Miguel A. Galindo

DNA-based routes to semiconducting nanomaterials

The controlled preparation and assembly of opto-electronic nanoscale materials is being tackled by top-down and bottom-up approaches. The latter draws inspiration from biology, where complex hierarchical systems are assembled from simpler building blocks. One of these, DNA, is proving especially useful: its size, stability, topology; the assorted chemical functional groups; plus its capacity for self-assembly provide a powerful nanoscale toolbox for materials preparation. Here we review recent research that shows the roles DNA can play in the preparation and organisation of semiconductor nanomaterials. Studies show that both hard inorganic and soft polymer materials can be directed to grow at nanoscale lengths using DNA and its constituents. In some cases the resulting materials have been used as components in simple electrical devices and the methodology has been extended to analytical tools. Intriguingly, these DNA-semiconductor hybrid materials have been found to self-assemble themselves, forming highly regular rope-like assemblies and conducting network structures.

Molecular architecture of redox-active half-sandwich Ru(II) cyclic assemblies. Interactions with biomolecules and anticancer activity

Tetranuclear cationic open boxes non-covalently bind DNA major groove. By contrast, they covalently bind cysteine after ligand exchange reactions. In addition, these systems exhibit potent antitumour activity circumventing cisplatin resistance.

Probing Metal-Ion Purine Interactions at DNA Minor-Groove Sites

The effect of the 2-amino group on metal ion binding at the N3-position of a purine base has been investigated using chelate-tethered derivatives. Reactions of diamine-tethered 2,6-diaminopurine (DAP) with divalent d-block metal ions Cu(II) and Cd(II) confirm that binding can occur, but this is much less prevalent than with adenine. In this regard DAP is similar to guanine where we have previously observed a general lack of N3-binding by divalent metal ions compared to adenine (e.g., Houlton et al., Angew. Chem., Int. Ed. 2000, 39, 2360; Chem.-Eur. J. 2000, 6, 4371). For the univalent d-block metals ions, Cu(I) and Ag(I), binding to adenine N3 is not observed in the solid state, as shown by reactions with dithioether-tethered adenine derivatives. Instead, depending on stoichiometry of the reaction, discrete (with metal/ligand ratio 1:2) or polymeric (with metal/ligand ratio 1:1) complexes were isolated and characterized by single crystal X-ray methods. In the former the nucleobases are pendant and involved in base-pair interactions, with both Watson-Crick...Watson-Crick and Hoogsteen...Hoogsteen type pairings present. For the coordination polymers a rather unexpected influence of the tether length on the site of nucleobase binding is found for bridging ligand binding modes involving the chelating diamine and the adeninyl group. Polymer chains derived with the shorter ethyl tether show binding at the N7 site of adeninyl, while binding at N1 is found in the longer propyl chain length.

Synthesis, Characterisation and Electrical Properties of Supramolecular DNA-Templated Polymer Nanowires of 2,5-(Bis-2-thienyl)-pyrrole

Supramolecular polymer nanowires have been prepared by using DNA-templating of 2,5-(bis-2-thienyl)-pyrrole (TPT) by oxidation with FeCl(3) in a mixed aqueous/organic solvent system. Despite the reduced capacity for strong hydrogen bonding in polyTPT compared to other systems, such as polypyrrole, the templating proceeds well. FTIR spectroscopic studies confirm that the resulting material is not a simple mixture and that the two types of polymer interact. This is indicated by shifts in bands associated with both the phosphodiester backbone and the nucleobases. XPS studies further confirm the presence of DNA and TPT, as well as dopant Cl(-) ions. Molecular dynamics simulations on a [{dA(24):dT(24)}/{TPT}(4)] model support these findings and indicate a non-coplanar conformation for oligoTPT over much of the trajectory. AFM studies show that the resulting nanowires typically lie in the 7-8 nm diameter range and exhibit a smooth, continuous, morphology. Studies on the electrical properties of the prepared nanowires by using a combination of scanned conductance microscopy, conductive AFM and variable temperature two-terminal I-V measurements show, that in contrast to similar DNA/polymer systems, the conductivity is markedly reduced compared to bulk material. The temperature dependence of the conductivity shows a simple Arrhenius behaviour consistent with the hopping models developed for redox polymers.

