Ligand Displacement Research Articles

Near-Edge Ligand Stripping and Robust Radiative Exciton Recombination in CdSe/CdS Core/Crown Nanoplatelets.

We address the relation between surface chemistry and optoelectronic properties in semiconductor nanocrystals using core/crown CdSe/CdS nanoplatelets passivated by cadmium oleate (Cd(Ol)2) as model systems. We show that addition of butylamine to a nanoplatelet (NPL) dispersion maximally displaces ∼40% of the original Cd(Ol)2 capping. On the basis of density functional theory simulations, we argue that this behavior reflects the preferential displacement of Cd(Ol)2 from (near)-edge surface sites. Opposite from CdSe core NPLs, core/crown NPL dispersions can retain 45% of their initial photoluminescence efficiency after ligand displacement, while radiative exciton recombination keeps dominating the luminescent decay. Using electron microscopy observations, we assign this robust photoluminescence to NPLs with a complete CdS crown, which prevents charge carrier trapping in the near-edge surface sites created by ligand displacement. We conclude that Z-type ligands such as cadmium carboxylates can provide full electronic passivation of (100) facets yet are prone to displacement from (near)-edge surface sites.

Characterization of the interaction of diosgenin with human serum albumin and α1-acid glycoprotein using biophysical and bioinformatic tools

Diosgenin (DIO), a steroidal sapogenin with high therapeutic potential, has been shown to exhibit a myriad of pharmacologically significant properties and is commonly used as a template for synthesizing steroidal drugs. The efficacy of bioactive compounds as a potential drug depends mainly upon their interaction with proteins in the circulatory system. Therefore, the interaction of DIO with the major carrier proteins in humans, i.e. human serum albumin (HSA) and α 1 -acid glycoprotein (AAG), was characterized using multispectroscopic and molecular docking techniques. Analysis of fluorescence enhancement data showed intermediate binding affinity for both DIO–HSA and DIO–AAG interactions. Circular dichroism spectral results revealed minimal conformational alterations in HSA upon DIO binding, but the effect on AAG was more significant. Competitive ligand displacement results suggested that DIO does not bind strongly to the main drug binding sites of HSA. However, DIO was found to favor binding to subdomain IB of HSA based on molecular docking data. For AAG, the binding location of DIO was determined for the two variants of AAG (A and F1*S variants) using molecular docking. For variant A, the binding site was situated in lobes I and II of the central binding pocket of the protein, while in variant F1*S, DIO was docked to a cleft on the protein surface. Hydrophobic interactions and van der Waals forces were mainly responsible for complexation between DIO and both proteins. Additionally, there was involvement of hydrogen bonding between DIO and both variants of AAG, but not between DIO and HSA. • AAG binds to DIO with slightly stronger affinity than HSA. • Hydrophobic forces are mainly responsible for DIO binding to both proteins. • DIO binds to HSA at subdomain IB. • DIO binds to variant F1*S of AAG at a cleft at the surface. • DIO binds to variant A of AAG at the central cavity.

Development of a fluorescent chemosensor for chloride ion detection in sweat using Ag+-benzimidazole complexes

The level of chloride ions (Cl⁻) in sweat is a recognized biomarker for the genetic disorder cystic fibrosis (CF). The accurate quantitation of chloride ions in sweat is therefore a vital diagnostic tool for this life-threatening disease. In this work, a fluorescent, chloride ion chemosensor was developed by exploiting the strong interaction between silver (Ag+) and chloride ions. Using the concept of ligand displacement, six Ag+-benzimidazole complexes were prepared as candidate chloride ion chemosensors. The Ag+-2-(Furan-2-yl)-1H-benzo[d]imidazole (Ag+-FBI) complex was identified as the optimal sensor owing to its Ag+-FBI high sensitivity (limit of detection = 19 μM), short response time (<3 min), and remarkable fluorescence turn-on response across a broad pH range (pH 6–9). The Ag+-FBI complex exhibited high selectivity for Cl⁻ ions and was successfully used to quantify chloride ions in artificial sweat samples containing multiple ions and other biological constituents. This unique, simple, and effective probe thus shows great potential for clinical diagnostic applications.

