Multiple expression of molecular information: enforced generation of different supramolecular inorganic architectures by processing of the same ligand information through specific coordination algorithms

A Simple Thermodynamic Model for Quantitatively Addressing Cooperativity in Multicomponent Self-Assembly Processes—Part 2: Extension to Multimetallic Helicates Possessing Different Binding Sites

The extended site-binding model, which explicitly separates intramolecular interactions (i.e., intermetallic and interligand) from the successive binding of metal ions to polytopic receptors, is used for unravelling the self-assembly of trimetallic double-stranded Cu(I) and triple-stranded Eu(III) helicates. A thorough analysis of the available stability constants systematically shows that negatively cooperative processes operate, in strong contrast with previous reports invoking either statistical behaviours or positive cooperativity. Our results also highlight the need for combining successive generations of complexes with common binding units, but with increasing metallic nuclearities, for rationalizing and programming multicomponent supramolecular assemblies.

Ligand-directed molecular architectures: self-assembly of two-dimensional rectangular metallacycles and three-dimensional trigonal or tetragonal prisms

Three angular ditopic ligands (1,3-bis(benzimidazol-1-ylmethyl)-4,6-dimethylbenzene L(1), 1,3-bis(benzimidazol-1-ylmethyl)-2,4,6-trimethylbenzene L(2), and 1,4-bis(benzimidazol-1-ylmethyl)-2,3,5,6-tetramethylbenzene L(3)) and one tripodal ligand 1,3,5-tris(benzimidazol-1-ylmethyl)-2,4,6-trimethylbenzene L(4) have been prepared. Reaction of these shape-specific designed ligands with different metal salts affords a series of discrete molecular architectures: [Ag(2)L(1)(2)](BF(4))(2) 1, [Ag(2)L(2)(2)](CF(3)SO(3))(2) 2, [CF(3)SO(3)(-) subset Ag(2)L(3)(2)]CF(3)SO(3) 3, [CF(3)SO(3)(-) subset Ag(2)L(3)(3)]CF(3)SO(3) 4, [ClO(4)(-) subset Cu(2)L(2)(4)](ClO(4))(3) 5, [4H(2)O subset Ni(2)L(2)(4)Cl(4)].6H(2)O 6, [BF(4)(-) subset Ag(3)L(4)(2)](BF(4))(2) 7, [ClO(4)(-) subset Ag(3)L(4)(2)](ClO(4))(2) 8, and [CuI(3)(2-) subset Cu(3)L(4)(2)](2)[Cu(2)I(4)] 9. The compounds were characterized by elemental analysis, ESI-MS, IR, and NMR spectroscopy, and X-ray crystallography. 1 is a dinuclear metallacycle with 2-fold rotational symmetry in which two syn-conformational L(1) ligands are connected by two linearly coordinated Ag(+) ions. 2 and 3 are structurally related, consisting of rectangular structures assembled from two linearly coordinated Ag(+) ions and two L(2) or L(3) ligands. The structure of 4 is a trigonal prismatic box consisting of two Ag(+) ions in trigonal planar coordination linked by three L(3) ligands, while the structures of 5 and 6 are tetragonal prismatic cages constructed by two square planar Cu(2+) or Ni(2+) ions linked by four L(2) ligands. The topologies of 7-9 are similar to that of 4; however, these three structures are assembled from three linearly coordinated Ag(+) or Cu(+) ions and two tripodal ligands, representing an alternative strategy to assembling a trigonal prism. (1)H NMR and ESI-MS were utilized to elucidate the solution structures of these macrocycles.

Porphyrins linked directly to the 5,5' positions of 2,2'-bipyridine: a new supramolecular building block and switch

The synthesis and coordination chemistry of two porphyrin dimers linked either at the 5,5' or the 4,4' positions of 2,2'-bipyridine are described. These compounds, which may serve a molecular tectons for the constructions of a variety of supramolecular arrays of diverse function, reveal that the ground- and excited-state electronic communication between the chromophores is only moderately affected by the complexation state of the bipyridyl moiety. The nature of the metal ion chelated by the bipyridine only slightly perturbs the ground-state spectra, and differences observed in the excited state are largely ascribed to the heavy atom effect. This work also shows that conformational changes in structural subunits, in this case induced by bipyridyl complexation of various metal ions, do not necessarily require reorganization of supramolecular systems.

Di-[1,10]-phenanthrolinyl diazines: a new family of bis-tridentate chelators

A series of three bis-tridentate bridging ligands has been prepared in which two 1,10-phenanthroline units have been symmetrically appended to a central pyridazine, pyrimidine, or pyrazine ring. These ligands have been treated with [Ru(tpy-d(11))Cl(3)] to afford both mono- and bimetallic complexes that show very self-consistent NMR properties. [structure: see text]

Toward self-organization and complex matter

Beyond molecular chemistry based on the covalent bond, supramolecular chemistry aims at developing highly complex chemical systems from components interacting through noncovalent intermolecular forces. Over the past quarter century, supramolecular chemistry has grown into a major field and has fueled numerous developments at the interfaces with biology and physics. Some of the conceptual advances and future challenges are profiled here.

