Discretized images of virus-contaminated leaves fed on by gypsy moths

Leaf grids used for analyses and simulations. These grids are discretized images of red oak leaves that were used in an experiment in which individual gypsy moth larvae were allowed to feed on single leaves for 24h. Each leaf was infected with at least one infectious cadaver of a first-instar larva killed by a baculovirus. Healthy fourth-instar larvae were then allowed to feed on the leaves (one leaf per larva) for 24 hours. The grids show the leaf area, as well as the location of the cadaver(s) and each larva's feeding history. The infection outcome for each larva is also recorded. Also included is an index file labeled 'Eakin_et_al_2014_leaf_grids.dat', which contains the file name for each leaf grid, the dimension of the grid (in pixels), the infection outcome for the larva (0=uninfected, 1 = infected), and the predicted probability of infection calculated using the infection model in the associated article. Lastly, there is also some R code titled 'visualize_leaf_grids.R' that will create a visual representation of the numerical leaf grids. See the README file for more details

Quantifying the Nucleation and Growth Kinetics of Electron Beam Nanochemistry with Liquid Cell Scanning Transmission Electron Microscopy

<div>In this article, we report on complex nanochemistry and transport phenomena associated with nanocrystal formation by electron beam induced growth and liquid cell electron microscopy (LCEM). We synthesized silver nanocrystals using scanning transmission electron microscopy (STEM) electron beam induced synthesis and systematically varied the electron dose rate, a parameter solely thought to regulate nanocrystal formation kinetics via the rate of metal precursor reduction. Rationally modifying the solution chemistry with tertiary butanol to scavenge radical oxidizing species established a strongly reducing environment and enabled repeatable LCEM experiments. Interestingly, nanocrystal growth rate decreased with increasing electron dose rate despite the predicted increase in reductant concentration. We present evidence that this counterintuitive trend stems from increased oxidizing radical concentration and radical recombination at high magnifications, which together decrease rate of precursor reduction. Nucleation rate was proportional only to imaging magnification, which we rationalized based on local radical accumulation at high magnification causing increased supersaturation and fast nucleation. Radiation chemistry and reactant diffusion scaling models yielded new scaling laws that quantitatively explained the observed effects of electron dose rate on nucleation and growth kinetics. Finally, we introduce a new reaction kinetic model that enables unraveling nucleation and growth kinetics to probe nucleation kinetics occurring at sub-nanometer length scales, which are typically not accessible with LCEM. Our systematic investigation of nanocrystal formation kinetics with LCEM indicates that the intricacies of radiation chemistry and reactant transport must be accounted for to effectively harness radical scavengers and electron beam induced growth to systematically probe nanocrystal formation kinetics. We expect the empirical trends, scaling laws, and reaction kinetic model presented here will be indispensable tools for in situ electron microscopists and materials chemists alike when designing, analyzing, and interpreting LCEM nanocrystal formation data.</div

Access to Indenones by Rhodium(III)-Catalyzed C–H Annulation of Arylnitrones with Internal Alkynes

Under redox-neutral conditions, rhodium(III)-catalyzed C–H annulation of <i>N</i>-<i>tert</i>-butyl-α-arylnitrones with internal alkynes has been realized for the synthesis of indenones under mild conditions. This reaction proceeded in moderate to high yields and with good functional group tolerance

Microheterogeneous Triplet Oxidation of Hydrophobic Organic Contaminants in Dissolved Black Carbon Solutions under Simulated Solar Irradiation

Dissolved black carbon (DBC) is proven to accelerate the triplet-mediated photodegradation of hydrophobic organic contaminants (HOCs). However, its photosensitization mechanisms are not clear. In this study, five HOCs including 2,4,6-trimethylphenol, N,N-dimethylaniline, 17β-estradiol, 17α-ethinylestradiol, and bisphenol A were selected as model compounds to explore the triplet-mediated phototransformation of HOCs in illuminated DBC solutions. All five HOCs presented high organic carbon-water partition coefficient (KOC) values in DBC solutions, indicating the strong sorption capacity of DBC for HOCs. When reaching sorption equilibrium, the apparent pseudo-first-order rate constants of HOCs vs log[DBC] were well fitted with a sorption-enhanced phototransformation model (R2 > 0.98). Using the sorption-enhanced phototransformation model, the degradation rates of HOCs determined at intra-DBC (kDBC,HOCs′) were 1–2 orders of magnitude higher than those observed in aqueous bulk solution (kHOCsaq). Moreover, typical triplet quenchers (2,4,6-trimethylphenol and oxygen) exhibited a microheterogeneous quenching effect on the triplet-mediated photodegradation of 17β-estradiol. Therefore, our results suggested that HOCs underwent a microheterogeneous photooxidative degradation process in DBC solutions. Furthermore, a sorption-enhanced phototransformation mechanism was proposed to elucidate the microheterogeneous photooxidative behavior of HOCs in DBC solutions. This study provides new insights into the fate and transport of HOCs in aquatic environments

Direct Visualization of Planar Assembly of Plasmonic Nanoparticles Adjacent to Electrodes in Oscillatory Electric Fields

