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Conditional Copper-Catalyzed Azide-Alkyne Cycloaddition by Catalyst Encapsulation.

ABSTRACT: Supramolecular encapsulation is known to alter chemical properties of guest molecules. We have applied this strategy of molecular encapsulation to temporally control the catalytic activity of a stable copper(I)-carbene catalyst. Encapsulation of the copper(I)-carbene catalyst by the supramolecular host cucurbit[7]uril (CB[7]) resulted in the complete inactivation of a copper-catalyzed alkyne-azide cycloaddition (CuAAC) reaction. The addition of a chemical signal achieved the near instantaneous activation of the catalyst, by releasing the catalyst from the inhibited CB[7] catalyst complex. To broaden the scope of our on-demand CuAAC reaction, we demonstrated the protein labeling of vinculin with the copper(I)-carbene catalyst, to inhibit its activity by encapsulation with CB[7] and to initiate labeling at any moment by adding a specific signal molecule. Ultimately, this strategy allows for temporal control over copper-catalyzed click chemistry, on small molecules as well as protein targets.

SUBMITTER: Breve TG

PROVIDER: S-EPMC7318279 | biostudies-literature | 2020 Jun

REPOSITORIES: biostudies-literature

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Conditional Copper-Catalyzed Azide-Alkyne Cycloaddition by Catalyst Encapsulation.

Brevé Tobias G TG Filius Mike M Araman Can C van der Helm Michelle P MP Hagedoorn Peter-Leon PL Joo Chirlmin C van Kasteren Sander I SI Eelkema Rienk R

Angewandte Chemie (International ed. in English) 20200407 24

Supramolecular encapsulation is known to alter chemical properties of guest molecules. We have applied this strategy of molecular encapsulation to temporally control the catalytic activity of a stable copper(I)-carbene catalyst. Encapsulation of the copper(I)-carbene catalyst by the supramolecular host cucurbit[7]uril (CB[7]) resulted in the complete inactivation of a copper-catalyzed alkyne-azide cycloaddition (CuAAC) reaction. The addition of a chemical signal achieved the near instantaneous a ...[more]

PMID: 32180306

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Project description:We described in a previous communication a variant of the popular Cu(I)-catalyzed azide-alkyne cycloaddition (AAC) process where 5 mol % of Cu(OAc)(2) in the absence of any added reducing agent is sufficient to enable the reaction. 2-Picolylazide (1) and 2-azidomethylquinoline (2) were found to be by far the most reactive carbon azide substrates that convert to 1,2,3-triazoles in as short as a few minutes under the discovered conditions. We hypothesized that the abilities of 1 and 2 to chelate Cu(II) contribute significantly to the observed high reaction rates. The current work examines the effect of auxiliary ligands near the azido group other than pyridyl for Cu(II) on the efficiency of the Cu(OAc)(2)-accelerated AAC reaction. The carbon azides capable of binding to the catalytic copper center at the alkylated azido nitrogen in a chelatable fashion were indeed shown to be superior substrates under the reported conditions. The chelation between carbon azide 11 and Cu(II) was demonstrated in an X-ray single-crystal structure. In a limited set of examples, the ligand tris(benzyltriazolylmethyl)amine (TBTA), developed by Fokin et al. for assisting the original Cu(I)-catalyzed AAC reactions, also dramatically enhances the Cu(OAc)(2)-accelerated AAC reactions involving nonchelating azides. This observation leads to the hypothesis of an additional effect of chelating azides on the efficiencies of Cu(OAc)(2)-accelerated AAC reactions, which is to facilitate the rapid reduction of Cu(II) to highly catalytic Cu(I) species. Mechanistic studies on the AAC reactions with particular emphasis on the role of carbon azide/copper interactions will be conducted based on the observations reported in this work. Finally, the immediate utility of the product 1,2,3-triazole molecules derived from chelating azides as multidentate metal coordination ligands is demonstrated. The resulting triazolyl-containing ligands are expected to bind with transition metal ions via the N(2) nitrogen of the 1,2,3-triazolyl group to form nonplanar coordination rings. The Cu(II) complexes of bidentate T1 and tetradentate T6 and the Zn(II) complex of T6 were characterized by X-ray crystallography. The structure of [Cu(T1)(2)(H(2)O)(2)](ClO(4))(2) reveals the interesting synergistic effect of hydrogen bonding, π-π stacking interactions, and metal coordination in forming a one-dimensional supramolecular construct in the solid state. The tetradentate coordination mode of T6 may be incorporated into designs of new molecule sensors and organometallic catalysts.

Project description:ObjectivesPolymerization shrinkage stress and factors involved in the stress development such as volumetric shrinkage and modulus were investigated in photo-CuAAC (photo-initiated copper(I)-catalyzed azide-alkyne cycloaddition) polymerization and compared with conventional BisGMA-based methacrylate polymerization for their use as alternative dental resins.MethodsTri-functional alkyne and di-functional azide monomers were synthesized for photo-CuAAC polymerization. Conversion kinetics, stress development and polymerization shrinkage were determined with FTIR spectroscopy, tensometery, and with a linometer, respectively, for CuAAC and BisGMA-based monomer mixtures using a camphorquinone/amine visible light photoinitiator system. Thermo-mechanical properties for the cured polymer matrices were characterized by dynamic mechanical analysis and in three-point bending on a universal testing machine. Polymerization kinetics, polymerization shrinkage stress, dynamic volumetric shrinkage, glass transition temperature (Tg), flexural modulus, flexural strength, and flexural toughness were compared between the two different resin systems.ResultsA glassy CuAAC polymer (Tg=62°C) exhibited 15-25% lower flexural modulus of 2.5±0.2GPa and flexural strength of 117±8MPa compared to BisGMA-based polymer (Tg=160°C) but showed considerably higher energy absorption around 7.1MJ×m-3 without fracture when strained to 11% via three-point bend compared to the flexural toughness of 2.7MJ×m-3 obtained from BisGMA-based polymer. In contrast to BisGMA-based polymers at 75% functional group conversion, the CuAAC polymerization developed approximately three times lower shrinkage stress with the potential to achieve quantitative conversion under ambient temperature photocuring conditions. Moreover, relatively equivalent dynamic volumetric shrinkage of around 6-7% was observed via both CuAAC and dimethacrylate polymerization, suggesting that the low shrinkage stress of CuAAC polymerization was due to delayed gelation along with slower rate of polymerization and the formation of a more compliant network structure.SignificanceCuAAC crosslinked networks possessed high toughness and low polymerization shrinkage stress with quantitative conversion, which eliminated obstacles associated with BisGMA-based dental resins including limited conversion, unreacted extractable moieties, brittle failure, and high shrinkage stress.

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Conditional Copper-Catalyzed Azide-Alkyne Cycloaddition by Catalyst Encapsulation.

Publications

Conditional Copper-Catalyzed Azide-Alkyne Cycloaddition by Catalyst Encapsulation.

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