Proton‑Prompted Ligand Exchange to Achieve High‑Efficiency CsPbI_(3) Quantum Dot Light‑Emitting Diodes

CsPbI_(3)perovskite quantum dots(QDs)are ideal materials for the next generation of red light-emitting diodes.However,the low phase stability of CsPbI_(3)QDs and long-chain insulating capping ligands hinder the improvement of device performance.Traditional in-situ ligand replacement and ligand exchange after synthesis were often difficult to control.Here,we proposed a new ligand exchange strategy using a proton-prompted insitu exchange of short 5-aminopentanoic acid ligands with long-chain oleic acid and oleylamine ligands to obtain stable small-size CsPbI_(3)QDs.This exchange strategy maintained the size and morphology of CsPbI_(3)QDs and improved the optical properties and the conductivity of CsPbI_(3)QDs films.As a result,high-efficiency red QD-based light-emitting diodes with an emission wavelength of 645 nm demonstrated a record maximum external quantum efficiency of 24.45%and an operational half-life of 10.79 h.

Chiral ionic liquids as chiral selectors for separation of tryptophan enantiomers by ligand exchange chromatography

Chiral ionic liquids (CILs) containing imidazolium cations and L-Proline (L-Pro) anions were applied as chiral selector to separate tryptophan (Trp) enantiomers on a C18 column by ligand exchange chromatography. Several factors influencing Trp enantiomers separation, such as alkyl chain length of CILs, concentrations of Cu2+ and CILs, pH of the mobile phase, flow rate, organic solvent and temperature, were studied. Under the optimal conditions, the Trp enantiomers could be successfully separated within 21 min with the resolution of 2.30. At the same time, some thermodynamical parameters were obtained. The experimental results show that the enthalpy values of the Trp enantiomers are negative, indicating that the separation process is exothermic. And the enthalpy values of D-Trp are larger than those of L-Trp, which indicates that L-Trp could form more stable ternary complexes with tryptophan enantiomers.

Investigation of Performances and Mechanism of Fluoride Removal by Fe(Ⅲ)-Loaded Ligand Exchange Cotton Cellulose Adsorbent

Novel adsorbent, Fe（Ⅲ）-loaded ligand exchange cotton cellulose adsorbent [Fe（Ⅲ） LECCA], was used to in vestigate the adsorption performances and mechanism of fluoride removal from aqueous solutions. The adsorbent was found to adsorb fluoride rapidly and effectively. The fluoride removal was influenced by pH. Adsorption mode followed first-order reaction at different temperature, theapparent adsorption activated energy Ea was 6.37 kJ·mol^-1, and adsorption enthalpy △H was 5.35 kJ·mol^-1. The adsorption enfluoride on adsorbent was 3.2 mmol·g^-1 （dry weight）. The maximal integer coordination ratio of fluoride with Fe（Ⅲ） LECCA was 3：1. The ligand exchange mechanism of adsorption was elucidated through chemical methods and IR spectral analysis.

Ligand Exchange of Colloidal ZnO Nanocrystals from the High Temperature and Nonaqueous Approach

Colloidal zinc oxide(ZnO) nanocrystals generated from the high temperature and nonaqueous approache are attractive for use in solution-processed electrical and optoelectronic devices. However, the asprepared colloidal ZnO nanocrystals by this approach are generally capped by ligands with long alkyl-chains,which is disadvantage for solution-processed devices due to hindering charge transport. Here we demonstrate an effective ligand exchange process for the colloidal ZnO nanocrystals from the high temperature and nonaqueous approach by using n-butylamine. The ligand exchange process was carefully characterized. The thin films based on colloidal ZnO nanocrystals after ligand exchange exhibited dramatically enhanced UV photoconductivity.

Preparation of novel chiral stationary phase based on click chemistry for ligand exchange chromatography

Click chemistry was applied to immobilize L-proline derivative onto azide-modified silica gel to give a novel chiral stationary phase （denoted as click-CSP） for ligand exchange chromatography. The developed protocol combines the benefits of operational simplicity, exceptionally mild conditions and high surface loadings. The enantioselectivity α of some DL-arnino acids on the click- CSP were found to be in the range from 1.13 to 3.46. The chromatographic resolutions of some DL-amino acids and the stability study firmly illustrate the potential of click chemistry for preparation chiral stationary phase for ligand exchange chromatography.

Enantioselective extraction of mandelic acid enantiomers based on chiral ligand exchange

Based on the chiral ligand exchange, the distribution behavior of mandelic acid enantiomers, and the partition of Cu2+ at different pH values were studied in a water/alcohol two-phase system containing Cu2+ and N-n-（dodecyl-L-proline（A）.） The influences of the solvent sort, the pH value, the concentrations of Cu2+ and chiral ligand on the partition coefficient（K） and separation factor（α） were discussed. The experimental results show that the A formed has more stable ternary complex with D-mandelic acid enantiomer than with L-mandelic acid enantiomer. There is an important influence of the pH value on K and α. When the pH values are less than 3.5, the formation of binary complexes is thermodynamically unfavourable. K and α become maximum when pH values are above 3.5 and the molar ratio of the chiral ligand to Cu2+ is 2∶1.

