Role of Hydrogen Bonding on the Design of New Hybrid Perovskites Unraveled by Machine Learning.

Selecting a set of reactants to accurately design a new low dimensional hybrid perovskite could greatly accelerate the discovery of materials with great potential in photovoltaics, or solid-state lighting. However, this design is challenging as most hybrid metal halides are not perovskites and no feature is clearly associated to the structural characteristics of the inorganic metal halide network. This work first demonstrates that the organic molecules are key parameters to determine the structure type of the inorganic network (i.e., perovskite versus non-perovskite). Then, machine learning (ML) algorithms are used to identify the key features of the organic cations leading to the perovskite structure type. Using a large dataset of hybrid metal halides, this work extracts the organic molecules of all hybrid lead halide compounds, calculates 2756 molecular descriptors and fingerprints for each of these molecules, and are able to predict through ML techniques if a specific organic amine will lead to the perovskite type with an accuracy up to 88.65%. Descriptors related to hydrogen bonding are identified as important features. Thus, a simple but reliable design principle could be demonstrated: the presence of primary ammonium cation is the primary condition to prepare hybrid lead halide perovskites regardless of their dimensionalities.

Beyond π-π Stacking: Understanding Inversion Symmetry Breaking in Crystalline Racemates.

The design of noncentrosymmetric (NCS) solid state materials, specifically how to break inversion symmetry between enantiomers, has intrigued chemists, physicists, and materials scientists for many years. Because the chemical complexity of molecular racemic building units is so varied, targeting these materials is poorly understood. Previously, three isostructural racemic compounds with a formula of [Cu(H2O)(bpy)2]2[MF6]2·2H2O (bpy = 2,2'=bipyridine; M = Ti, Zr, Hf) were shown to crystallize in the NCS space group Pna21, of polar, achiral crystal class mm2. In this work, we synthesized five new racemic compounds with the formula [Cu(H2O)(dmbpy)2]2[MF6]2·xH2O (dmbpy = 4,4'/5,5'-dimethyl-2,2'-bipyridine; M = Ti, Zr, Hf). Single crystal X-ray diffraction reveals that the five newly synthesized compounds feature equimolar combinations of Δ- and Λ-Cu(dmbpy)2(H2O)2+ complexes that are assembled into packing motifs similar to those found in the reported NCS structure but all crystallize in centrosymmetric (CS) space groups. Seven structural descriptors were created to analyze the intermolecular interactions on the assembly of Cu racemates in the CS and NCS structures. The structural analysis reveals that in the CS structures, the inversion center results from parallel heterochiral π-π stacking interactions between adjacent Cu racemates regardless of cation geometries, hydrogen bonding networks, or interlayer architectures, whereas in the NCS structure, nonparallel heterochiral π-π interactions between the adjacent Cu racemates preclude an inversion center. The parallel heterochiral π-π interactions in the CS structures can be rationalized by the restrained geometries of the methyl-substituted ligands. This work demonstrates that the introduction of nonparallel stacking can suppress the formation of an inversion center for an NCS racemate. A conceptual framework and practical approach linking the absence of inversion symmetry in racemates is presented for all NCS crystal classes.

Chemistry in the Molten State: Opportunities for Designing and Tuning the Emission Properties of Halide Perovskites.

A series of monolayered lead halide hybrid perovskites (HO2C(CH2)n-1NH3)2PbX4, named (Cn)2PbX4 (n = 4-6, X = Cl, Br), exhibiting a low congruent melting temperature (Tm) (Tm = 130 °C for (C4)2PbBr4), high stability in the molten state, and whitish type emission, are reported. From the synthesis in the molten state, rare solid solutions of mixed organic cations (Cn1-xCn'x)2PbX4 (n, n' = 4-6; X = Cl, Br; 0 ≤ x ≤1) as well as solid solutions of mixed halides (Cn)2Pb(X1-yX'y)4 (n = 4-6; X, X' = Cl, Br; 0 ≤ y ≤1) have been prepared and characterized (thermal behavior, powder X-ray diffraction (PXRD), photoluminescence properties). The impact of substitutions is significant on the thermal properties, lowering the Tm down to 100 °C for (C4)2Pb(Br0.25Cl0.75)4. The emission properties are slightly tuned in the case of mixed organic cation systems, whereas modifications are more dramatic in the case of mixed halide systems, leading to emission properties through the entire visible region. These results illustrate the great opportunities offered by the congruent melting properties of halide perovskites allowing syntheses in the molten state.

