Over the past decade, Airy beams have been the subject of extensive research, leading to new physical insights and various applications. In this Letter, we extend the concept of Airy beams to the quantum domain. We generate entangled photons in a superposition of two-photon Airy states via spontaneous parametric down conversion, pumped by a classical Airy beam. We show that the entangled Airy photons preserve the intriguing properties of classical Airy beams, such as free acceleration and reduced diffraction, while exhibiting non-classical anti-correlations. Finally, we discuss the advantages offered by entangled Airy photons for high-dimensional free-space quantum communications.
Two covalently linked donor–acceptor copper phenanthroline complexes (C–A dyads) of interest for solar energy conversion/storage schemes, [Cu(i)(Rphen(OMV)24+)2]9+ = RC+A48+ with RC+ = [Cu(i)Rphen2]+ involving 2,9-methyl (R = Me) or 2,9-phenyl (R = Ph)-phenanthroline ligands that are 5,6-disubstituted by 4-(n-butoxy) linked methylviologen electron acceptor groups (A2+ = OMV2+), have been synthesized and investigated via quantum chemical calculations and nanosecond laser flash spectroscopy in 1,2-difluorobenzene/methanol (dfb/MeOH) mixtures. Upon photoexcitation, charge transfer (CT) states RC2+A+A36+ are formed in less than one ns and decay by charge recombination on a time scale of 6–45 ns. The CT lifetime of RC2+A+A36+ has a strong dependence on MeOH solvent fraction when R = Me, but is unaffected if R = Ph. This solvent effect is due to coordination of MeOH solvent in MeC+A48+ (i.e. exciplex formation) allowed by conformational flattening of the ligand sphere, which cannot occur in PhC+A48+ having bulkier Phphen ligand framework. Interestingly, the decay time of the CT state increases for both species at low magnetic fields with a maximum increase of ca. 30% at ca. 150 mT, then decreases as the field is increased up to 1500 mT, the highest field investigated. This magnetic field effect (MFE) is due to magnetic modulation of the spin dynamics interconverting 3CT and 1CT states. A quantitative modeling according to the radical pair mechanism involving ab initio multireference calculations of the complexes revealed that the spin process is dominated by the effect of Cu hyperfine coupling. The external magnetic field suppresses the hyperfine coupling induced spin state mixing thereby lengthening the CT decay time. This effect is counteracted by the field dependent processes of T0–S mixing through the Δg-mechanism and by a local mode spin–orbit mechanism. Further, the maximum MFE is limited by a finite rate of direct recombination of 3CT states and the spin-rotational mechanism of spin relaxation. This study provides a first comprehensive characterization of Cu(ii)-complex spin chemistry and highlights how spin chemistry can be used to manipulate solar energy harvesting and storage materials.
In calculating transfer free energies of solvated substances, the coexisting crystal state is often taken as the reference. Furthermore, the free energy of this reference state is often assumed to remain constant upon changes made in solution. Yet little is known about the way added cosolutes impact the thermodynamic stability of the out-of-solution crystal phase. To provide insight into the changes in the activity of the coexisting solid state, we used caffeine, a well-studied hydrophobic compound that forms a hydrated crystal in saturated aqueous solutions. By using X-ray powder diffraction, we found that cosolutes, such as trehalose, sucrose, sodium sulfate, and polyethylene glycol (PEG) alter the unit cell volume of crystalline caffeine, in a concentration dependent manner. The dehydration of solid caffeine translates into an overall increase in its free energy, which can be directly calculated as the reversible ΠV work required to compress the crystal. We determined that trehalose, sucrose, and sodium sulfate increase the free energy of the solid, while PEG decreases it. For 2 mol/kg trehalose, this change in free energy corresponds to 17 % of the total change in solvation free energy of monomeric caffeine. Although our results indicate that cosolutes modify the free energy of the solid less than that of the solvated state, this effect is non negligible and measurable, suggesting that it should generally be taken into account as a contribution to changes in solubility, particularly whenever the solid phase is hydrated.
Phytochromes and related photoreceptors distinguish themselves for their long-wavelength absorption and large spectral shift between parental state and photoproduct. Both features are not well understood, partly due to lack of high-resolution structural data and insufficient support from quantum-chemical calculations. The red–green switching cyanobacteriochrome Slr1393g3 shows an absorption shift larger than 110 nm. Both parental state and photoproduct could be crystallized with high resolution, together with a “hybrid” form carrying the chromophore in parental state geometry, whereas the protein remained in the photoproduct conformation. The crystal structures reveal how chromophore and protein mutually regulate their conformational changes, yielding the observed spectral shift. Quantum-chemical calculations, based on these structures, provide a deeper understanding of the spectral tuning mechanisms.The three-dimensional (3D) crystal structures of the GAF3 domain of cyanobacteriochrome Slr1393 (Synechocystis PCC6803) carrying a phycocyanobilin chromophore could be solved in both 15-Z dark-adapted state, Pr, λmax = 649 nm, and 15-E photoproduct, Pg, λmax = 536 nm (resolution, 1.6 and 1.86 Å, respectively). The structural data allowed identifying the large spectral shift of the Pr-to-Pg conversion as resulting from an out-of-plane rotation of the chromophore’s peripheral rings and an outward movement of a short helix formed from a formerly unstructured loop. In addition, a third structure (2.1-Å resolution) starting from the photoproduct crystals allowed identification of elements that regulate the absorption maxima. In this peculiar form, generated during X-ray exposition, protein and chromophore conformation still resemble the photoproduct state, except for the D-ring already in 15-Z configuration and tilted out of plane akin the dark state. Due to its formation from the photoproduct, it might be considered an early conformational change initiating the parental state-recovering photocycle. The high quality and the distinct features of the three forms allowed for applying quantum-chemical calculations in the framework of multiscale modeling to rationalize the absorption maxima changes. A systematic analysis of the PCB chromophore in the presence and absence of the protein environment showed that the direct electrostatic effect is negligible on the spectral tuning. However, the protein forces the outer pyrrole rings of the chromophore to deviate from coplanarity, which is identified as the dominating factor for the color regulation.
