Title
Effect of the α-substituted chiral side chain on the helical conformation of N-substituted poly(p-benzamide)
Author
Akihiro Yokoyama, Tomoaki Saiki, Hyuma MasucIsa, Azumaya, Tsutomu Yokozawa
Year
2018
Journal
Polymer
Abstract
The effect of the side chain chiral center position on the secondary structure of oligomers and polymers of N-substituted 4-aminobenzoic acid was studied. Monomer 1 was prepared from l-alanine methyl ester hydrochloride in seven steps. The poly(p-benzamide) having an α-substituted side chain at the nitrogen atom (α-Me-PA) was obtained from the polymerization of 1 with triethylsilane, CsF, and 18-crown-6 in THF. The circular dichroism (CD) studies in solution demonstrated that α-Me-PA adopted a right-handed helical conformation in protic polar solvents, such as water and methanol, and a random structure in chloroform, indicating that solvophobic interactions played an important role in the helical folding of α-Me-PA. The tetramer of (S)-4-(sec-butylamino)benzoic acid was synthesized as a model compound of α-Me-PA. The single crystal X-ray analysis of the tetramer revealed that the right- and left-handed helical molecules existed in a one-to-one ratio in the crystal, and that the screw pitch of the right-handed helix was shorter than the left-handed helix.
Instrument
J-820
Keywords
Circular dichroism, Secondary structure, Chemical stability, Thermal stability, Polymers