Ligand Exchange Process Research Articles

Alkynyl ligands-induced growth of ultrathin nanowires arrays

Ligands are almost essential in the synthesis of nanostructures. In this work, we introduce the alkynyl ligands into the synthesis of ultrathin gold (Au) nanowires arrays. The strong binding affinity of the alkynyl ligands enables one-dimensional (1D) growth via the active surface growth mechanism. The scope of the ligand generality was systematically investigated, and the alkynyl ligand-induced nanowire growth processes were compared and contrasted with those involving thiolated ligands. While strong ligands are usually difficult to dissociate from the nanostructure surface and therefore problematic for post-synthetic processing, the alkynyl ligands are readily dissociable, making the alkynyl ligand-stabilized Au nanowires potentially more modifiable and applicable. As a demonstration, direct palladium (Pd) deposition on the Au nanowires was successfully carried out without any ligand exchange process.

Coordination of Quantum Dots in a Polar Solvent by Small-Molecule Imidazole Ligands.

Colloidal quantum dots (QDs) are attractive fluorophores for bioimaging and biomedical applications because of their favorable and tunable optoelectronic properties. In this study, the native hydrophobic ligand environment of oleate-capped sphalerite CdSe/ZnS core/shell QDs was quantitatively exchanged with a set of imidazole-bearing small-molecule ligands. Inductively coupled plasma-optical emission spectroscopy and 1H NMR were used to identify and quantify three different ligand exchange processes: Z-type dissociation of the Zn(oleate)2, L-type association of the imidazole, and X-type anionic exchange of oleate with Cl-, all of which contributed to the overall ligand exchange.

Ultrasmall Superparamagnetic Iron Oxide Nanoparticles as Nanocarriers for Magnetic Resonance Imaging: Development and In Vivo Characterization.

Ultrasmall superparamagnetic iron oxide nanoparticles (uSPIOs) are attractive platforms for the development of smart contrast agents for magnetic resonance imaging (MRI). Oleic acid-capped uSPIOs are commercially available yet hydrophobic, hindering in vivo applications. A hydrophilic ligand with high affinity toward uSPIO surfaces can render uSPIOs water-soluble, biocompatible, and highly stable under physiological conditions. A small overall hydrodynamic diameter ensures optimal pharmacokinetics, tumor delivery profiles, and, of particular interest, enhanced T 1 MR contrasts. In this study, for the first time, we synthesized a ligand that not only fulfills the as-proposed properties but also provides multiple reactive groups for further modifications. The synthesis delivers a facile approach using commercially available reactants, with resultant uSPIO-ligand constructs assembled through a single-step ligand exchange process. Structural and molecular size analyses confirmed size uniformity and small hydrodynamic diameter of the constructs. On average, 43 reactive amine groups were present per uSPIO nanoparticle. Its r 1 relaxivity has been tested on a 7 Tesla MR instrument and is comparable to that of the clinically available T 1 gadolinium-based contrast agent GBCA (1 vs 3 mM-1 s-1, respectively). A significant decrease in tumor T1 (15%) within 1 h of injection and complete signal recovery after 2 h were detected with a dose of 7 μg Fe/g mouse. The agent also has high r 2 relaxivity and can be used for T 2 contrast-enhanced MRI. Taken together, good relaxation and delivery properties and the presence of multiple surface reactive groups can facilitate its application as a universal MRI-compatible nanocarrier platform.

Efficient Vanadate Removal by Mg-Fe-Ti Layered Double Hydroxide

A series of novel layered double hydroxides (Mg-Fe-Ti-LDHs) containing Mg2+, Fe3+ and Ti4+ were prepared. The adsorption performance of Mg-Fe-Ti-LDHs on vanadate in aqueous solution was investigated and the effects of various factors on the adsorption process were examined, including initial vanadate concentration, adsorbent dosage, contact time, solution pH and coexisting ions. A preliminary discussion of the adsorption mechanism of vanadate was also presented. Results show that the adsorption efficiency of vanadate increased with the introduction of Ti4+ into the laminate of LDHs materials. The adsorption capacity of the materials also differed for different anion intercalated layers, and the Mg-Fe-Ti-LDHs with Cl− intercalation showed higher vanadate removal compared to the CO32− intercalated layer. Furthermore, Mg-Fe-Ti-CLDH showed higher vanadate removal compared to pre-calcination. The adsorption experimental data of vanadate on Mg-Fe-Ti-LDHs were consistent with the Langmuir adsorption isotherm model and the adsorption kinetics followed a pseudo-second order kinetic model. The pH of the solution significantly affected the vanadate removal efficiency. Meanwhile, coexisting ions PO43−, SO42− and NO3− exerted a significant influence on vanadate adsorption, the magnitude of the influence was related to the valence state of the coexisting anions. The possible adsorption mechanisms can be attributed to ion exchange and layered ligand exchange processes. The good adsorption capacity of Mg-Fe-Ti-LDHs on vanadate broadens the application area of functional materials of LDHs.