Two Distinct Cu(II)-V(IV) Superexchange Interactions with Similar Bond Angles in a Triangular "CuV2" Fragment.

The strength and sign of superexchange interactions are often predicted on the basis of the bond angles between magnetic ions, but complications may arise in situations with a nontrivial arrangement of the magnetic orbitals. We report on a novel molecular tetramer compound [Cu(H2O)dmbpy]2[V2O2F8] (dmbpy = 4,4'-dimethyl-2,2'-bipyridyl) that is composed of triangular "CuV2" fragments and displays a spin gap behavior. By combining first-principles calculations and electronic models, we reveal that superexchange Cu-V interactions carry drastically different coupling strengths along two Cu-F-V pathways with comparable bond angles in the triangular "CuV2" fragment. Counterintuitively, their strong disparity is found to originate from the restricted symmetry of the half-filled Cu dx2-y2 orbital stabilized by the crystal field, leading to one dominating antiferromagnetic Cu-V coupling in each fragment. We revisit the magnetic properties of the reported spin-gapped chain compound [enH2]Cu(H2O)2[V2O2F8] (enH2 = ethylene diammonium) containing similar triangular "CuV2" fragments, and the magnetic behavior of the molecular tetramer and the chain compounds is rationalized as that of weakly coupled spin dimers and spin trimers, respectively. This work demonstrates that fundamentally different magnetic couplings can be observed between magnetic ions with similar bond angles in a single spin motif, thus providing a strategy to introduce various exchange interactions combined with low dimensionality in heterometallic Cu(II)-V(IV) compounds.

A comprehensive library of fluorescent constructs of SARS-CoV-2 proteins and their initial characterisation in different cell types.

BACKGROUND INFORMATION: Comprehensive libraries of plasmids for SARS-CoV-2 proteins with various tags (e.g., Strep, HA, Turbo) are now available. They enable the identification of numerous potential protein-protein interactions between the SARS-CoV-2 virus and host proteins. RESULTS: We present here a large library of SARS CoV-2 protein constructs fused with green and red fluorescent proteins and their initial characterisation in various human cell lines including lung epithelial cell models (A549, BEAS-2B), as well as in budding yeast. The localisation of a few SARS-CoV-2 proteins matches their proposed interactions with host proteins. These include the localisation of Nsp13 to the centrosome, Orf3a to late endosomes and Orf9b to mitochondria. CONCLUSIONS AND SIGNIFICANCE: This library should facilitate further cellular investigations, notably by imaging techniques.

Molecular and cellular dissection of the oxysterol-binding protein cycle through a fluorescent inhibitor.

ORPphilins are bioactive natural products that strongly and selectively inhibit the growth of some cancer cell lines and are proposed to target intracellular lipid-transfer proteins of the oxysterol-binding protein (OSBP) family. These conserved proteins exchange key lipids, such as cholesterol and phosphatidylinositol 4-phosphate (PI(4)P), between organelle membranes. Among ORPphilins, molecules of the schweinfurthin family interfere with intracellular lipid distribution and metabolism, but their functioning at the molecular level is poorly understood. We report here that cell line sensitivity to schweinfurthin G (SWG) is inversely proportional to cellular OSBP levels. By taking advantage of the intrinsic fluorescence of SWG, we followed its fate in cell cultures and show that its incorporation at the trans-Golgi network depends on cellular abundance of OSBP. Using in vitro membrane reconstitution systems and cellular imaging approaches, we also report that SWG inhibits specifically the lipid transfer activity of OSBP. As a consequence, post-Golgi trafficking, membrane cholesterol levels, and PI(4)P turnover were affected. Finally, using intermolecular FRET analysis, we demonstrate that SWG directly binds to the lipid-binding cavity of OSBP. Collectively these results describe SWG as a specific and intrinsically fluorescent pharmacological tool for dissecting OSBP properties at the cellular and molecular levels. Our findings indicate that SWG binds OSBP with nanomolar affinity, that this binding is sensitive to the membrane environment, and that SWG inhibits the OSBP-catalyzed lipid exchange cycle.

Tuning the Oxidation States of Dopants: A Strategy for the Modulation of Material Photoluminescence Properties.

