316(Issue 1) pp:202-205
Publication Date(Web):1 December 2007
DOI:10.1016/j.jcis.2007.07.066
The preferred deposition of gold nanoparticles (Au NPs) onto microcrystal faces of α-cyclodextin/octanethiol inclusion compound was obtained. The immobilization of Au NPs is caused by the spatial replacing of the citrate shell of the NPs by the free dangling SH groups of the guest molecule.A preferred deposition of gold nanoparticles onto microcrystal faces of α-cyclodextin/octanethiol inclusion compound was obtained.
Co-reporter:Dorota Sendor Dr.;Boniface P. T. Fokwa Dr.;Richard Dronskowski Dr. Dr.
Angewandte Chemie 2007 Volume 119(Issue 33) pp:
Publication Date(Web):19 JUL 2007
DOI:10.1002/ange.200700314
Größenempfindliche Detektoren: Die Photoleitung von Cetineiten, kristallinen nanoporösen Oxoselenoantimonaten, wird durch Adsorption von Edelgasatomen herabgesetzt (siehe Bild; Z = Edelgas). Die Aufnahme eines Edelgases nimmt mit steigendem Atomradius ab, was mit der Abhängigkeit der Leitfähigkeitsänderung als Funktion der Gasatomradien gut übereinstimmt. Dies ermöglicht die Anwendung von Cetineiten für die Detektion von Edelgasen.
Co-reporter:M. Noyong;K. Gloddek;J. Mayer;Th. Weirich;U. Simon
Journal of Cluster Science 2007 Volume 18( Issue 1) pp:193-204
Publication Date(Web):2007 March
DOI:10.1007/s10876-006-0095-4
In this work we describe the formation of 1-dimensional (1D) assemblies of cysteamine functionalized gold nanoparticles on DNA using the complex cis-Pt (cis-Pt(NH3)2Cl2) as site specific linker and their immobilization on mica and silicon. The characterization by atomic force microscopy and electron microscopy served as complementary methods. Using atomic force microscopy with additional information of phase images the DNA as well as the Au particles can be visualized independently and be differentiated in the 1-dimensional aggregates. Electron microscopy shows individual particles are arranged as a string of pearls.
Co-reporter:Jürgen Nelles;Dorota Sendor;Andre Ebbers
Colloid and Polymer Science 2007 Volume 285( Issue 7) pp:729-736
Publication Date(Web):2007 April
DOI:10.1007/s00396-006-1622-4
Studies focusing on the functionalization of the surface of free silicon nanoparticles are presented. This functionalization is applied to hydrogen-terminated silicon nanoparticles to evaluate how far the well-known solution-phase chemistry of thermal-, radical-, Lewis acid- and UV light-mediated hydrosilylation can be applied to the surface chemistry of silicon nanoparticles. The efficiencies of hydrosilylation for thermal-, radical- and Lewis acid-mediated reactions on silicon nanoparticles surfaces, deduced from the intensity of the ν(Si–H) absorption, are found to be comparable.
Co-reporter:Dorota Sendor Dr.;Boniface P. T. Fokwa Dr.;Richard Dronskowski Dr. Dr.
Angewandte Chemie International Edition 2007 Volume 46(Issue 33) pp:
Publication Date(Web):19 JUL 2007
DOI:10.1002/anie.200700314
Recognizing nobility: The photoconduction of cetineites, crystalline nanoporous oxoselenoantimonates, is suppressed by the adsorption of noble gases. The gas uptake decreases with increasing atomic radius of the noble gas, leading to a smaller change in resistance upon adsorption. Thus, cetineites can be applied in noble-gas detection.
Co-reporter:Ulrich Simon;Dieter Fenske;Achim Müller
Journal of Cluster Science 2007 Volume 18( Issue 1) pp:1-3
Publication Date(Web):2007 March
DOI:10.1007/s10876-006-0096-3
Co-reporter:Eva Koplin, Christof M. Niemeyer and Ulrich Simon
Journal of Materials Chemistry A 2006 vol. 16(Issue 14) pp:1338-1344
Publication Date(Web):19 Jan 2006
DOI:10.1039/B516257B
The formation of DNA-assembled gold nanoparticle monolayers on a silicon substrate is reported. The electrical properties, obtained from temperature dependent dc and impedance measurements, reflect thermally activated hopping transport. The activation energy increases with the inter-particle spacing.
Co-reporter:Maike Siemons, Ulrich Simon
Sensors and Actuators B: Chemical 2006 Volume 120(Issue 1) pp:110-118
Publication Date(Web):14 December 2006
DOI:10.1016/j.snb.2006.01.049
p-Type semiconducting nanocrystalline CoTiO3:La (2 at.%) was synthesized via polyol method. X-ray diffraction (XRD) was used to confirm the materials structure. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to image the materials morphology. Thick films of the nanocrystalline material were applied with a laboratory roboting system to an 8 × 8 multielectrode substrate, developed for high-throughput impedance spectroscopy (HTIS). With this method it was shown that the base material doped with various metals (Au, Ce, Ir, Pd, Pt, Rh, Ru) in different concentrations (0.2–0.6 at.%) is applicable for the fast detection of ethanol, propylene and NO2, depending on the surface doping and the operation temperature.