Investigation of the Ligand Exchange Process on Gold Nanorods by Using Laser Desorption/Ionization Time-of-Flight Mass Spectrometry.

The ligand exchange process on gold nanorods (Au NRs) was explored by using laser desorption/ionization time-of-flight mass spectrometry (LDI-TOF-MS). Cetyltrimethylammonium bromide (CTAB) adsorbed on Au NRs was replaced with alkanethiol derivatives presenting different functional groups. The ligand exchange process was investigated under various conditions, such as in the presence of different functional groups in the ligands and with different concentrations of CTAB. The ligand-exchanged Au NRs were characterized by using a combination of UV–Vis spectroscopy and LDI-TOF-MS. Based on the results, it was revealed that LDI-TOF-MS analysis can provide crucial and distinct information about the degree of ligand exchange on Au NRs.

Surface-Fabrication of Fluorescent Hydroxyapatite for Cancer Cell Imaging and Bio-Printing Applications.

Hydroxyapatite (HAP) materials are widely applied as biomedical materials due to their stable performance, low cost, good biocompatibility and biodegradability. Here, a green, fast and efficient strategy was designed to construct a fluorescent nanosystem for cell imaging and drug delivery based on polyethyleneimine (PEI) and functionalized HAP via simple physical adsorption. First, HAP nanorods were functionalized with riboflavin sodium phosphate (HE) to provide them with fluorescence properties based on ligand-exchange process. Next, PEI was attached on the surface of HE-functionalized HAP (HAP-HE@PEI) via electrostatic attraction. The fluorescent HAP-HE@PEI nanosystem could be rapidly taken up by NIH-3T3 fibroblast cells and successfully applied to for cell imaging. Additionally, doxorubicin hydrochloride (DOX) containing HAP-HE@PEI with high loading capacity was prepared, and in-vitro release results show that the maximum release of DOX at pH 5.4 (31.83%) was significantly higher than that at pH 7.2 (9.90%), which can be used as a drug delivery tool for cancer therapy. Finally, HAP-HE@PEI as the 3D inkjet printing ink were printed with GelMA hydrogel, showing a great biocompatible property for 3D cell culture of RAW 264.7 macrophage cells. Altogether, because of the enhanced affinity with the cell membrane of HAP-HE@PEI, this green, fast and efficient strategy may provide a prospective candidate for bio-imaging, drug delivery and bio-printing.

In situ-Synthesized cadmium sulfide quantum dots in pore-forming protein and polysaccharide matrices for optical biosensing applications

The main limitation for practical implementation of quantum dots-based sensors and biosensors is the possible contamination of sensing media with quantum dots (QDs) moved out from the sensor structure, being critical for living systems measurements. Numerous efforts have addressed the challenge of pre-synthesized QDs incorporation into porous matrix provide, on the one hand, proper fixation of quantum dots in its volume and preserving a free analyte transfer from the sensing media to them - on the other hand. Here, we propose an alternative insight into this problem. Instead of using preliminary synthesized particles for doping a matrix, we have in situ synthesized cadmium sulfide QDs in porous biopolymeric matrices, both in an aqueous solution and on a mica substrate. The proposed technique allows obtaining QDs in a matrix acting simultaneously as a ligand passivating surface defects and preventing QDs aggregation. The conjugates were used as a photoluminescence sensor for the metal ions and glutathione detection in an aqueous media. Different kinds of sensor responses have been found depending on the analyte nature. Zinc ions' presence initiates the intraband QDs emission increases due to the reduction of non-radiative processes. The presence of copper ions, in contrast, leads to a gradual photoluminescence decrease due to the formation of the non-luminescent copper-based alloy in the QDs structure. Finally, the presence of glutathione initiates a ligand exchange process followed by some QDs surface treatment enhancing defect-related photoluminescence. As a result, three different kinds of sensor responses for three analytes allow claiming development of a new selective QD-based sensor suitable for biomedical applications.