Electric field-directed assembly of colloidal nanoparticles (NPs) has been widely adopted for fabricating functional thin films and nanostructured surfaces. While first-order electrokinetic effects on NPs are well-understood in terms of classical models, effects of second-order electrokinetics that involve induced surface charge are still poorly understood. Induced charge electroosmotic phenomena, such as electrohydrodynamic (EHD) flow, have long been implicated in electric field-directed NP assembly with little experimental basis. Here, we use in situ dark-field optical microscopy and plasmonic NPs to directly observe the dynamics of planar assembly of colloidal NPs adjacent to a planar electrode in low-frequency (<1 kHz) oscillatory electric fields. We exploit the change in plasmonic NP color resulting from interparticle plasmonic coupling to visualize the assembly dynamics and assembly structure of silver NPs. Planar assembly of NPs is unexpected because of strong electrostatic repulsion between NPs and indicates that there are strong attractive interparticle forces oriented perpendicular to the electric field direction. A parametric investigation of the voltage- and frequency-dependent phase behavior reveals that planar NP assembly occurs over a narrow frequency range below which irreversible ballistic deposition occurs. Two key experimental observations are consistent with EHD flow-induced NP assembly: (1) NPs remain mobile during assembly and (2) electron microscopy observations reveal randomly close-packed planar assemblies, consistent with strong interparticle attraction. We interpret planar assembly in terms of EHD fluid flow and develop a scaling model that qualitatively agrees with the measured phase regions. Our results are the first direct in situ observations of EHD flow-induced NP assembly and shed light on long-standing unresolved questions concerning the formation of NP superlattices during electric field-induced NP deposition

Direct Visualization of Planar Assembly of Plasmonic Nanoparticles Adjacent to Electrodes in Oscillatory Electric Fields

Electric field-directed assembly of colloidal nanoparticles (NPs) has been widely adopted for fabricating functional thin films and nanostructured surfaces. While first-order electrokinetic effects on NPs are well-understood in terms of classical models, effects of second-order electrokinetics that involve induced surface charge are still poorly understood. Induced charge electroosmotic phenomena, such as electrohydrodynamic (EHD) flow, have long been implicated in electric field-directed NP assembly with little experimental basis. Here, we use in situ dark-field optical microscopy and plasmonic NPs to directly observe the dynamics of planar assembly of colloidal NPs adjacent to a planar electrode in low-frequency (<1 kHz) oscillatory electric fields. We exploit the change in plasmonic NP color resulting from interparticle plasmonic coupling to visualize the assembly dynamics and assembly structure of silver NPs. Planar assembly of NPs is unexpected because of strong electrostatic repulsion between NPs and indicates that there are strong attractive interparticle forces oriented perpendicular to the electric field direction. A parametric investigation of the voltage- and frequency-dependent phase behavior reveals that planar NP assembly occurs over a narrow frequency range below which irreversible ballistic deposition occurs. Two key experimental observations are consistent with EHD flow-induced NP assembly: (1) NPs remain mobile during assembly and (2) electron microscopy observations reveal randomly close-packed planar assemblies, consistent with strong interparticle attraction. We interpret planar assembly in terms of EHD fluid flow and develop a scaling model that qualitatively agrees with the measured phase regions. Our results are the first direct in situ observations of EHD flow-induced NP assembly and shed light on long-standing unresolved questions concerning the formation of NP superlattices during electric field-induced NP deposition

Competitive Hole Transfer from CdSe Quantum Dots to Thiol Ligands in CdSe-Cobaloxime Sensitized NiO Films Used as Photocathodes for H₂ Evolution

Quantum dot (QD) sensitized NiO photocathodes rely on efficient photoinduced hole injection into the NiO valence band. A system of a mesoporous NiO film co-sensitized with CdSe QDs and a molecular proton-reduction catalyst was studied. While successful electron transfer from the excited QDs to the catalyst is observed, most of the photogenerated holes are instead quenched very rapidly (ps) by hole trapping at the surface thiols of the capping agent used as linker molecules. We confirmed our conclusion by first using a thiol free capping agent and second varying the thiol concentration on the QD’s surface. The later resulted in faster hole trapping as the thiol concentration increased. We suggest that this hole trapping by the linker limits the H₂ yield for this photocathode in a device

Bamboo-Structured Nitrogen-Doped Carbon Nanotube Coencapsulating Cobalt and Molybdenum Carbide Nanoparticles: An Efficient Bifunctional Electrocatalyst for Overall Water Splitting

Developing efficient bifunctional electrocatalysts based on inexpensive and earth-abundant materials for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is essential for large-scale renewable energy storage and conversion processes but remains a major challenge. In this study, a bamboo-structured nitrogen-doped carbon nanotube coencapsulated with metallic cobalt and Mo₂C nanoparticles (Co–Mo₂C@NCNT) is designed and synthesized by a successive pyrolysis approach and demonstrated to be an efficient and stable bifunctional electrocatalyst for overall water splitting in alkaline medium. Attributing to favorable synergy interaction in composition and structure, the resultant Co–Mo₂C@NCNT presents the superior performances toward HER, OER, and even overall water splitting in alkaline medium. To drive a current density of 10 mA cm^–2, it needs only an overpotential of ∼186 and ∼377 mV for the electrocatalytic HER and OER, respectively, and a relatively low cell voltage (∼1.628 V) for overall water electrolysis. The present finding would open a new avenue to design and develop electocatalytically active multicomponent architectures for overall water splitting