Co-reporter:Dorota Sendor, Thomas Weirich and Ulrich Simon
Chemical Communications 2005 (Issue 46) pp:5790-5792
Publication Date(Web):20 Oct 2005
DOI:10.1039/B509657J
We have isolated flexible Sb2O3 nanoribbons and nanorods as the main product from the disintegration of nanoporous oxoselenoantimonates of the cetineite type, the size of the one-dimensional nanomaterials obtained ranging up to 15 μm in length with diameters between 8 and 50 nm.
Co-reporter:Torsten Reuter;Stefan Neumeier;Günter Schmid;Eva Koplin
European Journal of Inorganic Chemistry 2005 Volume 2005(Issue 18) pp:
Publication Date(Web):20 JUL 2005
DOI:10.1002/ejic.200500385
Multilayer systems, consisting of Au55(PPh3)12Cl6 double layers and SiO2 barrier films of different thickness, have been generated and characterised. The formation of the double layer between the barrier films was carried out by using spin-coating techniques. For the generation of the SiO2 films, a plasma-assisted physical vapour deposition (PAPVD) procedure has been applied, based on an anodic plasma arc process. Samples of up to nine cluster/SiO2 combinations have been produced and have been characterised by AFM and SEM. Impedance measurements showed that there is a characteristic thermally activated frequency dependence of the capacitance of the different systems. The cluster layers interact by dipoles formed in the double layers at low frequencies. It has also been shown that multilayer systems with SiO2 films thicker than 15 nm tend to spontaneously crystallise. Furthermore, wetting problems during the spin-coating processes have been investigated. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
Co-reporter:Christof M. Niemeyer
European Journal of Inorganic Chemistry 2005 Volume 2005(Issue 18) pp:
Publication Date(Web):26 AUG 2005
DOI:10.1002/ejic.200500425
In this microreview we describe the principles of DNA-based assembly of metal nanoparticles in one, two and three dimensions. Different methods of liquid-phase synthesis of metal nanoparticles as well as their functionalisation with DNA are introduced. The concepts developed up to now for the assembly are explained, with selected examples to illustrate the properties of these assemblies as well as emerging applications. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
Co-reporter:Marion E. Franke Dr. Dr.
ChemPhysChem 2004 Volume 5(Issue 4) pp:
Publication Date(Web):14 APR 2004
DOI:10.1002/cphc.200301011
Solvate-supported proton transport in zeolite H-ZSM-5 was studied by means of complex impedance spectroscopy. The zeolite shows enhanced proton mobility in the presence of NH3and H2O that depends on the concentration of the solvate molecule, temperature (298–773 K), and the SiO2/Al2O3ratio of the zeolite (30–1000). In general, proton conductivity in H-ZSM-5 is most effectively supported in the presence of NH3and H2O at high concentrations, low temperatures, and low SiO2/Al2O3ratios (≤80). For the aluminum-rich samples desorption measurements reflect different transport mechanisms that depend on the respective temperature range. Up to about 393 K a Grotthus-like proton transport mechanism is assumed, whereas at higher temperatures (393–473 K) vehiclelike transport seems to dominate. The activation energies for NH4+and H3O+vehicle conductivity depend on the SiO2/Al2O3ratio, and the values are in the range of 49–59 and 39–49 kJ mol−1, respectively, and thus significantly lower than those for “pure” proton conduction in solvate-free samples.
Co-reporter:Andreas Frantzen Dr.;Jens Scheidtmann Dipl.-Phys.;Gerald Frenzer Dr.;Wilhelm F. Maier Dr.;Jörg Jockel Dr.;Thomas Brinz Dr.;Daniel Sers and Dr.
Angewandte Chemie 2004 Volume 116(Issue 6) pp:
Publication Date(Web):27 JAN 2004
DOI:10.1002/ange.200352424
Eine kombinatorische Prozesskette zur Synthese und Testung dicker Oxidfilme wurde für die Entwicklung neuer Gas-Sensoren aufgebaut. Teil dieser Kette ist die Synthese und Erzeugung von Mischoxidschichten mit variabler Zusammensetzung. Eine Materialbibliothek wurde auf einem Array von 8×8 Interdigitalelelektroden hergestellt (siehe Bild). Bei der Charakterisierung der Felder wurde die Abfolge der Prüfgase und die Umgebungstemperatur den Anforderungen entsprechend variiert.