Doped single-phase materials have been widely investigated owing to their easy to implement synthesis and the variety of their properties. This Minireview covers strategies for the co-stabilization and the ratio control of several oxidation states of dopants inserted in the same host. The tuning of the oxidation states of dopants opens up many possibilities for the optimization of specific properties and can be envisioned for various applications such as telecommunication, medicine, displays, lasers or lighting. Technics used for the quantification of each valence state of dopant are also emphasized, and the importance of high throughput methods for the discovery of efficient materials with dopants in multiple valence states is discussed.

National dose reference levels in computed tomography-guided interventional procedures-a proposal.

OBJECTIVES: To establish national reference levels (RLs) in interventional procedures under CT guidance as required by the 2013/59/Euratom European Directive. METHODS: Seventeen categories of interventional procedures in thoracic, abdominopelvic, and osteoarticular specialties (percutaneous infiltration, vertebroplasty, biopsy, drainage, tumor destruction) were analyzed. Total dose length product (DLP), number of helical acquisitions (NH), and total DLP for helical, sequential, or fluoroscopic acquisitions were recorded for 10 to 20 patients per procedure at each center. RLs were calculated as the 3rd quartiles of the distributions and target values for optimization process (TVOs) as the median. RLs and TVOs were compared with previously published studies. RESULTS: Results on 5001 procedures from 49 centers confirmed the great variability in patient dose for the same category of procedures. RLs were proposed for the DLPs and NHs in the seventeen categories. RLs in terms of DLP and NH were 375 mGy.cm and 2 NH for spinal or peri-spinal infiltration, 1630 mGy.cm and 3 NH for vertebroplasty, 845 mGy.cm and 4 NH for biopsy, 1950 mGy.cm and 8 NH for destruction of tumors, and 1090 mGy.cm and 5 NH for drainage. DLP and NH increased with the complexity of procedures. CONCLUSIONS: This study was the first nationwide multicentric survey to propose RLs for interventional procedures under CT guidance. Heterogeneity of practice in centers were found with different levels of patient doses for the same procedure. The proposed RLs will allow imaging departments to benchmark their practice with others and optimize their protocols. KEY POINTS: • National reference levels are proposed for 17 categories of interventional procedures under CT guidance. • Reference levels are useful for benchmarking practices and optimizing protocols. • Reference levels are proposed for dose length product and the number of helical acquisitions.

Correction to: National dose reference levels in computed tomography-guided interventional procedures-a proposal.

The original version of this article, published on 02 May 2020, unfortunately contained a mistake.

The transbilayer distribution of polyunsaturated phospholipids determines their facilitating effect on membrane deformation.

In the cell, membrane deformation and fission (collectively referred to as 'budding') is driven by specific protein machineries but is also influenced by lipid composition. We previously reported that phospholipids with polyunsaturated acyl chains facilitate membrane budding because they adapt their shape to membrane curvature, thereby decreasing membrane bending rigidity. The facilitating effect of polyunsaturated lipids was observed in experiments and simulations performed on membranes where the two bilayer leaflets had the same lipid composition. However, biological membranes are generally asymmetric. Here, we present coarse-grained molecular dynamics simulations on asymmetric phospholipid bilayers undergoing deformation via a pulling force along the bilayer normal. One leaflet contains monounsaturated C18:0-C18:1-phospholipids, whereas the opposite leaflet contains polyunsaturated C18:0-C22:6-phospholipids. When present in the monolayer orientated towards the pulling force and thereby in the convex face of the forming tube, C18:0-C22:6-phospholipids facilitate membrane tubulation. In contrast, C18:0-C22:6-phospholipids in the concave face of the tube have no effect. Analysis of lipid shape indicates that these contrasting effects arise from the superior ability of polyunsaturated phospholipids to swell in the convex leaflet, whereas mono and polyunsaturated phospholipids behave similarly in the concave leaflet. The leaflet-dependent effect of polyunsaturated phospholipids matches well their asymmetric distribution in biological membranes, notably in synaptic vesicles, which are produced by the fastest budding event in the body.

Hydrogen Bonding and Broad-Band Emission in Hybrid Zinc Halide Phosphors.

In solid-state lighting (SSL) applications, hybrid zinc halide phosphors are a promising family because they meet specific criteria such as high color rendering, low cost, and nontoxicity. However, contrary to hybrid lead halide phosphors, their quantum efficiencies are low and the origin of this luminescence remains unclear. To unravel this origin and provide new insights into enhancement of this emission, four hybrid zinc halides have been investigated. These four compounds exhibit similar crystal structures but different photoluminescence properties. We show that photoemission requires the formation of Vk centers, which can be promoted by specific hydrogen bonding. We anticipate that the selection of a specific environment for the zinc halide units could lead to a promising family of low-cost and environmentally friendly phosphors for SSL.

