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- ItemDirect Observation of Deformation in Microgel Filtration([London] : Macmillan Publishers Limited, part of Springer Nature, 2019) Linkhorst, John; Rabe, Jonas; Hirschwald, Lukas T.; Kuehne, Alexander J. C.; Wessling, MatthiasColloidal filtration processes using porous membranes suffer from productivity loss due to colloidal matter retention and continuous build-up by the retained matter. Especially during filtration of soft matter, the deformation of the individual colloids that make up the filter cake may be significant; however, this deformation and its impact remain unresolved so far. Yet, understanding the deformation on the single colloid level as well as on the ensemble level is important to be able to deconvolute filter cake properties from resistance increase of the membrane either by simultaneous internal adsorption or blocking of pores. Here, we report on the compression of a filter cake by filtrating soft microgels in a microfluidic channel in front of a model membrane. To study the single colloid deformation amorphous and crystalline domains were built up in front of the membrane and visualized on-line using confocal fluorescence microscopy while adjusting the degree of permeation, i.e., the transmembrane flux. Results show locally pronounced asymmetric deformation in amorphous domains, while the microgels in colloidal crystals approached regular polyeder shape. Increasing the flux beyond the maximum colloid deformation results in non-isochoric microgel behavior. The presented methodology enables a realistic description of complex colloidal matter deposits during filtration.
- ItemUltrathin niobium nanofilms on fiber optical tapers--a new route towards low-loss hybrid plasmonic modes([London] : Macmillan Publishers Limited, part of Springer Nature, 2015) Wieduwilt, Torsten; Tuniz, Alessandro; Linzen, Sven; Goerke, Sebastian; Dellith, Jan; Hübner, Uwe; Schmidt, Markus A.Due to the ongoing improvement in nanostructuring technology, ultrathin metallic nanofilms have recently gained substantial attention in plasmonics, e.g. as building blocks of metasurfaces. Typically, noble metals such as silver or gold are the materials of choice, due to their excellent optical properties, however they also possess some intrinsic disadvantages. Here, we introduce niobium nanofilms (~10 nm thickness) as an alternate plasmonic platform. We demonstrate functionality by depositing a niobium nanofilm on a plasmonic fiber taper and observe a dielectric-loaded niobium surface-plasmon excitation for the first time, with a modal attenuation of only 3–4 dB/mm in aqueous environment and a refractive index sensitivity up to 15 μm/RIU if the analyte index exceeds 1.42. We show that the niobium nanofilm possesses bulk optical properties, is continuous, homogenous and inert against any environmental influence, thus possessing several superior properties compared to noble metal nanofilms. These results demonstrate that ultrathin niobium nanofilms can serve as a new platform for biomedical diagnostics, superconducting photonics, ultrathin metasurfaces or new types of optoelectronic devices.
- ItemDetection of vancomycin resistances in enterococci within 3 1/2 Hours([London] : Macmillan Publishers Limited, part of Springer Nature, 2015) Schröder, U.-Ch.; Beleites, C.; Assmann, C.; Glaser, U.; Hübner, U.; Pfister, W.; Fritzsche, W.; Popp, J.; Neugebauer, U.Vancomycin resistant enterococci (VRE) constitute a challenging problem in health care institutions worldwide. Novel methods to rapidly identify resistances are highly required to ensure an early start of tailored therapy and to prevent further spread of the bacteria. Here, a spectroscopy-based rapid test is presented that reveals resistances of enterococci towards vancomycin within 3.5 hours. Without any specific knowledge on the strain, VRE can be recognized with high accuracy in two different enterococci species. By means of dielectrophoresis, bacteria are directly captured from dilute suspensions, making sample preparation very easy. Raman spectroscopic analysis of the trapped bacteria over a time span of two hours in absence and presence of antibiotics reveals characteristic differences in the molecular response of sensitive as well as resistant Enterococcus faecalis and Enterococcus faecium. Furthermore, the spectroscopic fingerprints provide an indication on the mechanisms of induced resistance in VRE.