Efficient stabilization of in situ fabrication of PtxPd1-x nanostructures for electro-oxidation of methanol in alkaline medium

Different binary PtxPd1-x alloys supported on Vulcan carbon XC-72R were synthesized by the displacement of ligands from organometallic compounds to be used as anodic electrode for methanol electro-oxidation in alkaline medium. The influence of the Pd addition during the synthesis of PtxPd1-x alloys in presence of octylamine as stabilizer was analyzed in terms of structure, chemical composition and electroactivity in the methanol oxidation reaction. The X-ray photoelectron spectroscopy analysis showed that the surface of the electrodes consisted of a metallic mixture and oxide states, which confirmed the change in the electronic properties during the alloy formation. The current density of Pt30Pd70/C during CV measurements was about 2.1 times higher than the one observed with Pt/C electrodes. The CO tolerance was also slightly improved under similar conditions. The work findings indicate that stabilized Pt30Pd70/C binary alloys can be used to design highly active anodic catalysts with potential applications in direct methanol fuel cells (DMFCs).

A mixed-valence diruthenium(II,III) complex endowed with high stability: from experimental evidence to theoretical interpretation.

We herein report the synthesis and multi-technique characterization of [Ru2Cl((2-phenylindol-3-yl)glyoxyl-l-leucine-l-phenylalanine)4], a novel diruthenium(ii,iii) complex obtained by reacting [Ru2(μ-O2CCH3)4Cl] with a dual indolylglyoxylyl dipeptide anticancer agent. We soon realised that the compound is very stable under several different conditions including aqueous buffers or organic solvents. It is also completely unreactive toward proteins. The high stability is also suggested by cellular experiments in a glioblastoma cell line. Indeed, while the parent ligand exerts high cytotoxic effects in the low μM range, the complex is completely non-cytotoxic against the same line, most probably because of the lack of ligand release. To investigate the reasons for such high stability, we carried out DFT calculations that are fully consistent with the experimental findings. The results highlight that the stability of [Ru2Cl((2-phenylindol-3-yl)glyoxyl-l-leucine-l-phenylalanine)4] relies on the nature of the ligand, including its steric hindrance that prevents the reaction of any nucleophilic group with the Ru2 core. Ligand displacement is the key step to allow reactivity with the biological targets of metal-based prodrugs. Accordingly, we discuss the implications of some important aspects that should be considered when active molecules are chosen as ligands for the synthesis of paddle-wheel-like complexes with medicinal applications.

Interactions between gold, thiol and As(iii) for colorimetric sensing.

As(iii) or arsenite is extremely toxic, and various colorimetric sensors were reported for its on-site detection. A highly cited example was based on gold nanoparticles (AuNPs) modified with a few thiol-containing compounds including dithiothreitol (DTT), reduced glutathione (GSH), and cysteine (Cys). As(iii) was believed to crosslink these surface ligands to aggregate AuNPs and produce a red-to-blue color change. Since As(iii) can also adsorb on AuNPs, we herein carefully studied this effect on these ligand-capped AuNPs. For citrate-capped AuNPs, 10 mM free citrate resulted in a strong blue color in the presence of As(iii) attributable to the elevated ionic strength, while common divalent cations resulted in no color change due to the chelation effect of free citrate. For AuNPs capped with the three thiol compounds, more than 5 mM As(iii) was needed to produce a color change, which was very different from the previously reported color change with nanomolar concentration of As(iii). Our color change was attributed to the displacement of the surface ligands by As(iii) instead of crosslinking by it. This conclusion was made based on the irreversibility of the color change, kinetics of the reaction, and high As(iii) concentration needed. This work has revealed that any two species from AuNPs, thiol and As(iii) can react. It also calls for care in the interpretation of related colorimetric sensing mechanisms, and the need to consider the previously overlooked As(iii) adsorption onto AuNPs.

