Regioselective Arylation of Amidoaryne Precursors via Ag-Mediated Intramolecular Oxy-Argentation.

An unprecedented silver-mediated intramolecular oxy-argentation of 3-amidoaryne precursors that quickly generates a heteroarylsilver species is developed. AgF acts as both a stoichiometric fluoride source and a reagent for the formation of a benzoxazolylsilver intermediate via aryne generation. Pd-catalyzed coupling reactions of (hetero)aryl iodides with a silver species, generated in situ, allow for the synthesis of various C7-arylated benzoxazoles. As a result, an aryl group is selectively introduced into the meta-position of 3-amidobenzyne precursors. Mechanistic studies have indicated the presence of a benzoxazolylsilver intermediate and revealed that the reaction proceeds via an intramolecular oxy-argentation process, which is initiated by a direct fluoride attack on the silyl group.

Narrow Near-Infrared Emission from InP QDs Synthesized with Indium(I) Halides and Aminophosphine.

Nonpyrophoric aminophosphines reacted with indium(III) halides in the presence of zinc chloride have emerged as promising phosphorus precursors in the synthesis of colloidal indium phosphide (InP) quantum dots (QDs). Nonetheless, due to the required P/In ratio of 4:1, it remains challenging to prepare large-sized (>5 nm), near-infrared absorbing/emitting InP QDs using this synthetic scheme. Furthermore, the addition of zinc chloride leads to structural disorder and the formation of shallow trap states inducing spectral broadening. To overcome these limitations, we introduce a synthetic approach relying on the use of indium(I) halide, which acts as both the indium source and reducing agent for aminophosphine. The developed zinc-free, single-injection method gives access to tetrahedral InP QDs with an edge length > 10 nm and narrow size distribution. The first excitonic peak is tunable from 450 to 700 nm by changing the indium halide (InI, InBr, InCl). Kinetic studies using phosphorus NMR reveal the coexistence of two reaction pathways, the reduction of transaminated aminophosphine by In(I) and via redox disproportionation. Etching the surface of the obtained InP QDs at room temperature with in situ-generated hydrofluoric acid (HF) leads to strong photoluminescence (PL) emission with a quantum yield approaching 80%. Alternatively, surface passivation of the InP core QDs was achieved by low-temperature (140 °C) ZnS shelling using the monomolecular precursor zinc diethyldithiocarbamate. The obtained InP/ZnS core/shell QDs that emit in a range of 507-728 nm exhibit a small Stokes shift (110-120 meV) and a narrow PL line width (112 meV at 728 nm).

Continuous Flow Synthesis of N-Sulfonyl-1,2,3-triazoles for Tandem Relay Cu/Rh Dual Catalysis.

The continuous flow synthesis of N-sulfonyl-1,2,3-triazoles, which are convenient reactive azavinyl carbene precursors, for tandem relay Cu/Rh dual catalysis has been developed. Most reactions readily proceeded at 75 °C in a short residence time of 13.09 min in the presence of 2.5 mol % of CuTC. The scope of the reactions was explored by synthesizing diversely functionalized N-sulfonyl and sulfamoyl triazoles in yields ranging from 92 to 98%. To demonstrate the scalability of the process, the reaction was conducted on a 5.4 mmol scale with residence and collection times of 13.09 and 60 min, respectively. Furthermore, a series of controlled experiments were performed to investigate the compatibility of Cu and Rh in a batch or a continuous flow system. Finally, the first integrated flow system using the azavinyl carbene intermediate under the tandem relay Cu/Rh dual catalysis was developed for the synthesis of various cis-diamino enones from alkynes and sulfonyl azides.

Prediction of Wave Transmission Characteristics of Low-Crested Structures with Comprehensive Analysis of Machine Learning.