The design and applications of multifunctional ligands

The properties of a metal coordination complex are determined as much by the ligand set--the molecules and ions coordinated to the metal centre--as by the nature of the metal itself. The design and use of new ligands is consequently a major part of chemical research. This review considers the role of multifunctional ligands in three separate and distinct areas of chemistry. In homogeneous catalysis, the role of hybrid and hemilabile ligands is considered, and the introduction of functionalities designed to overcome problems of separation, either by tethering or solubilising, is discussed. In supramolecular chemistry, functionalities enabling the recognition and sensing of cations and anions are examined. In addition, ligands containing two or more faces are discussed for their role in metallodendrimer formation and self-assembly reactions, and the use of bifunctional ligands in crystal engineering is addressed. The application of metal complexes in medicine is examined by consideration of cis-platin and its derivatives as anti-tumour agents. Imaging agents are also discussed with the uses of gadolinium MRI contrast agents and gamma-emitting technetium complexes highlighted.

A new polytopic bis-diazacrown-ether-polypyridine ligand and its complexes with Zn(II) salts and mononuclear and dendritic Ru(II) precursors. Synthesis, absorption spectra, redox behavior, and luminescence properties

The new polytopic receptor 1 containing two terpyridine, one phenanthroline, and two diazacrown-ether sites has been prepared using a modular approach. Such a new species contains several pieces of information in its structure which can be processed by different metal ions to give different supramolecular inorganic architectures. Actually, reaction of 1 with Zn(CH(3)COO)(2) in methanol, and subsequent anion exchange, afforded the intramolecular ring-type [Zn(1)](2+) complex, which appears to be formed by a self-assembling reaction. A different synthetic approach, stepwise synthesis, allowed us to synthesize the two multicomponent compounds [(bpy)(2)Ru(mu-1)Ru(bpy)(2)](4+) (Ru2; bpy = 2,2'-bipyridine) and [[(bpy)(2)Ru(mu-2,3-dpp)](2)Ru(mu-1)Ru[(mu-2,3-dpp)Ru(bpy)(2)](2)](12+) (Ru6; 2,3-dpp = 2,3-bis(2-pyridyl)pyrazine). The absorption spectra and luminescence properties of 1 and [Zn(1)](2+) are dominated by pi --> pi transitions and excited states. The absorption spectra of the ruthenium compounds are dominated by ligand-centered (LC) bands in the UV region and metal-to-ligand charge-transfer (MLCT) bands in the visible. The latter compounds undergo several reversible metal-centered oxidations and ligand-centered reductions in the potential window investigated (-2.0/+2.0 V versus SCE) and exhibit MLCT luminescence in both acetonitrile fluid solution at room temperature and in butyronitrile rigid matrix at 77 K. Both the redox and photophysical properties of Ru2 and Ru6 can be assigned to specific subunits of the multicomponent structures. The data indicate that the [Ru(bpy)(2)](2+) and the dendritic [Ru[(mu-2,3-dpp)Ru(bpy)(2)](2)](6+) fragments appended to the polytopic 1ligands behave as independent components of the multicomponent arrays.

IVIG-pools: regulatory gifts--transiting from harmony toward harmonious immunoglobulins: why? and why not?

Based on 'initial conditions' which depend on each donors' exposure to a unique environment, a pooled intravenous immunoglobulin (IVIG) product transfers its immunoglobulin molecule repertoire, unchanged, to the altered host. The relay function of the cell-bound receptors, especially that of the inhibitory Fc(gamma)RIIB, may then allow sufficient amplification to make regulatory activity possible. To the clinician, IVIG may be considered a tool to promote reversal of the dysregulation causing autoimmune disease. Generically, IVIG may be seen as a promoter allowing a progression from harm by an inflammatory/fibrotic reaction, then down-regulating toward restitutio ad integrum. By modifying natural processes, IVIG may play minor roles in promoting defense against spontaneous bleeding and, perhaps, stimulating remyelination. The wide spectrum of IVIG specificities, by reflecting evolutionary epitope selection, may not further destabilize cell/molecule disarray in the affected host. Benefit to the patient by IVIG treatment cannot be predicted nor can potentially severe or even fatal accidents entirely be excluded. Important aspects of IVIG treatment still await clarification including dosage, timing and the isotype form. In the foreseeable future it does not seem that biotechnological advances will match the physiologic harmony of IVIG, leaving antibody characteristics aside.

Dominant/recessive behavior in the expression of molecular information: self-assembly of inorganic macrocyclic architectures containing coordinatively unsaturated ligands

The polytopic ligand 1 contains three different metal ion binding subunits forming two substructures that code for the self-assembly of two different coordination structures (helicate and grid type) under metal ion complexation. Reaction with Cu(II) and Zn(II) ions generates the coordinatively unsaturated architectures 8 and 9 resulting from the formation of two double helicate arrangements. Their crystal structure has been determined by x-ray diffraction. These results show that the double helical motif is expressed at the expense of the grid type one, indicating the dominant/recessive behavior of the system. Together with earlier studies on the linear combination and crossover processing schemes, the dominant/recessive generation of 8 and 9 completes the demonstration of principle of the modes of multiple expression of molecular information in a multicode programmed chemical system.