Abstract
Compartmentalization of reactions is ubiquitous in biochemistry. Self-reproducing lipids are widely studied as chemical models of compartmentalized biological systems. Here, we explore the effect of catalyst location on copper-catalyzed azide–alkyne cycloadditions which drive the self-reproduction of micelles from phase-separated components. Tuning the hydrophilicity of the copper-ligand complex, so that hydro-phobic or -philic catalysts are used in combination with hydro-philic and -phobic coupling partners, provides a wide range of reactivity patterns. Analysis of the kinetic data shows that reactions with a hydrophobic catalyst are faster than with a hydrophilic catalyst. Diffusion-ordered spectroscopy experiments suggest compartmentalization of the hydrophobic catalyst inside micelles while the hydrophilic catalyst remains in the bulk aqueous phase. The autocatalytic effects observed can be tuned by varying reactant structure and coupling a hydrophilic alkyne and hydrophobic azide results in a more pronounced autocatalytic effect. We propose and test a model that rationalizes the observations in terms of the phase behavior of the reaction components and catalysts.
Highlights
Compartmentalized reactions may occur inside nano- or microscale species such as micelles, vesicles, and emulsion droplets.[1]
Findings in terms of the system’s phase behavior and how the As previously reported, reaction between hydrophilic maltose catalyst and the reaction events are localized by compartmen- azide 1 and hydrophobic aliphatic alkyne 2 via a CuAAC forms talization
This study has shown that a secondary catalyst promoting CuAAC reactions can be used to tune the kinetics of a system that is autocatalytic as a whole by virtue of phase behavior
Summary
Compartmentalized reactions may occur inside nano- or microscale species such as micelles, vesicles, and emulsion droplets.[1]. Lipid-based compartments have been studied as simple models of cellular membranes[9−11] and display complex aggregation behavior including deformation and division.[12−15] The chemical self-reproduction of synthetic micelles and vesicles has been used to drive the growth and division processes[16−18] and serve as minimal metabolic networks where compartmentalized reactions generate self-organizing components of the compartment.[19,20] In physical autocatalytic processes surfactants are initially slowly formed through the reaction of two phase separated reagents at the interface of a biphasic system (Figure 1A, step 1).[21−31] Once a critical concentration of the products is reached, supramolecular aggregates form allowing the reaction components to interact by compartmentalization and subsequent solubilization into the opposing phase, facilitating further surfactant formation (step 2).[24] The formation of these aggregates can probably be viewed most as an extension of the interface where phase separated reagents are capable of interacting. We examine different combinations of hydrophobic and Received: December 10, 2018 Published: January 30, 2019
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