Complex Formation of d‐Metal Ions at the Interface of TbIII‐Doped Silica Nanoparticles as a Basis of Substrate‐Responsive TbIII‐Centered Luminescence

The complex formation of d‐metal ions at the interface of Tb^III‐doped silica nanoparticles modified by amino groups is introduced as a route to sensing d‐metal ions and some organic molecules. Diverse modes of surface modification (covalent and noncovalent) are used to fix amino groups onto the silica surface. The interfacial binding of d‐metal ions and complexes is the reason for the Tb^III‐centered luminescence quenching. The regularities and mechanisms of quenching are estimated for the series of d‐metal ions and their complexes with chelating ligands. The obtained results reveal the interfacial binding of Cu^II ions as the basis of their quantitative determination in the concentration range 0.1–2.5 μM by means of steady‐state and time‐resolved fluorescence measurements. The variation of chelating ligands results in a significant effect on the quenching regularities due to diverse binding modes (inner or outer sphere) between amino groups at the interface of nanoparticles and Fe^III ions. The applicability of the steady‐state and time‐resolved fluorescence measurements to sense both Fe^III ions and catechols in aqueous solution by means of Tb^III‐doped silica nanoparticles is also introduced.     

Engineering Multifunctional DNA Hybrid Nanospheres through Coordination‐Driven Self‐Assembly

Developing simple and general approaches for the synthesis of nanometer‐sized DNA materials with specific morphologies and functionalities is important for various applications. Herein, a novel approach for the synthesis of a new set of DNA‐based nanoarchitectures through coordination‐driven self‐assembly of Fe^II ions and DNA molecules is reported. By fine‐tuning the assembly, Fe–DNA nanospheres of precise sizes and controlled compositions can be produced. The hybrid nanoparticles can be tailored for delivery of functional DNA to cells in vitro and in vivo with enhanced biological function. This highlights the potential of metal ion coordination as a tool for directing the assembly of DNA architectures, which conceptualizes a new pathway to expand the repertoire of DNA‐based nanomaterials. This methodology will advance both the fields of DNA nanobiotechnology and metal–ligand coordination chemistry.     

Iron(III)‐Quantity‐Dependent Aggregation–Dispersion Conversion of Functionalized Gold Nanoparticles

Developing gold nanoparticles (AuNPs) with well‐designed functionality is highly desirable for boosting the performance and versatility of inorganic–organic hybrid materials. In an attempt to achieve ion recognition with specific signal expressions, we present here 4‐piperazinyl‐1,8‐naphthalimide‐functionalized AuNPs for the realization of quantitative recognition of Fe^III ions with dual (colorimetric and fluorescent) output. The research takes advantage of 1) quantity‐controlled chelation‐mode transformation of the piperazinyl moiety on the AuNPs towards Fe^III, thereby resulting in an aggregation–dispersion conversion of the AuNPs in solution, and 2) photoinduced electron transfer of a naphthaimide fluorophore on the AuNPs, thus leading to reversible absorption and emission changes. The functional AuNPs are also responsive to pH variations. This strategy for realizing the aggregation–dispersion conversion of AuNPs with returnable signal output might exhibit application potential for advanced nanoscale chemosensors.     

Mussel‐Inspired Protein Nanoparticles Containing Iron(III)–DOPA Complexes for pH‐Responsive Drug Delivery

A novel bioinspired strategy for protein nanoparticle (NP) synthesis to achieve pH‐responsive drug release exploits the pH‐dependent changes in the coordination stoichiometry of iron(III)–3,4‐dihydroxyphenylalanine (DOPA) complexes, which play a major cross‐linking role in mussel byssal threads. Doxorubicin‐loaded polymeric NPs that are based on Fe^III–DOPA complexation were thus synthesized with a DOPA‐modified recombinant mussel adhesive protein through a co‐electrospraying process. The release of doxorubicin was found to be predominantly governed by a change in the structure of the Fe^III–DOPA complexes induced by an acidic pH value. It was also demonstrated that the fabricated NPs exhibited effective cytotoxicity towards cancer cells through efficient cellular uptake and cytosolic release. Therefore, it is anticipated that Fe^III–DOPA complexation can be successfully utilized as a new design principle for pH‐responsive NPs for diverse controlled drug‐delivery applications.     

