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Slowing Down of the Molecular Reorientation of Water in Concentrated Alkaline Solutions
Get PDFIt is generally accepted that the hydroxide ion (OH–) is a strong hydrogen bond acceptor and that its anomalously high diffusion constant in water results from a Grotthuss-like structural diffusion mechanism. However, the spatial extent over which OH– ions influence the dynamics of the hydrogen-bond network of water remained largely unclear. Here, we measure the ultrafast dynamics of OH groups of HDO molecules interacting with the deuterated hydroxide ion OD–. For solutions with OD– concentrations up to 4 M, we find that HDO molecules that are not directly interacting with the ions have a reorientation time constant of ∼2.7 ps, similar to that of pure liquid water. When the concentration of OD– ions is increased, the reorientation time constant increases, indicating a strong slowing down of the structural dynamics of the solution
Molecular packing structure of fibrin fibers resolved by X-ray scattering and molecular modeling
Get PDFFibrin is the major extracellular component of blood clots and a proteinaceous hydrogel used as a versatile biomaterial. Fibrin forms branched networks built of laterally associated double-stranded protofibrils. This multiscale hierarchical structure is crucial for the extraordinary mechanical resilience of blood clots, yet the structural basis of clot mechanical properties remains largely unclear due, in part, to the unresolved molecular packing of fibrin fibers. Here the packing structure of fibrin fibers is quantitatively assessed by combining Small Angle X-ray Scattering (SAXS) measurements of fibrin reconstituted under a wide range of conditions with computational molecular modeling of fibrin protofibrils. The number, positions, and intensities of the Bragg peaks observed in the SAXS experiments were reproduced computationally based on the all-atom molecular structure of reconstructed fibrin protofibrils. Specifically, the model correctly predicts the intensities of the reflections of the 22.5 nm axial repeat, corresponding to the half-staggered longitudinal arrangement of fibrin molecules. In addition, the SAXS measurements showed that protofibrils within fibrin fibers have a partially ordered lateral arrangement with a characteristic transverse repeat distance of 13 nm, irrespective of the fiber thickness. These findings provide fundamental insights into the molecular structure of fibrin clots that underlies their biological and physical properties
Temporal tracking of quantum-dot apatite across in vitro mycorrhizal networks shows how host demand can influence fungal nutrient transfer strategies
Get PDFArbuscular mycorrhizal fungi function as conduits for underground nutrient transport. While the fungal partner is dependent on the plant host for its carbon (C) needs, the amount of nutrients that the fungus allocates to hosts can vary with context. Because fungal allocation patterns to hosts can change over time, they have historically been difficult to quantify accurately. We developed a technique to tag rock phosphorus (P) apatite with fluorescent quantum-dot (QD) nanoparticles of three different colors, allowing us to study nutrient transfer in an in vitro fungal network formed between two host roots of different ages and different P demands over a 3-week period. Using confocal microscopy and raster image correlation spectroscopy, we could distinguish between P transfer from the hyphae to the roots and P retention in the hyphae. By tracking QD-apatite from its point of origin, we found that the P demands of the younger root influenced both: (1) how the fungus distributed nutrients among different root hosts and (2) the storage patterns in the fungus itself. Our work highlights that fungal trade strategies are highly dynamic over time to local conditions, and stresses the need for precise measurements of symbiotic nutrient transfer across both space and time
Strong coupling to generate complex birefringence - metasurface in the middle etalons
Get PDFWe have measured the optical signatures of strong coupling between the resonance of etalons and plasmon antenna arrays in transmission and polarization. Planar etalons in the middle of which a plasmon antenna array is placed show anticrossings in transmission between the etalon resonances and plasmon antenna resonance, which we map as function of frequency, etalon opening and oscillator strengh. We argue that the proper interpretation of strong coupling and the magnitude of the Rabi splitting requires a `metasurface-in-the-middle' cavity model, and is distinct from strong coupling between a cavity and a dispersive material. Furthermore, we quantitatively connect the Rabi splitting to the electrostatic antenna polarizability, i.e., the polarizability in absence of radiative damping corrections. Finally, we demonstrate that the strong coupling brings very strong polarization conversion effects, as the hybrid modes provide for a strong retardance that can be leveraged for linear birefringence and dichroism
Observation of Cooperative Purcell Enhancements in Antenna-Cavity Hybrids
