A Self-Assembled Iron(II) Metallacage as a Trap for Per- and Polyfluoroalkyl Substances in Water.

An anionic iron(II) tetrahedral molecular cage (FeMOP) was studied for its ability to interact with various per- and polyfluoroalkyl substances (PFASs) in aqueous media. Liquid chromatography tandem mass spectrometry revealed that longer-chain-length (more than six carbons) perfluorocarboxylic, -sulfonic, and fluorotelomers were removed from solution. In contrast, the steric bulk of N-ethyl substituted fluorosulfonamido acetic acid PFASs hindered association with the cage. Solution binding studies in D2O using 19F nuclear magnetic resonance (NMR) titrations and a Job plot show a 1:1 binding stoichiometry for perfluorohexanoic acid (PFHxA) and perfluoroheptanoic acid (PFHpA) with an association constant (Ka) of <103 and thus a favorable free energy of association (ΔG°). Perfluorononanoic acid (PFNA), on the other hand, forms an insoluble host-guest complex with FeMOP with a 1:1 host-guest ratio. Variable temperature (VT) NMR was used to determine the thermodynamic parameters of binding for a 1:1 FeMOP/PFHpA complex in water using a Curie-like model for fast-exchange processes. The extracted parameters suggest a low binding interaction (Ka < 103) driven by an increase in entropy from cage desolvation upon guest binding. The solid-state host-guest complexes formed from solution complexation of PFHxA, PFHpA, and PFNA into the cage were characterized by infrared spectroscopy (FT-IR) and powder X-ray diffraction (PXRD) methods. FT-IR studies suggest an interaction between the fluorocarbon groups of PFASs to the phenylsulfonate functional groups of the ligand. A docking model predicted by computation also indicates this interaction may occur, with the PFASs adsorbing onto the surface of the cage rather than forming a true host-guest complex within the internal cavity. PXRD studies reveal a crystal packing of the complex that is very similar to that of the water-treated FeMOP, with the exception of 1:2 FeMOP/PFNA and 1:1 and 2:1 FeMOP/PFHpA.

Highly Emissive Self-Assembled BODIPY-Platinum Supramolecular Triangles.

Light-emitting supramolecular coordination complexes (SCCs) have been widely studied for applications in the chemical and biological sciences. Herein, we report the coordination-driven self-assembly of two highly emissive platinum(II) supramolecular triangles (1 and 2) containing BODIPY-based bridging ligands. The metallacycles exhibit favorable anticancer activities against HeLa cells (IC50 of 6.41 and 2.11 µM). The characteristic ∼570 nm fluorescence of the boron dipyrromethene (BODIPY) moieties in the metallacycles permits their intracellular visualization using confocal microscopy. Additionally, the BODIPY fluorophore is an excellent photodynamic agent, making the metallacycles as ideal therapeutics for photodynamic therapy (PDT) and chemotherapy. In vitro studies demonstrate that the combination indexes against HeLa cells are 0.56 and 0.48 for 1 and 2, respectively, confirming their synergistic anticancer effect. More importantly, these SCCs also exhibit superior anticancer efficacy toward cisplatin-resistant A2780cis cell line by combining PDT and chemotherapy, showing promise in overcoming drug resistance. This study exploits a multicomponent approach to self-assembled metallacages that enables design of effective theranostic agents wherein the platinum acceptors are toxic chemotherapeutics and the BODIPY donors are imaging probes and photosensitizers. Since each piece may be independently tuned, i.e., Pt(II) polypyridyl fragment swapped for Pt(II) phosphine, the activity may be optimized without a total redesign of the system.

Coordination-Driven Self-Assembly of Ruthenium Polypyridyl Nodes Resulting in Emergent Photophysical and Electrochemical Properties.

Ruthenium polypyridyl complexes are among the most studied molecular species for photochemical applications such as light-harvesting and photocatalysis, with [Ru(bpy)3]2+ (bpy = 2,2'-bipyridine) serving as an iconic example. We report the use of the [Ru(bpy)2]2+ fragment as a 90° acceptor tecton (M) in coordination-driven self-assembly to synthesize a M4L4 metallacycle (L = 4,4'-bipyridine) and a M6L4 truncated tetrahedral cage [L = 2,4,6-tris(4-pyridyl)-1,3,5-triazine]. The M6L4 cage possesses emergent properties attributed to its unique electronic structure, which results in increased visible-light absorption and an emission band that decays biexponentially with times of 3 and 790 ns. The presence of multiple ruthenium centers in the cage results in multiple RuIII/II reduction events, with a cathodic shift of the first reduction relative to that of [Ru(bpy)3]Cl2 (0.56 V vs 1.05 V). The ligand-centered reduction shifts anodically (-1.29 vs -1.64 V) versus the first bpy reduction observed in the parent [Ru(bpy)3]Cl2. The photophysical properties are explained by the existence of two localized charge-transfer states in the cage molecule: one that draws upon the bipyridine π* orbitals and the other upon the 2,4,6-tris(4-pyridyl)-1,3,5-triazine π* orbitals.

Photophysical Enhancement of Triplet Emitters by Coordination-Driven Self-Assembly.