Highly Luminescent and Stable Hydroxypyridinonate Complexes: A Step Towards New Curium Decontamination Strategies

The photophysical properties, solution thermodynamics, and in vivo complex stabilities of Cm^III complexes formed with multidentate hydroxypyridinonate ligands, 3,4,3‐LI(1,2‐HOPO) and 5‐LIO(Me‐3,2‐HOPO), are reported. Both chelators were investigated for their ability to act as antenna chromophores for Cm^III, leading to highly sensitized luminescence emission of the metal upon complexation, with long lifetimes (383 and 196 μs for 3,4,3‐LI(1,2‐HOPO) and 5‐LIO(Me‐3,2‐HOPO), respectively) and remarkable quantum yields (45 % and 16 %, respectively) in aqueous solution. The bright emission peaks were used to probe the electronic structure of the 5f complexes and gain insight into ligand field effects; they were also exploited to determine the high (and proton‐independent) stabilities of the corresponding Cm^III complexes (log β₁₁₀=21.8(4) for 3,4,3‐LI(1,2‐HOPO) and log β₁₂₀=24.5(5) for 5‐LIO(Me‐3,2‐HOPO)). The in vivo complex stability for both ligands was assessed by using ²⁴⁸Cm as a tracer in a rodent model, which provided a direct comparison with the in vitro thermodynamic results and demonstrated the great potential of 3,4,3‐LI(1,2‐HOPO) as a therapeutic Cm^III decontamination agent.     

Lability‐Controlled Syntheses of Heterometallic Clusters

A bulky bidentate ligand was used to stabilize a macrocyclic [Fe^III₈Co^II₆] cluster. Tuning the basicity of the ligand by derivatization with one or two methoxy groups led to the isolation of a homologous [Fe^III₈Co^II₆] species and a [Fe^III₆Fe^II₂Co^III₂Co^II₂] complex, respectively. Lowering the reaction temperatures allowed isolation of [Fe^III₆Fe^II₂Co^III₂Co^II₂] clusters with all three ligands. Temperature‐dependent absorption data and corresponding experiments with iron/nickel systems indicated that the iron/cobalt self‐assembly process was directed by the occurrence of solution‐state electron‐transfer‐coupled spin transition (ETCST) and its influence on reaction intermediate lability.     

Mitochondrial‐DNA‐Targeted IrIII‐Containing Metallohelices with Tunable Photodynamic Therapy Efficacy in Cancer Cells

The development of DNA‐targeted photodynamic therapy (PDT) agents for cancer treatment has drawn substantial attention. Herein, the design and synthesis of dinuclear Ir^III‐containing luminescent metallohelices with tunable PDT efficacy that target mitochondrial DNA in cancer cells are reported. The metallohelices are fabricated using dynamic imine‐coupling chemistry between aldehyde end‐capped fac‐Ir(ppy)₃ handles and linear alkanediamine spacers, followed by reduction of the imine linkages. The length and odd–even character of the diamine alkyl linker determined the stereochemistry (helicates vs. mesocates). Compared to the helicates, the mesocates exhibit improved apoptosis‐induction upon white‐light irradiation. Molecular docking studies indicate that the mesocate with a proper length of diamine spacers shows stronger affinity for the minor groove of DNA. This study highlights the potential of DNA‐targeting Ir^III‐containing metallohelices as PDT agents.     

Synthesis and characterization of 4‐AMTT‐Pd(II) complex over Fe3O4@SiO2 as supported nanocatalyst for Suzuki‐Miyaura and Mizoroki‐heck cross‐coupling reactions in water

Immobilization of Pd(II) nanoparticles on silica‐coated modified magnetite particles has been readily achieved via a surface modification of Fe₃O₄ particles with 4‐amino‐5‐methyl‐4‐H‐1,2,4‐triazole‐3‐thiol (4‐AMTT) as a ligand. This magnetite nanocatalyst was characterized by various analyses such as FT‐IR, SEM/EDX, ICP‐AES, VSM, TEM, XRD, XPS and TGA. This nanocatalyst showed admirable catalytic activity for Suzuki‐Miyaura and Mizoroki‐Heck cross‐coupling reactions under mild conditions in water, and could be simply separated by an outer magnet and reused for several times.     

