Showing papers by "Nanosystems Initiative Munich published in 2014"
TL;DR: In this paper, a photoactive COF capable of visible-light driven hydrogen generation in the presence of Pt as a proton reduction catalyst (PRC) was reported. But the Pt-doped COF was not shown to be able to produce hydrogen from water.
Abstract: Covalent organic frameworks (COFs) have recently emerged as a new generation of porous polymers combining molecular functionality with the robustness and structural definition of crystalline solids. Drawing on the recent development of tailor-made semiconducting COFs, we report here on a new COF capable of visible-light driven hydrogen generation in the presence of Pt as a proton reduction catalyst (PRC). The COF is based on hydrazone-linked functionalized triazine and phenyl building blocks and adopts a layered structure with a honeycomb-type lattice featuring mesopores of 3.8 nm and the highest surface area among all hydrazone-based COFs reported to date. When illuminated with visible light, the Pt-doped COF continuously produces hydrogen from water without signs of degradation. With their precise molecular organization and modular structure combined with high porosity, photoactive COFs represent well-defined model systems to study and adjust the molecular entities central to the photocatalytic process.
713 citations
TL;DR: It is proposed that employing a hydroxyl anion/radical redox couple to efficiently relay the hole from the semiconductor to the scavenger leads to a marked increase in the H2 generation rate without using expensive noble metal co-catalysts.
Abstract: Photocatalytic efficiency can be limited by slow transfer of photoexcited holes and high charge recombination rates. Using a hydroxyl anion–radical redox couple leads to enhanced photocatalytic H2 generation on Ni-decorated CdS nanorods. Photocatalytic conversion of solar energy to fuels, such as hydrogen, is attracting enormous interest, driven by the promise of addressing both energy supply and storage1. Colloidal semiconductor nanocrystals have been at the forefront of these efforts owing to their favourable and tunable optical and electronic properties2,3,4 as well as advances in their synthesis5,6. The efficiency of the photocatalysts is often limited by the slow transfer and subsequent reactions of the photoexcited holes and the ensuing high charge recombination rates. Here we propose that employing a hydroxyl anion/radical redox couple to efficiently relay the hole from the semiconductor to the scavenger leads to a marked increase in the H2 generation rate without using expensive noble metal co-catalysts. The apparent quantum yield and the formation rate under 447 nm laser illumination exceeded 53% and 63 mmol g−1 h−1, respectively. The fast hole transfer confers long-term photostability on the system and opens new pathways to improve the oxidation side of full water splitting.
679 citations
TL;DR: PTI nanosheets show significantly enhanced visible-light driven photocatalytic activity toward hydrogen evolution compared to their bulk counterpart, which highlights the crucial role of morphology and surface area on the photocatallytic performance of carbon nitride materials.
Abstract: Nanosheets of a crystalline 2D carbon nitride were obtained by ionothermal synthesis of the layered bulk material poly(triazine imide), PTI, followed by one-step liquid exfoliation in water. Triazine-based nanosheets are 1-2 nm in height and afford chemically and colloidally stable suspensions under both basic and acidic conditions. We use solid-state NMR spectroscopy of isotopically enriched, restacked nanosheets as a tool to indirectly monitor the exfoliation process and carve out the chemical changes occurring upon exfoliation, as well as to determine the nanosheet thickness. PTI nanosheets show significantly enhanced visible-light driven photocatalytic activity toward hydrogen evolution compared to their bulk counterpart, which highlights the crucial role of morphology and surface area on the photocatalytic performance of carbon nitride materials.
558 citations
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TL;DR: In this article, a photoactive COF based on hydrazone-linked functionalized triazine and phenyl building blocks is proposed to produce hydrogen from water without signs of degradation.
Abstract: Covalent organic frameworks (COFs) have recently emerged as a new generation of porous polymers combining molecular functionality with the robustness and structural definition of crystalline solids. Drawing on the recent development of tailor-made semiconducting COFs, we here report on a new COF capable of visible-light driven hydrogen generation. The COF is based on hydrazone-linked functionalized triazine and phenyl building blocks and adopts a layered structure with a honeycomb-type lattice featuring mesopores of 3.8 nm and the highest surface area among all hydrazone-based COFs reported to date. When illuminated with visible light, the COF continuously produces hydrogen from water without signs of degradation. With their precise molecular organization and modular structure combined with high porosity, photoactive COFs represent well-defined model systems to study and adjust the molecular entities central to the photocatalyic process.
