Polypyrrole nanowires formed by polymerization of pyrrole on a DNA template self‐assemble into rope‐like structures. These ‘nanoropes’ may be quite smooth (diameters 5–30 nm) or may show frayed ends where individual strands are visible. A combination of electric force microscopy, conductive atomic force microscopy and two‐terminal current–voltage measurements show that they are conductive. Nanoropes adhere more weakly to hydrophobic surfaces prepared by silanization of SiO2 than to the clean oxide; this effect can be used to aid the combing of the nanoropes across microelectrode devices for electrical characterization.

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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.

A set of cyclic tetranuclear complexes of the metallacalix[4]arene type with formula [{Pt(en)(L)}(4)](4+) (en=ethylenediamine; 2: LH=5-chloro-2-hydroxypyrimidine (5-Cl-Hpymo); 3: LH=5-bromo-2-hydroxypyrimidine (5-Br-Hpymo); 4: LH=5-iodo-2-hydroxypyrimidine (5-I-Hpymo)) have been obtained from the reaction between cis-protected square-planar [Pt(en)(H(2)O)(2)](2+) metal entities and LH in aqueous media. Additionally, the binding properties of 2, 3, 4 and their congener [{Pt(en)(L)}(4)](4+) (1: LH=2-hydroxypyrimidine (Hpymo)) with calf thymus-DNA (ct-DNA) have been studied by using different techniques including circular and linear dichroism (CD and LD, respectively) and UV-visible absorbance spectroscopies, gel electrophoresis, fluorescence competitive-binding studies and atomic force microscopy (AFM). The results are consistent with significant non-covalent interactions taking place between the polynuclear cyclic species and ct-DNA. Moreover, gel electrophoresis, linear dichroism titrations and AFM images of ct-DNA with metallacalixarenes show ct-DNA coiling at low metallacalixarene concentrations and upon subsequent increments in metallacalixarene concentration ct-DNA can be seen to uncoil with concomitant formation of long and inflexible ct-DNA structures.

The reaction of [(cymene)RuCl(2)](2) with K(2)Hoxonate (H(3)oxonic = 4,6-dihydroxy-2-carboxy-1,3,5-triazine acid) in methanol leads to the formation of the dinuclear half-sandwich ruthenium(II) complex [(cymene)(2)Ru(2)(mu-Hoxonato)Cl(2)] (1a). Removal of the chloride ligands of 1a by treatment with AgCF(3)SO(3) yields [(cymene)(2)Ru(2)(mu-Hoxonato)(CF(3)SO(3))(2)] (1b), which, upon posterior reaction with N,N'-linkers (L = 4,4'-bipyridine (4,4'-bpy), 4,7-phenantroline (4,7-phen)), gives rise to the formation of the tetranuclear open boxes [(cymene)(4)Ru(4)(mu-Hoxonato)(2)(mu-N,N'-L)(2)](CF(3)SO(3))(4) (2a, L = 4,4'-bpy; 2b, L = 4,7-phen). These systems have been characterized by (1)H NMR, UV-vis, and ESI-MS. The single-crystal structures of the dinuclear precursor 1a and of the clathrate 2b 4,7-phen have been determined. The interaction of these systems with cysteine, mononucleotides, and calf-thymus DNA has been studied by means of (1)H NMR, UV-vis, circular dicroism, competitive binding assays, and atomic force microscopy imaging. The results show that the robust tetracationic ruthenium(II) cyclic systems 2a and 2b do not give ligand exchange reactions toward biorelevant ligands. Nevertheless, these systems are able to noncovalently bind to DNA, probably at the surface of the major groove, inducing significant conformational changes in this biomolecule. It is also interesting to note that compounds 2a and 2b, in spite of only giving supramolecular interactions with biomolecules, exhibit antitumor activity, particularly toward the human ovarian cancer cell line A2780cisR, showing acquired resistance to cisplatin, with respective 4.6 and 8.3 microM IC(50) values.

Tuning the conducting and photoluminescence properties of molecules comprising silver(i)–cytosine base pairs.

The oligonucleotide d(TX)9 , which consists of an octadecamer sequence with alternating non-canonical 7-deazaadenine (X) and canonical thymine (T) as the nucleobases, was synthesized and shown to hybridize into double-stranded DNA through the formation of hydrogen-bonded Watson-Crick base pairs. dsDNA with metal-mediated base pairs was then obtained by selectively replacing W-C hydrogen bonds by coordination bonds to central silver(I) ions. The oligonucleotide I adopts a duplex structure in the absence of Ag(+) ions, and its stability is significantly enhanced in the presence of Ag(+) ions while its double-helix structure is retained. Temperature-dependent UV spectroscopy, circular dichroism spectroscopy, and ESI mass spectrometry were used to confirm the selective formation of the silver(I)-mediated base pairs. This strategy could become useful for preparing stable metallo-DNA-based nanostructures.

Details of the mechanism of formation of supramolecular polymer nanowires by templating on DNA are revealed for the first time using AFM. Overall these data reveal that the smooth, regular, structures produced are rendered by highly dynamic supramolecular transformations occurring over the micrometre scale. In the initial stages of the process a low density of conducting polymer (CP) binds to the DNA as, essentially, spherical particles. Further reaction time produces DNA strands which are more densely packed with particles giving a beads-on-a-string appearance. The particles subsequently undergo dynamic reconfiguration so as to elongate along the template axis and merge to yield the highly regular, smooth morphology of the final nanowire. MD simulations illustrate the early stages of the process showing the binding of globular CP to duplex DNA, while the latter stages can be modeled effectively by a linear thermodynamic description based on the balance between the line energy, which accounts for adhesion of the material to the template, and its surface tension. This model accounts for the phenomena observed in the AFM studies: the relative success of DNA templating of polymers compared to metals; the slow approach to equilibrium; and the observed thinning and 'necking' phenomena as the structures transform from beads-on-a-string to smooth nanowire.