In-suit growth of Cu4SnS4 nanoplates on reduced graphene oxide (rGO) with ligand exchange exhibiting enhanced photodegradation property

In the present study, a novel Cu4SnS4/reduced graphene oxide (CTS/rGO) composite was successfully prepared using a simple one-pot heat-up method. Post-synthetic ligand exchange (LE) and annealing process were performed to further increase the dispersibility and the conductivity of the prepared composite. An unexpected phase transformation from CTS to Cu3SnS4 with an enhanced absorption in the near-infrared (NIR) region were observed after LE. Furthermore, the photodegradation of Rhodamine B (RhB) by the CTS/rGO composite was investigated. The CTS nanoplates with 10 wt% rGO treated through LE (CTS-10%rGO-LE) exhibited the highest (99.92%) degradation rate of RhB after 90 min of visible-light irradiation, which is approximately 10 and 1.28 times that of the pure CTS and the CTS-10%rGO treated using annealing (CTS-10%rGO-A). The enhancement of the photodegradation activity could be ascribed to the in-suit growth of CTS on rGO and the subsequent LE treatment, which effectively reduced the agglomeration of CTS and increased the electron-transfer ability of the composite materials. The CTS/rGO composite also exhibited high chemical stability of the photodegradation of RhB after four recycles. The electron paramagnetic resonance spectra reveal that ·OH and h+ are the main active species in the photocatalytic degradation of RhB with CTS-LE and CTS-10%rGO-LE photocatalysts. The in-suit growth of the CTS/rGO composite with a subsequent LE treatment has the potential to serve as an efficient photocatalysts for the degradation of organic pollutants.

Surface engineering of MOFs as a route to cobalt phosphide electrocatalysts for efficient oxygen evolution reaction

Exploring efficient routes for the fabrication of promising transition metal phosphides electrocatalysts towards oxygen evolution reaction (OER) has become a top priority in the field of water-splitting technology. Herein, a cobalt phosphide (CoxP) electrocatalyst composed of high-density small Co2P/CoP nanoparticles homogeneously embedded in one-dimensional (1-D) carbon has been synthesized by using surface-engineered cobalt benzimidazole zeolitic imidazolate framework (ZIF-9) rods as a precursor. The surface engineering strategy employs melamine to modify ZIF-9 by constructing robust Co coordination sites on ZIF-9 surface through the coordination of Co with nitrogen donor sites in melamine. DFT calculations indicate that the surface engineering of ZIF-9 triggered by melamine occurs not only at coordinatively unsaturated Co sites but also at coordinatively saturated Co sites via a thermodynamically favored ligand exchange process between benzimidazole in ZIF-9 and melamine. Subsequent reaction with red phosphorus at high temperature affords a 1-D material having high-density of CoxP reactive sites and facilitated charge/mass transport, leading to an outstanding electrocatalytic activity for OER—even comparable to commercial RuO2—and excellent electrochemical durability. This scalable strategy involving surface engineering of MOFs represents a breakthrough in the synthesis of efficient OER electrocatalysts in water electrolyzer application.

“Twin Lotus Flower” Adsorbents Derived from LaFe Cyanometallate for High-Performance Phosphorus Removal

Phosphorus (P) discharge is well recognized as the chief culprit of eutrophication and algal blooms. It is of pressing need to remove excessive phosphorus to protect the important watershed. Lanthanum (La) based materials are one type of attention-grabbing adsorbent due to their superior affinity to phosphate. Here, a La-Fe cyanometallate (CM) framework with a novel “twin lotus flower” structure was synthesized and rich hierarchical pores were fabricated via pyrolysis. The resultant “twin lotus flower” oxide of LaFe CM-500 was demonstrated to be a high-performance adsorbent for phosphate removal with a saturated capacity as high as 45.03 mg P/g. It also possessed superior removal ability for the stubborn low concentration of P pollution. The abundant hierarchical pores (from macropore to micropore) render a rapid diffusion of phosphate on the LaFe CM-500. The La components on porous adsorbent were verified to be the key active sites that form stable LaPO4 via a ligand exchange process. The effects of solution conditions (temperature, pH, co-existing ions, and humic acid) were also investigated, and a high selectivity for phosphate adsorption enables the as-prepared “twin lotus flower” adsorbent to be competitive in practical water body treatment.