Molecular and Electronic Structures of Six-Coordinate “Low-Valent” [M(^Mebpy)₃]⁰ (M = Ti, V, Cr, Mo) and [M(tpy)₂]⁰ (M = Ti, V, Cr), and Seven-Coordinate [MoF(^Mebpy)₃](PF₆) and [MX(tpy)₂](PF₆) (M = Mo, X = Cl and M = W, X = F)

The electronic structures of a series of so-called “low-valent” transition metal complexes [M­(^Mebpy)₃]⁰ and [M­(tpy)₂]⁰ (^Mebpy = 4,4′-dimethyl-2,2′-bipyridine and tpy = 2,2′,6′,2″-terpyridine) have been determined using a combination of X-ray crystallography, magnetochemistry, and UV–vis–NIR spectroscopy. More specifically, the crystal structures of the long-known complexes [Ti^IV(tpy^2–)₂]⁰ (<i>S</i> = 0, <b>6</b>), [V^IV(tpy^2–)₂] (<i>S</i> = ¹/₂, <b>7</b>), [Ti^III(^Mebpy^•)₃]⁰ (<i>S</i> = 0, <b>1</b>), [V^II(^Mebpy^•)₂(^Mebpy⁰)]⁰ (<i>S</i> = ¹/₂, <b>2</b>), and [Mo^III(^Mebpy^•)₃]⁰ (<i>S</i> = 0, <b>4</b>) have been determined for the first time. In all cases, the experimental results confirm the electronic structure assignments that we ourselves have recently proposed. Additionally, the six-coordinate complex [Mo^III(bpy⁰)₂Cl₂]­Cl·2.5CH₃OH (<i>S</i> = ³/₂, <b>13</b>), and seven-coordinate species [Mo^IVF­(^Mebpy^•)₂(^Mebpy⁰)]­(PF₆) (<i>S</i> = 0, <b>5</b>), [Mo^IVCl­(tpy^•)₂]­(PF₆)·CH₂Cl₂ (<i>S</i> = 0, <b>11</b>), and [W^VF­(tpy^•)­(tpy^2–)]­(PF₆)·CH₂Cl₂ (<i>S</i> = 0, <b>12</b>) have been synthesized and, for the first time, crystallographically characterized. Using the resulting data, plus that from previously published high-resolution X-ray structures of analogous compounds, it is shown that there is a linear correlation between the average C_py–C′_py bond distances in these complexes and the total charge (<i>n</i>) of the ligands, {(bpy)₃}^<i>n</i> and {(tpy)₂}^<i>n</i>. Hence, an assignment of the total charge of coordinated bpy or tpy ligands and, by extension, the oxidation state of the central metal ion can reliably be made on the basis of X-ray crystallography alone. In this study, the oxidation states of the metal ions range from +II to +V and in no case has an oxidation state of zero been validated. It is, therefore, highly misleading to use the term “low-valent” to describe any of the aforementioned neutral complexes

Molecular and Electronic Structures of the Members of the Electron Transfer Series [Mn(bpy)₃]^<i>n</i> (<i>n</i> = 2+, 1+, 0, 1−) and [Mn(tpy)₂]^<i>m</i> (<i>m</i> = 4+, 3+, 2+, 1+, 0). An Experimental and Density Functional Theory Study

The members of the electron transfer series [Mn­(bpy)₃]^<i>n</i> (<i>n</i> = 2+, 1+, 0, 1−) and [Mn­(tpy)₂]^<i>m</i> (<i>m</i> = 2+, 1+, 0) have been investigated using a combination of magnetochemistry, electrochemistry, and UV–vis–NIR spectroscopy; and X-ray crystal structures of [Mn^II(^Mebpy^•)₂(^Mebpy⁰)]⁰, [Li­(THF)₄]­[Mn^II(bpy^•)₃], and [Mn^II(tpy^•)₂]⁰ have been obtained (bpy = 2,2′-bipyridine; ^Mebpy = 4,4′-dimethyl-2,2′-bipyridine; tpy = 2,2′:6,2″-terpyridine; THF = tetrahydrofuran). It is the first time that the latter complex has been isolated and characterized. Through these studies, the electronic structures of each member of both series of complexes have been elucidated, and their molecular and electronic structures further corroborated by broken symmetry (BS) density functional theoretical (DFT) calculations. It is shown that all one-electron reductions that comprise the aforementioned redox series are ligand-based. Hence, all species contain a central high-spin Mn^II ion (<i>S</i>_Mn = 5/2). In contrast, the analogous series of Tc^II and Re^II complexes possess low-spin electron configurations