Impact of Bright-Dark Exciton Thermal Population Mixing on the Brightness of CsPbBr3 Nanocrystals.

Understanding the interplay between bright and dark exciton states is crucial for deciphering the luminescence properties of low-dimensional materials. The origin of the outstanding brightness of lead halide perovskites remains elusive. Here, we analyze temperature-dependent time-resolved photoluminescence to investigate the population mixing between bright and dark exciton sublevels in individual CsPbBr3 nanocrystals in the intermediate confinement regime. We extract bright and dark exciton decay rates and show quantitatively that the decay dynamics can only be reproduced with second-order phonon transitions. Furthermore, we find that any exciton sublevel ordering is compatible with the most likely population transfer mechanism. The remarkable brightness of lead halide perovskite nanocrystals rather stems from a reduced asymmetry between bright-to-dark and dark-to-bright conversion originating from the peculiar second-order phonon-assisted transitions that freeze bright-dark conversion at low temperatures together with the very fast radiative recombination and favorable degeneracy of the bright exciton state.

One-Step Synthesis of 3D Graphene Aerogel Supported Pt Nanoparticles as Highly Active Electrocatalysts for Methanol Oxidation Reaction.

Nowadays, two of the biggest obstacles restricting the further development of methanol fuel cells are excessive cost and insufficient catalytic activity of platinum-based catalysts. Herein, platinum nanoparticle supported graphene aerogel (Pt/3DGA) was successfully synthesized by a one-step hydrothermal self-assembly method. The loose three-dimensional structure of the aerogel is stabilized by a simple one-step method, which not only reduces cost compared to the freeze-drying technology, but also optimizes the loading method of nanoparticles. The prepared Pt/3DGA catalyst has a three-dimensional porous structure with a highly cross-linked, large specific surface area, even dispersion of Pt NPs and good electrical conductivity. It is worth noting that its catalytic activity is 438.4 mA/mg with long-term stability, which is consistent with the projected benefits of anodic catalytic systems in methanol fuel cells.. Our study provides an applicable method for synthesizing nano metal particles/graphene-based composites.

Research Strategy for Short-Peptide Fusion Inhibitors Based on 6-HB Core Structure against HIV-1: A Review.

Acquired Immune Deficiency Syndrome (AIDS) is a devastating infectious disease caused by the Human Immunodeficiency Virus type 1 (HIV-1). Enfuvirtide(T20) is the first HIV-1 fusion inhibitor for marketing, which plays an important role in AIDS treatment. However, in the clinical application process, T20 has several drawbacks, such as a high level of development of drug resistance, a short half-life in vivo, and rapid renal clearance, which severely limits the clinical application. Therefore, the development of novel fusion inhibitors to address T20 shortcomings has long been the research hotspot. Short peptides have a long half-life through modification and a high barrier to drug resistance, which is expected to solve the current fusion inhibitors dilemma. In this paper, we summarized six emerging R&D strategies for short peptide-based fusion inhibitors against HIV-1. We hope that this review will provide fresh insights into the development of novel fusion inhibitors, as well as ideas for other viral fusion inhibitor discoveries based on the common membrane fusion 6-HB core structure.

Facilely printed silk fibroin hydrogel microparticles as injectable long-lasting fillers.

There is a high demand from aging people for facial fillers with desirable biocompatibility and lasting filling effects to overcome facial depression. Novel injectable regenerated silk fibroin (RSF) microparticles were facilely printed from a glycidyl methacrylate-modified silk fibroin hydrogel to address this issue. The ß-sheet content and mechanical properties of the RSF hydrogel can be simply modulated by the number of freeze-thawing cycles, and the swelling rate of the RSF hydrogel in saline was negligible. The printed RSF microparticles were uniform, and their diameter was about 300-500 µm, which could be adjusted by the pore sizes of the printed screens. After the injection with a 26-gauge needle, the size distribution of RSF microparticles had no noticeable variation, suggesting that the microparticles could bear the shear strain without breaking during the injection. The in vitro experiments demonstrated that RSF not only had desirable biocompatibility but also facilitated fibroblast migration. The subcutaneous injection experiments demonstrated that the RSF microparticles formed a lasting spot in the injected site. The tissue sections revealed that the RSF microparticles were still distinct on week 8, and blood vessels formed around the microparticles. These promising data demonstrate that the printed RSF microparticles have great potential for facial rejuvenation.

Spectral Fingerprint of Quantum Confinement in Single CsPbBr3 Nanocrystals.

