| Abstract
| - Development of a guanine nanowire (G-wire) that is controllable and can be switched by externalsignals is important for the creation of molecular electronic technologies. Here, we constructed a G-wire inwhich the thymines of the main chain of d(G4T4G4) were replaced with 2,2‘-bipyridine units, which havetwo aromatic rings that rotate arbitrarily upon coordination with metal ions. Circular dichroism of the DNAoligonucleotides with or without the 2,2‘-bipyridine unit showed that divalent metal ions induce the bipyridine-containing oligonucleotide to switch from an antiparallel to a parallel G-quadruplex. Native polyacrylamidegel electrophoresis showed that the parallel-stranded G-quadruplex DNA had a high-order structure. Circulardichroism and native gel electrophoresis analyses suggested that adding Na2EDTA causes a reversestructural transition from a parallel-stranded high-order structure to an antiparallel G-quadruplex. Moreover,atomic force microscopy showed a long nanowire (∼200 nm) in the presence of Ni2+ but no significantimage in the absence of Ni2+ or in the presence of both Ni2+ and Na2EDTA. These observations revealedthat the parallel-stranded high-order structure is a G-wire containing numerous DNA oligonucleotide strandsbound together via divalent metal ion−2,2‘-bipyridine complexes. Finally, we found that alternating additionof Ni2+ and Na2EDTA can cycle the G-wire between the high-order and disorganized structures, with anaverage cycling efficiency of 0.95 (i.e., 5% loss per cycle). These results demonstrate that a DNAoligonucleotide incorporating the 2,2‘-bipyridine unit acts as a G-wire switch that can be controlled bychemical input signals, namely, divalent metal ions.
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