A Supramolecular Crosslinker To Give Salt‐Resistant Polyion Complex Micelles and Improved MRI Contrast Agents

Three‐component mixtures (diblock copolymer/metal ion/oligoligand) can assemble into micellar particles owing to a combination of supramolecular polymerization and electrostatic complex formation. Such particles cover a large range of compositions, but the electrostatic forces keeping them together make them rather susceptible to disintegration by added salt. Now it is shown how the salt stability can be tuned continuously by employing both a bis‐ligand and a tris‐ligand, and varying the ratio of these in the mixture. For magnetic ions such as Mn^II and Fe^III, the choice of the multiligand also affects the ion/water interaction and, hence, the magnetic relaxivity. As an example, Mn^II‐based nanoparticles with a very high longitudinal relaxivity (10.8 mm ⁻¹ s⁻¹) were investigated that are not only biocompatible but also feature strong contrast enhancement in target organs (liver, kidney), as shown by T₁‐weighted in vivo magnetic resonance imaging (MRI).     

Redox‐Assisted Self‐Assembly of a Water‐Soluble Cyanido‐Bridged Mixed Valence {CoIII/FeII}2 Square

The facile redox‐assisted assembly of a water‐soluble, extremely robust, cyanide‐bridged mixed‐valence [{Co^III{(Me)₂(μ‐ET)cyclen}}₂{(μ‐NC)₂Fe^II(CN)₄}₂]^2? square is reported. The preparation process involved the use of the enhanced lability of inert Co^III synthons triggered by outer‐sphere redox processes. Characterization of the final compounds has been carried out by NMR, UV/Vis, electrochemistry, and ICP analyses. DFT calculations have been conducted to optimize a structure that has the same hydrodynamic radius as that obtained from DOSY experiments. The new compound is extremely robust, surviving in aqueous solution within the 0–12 pH range for months. The species shows a high affinity for both protons and hydroxo ions in aqueous medium.     

A Non‐Heme Iron Photocatalyst for Light‐Driven Aerobic Oxidation of Methanol

Non‐heme (L)Fe^III and (L)Fe^III‐O‐Fe^III(L) complexes (L=1,1‐di(pyridin‐2‐yl)‐N,N‐bis(pyridin‐2‐ylmethyl)ethan‐1‐amine) underwent reduction under irradiation to the Fe^II state with concomitant oxidation of methanol to methanal, without the need for a secondary photosensitizer. Spectroscopic and DFT studies support a mechanism in which irradiation results in charge‐transfer excitation of a Fe^III?μ‐O?Fe^III complex to generate [(L)Fe^IV=O]²⁺ (observed transiently during irradiation in acetonitrile), and an equivalent of (L)Fe^II. Under aerobic conditions, irradiation accelerates reoxidation from the Fe^II to the Fe^III state with O₂, thus closing the cycle of methanol oxidation to methanal.     

Direct Observation of Ordered High‐Spin–Low‐Spin Intermediate States of an Iron(III) Three‐Step Spin‐Crossover Complex

A neutral mononuclear Fe^III complex [Fe^III(H‐5‐Br‐thsa‐Me)(5‐Br‐thsa‐Me)]?H₂O ( 1 ; H₂‐5‐Br‐thsa‐Me=5‐bromosalicylaldehyde methylthiosemicarbazone) was prepared that exhibited a three‐step spin‐crossover (SCO) with symmetry breaking and a 14 K hysteresis loop owing to strong cooperativity. Two ordered intermediate states of 1 were observed, 4HS–2LS and 2HS–4LS, which exhibited reentrant phase‐transition behavior. This study provides a new platform for examining multistability in SCO complexes.     