435 citations
TL;DR: A new ultrafast solid electrolyte of the composition Li11Si2PS12 is reported, which exhibits a higher room-temperature Li ion diffusivity than the present record holder Li10GeP2S12 and could be traced back to fast Li ion hopping in the crystalline lattice.
Abstract: We report on a new ultrafast solid electrolyte of the composition Li11Si2PS12, which exhibits a higher room-temperature Li ion diffusivity than the present record holder Li10GeP2S12. We discuss the high-pressure synthesis and ion dynamics of tetragonal Li11Si2PS12, and comparison is made with our investigations of related members of the LMePS family, i.e. electrolytes of the general formula Li11−xMe2−xP1+xS12 with Me = Ge, Sn : Li10GeP2S12, Li7GePS8, Li10SnP2S12. The structure and dynamics were studied with multiple complementary techniques and the macroscopic diffusion could be traced back to fast Li ion hopping in the crystalline lattice. A clear correlation between the diffusivity and the unit cell volume of the LGPS-type electrolytes was observed.
251 citations
TL;DR: In this article, a new covalent triazine framework based on fluorene building blocks is presented, along with a comprehensive elucidation of its local structure, porosity, and capacity for CO2 capture and H2 storage.
Abstract: Porous organic polymers have come into focus recently for the capture and storage of postcombusted CO2. Covalent triazine frameworks (CTFs) constitute a nitrogen-rich subclass of porous polymers, which offers enhanced tunability and functionality combined with high chemical and thermal stability. In this work a new covalent triazine framework based on fluorene building blocks is presented, along with a comprehensive elucidation of its local structure, porosity, and capacity for CO2 capture and H2 storage. The framework is synthesized under ionothermal conditions at 300–600 °C using ZnCl2 as a Lewis acidic trimerization catalyst and reaction medium. Whereas the materials synthesized at lower temperatures mostly feature ultramicropores and moderate surface areas as probed by CO2 sorption (297 m2 g−1 at 300 °C), the porosity is significantly increased at higher synthesis temperatures, giving rise to surface areas in excess of 2800 m2 g−1. With a high fraction of micropores and a surface area of 1235 m2 g−1, the CTF obtained at 350 °C shows an excellent CO2 sorption capacity at 273 K (4.28 mmol g−1), which is one of the highest observed among all porous organic polymers. Additionally, the materials have CO2/N2 selectivities of up to 37. The hydrogen adsorption capacity of 4.36 wt% at 77 K and 20 bar is comparable to that of other POPs, yet the highest among all CTFs studied to date.
150 citations
TL;DR: It is demonstrated that by electrostatically controlling the adhesion and mobility of DNA origami structures on mica surfaces by the simple addition of monovalent cations, large ordered 2D arrays of origami tiles can be generated.
Abstract: The arrangement of DNA-based nanostructures into extended higher order assemblies is an important step towards their utilization as functional molecular materials. We herein demonstrate that by electrostatically controlling the adhesion and mobility of DNA origami structures on mica surfaces by the simple addition of monovalent cations, large ordered 2D arrays of origami tiles can be generated. The lattices can be formed either by close-packing of symmetric, non-interacting DNA origami structures, or by utilizing blunt-end stacking interactions between the origami units. The resulting crystalline lattices can be readily utilized as templates for the ordered arrangement of proteins.
144 citations
TL;DR: A detailed comparison of the most commonly considered microcanonical entropy definitions shows that, for a broad class of systems that includes all standard classical Hamiltonian systems, only the Gibbs volume entropy fulfills all three laws of thermodynamics simultaneously.
Abstract: The recent experimental realization of exotic matter states in isolated quantum systems and the ensuing controversy about the existence of negative absolute temperatures demand a careful analysis of the conceptual foundations underlying microcanonical thermostatistics. Here we provide a detailed comparison of the most commonly considered microcanonical entropy definitions, focusing specifically on whether they satisfy or violate the zeroth, first, and second laws of thermodynamics. Our analysis shows that, for a broad class of systems that includes all standard classical Hamiltonian systems, only the Gibbs volume entropy fulfills all three laws simultaneously. To avoid ambiguities, the discussion is restricted to exact results and analytically tractable examples.
