Light-Driven Enantioselective Carbene-Catalyzed Radical-Radical Coupling

An enantioselective carbene-catalyzed radical-radical coupling of acyl imidazoles and racemic Hantzsch esters is disclosed. This method involves the coupling of an N-heterocyclic carbene-derived ketyl radical and a secondary sp³-carbon radical and allows access to chiral α-aryl aliphatic ketones in moderate-to-good yields and enantioselectivities without any competitive epimerization. The utility of this protocol is highlighted by the late-stage functionalization of various pharmaceutical compounds and is further demonstrated by the transformation of the enantioenriched products to biologically relevant molecules. Computational investigations reveal the N-heterocyclic carbene controls the double-facial selectivity of the ketyl radical and the alkyl radicals, respectively.     

CO2-adsorbent spongy electrode for non-aqueous Li–O2 batteries

Regulation of the Li₂CO₃ byproduct is the most critical challenge in the field of non-aqueous Li–O₂ batteries.Although considerable efforts have been devoted to preventing Li₂CO₃ formation,no approaches have suggested the ultimate solution of utilizing the clean Li₂O₂ reaction instead of that of Li₂CO₃.Even if extremely pure O₂ is used in a Li–O₂ cell,its complete elimination is impossible,eventually generating CO₂ gas during charge.In this paper,we present the new concept of a CO₂-adsorbent spongy electrode(CASE),which is designed to trap the evolved CO₂ using adsorption materials.Various candidates composed of amine functional groups(–NH2)for capturing CO₂ were screened,with quadrapurebenzylamine(QPBZA)exhibiting superior CO₂-adsorbing ability among the proposed candidates.Accordingly,we fabricated the CASE by sandwiching QPBZA between porous carbon layers,which facilitated the transport of gaseous products.The new electrode was demonstrated to effectively capture the evolved CO₂ during charge,therefore altering the reaction pathways to the ideal case.It is highly advantageous to mitigate the undesirable CO₂ incorporation in the next discharge,resulting in improved cyclability.This novel concept of a CO₂-sponging electrode provides an alternative route to the realization of practically meaningful Li–O₂ batteries.     

Determination of isomeric dibenzo[a,l]pyrene-adenine adducts by six different tandem mass spectrometric experiments

Six different tandem-mass-spectrometric experiments were evaluated to assess their ability to distinguish four isomeric, carcinogen-modified adenines. Metastable-ion dissociations and high-energy collisional activated decompositions (HE CAD) of fast-atom bombardment (FAB)-produced ions were followed on a four-sector tandem mass spectrometer. Precursor ions were also produced by electrospray on the four-sector instrument, and they were submitted to both high-energy and electrospray ionization (ESI)-source CAD. We contrasted these means of activation with low-energy (LE) CAD of electrospray-produced ions on a triple quadrupole instrument and with post-source decompositions (PSD) of ions produced by matrix-assisted laser desorption ionization (MALDI). The latter experiment was conducted with a time-of-flight mass spectrometer. The four subject molecules were isomeric dibenzo[a,l]pyrene (DB[a,l]P) adenine adducts, in which N1, N3, N7, and N ⁶ positions were substituted. We used similarity indicies (SI), which were calculated from the relative abundances of common fragment ions for the isomers, to confirm quantitatively that HE CAD of FAB and ESI-produced ions can distinguish two of three, and that LE CAD and MALDI-PSD can distinguish three of the three isomers that give qualitatively identical product-ion spectra. The results also show that LE CAD and MALDI-PSD have comparable discriminating capability for these three DBP adducts.     

A quantitative model to evaluate the ion-enrichment and ion-depletion effect at microchannel-nanochannel junctions

In a nanometer-scale fluidic channel (nanochannel), coions are depleted while counterions are concentrated due to the electric double layer (EDL) overlap. When an electric field is applied across the nanochannel, ions are enriched at one end and depleted at the other end of the nanochannel. This phenomenon is termed the ion-enrichment and ion-epletion (IEID) effect. In this paper, we develop a theoretical model to evaluate this effect. The model takes into accounts not only the biased electrophoretic migrations but also the net charge transportation caused by electroosmotic flow. In addition, we consider the conductance change inside the nanochannel in assessing the electric field strength across it. We employ our recently developed protocol to measure these values. We establish a protocol to measure/quantitate the IEID effect. Finally, we compare the calculated results with the experimentally measured data and show good agreements between them.     