- ItemStrong magnetic frustration and anti-site disorder causing spin-glass behavior in honeycomb Li2RhO3([London] : Macmillan Publishers Limited, part of Springer Nature, 2015) Katukuri, Vamshi M.; Nishimoto, Satoshi; Rousochatzakis, Ioannis; Stoll, Hermann; van den Brink, Jeroen; Hozoi, LiviuWith large spin-orbit coupling, the electron configuration in d-metal oxides is prone to highly anisotropic exchange interactions and exotic magnetic properties. In 5d5 iridates, given the existing variety of crystal structures, the magnetic anisotropy can be tuned from antisymmetric to symmetric Kitaev-type, with interaction strengths that outsize the isotropic terms. By many-body electronic-structure calculations we here address the nature of the magnetic exchange and the intriguing spin-glass behavior of Li2RhO3, a 4d5 honeycomb oxide. For pristine crystals without Rh-Li site inversion, we predict a dimerized ground state as in the isostructural 5d5 iridate Li2IrO3, with triplet spin dimers effectively placed on a frustrated triangular lattice. With Rh-Li anti-site disorder, we explain the observed spin-glass phase as a superposition of different, nearly degenerate symmetry-broken configurations.
- ItemOcean rogue waves and their phase space dynamics in the limit of a linear interference model([London] : Macmillan Publishers Limited, part of Springer Nature, 2016) Birkholz, Simon; Brée, Carsten; Veselić, Ivan; Demircan, Ayhan; Steinmeyer, GünterWe reanalyse the probability for formation of extreme waves using the simple model of linear interference of a finite number of elementary waves with fixed amplitude and random phase fluctuations. Under these model assumptions no rogue waves appear when less than 10 elementary waves interfere with each other. Above this threshold rogue wave formation becomes increasingly likely, with appearance frequencies that may even exceed long-term observations by an order of magnitude. For estimation of the effective number of interfering waves, we suggest the Grassberger-Procaccia dimensional analysis of individual time series. For the ocean system, it is further shown that the resulting phase space dimension may vary, such that the threshold for rogue wave formation is not always reached. Time series analysis as well as the appearance of particular focusing wind conditions may enable an effective forecast of such rogue-wave prone situations. In particular, extracting the dimension from ocean time series allows much more specific estimation of the rogue wave probability.
- ItemExplosive death induced by mean–field diffusion in identical oscillators([London] : Macmillan Publishers Limited, part of Springer Nature, 2017) Verma, Umesh Kumar; Sharma, Amit; Kamal, Neeraj Kumar; Kurths, Jürgen; Shrimali, Manish DevWe report the occurrence of an explosive death transition for the first time in an ensemble of identical limit cycle and chaotic oscillators coupled via mean–field diffusion. In both systems, the variation of the normalized amplitude with the coupling strength exhibits an abrupt and irreversible transition to death state from an oscillatory state and this first order phase transition to death state is independent of the size of the system. This transition is quite general and has been found in all the coupled systems where in–phase oscillations co–exist with a coupling dependent homogeneous steady state. The backward transition point for this phase transition has been calculated using linear stability analysis which is in complete agreement with the numerics.
- ItemStudying hydrogen bonding and dynamics of the acetylate groups of the Special Pair of Rhodobacter sphaeroides WT([London] : Macmillan Publishers Limited, part of Springer Nature, 2019) Gräsing, Daniel; Dziubińska-Kühn, Katarzyna M.; Zahn, Stefan; Alia, A.; Matysik, JörgAlthough the cofactors in the bacterial reaction centre of Rhodobacter sphaeroides wild type (WT) are arranged almost symmetrically in two branches, the light-induced electron transfer occurs selectively in one branch. As origin of this functional symmetry break, a hydrogen bond between the acetyl group of PL in the primary donor and His-L168 has been discussed. In this study, we investigate the existence and rigidity of this hydrogen bond with solid-state photo-CIDNP MAS NMR methods offering information on the local electronic structure due to highly sensitive and selective NMR experiments. On the time scale of the experiment, the hydrogen bond between PL and His-L168 appears to be stable and not to be affected by illumination confirming a structural asymmetry within the Special Pair.