The adoption of low-crested and submerged structures (LCS) reduces the wave behind a structure, depending on the changes in the freeboard, and induces stable waves in the offshore. We aimed to estimate the wave transmission coefficient behind LCS structures to determine the feasible characteristics of wave mitigation. In addition, various empirical formulas based on regression analysis were proposed to quantitatively predict wave attenuation characteristics for field applications. However, inherent variability of wave attenuation causes the limitation of linear statistical approaches, such as linear regression analysis. Herein, to develop an optimization model for the hydrodynamic behavior of the LCS, we performed a comprehensive analysis of 10 types of machine learning models, which were compared and reviewed on the prediction accuracy with existing empirical formulas. We found that, among the 10 models, the gradient boosting model showed the highest prediction accuracy with MSE of 1.0 × 10-3, an index of agreement of 0.996, a scatter index of 0.065, and a correlation coefficient of 0.983, which indicates a performance improvement over the existing empirical formulas. In addition, based on a variable importance analysis using explainable artificial intelligence, we determined the significant importance of the input variable for the relative freeboard (RC/H0) and the relative freeboard to water depth ratio (RC/h), which confirms that the relative freeboard was the most dominant factor for influencing wave attenuation in the hydraulic behavior around the LCS. Thus, we concluded that the performance prediction method using a machine learning model can be applied to various predictive studies in the field of coastal engineering, deviating from existing empirical-based research.

Substrate Effect of Platinum-Decorated Carbon on Enhanced Hydrogen Oxidation in PEMFC.

Environmentally sustainable fuel cells with high efficiency have attracted much attention as a promising approach to resolving future energy problems. However, some obstacles must be overcome, such as corrosion, water control, and long-term degradation. Herein, we investigated the improved electrochemical performance and hydrogen oxidation reaction (HOR) mechanism of platinum loaded on carbon nanotube (Pt/CNT) catalyst by conducting experimental and theoretical studies. The Pt/CNT catalyst had a larger active area than the Pt/C (platinum loaded on carbon black) catalyst and also exhibited improved performance due to its long-term stability. In addition, the charge-transfer resistance of Pt/CNT (61.2 Ω cm2) is much smaller than that of Pt/C (90.2 Ω cm2), indicating that the CNT support offers good electron transfer. To further understand the hydrogen dissociation mechanisms of Pt/CNT and Pt/C, we investigated the adsorption characteristics and electron transfer of the catalysts with optimized geometry using the density functional theory (DFT). Pt/CNT exhibited higher adsorption energy and electron transfer than Pt/C, which leads to improved HOR. The integrated experimental and theoretical study conducted here suggests that Pt/CNT is a promising candidate for maintaining the performance of cathode catalysts in the polymer electrolyte membrane fuel cell.

Evolution from unimolecular to colloidal-quantum-dot-like character in chlorine or zinc incorporated InP magic size clusters.

Magic-sized clusters (MSCs) can be isolated as intermediates in quantum dot (QD) synthesis, and they provide pivotal clues in understanding QD growth mechanisms. We report syntheses for two families of heterogeneous-atom-incorporated InP MSCs that have chlorine or zinc atoms. All the MSCs could be directly synthesized from conventional molecular precursors. Alternatively, each series of MSCs could be prepared by sequential conversions. 386-InP MSCs could be converted to F360-InP:Cl MSCs, then to F399-InP:Cl MSCs. Similarly, F360-InP:Zn MSCs could be converted to F408-InP:Zn MSCs, then to F393-InP:Zn MSCs. As the conversion proceeded, evolution from uni-molecule-like to QD-like characters was observed. Early stage MSCs showed active inter-state conversions in the excited states, which is characteristics of small molecules. Later stage MSCs exhibited narrow photoinduced absorptions at lower-energy region like QDs. The crystal structure also gradually evolved from polytwistane to more zinc-blende.

Synthesis of far-red- and near-infrared-emitting Cu-doped InP/ZnS (core/shell) quantum dots with controlled doping steps and their surface functionalization for bioconjugation.