Stagewise Dilute-Acid Pretreatment and Enzyme Hydrolysis of Distillers’ Grains and Corn Fiber

Distillers’ grains and corn fiber are the coproducts of the corn dry grind and wet milling industries, respectively. Availability of distillers’ grains and corn fiber at the ethanol plant and their high levels of lignocellulosic material make these coproducts attractive feedstocks for conversion to ethanol. In this study, dilute sulfuric acid hydrolysis of these coproducts was investigated in a multistage scheme. After the completion of each pretreatment stage, the liquid substrate was separated and reused in the succeeding pretreatment stage with a fresh substrate. The substrate from each stage was also subjected to enzyme hydrolysis in a separate experiment. The sulfuric acid concentration and the substrate loading were maintained at 1.0 vol% and 15.0 wt.%, respectively, and the temperature was maintained at 120 °C in all the experiments. Experiments were also performed to study the effect of removing oil from the samples prior to the pretreatment. The highest concentration of monomeric sugars (MS) was observed when three stages of pretreatment were followed by the enzyme reaction. The enzyme hydrolysis of the three-stage pretreated dried distillers’ grains and corn fiber yielded 122.6 ± 5.8 and 184.5 ± 4.1 mg/mL of MS, respectively. The formation of inhibitory products was also monitored.     

Sharp gradient estimates for quasilinear elliptic equations with p(x) growth on nonsmooth domains

In this paper, we study quasilinear elliptic equations with the nonlinearity modelled after the $p(x)$-Laplacian on nonsmooth domains and obtain sharp Calderón–Zygmund type estimates in the variable exponent setting. In a recent work of [12], the estimates obtained were strictly above the natural exponent and hence there was a gap between the natural energy estimates and estimates above $p(x)$, see (1.3) and (1.4). Here, we bridge this gap to obtain the end point case of the estimates obtained in [12], see (1.5). In order to do this, we have to obtain significantly improved a priori estimates below $p(x)$, which is the main contribution of this paper. We also improve upon the previous results by obtaining the estimates for a larger class of domains than what was considered in the literature.     

Receptor-mediated endocytosis modeling of antibody-drug conjugates to the released payload within the intracellular space considering target antigen expression levels

An antibody-drug conjugate (ADC) is one of the effective treatment modalities designed as a targeted therapy for treating tumors. Certain ADCs such as brentuximab vedotin are known to kill negative tumor cells indirectly via membrane permeability and bystander-killing effect and to kill positive tumor cells directly. In this study, we propose a mathematical model to describe the ADC-receptor endocytosis mechanism and to predict payloads over a time profile more accurately, while considering target antigen-positive (Ag+)/negative (Ag--) cells. We discuss how the target-antigen expression levels derived using a ratio of Ag+ to Ag-- cells determine the payload release in the intracellular space. The model is aimed at capturing the amount of the payloads based on the target expression levels with the total number of cells fixed. The results indicate that (i) the profile of the total payloads over a time within the intracellular space is less influenced by the target expression levels after a time period, but the slope at the growth phase in which the payload increases is determined by the target expression levels, (ii) the change in the area under the curve of the total intracellularly released payload with a change in the ratio of Ag+ to Ag-- cells is more significant due to the initial ADC injection, (iii) the fluctuations in the released payloads within the Ag+ cells increase as the target expression levels decrease, unlike in the case of Ag-- cells or extracellular space. In addition, the time $t_{max}$ that corresponds to the maximum payload concentration $C_{max}$ is shifted towards the right as the target-antigen levels decrease, and it is strengthened by an increase in the initial free ADCs. The proposed model may reduce the discrepancy between the experiment and the model in the prediction of payloads over time profile.