The quantum yields of organic fluorophores used as donors in coordination-driven self-assembly often suffer from the heavy atom effect of nearby metal sites. Here, the role of intersystem crossing from a deactivating process to one that delivers emissive triplet states was reversed. A phosphorescent trans bis-N-heterocyclic carbene platinum(II) compound, Pt(dhim)2 (C≡C-4-py)2 (D1; dhim=1,3-dihexyl-2-H-imidazol-2-ylidene), was used along with other linear donors 4,4'-bipyridine (D2) and 1,4-bis(4-pyridyl ethynyl)benzene (D3) in self-assembly reactions with Pt(dtbpy)X2 acceptors (dtbpy=4,4'-di-tert-butyl-2,2'-bipyridine) to afford three metallacycles. Photophysical investigations revealed that, although the building blocks used to construct M1 have relatively low quantum yields (Φ=1.2 and <1 % for D1 and 2, respectively), the metallacycle has a quantum yield of 14 %. This increase reflects a change in radiative rate constant from 3.6×104  s-1 for D1 to 2.1×105  s-1 for M1.

Coordination-Driven Self-Assembly of Silver(I) and Gold(I) Rings: Synthesis, Characterization, and Photophysical Studies.

In this work, we investigate the self-assembly between Ag(I) and Au(I) centers and pyridyl donors to form hexagonal metallacycles and related linear complexes. The precipitation of hexagonal metallacycles upon assembly in chloroform/methanol mixtures results in high solid-state photo-stability. Whereas, the Ag(I) species have fast kinetics and high formation constants in acetone, this solvent interferes in the formation of the analogous Au(I) complexes. The photophysical properties of this suite of metallacycles was investigated including steady-state absorption, emission, and time-resolved lifetime measurements. All ligands and hexagons exhibited ligand-centered singlet emissions with ground-state absorption and emission perturbed upon coordination. The ligand-based fluorescent photoluminescence was affected by the heavy-atom effect when halide or metals are present, attenuating quantum yields as evidenced by increases in the experimentally measured non-radiative rate constants. The formation of group 11 metallacycles is motivated by their potential applications in mixed-matrix materials wherein metal ions can interact with substrate to facilitate separations chemistry with reduced energy requirements, in particular the isolation of ethylene and light olefins. Existing processes involve cryogenic distillation, an energy intensive and inefficient method.

Mixed-matrix materials using metal-organic polyhedra with enhanced compatibility for membrane gas separation.

Discrete metal-organic polyhedra (MOPs) containing copper(ii), palladium(ii), and iron(ii) nodes were synthesized as fillers for mixed-matrix materials (MMMs) with a polyvinylidine fluoride (PVDF) polymer phase and contrasted against an MMM containing a metal-organic framework, MOF-5. When a given MOP was soluble in the precursor solutions, the resulting MMMs were thin, flexible, and homogeneous based on microscopy and SEM imaging. Analogous MMM formation using either insoluble MOPs or the inherent insoluble MOF-5 showed a higher degree of phase separation and inhomogeneity. Even when a MOP was not fully soluble, a significant particle size decrease was observed in contrast to the MOF-5 materials wherein the crystallites remained largely intact. This is a consequence of solubilizing the MOP fillers into the polymer solvent. The crystallinity and thermal stabilities of the MMMs were compared to pure PVDF using powder X-ray diffraction, and differential scanning calorimetry, indicating that the incorporation of MOPs both decreased overall crystallinity as well as increased thermal stability. In addition, MMMs containing PdMOP and FeMOP showed improved gas permeabilities relative to pure PVDF for H2, N2, CH4, and CO2, with the 10 wt% FeMOP membrane more selective for CO2 over N2 and H2.

Increasing phosphorescent quantum yields and lifetimes of platinum-alkynyl complexes with extended conjugation.

The emission of platinum-alkynyl complexes with terminal pyridyl moieties changes upon simple alkylation reactions. Due to growing interest in photovoltaics, photocatalysis, and light-emitting devices, understanding the nature of these changes is important to develop simple synthetic pathways for the rational design of photophysically active molecules. Herein, the choice of ligand isomer, methylation, and Pt-coordination environment on phosphorescent quantum yields, lifetimes, and associated radiative and non-radiative rate constants of eight organometallic complexes were studied. Single-crystal X-ray diffraction experiments and computational studies provide evidence for stabilization of metallo-cumulene resonance forms whose increased rigidities manifest in the observed photophysical changes. This effect is more pronounced for 4-ethynylpyridyl complexes over 3-ethynylpyridyl variants since the metallo-cumulene form shifts electron density to the electronegative N-atom at the para site. Furthermore, the use of σ-donating N-heterocyclic carbenes to complete the Pt-coordination environment enhanced the quantum yield of phosphorescence as high as 39% (λmax = 512 nm) with a lifetime of 21.2 µs.

Decabromodiphenyl ether in indoor dust from different microenvironments in a university in the Philippines.

This study was conducted to develop a method for the determination of decabromodiphenyl ether (BDE-209) in indoor dust from different microenvironments in a university in the Philippines. BDE-209 was extracted from dust samples by ultrasonication and determined by HPLC-UV. The determination was performed using external calibration and internal standard calibration. Internal standard calibration was shown to be more precise and sensitive than external calibration. The linearity for the concentration range of 0-300 µg L(-1) BDE-209 was good (R(2)=0.993). The % absolute recovery and the % RSD for n=8 spiked dust analysis based on a 0.2 g dust sample was 57% and 19%, respectively. The method detection limit was 285 ng g(-1). All dust samples showed detectable levels of BDE-209 with some at levels below the quantification limits. The concentrations of BDE-209 in the quantified samples are within the range of 1103-4117 ng g(-1) with an average concentration of 2172 ng g(-1). The levels of BDE-209 found in the dust samples are comparable to those reported in house and workplace dusts from other Asian countries. Although not conclusive, it has been shown empirically that BDE-209 concentrations are higher in sampling sites containing more possible BDE-209 sources like electrical and electronic equipment.