Investigation of the Neighboring Residue Effects on Protein Chemical Shifts

In this study, we report nearest neighbor residue effects statistically determined from a chemical shift database. For an amino acid sequence XYZ, we define two correction factors, Δ(XY)n,s and Δ(YZ)n,s, representing the effects on Y's chemical shifts from the preceding residue (X) and the following residue (Z), respectively, where X, Y, and Z are any of the 20 naturally occurring amino acids, n stands for 1HN, 15N, 1Hα, 13Cα, 13Cβ, and 13C‘ nuclei, and s represents the three secondary structural types β-strand, random coil, and α-helix. A total of ∼14400 Δ(XY)n,s and Δ(YZ)n,s, representing nearly all combinations of X, Y, Z, n, and s, have been quantitatively determined. Our approach overcomes the limits of earlier experimental methods using short model peptides, and the resulting correction factors have important applications such as chemical shift prediction for the folded proteins. More importantly, we have found, for the first time, a linear correlation between the Δ(XY)n,s (n = 15N) and the 13Cα chemical shifts of the preceding residue X. Since 13Cα chemical shifts of the 20 amino acids, which span a wide range of 40−70 ppm, are largely dominated by one property, the electron density of the side chain, the correlation indicates that the same property is responsible for the effect on the following residue. The influence of the secondary structure on both the chemical shifts and the nearest neighbor residue effect are also investigated

Size-Dependent Dissociation pH of Thiolate Ligands from Cadmium Chalcogenide Nanocrystals

A method, pseudo steady-state titration, is introduced for determining the precipitation pH of nanocrystals coated by electron-donating ligands. CdSe nanocrystals coated with hydrophilic deprotonated thiol (thiolate) ligands were studied systematically. For comparison, CdTe and CdS nanocrystals coated with the same types of ligands were also examined. The results show that the precipitation of the nanocrystals is caused by the dissociation of the nanocrystal−ligand coordinating bonds from the nanocrystal surface. The ligands are removed from the surface due to protonation in a relatively low pH range, between 2 and 7 depending on the size, approximately within the quantum confinement size regime, and chemical composition (band gap) of the nanocrystals. In contrast, the redispersion of the nanocrystals was found to be solely determined by the deprotonation of the ligands. The size-dependent dissociation pH of the ligands was tentatively used as a means for determining the size-dependent free energy associated with the formation of a nanocrystal−ligand coordinating bond

Highly Luminescent, Stable, and Water-Soluble CdSe/CdS Core−Shell Dendron Nanocrystals with Carboxylate Anchoring Groups

A dendron ligand with two carboxylate anchoring groups at its focal point and eight hydroxyl groups as its terminal groups was found to efficiently convert as-synthesized CdSe/CdS core−shell nanocrystals in toluene to water-soluble dendron-ligand stabilized nanocrystals (dendron nanocrystals). The resulting dendron nanocrystals retained 60% of the photoluminescence value of the original CdSe/CdS core−shell nanocrystals in toluene and were significantly brighter than the similar dendron nanocrystals with thiolate (deprotonated thiol group) as the anchoring group which retained just 10% of the photoluminescence value of the original CdSe/CdS core−shell nanocrystals in toluene. The carboxylate-based dendron nanocrystals survived UV irradiation in air for at least 13 days, about 9 times better than the thiolate-based dendron nanocrystals (35 h) and similar to that of the thiolate-based dendron-box stabilized CdSe/CdS core−shell nanocrystals (box nanocrystals). Upon UV irradiation, the dendron nanocrystals became even 2 times brighter than the original CdSe/CdS core−shell nanocrystals in toluene, and the UV-brightened PL can retain the brightness for at least several months. These stable and bright dendron nanocrystals were soluble in various aqueous media, including all common biological buffer solutions tested, for at least 1.5 years. In addition to their superior performance, the synthetic chemistry of carboxylate dendron ligands and the corresponding dendron nanocrystals is relatively simple and with high yield

Highly Luminescent, Stable, and Water-Soluble CdSe/CdS Core−Shell Dendron Nanocrystals with Carboxylate Anchoring Groups

A dendron ligand with two carboxylate anchoring groups at its focal point and eight hydroxyl groups as its terminal groups was found to efficiently convert as-synthesized CdSe/CdS core−shell nanocrystals in toluene to water-soluble dendron-ligand stabilized nanocrystals (dendron nanocrystals). The resulting dendron nanocrystals retained 60% of the photoluminescence value of the original CdSe/CdS core−shell nanocrystals in toluene and were significantly brighter than the similar dendron nanocrystals with thiolate (deprotonated thiol group) as the anchoring group which retained just 10% of the photoluminescence value of the original CdSe/CdS core−shell nanocrystals in toluene. The carboxylate-based dendron nanocrystals survived UV irradiation in air for at least 13 days, about 9 times better than the thiolate-based dendron nanocrystals (35 h) and similar to that of the thiolate-based dendron-box stabilized CdSe/CdS core−shell nanocrystals (box nanocrystals). Upon UV irradiation, the dendron nanocrystals became even 2 times brighter than the original CdSe/CdS core−shell nanocrystals in toluene, and the UV-brightened PL can retain the brightness for at least several months. These stable and bright dendron nanocrystals were soluble in various aqueous media, including all common biological buffer solutions tested, for at least 1.5 years. In addition to their superior performance, the synthetic chemistry of carboxylate dendron ligands and the corresponding dendron nanocrystals is relatively simple and with high yield

Quaterization Derivatization with Bis(Pyridine) Iodine Tetrafluoroboride: High-Sensitivity Mass Spectrometric Analysis of Unsaturated Fatty Acids in Human Thyroid Tissues

