22 results
Search Results
Now showing 1 - 10 of 22
- Item(Metallo)porphyrins for potential materials science applications(Frankfurt, M. : Beilstein-Institut zur Förderung der Chemischen Wissenschaften, 2017-8-29) Smykalla, Lars; Mende, Carola; Fronk, Michael; Siles, Pablo F.; Hietschold, Michael; Salvan, Georgeta; Zahn, Dietrich R.T.; Schmidt, Oliver G.; Rüffer, Tobias; Lang, HeinrichThe bottom-up approach to replace existing devices by molecular-based systems is a subject that attracts permanently increasing interest. Molecular-based devices offer not only to miniaturize the device further, but also to benefit from advanced functionalities of deposited molecules. Furthermore, the molecules itself can be tailored to allow via their self-assembly the potential fabrication of devices with an application potential, which is still unforeseeable at this time. Herein, we review efforts to use discrete (metallo)porphyrins for the formation of (sub)monolayers by surface-confined polymerization, of monolayers formed by supramolecular recognition and of thin films formed by sublimation techniques. Selected physical properties of these systems are reported as well. The application potential of those ensembles of (metallo)porphyrins in materials science is discussed.
- ItemSynthesis, spectroscopic characterization and thermogravimetric analysis of two series of substituted (metallo)tetraphenylporphyrins(Frankfurt, M. : Beilstein-Institut zur Förderung der Chemischen Wissenschaften, 2017-6-2) Al-Shewiki, Rasha K.; Mende, Carola; Buschbeck, Roy; Siles, Pablo F.; Schmidt, Oliver G.; Rüffer, Tobias; Lang, HeinrichSubsequent treatment of H2TPP(CO2H)4 (tetra(p-carboxylic acid phenyl)porphyrin, 1) with an excess of oxalyl chloride and HNR2 afforded H2TPP(C(O)NR2)4 (R = Me, 2; iPr, 3) with yields exceeding 80%. The porphyrins 2 and 3 could be converted to the corresponding metalloporphyrins MTPP(C(O)NR2)4 (R = Me/iPr for M = Zn (2a, 3a); Cu (2b, 3b); Ni (2c, 3c); Co (2d, 3d)) by the addition of 3 equiv of anhydrous MCl2 (M = Zn, Cu, Ni, Co) to dimethylformamide solutions of 2 and 3 at elevated temperatures. Metalloporphyrins 2a–d and 3a–d were obtained in yields exceeding 60% and have been, as well as 2 and 3, characterized by elemental analysis, electrospray ionization mass spectrometry (ESIMS) and IR and UV–vis spectroscopy. Porphyrins 2, 2a–d and 3, 3a–d are not suitable for organic molecular beam deposition (OMBD), which is attributed to their comparatively low thermal stability as determined by thermogravimetric analysis (TG) of selected representatives.
- ItemMolecular Insights into Division of Single Human Cancer Cells in On-Chip Transparent Microtubes(Washington, DC : Soc., 2016) Xi, Wang; Schmidt, Christine K.; Sanchez, Samuel; Gracias, David H.; Carazo-Salas, Rafael E.; Butler, Richard; Lawrence, Nicola; Jackson, Stephen P.; Schmidt, Oliver G.In vivo, mammalian cells proliferate within 3D environments consisting of numerous microcavities and channels, which contain a variety of chemical and physical cues. External environments often differ between normal and pathological states, such as the unique spatial constraints that metastasizing cancer cells experience as they circulate the vasculature through arterioles and narrow capillaries, where they can divide and acquire elongated cylindrical shapes. While metastatic tumors cause most cancer deaths, factors impacting early cancer cell proliferation inside the vasculature and those that can promote the formation of secondary tumors remain largely unknown. Prior studies investigating confined mitosis have mainly used 2D cell culture systems. Here, we mimic aspects of metastasizing tumor cells dividing inside blood capillaries by investigating single-cell divisions of living human cancer cells, trapped inside 3D rolled-up, transparent nanomembranes. We assess the molecular effects of tubular confinement on key mitotic features, using optical high- and super-resolution microscopy. Our experiments show that tubular confinement affects the morphology and dynamics of the mitotic spindle, chromosome arrangements, and the organization of the cell cortex. Moreover, we reveal that membrane blebbing and/or associated processes act as a potential genome-safety mechanism, limiting the extent of genomic instability caused by mitosis in confined circumstances, especially in tubular 3D microenvironments. Collectively, our study demonstrates the potential of rolled-up nanomembranes for gaining molecular insights into key cellular events occurring in tubular 3D microenvironments in vivo.