In this study, we designed and synthesized far-red- and near-infrared-emitting Cu-doped InP-based quantum dots (QDs), and we also demonstrated their highly specific and sensitive biological imaging ability. Cu-doped InP/ZnS (core/shell) QDs were prepared using the hot colloidal synthesis method in the organic phase. The ZnS shell passivates the surface and improves the photoluminescence (PL) intensity. However, the InP : Cu/ZnS (core : dopants/shell) QDs, which were obtained after the Cu dopant was incorporated into bare InP QDs, followed by ZnS shell coating, had relatively low PL intensities (maximum PL quantum yield (QY) was only ∼16%) presumably due to the formation of defect sites in the InP-core QDs caused by dopant migration from the InP core to the ZnS shell. We prepared high-quality InP/ZnS : Cu/ZnS (core/shell : dopant/outer-shell) QDs, where thin ZnS shell layers were grown on bare InP QDs prior to Cu ion doping to prevent dopant migration and obtained PL QYs as high as 40%. The native hydrophobic ligands of the as-synthesized Cu-doped QDs were replaced with hydrophilic ligands including dihydrolipoic acid and a zwitterionic ligand, which rendered the QDs water-soluble. These QDs exhibited remarkable colloidal stabilities over a wide pH range, with hydrodynamic diameters less than 10 nm. Modified QD surfaces can also be used in conjugation with other functional moieties to apply highly specific and sensitive imaging probes with very low background levels. As a proof-of-concept study, we successfully demonstrated the selective imaging of streptavidin beads with biotin-conjugated QDs. These decorated Cu-doped InP/ZnS (core/shell) QDs are promising biological-probe candidates for imaging and assaying with reduced concerns regarding toxicity.

Chan-Lam coupling reaction of sulfamoyl azides with arylboronic acids for synthesis of unsymmetrical N-arylsulfamides.

An efficient method was developed for the synthesis of unsymmetrical N-arylsulfamides using sulfamoyl azides and arylboronic acids in the presence of 10 mol% of copper chloride as the catalyst. The reaction was facilitated in MeOH in an open flask at room temperature. Unlike the coupling of sulfamides and boronic acids, the use of sulfamoyl azides was found to be beneficial with respect to the yield and reaction time.

Active Methanol Oxidation Reaction by Enhanced CO Tolerance on Bimetallic Pt/Ir Electrocatalysts Using Electronic and Bifunctional Effects.

Platinum-based metal alloys have been generally developed to provide high carbon monoxide resistance in the anodes of direct methanol fuel cells. We report the potential of bimetallic platinum/iridium electrocatalysts in preserving the outstanding carbon monoxide tolerance obtained from both experimental and theoretical studies, which represents the enhanced electrochemical performance of methanol oxidation and the in-depth and stepwise investigations for reaction mechanisms, respectively. In this study, the findings highlight the dual-enhancement characteristics of low carbon monoxide adsorption energy (electronic effect) and carbon monoxide oxidative removal (bifunctional effect) compared with various electrocatalysts such as platinum, iridium, and platinum/ruthenium alloys. In addition, the reaction affinity of platinum/iridium alloys for methanol dehydrogenation is also studied in accordance with atomistic properties, such as adsorption energy and electronic band gap, to understand the electrochemical performance compared to Pt. The results obtained indicate that the platinum/iridium alloy surface played diverse roles in terms of its multifunctional behaviors for carbon monoxide tolerance, including the favorable mechanism of methanol dehydrogenation. It turns out that throughout the theoretical in-depth studies, platinum/iridium alloys are promising candidates in terms of the extension for electrocatalytic material designs that differ from Ru in direct methanol fuel cells.

Mn(III)-Iodosylarene Porphyrins as an Active Oxidant in Oxidation Reactions: Synthesis, Characterization, and Reactivity Studies.

