Self-assembled metalla-bowls for selective sensing of multi-carboxylate anions

Two new tetranuclear cationic metalla-bowls 4 and 5 were self-assembled from a bis-pyridine amide ligand (H(2)L) (1) and arene-ruthenium acceptors, [(Ru(2)(μ-η(4)-C(2)O(4))(η(6)-p-cymene)(2)](O(3)SCF(3))(2) (2) and [Ru(2)(dhnd)(η(6)-p-cymene)(2)](O(3)SCF(3))(2) (dhnd = 6,11-dihydroxy-5,12-naphthacenedionato) (3), respectively. The metalla-bowls were characterized by multinuclear NMR, ESI-MS, UV-Vis spectroscopy, and single crystal X-ray diffraction study of 4. The crystal structure of 4 reveals unambiguous proof for the molecular shape of the metalla-bowl and the encapsulation of one triflate anion in the cavity through hydrogen bonding. The metalla-bowl 5 has been evaluated for anion binding studies by use of amide ligand as a hydrogen bond donor and arene-Ru acceptor as a signalling unit. UV-Vis titration studies showed that 5 selectively binds with multi-carboxylate anions such as oxalate, tartrate and citrate in a 1?:?1 fashion with high binding constants of 4.0-5.5 × 10(4) M(-1). Furthermore, the addition of multi-carboxylate anions into a solution of 5 gave rise to a large enhancement of fluorescence intensity attributable to the blocking of a photo-induced electron transfer process from the arene-ruthenium moiety to the amidic donor in 5. However, the fluorescence intensity almost remains unchanged upon addition of other anions including F(-), Cl(-), PF(6)(-), MeCOO(-), NO(3)(-) and PhCOO(-), as identically seen in the UV-Vis titration experiments, pointing to the high selectivity of 5 for the sensing of multi-carboxylate anions.     

Self-assembled molecular squares containing metal-based donor: synthesis and application in the sensing of nitro-aromatics

Self-assemblies between a linear Pt-based donor and ferrocene- chelated metallic acceptors produced novel heterometallic squares 4 and 5, which show fluorescence quenching upon the addition of nitro-aromatics.     

Selective Structural Transformation of Supramolecules to Multinuclear Heterosubstituted Pt Complexes via Ligand Exchange

Selective triflate to chlorine ligand exchange reaction between ditriflate and dichloride Pt complexes producing pure heterosubstituted complexes is demonstrated. We show that this reaction can be applied for selective chlorination of supramolecules leading to their structural transformation into multinuclear mono-chlorinated Pt(II) complexes. The X-ray structure of complex of 4,4′-bipyridine with two molecules of (Et₃P)₂Pt(Cl)OTf is reported.     

Designed post-self-assembly structural and functional modifications of a truncated tetrahedron

Post-self-assembly modifications of a discrete metal-organic supramolecular structure have been developed. Such modifications allow the properties of the self-assembled supramolecular species to be changed in a simple and efficient manner (>90% yield). Initiated by the application of chemical stimuli, the post-self-assembly modifications described herein result in three distinct changes to the supramolecular system: an individual building-block component change, an overall structural modification, and a functional evolution of a [6+4] metal-organic supramolecular structure. The three modifications have been carefully examined by a range of characterization methods, including NMR and UV-vis spectroscopy, electrospray ionization mass spectrometry, pulsed field gradient spin echo NMR measurements, electrochemical analysis, and computational simulations.     

Post-self-assembly covalent chemistry of discrete multicomponent metallosupramolecular hexagonal prisms

The multicomponent coordination-driven self-assembly of hexakis[4-(4-pyridyl)phenyl]benzene, cis-(PEt(3))(2)Pt(II)(OTf)(2), and amine- or maleimide-functionalized isophthalate forms discrete hexagonal prisms as single reaction products. The amino or maleimide groups decorating the isophthalate pillars of the prisms provide reactive sites for post-self-asssembly modifications. In this communication, we demonstrate that the hexagonal prisms can be functionalized without disrupting the prismatic cores, enabling the incorporation of new functionalities under mild conditions.     

Hydrogen bond partner reorganization in the coadsorption of a monodendron and pyridylethynyl derivatives

Hydrogen bonds with high selectivity and directionality are significant in harnessing molecules to form 2D supramolecular nanostructures. The competition and reorganization of hydrogen bond partners determine the ultimate molecular assembly and pattern in a 2D supramolecular system. In this study, multicomponent assemblies of a monodendron (5-benzyloxy-isophthalic acid derivative, BIC) and pyridylethynyl derivatives [1,4-bis(4-pyridylethynyl)-2,3-bis-dodecyloxy-benzene (PBPC12) and 1,4-bis(4-pyridylethynyl)-2,3-bis-octadecyloxy-benzene (PBPC18)] have been studied by scanning tunneling microscopy (STM) on a graphite surface. BIC molecules are able to associate with PBPC12 and PBPC18 molecules to induce the rearrangement of hydrogen bond partners and form coassembly structures. Interestingly, BIC acts as a template molecule in the coassembly process, and these multicomponent structures exhibit similar structural features to the assembly structures of BIC itself. The structural details of the coassembled structures are revealed by high-resolution STM images, and their relationship with the original BIC assemblies is discussed. These results provide important insights into the design and fabrication of hydrogen-bond-directed multicomponent molecular nanostructures on solid surfaces.     

Coordination-driven self-assembly of M3L2 trigonal cages from preorganized metalloligands incorporating octahedral metal centers and fluorescent detection of nitroaromatics

The design and preparation of novel M(3)L(2) trigonal cages via the coordination-driven self-assembly of preorganized metalloligands containing octahedral aluminum(III), gallium(III), or ruthenium(II) centers is described. When tritopic or dinuclear linear metalloligands and appropriate complementary subunits are employed, M(3)L(2) trigonal-bipyramidal and trigonal-prismatic cages are self-assembled under mild conditions. These three-dimensional cages were characterized with multinuclear NMR spectroscopy ((1)H and (31)P) and high-resolution electrospray ionization mass spectrometry. The structure of one such trigonal-prismatic cage, self-assembled from an arene ruthenium metalloligand, was confirmed via single-crystal X-ray crystallography. The fluorescent nature of these prisms, due to the presence of their electron-rich ethynyl functionalities, prompted photophysical studies, which revealed that electron-deficient nitroaromatics are effective quenchers of the cages' emission. Excited-state charge transfer from the prisms to the nitroaromatic substrates can be used as the basis for the development of selective and discriminatory turn-off fluorescent sensors for nitroaromatics.     

Dual-Emissive Platinum(II) Metallacage with a Sensitive Oxygen Response for Imaging of Hypoxia and Imaging-Guided Chemotherapy

Imaging of hypoxia in vivo helps with accurate cancer diagnosis and evaluation of therapeutic outcomes. A Pt^II metallacage with oxygen-responsive red phosphorescence and steady fluorescence for in vivo hypoxia imaging and chemotherapy is reported. The therapeutic agent and diagnostic probe were integrated into the metallacage through heteroligation-directed self-assembly. Nanoformulation by encapsulating the metallacage into nanoparticles greatly enhanced its stability the in physiological environment, rendering biomedical applications feasible. Apart from enhanced red phosphorescence upon hypoxia, the ratio between red and blue emissions, which only varies with intracellular oxygen level, provides a more precise standard for hypoxia imaging and detection. Moreover, in vivo explorations demonstrate the promising potential applications of the metallacage-loaded nanoparticles as theranostic agents for tumor hypoxia imaging and chemotherapy.