skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.


Title: ortho ‐Phenylene‐Based Macrocyclic Hydrocarbons Assembled Using Olefin Metathesis
While many foldamer systems reliably fold into well‐defined secondary structures, higher order structure remains a challenge. A simple strategy for the organization of folded subunits in space is to link them together within a macrocycle. Previous work has shown thato‐phenylenes can be co‐assembled with rod‐shaped linkers into twisted macrocycles, showing an interesting synergy between folding and thermodynamically controlled macrocyclization. In these systems the foldamer units were largely decoupled from each other both conformationally and electronically. Here, we show that hydrocarbon macrocycles, with very short ethenylene linkers, can be assembled fromo‐phenylenes using olefin metathesis. Characterization by NMR spectroscopy, X‐ray crystallography, and ab initio calculations shows that the products are approximately triangular trimer macrocycles with helicalo‐phenylene corners in a heterochiral configuration. Their photophysics are dominated by the 4,4'‐diphenylstilbene moieties, the longest conjugated segments, with further conjugation broken by the twisting of theo‐phenylenes.  more » « less
Award ID(s):
1608213 1904236
PAR ID:
10183171
Author(s) / Creator(s):
 ;  ;  ;  
Publisher / Repository:
Wiley Blackwell (John Wiley & Sons)
Date Published:
Journal Name:
European Journal of Organic Chemistry
Volume:
2020
Issue:
34
ISSN:
1434-193X
Page Range / eLocation ID:
p. 5620-5625
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. null (Ed.)
    The self-assembly of foldamers into macrocycles is a simple approach to non-biological higher-order structure. Previous work on the co-assembly of ortho -phenylene foldamers with rod-shaped linkers has shown that folding and self-assembly affect each other; that is, the combination leads to new emergent behavior, such as access to otherwise unfavorable folding states. To this point this relationship has been passive. Here, we demonstrate control of self-assembly by manipulating the foldamers' conformational energy surfaces. A series of o -phenylene decamers and octamers have been assembled into macrocycles using imine condensation. Product distributions were analyzed by gel-permeation chromatography and molecular geometries extracted from a combination of NMR spectroscopy and computational chemistry. The assembly of o -phenylene decamers functionalized with alkoxy groups or hydrogens gives both [2 + 2] and [3 + 3] macrocycles. The mixture results from a subtle balance of entropic and enthalpic effects in these systems: the smaller [2 + 2] macrocycles are entropically favored but require the oligomer to misfold, whereas a perfectly folded decamer fits well within the larger [3 + 3] macrocycle that is entropically disfavored. Changing the substituents to fluoro groups, however, shifts assembly quantitatively to the [3 + 3] macrocycle products, even though the structural changes are well-removed from the functional groups directly participating in bond formation. The electron-withdrawing groups favor folding in these systems by strengthening arene–arene stacking interactions, increasing the enthalpic penalty to misfolding. The architectural changes are substantial even though the chemical perturbation is small: analogous o -phenylene octamers do not fit within macrocycles when perfectly folded, and quantitatively misfold to give small macrocycles regardless of substitution. Taken together, these results represent both a high level of structural control in structurally complex foldamer systems and the demonstration of large-amplitude structural changes as a consequence of a small structural effects. 
    more » « less
  2. Abstract ortho‐Phenylenes are one of the simplest classes of aromatic foldamers, adopting helical geometries because of aromatic stacking interactions. The folding and misfolding ofortho‐phenylenes are slow on the NMR timescale at or below room temperature, allowing detection of folding states using1H NMR spectroscopy. Herein, anortho‐phenylene hexamer is coupled with a RAFT chain transfer agent (CTA) on each repeat unit. A variety of acrylic monomers are polymerized onto the CTA‐functionalizedortho‐phenylene using PET‐RAFT to yield functionalized star polymers withortho‐phenylene cores. The steric bulk of the acrylate monomer units as well as the chain length of each arm of the star polymer is varied.1H NMR spectroscopy shows that the folding of theortho‐phenylenes do not vary, providing a robust helical core for star polymer systems. 
    more » « less
  3. Abstract Macrocycles are unique molecular structures extensively used in the design of catalysts, therapeutics and supramolecular assemblies. Among all reactions reported to date, systems that can produce macrocycles in high yield under high reaction concentrations are rare. Here we report the use of dynamic hindered urea bond (HUB) for the construction of urea macrocycles with very high efficiency. Mixing of equal molar diisocyanate and hindered diamine leads to formation of macrocycles with discrete structures in nearly quantitative yields under high concentration of reactants. The bulkyN-tert-butyl plays key roles to facilitate the formation of macrocycles, providing not only the kinetic control due to the formation of the cyclization-promotingcisC = O/tert-butyl conformation, but also possibly the thermodynamic stabilization of macrocycles with weak association interactions. The bulkyN-tert-butyl can be readily removed by acid to eliminate the dynamicity of HUB and stabilize the macrocycle structures. 
    more » « less
  4. Heterogeneous “linkers” are incorporated into polymers for a number of reasons, most commonly to facilitate the coupling of the targeted backbone segments. Due to their inclusion in the backbone, these linkers have the potential to affect the overall properties of the copolymer, even when present in relatively low weight percentages. To characterize the degree of impact of some common linkers, a set of polymers that incorporate both degradable sequenced segments and linkers were synthesized and systematically examined. Seven sequence-controlled olefin containing ester macrocycles were prepared, each with a unique central moiety, including a five-carbon alkyl chain, diethylene glycol, a urea, a thioether, a triazole, a bioaromatic, and an extension of the ester sequence. The macrocycles were polymerized via ED-ROMP to yield seven polymers that vary only in the the linker segment. The properties of all polymers were compared to determine the relative dominance of the different linker types. The properties tested in the study included thermal behavior, mechanical characteristics, hydrolytic degradation and film qualities. The thermal and mechanical properties proved to be dependent primarily on the ability of the linker to promote interchain interactions, as well as the weight fraction of the linker, whereas the hydrolytic degradation was dominated by the relative hydrophobicity of the linker groups. In all cases, the linker identity was a significant contributer to the behavior. 
    more » « less
  5. Just like atoms combine into molecules, colloids can self-organize into predetermined structures according to a set of design principles. Controlling valence—the number of interparticle bonds—is a prerequisite for the assembly of complex architectures. The assembly can be directed via solid “patchy” particles with prescribed geometries to make, for example, a colloidal diamond. We demonstrate here that the nanoscale ordering of individual molecular linkers can combine to program the structure of microscale assemblies. Specifically, we experimentally show that covering initially isotropic microdroplets withNmobile DNA linkers results in spontaneous and reversible self-organization of the DNA intoZ(N) binding patches, selecting a predictable valence. We understand this valence thermodynamically, deriving a free energy functional for droplet–droplet adhesion that accurately predicts the equilibrium size of and molecular organization within patches, as well as the observed valence transitions withN. Thus, microscopic self-organization can be programmed by choosing the molecular properties and concentration of binders. These results are widely applicable to the assembly of any particle with mobile linkers, such as functionalized liposomes or protein interactions in cell–cell adhesion. 
    more » « less