Biomedical subjects

Namiki Toyama

Publications and source records attributed to Namiki Toyama.

3 recordsLinked to original sources

PubMed2003

A discrete self-assembled metal array in artificial DNA.

DNA has a structural basis to array functionalized building blocks. Here we report the synthesis of a series of artificial oligonucleotides, d(5'-GH(n)C-3') (n = 1 to 5), with hydroxypyridone nucleobases (H) as flat bidentate ligands. Right-handed double helices of the oligonucleotides, nCu2+.d(5'-GH(n)C-3')2 (n = 1 to 5), were quantitatively formed through copper ion (Cu2+)-mediated alternative base pairing (H-Cu2+-H), where the Cu2+ ions incorporated into each complex were aligned along the helix axes inside the duplexes with the Cu2+-Cu2+ distance of 3.7 +/- 0.1 angstroms. The Cu2+ ions were coupled ferromagnetically with one another through unpaired d electrons to form magnetic chains.

Base Pairing↗

PubMed2003

Artificial metallo-DNA: structural control and discrete metal assembly.

To array Cu2+ ions within a double-stranded DNA along the helix axis in a controllable manner, a series of artificial oligonucleotides, d(5'-GHnC-3') (n = 1-5), were synthesized, where H is a hydroxypyridone nucleobase. Right-handed double helices of the oligonucleotides, nCu2+ x d(5'-GHnC-3')2 (n = 1-5), were quantitatively formed through Cu2+-mediated metallo-base pairing (H-Cu2+-H). The Cu2+ ions incorporated into each duplex were aligned along the helix axes with the Cu2+-Cu2+ distance of 3.7 +/- 0.1 A. The unpaired d electrons of the Cu2+ ions were coupled ferromagnetically with one another to form magnetic chains.

DNA↗

PubMed2002

Efficient incorporation of a copper hydroxypyridone base pair in DNA.

Recently, we reported the first artificial nucleoside for alternative DNA base pairing through metal complexation (J. Org. Chem. 1999, 64, 5002-5003). In this regard, we report here the synthesis of a hydroxypyridone-bearing nucleoside and the incorporation of a neutral Cu(2+)-mediated base pair of hydroxypyridone nucleobases (H-Cu-H) in a DNA duplex. When the hydroxypyridone bases are incorporated into the middle of a 15 nucleotide duplex, the duplex displays high thermal stabilization in the presence of equimolar Cu(2+) ions in comparison with a duplex containing an A-T pair in place of the H-H pair. Monitoring temperature dependence of UV-absorption changes verified that a Cu(2+)-mediated base pair is stoichiometrically formed inside the duplex and dissociates upon thermal denaturation at elevated temperature. In addition, EPR and CD studies suggested that the radical site of a Cu(2+) center is formed within the right-handed double-strand structure of the oligonucleotide. The present strategy could be developed for controlled and periodic spacing of neutral metallobase pairs along the helix axis of DNA.

Base Pairing↗