116 citations
TL;DR: The way from the investigation of single cell dynamics to the recent developments of microfluidic techniques for particle and cell sorting using hydrodynamic forces is traced, which promise to revolutionize medical analyses for personalized point-of-care diagnosis.
101 citations
TL;DR: In this article, a unified introduction to the symmetry analysis and its action on the motion in one-dimensional periodic, both in time and space, potentials is presented. And the analysis is further generalized to quasi-periodic drives, higher space dimensions, and quantum dynamics.
91 citations
TL;DR: It is found that state-of-the-art pentacene films (grown on SiO2 at elevated temperature) are structurally not homogeneous but exhibit two interpenetrating phases at sub-micrometre scale, documented by a shifted vibrational resonance.
Abstract: Controlling the domain size and degree of crystallization in organic films is highly important for electronic applications such as organic photovoltaics, but suitable nanoscale mapping is very difficult. Here we apply infrared-spectroscopic nano-imaging to directly determine the local crystallinity of organic thin films with 20-nm resolution. We find that state-of-the-art pentacene films (grown on SiO2 at elevated temperature) are structurally not homogeneous but exhibit two interpenetrating phases at sub-micrometre scale, documented by a shifted vibrational resonance. We observe bulk-phase nucleation of distinct ellipsoidal shape within the dominant pentacene thin-film phase and also further growth during storage. A faint topographical contrast as well as X-ray analysis corroborates our interpretation. As bulk-phase nucleation obstructs carrier percolation paths within the thin-film phase, hitherto uncontrolled structural inhomogeneity might have caused conflicting reports about pentacene carrier mobility. Infrared-spectroscopic nano-imaging of nanoscale polymorphism should have many applications ranging from organic nanocomposites to geologic minerals.
TL;DR: This work immobilizes a two-stage DSD reaction cascade comprised of a “sender” and a ”receiver” gate onto a DNA origami platform and results indicate that for the 20 nm distance a fraction of signal strands is transferred locally to a receiver gate on the same platform, probably involving direct physical contact between the gates.
Abstract: Colocalization can strongly alter the kinetics and efficiency of chemical processes. For instance, in DNA-templated synthesis unfavorable reactions are sped up by placing reactants into close proximity onto a DNA scaffold. In biochemistry, clustering of enzymes has been demonstrated to enhance the reaction flux through some enzymatic cascades. Here we investigate the effect of colocalization on the performance of DNA strand displacement (DSD) reactions, an important class of reactions utilized in dynamic DNA nanotechnology. We study colocalization by immobilizing a two-stage DSD reaction cascade comprised of a “sender” and a “receiver” gate onto a DNA origami platform. The addition of a DNA (or RNA) input strand displaces a signal strand from the sender gate, which can then transfer to the receiver gate. The performance of the cascade is found to vary strongly with the distance between the gates. A cascade with an intermediate gate distance of ≈20 nm exhibits faster kinetics than those with larger distances, whereas a cascade with smaller distance is corrupted by excessive intraorigami leak reactions. The 20 nm cascade is found to be considerably more robust with respect to a competing reaction, and implementation of multiple receiver gates further increases this robustness. Our results indicate that for the 20 nm distance a fraction of signal strands is transferred locally to a receiver gate on the same platform, probably involving direct physical contact between the gates. The performance of the cascade is consistent with a simple model that takes “local” and “global” transfer processes into account.
TL;DR: In this paper, the optical properties of emission centers forming in radial heterostructure GaAs-Al0.3Ga0.7As nanowires were investigated and it was shown that these emitters exhibit quantum-dot-like characteristics.
Abstract: We probe and control the optical properties of emission centers forming in radial heterostructure GaAs-Al0.3Ga0.7As nanowires and show that these emitters, located in Al0.3Ga0.7As layers, can exhibit quantum-dot like characteristics. We employ a radio frequency surface acoustic wave to dynamically control their emission energy, and occupancy state on a nanosecond time scale. In the spectral oscillations, we identify unambiguous signatures arising from both the mechanical and electrical component of the surface acoustic wave. In addition, different emission lines of a single emission center exhibit pronounced anticorrelated intensity oscillations during the acoustic cycle. These arise from a dynamically triggered carrier extraction out of the emission center to a continuum in the radial heterostructure. Using finite element modeling and Wentzel–Kramers–Brillouin theory we identify quantum tunneling as the underlying mechanism. These simulation results quantitatively reproduce the observed switching and sho...
