Complete Suppression of Phase Segregation in Mixed-Halide Perovskite Nanocrystals under Periodic Heating.

Under continuous light illumination, it is known that localized domains with segregated halide compositions form in semiconducting mixed-halide perovskites, thus severely limiting their optoelectronic applications due to the negative changes in bandgap energies and charge-carrier characteristics. Here mixed-halide perovskite CsPbBr1.2 I1.8 nanocrystals are deposited onto an indium tin oxide substrate, whose temperature can be rapidly changed by ≈10 °C in a few seconds by applying or removing an external voltage. Such a sudden temperature change induces a temporary transition of CsPbBr1.2 I1.8 nanocrystals from the segregated phase to the mixed phase, the latter of which can be permanently maintained when the light illumination is coupled with periodic heating cycles. These findings mark the emergence of a practical solution to the detrimental phase-segregation problem, given that a small temperature modulation is readily available in various fundamental studies and practical devices of mixed-halide perovskites.

Integrated Lipidomic and Metabolomics Analysis Revealing the Effects of Frozen Storage Duration on Pork Lipids.

Frozen storage is an important strategy to maintain meat quality for long-term storage and transportation. Lipid oxidation is one of the predominant causes of the deterioration of meat quality during frozen storage. Untargeted lipidomic and targeted metabolomics were employed to comprehensively evaluate the effect of frozen duration on pork lipid profiles and lipid oxidative products including free fatty acids and fatty aldehydes. A total of 688 lipids, 40 fatty acids and 14 aldehydes were successfully screened in a pork sample. We found that ether-linked glycerophospholipids, the predominant type of lipids, gradually decreased during frozen storage. Of these ether-linked glycerophospholipids, ether-linked phosphatidylethanolamine and phosphatidylcholine containing more than one unsaturated bond were greatly influenced by frozen storage, resulting in an increase in free polyunsaturated fatty acids and fatty aldehydes. Among these lipid oxidative products, decanal, cis-11,14-eicosenoic acid and cis-5,8,11,14,17-dicosapentaenoic acid can be considered as potential indicators to calculate the freezing time of unknown frozen pork samples. Moreover, over the three-month frozen storage, the first month was a rapid oxidation stage while the other two months were a slow oxidation stage.

A strategy for accurately and sensitively quantifying free and esterified fatty acids using liquid chromatography mass spectrometry.

Fatty acid (FA) composition of foods dictates a diversity of aspects regarding food quality, ranging from product shelf life, sensory properties to nutrition. There is a challenge to quantitate FAs using liquid chromatography-mass spectrometry due to poor ionization efficiency and matrix effects. Here, an isotopic-tagged derivatization strategy was established to accurately and sensitively quantify free and esterified FAs. After derivatization reaction, the detection sensitivity of FAs was remarkably improved and the limit of quantitation was lower than 100 ng/L. The quantitative errors caused by matrix effects were diminished benefiting from isotope-derivatized internal standards. The established quantitation strategy was successfully applied to verify both free and esterified FA contents in meat after different post-harvest procedures, finding that free polyunsaturated FAs increased significantly during freezing process.

Electron-phonon coupling-assisted universal red luminescence of o-phenylenediamine-based carbon dots.

Due to the complex core-shell structure and variety of surface functional groups, the photoluminescence (PL) mechanism of carbon dots (CDs) remain unclear. o-Phenylenediamine (oPD), as one of the most common precursors for preparing red emissive CDs, has been extensively studied. Interestingly, most of the red emission CDs based on oPD have similar PL emission characteristics. Herein, we prepared six different oPD-based CDs and found that they had almost the same PL emission and absorption spectra after purification. Structural and spectral characterization indicated that they had similar carbon core structures but different surface polymer shells. Furthermore, single-molecule PL spectroscopy confirmed that the multi-modal emission of those CDs originated from the transitions of different vibrational energy levels of the same PL center in the carbon core. In addition, the phenomenon of "spectral splitting" of single-particle CDs was observed at low temperature, which confirmed these oPD-based CDs were unique materials with properties of both organic molecules and quantum dots. Finally, theoretical calculations revealed their potential polymerization mode and carbon core structure. Moreover, we proposed the PL mechanism of red-emitting CDs based on oPD precursors; that is, the carbon core regulates the PL emission, and the polymer shell regulates the PL intensity. Our work resolves the controversy on the PL mechanism of oPD-based red CDs. These findings provide a general guide for the mechanism exploration and structural analysis of other types of CDs.