Ab initio mechanism revealing for tricalcium silicate dissolution

Dissolution of minerals in water is ubiquitous in nature and industry, especially for the calcium silicate species. However, the behavior of such a complex chemical reaction is still unclear at atomic level. Here, we show that the ab initio molecular dynamics and metadynamics simulations enable quantitative analyses of reaction pathways, thermodynamics and kinetics of the calcium ion dissolution from the tricalcium silicate (Ca3SiO5) surface. The calcium sites with different coordination environments lead to different reaction pathways and free energy barriers. The low free energy barriers result in that the detachment of the calcium ion is a ligand exchange and auto-catalytic process. Moreover, the water adsorption, proton exchange and diffusion of water into the surface layer accelerate the leaching of the calcium ion from the surface step by step. The discovery in this work thus would be a landmark for revealing the mechanism of tricalcium silicate hydration.

High-efficiency capture and removal of phosphate from wastewater by 3D hierarchical functional biomass-derived carbon aerogel

The development of functional biomass-based carbon aerogels (CAs) with excellent mechanical flexibility and ultra-high phosphate capture capacity is crucial for capture and recovery of phosphate from waste water. Herein, a functional biomass-derived CA (MgO@SL/CMC CA) with an ordered wave-shaped layered structure and excellent compressibility was fabricated with the aim of creating a material with efficient phosphate capture performance. The incorporation of sulfonomethylated lignin (SL) significantly improves the mechanical flexibility of MgO@SL/CMC CA. Numerous MgO nano-particles (NPs), which act as principal adsorption sites, were uniformly anchored on the MgO@SL/CMC CA. The prepared MgO@SL/CMC CA with high Mg content (20.34 wt%) exhibited an ultra-high phosphate capture capacity (218.51 mg P g−1 for adsorbent or 644.58 mg P g−1 for MgO), excellent adsorptive selectivity for phosphate and a wide pH range of application (2–8). Notably, more than 81.95% of the phosphate capture capacity was retained after six cyclic adsorption-desorption tests. A considerable effective treatment volume (468 BV) of actual wastewater (1.7 mg P L−1) could be achieved by the MgO@SL/CMC CA in the fixed-bed adsorption column. Research into the adsorption mechanism reveals that monolayer chemisorption of phosphate occurs on the MgO@SL/CMC CA through a ligand exchange process. The combination of favorable flexibility, green raw materials and superior phosphate capture performance endows MgO@SL/CMC CA with great application potential in the practical treatment of wastewater.

A Strong and Rigid Coordination Adaptable Network that Can Be Reprocessed and Recycled at Mild Conditions

A Strong and Rigid Coordination Adaptable Network that Can Be Reprocessed and Recycled at Mild Conditions

Reactions of Arsenoplatin-1 with Protein Targets: A Combined Experimental and Theoretical Study.

Arsenoplatin-1 (AP-1) is a dual-action anticancer metallodrug with a promising pharmacological profile that features the simultaneous presence of a cisplatin-like center and an arsenite center. We investigated its interactions with proteins through a joint experimental and theoretical approach. The reactivity of AP-1 with a variety of proteins, including carbonic anhydrase (CA), superoxide dismutase (SOD), myoglobin (Mb), glyceraldehyde 3-phosphate dehydrogenase (GAPDH), and human serum albumin (HSA), was analyzed by means of electrospray ionization mass spectrometry (ESI MS) measurements. In accordance with previous observations, ESI MS experiments revealed that the obtained metallodrug–protein adducts originated from the binding of the [(AP-1)-Cl]+ fragment to accessible protein residues. Remarkably, in two cases, i.e., Mb and GAPDH, the formation of a bound metallic fragment that lacked the arsenic center was highlighted. The reactions of AP-1 with various nucleophiles side chains of neutral histidine, methionine, cysteine, and selenocysteine, in neutral form as well as cysteine and selenocysteine in anionic form, were subsequently analyzed through a computational approach. We found that the aquation of AP-1 is energetically disfavored, with a reaction free energy of +19.2 kcal/mol demonstrating that AP-1 presumably attacks its biological targets through the exchange of the chloride ligand. The theoretical analysis of thermodynamics and kinetics for the ligand-exchange processes of AP-1 with His, Met, Cys, Sec, Cys–, and Sec– side chain models unveils that only neutral histidine and deprotonated cysteine and selenocysteine are able to effectively replace the chloride ligand in AP-1.

