Mitsunobu Nakamura

The molecular arrangement of functional chromophores is essential to construct functional nanomaterials. Synthetic DNA has been used as a structural scaffold to control and construct molecular assembly. We now describe the formation of artificial DNA/porphyrin complexes where porphyrins working as photoactive molecules were placed at specific locations on the DNA through a non-covalent interaction. Spectroscopic analysis by UV/vis, circular dichroism (CD), and melting temperature measurements showed that the binding of water-soluble porphyrin derivatives with methylpyridinium groups (TMPyP and DMPyP) to DNA can be directed by hydrophobic cavities composed of a pair of abasic site analogs (dS). CD measurements showed that the two porphyrins can be accommodated at two specific sites when the DNA molecule had two cavities, as evidenced by the exciton-coupled CD spectra of the porphyrins. Photoelectrochemical experiments showed that the DNA complexes accommodating DMPyP at specific locations can respond to light excitation to generate a photocurrent when immobilized on the electrode surface. Our results demonstrated that the control of the porphyrin binding using the dS/dS pair is a useful approach to construct artificial DNA with porphyrin molecules, leading to the design of photoresponsive materials and photoelectrochemical sensors.

B- to Z-DNA transitions play a crucial role in biological systems and have attracted the interest of researchers for their applications in DNA nanotechnology. DNA and DNA analogues have also been used as templates to construct helical chromophore associations with π interactions. In this work, the B- to Z-DNA transition-induced switching of pyrene in an association manner was evaluated using DNA duplexes with non-nucleosidic pyrene residues in the middle of d(CG) repeat sequences. One of the pyrene-labeled DNAs was shown to exhibit inverted exciton coupled circular dichroism signals upon pyrene association through a B- to Z-DNA transition. This observation indicates that pyrene association switches the DNA conformation from right- to left-handed. Interestingly, the fluorescence of the pyrene-labeled DNA duplex also dynamically changed upon switching of the pyrene in an association-based manner. Taken together, these studies demonstrate that pyrene-labeled DNA shows promise as a chiroptical molecular switch.

The construction of zipper-like chromophore-arrays in the major groove of duplex DNA remains a challenge because only a few chromophores for this application have been discovered. To address the challenge, dual-chromophore labeled DNAs having a self-complementary sequence were prepared using a solid-phase, post-synthetic, copper-catalyzed, alkyne-azide cycloaddition. The resulting chromophore-arrays on the labeled DNA duplexes were characterized. The dual-tetraphenylethene (TPE) or dual-pyrene (Py) labeled DNA formed self-complementary B-form duplexes and resulted in the construction of chromophore-arrays in the major groove. The TPE-arrays, in which TPEs were arranged in a zipper-like fashion, slightly destabilized the duplex because of their bulkiness and exhibited aggregation-induced-emission. The Py-arrays, in which Pys were not arranged in a zipper-like fashion, had no effect on duplex stability and exhibited weak excimer emission because Py was sufficiently small for free rotation in the major groove.

We here describe a photocurrent generation system exploiting gold nanoparticles (AuNPs) that cover perylenediimide-DNA complexes on electrode surfaces. Enhanced photocurrents were generated by the irradiation of the AuNPs, attributed to the efficient excitation of the perylenediimides by a local electric field on the surface of the AuNPs.