Electrical control of biexciton Auger recombination in single CdSe/CdS nanocrystals.

The Auger recombination effect is strongly enhanced in semiconductor nanocrystals due to the quantum confinement, and various strategies in chemical synthesis have been employed so far to suppress this nonradiative decay pathway of multiple excitons. Here we apply external electric fields on single CdSe/CdS giant nanocrystals at room temperature, showing that the biexciton Auger and single-exciton radiative rates can be averagely decreased by ∼40 and ∼10%, respectively. In addition to a reduced overlap of the electron-hole wavefunctions, the large decrease of biexciton Auger rate could be contributed by the enhanced exciton-exciton repulsion, while the electron-hole exchange interaction might be weakened to cause the relatively small decrease of the single-exciton radiative rate. The above findings have thus proved that the external electric field can serve as a post-synthetic knob to tune the exciton recombination dynamics in semiconductor nanocrystals towards their efficient applications in various optoelectronic devices.

Isotope-Coded Chemical Derivatization Method for Highly Accurately and Sensitively Quantifying Short-Chain Fatty Acids.

Short-chain fatty acids (SCFAs) are major gut microbiota-derived metabolites, which can reshape the intestine and regulate gut immunity. The application of conventional GC methods has been hampered for quantifying low-concentrated SCFAs, such as in serum, saliva, and digesta of germ-free animals. Herein, we established a LC-MS method to quantify SCFAs after 5-(dimethylamino)-1-carbohydrazide-isoquinoline (DMAQ) derivatization. The DMAQ derivatization significantly enhanced the detection sensitivity and improved separation of SCFAs. 2-methylbutyric acid and 3-methylbutyric acid were separately quantitated. Moreover, the matrix effect was diminished using DMAQ-13C/15N-tagged SCFAs as internal standards. The established quantitation method was successfully applied in the analysis of plasma and cecum digesta collected from neonatal piglets, revealing that significant increases in biological SCFA contents in cecum digesta were closely related to the variation of gut microbial diversity. The established quantitation method is capable of sensitively and comprehensively quantifying SCFAs that may provide insights into underlying gut-microbiota functions.

Universal Existence of Localized Single-Photon Emitters in the Perovskite Film of All-Inorganic CsPbBr3 Microcrystals.

All-inorganic halide perovskites have drawn a lot of research attention very recently owing to their potential solution to the instability issue currently faced by the organic-inorganic counterparts. Meanwhile, the halide perovskites in a solid film are manifested as microscale morphologies whose functionalities are unavoidably affected by the interior or exterior presence of various nanoscale entities. Here all-inorganic solid films are fabricated with varying densities of single CsPbBr3 microcrystals, showing that very sharp photoluminescence peaks can be universally observed at 4 K with the linewidths being as narrow as hundreds of µeV. The single-photon emission nature is confirmed for such a photoluminescence peak, whose intensity is completely quenched above ≈30 K to suggest its possible origin from a low potential-energy region of the single microcrystal. The discovery of such a novel emitting species in halide perovskites, with the enriched structure-property relationship, will surely impart significant influences on the advancement of relevant optoelectronic devices and quantum-light sources.

Single-Cell Transcriptome Sequencing and Proteomics Reveal Neonatal Ileum Dynamic Developmental Potentials.

The neonatal period is a crucial time during development of the mammalian small intestine. Moreover, neonatal development and maturation of the small intestine are exceptionally important for early growth, successful weaning, and postweaning growth and development, in order to achieve species-specific milestones. Although several publications recently characterized intestinal epithelial cell diversity at the single-cell level, it remains unclear how differentiation and molecular interactions take place between types and subtypes of epithelial cells during the neonatal period. A single-cell RNA sequencing (scRNA-seq) survey of 40,186 ileal epithelial cells and proteomics analysis of ileal samples at 6 time points in the swine neonatal period were performed. The results revealed previously unknown developmental changes: specific increases in undifferentiated cells, unique enterocyte differentiation, and time-dependent reduction in secretory cells. Moreover, we observed specific transcriptional factors, ligand-receptor pairs, G protein-coupled receptors, transforming growth factor ß, bone morphogenetic protein signaling pathways, and gut mucosal microbiota playing vital roles in ileal development during the neonatal window. This work offers new comprehensive information regarding ileal development throughout the neonatal period. Reference to this data set may assist in the creation of novel interventions for inflammation-, metabolism-, and proliferation-related gut pathologies. IMPORTANCE We found previously unknown neonatal ileum developmental potentials: specific increases in undifferentiated cells, unique enterocyte differentiation, and time dependent reduction in secretory cells. Specific transcriptional factors (TFs), ligand-receptor pairs, G protein-coupled receptors, transforming growth factor ß, bone morphogenetic protein signaling pathways, and the gut mucosal microbiota are involved in this process. Our results may assist in the creation of novel interventions for inflammation-, metabolism-, and proliferation-related gut pathologies.