Unique Ligand Exchange Dynamics of Metal–Organic Polyhedra for Vitrimer-like Gas Separation Membranes

Unique Ligand Exchange Dynamics of Metal–Organic Polyhedra for Vitrimer-like Gas Separation Membranes

Highly efficient P uptake by Fe3O4 loaded amorphous Zr-La (carbonate) oxides: Electrostatic attraction, inner-sphere complexation and oxygen vacancies acceleration effect

Bimetallic oxides composites have received an increasing attention as promising adsorbents for aqueous phosphate (P) removal in recent years. In this study, a novel magnetic composite MZLCO was prepared by hybridizing amorphous Zr-La (carbonate) oxides (ZLCO) with nano-Fe3O4 through a one-pot solvothermal method for efficient phosphate adsorption. Our optimum sample of MZLCO-45 exhibited a high Langmuir maximum adsorption capacity of 96.16 mg P/g and performed well even at low phosphate concentration. The phosphate adsorption kinetics by MZLCO-45 fitted well with the pseudo-second-order model, and the adsorption capacity could reach 79% of the ultimate value within the first 60 min. The phosphate adsorption process was highly pH-dependent, and MZLCO-45 performed well over a wide pH range of 2.0-8.0. Moreover, MZLCO-45 showed a strong selectivity to phosphate in the presence of competing ions (Cl−, NO3−, SO42−, HCO3−, Ca2+, and Mg2+) and a good reusability using the eluent of NaOH/NaCl mixture, then 64% adsorption capacity remained after ten recycles. The initial 2.0 mg P/L in municipal wastewater and surface water could be efficiently reduced to below 0.1mg P/L by 0.07 g/L MZLCO-45, and the phosphate removal efficiencies were 95.7% and 96.21%, respectively. Phosphate adsorption mechanisms by MZLCO-45 could be attributed to electrostatic attraction and the inner-sphere complexation via ligand exchange forming Zr/La-O-P, -OH and CO32− groups on MZLCO-45 surface played important roles in the ligand exchange process. The existence of oxygen vacancies could accelerate the phosphate absorption rate of the MZLCO-45 composites.

Second harmonic scattering multipole analysis of ligand-decorated gold nanoparticles

Ligand decoration of noble metallic nanoparticles is often needed for some applications, such as biochemical sensing, catalysis and nanotechnology, and the understanding of its process is of great importance. The second harmonic scattering (SHS) technique with advantages of surface-sensitivity and label-free detection, provides intrinsic information for such a research. In this work, the second harmonic(SH) scattering patterns of two types of ligands (cetyltrimethylammonium chloride and L-cysteine) capped gold nanoparticles (GNPs) with the same radii are measured. Both the intensities and shapes of the SH scattering patterns are changed after the ligand exchange process. In order to explain the pattern changes, the analytic expressions of SH scattering are derived theoretically for a relatively large nanoparticle based on Dadap’s multipolar theory. Considering the derived relationship between the multipole (up to octopole) contributions and the power of the nanosphere radius, the effective size effect is introduced to express the SH scattering signal change for different ligand decorations and well explain the experimental results. This theory provides a new perspective of the SH scattering response to different capping ligands and offers a possible quantitative method to analyze interface physical chemistry for ligands on the surface of nanoparticles.

FTIR study of the surface-ligand exchange reaction with glutathione on biocompatible rod-shaped CdSe/CdS semiconductor nanocrystals

CdS/CdSe nanorods are expected to be unique fluorescent labels. For solubilizing into water, their surface ligand has been exchanged to glutathione (GSH). This ligand exchange process was examined by FTIR, revealing the influence of the coverage ratio of GSH.

Chiral CuS nanoparticles and their photothermal properties

Chiral CuS NPs were prepared through a ligand-exchange process and CPL-controlled photothermal performance was realized.

Surface Decomposition and Healing in Solution-Phase Ligand Exchange for Efficient Colloidal Quantum Dot Solar Cells

The efficiency of solution-processed colloidal quantum dot (CQD) thin-film solar cells has been significantly improved recently. However, there is still potential for efficiency improvements, which can be realized through a deeper understanding of surface chemical treatment for CQDs. In this study, we developed CQD thin-film solar cells with an improved power conversion efficiency (PCE) of 11.97%. We accomplished this by simply controlling the species and their molar concentrations used in the surface chemical treatment in the solutionphase ligand exchange process. Iodine treatment that generates conductive CQDs induces surface defects via cationic decomposition of the CQD surface; healing the CQD surface requires an excess of lead cations in the solution-phase ligand exchange process. Accordingly, we found that manufacturing CQD thin-film solar cells that have high efficiencies requires well-controlled surface treatment to effectively exchange surface ligands and simultaneously minimize surface defects on the CQD surface.