265137-18-6Relevant academic research and scientific papers
Synthesis and hierarchical structures of amphiphilic polyphenylacetylenes carrying L-valine pendants
Li, Bing Shi,Cheuk, Kevin K.L.,Ling, Liansheng,Chen, Junwu,Xiao, Xudong,Bai, Chunli,Tang, Ben Zhong
, p. 77 - 85 (2003)
In this work, we synthesized amino acid-containing poly(phenylacetylene)s and demonstrated the possibility of tuning their hierarchical structures by internal and external perturbations. A valine-acetylene adduct, 4-ethynylbenzoyl-L-valine methyl ester (5), was readily polymerized by [Rh(nbd)Cl]2, and the resultant polyester (1) was selectively hydrolyzed by KOH to its polyacid congener, poly(4-ethynylbenzoyl-L-valine) (2). (Supra)molecular structures of the polymers were characterized by NMR, IR, UV, CD, and AFM techniques. The macromolecules took helical chain conformations in solutions. Their Cotton effects varied to different extents, when the polymer, solvent, and pH changed respectively from i to 2, from methanol to THF, and from neutral to basic. Upon evaporation of their methanol solutions, 1 and 2 self-assembled into micellar spheres and helical cables, respectively. Changing the solvent of i to THF changed its folding structure to helical cables, while increasing the pH of the methanol solution of 2 led to the formation of random threads. The denaturation from helical cables to random threads is probably caused by the cleavage of interstrand hydrogen bonds by base-mediated ionization of carboxyl groups of the valine pendants.
Raman Optical Activity (ROA) as a New Tool to Elucidate the Helical Structure of Poly(phenylacetylene)s
Casado, Juan,Freire, Félix,Medina, Samara,Palomo, Luis,Qui?oá, Emilio,Ramírez, Francisco J.,Rodríguez, Rafael
supporting information, p. 9080 - 9087 (2020/04/15)
Poly(phenylacetylene)s are a family of helical polymers constituted by conjugated double bonds. Raman spectra of these polymers show a structural fingerprint of the polyene backbone which, in combination with its helical orientation, makes them good candidates to be studied by Raman optical activity (ROA). Four different well-known poly(phenylacetylene)s adopting different scaffolds and ten different helical senses have been prepared. Raman and ROA spectra were recorded and allowed to establish ROA-spectrum/helical-sense relationships: a left/right-handed orientation of the polyene backbone (Mhelix/Phelix) produces a triplet of positive/negative ROA bands. Raman and ROA spectra of each polymer exhibited the same profile, and the sign of the ROA spectrum was opposite to the lowest-energy electronic circular dichroism (ECD) band, indicating a resonance effect. Resonance ROA appears then as an indicator of the helical sense of poly(phenylacetylene)s, especially for those with an extra Cotton band in the ECD spectrum, where a wrong helical sense is assigned based on ECD, while ROA alerts of this misassignment.