Get PDFLocalizing light to nanoscale volumes through nanoscale resonators that are low loss and precisely tailored in spectrum to properties of matter is crucial for classical and quantum light sources, cavity QED, molecular spectroscopy, and many other applications. To date, two opposite strategies have been identified: to either use plasmonics with deep subwavelength confinement yet high loss and very poor spectral control, or instead microcavities with exquisite quality factors yet poor confinement. In this work we realize hybrid plasmonic-photonic resonators that enhance the emission of single quantum dots, profiting both from plasmonic confinement and microcavity quality factors. Our experiments directly demonstrate how cavity and antenna jointly realize large cooperative Purcell enhancements through interferences. These can be controlled to engineer arbitrary Fano lineshapes in the local density of optical states
Nanocube Imprint Lithography
Get PDFIn recent years, imprint lithography has emerged as a promising patterning technique capable of high-speed and volume production. In this work, we report highly reproducible one-step printing of metal nanocubes. A dried film of monocrystalline silver cubes serves as the resist and a soft polydimethylsiloxane (PDMS) stamp directly imprints the final pattern. The use of atomically smooth and sharp faceted nanocubes facilitates the printing of high-resolution and well-defined patterns with face-to-face alignment between adjacent cubes. It also permits digital control over the linewidth of patterns such as straight lines, curves and complex junctions over an area of several square millimeters. Single-particle lattices as well as three-dimensional (3D) nanopatterns are also demonstrated with an aspect ratio up to 5 in the vertical direction. The high fidelity nanocube patterning combined with the previously demonstrated epitaxial overgrowth can enable curved (single) crystals from solution at room temperature or highly efficient transparent conductors
Change in Tetracene Polymorphism Facilitates Triplet Transfer in Singlet Fission-Sensitized Silicon Solar Cells
Get PDFSinglet fission in tetracene generates two triplet excitons per absorbed photon. If these triplet excitons can be effectively transferred into silicon (Si), then additional photocurrent can be generated from photons above the bandgap of Si. This could alleviate the thermalization loss and increase the efficiency of conventional Si solar cells. Here, we show that a change in the polymorphism of tetracene deposited on Si due to air exposure facilitates triplet transfer from tetracene into Si. Magnetic field-dependent photocurrent measurements confirm that triplet excitons contribute to the photocurrent. The decay of tetracene delayed photoluminescence was used to determine a transfer efficiency of ∼36% into Si. Our study suggests that control over the morphology of tetracene during the deposition will be of great importance to boost the triplet transfer yield further
Performance analysis and model-free design of deracemisation via temperature-cycles
Get PDFSolid-state deracemisation via temperature-cycles is a technique that has shown to be effective to isolate the pure enantiomer of a conglomerate forming compound. This process has a large number of operating parameters that can be adjusted according to system-specific properties. On the one hand, this feature makes the process flexible and prone to optimisation. On the other hand, the design space is so large that the experimental optimisation of the process can become long and cumbersome. In this work we achieve two results. First, we show that deracemisation via temperature-cycles works very effectively for two new experimental systems, namely the chiral compounds 2-(benzylideneamino)-2-(2-chlorophenyl)acetamide (CPG) and 3,3-dimethyl-2-((naphthalen-2-ylmethylene)amino) butanenitrile (tLEU). Secondly, we propose a new approach for the design of an effective deracemisation process via temperature-cycles for a new compound. Therefore, in this work, we investigate the effect of different operating conditions, namely the initial enantiomeric excess, the cooling rate, the temperature range, and the catalyst concentration, on the performance of deracemisation via T-cycles for the new compounds, CPG and tLEU, and for -(2-methylbenzylidene)-phenylglycine amide (NMPA) already studied in a previous paper. Based on these outcomes, we conclude by proposing a model-free screening strategy for the design of an effective deracemisation process via temperature-cycles for a new compound
Simultaneous sensing and imaging of individual biomolecular complexes enabled by modular DNA–protein coupling
Get PDFMany proteins form dynamic complexes with DNA, RNA, and other proteins, which often involves protein conformational changes that are key to function. Yet, methods to probe these critical dynamics are scarce. Here we combine optical tweezers with fluorescence imaging to simultaneously monitor the conformation of individual proteins and their binding to partner proteins. Central is a protein–DNA coupling strategy, which uses exonuclease digestion and partial re-synthesis to generate DNA overhangs of different lengths, and ligation to oligo-labeled proteins. It provides up to 40 times higher coupling yields than existing protocols and enables new fluorescence-tweezers assays, which require particularly long and strong DNA handles. We demonstrate the approach by detecting the emission of a tethered fluorescent protein and of a molecular chaperone (trigger factor) complexed with its client. We conjecture that our strategy will be an important tool to study conformational dynamics within larger biomolecular complexes