Co-reporter:Andreas Frantzen Dr.;Jens Scheidtmann Dipl.-Phys.;Gerald Frenzer Dr.;Wilhelm F. Maier Dr.;Jörg Jockel Dr.;Thomas Brinz Dr.;Daniel Sers and Dr.
Angewandte Chemie International Edition 2004 Volume 43(Issue 6) pp:
Publication Date(Web):27 JAN 2004
DOI:10.1002/anie.200352424
A combinatorial work flow for the rapid synthesis and testing of thick oxide films for the development of new gas sensors with improved sensitivity and selectivity involves the synthesis and deposition of mixed-oxide films of variable composition. The library is based on the sol–gel synthesis of mixed oxides on an array of 8×8 interdigitated electrodes. For the characterization of the sensor arrays, test gas sequences and sensor temperatures were varied.
Co-reporter:Viktoria Torma;Olivia Vidoni;Günter Schmid
European Journal of Inorganic Chemistry 2003 Volume 2003(Issue 6) pp:
Publication Date(Web):3 MAR 2003
DOI:10.1002/ejic.200390143
Electron-transfer processes in complex chemistry are usually described by Taube’s “outer sphere” and “inner sphere” mechanisms. A behaviour related to these electron-transfer mechanisms in complex chemistry can be observed for charge-transfer transport between ligand protected Au55 nanoclusters. A linear dependence between cluster-cluster distance and activation energy for electron transfer is observed if a noncovalent linkage exists; this interaction is independent of the distance in covalently linked clusters. Instead, the activation energy depends on the electronic nature of the linking molecules. The dithiols 1,5-dithionaphthaline (1), 4,4′-thiobis(benzenethiol) (2), and 2,8-dithio-6-hydroxypurine (3) have been used as bifunctional covalent linkers either in their monomeric form (2) or, in the presence of air, dimerized via S−S bonds (1, 2, 3), causing an increase in the distance between the clusters and leading to the cluster networks 4−7. Noncovalent cluster networks are formed either by pellets of clusters with monodentate ligands in 8 and 11, linked only by van der Waals forces, or by using bifunctional spacers that interact with the clusters by ion attractions (9, 10). A study of the activation energies clearly indicates that in the case of noncovalently organized nanoparticles only the cluster spacing is of relevance, even if conjugated π-systems like in 10 are used. This behaviour corresponds to an outer-sphere mechanism. On the contrary, for covalently linked clusters the distances between them does not play a visible role. The activation energies all lie below those of the noncovalent examples, and a relation between cluster-cluster distance and activation energy is not obvious. In those cases the relationship suggests an inner-sphere mechanism where the transport properties of the spacer play a decisive role. These findings possibly help to explain contradictory reports on the conductivity behaviour of organic molecules. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Co-reporter:U Simon, M.E Franke
Microporous and Mesoporous Materials 2000 Volume 41(1–3) pp:1-36
Publication Date(Web):December 2000
DOI:10.1016/S1387-1811(00)00291-2
We report on the electrical properties of zeolites, molecular and nanoscaled guests in porous solids as well as of microporous semiconductors, which have been examined by means of impedance spectroscopy or related methods. Selected examples give an insight into charge transport phenomena and show how charge transport and relaxation can be affected by host/guest interactions. In this context, potential applications in chemical sensing and catalysis are introduced.
Co-reporter:Luz Rodríguez-González, Florian Hermes, Marko Bertmer, Enrique Rodríguez-Castellón, Antonio Jiménez-López, Ulrich Simon
Applied Catalysis A: General (10 September 2007) Volume 328(Issue 2) pp:
Publication Date(Web):10 September 2007
DOI:10.1016/j.apcata.2007.06.003
The acid properties of H-ZSM-5 zeolites with different SiO2/Al2O3 ratios (30, 50, 80, 150, 280 and 1000) were examined by means of the temperature programmed desorption of ammonia (NH3-TPD). Different pretreatments together with a comparison of different curve-fitting methods after desorption of ammonia were used to differentiate between different adsorption sites. 27Al-MAS-NMR spectroscopy was applied to distinguish the framework (AlF) from the extra-framework aluminum (AlEF). Both techniques reveal that the concentration of Brønsted acid sites is lower than expected when considering the aluminum content. The strength of the Brønsted acid sites, determined by a theoretical model assuming the free readsorption of ammonia, is found to be in the range of ΔH = 129–161 kJ mol−1 and shows variations in the acid strength to be less than σ = 12 kJ mol−1.The acid properties of H-ZSM-5 zeolites with different SiO2/Al2O3 ratios (30, 50, 80, 150, 280 and 1000) were examined by means of the temperature programmed desorption of ammonia (NH3-TPD). The strength of the Brønsted acid sites, determined by a theoretical model assuming the free readsorption of ammonia, is found to be in the range of ΔH = 129–161 kJ mol−1 and shows variations in the acid strength to be less than σ = 12 kJ mol−1.