A Mixed‐Valence {Fe13} Cluster Exhibiting Metal‐to‐Metal Charge‐Transfer‐Switched Spin Crossover

It is promising and challenging to manipulate the electronic structures and functions of materials utilizing both metal‐to‐metal charge transfer (MMCT) and spin‐crossover (SCO) to tune the valence and spin states of metal ions. Herein, a metallocyanate building block is used to link with a Fe^II‐triazole moiety and generates a mixed‐valence complex {[(Tp^4‐Me)Fe^III(CN)₃]₉[Fe^II₄(trz‐ph)₆]}?[Ph₃PMe]₂?[(Tp^4‐Me)Fe^III(CN)₃] ( 1 ; trz‐ph=4‐phenyl‐4H‐1,2,4‐triazole). Moreover, MMCT occurs between Fe^III and one of the Fe^II sites after heat treatment, resulting in the generation of a new phase, {[(Tp^4‐Me)Fe^II(CN)₃][(Tp^4‐Me)Fe^III(CN)₃]₈ [Fe^IIIFe^II₃(trz‐ph)₆]}? [Ph₃PMe]₂?[(Tp^4‐Me)Fe^III(CN)₃] ( 1 a ). Structural and magnetic studies reveal that MMCT can tune the two‐step SCO behavior of 1 into one‐step SCO behavior of 1 a . Our work demonstrates that the integration of MMCT and SCO can provide a new alternative for manipulating functional spin‐transition materials with accessible multi‐electronic states.     

Tuning the Cellular Uptake Properties of Luminescent Heterobimetallic Iridium(III)–Ruthenium(II) DNA Imaging Probes

The synthesis of two new luminescent dinuclear Ir^III–Ru^II complexes containing tetrapyrido[3,2‐a:2′,3′‐c:3′′,2′′‐h:2′′′,3′′′‐j]phenazine (tpphz) as the bridging ligand is reported. Unlike many other complexes incorporating cyclometalated Ir^III moieties, these complexes display good water solubility, allowing the first cell‐based study on Ir^III–Ru^II bioprobes to be carried out. Photophysical studies indicate that emission from each complex is from a Ru^II excited state and both complexes display significant in vitro DNA‐binding affinities. Cellular studies show that each complex is rapidly internalised by HeLa cells, in which they function as luminescent nuclear DNA‐imaging agents for confocal microscopy. Furthermore, the uptake and nuclear targeting properties of the complex incorporating cyclometalating 2‐(4‐fluorophenyl)pyridine ligands around its Ir^III centre is enhanced in comparison to the non‐fluorinated analogue, indicating that fluorination may provide a route to promote cell uptake of transition‐metal bioprobes.     

Well‐Defined Metal–Organic Framework Hollow Nanocages

Metal–organic frameworks (MOFs) have demonstrated great potentials in a variety of important applications. To enhance the inherent properties and endow materials with multifunctionality, the rational design and synthesis of MOFs with nanoscale porosity and hollow feature is highly desired and remains a great challenge. In this work, the formation of a series of well‐defined MOF (MOF‐5, Fe^II‐MOF‐5, Fe^III‐MOF‐5) hollow nanocages by a facile solvothermal method, without any additional supporting template is reported. A surface‐energy‐driven mechanism may be responsible for the formation of hollow nanocages. The addition of pre‐synthesized poly(vinylpyrrolidone)‐ (PVP) capped noble‐metal nanoparticles into the synthetic system of MOF hollow nanocages yields the yolk–shell noble metal@MOF nanostructures. The present strategy to fabricate hollow and yolk–shell nanostructures is expected to open up exciting opportunities for developing a novel class of inorganic–organic hybrid functional nanomaterials.     

FerriIridium: A Lysosome‐Targeting Iron(III)‐Activated Iridium(III) Prodrug for Chemotherapy in Gastric Cancer Cells

Reported is the Fe^III‐activated lysosome‐targeting prodrug FerriIridium for gastric cancer theranostics. It contains a meta‐imino catechol group that can selectively bond to, and be oxidized by, free Fe^III inside the cell. Subsequent oxidative rearrangement releases Fe^II and hydrolyses the amine bond under acidic conditions, forming an aminobipyridyl Ir complex and 2‐hydroxybenzoquinone. Thus, Fe^II catalyzes the Fenton reaction, transforming hydrogen peroxide into hydroxyl radicals, the benzoquinone compounds interfere with the respiratory chain, and conversion of the prodrug into the Ir complex leads to an increase in phosphorescence and toxicity. These properties, combined with the high Fe^III content and acidity of cancer cells, make FerriIridium a selective and efficient theranostic agent (IC₅₀=9.22 μm for AGS cells vs. >200 μm for LO2 cells). FerriIridium is the first metal‐based compound that has been developed for chemotherapy using Fe^III to enhance both selectivity and potency.     

