Hexanuclear Ln6L6 Complex Formation by using an Unsymmetric Ligand

Multinuclear, self‐assembled lanthanide complexes present clear opportunities as sensors and imaging agents. Despite the widely acknowledged potential of this class of supramolecule, synthetic and characterization challenges continue to limit systematic studies into their self‐assembly restricting the number and variety of lanthanide architectures reported relative to their transition metal counterparts. Here we present the first study evaluating the effect of ligand backbone symmetry on multinuclear lanthanide complex self‐assembly. Replacement of a symmetric ethylene linker with an unsymmetric amide at the centre of a homoditopic ligand governs formation of an unusual Ln6L6 complex with coordinatively unsaturated metal centres. The choice of triflate as a counterion, and the effect of ionic radii are shown to be critical for formation of the Ln6L6 complex. The atypical Ln6L6 architecture is characterized using a combination of mass spectrometry, luminescence, DOSY NMR and EPR spectroscopy measurements. Luminescence experiments support clear differences between comparable Eu6L6 and Eu2L3 complexes, with relatively short luminescent lifetimes and low quantum yields observed for the Eu6L6 structure indicative of non‐radiative decay processes. Synthesis of the Gd6L6analogue allows three distinct Gd···Gd distance measurements to be extracted using homo‐RIDME EPR experiments

Design of lanthanide based metal-organic polyhedral cages for application in catalysis, sensing, separation and magnetism

Lanthanide organic polyhedral cage complexes are a class of supramolecular compounds that present exciting opportunities in applications ranging from sensing to catalysis and magnetism. Metal organic polyhedra incorporating transition metal vertices bridged by organic ligands have been extensively studied. By contrast analogous lanthanide complexes, which present additional benefits beyond those of their transition metal counterparts, remain an underrepresented class of supramolecule. One unique property of lanthanide organic cages is the luminescence properties bestowed by the metal ions which offer interesting opportunities in imaging applications, whilst the large ionic radii of the trivalent ions enables the formation of novel structures with opportunities to incorporate ancillary ligands not possible for transition metal structures. This review summarizes the key developments in synthesis and characterization of lanthanide metal organic cages, allowing general structural trends to emerge and highlights the exciting applications already demonstrated for these complexes

DNA Intercalation Facilitates Efficient DNA-Targeted Covalent Binding of Phenanthriplatin

Phenanthriplatin, a monofunctional anticancer agent derived from cisplatin, shows significantly more rapid DNA covalent-binding activity compared to its parent complex. To understand the underlying molecular mechanism, we used single-molecule studies with optical tweezers to probe the kinetics of DNA-phenanthriplatin binding as well as DNA binding to several control complexes. The time-dependent extensions of single -DNA molecules were monitored at constant applied forces and compound concentrations, followed by rinsing with a compound-free solution. DNA-phenanthriplatin association consisted of fast and reversible DNA lengthening with time constant 10 s, followed by slow and irreversible DNA elongation that reached equilibrium in 30 min. In contrast, only reversible fast DNA elongation occured for its stereoisomer trans-phenanthriplatin, suggesting that the distinct two-rate kinetics of phenanthriplatin is sensitive to the geometric conformation of the complex. Furthermore, no DNA unwinding was observed for pyriplatin, in which the phenanthridine ligand of phenanthriplatin is replaced by the smaller pyridine molecule, indicating that the size of the aromatic group is responsible for the rapid DNA elongation. These findings suggest that the mechanism of binding of phenanthriplatin to DNA involves rapid, partial intercalation of the phenanthridine ring followed by slower substitution of the adjacent chloride ligand by, most likely, the N7 atom of a purine base. The cis isomer affords the proper stereochemistry at the metal center to facilitate essentially irreversible DNA covalent binding, a geometric advantage not afforded by trans-phenanthriplatin. This study demonstrates that reversible DNA intercalation provides a robust transition state that is efficiently converted to an irreversible DNA-Pt bound state.National Institutes of Health (U.S.) (Grant CA034992)National Institutes of Health (U.S.) (Grant AG045144)National Institutes of Health (U.S.) (Grant CA211184

Self-assembly of a trigonal bipyramidal architecture with stabilisation of iron in three spin states.