Interaction with the heparin-derived binding inhibitors destabilizes galectin-3 protein structure

The β-galactoside-binding protein, galectin-3, is extensively involved in cancer development, progression and metastasis through multiple mechanisms. Inhibition of the galectin-3-mediated actions is increasingly considered as a promising therapeutic approach for cancer treatment. Our early studies have identified several novel galectin-3 binding inhibitors from chemical modification of the anticoagulant drug heparin. These heparin-derived galectin-3 binding inhibitors, which show no anticoagulant activity and bind to the galectin-3 canonical carbohydrate-binding site, induce galectin-3 conformational changes and inhibit galectin-3-mediated cancer cell adhesion, invasion and angiogenesis in vitro and reduce metastasis in mice. In this study, we determined the binding affinities of these heparin-derived ligands to galectin-3 using an isothermal titration calorimetry (ITC) ligand displacement approach. Such ITC experiments showed that the 2-de-O-sulphated, N-acetylated (compound E) and 6-de-O-sulphated, N-acetylated (F) heparin-derived ligands and their ultra-low molecular weight sub-fractions (E3 and F3) bind to galectin-3 with KD ranging from 0.96 to 1.32 mM.Differential scanning fluorimetry analysis revealed that, in contrast to the disaccharide ligand, N-acetyl-lactosamine, which binds to the fully folded form of galectin-3 and promotes galectin-3 thermal stability, the heparin-derived ligands preferentially bind to the unfolded state of galectin-3 and cause destabilization of the galectin-3 protein structure. These results provide molecular insights into the interaction of galectin-3 with the heparin-derived ligands and explain the previously demonstrated in vitro and in vivo effects of these binding inhibitors on galectin-3-mediated cancer cell behaviours.

Alkyne/Ruthenium(II) Complex-Based Ratiometric Surface-Enhanced Raman Scattering Nanoprobe for In Vitro and Ex Vivo Tracking of Carbon Monoxide.

Here, we report a surface-enhanced Raman scattering (SERS) nanosensor for real-time ratiometric detection of carbon monoxide (CO) based on a ligand displacement mechanism. This nanoprobe consists of a gold-silver (Au-Ag) alloy nanoparticle core as the highly active SERS substrate, an alkyne/ruthenium(II) (alkyne/Ru(II)) complex immobilized on the surface as the CO-sensing element, and a porous silica shell to improve the stability and biocompatibility of the particle. Displacement of the alkyne ligand by CO results in a decrease of the alkyne vibrations and an increase of the metal carbonyl complex signals, thus allowing the effective ratiometric detection of CO in real-time. The great potential of this assay for CO detection is validated in clean buffer environments, live cells, and tissue slices.

Competitive Fluorescent Ligand Assay for Inositol 1,4,5-Trisphosphate.

We present a novel method, termed competitive fluorescent ligand assay for inositol 1,4,5-trisphosphate (CFLA-IP3), to measure inositol 1,4,5-trisphosphate (IP3). This method is based on fluorescence resonance energy transfer (FRET) between two fluorescent molecules, a fluorescent IP3-binding protein and its fluorescent ligand. Binding of these fluorescent molecules generates a FRET signal, and the IP3-dependent decrease in the FRET signal due to displacement of the fluorescent ligand is detected by fluorescence microscopy.

Coordination and Dehydrogenation of Diphosphine-Borane Ph2PCH2PPh2·BH3 at a Heterometallic MoRe Center to Give an Agostic Boryl-Bridged Derivative.

The coordination chemistry of the title diphosphine-borane adduct at heterometallic MoRe centers was examined through its reactions with the hydride complex [MoReCp(μ-H)(μ-PCy2)(CO)5(NCMe)] (Cp = η5-C5H5). The latter reacted rapidly with stoichiometric amounts of dppm·BH3 (dppm = Ph2PCH2PPh2) in refluxing toluene solution, with displacement of the nitrile ligand, to give [MoReCp(μ-H)(μ-PCy2)(CO)5(κ1P-dppm·BH3)], with a P-bound diphosphine-borane ligand arranged trans to the PCy2 group. Decarbonylation of the latter complex was accomplished rapidly upon irradiation with visible-UV light in toluene solution at 263 K, to give the agostic derivative [MoReCp(μ-H)(μ-PCy2)(CO)4(κ1P,η2-dppm·BH3)] as major product (Mo-Re = 3.2075(5) Å), along with small amounts of the diphosphine-bridged complex [MoReCp(μ-H)(μ-PCy2)(CO)4(μ-dppm)]. Extended photolysis of the agostic complex at 288 K promoted an unprecedented dehydrogenation process involving the borane group and the hydride ligand, to give the diphosphine-boryl complex [MoReCp(μ-η2:κ2P,B-H2B·dppm)(μ-PCy2)(CO)4] (Mo-Re = 3.075(1) Å). The latter displayed a boryl ligand in a novel bridging coordination mode, it being σ-bound to one of the metal atoms (B-Re = 2.38(2) Å) while interacting with the second metal atom via a strong side-on tricentric B-H-M interaction (B-Mo = 2.31(1); H-Mo = 1.9(1) Å). The overall dehydrogenation process was endergonic by 43 kJ/mol, according to density functional theory calculations.