Mn(III)-iodosylarene porphyrin adducts, [Mn(III)(ArIO)(Porp)]+, were synthesized by reacting electron-deficient Mn(III) porphyrin complexes with iodosylarene (ArIO) at -60 °C and characterized using various spectroscopic methods. The [Mn(III)(ArIO)(Porp)]+ species were then investigated in the epoxidation of olefins under stoichiometric conditions. In the epoxidation of olefins by the Mn(III)-iodosylarene porphyrin species, epoxide was formed as the sole product with high chemoselectivities and stereoselectivities. For example, cyclohexene oxide was formed exclusively with trace amounts of allylic oxidation products; cis- and trans-stilbenes were oxidized to the corresponding cis- and trans-stilbene oxides, respectively. In the catalytic epoxidation of cyclohexene by an electron-deficient Mn(III) porphyrin complex and sPhIO at low temperature (e.g., -60 °C), the Mn(III)-iodosylarene porphyrin species was evidenced as the active oxidant that effects the olefin epoxidation to give epoxide as the product. However, at high temperature (e.g., 0 °C) or in the case of using an electron-rich manganese(III) porphyrin catalyst, allylic oxidation products, along with cyclohexene oxide, were yielded, indicating that the active oxidant(s) was not the Mn(III)-iodosylarene adduct but probably high-valent Mn-oxo species in the catalytic reactions. We also report the conversion of the Mn(III)-iodosylarene porphyrins to high-valent Mn-oxo porphyrins under various conditions, such as at high temperature, with electron-rich porphyrin ligand, and in the presence of base (OH-). The present study reports the first example of spectroscopically well-characterized Mn(III)-iodosylarene porphyrin species being an active oxidant in the stoichiometric and catalytic oxidation reactions. Other aspects, such as one oxidant versus multiple oxidants debate, also were discussed.

3-Hydroxy-2-(trialkylsilyl)phenyl Triflate: A Benzyne Precursor Triggered via 1,3-C-sp2-to-O Silyl Migration.

3-Hydroxy-2-(trialkylsilyl)phenyl triflates are presented as new versatile hydroxyaryne precursors. These are base-activated aryne precursors induced via a C-sp2-to-O 1,3-Brook rearrangement. The reaction of various arynophiles and 3-trialkylsiloxybenzyne generated from 3-hydroxy-2-(trialkylsilyl)phenyl triflate efficiently afforded highly regioselective phenol derivatives. Furthermore, through crossover experiments, the intramolecular mechanism of silyl migration was demonstrated.

SnS4(4-), SbS4(3-), and AsS3(3-) Metal Chalcogenide Surface Ligands: Couplings to Quantum Dots, Electron Transfers, and All-Inorganic Multilayered Quantum Dot Sensitized Solar Cells.

Three inorganic capping ligands (ICLs) for quantum dots (QDs), SnS4(4-), SbS4(3-) and AsS3(3-), were synthesized and the energy levels determined. Proximity between the ICL LUMO and QD conduction level governed the electronic couplings such as absorption shift upon ligand exchange, and electron transfer rate to TiO2. QD-sensitized solar cells were fabricated, using the ICL-QDs and also using QD multilayers layer-by-layer assembled by bridging coordinations, and studied as a function of the ICL ligand and the number of QD layers.

Association between household income and overweight of Korean and American children: trends and differences.

The prevalence of overweight in children has been dramatically increasing worldwide, and socioeconomic status is an important risk factor. The purpose of this study was to examine the hypothesis that household income is negatively associated with overweight in Korean and American girls and boys. In the study, 2117 children 7 to 12 years of age from the Korean National Health and Nutrition Examination Survey between 2001 and 2007 and 3016 children from the US National Health and Nutrition Examination Survey between 2001 and 2006 were included. Overweight is defined as the sex- and age-specific body mass index cutoffs recommended by the International Obesity Task Force. Lower household income significantly increased the risk for overweight in Korean boys, irrespective of adjustments. The negative association between household income and overweight of American boys disappeared after adjusting for the frequency of dining out and TV viewing time. There was no significant association between household income and overweight of Korean and American girls. As household income increased, the intake of energy from protein was increased, but energy from carbohydrates was decreased in Korean boys. On the other hand, as household income increased, energy intake from carbohydrates was increased and energy intake from proteins decreased in American boys. In conclusion, positive association between household income and overweight was found in Korean boys, but not in Korean girls and American boys and girls. Effects solely targeting reduction in income disparities cannot effectively reduce sex disparities in overweight of children.

Correlation of erythrocyte fatty acid composition and dietary intakes with markers of atherosclerosis in patients with myocardial infarction.