- ItemUltrafast in cellulo photoinduced dynamics processes of the paradigm molecular light switch [Ru(bpy)2dppz]2+([London] : Macmillan Publishers Limited, part of Springer Nature, 2016) De la Cadena, Alejandro; Davydova, Dar’ya; Tolstik, Tatiana; Reichardt, Christian; Shukla, Sapna; Akimov, Denis; Heintzmann, Rainer; Popp, Jürgen; Dietzek, BenjaminAn in cellulo study of the ultrafast excited state processes in the paradigm molecular light switch [Ru(bpy)2dppz]2+ by localized pump-probe spectroscopy is reported for the first time. The localization of [Ru(bpy)2dppz]2+ in HepG2 cells is verified by emission microscopy and the characteristic photoinduced picosecond dynamics of the molecular light switch is observed in cellulo. The observation of the typical phosphorescence stemming from a 3MLCT state suggests that the [Ru(bpy)2dppz]2+ complex intercalates with the DNA in the nucleus. The results presented for this benchmark coordination compound reveal the necessity to study the photoinduced processes in coordination compounds for intracellular use, e.g. as sensors or as photodrugs, in the actual biological target environment in order to derive a detailed molecular mechanistic understanding of the excited-state properties of the systems in the actual biological target environment.
- ItemPhysical plasma-triggered ROS induces tumor cell death upon cleavage of HSP90 chaperone([London] : Macmillan Publishers Limited, part of Springer Nature, 2019) Bekeschus, Sander; Lippert, Maxi; Diepold, Kristina; Chiosis, Gabriela; Seufferlein, Thomas; Azoitei, NinelHSP90 is a ubiquitously expressed molecular chaperone implicated in the correct folding and maturation of a plethora of proteins including protein kinases and transcription factors. While disruption of chaperone activity was associated with augmented cancer cell death and decreased tumor growth both in vitro and in vivo, the regulation of HSP90 is not clearly understood. Here we report that treatment of cancer cells with cold physical plasma, an emerging and less aggressive tumor therapy, resulted in ROS generation which subsequently triggered the cleavage of HSP90. Notably, cleavage of HSP90 was followed by the degradation of PKD2, a crucial regulator of tumor growth and angiogenesis. Pre-sensitization of cancer cells with subliminal doses of PU-H71, an HSP90 inhibitor currently under clinical evaluation, followed by treatment with cold-plasma, synergistically and negatively impacted on the viability of cancer cells. Taken together, cold-plasma can be used in conjunction with pharmacologic treatment in order to target the expression and activity of HSP90 and the downstream client proteins implicated in various cancer cell capabilities.
- ItemEnergetic electron assisted synthesis of highly tunable temperature-responsive collagen/elastin gels for cyclic actuation: macroscopic switching and molecular origins([London] : Macmillan Publishers Limited, part of Springer Nature, 2019) Wilharm, Nils; Fischer, Tony; Ott, Florian; Konieczny, Robert; Zink, Mareike; Beck-Sickinger, Annette G.; Mayr, Stefan G.Thermoresponsive bio-only gels that yield sufficiently large strokes reversibly and without large hysteresis at a well-defined temperature in the physiological range, promise to be of value in biomedical application. Within the present work we demonstrate that electron beam modification of a blend of natural collagen and elastin gels is a route to achieve this goal, viz. to synthesize a bioresorbable gel with largely reversible volume contractions as large as 90% upon traversing a transition temperature that can be preadjusted between 36 °C and 43 °C by the applied electron dose. Employing circular dichroism and temperature depending confocal laser scanning microscopy measurements, we furthermore unravel the mechanisms underlying this macroscopic behavior on a molecular and network level, respectively and suggest a stringent picture to account for the experimental observations. © 2019, The Author(s).