Double-stranded supramolecular assembly through salt bridge formation between rigid and flexible amidine and carboxylic acid strands.
A series of monomeric strands consisting of m-terphenyl backbones with chiral rigid C-linked (3) and flexible N-linked (5) formamidines and achiral carboxylic acid (4) and flexible carboxymethyl (6) residues were synthesized, and their duplex formations through amidinium-carboxylate salt bridges were investigated by NMR, circular dichroism (CD), and UV-visible spectroscopies. The salt bridge-derived duplex formation was largely dependent on the structures of the formamidine and carboxylic acid strands, and the C-linked formamidine strand 3 formed a more stable duplex with the complementary carboxylic acid strands (4 and 6) than did the flexible N-linked formamidine strand 5. The single crystal X-ray analysis revealed that the duplex 5.4 has a skewed right-handed double helical structure. A complementary duplex dimer was also synthesized from the dimers of 5 and 4 joined by diacetylene linkers. Variable-temperature CD measurements indicated that the duplex possesses a dynamic double helical structure resulting from the flexible N-linked formamidine units.
Iida
Hiroki
H
Department of Molecular Design and Engineering, Graduate School of Engineering, Nagoya University, Chikusa-ku, Nagoya 464-8603, Japan.
Shimoyama
Munenori
M
Furusho
Yoshio
Y
Yashima
Eiji
E
D000578:Amidines / Q000138:chemical synthesis* / Q000737:chemistry; D002264:Carboxylic Acids / Q000138:chemical synthesis* / Q000737:chemistry; D018360:Crystallography, X-Ray; D015394:Molecular Structure; D012492:Salts / Q000737:chemistry*; D013237:Stereoisomerism; D013696:Temperature
D000578:Amidines; D002264:Carboxylic Acids; D012492:Salts