Merrittoneil9685

Strain engineering provides an effective way of tailoring the electronic and optoelectronic properties of semiconductor nanomaterials and nanodevices, giving rise to novel functionalities. Here, we present direct experimental evidence of strain-induced modifications of hole mobility in individual gallium arsenide (GaAs) nanowires, using in situ transmission electron microscopy (TEM). The conductivity of the nanowires varied with applied uniaxial tensile stress, showing an initial decrease of ∼5-20% up to a stress of 1-2 GPa, subsequently increasing up to the elastic limit of the nanowires. This is attributed to a hole mobility variation due to changes in the valence band structure caused by stress and strain. The corresponding lattice strain in the nanowires was quantified by in situ four dimensional scanning TEM and showed a complex spatial distribution at all stress levels. Meanwhile, a significant red shift of the band gap induced by the stress and strain was unveiled by monochromated electron energy loss spectroscopy.Interlayer excitons in heterobilayers of transition-metal dichalcogenides (TMDCs) have generated enormous interest due to their permanent vertical dipole moments and long lifetimes. However, the effects of mechanical strain on the optoelectronic properties of interlayer excitons in heterobilayers remain relatively uncharacterized. Here, we experimentally demonstrate strain tuning of Γ-K interlayer excitons in molybdenum disulfide and tungsten diselenide (MoS2/WSe2) wrinkled heterobilayers and obtain a deformation potential constant of ∼107 meV/% uniaxial strain, which is approximately twice that of the intralayer excitons in the constituent monolayers. We further observe a nonmonotonic dependence of the interlayer exciton photoluminescence intensity with strain, which we interpret as being due to the sensitivity of the Γ point to band hybridization arising from the competition between in-plane strain and out-of-plane interlayer coupling. Strain engineering with interlayer excitons in TMDC heterobilayers offers higher strain tunability and new degrees of freedom compared to their monolayer counterparts.Two-dimensional (2D) PtSe2 has emerged as a promising ultrathin electrocatalyst due to its excellent catalytic activity and conductivity. However, the PtSe2 basal plane is inert for the hydrogen evolution reaction (HER), which greatly limits its electrocatalytic performance. Here, in light of theoretical calculations, we designed a facile approach for activating the 2D PtSe2 basal plane for the HER by simultaneously introducing atomic vacancies of Se, Pt, and Pt clusters through a mild Ar plasma treatment. We tracked changes in the structures and catalytic performance of PtSe2 by combining microscopic imaging, spectroscopic mapping, and electrochemical measurements in microcells. The highest performance of the activated PtSe2 basal plane that we obtained was superior to those of other 2D transition metal dichalcogenide-based electrocatalysts measured in microcells in terms of the overpotential, the Tafel slope, and the exchange current density. This study demonstrates the great potential of activated 2D PtSe2 as an ultrathin catalyst for the HER and provides new insights on the rational design of 2D electrocatalysts.N-heterocyclic carbenes (NHCs) have emerged as versatile and robust ligands for noble metal surface modifications due to their ability to form compact, self-assembled monolayers. Despite a growing body of research, previous NHC surface modification schemes have employed just two structural motifs the benzimidazolium NHC and the imidazolium NHC. However, different NHC moieties, including saturated NHCs, are often more effective in homogenous catalysis chemistry than these aforementioned motifs and may impart numerous advantages to NHC surfaces, such as increased stability and access to chiral groups. This work explores the preparation and stability of NHC-coated gold surfaces using imidazolium and imidazolinium NHC ligands. X-ray photoelectron spectroscopy and surface-enhanced Raman spectroscopy demonstrate the attachment of NHC ligands to the gold surface and show enhanced stability of imidazolinium compared to the traditional imidazolium under harsh acidic conditions.Developed herein is a Cu(II)-catalyzed Meyer-Schuster-type rearrangement of alkyne-tethered cyclohexadienone for the construction of m-enone-substituted phenols. The reaction involves an uncommon 5-exo-trig 1,6-enyne cyclization of alkyne-tethered-cyclohexadienone, aromatization-triggered C-O bond cleavage, and an electrocyclic 4π-ring-opening of oxetene intermediate. This atom-efficient transformation provides access to a wide range of synthetically important α-(m-substituted phenol)-α,β-unsaturated ketones, featuring a broad scope with labile functional group tolerance. The gram-scale demonstration makes this transformation synthetically viable. The synthetic application of α,β-unsaturated ketones is also showcased.The long-lasting proton signals in bones are identified as long-chain fatty acids, including saturated, mono-, and di-unsaturated fatty acids, with direct nuclear magnetic resonance evidence. We used intramuscular bones from Atlantic Herring fish to avoid interference from lipid-rich marrows. The key is to recognize that these signals are from mobile phase materials and study them with J-coupled correlation spectroscopies under magic angle spinning conditions. We kept extensive 1H-spin-echo records that allowed us to examine the effect of magic angle spinning on the transverse relaxation time of water and lipids over time. While it is impossible to distinguish based on chemical shifts, the relaxation data suggest that the signals are more consistent with the interpretation