- ItemA size dependent evaluation of the cytotoxicity and uptake of nanographene oxide(London [u.a.] : RSC, 2015) Mendes, Rafael Gregorio; Koch, Britta; Bachmatiuk, Alicja; Ma, Xing; Sanchez, Samuel; Damm, Christine; Schmidt, Oliver G.; Gemming, Thomas; Eckert, Jürgen; Rümmeli, Mark H.Graphene oxide (GO) has attracted great interest due to its extraordinary potential for biomedical application. Although it is clear that the naturally occurring morphology of biological structures is crucial to their precise interactions and correct functioning, the geometrical aspects of nanoparticles are often ignored in the design of nanoparticles for biological applications. A few in vitro and in vivo studies have evaluated the cytotoxicity and biodistribution of GO, however very little is known about the influence of flake size and cytotoxicity. Herein, we aim at presenting an initial cytotoxicity evaluation of different nano-sized GO flakes for two different cell lines (HeLa (Kyoto) and macrophage (J7742)) when they are exposed to samples containing different sized nanographene oxide (NGO) flakes (mean diameter of 89 and 277 nm). The obtained data suggests that the larger NGO flakes reduce cell viability as compared to smaller flakes. In addition, the viability reduction correlates with the time and the concentration of the NGO nanoparticles to which the cells are exposed. Uptake studies were also conducted and the data suggests that both cell lines internalize the GO nanoparticles during the incubation periods studied.
- ItemTuning the magneto-optical response of TbPc2 single molecule magnets by the choice of the substrate(London [u.a.] : RSC, 2015) Robaschik, Peter; Fronk, Michael; Toader, Marius; Klyatskaya, Svetlana; Ganss, Fabian; Siles, Pablo F.; Schmidt, Oliver G.; Albrecht, Manfred; Hietschold, Michael; Ruben, Mario; Zahn, Dietrich R.T.; Salvan, GeorgetaIn this work, we investigated the magneto-optical response of thin films of TbPc2 on substrates which are relevant for (spin) organic field effect transistors (SiO2) or vertical spin valves (Co) in order to explore the possibility of implementing TbPc2 in magneto-electronic devices, the functionality of which includes optical reading. The optical and magneto-optical properties of TbPc2 thin films prepared by organic molecular beam deposition (OMBD) on silicon substrates covered with native oxide were investigated by variable angle spectroscopic ellipsometry (VASE) and magneto-optical Kerr effect (MOKE) spectroscopy at room temperature. The magneto-optical activity of the TbPc2 films can be significantly enhanced by one to two orders of magnitude upon changing the molecular orientation (from nearly standing molecules on SiO2/Si substrates to nearly lying molecules on perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) templated SiO2/Si substrates) or by using metallic ferromagnetic substrates (Co).
- ItemMagnetofluidic platform for multidimensional magnetic and optical barcoding of droplets(Cambridge : RSC, 2014) Lin, Gungun; Makarov, Denys; Medina-Sánchez, Mariana; Guix, Maria; Baraban, Larysa; Cuniberti, Gianaurelio; Schmidt, Oliver G.We present a concept of multidimensional magnetic and optical barcoding of droplets based on a magnetofluidic platform. The platform comprises multiple functional areas, such as an encoding area, an encoded droplet pool and a magnetic decoding area with integrated giant magnetoresistive (GMR) sensors. To prove this concept, penicillin functionalized with fluorescent dyes is coencapsulated with magnetic nanoparticles into droplets. While fluorescent dyes are used as conventional optical barcodes which are decoded with an optical decoding setup, an additional dimensionality of barcodes is created by using magnetic nanoparticles as magnetic barcodes for individual droplets and integrated micro-patterned GMR sensors as the corresponding magnetic decoding devices. The strategy of incorporating a magnetic encoding scheme provides a dynamic range of ~40 dB in addition to that of the optical method. When combined with magnetic barcodes, the encoding capacity can be increased by more than 1 order of magnitude compared with using only optical barcodes, that is, the magnetic platform provides more than 10 unique magnetic codes in addition to each optical barcode. Besides being a unique magnetic functional element for droplet microfluidics, the platform is capable of on-demand facile magnetic encoding and real-time decoding of droplets which paves the way for the development of novel non-optical encoding schemes for highly multiplexed droplet-based biological assays.
- ItemPrecise Localization and Control of Catalytic Janus Micromotors Using Weak Magnetic Fields(London : Sage Publishing, 2015) Khalil, Islam S. M.; Magdanz, Veronika; Sanchez, Samuel; Schmidt, Oliver G.; Misra, SarthakWe experimentally demonstrate the precise localization of spherical Pt-Silica Janus micromotors (diameter 5 μm) under the influence of controlled magnetic fields. First, we control the motion of the Janus micromotors in two-dimensional (2D) space. The control system achieves precise localization within an average region-of-convergence of 7 μm. Second, we show that these micromotors provide sufficient propulsion force, allowing them to overcome drag and gravitational forces and move both downwards and upwards. This propulsion is studied by moving the micromotors in three-dimensional (3D) space. The micromotors move downwards and upwards at average speeds of 19.1 μm/s and 9.8 μm/s, respectively. Moreover, our closed-loop control system achieves localization in 3D space within an average region-of-convergence of 6.3 μm in diameter. The precise motion control and localization of the Janus micromotors in 2D and 3D spaces provides broad possibilities for nanotechnology applications.