Co-reporter:J. Ruff, J. Steitz, A. Buchkremer, M. Noyong, H. Hartmann, A. Besmehn and U. Simon
Journal of Materials Chemistry A 2016 - vol. 4(Issue 16) pp:NaN2841-2841
Publication Date(Web):2016/03/24
DOI:10.1039/C6TB00674D
In this work the effect of multivalency on the stability of NIR-absorbing HAuNSs and AuNRs functionalized by mono-, bi- and tridentate polyethyleneglycol (PEG) thiol ligands is reported. Comparison of commercially-available monodentate and self-synthesized bi- and tridentate methoxy terminated thiol-polyethyleneglycol ligands having molecular weights of around 5000 Da shows the stability increase of HAuNSs and AuNRs for bi- and tridentate ligands, attributed to the multivalency of the ligands. The stability was explored according to three different aspects: (1) stability towards competition reactions with the strong binding ligand dithiothreitol, (2) resistance towards oxidative Au dissolution with potassium cyanide, and (3) colloidal stability, tested by the addition of NaCl. Our PEGylation approach leads to AuNRs where the CTAB concentration is below the detection limit of the performed analytical methods, which is vital for any clinical applications. Furthermore, we found strikingly high biocompatibility after PEGylation for both particle types whereby we observed no significant difference in cytotoxicity comparing the mono-, bi- and tridentate PEGylated species.
Co-reporter:Katrin G. Witten, Jan C. Bretschneider, Thomas Eckert, Walter Richtering and Ulrich Simon
Physical Chemistry Chemical Physics 2008 - vol. 10(Issue 14) pp:NaN1875-1875
Publication Date(Web):2008/02/22
DOI:10.1039/B719762D
The DNA mediated assembly of complementary DNA-functionalized gold nanoparticles (DNA–AuNP) was investigated by means of UV/Vis-spectroscopy and Dynamic Light Scattering (DLS). The melting temperature of the aggregates was determined to be Tm = 31 °C. Characterization of the assembly at 20 °C, 25 °C and 30 °C showed a decrease of the initial assembly growth rate with increasing temperature. The correlation of the wavelengths at the absorbance maxima λmax and the hydrodynamic radii Rh of the AuNP assemblies proved the dependence of the optical properties on the assembly size while at higher assembly temperature (30 °C) a larger redshift of λmax with increasing Rh was observed than at lower temperatures. This tendency might give information about the dependence of the internal structure of the DNA–AuNP assemblies on assembly temperature. It is assumed that at higher temperatures more compact assemblies are built than at lower temperatures of 20 °C and 25 °C. To the best of our knowledge, this is the first systematic time-resolved in situ investigation of DNA-mediated AuNP assembly by UV/Vis-spectroscopy and DLS.
Co-reporter:Monika Fischler and Ulrich Simon
Journal of Materials Chemistry A 2009 - vol. 19(Issue 11) pp:NaN1523-1523
Publication Date(Web):2009/01/06
DOI:10.1039/B812225C
The connection between metal nanoparticles and biomolecular systems has been intensively studied in recent decades as this field promises a vast variety of new applications. In this context DNA has been widely used in combination with nanoparticles for the generation of complex nanoarchitectures. Herein we would like to highlight some recent advances in gold nanoparticle–DNA research that demonstrate distinct functionality and open the prospect of a broad range of innovative applications in nanoelectronics, medicine, sensors, and various other areas related to material science.
Co-reporter:Monika Fischler, Alla Sologubenko, Joachim Mayer, Guido Clever, Glenn Burley, Johannes Gierlich, Thomas Carell and Ulrich Simon
Chemical Communications 2008(Issue 2) pp:NaN171-171
Publication Date(Web):2007/11/29
DOI:10.1039/B715602B
We present a new type of azide-functionalized gold nanoparticle and their coupling to an alkyne-modified DNA duplex using the copper(I)-catalyzed Huisgen cycloaddition (‘click chemistry’), resulting in a chain-like assembly of nanoparticles on the DNA template.
Co-reporter:Peirong Chen, Dieter Rauch, Philipp Weide, Simon Schönebaum, Thomas Simons, Martin Muhler, Ralf Moos and Ulrich Simon
Catalysis Science & Technology (2011-Present) 2016 - vol. 6(Issue 10) pp:NaN3366-3366
Publication Date(Web):2016/04/20
DOI:10.1039/C6CY00452K
Proton transport studies revealed the different influence of Fe and Cu cations on the NH3–zeolite interaction and the NO–zeolite interaction in the presence of adsorbed NH3. At low temperatures, after NH3 saturation, Cu-ZSM-5 is more reactive than Fe-ZSM-5 for NO activation forming highly mobile NH4+ intermediates.
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