Doped Lead Halide White Phosphors for Very High Efficiency and Ultra-High Color Rendering.

Near-UV-pumped white-light-emitting diodes with ultra-high color rendering and decreased blue-light emission is highly desirable. However, discovering a single-phase white light emitter with such characteristics remains challenging. Herein, we demonstrate that Mn doping as low as 0.027 % in the hybrid post-perovskite type (TDMP)PbBr4 (TDMP=trans-2,5-dimethylpiperaziniium) enables to achieve a bright pure white emission replicating the spectrum of the sun's rays. Thus, a white phosphor exhibiting an emission with CIE coordinates (0.330, 0.365), a high photoluminescence quantum yield of 60 % (new record for white light emission of hybrid lead halides), and an ultra-high color rendering index (CRI=96, R9=91.8), corresponding to the record value for a single phase emitter was obtained. The investigation of the photoluminescence properties revealed how free excitons, self-trapped excitons, and low amount of Mn dopants are coupled to give rise to such pure white emission.

Exciton Self-Trapping in Hybrid Lead Halides: Role of Halogen.

Low-dimensional hybrid lead halides have recently been reported as efficient white light emitters. However, unlike lead halide 3D perovskites, most of the reported low-dimensional materials with broad-band emission crystallize in different structure types according to their halogen composition (i.e., Cl, Br, and I) for a selected organic molecule. Because of the absence of isostructural halide series, the role of chemistry in the self-trapping of the excitons at the origin of the broad-band emission remains unclear. Among the most efficient white phosphors, hybrid lead bromide (TDMP)PbBr4 (TDMP = trans-2,5-dimethylpiperazinium) built of post-perovskite type chains exhibits a record photoluminescence quantum yield for hybrid lead halides. In this article, the two new isostructural (TDMP)PbX4 chloride and iodide analogues could be synthesized and structurally characterized. A comparison of the optical properties of the lead halide series reveals a strong dependence of the nature of the halogen (Cl, Br, or I) on the trapping/detrapping of the excitons and the resulting emission intensities, wavelengths, and band broadness.

PackMem: A Versatile Tool to Compute and Visualize Interfacial Packing Defects in Lipid Bilayers.

The analysis of the structural organization of lipid bilayers is generally performed across the direction normal to the bilayer/water interface, whereas the surface properties of the bilayer at the interface with water are often neglected. Here, we present PackMem, a bioinformatic tool that performs a topographic analysis of the bilayer surface from various molecular dynamics simulations. PackMem unifies and rationalizes previous analyses based on a Cartesian grid. The grid allows identification of surface regions defined as lipid-packing defects where lipids are loosely packed, leading to cavities in which aliphatic carbons are exposed to the solvent, either deep inside or close to the membrane surface. Examples are provided to show that the abundance of lipid-packing defects varies according to the temperature and to the bilayer composition. Because lipid-packing defects control the adsorption of peripheral proteins with hydrophobic insertions, PackMem is instrumental for us to understand and quantify the adhesive properties of biological membranes as well as their response to mechanical perturbations such as membrane deformation.

Structural and Spectroscopic Investigations of Two [Cu4X6]2- (X = Cl-, Br-) Clusters: A Joint Theoretical and Experimental Work.

Herein we report a joint experimental and theoretical investigation on two tetranuclear Cu(I) clusters stabilized by halide ligands. These clusters are of high interest due to their spectroscopic and optical properties, more precisely both clusters exhibit thermochromism. The compounds synthesized by the hydrothermal method have been characterized by single-crystal X-ray diffraction, UV-visible spectroscopy and quantum calculations. Modeled structures have been investigated by means of DFT and TD-DFT methods. Anharmonic computations have been performed to better achieve the vibrational investigation. Computations of the triplet excited states permit us to get more insights into the structure and electronic structure of the excited states responsible for the luminescence properties. Calculations are in agreement with the observed phosphorescence wavelengths.

Interdigitation between Triglycerides and Lipids Modulates Surface Properties of Lipid Droplets.