Gold Nanoparticles as Boron Carriers for Boron Neutron Capture Therapy: Synthesis, Radiolabelling and In vivo Evaluation.

Background: Boron Neutron Capture Therapy (BNCT) is a binary approach to cancer therapy that requires accumulation of boron atoms preferentially in tumour cells. This can be achieved by using nanoparticles as boron carriers and taking advantage of the enhanced permeability and retention (EPR) effect. Here, we present the preparation and characterization of size and shape-tuned gold NPs (AuNPs) stabilised with polyethylene glycol (PEG) and functionalized with the boron-rich anion cobalt bis(dicarbollide), commonly known as COSAN. The resulting NPs were radiolabelled with 124I both at the core and the shell, and were evaluated in vivo in a mouse model of human fibrosarcoma (HT1080 cells) using positron emission tomography (PET). Methods: The thiolated COSAN derivatives for subsequent attachment to the gold surface were synthesized by reaction of COSAN with tetrahydropyran (THP) followed by ring opening using potassium thioacetate (KSAc). Iodination on one of the boron atoms of the cluster was also carried out to enable subsequent radiolabelling of the boron cage. AuNPs grafted with mPEG-SH (5 Kda) and thiolated COSAN were prepared by ligand displacement. Radiolabelling was carried out both at the shell (isotopic exchange) and at the core (anionic absorption) of the NPs using 124I to enable PET imaging. Results: Stable gold nanoparticles simultaneously functionalised with PEG and COSAN (PEG-AuNPs@[4]−) with hydrodynamic diameter of 37.8 ± 0.5 nm, core diameter of 19.2 ± 1.4 nm and ξ-potential of −18.0 ± 0.7 mV were obtained. The presence of the COSAN on the surface of the NPs was confirmed by Raman Spectroscopy and UV-Vis spectrophotometry. PEG-AuNPs@[4]− could be efficiently labelled with 124I both at the core and the shell. Biodistribution studies in a xenograft mouse model of human fibrosarcoma showed major accumulation in liver, lungs and spleen, and poor accumulation in the tumour. The dual labelling approach confirmed the in vivo stability of the PEG-AuNPs@[4]−. Conclusions: PEG stabilized, COSAN-functionalised AuNPs could be synthesized, radiolabelled and evaluated in vivo using PET. The low tumour accumulation in the animal model assayed points to the need of tuning the size and geometry of the gold core for future studies.

Modulation of Gas-Phase Lithium Cation Basicities by Microsolvation.

In contrast to the extensive knowledge of lithium cation affinities and basicities, the thermochemistry of microsolvated lithium cations is much less explored. Here, we determine the relative stabilities of Li(A,B)n+ complexes, n = 2 and 3, by monitoring their gas-phase reactions with A and B substrate molecules, A/B = Me2O, Et2O, tetrahydrofuran, and MeCN, in a three-dimensional quadrupole-ion trap mass spectrometer. Kinetic analysis of the observed ligand displacement reactions affords equilibrium constants, which are then converted into Gibbs reaction energies. In addition, we use high-level quantum chemical calculations to predict the structures and sequential ligand dissociation energies of the homoleptic Li(A)n+ complexes, n = 1-3. As expected, the ligands dissociate more easily from complexes in higher coordination states. However, the very nature of the ligand also matters. Ligands with different steric demands can, thus, invert their relative Li+ affinities depending on the coordination state of the metal center. This finding shows that microsolvation of Li+ can result in specific effects, which are not recognized if the analysis takes into account only simple lithium cation affinities and basicities.

Mixed Ligand Shell Formation upon Catechol Ligand Adsorption on Hydrophobic TiO2 Nanoparticles.