of phospholipid membranes than triglycerides in lipid droplets. In particular, the simultaneous T2 changes in water and lipids suggest that the centrifugal impact of magic angle spinning alters the lipid's structure in very tight spaces. Additional evidence of phospholipid membranes came from the choline-γ resonance at 3.2 ppm in fresh samples, which disappears with magic angle spinning. Thus, the fatty acid signals are at least partially from membrane bilayer structures, and we propose that they are linked to the submicroscopic vascularization channels similar to the dense canaliculi network in mammalian bones. Our detection of phospholipids from bones depended critically on two factors (1) the elimination of the overwhelming triglyceride signals from marrows and (2) the preservation of water that biomembranes require. The relaxation data reveal aspects of lipid fluidity that have not been elucidated by previous order parameter studies on model membranes. Relaxation times have long been considered difficult to interpret. A robust and renewed understanding may be beneficial.Understanding molecular mechanisms of enzymatic reactions is of vital importance in biochemistry and biophysics. Here, we introduce new functions of hybrid quantum mechanical/molecular mechanical (QM/MM) calculations in the GENESIS program to compute the minimum-energy pathways (MEPs) and free-energy profiles of enzymatic reactions. For this purpose, an interface in GENESIS is developed to utilize a highly parallel electronic structure program, QSimulate-QM (https//qsimulate.com), calling it as a shared library from GENESIS. Second, algorithms to search the MEP are implemented, combining the string method (E et al. J. Chem. https://www.selleckchem.com/products/sodium-hydroxide.html Phys. 2007, 126, 164103) with the energy minimization of the buffer MM region. The method implemented in GENESIS is applied to an enzyme, triosephosphate isomerase, which converts dihyroxyacetone phosphate to glyceraldehyde 3-phosphate in four proton-transfer processes. QM/MM-molecular dynamics simulations show performances of greater than 1 ns/day with the density functional tight binding (DFTB), and 10-30 ps/day with the hybrid density functional theory, B3LYP-D3. These performances allow us to compute not only MEP but also the potential of mean force (PMF) of the enzymatic reactions using the QM/MM calculations. The barrier height obtained as 13 kcal mol-1 with B3LYP-D3 in the QM/MM calculation is in agreement with the experimental results. The impact of conformational sampling in PMF calculations and the level of electronic structure calculations (DFTB vs B3LYP-D3) suggests reliable computational protocols for enzymatic reactions without high computational costs.Longipetalol A (1) is an unprecedented highly modified triterpenoid with a unique 1,2-seco-3-(2-oxo-phenylethyl)-17α-13,30-cyclodammarane skeleton, featuring an acetal-lactone fragment. It was isolated from Dichapetalum longipetalum along with two additional derivatives, namely, longipetalols B (2) and C (3). Their structures were elucidated using spectroscopic analyses combined with single-crystal X-ray diffraction. Compounds 1, 2, and 3 exhibited inhibitory effects on nitric oxide production in lipopolysaccharide-induced RAW264.7 macrophages.Herein, we report the synthesis, characterization, and photophysical properties of the crown-like structure of [3]cyclo-1,8-pyrenes (compounds 9 and 10). Planar pyrenyl arylene-ethynylene macrocycles are used as the precursors to synthesize these pyrene-based cycloarenes by [4 + 2] cycloaddition reaction with good yields. These molecules are confirmed by nuclear magnetic resonance spectroscopy and high-resolution mass spectrometry. The structure of 9 was unambiguously determined by single-crystal X-ray diffraction. Their photophysical properties are investigated by steady-state absorption, fluorescence, and time-resolved fluorescence spectroscopies, combined with theoretical calculations.Obesity-associated insulin resistance plays a central role in the pathogenesis of type 2 diabetes. A promising approach to decrease insulin resistance in obesity is to inhibit the protein tyrosine phosphatases that negatively regulate insulin receptor signaling. The low-molecular-weight protein tyrosine phosphatase (LMPTP) acts as a critical promoter of insulin resistance in obesity by inhibiting phosphorylation of the liver insulin receptor activation motif. Here, we report development of a novel purine-based chemical series of LMPTP inhibitors. These compounds inhibit LMPTP with an uncompetitive mechanism and are highly selective for LMPTP over other protein tyrosine phosphatases. We also report the generation of a highly orally bioavailable purine-based analogue that reverses obesity-induced diabetes in mice.Interactions between distant DNA segments play important roles in various biological processes, such as DNA recombination. Certain restriction enzymes create DNA loops when two sites are held together and then cleave the DNA. DNA looping is important during DNA synapsis. Here we investigated the mechanisms of DNA looping by restriction enzyme SfiI by measuring the properties of the system at various temperatures. Different sized loop complexes, mediated by SfiI-DNA interactions, were visualized with AFM. The experimental results revealed that small loops are more favorable compared to other loop sizes at all temperatures. Our theoretical model found that entropic cost dominates at all conditions, which explains the preference for short loops. Furthermore, specific loop sizes were predicted as favorable from an energetic point of view. These predictions were tested by experiments with transiently assembled SfiI loops on a substrate with a single SfiI site.