Intracellular lipid droplets (LDs) are the main cellular site of metabolic energy storage. Their structure is unique inside the cell, with a core of esterified fatty acids and sterols, mainly triglycerides and sterol esters, surrounded by a single monolayer of phospholipids. Numerous peripheral proteins, including several that were previously associated with intracellular compartments surrounded by a lipid bilayer, have been recently shown to target the surface of LDs, but how they are able to selectively target this organelle remains largely unknown. Here, we use atomistic and coarse-grained molecular dynamics simulations to investigate the molecular properties of the LD surface and to characterize how it differs from that of a lipid bilayer. Our data suggest that although several surface properties are remarkably similar between the two structures, key differences originate from the interdigitation between surface phospholipids and core neutral lipids that occurs in LDs. This property is extremely sensitive to membrane undulations, unlike in lipid bilayers, and it strongly affects both lipid-packing defects and the lateral pressure profile. We observed a marked change in overall surface properties for surface tensions >10 mN/m, indicative of a bimodal behavior. Our simulations provide a comprehensive molecular characterization of the unique surface properties of LDs and suggest how the molecular properties of the surface lipid monolayer can be modulated by the underlying neutral lipids.

Two-Step Design of a Single-Doped White Phosphor with High Color Rendering.

A strategy to design step by step an inorganic single-doped white phosphor is demonstrated. The method consists in tuning different contributions of the emission by successively controlling the chemical compositions of the solid solution or nanosegregated host matrix and the oxidation states of the single dopant. We use this approach to design a white phosphor Na4CaMgSc4Si10O30:Eu with excellent color rendering (CRI > 90) that is similar to common mixed-phosphor light sources but for a single-phase. We show that this methodology can also be extended to other phosphors for use in diverse applications such as biomedicine or telecommunications.

The ubiquitous distribution of late embryogenesis abundant proteins across cell compartments in Arabidopsis offers tailored protection against abiotic stress.

Late embryogenesis abundant (LEA) proteins are hydrophilic, mostly intrinsically disordered proteins, which play major roles in desiccation tolerance. In Arabidopsis thaliana, 51 genes encoding LEA proteins clustered into nine families have been inventoried. To increase our understanding of the yet enigmatic functions of these gene families, we report the subcellular location of each protein. Experimental data highlight the limits of in silico predictions for analysis of subcellular localization. Thirty-six LEA proteins localized to the cytosol, with most being able to diffuse into the nucleus. Three proteins were exclusively localized in plastids or mitochondria, while two others were found dually targeted to these organelles. Targeting cleavage sites could be determined for five of these proteins. Three proteins were found to be endoplasmic reticulum (ER) residents, two were vacuolar, and two were secreted. A single protein was identified in pexophagosomes. While most LEA protein families have a unique subcellular localization, members of the LEA_4 family are widely distributed (cytosol, mitochondria, plastid, ER, and pexophagosome) but share the presence of the class A α-helix motif. They are thus expected to establish interactions with various cellular membranes under stress conditions. The broad subcellular distribution of LEA proteins highlights the requirement for each cellular compartment to be provided with protective mechanisms to cope with desiccation or cold stress.

Fine-Tuning the Properties of Doped Multifunctional Materials by Controlled Reduction of Dopants.

The physical properties of doped multifunctional compounds are commonly tuned by controlling the amount of dopants, but this control is limited because all the properties are influenced simultaneously by this single parameter. Here, we present a strategy that enables the fine-tuning of a specific combination of properties by controlling the reduction of dopants. The feasibility of this approach was demonstrated by optimizing the near-IR photoluminescence of strontium titanate SrTiO3 :Ni for potential applications in biomedicine for a range of absorbance in the visible/near-IR region. We discussed how material properties, such as luminescence, conductivity, or photocatalytic properties can be designed by carefully controlling the ratio of dopants in different oxidation states.

A p-Type Zinc-Based Metal-Organic Framework.

An original concept for the property tuning of semiconductors is demonstrated by the synthesis of a p-type zinc oxide (ZnO)-like metal-organic framework (MOF), (ZnC2O3H2)n, which can be regarded as a possible alternative for ZnO, a natural n-type semiconductor. When small oxygen-rich organic linkers are introduced to the Zn-O system, oxygen vacancies and a deep valence-band maximum, the two obstacles for generating p-type behavior in ZnO, are restrained and raised, respectively. Further studies of this material on the doping and photoluminescence behaviors confirm its resemblance to metal oxides (MOs). This result answers the challenges of generating p-type behavior in an n-type-like system. This concept reveals that a new category of hybrid materials, with an embedded continuous metal-oxygen network, lies between the MOs and MOFs. It provides concrete support for the development of p-type hybrid semiconductors in the near future and, more importantly, the enrichment of tuning possibilities in inorganic semiconductors.