Modifying the surfaces of metal oxide nanoparticles (NPs) with monolayers of ligands provides a simple and direct method to generate multifunctional coatings by altering their surface properties. This works best if the composition of the monolayers can be controlled. Mussel-inspired, noninnocent catecholates stand out from other ligands like carboxylates and amines because they are redox-active and allow for highly efficient surface binding and enhanced electron transfer to the surface. However, a comprehensive understanding of their surface chemistry, including surface coverage and displacement of the native ligand, is still lacking. Here, we unravel the displacement of oleate (OA) ligands on hydrophobic, OA-stabilized TiO2 NPs by catecholate ligands using a combination of one- and two-dimensional nuclear magnetic resonance (NMR) spectroscopy techniques. Conclusive pictures of the ligand shells before and after surface modification with catecholate were obtained by 1H and 13C NMR spectroscopy (the 13C chemical shift being more sensitive and with a broader range). The data could be explained using a Langmuir-type approach. Gradual formation of a mixed ligand shell was observed, and the surface processes of catecholate adsorption and OA desorption were quantified. Contrary to the prevailing view, catecholate displaces only a minor fraction (∼20%) of the native OA ligand shell. At the same time, the total ligand density more than doubled from 2.3 nm-2 at native oleate coverage to 4.8 nm-2 at maximum catecholate loading. We conclude that the catecholate ligand adsorbs preferably to unoccupied Ti surface sites rather than replacing native OA ligands. This unexpected behavior, reminiscent of the Vroman effect for protein corona formation, appears to be a fundamental feature in the widely used surface modification of hydrophobic metal oxide NPs with catecholate ligands. Moreover, our findings show that ligand displacement on OA-capped TiO2 NPs is not suited for a full ligand shell refunctionalization because it produces only mixed ligand shells. Therefore, our results contribute to a better understanding and performance of photocatalytic applications based on catecholate ligand-sensitized TiO2 NPs.

A Germylene Supported by Two 2-Pyrrolylphosphane Groups as Precursor to PGeP Pincer Square-Planar Group 10 Metal(II) and T-Shaped Gold(I) Complexes.

An efficient synthesis of 2-di-tert-butylphosphanylmethylpyrrole (HpyrmPtBu2 ), by treating 2-dimethylaminomethylpyrrole (HpyrmNMe2 ) with tBu2 PH at 135 °C in the absence of any solvent, has allowed the preparation of the new PGeP germylene Ge(pyrmPtBu2 )2 (1), by treating [GeCl2 (dioxane)] with LipyrmPtBu2 , in which the Ge atom is stabilized by intramolecular interactions with one (solid state) or both (solution) of its phosphane groups. Reactions of germylene 1 with Group 10 metal dichlorido complexes containing easily displaceable ligands have led to [MCl{κ3 P,Ge,P-GeCl(pyrmPtBu2 )2 }] [M=Ni (2), Pd (3), Pt (4)], which have an unflawed square-planar metal environment. Treatment of germylene 1 with [AuCl(tht)] (tht=tetrahydrothiophene) rendered [Au{κ3 P,Ge,P-GeCl(pyrmPtBu2 )2 }] (5), which is a rare case of a T-shaped gold(I) complex. The hydrolysis of 5 gave the linear gold(I) derivative [Au(κP-HpyrmPtBu2 )2 ]Cl (6). Complexes 2-5 contain a PGeP pincer chloridogermyl ligand that arises from the insertion of the Ge atom of germylene 1 into a M-Cl bond of the corresponding metal reagent. The bonding in these molecules has been studied by DFT/NBO/QTAIM calculations. These results demonstrate that the great flexibility of germylene 1 makes it a better precursor to PGeP pincer complexes than the previously known germylenes of this type.

