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Energy exchange between Nd3+ and Er3+ centers within molecular complexes
No full textThe controlled and reproducible molecular assemblies incorporating lanthanide centers represents a crucial step in driving forward up- and down-conversion processes. This challenge calls for the development of strategies to facilitate the efficient in-situ segregation of different Ln metal ions into distinct positions within the molecule. The unique family of pure [LnLn′Ln] heterometallic coordination compounds previously developed by us represents an ideal platform for studying the desired Ln-to-Ln′ energy transfer (ET). In this context, we report here the new pure one-step synthetically produced [ErNdEr] (3) complex, which allows for the first time at the molecular level to study the mechanisms behind Nd-to-Er energy transfer. To further assess the photophysical properties of this complex, the analogous [LuNdLu] (1) and [ErLaEr] (2) complexes have been also prepared and photophysically studied. Efficient sensitization via the two β-diketones employed as main ligands was proben for both Nd3+ and Er3+ ions, resulting in highly resolved emission spectra and sufficiently long excited state lifetimes, which allowed to further assess the Ln-to-Ln′ ET. This intermetallic transfer was first detected by comparing the emission spectra of iso-absorbant solutions and demonstrated by comparing the lifetime values with or without the lanthanide quencher (Er3+), as well as with a deep analysis of the excitation spectrum of the three complexes. Thus, a very unique phenomenon was discovered, consisting in a mutual Nd-to-Er and Er-to-Nd ET with no net increase of brightness by any metal ; while Nd3+ transfers the energy received from the antena to Er3+, the sensitization of the latter results into back-transfer to Nd3+ to a non-emissive, thus silent state
Head Group Dependence and Kinetic Bottlenecks of Gas- phase Thermal PFAS Destruction
No full textVarying and sometimes con[icting temperatures and products have been reported from studies addressing thermal PFAS destruction, often because decomposition pathways are highly dependent on the respective experimental system. Here we applied highest-level coupled cluster calculations to isolate and identify the major processes during thermal PFAS destruction in the gas phase with relevance to incineration, thermal oxidation, and other thermal treatment technologies in which PFAS and their volatile decomposition products desorb into the gas phase. All investigated per[uoroalkyl acids decompose via unimolecular head group loss, either through HF elimination or homolytic bond cleavage as a function of head group type. In contrast, all investigated [uorotelomers undergo initial hydrogen abstraction from the characteristic C2H4 moiety by hydroxyl radicals under representative incineration conditions, followed by radical decomposition. Subsequent formation of per[uoroalkanes including CF4 can then be prevented by supplying su`cient hydrogen donors such as hydrocarbon fuel and water as well as by scavenging released [uorine. This leads to the generation of stable 1H-per[uoroalkanes. While parent PFAS decomposition proceeds at gas-phase temperatures ≤700 °C, carbon-carbon cleavage of 1H-per[uoroalkanes requires up to ~950 °C at 2 seconds gas residence time, making this step the kinetic bottleneck on the way to complete thermal PFAS mineralization
pH drives electron density fluctuations that enhance electric field-induced liquid flow
No full textLiquid flow along a charged interface is commonly described by classical continuum theory, which represents the electric double layer by uniformly distributed point charges. The electrophoretic mobility of hydrophobic nanodroplets in water doubles in magnitude when the pH is varied from neutral to mildly basic (pH 7 to pH 11). Classical continuum theory predicts that this increase in mobility is due to an increased surface charge. Here, by combining all-optical measurements of surface charge and molecular structure, as well as electronic structure calculations, we show that surface charge and molecular structure at the nanodroplet surface are identical at neutral and mildly basic pH. We propose that the force that propels the droplets originates from two factors: Negative charge on the droplet surface due to charge transfer from and within water, and anisotropic gradients in the fluctuating polarization induced by the electric field. Both charge density fluctuations couple with the external electric field, and lead to droplet flow. Replacing chloride by hydroxide doubles both the charge conductivity via the Grotthuss mechanism, and the droplet mobility. This general mechanism deeply impacts a plethora of processes in biology, chemistry, and nanotechnology and provides an explanation of how pH influences hydrodynamic phenomena and the limitations of classical continuum theory currently used to rationalize these effects
Copper-Catalyzed Disruption of a Cascade Reaction: Synthesis of γ-Ketoamides from Nitrones and Ynamides
No full textA thermal dipolar cycloaddition and rearrangement reaction to form pyrrolines has been redirected towards the synthesis of γ-keto- and γ-aldoamides from nitrones and ynamides with a Cu(II) catalyst. A copper-coordinated iminium intermediate is proposed to initiate a diastereoselective rearrangement for C–C bond formation and a combination of catalyst and nitrone protecting group balance the desired reactivity, diastereoselectivity, and sensitivity to hydrolysis. Reaction optimization is described in addition to scope, mechanistic studies, and conversion of γ-ketoamides to 1,4-diones. This catalytic method showcases distinct copper-catalyzed reactivity of N-alkenylnitrones for the synthesis of 1,4-dicarbonyl compounds
Rethinking Oxygen Redox: Does Oxygen Dimerisation Occur without Oxidation in Li2NiO3?
