Noncovalent synthesis of homo and hetero-architectures of supramolecular polymers via secondary nucleation.

The synthesis of supramolecular polymers with controlled architecture is a grand challenge in supramolecular chemistry. Although living supramolecular polymerization via primary nucleation has been extensively studied for controlling the supramolecular polymerization of small molecules, the resulting supramolecular polymers have typically exhibited one-dimensional morphology. In this report, we present the synthesis of intriguing supramolecular polymer architectures through a secondary nucleation event, a mechanism well-established in protein aggregation and the crystallization of small molecules. To achieve this, we choose perylene diimide with 2-ethylhexyl chains at the imide position as they are capable of forming dormant monomers in solution. Activating these dormant monomers via mechanical stimuli and hetero-seeding using propoxyethyl perylene diimide seeds, secondary nucleation event takes over, leading to the formation of three-dimensional spherical spherulites and scarf-like supramolecular polymer heterostructures, respectively. Therefore, the results presented in this study propose a simple molecular design for synthesizing well-defined supramolecular polymer architectures via secondary nucleation.

DNA-based communication in populations of synthetic protocells.

Developing molecular communication platforms based on orthogonal communication channels is a crucial step towards engineering artificial multicellular systems. Here, we present a general and scalable platform entitled 'biomolecular implementation of protocellular communication' (BIO-PC) to engineer distributed multichannel molecular communication between populations of non-lipid semipermeable microcapsules. Our method leverages the modularity and scalability of enzyme-free DNA strand-displacement circuits to develop protocellular consortia that can sense, process and respond to DNA-based messages. We engineer a rich variety of biochemical communication devices capable of cascaded amplification, bidirectional communication and distributed computational operations. Encapsulating DNA strand-displacement circuits further allows their use in concentrated serum where non-compartmentalized DNA circuits cannot operate. BIO-PC enables reliable execution of distributed DNA-based molecular programs in biologically relevant environments and opens new directions in DNA computing and minimal cell technology.

Modulation of Higher-order Behaviour in Model Protocell Communities by Artificial Phagocytosis.

Collective behaviour in mixed populations of synthetic protocells is an unexplored area of bottom-up synthetic biology. The dynamics of a model protocell community is exploited to modulate the function and higher-order behaviour of mixed populations of bioinorganic protocells in response to a process of artificial phagocytosis. Enzyme-loaded silica colloidosomes are spontaneously engulfed by magnetic Pickering emulsion (MPE) droplets containing complementary enzyme substrates to initiate a range of processes within the host/guest protocells. Specifically, catalase, lipase, or alkaline phosphatase-filled colloidosomes are used to trigger phagocytosis-induced buoyancy, membrane reconstruction, or hydrogelation, respectively, within the MPE droplets. The results highlight the potential for exploiting surface-contact interactions between different membrane-bounded droplets to transfer and co-locate discrete chemical packages (artificial organelles) in communities of synthetic protocells.

Enzyme-powered motility in buoyant organoclay/DNA protocells.

Reconstitution and simulation of cellular motility in microcompartmentalized colloidal objects have important implications for microcapsule-based remote sensing, environmentally induced signalling between artificial cell-like entities and programming spatial migration in synthetic protocell consortia. Here we describe the design and construction of catalase-containing organoclay/DNA semipermeable microcapsules, which in the presence of hydrogen peroxide exhibit enzyme-powered oxygen gas bubble-dependent buoyancy. We determine the optimum conditions for single and/or multiple bubble generation per microcapsule, monitor the protocell velocities and resilience, and use remote magnetic guidance to establish reversible changes in the buoyancy. Co-encapsulation of catalase and glucose oxidase is exploited to establish a spatiotemporal response to antagonistic bubble generation and depletion to produce protocells capable of sustained oscillatory vertical movement. We demonstrate that the motility of the microcapsules can be used for the flotation of macroscopic objects, self-sorting of mixed protocell communities and the delivery of a biocatalyst from an inert to chemically active environment. These results highlight new opportunities to constructing programmable microcompartmentalized colloids with buoyancy-derived motility.

Supramolecular Switching of Ion-Transport in Nanochannels.

Noncovalent approaches to achieve smart ion-transport regulation in artificial nanochannels have garnered significant interest in the recent years because of their advantages over conventional covalent routes. Herein, we demonstrate a simple and generic approach to control the surface charge in mesoporous silica nanochannels by employing π-electron-rich charged motifs (pyranine-based donors) to interact with the surface of mesoporous silica modified with π-electron-deficient motifs (viologen-based acceptors) through a range of noncovalent forces, namely, charge-transfer, electrostatic, and hydrophobic interactions. The extent of each of these interactions was independently controlled by molecular design and pH, while employing them in a synergistic or antagonistic fashion to modulate the binding affinity of the charged motifs. This enabled the precise control of the surface charge of the nanochannels to achieve multiple ion-transport states.

Supramolecular gating of ion transport in nanochannels.

Several covalent strategies towards surface charge-reversal in nanochannels have been reported with the purpose of manipulating ion transport. However, covalent routes lack dynamism, modularity and post-synthetic flexibility, and hence restrict their applicability in different environments. Here, we introduce a facile non-covalent approach towards charge-reversal in nanochannels (<10 nm) using strong charge-transfer interactions between dicationic viologen (acceptor) and trianionic pyranine (donor). The polarity of ion transport was switched from anion selective to ambipolar to cation selective by controlling the extent of viologen bound to the pyranine. We could also regulate the ion transport with respect to pH by selecting a donor with pH-responsive functional groups. The modularity of this approach further allows facile integration of various functional groups capable of responding to stimuli such as light and temperature to modulate the transport of ions as well as molecules.

Glucose- and pH-responsive charge-reversal surfaces.

We have shown a pH- and glucose-responsive charge reversal on silica surface through heterogeneous functionalization utilizing amines and boronic acid moieties. The dual responsiveness of the charge reversal has been unambiguously demonstrated through the desorption of charged chromophores. Interestingly, we observed a concentration-dependent desorption response to glucose at physiologically relevant levels.

Adaptive pores: charge transfer modules as supramolecular handles for reversible pore engineering of mesoporous silica.

We introduce a non-covalent pore engineering approach to achieve exceptional reversibility of functionalization in SBA-15 through viologen-pyranine charge transfer (CT) modules. By employing alkyl derivatives of pyranine as donors, we could exploit the strong CT interactions between pyranine and viologen to reversibly modify the pore size and philicity. The fast binding of the donors enables quick and facile functionalization within minutes at room temperature. The modularity of the approach enables modification of pores with custom-designed compositions, components, and functions. The high selectivity exhibited by viologen on the pore wall facilitated its use in a CT affinity column.