skip to main content

Explore Research Products in the NSF-PAR

Title: Synthesis and Light‐Mediated Structural Disruption of an Azobenzene‐Containing Helical Poly(isocyanide)
Abstract

Helical poly(isocyanide)s are an important class of synthetic polymers possessing a static helical structure. Since their initial discovery, numerous examples of these helices have been fabricated. In this contribution, the synthesis of a chiral, azobenzene (azo)‐containing isocyanide monomer is reported. Upon polymerization with nickel(II) catalysts, a well‐defined circular dichroism (CD) trace is obtained, corresponding to the formation of a right‐handed polymeric helix. The helical polymer, dissolved in chloroform and irradiated with UV light (365 nm), undergoes acistotransisomerization of the azobenzene side‐chains. After the isomerization, a change in conformation of the helix occurs, as evidenced by CD spectroscopy. When the solution is irradiated with LED light, the polymer returns to a right‐handed helical conformation. To open up the possibility for chain‐end post‐polymerization modification of this light‐responsive system, an alkyne‐functionalized nickel(II) catalyst is also used in the polymerization of the azobenzene monomer, resulting in a stimuli‐responsive, terminal‐alkyne‐containing helical poly(isocyanide).

  more » « less
Award ID(s):
1902917
NSF-PAR ID:
10458921
Author(s) / Creator(s):
 ;  ;  
Publisher / Repository:
Wiley Blackwell (John Wiley & Sons)
Date Published:
Journal Name:
Macromolecular Rapid Communications
Volume:
41
Issue:
1
ISSN:
1022-1336
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; ( , Polymer chemistry)
    null (Ed.)
    We report poly(isocyanide)-based random copolymers (co-PIC) featuring alkoxycarbonyl-based side-chains synthesized via the metal-catalyzed controlled polymerization of chiral and achiral isocyanide monomers. The pyridine-functionalized achiral monomer provides functional sites while the chiral monomer drives the formation of a one-handed preferred helix. The side-chain functionalized helical polymer undergoes self-assembly with palladated pincer ligands, as evidenced by 1H NMR and UV-Vis spectroscopies. Circular dichroism (CD) spectroscopy confirms that the side-chain self-assembly does not affect the backbone helicity. We construct supramolecular helical brush copolymers via the metal coordination of the co-PIC backbone with telechelic poly(styrene)s. 1H NMR and UV-Vis spectroscopies confirm the metal coordination, and CD measurements suggest that the backbone retains its helical conformation. Additionally, viscometry measurements verify the formation of high molecular weight polymers while dynamic light scattering confirms the increasing hydrodynamic radii of the resulting supramolecular brush copolymers. Our methodology constructs complex 3D materials with fully synthetic, secondary structure containing building blocks. We view this as a platform for building architecturally controlled 3D supramolecular materials with high degrees of complexity. 
    more » « less
  2. ; ; ; ; ; ( , Advanced Functional Materials)
    Abstract

    The fabrication of truly hierarchically folded single‐chain polymeric nanoparticles with primary, secondary, and defined 3D architecture is still an unfulfilled goal. In this contribution, a polymer is reported that folds into a well‐defined 3D structure from a synthetic sheet‐helix block copolymer. The sheet‐like poly(p‐phenylene vinylene) (PPV) block is synthesized via the ring‐opening metathesis polymerization of a thymine‐bearing dialkoxy‐substituted [2.2]paracyclophane‐1,9‐diene. The PPV block is terminated with a Pd complex using a Pd‐containing chain‐terminating agent. The terminal Pd complex catalyzes the polymerization of isocyanide monomers with side‐chains containing either a chiral menthol or an achiral diaminopyridine resulting in the formation of a helical poly(isocyanide) (PIC) random copolymer. The PIC side‐chains are capable of engaging in complementary hydrogen‐bonding with thymine units along the PPV block resulting in the folding of the two secondary structural domains into a well‐defined 3D structure. The folding and unfolding of the polymer in both chloroform and THF are monitored using dynamic light scattering and NMR spectroscopy. This work is the first example of a hierarchically folded synthetic polymer featuring a defined 3D structure achieved by using two different polymer backbones with two distinct secondary structures.

     
    more » « less
  3. ; ( , Macromolecular Rapid Communications)
    Abstract

    True tertiary architectures with defined local secondary structures are rare in synthetic systems. Adapting well‐developed synthetic building blocks and controlling their folding through diverse interactions can be a general approach toward this goal. In this contribution, the synthesis of 3D hierarchical assemblies with distinct secondary domains formed through the intramolecular folding of a block copolymer containing a coil‐like poly(styrene) (PS) block with a helical poly(isocyanide) block induced by phenyl‐pentafluorophenyl quadrupole interactions is reported. The PS block is prepared via atom‐transfer radical polymerization and end functionalized with a nickel complex that serves as a macroinitiator for the polymerization of chiral isocyanides bearing pentafluorophenyl pendants. The folding behavior of the coil‐helix block copolymers is investigated by dynamic light scattering, NMR spectroscopy, wide‐angle X‐ray scattering, and differential scanning calorimetry.

     
    more » « less
  4. ; ; ; ( , Polymer Chemistry)
    We report the first heterotelechelic helical poly(methacrylamide) (PMAc) bearing orthogonal supramolecular binding sites on its chain-ends synthesized through a combination of reversible addition–fragmentation chain-transfer (RAFT) polymerization and thiol–bromo “click” chemistry. The heterotelechelic PMAc was assembled with two monotelechelic polymers featuring different secondary structures, namely a coil-like poly(styrene) and a helical poly(isocyanide), resulting in the formation of a coil–helix–helix supramolecular triblock copolymer through orthogonal metal coordination and hydrogen bonding interactions. Triblock assembly was confirmed through 1 H NMR spectroscopy, isothermal titration calorimetry (ITC) and viscometry. The individual polymer blocks retained their secondary structures in the final triblock copolymer, as evidenced by circular dichroism (CD) spectroscopy. Our synthetic strategy expands the toolbox of triblock copolymers featuring structural motifs similar to the ones found in proteins and provides the potential for the development of other complex multifunctional polymeric ensembles. 
    more » « less
  5. ; ; ; ; ; ; ; ; ; ; et al ( , Communications Chemistry)
    Abstract

    The discovery and application of new types of helical peptidic foldamers have been an attractive endeavor to enable the development of new materials, catalysts and biological molecules. To maximize their application potential through structure-based design, it is imperative to control their helical handedness based on their molecular scaffold. Herein we first demonstrate the generalizability of the solid-state right-handed helical propensity of the 413-helix of L-α/L-sulfono-γ-AA peptides that as short as 11-mer, using the high-resolution X-ray single crystallography. The atomic level folding conformation of the foldamers was also elucidated by 2D NMR and circular dichroism under various conditions. Subsequently, we show that the helical handedness of this class of foldamer is controlled by the chirality of their chiral side chains, as demonstrated by the left-handed 413-helix comprising 1:1 D-α/D-sulfono-γ-AA peptide. In addition, a heterochiral coiled-coil-like structure was also revealed for the first time, unambiguously supporting the impact of chirality on their helical handedness. Our findings enable the structure-based design of unique folding biopolymers and materials with the exclusive handedness or the racemic form of the foldamers in the future.

     
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email