Magnetic Anisotropy of Cyanide‐Bridged Core and Core–Shell Coordination Nanoparticles Probed by X‐ray Magnetic Circular Dichroism

The local symmetry and local magnetic properties of 6 nm‐sized, bimetallic, cyanide‐bridged CsNiCr(CN)₆ coordination nanoparticles 1 and 8 nm‐sized, trimetallic, CsNiCr(CN)₆@CsCoCr(CN)₆ core–shell nanoparticles 2 were studied by X‐ray absorption spectroscopy (XAS) and X‐ray magnetic circular dichroism (XMCD). The measurements were performed at the Ni^II, Co^II, and Cr^III L_2,3 edges. This study revealed the presence of distorted Ni^II sites located on the particle surface of 1 that account for the uniaxial magnetic anisotropy observed by SQUID measurements. For the core–shell particles, a combination of the exchange anisotropy between the core and the shell and the pronounced anisotropy of the Co^II ions is the origin of the large increase in coercive field from 120 to 890 Oe on going from 1 to 2 . In addition, XMCD allows the relative orientation of the magnetic moments throughout the core–shell particles to be determined. While for the bimetallic particles of 1 , alignment of the magnetic moments of Cr^III ions with those of Ni^II ions leads to uniform magnetization, in the core–shell particles 2 the magnetic moments of the isotropic Cr^III follow those of Co^II ions in the shell and those of Ni^II ions in the core, and this leads to nonuniform magnetization in the whole nanoobject, mainly due to the large difference in local anisotropy between the Co^II ions belonging to the surface and the Ni^II ions in the core.     

Fast and Long‐Lasting Iron(III) Reduction by Boron Toward Green and Accelerated Fenton Chemistry

Generation of hydroxyl radicals in the Fenton system (Fe^II/H₂O₂) is seriously limited by the sluggish kinetics of Fe^III reduction and fast Fe^III precipitation. Here, boron crystals (C‐Boron) remarkably accelerate the Fe^III/Fe^II circulation in Fenton‐like systems (C‐Boron/Fe^III/H₂O₂) to produce a myriad of hydroxyl radicals with excellent efficiencies in oxidative degradation of various pollutants. The surface B?B bonds and interfacial suboxide boron in the surface B₁₂ icosahedra are the active sites to donate electrons to promote fast Fe^III reduction to Fe^II and further enhance hydroxyl radical production via Fenton chemistry. The C‐Boron/Fe^III/H₂O₂ system outperforms the benchmark Fenton (Fe^II/H₂O₂) and Fe^III‐based sulfate radical systems. The reactivity and stability of crystalline boron is much higher than the popular molecular reducing agents, nanocarbons, and other metal/metal‐free nanomaterials.     

Iron‐ and Bismuth‐Catalyzed Asymmetric Mukaiyama Aldol Reactions in Aqueous Media

We have developed asymmetric Mukaiyama aldol reactions of silicon enolates with aldehydes catalyzed by chiral Fe^II and Bi^III complexes. Although previous reactions often required relatively harsh conditions, such as strictly anhydrous conditions, very low temperatures (?78 °C), etc., the reactions reported herein proceeded in the presence of water at 0 °C. To find appropriate chiral water‐compatible Lewis acids for the Mukaiyama aldol reaction, many Lewis acids were screened in combination with chiral bipyridine L1 , which had previously been found to be a suitable chiral ligand in aqueous media. Three types of chiral catalysts that consisted of a Fe^II or Bi^III metal salt, a chiral ligand ( L1 ), and an additive have been discovered and a wide variety of substrates (silicon enolates and aldehydes) reacted to afford the desired aldol products in high yields with high diastereo‐ and enantioselectivities through an appropriate selection of one of the three catalytic systems. Mechanistic studies elucidated the coordination environments around the Fe^II and Bi^III centers and the effect of additives on the chiral catalysis. Notably, both Brønsted acids and bases worked as efficient additives in the Fe^II‐catalyzed reactions. The assumed catalytic cycle and transition states indicated important roles of water in these efficient asymmetric Mukaiyama aldol reactions in aqueous media with the broadly applicable and versatile catalytic systems.