Products of the initial reduction of the Phillips catalyst by olefins

The organic products of the reaction between Cr(VI)/silica and ethylene, propene, 2-pentene, 1-hexene, or cyclohexene at temperatures between 25 and 150 °C were investigated to understand the formation of chromium sites active for polymerization. A wide assortment of products were obtained, either directly or through ligand displacement or extraction, which depended on the specific olefin and the conditions. Hydrocarbon products were released under conditions relevant to commercial operation and indicated both polymerization and acid catalysis: short olefin oligomers (from polymerization), alkanes (possibly from hydride transfer), internal olefins (from double bond shift) and isoalkylbenzenes (from skeletal isomerization and alkylation of the diluent benzene). Aldehydes, ketones, and alcohols were found in polar organic extraction media, some the result of aldol condensations in the extraction medium. Surface carboxylates, evident by in situ IR spectroscopy, could be detached from the catalyst only through hydrolysis. The high threshold to desorb oxygenates implies that the chromium sites retain self-generated ligands. The nature of these ligands depends on the reductant, and, consequently, the result may be an active or an inactive site. Consistently, reduction of Cr(VI)/silica by various olefins resulted in catalysts with different polymerization behavior, and addition of external ligands to Cr(II)/silica led to a poisoned or to an active catalyst, depending on the ligand.

Synthesis and Structure-Affinity Relationship of Small Molecules for Imaging Human CD80 by Positron Emission Tomography.

The costimulatory molecule CD80 is an early marker for immune activation. It is upregulated on activated antigen-presenting cells. We aimed at developing a tracer for imaging CD80 by positron emission tomography (PET). Novel CD80 ligands were synthesized and tested by SPR for affinity to human CD80 (hCD80) and displacement of endogenous ligands. Several compounds bound with one-digit nanomolar affinity to hCD80 and displaced CTLA-4 and CD28 at nanomolar concentrations. A structure-affinity relationship study revealed relevant moieties for strong affinity to hCD80 and positions for further modifications. Lead compound MT107 (7f) was radiolabeled with carbon-11. In vitro, [11C]MT107 showed specific binding to hCD80-positive tissue and high plasma protein binding. In vivo, [11C]MT107 accumulated in liver, gall bladder, and intestines but only scarcely in hCD80-positive xenografts. The unfavorable in vivo performance may result from high plasma protein binding and extensive biliary excretion.

Effects of TAK-639, a novel topical C-type natriuretic peptide analog, on intraocular pressure and aqueous humor dynamics in mice

Primary open-angle glaucoma (POAG) is a leading cause of irreversible blindness, and individuals with ocular hypertension are at risk to develop POAG. Currently, the only modifiable risk factor for glaucoma progression is lowering of intraocular pressure (IOP). A novel mechanism for lowering IOP involves activation of the type B natriuretic peptide receptor (NPR-B), the naturally occurring agonist of which is C-type natriuretic peptide (CNP). Being a cyclic peptide of 22 amino acids, CNP does not readily penetrate the cornea and its ocular hypotensive effect requires intraocular injection. TAK-639 is a synthetic, cornea-permeable, 9-amino acid CNP analog has been studied for the treatment of ocular hypertension and POAG. We assessed TAK-639 in a receptor binding profile and the effects of TAK-639 on NPR-B-mediated cyclic GMP production in cultured transformed human trabecular meshwork (TM) cells (GTM-3). We also evaluated the effects of topical ocular administration of TAK-639 on mouse IOP and aqueous humor dynamics. Among 89 non-natriuretic peptide receptors, transporters, and channels evaluated, TAK-639 at 10 μM displaced ligand binding by more than 50% to only two receptors: the type 2 angiotensin receptor (IC50 = 8.2 μM) and the cholecystokinin A receptor (IC50 = 25.8 μM). In vitro, TAK-639 selectively activates NPR-B (EC50 = 61 ± 11 nM; GTM-3 cells) relative to NPR-A (EC50 = 2179 ± 670 nM; 293T cells). In vivo, TAK-639 lowered mouse IOP by three mechanisms: increase in aqueous humor outflow facility (C), reduction in the aqueous humor formation rate (Fin), and reduction in episcleral venous pressure (Pe). The maximum mean IOP decreases from baseline were −12.1%, −21.0%, and −36.1% for 0.1%, 0.3%, and 0.6% doses of TAK-639, respectively. Maximum IOP-lowering effect was seen at 2 h, and the duration of action was >6 h. With TAK-639 0.6%, at 2 h post-dose, aqueous outflow facility (C) increased by 155.8%, Fin decreased by 41.0%, the uveoscleral outflow rate (Fu) decreased by 52.6%, and Pe decreased by 31.5% (all p < 0.05). No ocular adverse effects were observed. TAK-639 is an efficacious IOP-lowering agent, with a unique combination of mechanisms of action on both aqueous formation and aqueous outflow facility. Further study of this mechanism of treatment may optimize pharmacologic outcomes and provide disease management in patients with POAG and ocular hypertension.

