RESUMEN

The growth of crystals of aromatic compounds from water much depends on the nature of the water solubilizing functions that they carry. Rationalizing crystallization from water, and structure elucidation, of aromatic molecular and supramolecular systems is of general value across various fields of chemistry. Taking helical aromatic foldamers as a test case, we have validated several short polar side chains as efficient substituents to provide both solubility in, and crystal growth ability from, water. New 8-amino-2-quinolinecarboxylic acids bearing charged or neutral aminomethyl, carboxymethyl, sulfonic acid, or bis(hydroxymethyl)-methoxy side chains in position 4 or 5, were prepared on a multi gram scale. Fmoc protection of the main chain amine and suitable protections of the side chains ensured compatibility with solid phase synthesis. One tetrameric and five octameric oligoamides displaying these side chains were synthesized and shown to be soluble in water. In all cases but one, crystals were obtained using the hanging drop method, thus validating the initial design principle to combine polarity and rigidity. The only case that resisted crystallization appeared to be due to exceedingly high water solubility endowed by eight sulfonic acid functions. The neutral side chain did provide crystal growth ability from water but contributed poorly to solubility.

RESUMEN

Disulfide bridge formation was investigated in helical aromatic oligoamide foldamers. Depending on the position of thiol-bearing side chains, exclusive intramolecular or intermolecular disulfide bridging may occur. The two processes are capable of self-sorting, presumably by dynamic exchange. Quantitative assessment of helix handedness inversion rates showed that bridging stabilizes the folded structures. Intermolecular disulfide bridging serendipitously yielded a well-defined, C2 -symmetrical, two-helix bundle-like macrocyclic structure in which complete control over relative handedness, that is, helix-helix handedness communication, is mediated remotely by the disulfide bridged side chains in the absence of contacts between helices. MM calculations suggest that this phenomenon is specific to a given side chain length and requires disulfide functions.

RESUMEN

A dynamic-covalent metal-containing polymer was synthesized by the condensation of linear diamine and dialdehyde subcomponents around copper(I) templates in the presence of bidentate phosphine ligands. In solution, the red polymers undergo a sol-gel transition upon heating to form a yellow gel, a process that can be either reversible or irreversible depending on the solvent used. When fabricated into a light-emitting electrochemical cell (LEC), the polymer emits infrared light at low voltage. As the voltage is increased, a blue shift in the emission wavelength is observed until yellow light is emitted, a process which is gradually reversed over time upon lowering the voltage. The mechanism underlying these apparently disparate responses is deduced to be due to loss of the copper phosphine complex from the polymer.

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Surface-confined double-helical polymers are generated by dynamic covalent assembly with preservation of chirality, metal coordination environment, and oxidation state of the precursor complexes. This one-step procedure involves both in solution and solution-to-surface assembly and resulted in chiral interfaces where pairs of ligands are wrapped around arrays of metal ions. In-plane XRD experiments revealed the formation of a highly ordered structure along the substrate surface. The chirality of the surfaces is expressed by the selective recognition of 3,4-dihydroxyphenylalanine (DOPA). The CD measurements show a response of the Δ-polymer-modified quartz substrates toward D-DOPA, whereas no change was observed after treatment with L-DOPA. These coordination-based interfaces assembled on metal-oxide substrates in combination with a redox-probe, [Os(bpy)3](PF6)2, in solution can resemble the behavior of a rectifier.

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RESUMEN

A new type of water-soluble copper-containing polymer has been synthesized using the technique of subcomponent self-assembly. Copper(I)-directed imine bond formation between triethylene glycol functionalized 1,2-phenylenediamine and 2,9-diformylphenanthroline subcomponents resulted in the formation of a chain in which two conjugated helical ligand strands wrap around a linear array of metal ions. Characterization data from a variety of analytical methods are consistent with our formulation of this material. After purification by dialysis, the polymer was shown to possess several properties of conceptual and practical interest. (1) Individual double-helical strands appear to further aggregate through entanglement of their side chains to form well-defined superstructures such as nanoscale bow ties and macrocycles, which can be imaged on a surface. (2) The material's copper(I) ions underwent reversible electrochemical oxidation in solution, whereas analogous model compounds were observed to decompose upon oxidation: the polymer's greater length appeared to stabilize oxidized states through delocalization or entrapment. (3) Photophysical measurements reveal this material to be photo- and electroluminescent. It has been successfully used for the fabrication of electroluminescent devices and shows a weak emission of white-blue light with CIE coordinates of (0.337, 0.359). This study further demonstrates the utility of the technique of subcomponent self-assembly for the straightforward generation of materials with useful properties.