Accurate quantification of disease-related unsaturated fatty acids (UFAs) in biomedical samples plays an important role in clinical diagnosis. Here, we reported a quaterization derivatization-stable isotope labeling strategy for accurate quantitative analysis of UFAs by high-performance liquid chromatography-mass spectrometry. [d0]/[d10]-Bis­(pyridine) iodine tetrafluoroboride ([d0]/[d10]-IPy2BF4) was employed as the carbon–carbon double bond derivatization reagent with high efficiency and high specificity, to introduce a charge tag on UFAs and avoid the interference of saturated fatty acids. After labeling, the detection sensitivity was significantly enhanced by up to three orders of magnitude compared to intact UFAs. The standard curves showed good linearity (R2 > 0.999) over a wide concentration range. This strategy was successfully applied to determine the content of 12 UFAs in human thyroid carcinoma and para-carcinoma tissues. A significant difference was found in the content of several UFAs between these two kinds of tissues (p < 0.05). These results indicated that the proposed strategy may be valuable for the discovery of abnormal UFA content in early clinical diagnosis

Highly Stable Red Quantum Dot Light-Emitting Diodes with Long <i>T</i>₉₅ Operation Lifetimes

Quantum dot light-emitting diodes (QLEDs) with an excellent external quantum efficiency (EQE) and an excellent lifetime almost meet the requirements for low-brightness displays. However, the short operation lifetime under high brightness limits the application of QLEDs in outdoor displays and lightings. Herein, we report a highly efficient, stable red QLED using co-doped lithium and magnesium as well as a magnesium oxide shell-coated zinc oxide nanoparticle layer as an electron transport layer (ETL). The optimized QLED has a high peak EQE of 20.6%, a low efficiency roll-off at high current, and a remarkably long lifetime T95 of >11000 h at 1000 cd m–2, which is an indication of the realization of the most stable red QLED to date. The improvement in the long term stability of the QLED is attributed to the use of a co-doped and shell-coated zinc oxide ETL with a reduced level of electron injection to improve the charge balance in the device

Improving Performance of InP-Based Quantum Dot Light-Emitting Diodes by Controlling Defect States of the ZnO Electron Transport Layer

ZnO nanoparticles (NPs) are currently the benchmark of electron transport materials for preparing indium phosphide (InP)-based environmentally friendly quantum dot light-emitting diodes (QLEDs). However, the defect-dependent exciton quenching and charge injection limiting behavior at the ZnO/quantum dot (QD) interface seriously restrict the improvement in device performance. Herein, we report a strategy based on Li doping and MgO shell coating to regulate the defect state of ZnO to improve the performance of InP-based QLEDs. It is found that Li doping passivates the intrinsic defect states of ZnO NPs and improves the electron mobility and reduces the spontaneous charge transfer at the ZnO/QD interface and the current leakage of QLEDs. The MgO shell passivates the surface oxygen defects of ZnO NPs, thus reducing the exciton quenching and non-radiative recombination centers at the ZnO/QD interface, resulting in enhanced QLED performance. As a result, the optimized QLED prepared by Li-doped and MgO shell-coated ZnO NPs shows an external quantum efficiency of 9.7% and a brightness of 22,200 cd m–2 at 4.2 V, which are, respectively, 2.6 and 7 times higher than those of a QLED based on pure ZnO. This work shows that controlling the defect states of the ZnO electron transport layer by ion doping and shell coating provides an effective way to obtain high-performance environment-friendly QLEDs

Ultrasmooth Quantum Dot Micropatterns by a Facile Controllable Liquid-Transfer Approach: Low-Cost Fabrication of High-Performance QLED

Fabrication of a high quality quantum dot (QD) film is essentially important for a high-performance QD light emitting diode display (QLED) device. It is normally a high-cost and multiple-step solution-transfer process where large amounts of QDs were needed but with only limited usefulness. Thus, developing a simple, efficient, and low-cost approach to fabricate high-quality micropatterned QD film is urgently needed. Here, we proposed that the Chinese brush enables the controllable transfer of a QD solution directly onto a homogeneous and ultrasmooth micropatterned film in one step. It is proposed that the dynamic balance of QDs was enabled during the entire solution transfer process under the cooperative effect of Marangoni flow aroused by the asymmetric solvent evaporation and the Laplace pressure different by conical fibers. By this approach, QD nanoparticles were homogeneously transferred onto the desired area on the substrate. The as-prepared QLED devices show rather high performances with the current efficiencies of 72.38, 26.03, and 4.26 cd/A and external quantum efficiencies of 17.40, 18.96, and 6.20% for the green, red, and blue QLED devices, respectively. We envision that the result offers a low-cost, facile, and practically applicable solution-processing approach that works even in air for fabricating high-performance QLED devices

Photoluminescence Lifetimes and Thermal Degradation of Mn²⁺-Doped CsPbCl₃ Perovskite Nanocrystals

The Mn2+-doped CsPbCl3 nanocrystals (NCs) with a low Mn2+ doping concentration were synthesized using different reaction temperatures to control the NC size from 5.3 to 17.4 nm and then were studied by means of steady-state and time-resolved photoluminescence (PL) spectroscopy at various temperatures. The Mn2+ emissions with different quantum yields in the doped NCs in hexane exhibited nearly size-independent and single-exponential decay lifetimes of 1.8 ms at room temperature. The PL lifetimes in all Mn2+ in CsPbCl3-doped NCs had similar temperature dependence from 80 to 300 K, whereas they were size-dependent at elevated temperatures, reflecting thermal degradation of doped NCs. The degradation mechanisms of Mn2+ PL were attributed to the amount of surface defects as nonradiative recombination centers generated in size-unchanged and grown Mn2+:CsPbCl3 NCs. The study provides the detailed understanding of the thermal degradation mechanisms in doped perovskite NCs for optoelectronic applications