The purpose of this study was to examine the hypothesis that erythrocytes that are low in n-3 fatty acids and high in trans-fatty acids and nutrient intakes are associated with the risk of atherosclerosis. Fifty patients with acute nonfatal myocardial infarction were recruited to measure their dietary intake, erythrocyte fatty acid composition, intima medial thickness (IMT), and the Gensini score, which are markers of atherosclerosis. Trans-oleic acid of erythrocytes was positively (P = .05) correlated with the carotid IMT. After adjusting for age, sex, and energy intake, the IMT was negatively associated with the intake of protein, fat, phosphate, zinc, vitamin B(1), vitamin B(2), vitamin B(6), niacin, linoleic acid, linolenic acid, total fatty acids, total n-3 fatty acids, and total n-6 fatty acids. The Gensini score was also negatively associated with the intake of protein, fat, phosphate, sodium, zinc, vitamin E, vitamin B(1), vitamin B(2), vitamin B(6), niacin, linolenic acid, total fatty acids, and total n-3 fatty acids. In conclusion, lower levels of trans-oleic acid (elaidic acid) in erythrocytes and higher intakes of vitamins, minerals, and n-3 fatty acids were associated with the decreased risk of atherosclerosis. However, these findings need further investigation in randomized controlled clinical trials before public health recommendations for atherosclerosis prevention can be made.

Changes in brain activation induced by the training of hypothesis generation skills: an fMRI study.

The aim of the present study is to investigate the learning-related changes in brain activation induced by the training of hypothesis generation skills regarding biological phenomena. Eighteen undergraduate participants were scanned twice with functional magnetic resonance imaging (fMRI) before and after training over a period of 2 months. The experimental group underwent eight biological hypothesis generation training programs, but the control group was not given any during the 2-month period. The results showed that the left frontal gyri, the cingulate gyrus, and the cuneus were activated during hypothesis generation. In addition, the brain activation of the trained group increased in the left inferior and the superior frontal gyri, which are related to working memory load and higher-order inferential processes. However, the activation after training decreased in the occipito-parietal route, which is associated with the perception and the analysis processes of visual information. Furthermore, the results have suggested that the dorsolateral prefrontal cortex (DLPFC) region is the critical area in the training of hypothesis generation skills.

Increased information transmission during scientific hypothesis generation: mutual information analysis of multichannel EEG.

Hypothesis generation has been regarded as one of the core reasoning processes in creative thinking and scientific discovery. To investigate changes in the amount of information transmission during scientific hypothesis generation, the averaged cross-mutual-information (A-CMI) of EEGs was estimated. Twenty-five 5th grade students were sampled in this study. EEG signals from 16 electrodes on each subject's scalp were recorded using a 32-channel EEG system. In order to generate hypotheses, the students were asked to observe 20 quail eggs that gave rise to questions such as: Why do different sizes and shapes of patterns appear on the surface of the eggs? After the observation, they were asked to generate a scientific hypothesis-a tentative causal explanation for the evoked question. The results of experimentation indicated several distinct brain activities during hypothesis generation interacting between different local brain regions. In addition, it was observed that the amount of information transmission during hypothesis generation increased in a large part of the brain region encompassing the temporal, parietal, and occipital cortexes, which implies the use of declarative and procedural memory systems. Furthermore, this study suggested the possibility that neuropsychological approaches may be potential tools to investigate the neuronal activity of EEGs during hypothesis generation.

Differences in brain information transmission between gifted and normal children during scientific hypothesis generation.

The purpose of the present study was to investigate differences in neural information transmission between gifted and normal children involved in scientific hypothesis generation. To investigate changes in the amount of information transmission, the children's averaged-cross mutual information (A-CMI) of EEGs was estimated during their generation of scientific hypotheses. We recorded EEG from 25 gifted and 25 age-matched normal children using 16 electrodes on each subject's scalp. To generate hypotheses, the children were asked to observe 20 "quail eggs" that gave rise to questions. After observation, they were asked to generate a scientific hypothesis--a tentative causal explanation for the questions evoked. The results of this study revealed several distinguishing brain activities between gifted and normal children during hypothesis generation. In contrast to normal children, gifted children showed increased A-CMI values between the left temporal and central, between the left temporal and parietal, and between the left central and parietal locations while generating a hypothesis. These results suggested that gifted children more efficiently distribute the cognitive resources essential to cope with hypothesis generation.