Toshihiro Ihara

Detection of higher-ordered DNA sequence by using terbium(III) luminescence

The detection of higher-ordered sequences of DNA such as the dyad symmetrical sequence was investigated using Tb(III) luminescence, based on energy transfer from excited bases in a single stranded DNA probe. An oligonucleotide carrying an iminodiacetic acid function as metal chelating moiety was used as the probe. The Tb(III) complex with this probe gave luminescence characteristic of Tb(III). The intensity of this luminescence was considerably suppressed when bound to the targeted double stranded DNA to form a triple helix. This behavior was especially pronounced when the probe forms a 2:1 (probe strand: Tb(III)) complex on the target double strand carrying a dyad symmetrical base sequence. When the analyte DNA strand does not contain a complementary sequence to the probe, the intensity of the luminescence was scarcely influenced. This characteristic luminescence change will be useful for detecting target genes having a higher-ordered sequence.

Bis-9-acridinyl derivative containing a viologen linker chain: Electrochemically active intercalator for reversible labelling of DNA

A new synthetic bis-9-acridinyl derivative containing a viologen linker chain binds strongly to DNA and shows a typical cyclic voltammogram, indicating a potential for use as a reversible electochemical labelling agent for DNA.

Synthetic DNA Ligands Conjugated with Metal Binding Moiety. Regulation of the Interaction with DNA by Metal Ions and the Ligand Effect on Metal Assisted DNA Cleaving

Abstract Various functionalized molecules were synthesized by covalently conjugating DNA intercalators with metal chelators which carry such metal-binding functional groups as ethers, polyamines, and carboxylates. Systematic studies were made on the interaction of these conjugates with DNA in the presence and in the absence of metal ions. DNA binding of the conjugates were strongly affected by coexisting metal ions. This can be accounted for by the change in the net charge and in the conformation of the conjugates through complexation with metal ions. In some of the complexes thus obtained (DNA-intercalator-metal ion ternary complexes), DNA underwent a metal assisted cleavage of the strand, the activities of which were highly dependent on the nature of metal chelating moieties adopted. It is likely that a residual Lewis acidity on the metal in the complex and the strain in the DNA backbone induced by intercalation contribute to facilitate DNA cleavage.

Novel method of detecting mismatch on DNA by using photo-induced electron transfer through DNA

Abstract Novel methodology for detecting a defect on double stranded DNA was presented, the principle being based on the dependence of the efficiency of photo-induced electron transfer through double stranded DNA on the structural disorders in the base stacking. The efficiency of photo-induced electron transfer between 5,10,15,20-tetrakis( N -methylpyridinium-4-yl)-21H,23H-porphine tetrachloride and N , N ′-dimethyl-4,7-phenanthrolinium dichloride on double stranded DNA was changed by several base-mispairing on the double stranded DNA. This phenomenon will be useful for the development of the convenient method of detecting mismatch on DNA duplex in homogeneous solution.

A zwitterionic anthraquinone derivative : first zwitterionic DNA binding ligand

The anthraquinone derivative (2) is the first example of a zwitterionic DNA-binding ligand, interacting with DNA through outside binding rather than through intercalation which is characteristic of its cationic, parent compound (1).