Lead halide perovskite nanocrystals are promising materials for classical and quantum light emission. To understand these outstanding properties, a thorough analysis of the band-edge exciton emission is needed, which is not reachable in ensemble and room-temperature studies because of broadening effects. Here, we report on a cryogenic-temperature study of the photoluminescence of single CsPbBr3 nanocrystals in the intermediate quantum confinement regime. We reveal the size-dependence of the spectral features observed: the bright triplet exciton energy splittings, the trion and biexciton binding energies, and the optical phonon replica spectrum. In addition, we show that bright triplet energy splittings are consistent with a pure exchange model and that the variety of polarization properties and spectra recorded can be rationalized simply by considering the orientation of the emitting dipoles and the populations of the emitting states.

Optical Spectroscopy of Single Colloidal CsPbBr3 Perovskite Nanoplatelets.

Optically bright lead halide perovskite nanocrystals of different morphologies ranging from nanocubes to flat nanoplatelets to elongated nanowires have been reported. The morphology of the nanocrystals is expected to affect various properties such as the band edge energy and the electron-hole exchange interaction. However, aside from nanocubes, the investigation of optical properties in the lead halide perovskite nanocrystals of different morphologies at the single emitter level has been lacking. We have performed optical spectroscopy in single CsPbBr3 nanoplatelets and observed single photon emission without blinking. Furthermore, the photoluminescence emission exhibits excitonic fine structure peaks similar to what has been previously observed in nanocubes. Our work stimulates further investigations into the excitonic and quantum optics properties when the lateral size and morphology can be further controlled in lead halide perovskite nanocrystals.

Lead detoxification activity and ADMET hepatotoxicity of N-(alpha-L-arabino-furanos-1-yl)-L-cysteine.

N-(alpha-L-Arabinofuranos-1-yl)-L-cysteine was stereoselectively prepared from L-arabinose and l-cysteine. Its in vivo detoxification action was evaluated on lead loaded mice at the doses of 0.1, 0.2, and 0.4 mmol/kg. The results show that lead accumulation in the livers, kidneys, brains, and femurs of the treated mice could be efficiently decreased by N-(alpha-L-arabinofuranos-1-yl)-L-cysteine, even at the dose of 0.1 mmol/kg. Compared with the lead detoxification efficacy, 0.4 mmol/kg of N-(alpha-L-arabinofuranos-1-yl)-L-cysteine did not affect the essential metals in the treated mice, such as Fe, Cu, Zn, and Ca. In the apparent permeability coefficient test, the values of P(app)(A-->B), P(app)(B-->A), and P(app)(A-->B)/P(app)(B-->A) indicated that N-(alpha-L-arabinofuranos-1-yl)-L-cysteine was transported actively across the Caco-2 cell monolayer. Silico molecular modeling results predicted that N-(alpha-L-arabinofuranos-1-yl)-L-cysteine had no hepatotoxicity.

Stereoselective synthesis of natural N-(1-Deoxy-D-beta-fructos-1-yl)-L-amino acids and their effect on lead decorporation.

N-(1-Deoxy-D-fructos-1-yl)-l-amino acids isolated from hog liver are endogenous lead decorporation substances with low toxicity and cell membrane crossing ability. To simulate the effect of the natural N-(1-deoxy-D-fructos-1-yl)-l-amino acids on lead decorporation, a series of the epimerically pure N-(1-deoxy-D-fructos-1-yl)-l-amino acids (6a-e beta) were synthesized, and their usefulness as antagonists of lead intoxication was investigated. The results suggest that after treatment with 6a-e beta the liver, kidney, bone, and brain, lead levels of mice were significantly reduced in comparison with the control group. Except for bone and brain lead levels of the mice after chelating treatment with 6d beta, all of the other tissue lead levels of mice after chelating treatment with 6a-e beta are significantly lower than those of mice after treatment with dl-penicillamine (p < 0.05). All fecal lead levels of mice after treatment with 6a-e beta are significantly higher than those of mice after treatment with 0.9% saline (controls) and dl-penicillamine (p < 0.05-0.01). The effects of all chelating agents on urinary excretion of lead in mice are clearly superior to the control (p < 0.05-0.01). The results of the present studies on repeated lead exposure indicated that at tested levels of i.p. injections, the fructose-amino acids were effective antagonists of lead poisoning under the experimental conditions. After treatment with the chelators, the concentration of essential metals in mice did not exhibit change as compared to the control. The effects of the compounds on cadmium decorporation were also investigated, and similar results were observed.