TL;DR: It is shown that within selected parameter regimes, noise η(t) of the mean value 〈η( t)〉=F can be significantly more effective than the deterministic force F: the motor can move much faster, its velocity fluctuations are much smaller, and the motor efficiency increases several times.
Abstract: We study a noisy drive mechanism for efficiency enhancement of Brownian motors operating on the microscale domain. It was proven [J. Spiechowicz et al., J. Stat. Mech. (2013) P02044] that biased noise $\ensuremath{\eta}(t)$ can induce normal and anomalous transport processes similar to those generated by a static force $F$ acting on inertial Brownian particles in a reflection-symmetric periodic structure in the presence of symmetric unbiased time-periodic driving. Here, we show that within selected parameter regimes, noise $\ensuremath{\eta}(t)$ of the mean value $\ensuremath{\langle}\ensuremath{\eta}(t)\ensuremath{\rangle}=F$ can be significantly more effective than the deterministic force $F$: the motor can move much faster, its velocity fluctuations are much smaller, and the motor efficiency increases several times. These features hold true in both normal and absolute negative mobility regimes. We demonstrate this with detailed simulations by resource to generalized white Poissonian noise. Our theoretical results can be tested and corroborated experimentally by use of a setup that consists of a resistively and capacitively shunted Josephson junction. The suggested strategy to replace $F$ by $\ensuremath{\eta}(t)$ may provide a new operating principle in which micro- and nanomotors could be powered by biased noise.
TL;DR: It is discovered that the directed large-scale cell flow altered fluctuations in cellular motion at short length scales: vorticity maps showed a reduced frequency of swirl formation in channel flow compared with resting sheets of equal cell density.
TL;DR: Using finite element modeling and Wentzel-Kramers-Brillouin theory, quantum tunneling is identified as the underlying mechanism for spectral oscillations of emission centers forming in radial heterostructure GaAs-Al0.7As and these emission centers are spatially separated from the continuum by >10.5 nm.
Abstract: We probe and control the optical properties of emission centers forming in radial het- erostructure GaAs-Al0.3Ga0.7As nanowires and show that these emitters, located in Al0.3Ga0.7As layers, can exhibit quantum-dot like characteristics. We employ a radio frequency surface acoustic wave to dynamically control their emission energy and occupancy state on a nanosec- ond timescale. In the spectral oscillations we identify unambiguous signatures arising from both the mechanical and electrical component of the surface acoustic wave. In addition, differ- ent emission lines of a single quantum dot exhibit pronounced anti-correlated intensity oscilla- tions during the acoustic cycle. These arise from a dynamically triggered carrier extraction out of the quantum dot to a continuum in the radial heterostructure. Using finite element modeling and Wentzel-Kramers-Brillouin theory we identify quantum tunneling as the underlying mech- anism. These simulation results quantitatively reproduce the observed switching and show that in our systems these quantum dots are spatially separated from the continuum by > 10.5 nm.
TL;DR: Generalized measurements of an observable performed on a quantum system during a force protocol are investigated and conditions that guarantee the validity of the Jarzynski equality and the Crooks relation are formulated.
Abstract: Generalized measurements of an observable performed on a quantum system during a force protocol are investigated and conditions that guarantee the validity of the Jarzynski equality and the Crooks relation are formulated. In agreement with previous studies by M. Campisi, P. Talkner, and P. H\"anggi [Phys. Rev. Lett. 105, 140601 (2010); Phys. Rev. E 83, 041114 (2011)], we find that these fluctuation relations are satisfied for projective measurements; however, for generalized measurements special conditions on the operators determining the measurements need to be met. For the Jarzynski equality to hold, the measurement operators of the forward protocol must be normalized in a particular way. The Crooks relation additionally entails that the backward and forward measurement operators depend on each other. Yet, quite some freedom is left as to how the two sets of operators are interrelated. This ambiguity is removed if one considers selective measurements, which are specified by a joint probability density function of work and measurement results of the considered observable. We find that the respective forward and backward joint probabilities satisfy the Crooks relation only if the measurement operators of the forward and backward protocols are the time-reversed adjoints of each other. In this case, the work probability density function conditioned on the measurement result satisfies a modified Crooks relation. The modification appears as a protocol-dependent factor that can be expressed by the information gained by the measurements during the forward and backward protocols. Finally, detailed fluctuation theorems with an arbitrary number of intervening measurements are obtained.