Hollow InVO4 Nanocuboid Assemblies toward Promoting Photocatalytic N2 Conversion Performance.

The unique InVO4 mesocrystal superstructure, particularly with cubical skeleton and hollow interior, which consists of numerous nanocube building blocks, closely stacking by stacking, aligning by aligning, and sharing the same crystallographic orientations, is successfully fabricated. The synergy of a reaction-limited aggregation and an Ostwald ripening process is reasonably proposed for the growth of this unique superstructure. Both single-particle surface photovoltage and confocal fluorescence spectroscopy measurements demonstrate that the long-range ordered mesocrystal superstructures can significantly retard the recombination of electron-hole pairs through the creation of a new pathway for anisotropic electron flow along the inter-nanocubes. This promising charge mobility feature of the superstructure greatly contributes to the pronounced photocatalytic performance of the InVO4 mesocrystal toward fixation of N2 into NH3 with the quantum yield of 0.50% at wavelength of 385 nm.

Factors controlling the oxygen isotopic composition of lacustrine authigenic carbonates in Western China: implications for paleoclimate reconstructions.

In the carbonate-water system, at equilibrium, the oxygen isotopic composition of carbonate is dependent not only on the temperature but also on the isotopic composition of host water in which the carbonate is formed. In this study, lake surface sediment and water samples were collected from 33 terminal lakes in Western China to evaluate controls on the oxygen isotopic composition of lacustrine authigenic carbonates (δ18Ocarb) and its spatial distribution. Our results show that water oxygen isotopic composition (δ18Owater) rather than lake summer water temperature (Twater), is the main determinant of δ18Ocarb, irrespective of whether oxygen isotope equilibrium is achieved. There are significant linear correlations between δ18Ocarb and elevation, as well as that between δ18Ocarb and latitude for lakes located on the Tibetan Plateau. In Western China, the spatial distribution of δ18Ocarb is consistent with that of δ18Owater, and is ultimately controlled by the isotopic composition of local precipitation (δ18Oprecipitation) that depends on the source of water vapor. Therefore, changes in δ18Ocarb can be predominantly interpreted as variations of δ18Owater, which in turn represent changes in δ18Oprecipitation for paleoclimate reconstructions in this region, and may be relevant to studies of other areas.

Human transporters, PEPT1/2, facilitate melatonin transportation into mitochondria of cancer cells: An implication of the therapeutic potential.

Melatonin is present in virtually all organisms from bacteria to mammals, and it exhibits a broad spectrum of biological functions, including synchronization of circadian rhythms and oncostatic activity. Several functions of melatonin are mediated by its membrane receptors, but others are receptor-independent. For the latter, melatonin is required to penetrate membrane and enters intracellular compartments. However, the mechanism by which melatonin enters cells remains debatable. In this study, it was identified that melatonin and its sulfation metabolites were the substrates of oligopeptide transporter (PEPT) 1/2 and organic anion transporter (OAT) 3, respectively. The docking analysis showed that the binding of melatonin to PEPT1/2 was attributed to their low binding energy and suitable binding conformation in which melatonin was embedded in the active site of PEPT1/2 and fitted well with the cavity in three-dimensional space. PEPT1/2 transporters play a pivotal role in melatonin uptake in cells. Melatonin's membrane transportation via PEPT1/2 renders its oncostatic effect in malignant cells. For the first time, PEPT1/2 were identified to localize in the mitochondrial membrane of human cancer cell lines of PC3 and U118. PEPT1/2 facilitated the transportation of melatonin into mitochondria. Melatonin accumulation in mitochondria induced apoptosis of PC3 and U118 cells. Thus, PEPT1/2 can potentially be used as a cancer cell-targeted melatonin delivery system to improve the therapeutic effects of melatonin in cancer treatment.