F?(H2O)+CH3I Ligand Exchange Reaction Dynamics

Single hydration of the gas phase F^-+CH3I→CH3F reaction allows to probe solvent effects on a fundamental nucleophilic substitution reaction.At the same time,the addition of a solvent molecule opens alternative product channels.Here,we present crossed beam imaging results on the dynamics of the F^-(H2O)+CH3I→[FCH3I]^-+H2O ligand exchange pathway at collision energies between 0.3 and 2.6 eV.Product kinetic energies are constrained by the stability requirement of the weakly bound product complexes.This implies substantial internal excitation of the water molecule and disfavors effcient energy redistribution in an intermediate complex,which is reflected by the suppression of low kinetic energies as collision energy increases.At 0.3 eV,internal nucleophilic displacement is important and is discussed in light of the competing nucleophilic substitution pathways that form I^- and I^-(H2O).

Separation of Neutral Amino Acids with Ligand Exchange Resins

Four neutral amino acids (Gly, Ala,.Val and Leu) were separated with ligand exchange resins. The separation capacity of the ligand exchange resins is compared with that of common ion exchange resins. The effects of eluent, column temperature, and central metal ions of the support on the separation are studied. The relationship between matrix structure of resins and their separation capacity is analysed.

Thin-Layer Chromatographic Separation of Amino Acid Enantiomers using Ligand Exchange

Silica gel thin-layer plates covered with L-arginine and copper acetate were used for the separation of amino acid enantiomers, The chromatographic selectivity and the effects of plate different preparation methods, sample molecular structure and solvent compositions on resolution performance were also discussed.

Ligand Exchange Reaction of Ferrocene with Substituted Benzenes

Ligand exchange reaction is one of the typical reactions of ferrocene. In this paper, ligand exchange reactions were carried out between ferrocene and various substituted benzenes using aluminum chloride catalysis. The product yields of the reactions with alkanoyl- and alkoxybenzenes were low because of the coordination of aluminum chloride to the oxygens of the benzene substituents. Comparing the reactions using o- and p-dimethoxybenzene, the former was revealed to be less reactive;this is likely due to the deviation of the π-electrons of its benzene ring being larger.

Single atom Pd1/ZIF-8 catalyst via partial ligand exchange

A partial ligand exchange strategy for fabricating catalytically active single palladium site immobilized on zeolitic imidazolate framework-8(ZIF-8,Pd1/ZIF-8)is proposed in this work.The one-step synthesis simply involves reacting Na_(2)PdCl_(4) with ZIF-8 in solvent.The Cl ligands of Na_(2)PdCl_(4) exchanged with 2-methylimidazole(2-MeIm)of the framework,resulting in the anchoring Pd on the framework and dissociation of Zn into the solution.The whole synthesis is performed at ambient conditions and the crystalline integrity of ZIF-8 is well retained.The resulting Pd_(1)/ZIF-8 is extensively characterized by different techniques which confirm the proposed mechanism.Pd_(1)/ZIF-8 is also successfully applied in the size-selective semi-hydrogenation of alkynes.

Removal of trace arsenic(V) and phosphate from water by a highly selective ligand exchange adsorbent

A highly selective ligand exchange type adsorbent was developed for the removal of trace arsenic（V） （As（V）） and phosphate from water. This adsorbent was prepared by loading zirconium（IV） on monophosphonic acid resin. This adsorbent was able to remove toxic anions efficiently at wide pH ranges. However, low pH was preferable for maximum breakthrough capacity in an adsorption operation. The effiect of a large amount of competing anions such as chloride, bicarbonate, and sulfate on the adsorption systems of As（V） and phosphate anions was investigated. The experimental findings revealed that the As（V） and phosphate uptakes were not affiected by these competing anions despite the enhancement of the breakthrough points and total adsorption. Phosphate anion was slightly preferable than As（V） in their competitive adsorption by the adsorbent. The adsorbed As（V） and phosphate on the Zr（IV）-loaded resin were quantitatively eluted with 0.1 mol/L sodium hydroxide solution, and the adsorbent was regenerated by 0.5 mol/L sulfuric acid. During several cycles of adsorption-elution-regeneration operations, no Zr（IV） was detected in the column efiuents. Therefore, the Zr（IV）- loaded monophosphonic acid resin is an efiective ligand exchange adsorbent for removing trace concentrations of As（V） and phosphate from water.