- ItemPhotoluminescence investigation of strictly ordered Ge dots grown on pit-patterned Si substrates(Bristol : IOP Publ., 2015) Brehm, Moritz; Grydlik, Martyna; Tayagaki, Takeshi; Langer, Gregor; Schäffler, Friedrich; Schmidt, Oliver G.We investigate the optical properties of ordered Ge quantum dots (QDs) by means of micro-photoluminescence spectroscopy (PL). These were grown on pit-patterned Si(001) substrates with a wide range of pit-periods and thus inter QD-distances (425–3400 nm). By exploiting almost arbitrary inter-QD distances achievable in this way we are able to choose the number of QDs that contribute to the PL emission in a range between 70 and less than three QDs. This well-defined system allows us to clarify, by PL-investigation, several points which are important for the understanding of the formation and optical properties of ordered QDs. We directly trace and quantify the amount of Ge transferred from the surrounding wetting layer (WL) to the QDs in the pits. Moreover, by exploiting different pit-shapes, we reveal the role of strain-induced activation energy barriers that have to be overcome for charge carriers generated outside the dots. These need to diffuse between the energy minimum of the WL in and between the pits, and the one in the QDs. In addition, we demonstrate that the WL in the pits is already severely intermixed with Si before upright QDs nucleate, which further enhances intermixing of ordered QDs as compared to QDs grown on planar substrates. Furthermore, we quantitatively determine the amount of Ge transferred by surface diffusion through the border region between planar and patterned substrate. This is important for the growth of ordered islands on patterned fields of finite size. We highlight that the Ge WL-facets in the pits act as PL emission centres, similar to upright QDs.
- ItemRetrieving spin textures on curved magnetic thin films with full-field soft X-ray microscopies([London] : Nature Publishing Group UK, 2015) Streubel, Robert; Kronast, Florian; Fischer, Peter; Parkinson, Dula; Schmidt, Oliver G.; Makarov, DenysX-ray tomography is a well-established technique to characterize 3D structures in material sciences and biology; its magnetic analogue--magnetic X-ray tomography--is yet to be developed. Here we demonstrate the visualization and reconstruction of magnetic domain structures in a 3D curved magnetic thin films with tubular shape by means of full-field soft X-ray microscopies. The 3D arrangement of the magnetization is retrieved from a set of 2D projections by analysing the evolution of the magnetic contrast with varying projection angle. Using reconstruction algorithms to analyse the angular evolution of 2D projections provides quantitative information about domain patterns and magnetic coupling phenomena between windings of azimuthally and radially magnetized tubular objects. The present approach represents a first milestone towards visualizing magnetization textures of 3D curved thin films with virtually arbitrary shape.
- ItemMagnetism in curved geometries(Bristol : IOP Publ., 2016) Streubel, Robert; Fischer, Peter; Kronast, Florian; Kravchuk, Volodymyr P.; Sheka, Denis D.; Gaididei, Yuri; Schmidt, Oliver G.; Makarov, DenysExtending planar two-dimensional structures into the three-dimensional space has become a general trend in multiple disciplines, including electronics, photonics, plasmonics and magnetics. This approach provides means to modify conventional or to launch novel functionalities by tailoring the geometry of an object, e.g. its local curvature. In a generic electronic system, curvature results in the appearance of scalar and vector geometric potentials inducing anisotropic and chiral effects. In the specific case of magnetism, even in the simplest case of a curved anisotropic Heisenberg magnet, the curvilinear geometry manifests two exchange-driven interactions, namely effective anisotropy and antisymmetric exchange, i.e. Dzyaloshinskii–Moriya-like interaction. As a consequence, a family of novel curvature-driven effects emerges, which includes magnetochiral effects and topologically induced magnetization patterning, resulting in theoretically predicted unlimited domain wall velocities, chirality symmetry breaking and Cherenkov-like effects for magnons. The broad range of altered physical properties makes these curved architectures appealing in view of fundamental research on e.g. skyrmionic systems, magnonic crystals or exotic spin configurations. In addition to these rich physics, the application potential of three-dimensionally shaped objects is currently being explored as magnetic field sensorics for magnetofluidic applications, spin-wave filters, advanced magneto-encephalography devices for diagnosis of epilepsy or for energy-efficient racetrack memory devices. These recent developments ranging from theoretical predictions over fabrication of three-dimensionally curved magnetic thin films, hollow cylinders or wires, to their characterization using integral means as well as the development of advanced tomography approaches are in the focus of this review.