Selection between Competing Self-Reproducing Lipids: Succession and Dynamic Activation

Self-replicating nanomaterials as a new generation of smart nanostructures

Self-replication is the process by which a system or entity autonomously reproduces or generates copies of itself, transmitting hereditary information through its molecular structure. Self-replication can be attractive for various researchers, ranging from biologists focused on uncovering the origin of life, to synthetic chemists and nanotechnologists studying synthetic machines and nanorobots. The capability of a single structure to act as a template to produce multiple copies of itself could allow the bottom-up engineering of progressively complex reaction networks and nanoarchitectures from simple building blocks. Herein, we review nucleic acid-based and amino acid-based self-replicating systems and completely synthetic artificial systems and specially focused on specific aspects of self-replicating nanomaterials. We describe their mechanisms of action and provide a full discussion of the principal requirements for achieving nanostructures capable of self-replication.

Amplification of Asymmetry via Structural Transitions in Supramolecular Polymer-Surfactant Coassemblies

Asymmetric structures are widespread in nature and essential for life and biointeractive materials. Although nature uniformly operates with homochirality, the hierarchical control of asymmetry in synthetic, water-soluble molecular systems is still underexplored. In this work, we present the amplification of helical asymmetry of benzene-1,3,5-tricarboxamide (BTA) supramolecular polymers by coassembly with homochiral nonionic surfactants. For these mixtures, a strong amplification of asymmetry was observed from the surfactant's molecular chirality to a preferred helicity of the coassembled polymers. This amplification showed maxima at identical stoichiometric ratios for structurally distinct chiral surfactants, demonstrating the similarity of the coassembly mechanism. Notably, the surfactant-induced asymmetry was completely overridden by the introduction of stereogenic centers into the BTA structure, emphasizing the subtlety of the amplification process. Using a combination of spectroscopy and microscopy, we found that surfactants coassemble with the supramolecular polymers to change fiber morphology from racemic double helices to single helices with a preferred handedness. Furthermore, the coassemblies showed a unique combination of structures and dynamics. Our results elucidate the consequences of supramolecular polymer-surfactant coassembly, offering valuable insights into the resulting asymmetric structures.

A Chemical Reaction Network Drives Complex Population Dynamics in Oscillating Self-Reproducing Vesicles

We report chemically fueled oscillations of vesicles. The population cycling of vesicles is driven by their self-reproduction and collapse within a biphasic reaction network involving the interplay of molecular and supramolecular events. We studied the oscillations on the molecular and supramolecular scales and tracked vesicle populations in time by interferometric scattering microscopy and dynamic light scattering. Complex supramolecular events were observed during oscillations─including vesicle reproduction, growth, and decomposition─and differences in the number, size, and mass of aggregates can often be observed within and between pulses. This system's dynamic behavior is reminiscent of a reproductive cycle in living cells.

From autocatalysis to survival of the fittest in self-reproducing lipid systems

Studying autocatalysis - in which molecules catalyse their own formation - might help to explain the emergence of chemical systems that exhibit traits normally associated with biology. When coupled to other processes, autocatalysis can lead to complex systems-level behaviour in apparently simple mixtures. Lipids are an important class of chemicals that appear simple in isolation, but collectively show complex supramolecular and mesoscale dynamics. Here we discuss autocatalytic lipids as a source of extraordinary behaviour such as primitive chemical evolution, chemotaxis, temporally controllable materials and even as supramolecular catalysts for continuous synthesis. We survey the literature since the first examples of lipid autocatalysis and highlight state-of-the-art synthetic systems that emulate life, displaying behaviour such as metabolism and homeostasis, with special consideration for generating structural complexity and out-of-equilibrium models of life. Autocatalytic lipid systems have enormous potential for building complexity from simple components, and connections between physical effects and molecular reactivity are only just beginning to be discovered.

A Doubly Dissipative System Driven by Chemical and Radiative Stimuli

The operation of a dissipative network composed of two or three different crown-ether receptors and an alkali metal cation can be temporally driven by the use (combined or not) of two orthogonal stimuli of a different nature. More specifically, irradiation with light at a proper wavelength and/or addition of an activated carboxylic acid, are used to modulate the binding capability of the above crown-ethers towards the metal ion, allowing to control over time the occupancy of the metal cation in the crown-ether moiety of a given ligand. Thus, application of either or both of the stimuli to an initially equilibrated system, where the metal cation is distributed among the crown-ether receptors depending on the different affinities, causes a programmable change in the receptor occupancies. Consequently, the system is induced to evolve to one or more out-of-equilibrium states with different distributions of the metal cation among the different receptors. When the fuel is exhausted or/and the irradiation interrupted, the system reversibly and autonomously goes back to the initial equilibrium state. Such results may contribute to the achievement of new dissipative systems that, taking advantage of multiple and orthogonal stimuli, are featured with more sophisticated operating mechanisms and time programmability.

Light-Fueled Primitive Replication and Selection in Biomimetic Chemical Systems

The concept of chemically evolvable replicators is central to abiogenesis. Chemical evolvability requires three essential components: energy-harvesting mechanisms for nonequilibrium dissipation, kinetically asymmetric replication and decomposition pathways, and structure-dependent selective templating in the autocatalytic cycles. We observed a UVA light-fueled chemical system displaying sequence-dependent replication and replicator decomposition. The system was constructed with primitive peptidic foldamer components. The photocatalytic formation-recombination cycle of thiyl radicals was coupled with the molecular recognition steps in the replication cycles. Thiyl radical-mediated chain reaction was responsible for the replicator death mechanism. The competing and kinetically asymmetric replication and decomposition processes led to light intensity-dependent selection far from equilibrium. Here, we show that this system can dynamically adapt to energy influx and seeding. The results highlight that mimicking chemical evolution is feasible with primitive building blocks and simple chemical reactions.

Transient self-assembly of metal-organic complexes

Implementing transient processes in networks of dynamic molecules holds great promise for developing new functional behaviours. Here we report that trichloroacetic acid can be used to temporarily rearrange networks of dynamic imine-based metal complexes towards new equilibrium states, forcing them to express complexes otherwise unfavourable in their initial equilibrium states. Basic design principles were determined for the creation of such networks. Where a complex distribution of products was obtained in the initial equilibrium state of the system, the transient rearrangement temporarily yielded a simplified output, forcing a more structured distribution of products. Where a single complex was obtained in the initial equilibrium state of the system, the transient rearrangement temporarily modified the properties of this complex. By doing so, the mechanical properties of an helical macrocyclic complex could be temporarily altered by rearranging it into a [2]catenane.

Anion-assisted amidinium exchange and metathesis

Dynamic covalent chemistry has become an invaluable tool for the design and preparation of adaptable yet robust molecular systems. Herein we explore the scope of a largely overlooked dynamic covalent reaction - amidinium exchange - and report on conditions that allow formal amidinium metathesis reactions.