TL;DR: A DNA origami microarray is demonstrated, which is compatible with the requirements of single molecule fluorescence and super-resolution microscopy and facilitates automated read-out and data analysis and finds considerable variability within the array.
Abstract: The combination of molecular self-assembly based on the DNA origami technique with lithographic patterning enables the creation of hierarchically ordered nanosystems, in which single molecules are positioned at precise locations on multiple length scales. Based on a hybrid assembly protocol utilizing DNA self-assembly and electron-beam lithography on transparent glass substrates, we here demonstrate a DNA origami microarray, which is compatible with the requirements of single molecule fluorescence and super-resolution microscopy. The spatial arrangement allows for a simple and reliable identification of single molecule events and facilitates automated read-out and data analysis. As a specific application, we utilize the microarray to characterize the performance of DNA strand displacement reactions localized on the DNA origami structures. We find considerable variability within the array, which results both from structural variations and stochastic reaction dynamics prevalent at the single molecule level.
TL;DR: This paper finds a general expression for the corresponding non-normalized density which is fully determined by the particles velocity distribution, the anomalous diffusion exponent α, and the diffusion coefficient K(α).
Abstract: Motion of particles in many systems exhibits a mixture between periods of random diffusive-like events and ballistic-like motion. In many cases, such systems exhibit strong anomalous diffusion, where low-order moments $\ensuremath{\langle}|x(t){|}^{q}\ensuremath{\rangle}$ with $q$ below a critical value ${q}_{c}$ exhibit diffusive scaling while for $qg{q}_{c}$ a ballistic scaling emerges. The mixed dynamics constitutes a theoretical challenge since it does not fall into a unique category of motion, e.g., the known diffusion equations and central limit theorems fail to describe both aspects. In this paper we resolve this problem by resorting to the concept of infinite density. Using the widely applicable L\'evy walk model, we find a general expression for the corresponding non-normalized density which is fully determined by the particles velocity distribution, the anomalous diffusion exponent $\ensuremath{\alpha}$, and the diffusion coefficient ${K}_{\ensuremath{\alpha}}$. We explain how infinite densities play a central role in the description of dynamics of a large class of physical processes and discuss how they can be evaluated from experimental or numerical data.
TL;DR: In this paper, the authors explore the possibility of entangling an excitonic two-level system in a semiconductor quantum dot with a cavity defined on a photonic crystal by sweeping the cavity frequency across its resonance with the exciton transition.
Abstract: We explore the possibility of entangling an excitonic two-level system in a semiconductor quantum dot with a cavity defined on a photonic crystal by sweeping the cavity frequency across its resonance with the exciton transition. The dynamic cavity detuning is established by a radio frequency surface acoustic wave (SAW). It induces Landau-Zener transitions between the excitonic and the photonic degrees of freedom and thereby creates a superposition state. We optimize this scheme by using tailored Fourier-synthesized SAW pulses with up to five harmonics. The theoretical study is performed with a master equation approach for present state-of-the-art setups. Assuming experimentally demonstrated system parameters, we show that the composed pulses increase both the maximum entanglement and its persistence. The latter is only limited by the dominant dephasing mechanism, i.e., the photon loss from the cavity.
TL;DR: In this paper, the results of transient thermopower experiments, performed at room temperature on yttrium iron garnet/platinum bilayers, were presented, and they were interpreted in terms of the spin Seebeck effect.
Abstract: In this Letter, we present the results of transient thermopower experiments, performed at room temperature on yttrium iron garnet/platinum bilayers. Upon application of a time-varying thermal gradient, we observe a characteristic low-pass frequency response of the ensuing thermopower voltage with cutoff frequencies of up to 37 MHz. We interpret our results in terms of the spin Seebeck effect, and argue that small wavevector magnons are of minor importance for the spin Seebeck effect in our thin film hybrid structures.
TL;DR: In this paper, the optical gap of the organic semiconductor [1]benzothieno[3,2-b], and its 2,7-dibrominated analogue is measured in solution and in the crystalline state by means of UV-vis and emission spectroscopy.
Abstract: The optical gap of the organic semiconductor [1]benzothieno[3,2-b]benzothiophene and its 2,7-dibrominated analogue is measured in solution and in the crystalline state by means of UV-vis and emission spectroscopy. Bromination leads to a change in molecular packing from herringbone to π-stacked, resulting in a marked shift in the absorption and emission spectra which is found to be in accordance with TDDFT calculations.