Viruses have been of interest to mankind since their discovery as small infectious agents in the nineteenth century. Because many viruses cause diseases to humans and agriculture, they were rigorously studied for biological and medical purposes. Viruses have remarkable properties such as the symmetry and self-assembly of their protein envelope, maturation into infectious virions, structural stability, and disassembly. Solution X-ray scattering can probe structures and reactions in solutions, down to subnanometer spatial resolution and millisecond temporal resolution. It probes the bulk solution and reveals the average shape and average mass of particles in solution and can be used to study kinetics and thermodynamics of viruses at different stages of their life cycle. Here we review recent work that demonstrates the capabilities of solution X-ray scattering to study in vitro the viral life cycle.
Solid-supported phospholipid bilayers are versatile model structures for mimicking the biological cell membrane, and are increasingly utilized as functional interface components of biosensors and other bio-micro- and nanofluidic devices. In the context of biosensor development, membrane-embedded peptides have gained importance as bio-recognition elements, targeting diverse analytes including proteins, nucleic acids, bacteria, metal ions, enzymes and antibodies. For example, the neuropeptide oxytocin has a key role during labor and lactation as well as in the development of social behavior. Divalent cations such as Zn2+ and Cu2+ vitally affect the activity of oxytocin upon binding. Deviations in the quantity and whereby binding of such ions to oxytocin are associated with diseases; e.g., multiple sclerosis, Alzheimer, and autism spectrum disorder (ASD). We developed an immunofluorescence assay to verify and quantify lipid bilayer membrane-integration of oxytocin-cholesterol conjugate, which was designed and synthesized as membrane-associated recognition element for a surface acoustic resonance (SAR) sensor. In our study, a microfluidic open-volume superfusion device, the Biopen, was used to deposit small unilamellar vesicles, prepared from 1-palmitoyl-2-oleoyl phosphatidylcholine (POPC) and oxytocin-conjugated cholesterol, onto a glass surface, where they transformed into extended patches of planar surface-supported bilayer. Thereafter, oxytocin endogenous carrier protein neurophysin-1 (primary antibody) and a fluorescently tagged secondary antibody, were sequentially delivered to the membrane. An antibody binding dependence on oxytocin-concentration was determined by means of fluorescence microscopy, and an optimal concentration for sensor applications was established. The fluorescence assay can be directly transferred to the SAR sensor, where a supported bilayer is established as sensing layer in order to quantify interactions between oxytocin and molecules of interest in a quantitative manner with high sensitivity, fundamentally supporting the development of new diagnostic and therapeutic options for the early detection of neurological and neurodegenerative conditions.
In the past four decades, the chemistry of 1,1‐ and 1,2‐bisboronate compounds has been extensively explored. Many interesting structural features and reaction patterns have emerged, and more importantly, these compounds now feature prominently in both metal‐catalyzed and metal‐free transformations for the formation of CC bonds and C–heteroatom and other processes. This chapter aims to highlight the recent development in this rising research field, focusing on the synthesis of 1,1‐ and 1,2‐bisboronate compounds and their reactivity and selectivity that originate from the use of these bisboronates.
Coordination polymers (CPs) and coordination network solids such as metal-organic frameworks (MOFs) have gained increasing interest during recent years due to their unique properties and potential applications. Preparing 3D printed structures using CP would provide many advantages towards utilization in fields such as catalysis and sensing. So far, functional 3D structures were printed mostly by dispersing pre-synthesized particles of CPs and MOFs within a polymerizable carrier. This resulted in a CP active material dispersed within a 3D polymeric object, which may obstruct or impede the intrinsic properties of the CP. Here, we present a new concept for obtaining 3D free-standing objects solely composed of CP material, starting from coordination metal complexes as the monomeric building blocks, and utilizing the 3D printer itself as a tool to in situ synthesize a coordination polymer during printing, and to shape it into a 3D object, simultaneously. To demonstrate this, a 3D-shaped nickel tetra-acrylamide monomeric complex composed solely of the CP without a binder was successfully prepared using our direct print-and-form approach. We expect that this work will open new directions and unlimited potential in additive manufacturing and utilization of CPs.
This paper reads Marcel L’Herbier’s The Inhuman Woman as an exemplary expression of a posthuman moment in modernism. Drawing on comparisons with the art of Fernand Léger and James Joyce, it highlights several elements of the film’s aesthetic – its heavily stylized compositions, its striking use of set design and costumes to subvert the visual syntax of foreground and background, its eroticization of technology, its disassembly of the human figure – in order to demonstrate the continuity between a high-modernist discourse on machine-life and current issues in posthuman theory. Both modernism and posthumanism respond to an epochal event within modernity, a technological acceleration of reality that reshapes ontological grammars. Both contemplate reality as a middle ground of mechanical and vital processes. And both are committed to a Copernican decentering of the human eye from its place of privilege in received models of phenomenal experience.
By designing an actuator composed of thin layers with different coefficients of thermal expansion (CTE) together with an electrically conductive layer, the CTE mismatch can be utilized to produce s...