Reactions of Pd(II) with chelate-tethered 2,6-diaminopurine derivatives: N3-coordination and reaction of the purine system.

Alkyldiamine-tethered derivatives of 2,6-diaminopurine, ethylenediamine-N9-propyl-2,6-diaminopurine, L1, and ethylenediamine-N9-ethyl-2,6-diaminopurine, L2, react with Pd(II) to give N3-coordinated complexes. However, the exact nature of the resulting complex is dependent on the reaction conditions. With PdCl(2)(MeCN)(2) in MeCN/H(2)O the expected [PdCl(N3-2,6-DAP-alkyl-en)](+) complex, 1, is formed with L1 chelating the metal center in a tridentate manner through the diamine function and N3 of the purine base. However, under the same conditions the shorter, ethyl-tethered, L2 gives a complex dication, 2, containing a tetradentate ligand forming simultaneously 5-, 6-, and 7-membered chelate rings. This resulting acetamidine, derived by addition to coordinated MeCN, appears to be the first such case involving the 2-amino group of a purine. The ethyl-analogue of 1, [PdCl(N3-2,6-DAP-Et-en)](+) 3, was prepared by reaction of L2 with K(2)PdCl(4) in aqueous media.

Mononucleotide recognition by cyclic trinuclear palladium(ii) complexes containing 4,7-phenanthroline N,N bridgesElectronic supplementary information (ESI) available: ORTEP view of the [((S,S)-dach)Pd(4,7-phen)]36+ cations in the crystal structure of 2b. Experimental details of the partial crystal structure solution of 2b. See http://www.rsc.org/suppdata/dt/b4/b402602k/

Reaction of [(dach)Pd(NO3)2] entities (dach = (R,R)-1,2-diaminocyclohexane, (S,S)-1,2-diaminocyclohexane) and 4,7-phenanthroline (phen) providing, respectively, 90 and 120 degrees bond angles, leads to the formation of two novel positively charged homochiral cyclic trinuclear metallacalix[3]arene species [((R,R)-1,2-diaminocyclohexane)Pd(phen)]3(NO3)6 (2a) and [((S,S)-1,2-diaminocyclohexane)Pd(phen)]3(NO3)6 (2b). These species have been characterised by 1)H NMR and X-ray diffraction methods (2b), showing that they possess accessible cavities suited for supramolecular recognition processes. We prove, indeed, from 1H NMR studies the inclusion of mononucleotides inside the cavity of the trinuclear species [(ethylenediamino)Pd(phen)]3(6+) (1), [((R,R)-1,2-diaminocyclohexane)Pd(phen)]3(6+) (2a) and [((S,S)-1,2-diaminocyclohexane)Pd(phen)]3(6+) (2b) in aqueous solution. Association constants (K(ass)) range from 85 +/- 6 M(-1) for the interaction between [(ethylenediamine)Pd(phen)]3(6+) and adenosine monophosphate to 37 +/- 4 M(-1) for the interaction between [(1,2-diaminocyclohexane)Pd(phen)]3(6+) and thymidine monophosphate. We invoke the synergy of electrostatic, anion-pi and pi-pi interactions to explain the recognition of mononucleotides inside the cavity of the metallacalix[3]arenes.

DNA-based Inorganic and Polymer Nanowires: Synthesis, Characterization and Electrical Properties of Nanoelectronic Components

Individual DNA molecules have been used as templates for the formation of conducting nanowires. Both binary compound and molecular‐based materials have been prepared with this method. The nanowires are electrically conducting as confirmed by I/V measurements of single‐wire two‐terminal devices. Polymer‐based nanowires are shown to spontaneously aggregate over time to form nanoropes.