Ternary Copper(II) and Nickel(II) chelates of 2,2′-Bipyridyl and glycine: X-ray structures, kinetics, DNA binding and cleavage activities

Ternary copper(II) and nickel(II) chelates of 2,2′-bipyridyl and glycine ligands with the formula of [Cu(BPy)(Gly)Cl] 1, [Cu(BPy)(Gly)(H2O)]NO32 and [Ni(BPy)(Gly)(H2O)2]Cl·H2O 3 were synthesized and structurally characterized by using X-ray crystallography. Copper(II) compounds 1 and 2 form slightly distorted square-pyramidal coordination geometries of CuN3ClO and CuN3O2, respectively. Whereas, nickel(II) compound 3 shows an octahedral coordination geometry of NiN3O3. Kinetic measurements have been made with the objective of correlating the influence of geometry. The thiourea substitution reaction of 1 in water is a monophasic process that involves the subsequent displacement of chloride ligand with k2300 = 21.1 ± 0.8 M−1s−1. The activation parameters, ΔH# = 79.2 ± 2.5 kJ mol−1 and ΔS# = 68.4 ± 8.7 J K−1 mol−1, for the chloride substitution reactions indicate that the reaction follows a dissociative mechanism. The interactions of compounds 2 and 3 towards DNA were examined with the help of absorption spectroscopic technique. The binding constants (Kb) of 2 and 3 to DNA were found to be 4.7 × 105 and 2.4 × 105 M−1, respectively, indicating that both compounds show good binding activity to calf thymus DNA. The nuclease mimic activity of both 2 and 3 was also assessed by its ability to cleave super coiled plasmid DNA to nicked and linear forms in the absence of any external additives. On the other hand, the quasi-reversible CuII/CuI redox couple slightly improves its reversibility with a considerable decrease in current intensity. All the experimental results indicated that the bipyridyl mixed copper(II) complex 2 intercalates more effectively into the DNA base pairs.

Confined Growth of Quantum Dots in Silica Spheres by Ion Exchange of “Trapped NH4+” for White-Light Emission

Summary Great interest has recently emerged in the development of quantum dots (QDs) that are capable of direct white-light emission for solid-state lighting. The conventional synthesis routes often involve surface modification and ligand displacement, which usually lead to undesired QD aggregation and fluorescence quenching. Here, we report a new strategy to synthesize QDs (ZnS, CdS, CdTe, and CsPbBrxI3-x) directly in colloidal SiO2 to produce QDs@SiO2 composites, displaying direct white-light emissions. By taking advantage of the NH4+ trapped inside the silica colloids, we introduce metal cations through ion-exchange reactions into the microporous network of silica and then produce QDs directly within the silica colloids. This “trapped-NH4+” strategy represents a new platform for the synthesis of novel functional nanocomposites by allowing convenient incorporation of various nanoparticles into sol-gel-derived colloidal matrices.

Monophosphine Ligands Promote Pd-Catalyzed C–S Cross-Coupling Reactions at Room Temperature with Soluble Bases

The Pd-catalyzed cross-coupling of thiols with aromatic electrophiles is a reliable method for the synthesis of aryl thioethers, which are important compounds for pharmaceutical and agricultural applications. Since thiols and thiolates strongly bind late transition metals, previous research has focused on catalysts supported by chelating, bisphosphine ligands, which were considered less likely to be displaced during the course of the reaction. We show that by using monophosphine ligands instead, more effective catalysis can be achieved. Notably, compared to previous methods, this increased reactivity allows for the use of much lower reaction temperature, soluble bases, and base-sensitive substrates. In contrast to conventional wisdom, our mechanistic data suggest that the extent of displacement of phosphine ligands by thiols is, firstly, not correlated with the ligand bulk or thiol nucleophilicity, and secondly, not predictive of the effectiveness of a given ligand in combination with palladium.