Stability Enhancement of a π-Stacked Helical Structure Using Substituents of an Amino Acid Side Chain: Helix Formation via a Nucleation-Elongation Mechanism.
J Am Chem Soc
; 144(13): 6080-6090, 2022 04 06.
Article
en En
| MEDLINE
| ID: mdl-35325538
ABSTRACT
Molecular design involving the incorporation of an α-amino acid residue into the side chain or main chain of a polymer is often used to stabilize artificial molecular architectures through intramolecular hydrogen bonding. However, this molecular design strategy rarely considers the importance of interactions between substituents at the α-position of amino acid moieties, as found in nature. Herein, we report the synthesis of a novel series of π-stacked helical poly(quinolylene-2,3-methylene) with amino acid derivatives bearing different substituents at the α-position. We found that the thermal stability of π-stacked helical poly(quinolylene-2,3-methylene) is significantly improved by packing the substituents in the empty spaces between the side chains. In particular, when a bulky cyclohexyl alanine derivative was used as the side chain, the π-stacked helical structure maintained its stability even in dimethylsulfoxide, a hydrogen bond competitor. The stabilization of the π-stacked structure by the amino acid substituents resulted in a unique polymerization behavior involving nucleation-elongation steps. In the case of derivatives with leucine and cyclohexyl alanine, which form stable π-stacked helical structures, metastable structures with entangled main chains were formed in the initial polymerization stage. These structures subsequently underwent an irreversible structural change to achieve a thermodynamically stable helical π-stacked conformation as a nucleus for subsequent polymerization. Thereafter, the polymerization reaction proceeded with the elongation of the π-stacked helical structure. Differences in the stability of these systems indicated that the amino acid substituents on the side chains determine the most thermodynamically stable π-stacked helical structure.
Texto completo:
1
Colección:
01-internacional
Base de datos:
MEDLINE
Asunto principal:
Alanina
/
Aminoácidos
Idioma:
En
Revista:
J Am Chem Soc
Año:
2022
Tipo del documento:
Article