Modification of Chiral Stationary Phases with L-Proline as a Selector for Ligand-exchange Chromatography via Introducing Hydrophobic Groups

Three chiral stationary phases（CSPl, CSP2 and CSP3） for ligand-exchange chromatography were prepared by firstly using dimethylchlorosilane as an endcapping reagent for decreasing residual silanol groups on the surface of silica gel, and then modifying the surface of silica gel with allyl glycidyl ether and alkenes through the hydrosilation reaction, and lastly introducing L-proline as a chiral selector. The enantiomer resolutions of 14 amino acids and 2 hydroxyl acids were completed on the CSPs by using an aqueous solution of Cu（Ac）2 as mobile phase at a flow rate of 1.0 mL/min and column temperature of 40 ℃ with detection at UV 254 nm. In terms of enantioseleetivity a, column efficiency and resolution Rs, the chromatographic behaviors of the analytes on the CSPs were discussed via comparing them to those on the CSP4 prepared via the reference method. The results show that enantioselectivity a, column efficiency and resolution Rs of the analytes on the CSPs could be improved by using the above modifying method.

Enantioseparation of Dencichine and D-Isomer on L-Cysteine Derivative Phase by Ligand-exchange Chromatography

The enantioseparation of dencichine and its D-isomer was achieved on a novel chiral stationary phase via coating N-（2-hydroxyl-3-octoxyl） propyl-S-benzyl-（L）-cysteine on YWG-C18 phase by ligand exchange chromatography.

Multiple-Sized Amphiphilic Janus Gold Nanoparticles by Ligand Exchange at Toluene/Water Interface

Amphiphilic Janus gold nanoparticles （GNPs） are prospected to encapsulate drug molecules in cancer therapy and to serve as heterogeneous catalysts at oil/water interfaces, where Janus GNPs with differ- ent sizes are required. In this work, multiple-sized precursor GNPs were synthesized by seeded growth method protected with tris（hydroxymethyl）phosphine oxide （THPO） ligand molecule, and a ligand ex- change reaction with triphenylphosphine （PPh3） at the toluene/water interface was employed to prepare amphiphilic Janus GNPs. UV-vis and transmission electron microscopy （TEM） analyses indicate that the as-prepared GNPs are nanocrystals with average diameters of 2.3 nm, 9.5 nm, 16.1 nm and 18.8 nm, re- spectively. Contact angle, Raman and X-ray photonic spectroscopy （XPS） analyses reveal that the self- assembled GNP films exhibit hydrophilic on one side and hydrophobic on another, owing to the adsorption of hydrophilic ligands （THPO and THP） and a similar amount of hydrophobic ligands （PPh3 and PPh30）. Angle-resolved XPS analysis further demonstrates that the individual GNPs actually possess hydro- philic and hydmphobic compartments on the surface, which regularly packed by supramolecular interactions at toluene/water interface to form the self-assembled GNP films.

Significance of Ligand Exchange Relating to Sulfate in Retarding Acidification of Variable Charge Soils Caused by Acid Rain

For the purpose of evaluating the role of ligand exchange of sulfate ions in retarding the rate of acidification of variable charge soils, the changes in pH after the addition of different amounts of HNO_3 or H_2SO_4 to representative soils of China were measured. A difrerence between pH changes caused by the two kinds of acids was observed only for variable charge soils and kaolinite, but not for consted charge soils and bentonite. The larger the proportion of H_2SO_4 in the HNO_3-H_2SO_4 mixture, the lower the calculated H￣+ ion activities remained in the suspension. The difference in H￣+ ion activities between H_2SO_4 systems and HNO_3 systems was larger for soils with a low base-saturation (BS) percentage than those with a high BS percentage. The removal of free iron oxides from the soil led to a decrease in the difference, while the coating of Fe_2O_3 ona bentonite resulted in a remarkable appearance of the difference. The effect of ligand exchange on the acidity status of the soil varied with the soil type. SurfaCe soils with a hash organic matter content showed a less pronounced effect of ligand exchange than subsoils did. It was estimated that when acid rain chiefly containing H_2SO_4 was deposited on variable charge soils the acidilication rate might be slower by 20%-40% than that when the acid rain chiefly contained HNO_3 for soils with a high organic matter content, and that the rate might be half of that caused by HNO_3 for soils with a low organic matter content, especially for latosols.

