Junya Yoshida

Chiral introduction of positive charges to PNA for double-duplex invasion to versatile sequences

Invasion of two PNA strands to double-stranded DNA is one of the most promising methods to recognize a predetermined site in double-stranded DNA (PNA = peptide nucleic acid). In order to facilitate this ‘double-duplex invasion’, a new type of PNA was prepared by using chiral PNA monomers in which a nucleobase was bound to the α-nitrogen of N-(2-aminoethyl)-d-lysine. These positively charged monomer units, introduced to defined positions in Nielsens PNAs (poly[N-(2-aminoethyl)glycine] derivatives), promoted the invasion without impairing mismatch-recognizing activity. When pseudo-complementary nucleobases 2,6-diaminopurine and 2-thiouracil were bound to N-(2-aminoethyl)-d-lysine, the invasion successfully occurred even at highly G–C-rich regions [e.g. (G/C)7(A/T)3 and (G/C)8(A/T)2] which were otherwise hardly targeted. Thus, the scope of sequences available as the target site has been greatly expanded. In contrast with the promotion by the chiral PNA monomers derived from N-(2-aminoethyl)-d-lysine, their l-isomers hardly invaded, showing crucial importance of the d-chirality. The promotion of double-duplex invasion by the chiral (d) PNA monomer units was ascribed to both destabilization of PNA/PNA duplex and stabilization of PNA/DNA duplexes.

Anion substitution in hydrogen-bonded organic conductors: the chemical pressure effect on hydrogen-bond-mediated phase transition

We have synthesized three kinds of novel hydrogen-bonded (H-bonded) organic conductor, β′-[H3(Cat-EDO-TTF)2]X (X = ClO4, PF6, AsF6; Cat-EDO-TTF = catechol-fused ethylenedioxytetrathiafulvalene), as anion-substituted analogues of the parent BF4 salt (X = BF4). These salts are all isostructural, however, only the BF4 salt shows a phase transition, upon which the molecular arrangement and physical properties are drastically changed in cooperation with bending of the H-bond. A systematic comparison of their crystal and electronic structures disclosed that a significant chemical pressure is generated by the present anion substitution, causing differences in their physical properties and phase transition nature. Interestingly, this chemical pressure is highly anisotropic, which exclusively changes the side-by-side interactions between the Cat-EDO-TTF skeletons in the π-stacking layer. Therefore, we conclude that this unique phase transition is caused by a cooperation of the intercolumnar side-by-side interactions with the π–π intra-dimer interactions and H-bond bending.