No full textIn layered lithium transition metal oxide cathodes, high voltage operation is accompanied by the formation of oxygen dimers, which are widely used as an indicator of oxygen-redox activity. However, understanding the role that oxygen dimerisation plays in facilitating charge compensation is still needed. Here, Li2NiO3 (a 3d8L2-containing compound, where L is a ligand hole) is studied as a model system, where oxygen dimerisation is shown to occur without cathode oxidation. Electrochemical cycling results in a net reduction of the cathode structure, accompanied by structural transformations, despite spectroscopic features of oxygen dimers arising at the top of charge. Oxygen dimerisation is shown to coexist alongside a structurally transformed and electronically reduced cathode structure, thus raising questions about its origin with respect to delithiation
Achiral plasmonic antennas enhance differential absorption to increase preferential detection of chiral single molecules
No full textPlasmonic antennas increase the photon flux in their vicinity, which can lead to plasmon-enhanced fluorescence for molecules near these nanostructures. Here, we combine plasmon-coupled fluorescence and fluorescence-detected circular dichroism to build a specific and sensitive detection strategy for chiral single molecules. Electromagnetic simulations indicate that a two-dimensional gold nanoparticle dimer antenna enhances the electric field and optical chirality of a plane wave in its near field. Furthermore, this optical chirality enhancement can be tuned based on the polarization of the incident electric field, such that enhancing the optical chirality via these antennas will increase the differential absorption of parity-inverted fields. We measured the fluorescence from single molecules of chiral absorbers—Cy5 J-dimers assembled in double-stranded DNA backbones—and achieved increased detectability of these right-handed molecules near achiral Au NP dimer antennas under right circularly polarized illumination. This strategy offers a new approach to distinguishing weakly fluorescent enantiomers
Carbon-Resource Recovery from Vinyl Polymers of Cyclic Ketene Acetal Esters Using High-Temperature Water
No full textVinyl polymer prepared from 2-methylene-4H-benzo[d][1,3]dioxin-4-one (MBDO), a cyclic ketene acetal ester, is a chemically recyclable polymer that is hydrolyzed to salicylic acid (SA) and acetic acid (AA). Despite this potential, the polymer, poly-MBDO required a strong acid or base in organic solvent for the hydrolysis. In this study, we report the quantitative conversion of poly-MBDO to phenol by treatment in high-temperature water. Hydrolysis of poly-MBDO afforded SA, which underwent rapid decarboxylation to phenol. For example, poly-MBDO quantitatively afforded phenol upon heating in water at 300 °C for 5 min and freeze-drying. Although the hydrolysis of the main chain was incomplete, the products were volatile and removed by drying the reaction mixture, leaving the residue of pure phenol. Since SA is industrially synthesized from phenol and CO2, the synthesis of poly-MBDO from phenol is in principle possible. The quantitative conversion of poly-MBDO to phenol can also be considered as upcycling, since phenol is a raw material for various fine chemicals
Heterogeneous Doping via Nanoscale Coating Impacts Mechanics of Li Intrusion in Brittle Solid Electrolytes