TL;DR: In this paper, a zinc orthotitanate (Zn2TiO4) was successfully synthesized via the wet chemical sol-gel route assisted with a structure-directing diblock copolymer template.
Abstract: Foam-like zinc orthotitanate (Zn2TiO4) is successfully synthesized via the wet chemical sol–gel route assisted with a structure-directing diblock copolymer template. The wet chemical route enables spray deposition of Zn2TiO4 films. Calcination temperature of the spray-deposited films is shown to be crucial for the synthesis of the compound phase, Zn2TiO4. Surface composition and optical properties of the films are also studied. Finally, Zn2TiO4 films are shown to offer a reasonable functioning as an electron acceptor in dye-sensitized solar cells, with the best preliminary performance reported so far.
TL;DR: In this paper, the authors reported the facile production of single-layered tin sulfide nanosheets by a direct solid-state reaction, followed by quantitative liquid exfoliation in water.
Abstract: We report on the facile production of single-layered tin sulfide nanosheets by a direct solid-state reaction, followed by quantitative liquid exfoliation in water. The new solid solution of SnS2 and Li2S with composition Li4xSn1−xS2 serves as a versatile solid-state precursor with tunable relative lithium and tin content. The end member Li2SnS3, corresponding to the solid solution composition Li3x[LixSn1−xS2], crystallizes in the well-known A2BO3 structure type with mixed Li/Sn layers alternating with pure Li layers in the cationic substructure, which is interleaved with sulfur layers. The bonding in the Li layers can be regarded as ionic, while the Sn–S bonds have substantial covalent character. The resulting inherent anisotropy allows for the facile production of unilamellar chalcogenide nanosheets with thicknesses below 1 nm and lateral sizes of tens of microns, simply by shaking the crystalline precursor in water. The quantitative exfoliation into single-layered nanosheets was confirmed using optical microscopy, AFM, TEM, as well as X-ray diffraction of freestanding films produced from the colloidal suspension by centrifugation. Upon annealing, the as-obtained nanosheets are converted into SnS2 without sacrificing their favorable dispersion properties in water. The presented method allows for the cheap and scalable production of unilamellar chalogenide nanosheets for various potential applications, such as in electronic devices, solar cells, sensors, or battery technology. We expect this method to be generic and transferable to the synthesis of other metal chalcogenides. The use of solid solutions as solid-state precursors, featuring a large compositional range and potential for doping with other metals, may ultimately allow for the controlled introduction of defect levels and rational band-gap engineering in nanosheet materials.
TL;DR: In this paper, a block copolymer-assisted sol-gel synthesis route is used to obtain zinc oxide (ZnO) thin films with a nanogrid-like morphology.
Abstract: Via a block copolymer-assisted sol–gel synthesis route, zinc oxide (ZnO) thin films are obtained with a nanogrid-like morphology. During annealing of the hybrid ZnO films, the templating polymer undergoes structural rearrangements. Solvent annealing is done using tetrahydrofuran (THF) vapor and hence used as a tool to tune the pore size of the final grid-like films. A calcination step is performed to remove the polymer template and to study the effect of solvent annealing on the final ZnO nano-grid film. The surface structures of the films are investigated via scanning electron microscopy (SEM) and atomic force microscopy (AFM). In addition, the evolution in the structural length scales in the film volume is probed using grazing incidence small angle X-ray scattering (GISAXS).
TL;DR: The step‐by‐step elongation of precise linear oligo(ethanamino) amides by making use of the artificial amino acid succinoyl‐tetraethylene pentamine (Stp) for solid‐phase‐assisted synthesis enabled us to identify the optimal oligomer Stp30‐W with a length of 30 Stp units, with which effective gene transfer occurs in the absence of cytotoxicity.