From PubMed via Jisc Publications RouterPublication status: aheadofprintSelf-assembly and characterisation of a supramolecular trigonal bipyramidal iron cage containing an [Fe (μ -F) (Fe ) ] star motif at its core is reported. The complex can be formed in a one step reaction using an heterotopic ligand that supports site-specific incorporation of iron in three distinct electronic configurations: low-spin Fe , high-spin Fe and high-spin Fe , with iron(II) tetrafluoroborate as the source of the bridging fluorides. Formation of a μ -F bridged mixed-valence Fe -Fe star is unprecedented. The peripheral high-spin Fe centres of the mixed-valence tetranuclear star incorporated in the iron cage are highly anisotropic and engage in F-mediated antiferromagnetic exchange with the central Fe ion

Cation- and anion-exchanges induce multiple distinct rearrangements within metallosupramolecular architectures

Different anionic templates act to give rise to four distinct Cd II-based architectures: a Cd2L3 helicate, a Cd8L12 distorted cuboid, a Cd10L15 pentagonal prism, and a Cd12L18 hexagonal prism, which respond to both anionic and cationic components. Interconversions between architectures are driven by the addition of anions that bind more strongly within a given product framework. The addition of FeII prompted metal exchange and transformation to a Fe4L6 tetrahedron or a Fe10L15 pentagonal prism, depending on the anionic templates present. The equilibrium between the Cd12L18 prism and the Cd2L3 triple helicate displayed concentration dependence, with higher concentrations favoring the prism. The Cd12L18 structure serves as an intermediate en route to a hexafluoroarsenate-templated Cd10L15 complex, whereby the structural features of the hexagonal prism preorganize the system to form the structurally related pentagonal prism. In addition to the interconversion pathways investigated, we also report the single-crystal X-ray structure of bifluoride encapsulated within a Cd10L15 complex and report solution state data for J-coupling through a CH··· F- hydrogen bond indicating the strength of these interactions in solution

DNA intercalation facilitates efficient DNA-targeted covalent binding of phenanthriplatin

Phenanthriplatin, a monofunctional anticancer agent derived from cisplatin, shows significantly more rapid DNA covalent-binding activity compared to its parent complex. To understand the underlying molecular mechanism, we used single-molecule studies with optical tweezers to probe the kinetics of DNA–phenanthriplatin binding as well as DNA binding to several control complexes. The time-dependent extensions of single λ-DNA molecules were monitored at constant applied forces and compound concentrations, followed by rinsing with a compound-free solution. DNA–phenanthriplatin association consisted of fast and reversible DNA lengthening with time constant τ ≈ 10 s, followed by slow and irreversible DNA elongation that reached equilibrium in ∼30 min. In contrast, only reversible fast DNA elongation occured for its stereoisomer trans-phenanthriplatin, suggesting that the distinct two-rate kinetics of phenanthriplatin is sensitive to the geometric conformation of the complex. Furthermore, no DNA unwinding was observed for pyriplatin, in which the phenanthridine ligand of phenanthriplatin is replaced by the smaller pyridine molecule, indicating that the size of the aromatic group is responsible for the rapid DNA elongation. These findings suggest that the mechanism of binding of phenanthriplatin to DNA involves rapid, partial intercalation of the phenanthridine ring followed by slower substitution of the adjacent chloride ligand by, most likely, the N7 atom of a purine base. The cis isomer affords the proper stereochemistry at the metal center to facilitate essentially irreversible DNA covalent binding, a geometric advantage not afforded by trans-phenanthriplatin. This study demonstrates that reversible DNA intercalation provides a robust transition state that is efficiently converted to an irreversible DNA-Pt bound state

Amino Functionality Enables Aqueous Synthesis of Carboxylic Acid-Based MOFs at Room Temperature by Biomimetic Crystallisation

Enzyme immobilisation within Metal-Organic Frameworks (MOFs) is a promising solution to avoid denaturation and thereby utilise the desirable properties of enzymes outside of their native environments. The biomimetic mineralization strategy employs biomacromolecules as nucleation agents to promote the crystallisation of MOFs in water at room temperature, thus overcoming pore size limitations presented by traditional post-assembly encapsulation. Most biomimetic crystallisation studies reported to date have employed zeolitic imidazole frameworks (ZIFs). Herein, we expand the library of MOFs suitable for biomimetic mineralisation to include zinc(II) MOFs incorporating functionalised terephthalic acid linkers, and study the catalytic performance of the enzyme@MOFs. Amine functionalisation of terephthalic acids is shown to accelerate the formation of crystalline MOFs enabling new enzyme@MOFs to be synthesised. The structure and morphology of the enzyme@MOFs were characterised by PXRD, FTIR and SEM-EDX and the catalytic potential was evaluated. Increasing the linker length whilst retaining the amino moiety, gave rise to a family of linkers, however, MOFs generated with the 2, 2’-amino terephthalic acid linker displayed the best catalytic performance. Our data also illustrates that the pH of the reaction mixture affects the crystal structure of the MOF and this structural transformation impacts the catalytic performance of the enzyme@MOF.<br/