Reusable and pH-Stable Luminescent Sensors for Highly Selective Detection of Phosphate.

Phosphate sensors have been actively studied owing to their importance in water environment monitoring because phosphate is one of the nutrients that result in algal blooms. As with other nutrients, seamless monitoring of phosphate is important for understanding and evaluating eutrophication. However, field-deployable phosphate sensors have not been well developed yet due to the chemical characteristics of phosphate. In this paper, we report on a luminescent coordination polymer particle (CPP) that can respond selectively and sensitively to a phosphate ion against other ions in an aquatic ecosystem. The CPPs with an average size of 88.1 ± 12.2 nm are embedded into membranes for reusable purpose. Due to the specific binding of phosphates to europium ions, the luminescence quenching behavior of CPPs embedded into membranes shows a linear relationship with phosphate concentrations (3-500 µM) and detection limit of 1.52 µM. Consistent luminescence signals were also observed during repeated measurements in the pH range of 3-10. Moreover, the practical application was confirmed by sensing phosphate in actual environmental samples such as tap water and lake water.

Ion-Selective Electrode Based on a Novel Biomimetic Nicotinamide Compound for Phosphate Ion Sensor.

Phosphorus is not only an import nutrient to aquatic habitats, but it also acts as a growth inhibitor in aquatic ecosystems; however, it also aggravates environmental issues, such as eutrophication. There is a growing interest in rapid phosphorus detection to manage and protect water resources. Due to the large molecular structure and high hydration energy of phosphate ions, ion-selective electrodes (ISEs) remain in their infancy for real-time measurements in terms of practical application. In this study, a newly developed ionophore based on a biomimetic nicotinamide functional group was used to detect phosphate selectively, displaying efficient binding through charge interactions and hydrogen bonds. The ISE membrane containing silicone rubber demonstrated an effective detection performance over a long period of time. With a dynamic range between 10-6 and 10-2 M and a limit of detection of 0.85 × 10-6 M (26 µg/L), the newly synthesized ISE membranes demonstrated selectivity for phosphate ions over other ions, including acetate, sulfate, and chloride.

Carbaporphyrin Dimers That Bear a Rigid Naphthalene Motif as an Internal Strap.

The first fully connected aromatic carbaporphyrin dimer (6) and its bis-Pd complex (6-Pd2) that bear a rigid naphthalene motif as an internal strap were synthesized. These dimers consisted of two aromatic carbaporphyrins that shared a naphthalene motif. The π-electron conjugation of the obtained macrocycles was proposed to have two separated local 22 π-electron pathways and a 34 π-electron pathway. Their weak aromaticity was fully supported by 1H NMR spectroscopy, NICS values, ACID calculations, and ICSS plots.

Conformationally Locked Tolans, ß-Sheet Structures, and Photophysical Properties.

Conformationally locked tetrasubstituted tolans were synthesized by introducing a tether on the tolan. To demonstrate the utilities of these motifs, a ß-hairpin structure (15) was synthesized, and its additional stabilizing effects were evaluated. Moreover, the photophysical properties of cyclic tolans and their ß-sheet structure were investigated. The fluorescence quantum yield of cyclic tolan 12 is >1000 times stronger than its congener 1 in CH3CN.

Shape-Induced, Hexagonal, Open Frameworks: Rubidium Ion Complexed Cucurbituril.

A honeycomb structure is shown by the one-dimensional coordination polymer comprising D6h -symmetric cucurbituril molecules and rubidium ions (see picture). The cucurbituril molecules stack atop one another and show coordination of their carbonyl groups to the rubidium ions in between. The shape and symmetry of the building blocks encourage the coordination polymer chains to be arranged in such a way as to produce an open-framework structure with large, linear, hexagonal channels.

A Two-Dimensional Polyrotaxane with Large Cavities and Channels: A Novel Approach to Metal-Organic Open-Frameworks by Using Supramolecular Building Blocks.

A seven-membered molecular necklace composed of six copper ions and six pseudorotaxane units behaves as a secondary building block in the formation of a two-dimensional polyrotaxane network with large voids. This novel metal-organic framework allows size-selective anion exchange as well as the exchange of coordinated ligands. Thus a new synthetic strategy has been identified for modular porous solids which utilizes large, rigid, interlocked supermolecules as primary or secondary building blocks.

Selective Inclusion of a Hetero-Guest Pair in a Molecular Host: Formation of Stable Charge-Transfer Complexes in Cucurbit[8]uril.

Two different molecules are selectively included in cucurbit[8]uril to form a stable 1:1:1 ternary complex, which has been characterized by X-ray crystallography. The inclusion of a hetero-guest pair (a pyridinium derivative (blue) and 2,6-dihydroxynaphthalene (magenta)) in the molecular host is driven and stabilized by a charge-transfer interaction between the electron-rich and electron-deficient guests.