No full textLithium metal electroplating and short-circuiting limit fast charging in solid-state batteries, yet the mechanisms and methods to regulate lithium intrusions are not well-understood. In this work, we discover that nanoscale heterogeneous Ag+ doping dramatically affects lithium intrusion in Li6.6La3Zr1.6Ta0.4O12 (LLZO), a brittle solid electrolyte. We generate nanoscale Ag+ doping by thermally annealing a 3-nm-thick metallic film. The metallic Ag undergoes Ag-Li ion exchange, completely disappears, and diffuses into LLZO bulk and grain boundaries to a depth of 20-50 nm. Density functional theory calculations predict this Ag-Li ion exchange exhibits negligible impact on electronic properties. Mechanically, nanoindentation experiments (n = 69) show a fivefold increase in the force required to fracture Ag+ surface-doped LLZO (Ag+-LLZO), providing direct evidence that surface modification due to Ag+ incorporation prevents crack opening. Conducting 121 plating experiments via operando microprobe scanning electron microscopy, we further confirm that the Ag+-LLZO surface exhibits improved lithium plating even under a large local indentation stress of 3 GPa. Surprisingly, microprobe plating reveals that Ag+ increases the diameter of plated Li at failure by more than 4 times, demonstrating its role in enhancing the defect tolerance of LLZO. Our study reveals a chemo-mechanical mechanism via surface heterogeneous doping, complementing the present bulk design rules to prevent mechanical failures in solid-state batteries
Interactional fingerprints offer an accessible, rapid, means to characterise graphene oxide.
No full textGraphene-based materials (GBMs), including graphene oxide and graphene, are atomically thin materials with great promise, but efforts to realise this promise have been hampered by inconsistent material supply and the lack of rapid, accessible, characterisation methods. Here we present a new approach, based on surface interaction with a series of probe molecules, to rapidly provide a qualitative characterisation of graphene oxide materials at low cost, using widely available instruments. We demonstrate that our method can make qualitative comparisons, allowing us to observe if batches of material differ. Furthermore, in some circumstances it can quantify systematic differences, such as surface modification. We propose this approach may prove a valuable quality control method for materials producers and users alike and, since many applications of graphene oxide ¬— and 2D materials in general — depend on surface interactions, and suggest this kind characterisation may be valuable beyond rapid QC, in GBMs and other materials
NetSci: A Library for High Performance Biomolecular Simulation Network Analysis Computation
No full textWe present the Netsci program - an open-source scientific software package that leverages GPU acceleration and a k-nearest-neighbor algorithm in order to estimate the mutual information (MI) between data in a set. The GPU acceleration presented here, as an improvement upon existing estimators, enables calculation speeds several orders of magnitude faster than CPU-based implementations, all with dataset size limits determined only by the available hardware. To demonstrate the validity and usefulness of Netsci, we show that the MI is correctly computed for the analytically-verifiable two-dimensional Gaussian distribution, and we also reproduce the generalized correlation (GC) analysis performed in an earlier study on the B1 domain of protein G. In addition, we apply Netsci to the analysis of molecular dynamics simulations of the Sarcoendoplasmic Reticulum Calcium-ATPase (SERCA) pump. Specifically, we use Netsci to understand the allosteric mechanisms and pathways of SERCA, and compare the differential effects of the binding of two nucleotides, ATP and 2\u27-deoxy-ATP (dATP). We determine that ATP binding to SERCA, compared to dATP, induces differential allosteric effects. The most likely information pathways from the bound nucleotide to the calcium binding domain are also predicted using our MI estimator in combination with network analysis tools on the SERCA pump, which differs based on the bound nucleotide. Netsci is shown to be a useful program for the estimation of MI and GC within general datasets, and for the analysis of intraprotein communication and information transfer, in particular