Abstract: The optimization of synthetic carriers for gene transfer remains a major challenge. Cationic polymers such as polyethylenimine (PEI) often show increasing gene transfer activity with increasing molecular weight, but this favorable effect is accompanied by an undesired increase in cytotoxicity. Moreover, the polydispersity of polymers prevents accurate determination of optimum size. Herein we describe the step-by-step elongation of precise linear oligo(ethanamino) amides by making use of the artificial amino acid succinoyl-tetraethylene pentamine (Stp) for solid-phase-assisted synthesis. This procedure enabled us to identify the optimal oligomer Stp30-W (8.4 kDa) with a length of 30 Stp units, with which effective gene transfer occurs in the absence of cytotoxicity. The transfection efficiency of Stp30-W exceeded that of standard linear PEI (22 kDa) by sixfold; nevertheless, Stp30-W exhibited tenfold lower cytotoxicity. In addition to the lower molecular weight, the succinate spacer between the oligoamine units may also contribute to the favorable biocompatibility. The cytotoxicity of the cationic polymer PEI is a major concern for use as a carrier for gene delivery, so this comparison between linear PEI and the new Stp oligomers is particularly relevant.
TL;DR: Monolayer self-assembly of a hexabrominated, three-fold symmetric aromatic molecule is studied at the heptanoic acid-graphite interface and comparison with theoretical entropy estimates suggests a minor influence of solvation.
TL;DR: In this paper, an integrated sensing platform for the detection of various chemical analytes via translating the photonic stopband shift of a one-dimensional photonic crystal (PC) into an electrical current change is proposed.
Abstract: An innovative integrated sensing platform for the detection of various chemical analytes via translating the photonic stop-band shift of a one-dimensional photonic crystal (PC) into an electrical current change is proposed. The miniaturized sensing platform features an organic light-emitting diode (OLED) as a light source and an organic photodetector (OPD) as a light sensor and allows for the detection of ethanol vapor concentrations down to ≈ 10 parts per million (ppm) in nitrogen, which corresponds to a stop-band shift of ≈ 27 pm. The resolution of the proposed platform exceeds the capabilities of most commercial spectrometers and by far the human eye, while, at the same time, such a sensor is less expensive and less power consuming than a spectrometer. The presented setup is generic and can detect optical changes in the transmission of PCs, which can be induced by both vapor adsorption or by a liquid analyte, as demonstrated with a microfluidic setup.
TL;DR: In this article, the authors studied the transport in an asymmetric superconducting quantum interference device (SQUID) composed of a loop with three capacitively and resistively shunted Josephson junctions: two in series in one arm and the remaining one in the other arm.
Abstract: We study transport in an asymmetric superconducting quantum interference device (SQUID) which is composed of a loop with three capacitively and resistively shunted Josephson junctions: two in series in one arm and the remaining one in the other arm. The loop is threaded by an external magnetic flux and the system is subjected to both a time-periodic and a constant current. We formulate the deterministic and, as well, the stochastic dynamics of the SQUID in terms of the Stewart-McCumber model and derive an equation for the phase difference across one arm, in which an effective periodic potential is of the ratchet type, i.e., its reflection symmetry is broken. In doing so, we extend and generalize an earlier study by Zapata et al. [Phys. Rev. Lett. 77, 2292 (1996)] and analyze directed transport in wide parameter regimes: covering the overdamped to the moderate damping regime up to its fully underdamped regime. As a result we detect the intriguing features of a negative (differential) conductance, repeated voltage reversals, noise-induced voltage reversals, and solely thermal noise-induced ratchet currents. We identify a set of parameters for which the ratchet effect is most pronounced and show how the direction of transport can be controlled by tailoring the external magnetic flux.
TL;DR: The present structure-activity relationship study of MTX-based ligands pinpoints the concept of synthetic polyglutamylation as a promising approach for optimizing bioactivity of antifolate conjugates, which might be considered as a useful tool also in context of other drug delivery systems.
Abstract: The antifolate drug methotrexate (MTX) can serve as a dual-functional ligand in antitumoral drug delivery, inducing both a folate receptor mediated cellular uptake and an intracellular cytotoxic action. Bioactivity of MTX however changes by conjugation; the activity can be affected by the hampered intracellular conversion to more potent poly-γ-glutamyl derivatives. Therefore, in a cancer combination therapy approach for the codelivery of cytotoxic dsRNA polyinosinic–polycytidylic acid poly(I:C), a set of molecularly precise oligo(ethanamino)amides were synthesized comprising poly(ethylene glycol) conjugated MTX ligands. The conjugates differed in the number of additional glutamic acid residues to investigate the effect of different degrees of synthetic “a priori” polyglutamylation. The bioactivity of these compounds concerning dihydrofolate reductase (DHFR) inhibition, cytotoxicity, nucleic acid binding potency, cellular uptake of poly(I:C) polyplexes, and combined antifolate/poly(I:C) toxicity was invest...