Hg(II)-mediated intramolecular cyclization reaction in aqueous media and its application as Hg(II) selective indicator.

The Hg(II)-specific intramolecular cyclization reaction of ethynyl phenols was carried out for the first time in semiaqueous media at ambient temperature. The reaction unit (ethynyl phenol) was coupled with a malononitrile derivative (signal unit), which afforded the chromogenic Hg(II) indicator 7. The reaction of the chromogenic Hg(II) indicator 7 was further optimized in DMSO/water (3:7, v/v) (10 mM PBS buffer, pH = 7.0). Compound 7 displays a color change from blue to pale yellow in the presence of Hg(II).

A convergent coordination chemistry-based approach to dissymmetric macrocyclic cofacial porphyrin complexes.

We report a highly convergent and modular approach for the synthesis of dissymmetric cofacial porphyrin complexes, which is based upon the weak-link approach to supramolecular coordination chemistry. Specifically, we have utilized a halide-induced ligand rearrangement reaction, which is capable of providing heteroligated mixed-metal porphyrin complexes in quantitative yield. Significantly, the adoption of a coordination chemistry based approach for the synthesis of these complexes allows for facile in situ regulation of the porphyrin-porphyrin interactions through the addition of external chemical stimuli.

Triple-Decker Complexes Formed via the Weak Link Approach.

Through the weak link approach and a halide-induced ligand rearrangement process, semi-open and condensed triple-decker complexes (TDCs) were prepared and fully characterized. These triple-decker structures with tailorable layers through choice of hemilabile ligand starting materials can be chemically opened and closed to expose the interior layer in a reversible fashion using small-molecule and elemental anion ligand substitution reactions.

Transition metal ion directed supramolecular assembly of one- and two-dimensional polyrotaxanes incorporating cucurbituril.

This paper reports a synthetic strategy to construct one- and two-dimensional (1D and 2D) polyrotaxanes, in which a number of rings are threaded onto a coordination polymer, by the combination of self-assembly and coordination chemistry. Our approach to construct polyrotaxanes with high structural regularity involves threading a cucurbituril (CB) "bead" with a short "string" to form a stable pseudorotaxane, followed by linking the pseudorotaxanes with metal ions as "linkers" to organize into a 1D or 2D polyrotaxane. A 4- or 3-pyridylmethyl group is attached to each end of 1,4-diaminobutane or 1,5-diaminopentane to produce the short "strings", which then react with the cucurbituril "bead" to form stable pseudorotaxanes. The reaction of the pseudorotaxanes with various transition metal ions including CuII, CoII, NiII, AgI, and CdII produces 1D or 2D polyrotaxanes, in which many molecular "beads" are threaded onto 1D or 2D coordination polymers as confirmed by X-ray crystallography. The overall structure of a polyrotaxane is the result of interplay among various factors that include the coordination preferences of the metal ion, spatial disposition of the donor atoms with respect to the CB beads in the pseudorotaxane, and the size and coordination ability of the counteranion.

Designed self-assembly of molecular necklaces.

This paper reports an efficient strategy to synthesize molecular necklaces, in which a number of small rings are threaded onto a large ring, utilizing the principles of self-assembly and coordination chemistry. Our strategy involves (1) threading a molecular "bead" with a short "string" to make a pseudorotaxane and then (2) linking the pseudorotaxanes with a metal complex with two cis labile ligands acting as an "angle connector" to form a cyclic product (molecular necklace). A 4- or 3-pyridylmethyl group is attached to each end of 1,4-diaminobutane or 1,5-diaminopentane to produce the short "strings" (C4N4(2+), C4N3(2+), C5N4(2+), and C5N3(2+)), which then react with a cucurbituril (CB) "bead" to form stable pseudorotaxanes (PR44(2+), PR43(2+), PR54(2+), and PR53(2+), respectively). The reaction of the pseudorotaxanes with Pt(en)(NO(3))(2) (en = ethylenediamine) produces a molecular necklace [4]MN, in which three molecular "beads" are threaded on a triangular framework, and/or a molecular necklace [5]MN, in which four molecular "beads" are threaded on a square framework. Under refluxing conditions, the reaction with PR44(2+) or PR54(2+) yields exclusively [4]MN (MN44T or MN54T, respectively), whereas that with PR43(2+) or PR53(2+) produces exclusively [5]MN (MN43S or MN53S, respectively). The products have been characterized by various methods including X-ray crystallography. At lower temperatures, on the other hand, the reaction with PR44(2+) or PR54(2+) affords both [4]MN and [5]MN. The supermolecules reported here are the first series of molecular necklaces obtained as thermodynamic products. The overall structures of the molecular necklaces are strongly influenced by the structures of pseudorotaxane building blocks, which is discussed in detail on the basis of the X-ray crystal structures. The temperature dependence of the product distribution observed in this self-assembly process is also discussed.