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A general method for preparing Fe(4)L(4) face-capped tetrahedral cages through subcomponent self-assembly was developed and has been demonstrated using four different C(3)-symmetric triamines, 2-formylpyridine, and iron(II). Three of the triamines were shown also to form Fe(2)L(3) helicates when the appropriate stoichiometry of subcomponents was used. Two of the cages were observed to have nearly identical Fe-Fe distances in the solid state, which enabled their ligands to be coincorporated into a collection of mixed cages. Only one of the cages combined a sufficiently large cavity with the sufficiently small pores required for guest binding, taking up a wide variety of guest species in size- and shape-selective fashion.

RESUMEN

The condensation of linear diamine and dialdehyde subcomponents around copper(I) templates in the presence of bulky trioctylphosphine ancillary ligands gave a linear, conjugated polymeric material in DMSO solution. This polymer solution was observed to undergo sol-to-gel transition as the temperature was raised to 140 °C, in contrast with the behavior of most gel-forming polymers, which do so upon cooling. We attribute the sol-to-gel transition to the formation of Cu(I)N(4) cross-links as the equilibria 2[Cu(I)N(2)P(2)] ⇄ [Cu(I)N(4)] + [CuP(n)](+) + (4 - n)P favor the right-hand side at higher temperatures. The material was also observed to exhibit thermochromism and photoluminescence, with the color and intensity of both absorption and emission exhibiting temperature dependence. This material thus responds predictably to combinations of stimuli (heat, light, mechanical shear) in an interconnected way, as is required to generate complex function.

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Molecular subcomponents such as phosphate groups are often passed between biomolecules during complex signalling cascades, the flow of which define the motion of the machinery of life. Here, we show how an abiological system consisting of organic subcomponents knitted together by metal-ion coordination can respond to simple signals in complex ways. A Cu(I)(3) helicate transformed into its Zn(II)(2)Cu(I) analogue following the addition of zinc(II), and the ejected copper(I) went on to induce the self-assembly of a Cu(I)(2) helicate from other free subcomponents present in solution. The addition of an additional subcomponent, 8-aminoquinoline, resulted in the formation of a third, more stable Cu(I)(3) helicate, requiring the destruction of both the Zn(II)(2)Cu(I) and Cu(I)(2) helicates to scavenge sufficient Cu(I) for the new structure. This system thus demonstrates two examples in which the application of one signal provokes two distinct responses involving the creation or destruction of complex assemblies as the system seeks thermodynamic equilibrium following perturbation.

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A rigid, helical macrocycle that contains two copper(I) ions has been synthesized through subcomponent self-assembly. Although it does not obey the "rule of coordinative saturation", this macrocycle could be prepared through subcomponent substitution starting from a tri(copper(I)) helicate, in a reaction in which copper(I) was ejected. The macrocycle was observed to readily participate in a sequence of transformations between helical structures mediated by the electronic effects of substituents, entropic effects, the conformational preferences of organic building blocks, and the coordinative preferences of the metal ion. The thermodynamic parameters governing the interconversion of an "open" helicate and the "closed" macrocycle were determined through van 't Hoff analysis, allowing quantification of the entropic driving force for macrocyclization.

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The increasing importance of hydrogenase enzymes in the new energy research field has led us to examine the structure and dynamics of potential hydrogenase mimics, based on a ferrocene-peptide scaffold, using molecular dynamics (MD) simulations. To enable this MD study, a molecular mechanics force field for ferrocene-bearing peptides was developed and implemented in the CHARMM simulation package, thus extending the usefulness of the package into peptide-bioorganometallic chemistry. Using the automated frequency-matching method (AFMM), optimized intramolecular force-field parameters were generated through quantum chemical reference normal modes. The partial charges for ferrocene were derived by fitting point charges to quantum-chemically computed electrostatic potentials. The force field was tested against experimental X-ray crystal structures of dipeptide derivatives of ferrocene-1,1'-dicarboxylic acid. The calculations reproduce accurately the molecular geometries, including the characteristic C2-symmetrical intramolecular hydrogen-bonding pattern, that were stable over 0.1 micros MD simulations. The crystal packing properties of ferrocene-1-(D)alanine-(D)proline-1'-(D)alanine-(D)proline were also accurately reproduced. The lattice parameters of this crystal were conserved during a 0.1 micros MD simulation and match the experimental values almost exactly. Simulations of the peptides in dichloromethane are also in good agreement with experimental NMR and circular dichroism (CD) data in solution. The developed force field was used to perform MD simulations on novel, as yet unsynthesized peptide fragments that surround the active site of [Ni-Fe] hydrogenase. The results of this simulation lead us to propose an improved design for synthetic peptide-based hydrogenase models. The presented MD simulation results of metallocenes thereby provide a convincing validation of our proposal to use ferrocene-peptides as minimal enzyme mimics.

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