Multicomponent (<i>n</i> ≥ 3) Sorption Isotherms in Reversed-Phase Liquid Chromatography: The Effect of Immobilized Eluent on the Retention of Analytes

The experimental technique of tracer pulse chromatography was used to simultaneously measure the uptake of eluent components by a C18-bonded reversed-phase liquid chromatography (RPLC) packing and the retention factors for a series of test analytes over the full range of eluent composition for methanol and acetonitrile with water. The primary objective of the research was to determine whether or not the uptake of eluent components immobilized as part of the stationary phase would influence the retention of analyte standards. Both acetonitrile and methanol were absorbed in or adsorbed on the C18-bonded phase with the maximum amount of acetonitrile sorbed being about four times that of methanol. The thermodynamic void volume of the column and the excess sorption isotherms of acetonitrile, methanol, and water in binary aqueous/organic mixtures were determined directly from the tracer pulse experiments. The absolute sorption isotherms of the eluent components were indirectly estimated by a combination of techniques. Regression analysis of the nonstationary inflection point of the excess isotherms provided an estimate of the volume of eluent sorbed by the stationary phase but only over a limited eluent composition range. In order to expand the applicable composition range, several commonly used “unretained” probe solutes were tested to determine the accuracy of the assumption that the retention volumes of these solutes provided a viable measure of the kinetic void volume (mobile-phase volume) of the column. The difference between the thermodynamic and kinetic void volumes provided an estimate of the absolute volume of eluent present in the stationary phase. The experimental results showed that some solutes, viz., water and thiourea, did provide an accurate measure of the mobile-phase volume but only over a limited range of eluent composition. Using deuterated water as the unretained dead time marker for water-rich eluents combined with the regression results from excess isotherm data, the absolute volume of eluent sorbed by the stationary phase could be estimated over the full range of eluent composition. The effect of this uptake of eluent on the retention of the test solutes appeared to be minimal for this particular set of test analytes

Layered Bimetallic Iron–Nickel Alkoxide Microspheres as High-Performance Electrocatalysts for Oxygen Evolution Reaction in Alkaline Media

Herein, we report a simple solvothermal process to synthesize a series of FexNi1–x-glycerolates (FeNiGly, x = 0, 0.25, 0.5, 0.75, and 1) and explore them as high-performance electrocatalysts for oxygen evolution reaction (OER) in alkaline media. These FeNiGly samples bear unique structures of hierarchical microspheres assembled by the interlaced ultrathin nanosheets or loosely aggregated nanoparticles, which ensure the electrocatalytic systems more efficient and accessible for the OER process. The FeNiGly exhibits an excellent OER activity with quite low overpotential of ∼320 and ∼380 mV to achieve the current density of 10 and 50 mA cm–2 in 1.0 M KOH solutions, respectively. Moreover, the FeNiGly also presents a good durability in alkaline electrolytes. The superior OER performance would be associated with the unique structures and strong electronic interaction between Fe and Ni in the FeNiGly

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

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

Additional file 1 of RAB4A GTPase regulates epithelial-to-mesenchymal transition by modulating RAC1 activation

Additional file 1. Supplementary Tables and Figure

Sorption Isotherms of Ternary Eluents in Reversed-Phase Liquid Chromatography

The experimental technique of mass spectrometric tracer pulse chromatography was used to measure the excess volume of each eluent component for binary and ternary mixtures of water, acetonitrile, and methanol on a C18-bonded silica RPLC packing over the full composition range. The tracer pulse method allowed the direct measurement of excess volumes of each eluent component without numerical integration, assumed isotherm equation, detector calibration, or off-line analysis of the eluent composition. Absolute isotherms were estimated from the experimental data for excess volumes by use of various strategies for the estimation of the volumes of the stationary and mobile phases in dynamic equilibrium with eluents of varying composition. The results indicate that all three eluent components interacted with the alkane bonded phase. Some components were selectively taken up as part of the stationary phase while other components were selectively excluded so the composition of eluent in or on the stationary phase often significantly differed from the composition of the bulk eluent. The exact composition of the stationary phase (bonded phase plus immobilized eluent) was dependent upon the type and composition of the bulk eluent

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

sj-docx-1-chl-10.1177_17475198221150384 – Supplemental material for Fischer indole synthesis in DMSO/AcOH/H2O under continuous flow conditions

Supplemental material, sj-docx-1-chl-10.1177_17475198221150384 for Fischer indole synthesis in DMSO/AcOH/H2O under continuous flow conditions by Mei Wang, Shenghu Yan, Yue Zhang and Shunlin Gu in Journal of Chemical Research</p