Rational design of smart adsorbent equipped with a sensitive indicator via ligand exchange:A hierarchical porous mixed-ligand MOF for simultaneous removal and detection of Hg^(2+)

The increasing accumulation of toxic mercury species in water environment has posed a serious health threat worldwide, making it inevitable to develop the versatile materials to achieve efficient prevention and remediation of mercury pollution. Guided by the solvent-assisted ligand exchange (SALE) approach, this work rationally constructed a mixed-ligand NH2-UiO-66-SH (NSU66) with hierarchical-pore structure by incorporating the thiol-rich ligands (H2DMBD) into the water-stable NH2-UiO-66 (NU66) precursor to act as a smart adsorbent equipped with sensitive detector for simultaneous sensing and removal of Hg2+. Unlike the traditional adsorbents, the as-prepared NSU66 not only exhibits a remarkable removal ability with fast capture rate (within 60.0 min), large uptake capacity (265.29 mg/g), and qualified selectivity, but also possesses satisfactory sensing capability, accompanied by low detection limit (3.50 × 10−2 µM), wide linear range (1.00–99.7 µM), high specificity, and strong anti-interference capability. The detection function plays a vital role in indicating the removal behavior and the pre-enrichment effect of adsorption process correspondingly improves the sensitivity of indicator. Notably, the sensing and trapping capabilities of NSU66 are significantly improved compared to the NU66, which stems from the delicate design of the mixed-ligand and hierarchical-pore structure. Furthermore, proven excellent stability and recyclability emphasize the feasibility of NSU66 in practical applications. These results suggest that the smart NSU66 adsorbent can serve as a favorable platform for early warning and guided removal of toxic Hg2+ in water.

Investigation on Ligand Exchange Kinetics on CdSe/ZnS Quantum Dot Surface Utilizing Pyrene as Flourescent Probe

Direct ligand exchange kinetics between hydrophilic molecules and quantum dots（QDs） was investigated. Meanwhile, pyrene was exploited as probe to detect the efficiency of the ligand exchange reaction between octade- cylamine-coated QDs（ODA-QDs） and different ligands[ligand 1： NH2G3-OH, ligand 2： G4.5-PEG5-FA5, ligand 3： （COOH）2G3-OH or ligand 4： G4.5-PEG1-FAl]. It was indicated that water-soluble QDs exhibit the same fluores- cence and absorption spectra as ODA-QDs when they were dissolved in chloroform. Furthermore, the cellular expe- riments demonstrated that the folic acid（FA） targeting poly（amidoamine）（PAMAM） modified QD conjugates could be used as molecular targeting sensing systems for nanoparticle probes.

Kinetic study on the ligand exchange reactions between bis(alkylxanthato)palladium(II)and bis(N,N-dialkyldithiocarbamato)palladium(II)by high-performance liquid chromatography

The rate constants and equilibrium constants of ligand exchange reactions between his (alkylxanthato)palladium(Ⅱ),Pd(S_2COR)_2(R=Am,n-Hex,Bz),and bis(N,N-dialkyldithiocarbamato) palladium(Ⅱ),Pd(S_2CNR_2)_2(K=Et,n-Pr,n-Bu),in chloroform solution have been determined in a temperature range of 20—50°C by means of high-performance liquid chromatography.It was found that both the forward and reverse reactions are of second order.All of the equilibrium constants K determined are 10.3±1.0,much greater than the value(K=4)calculated statistically which indicates that the ternary complexes are more stable than the binary complexes.The experimental results revealed that the reaction rate decreases with the increase in the size of R and R^1 groups and the latter are more remarkable,consistent with the deduction of steric effect.The activation parameters of the reactions have been calculated.In reaction series(11)and(12)(in the text)the isokinetic tempera- tures B=390±8K and β=346±15 K have been observed respectively.A plausiblemechanism in- volving an eight-membered ring intermediate has been proposed on the basis of experimental results.

Control of the interparticle spacing in superparamagnetic iron oxide nanoparticle clusters by surface ligand engineering

Polymer-mediated self-assembly of superparamagnetic iron oxide（SPIO） nanoparticles allows modulation of the structure of SPIO nanocrystal cluster and their magnetic properties. In this study, dopamine-functionalized polyesters（DApolyester） were used to directly control the magnetic nanoparticle spacing and its effect on magnetic resonance relaxation properties of these clusters was investigated. Monodisperse SPIO nanocrystals with different surface coating materials（poly（ε-caprolactone）, poly（lactic acid）） of different molecular weights containing dopamine（DA） structure（DA-PCL2k,DA-PCL1k, DA-PLA1k）） were prepared via ligand exchange reaction, and these nanocrystals were encapsulated inside amphiphilic polymer micelles to modulate the SPIO nanocrystal interparticle spacing. Small-angle x-ray scattering（SAXS）was applied to quantify the interparticle spacing of SPIO clusters. The results demonstrated that the tailored magnetic nanoparticle clusters featured controllable interparticle spacing providing directly by the different surface coating of SPIO nanocrystals. Systematic modulation of SPIO nanocrystal interparticle spacing can regulate the saturation magnetization（Ms） and T2 relaxation of the aggregation, and lead to increased magnetic resonance（MR） relaxation properties with decreased interparticle spacing.