Energy landscaping in supramolecular materials

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This review details recent developments in the design of supramolecular materials with customizable properties that can be coordinated in space and time. We highlight examples where both kinetic and thermodynamic considerations are incorporated in design, to address three challenges: control of order/disorder in supramolecular assembly; formation of structures with distinct functional domains; formation of out-of-equilibrium structures with controlled lifetimes. The examples that are discussed are based on self-assembling peptide and saccharide-based amphiphiles. These biomolecular amphiphiles are of low complexity and ideally suited to fundamental, systematic studies while they are also considered for applications in environmental remediation, food science, cosmetics and nanomedicine.

Introduction

This review covers recent developments in the control of properties, using kinetic and thermodynamic considerations, of supramolecular materials derived from simple biomolecules [1, 2]. A wide variety of synthetic and biological compounds are able to form ordered nanostructures based on reversible interactions. For applications in cosmetics, food, personal care, biomedicine and nanotechnology, simple bio-derived molecules, such as derivatives of short peptides and simple sugars, are of particular interest as they are scalable, low-cost while they are tremendously versatile. In this review we will discuss selected examples from the recent literature which demonstrate how molecular design, combined with thermodynamic and kinetic considerations can give rise to materials with uniquely addressable, customizable and tunable supramolecular properties. Examples will be discussed based on the ability to control order and disorder at the supramolecular and nanoscopic level; control separation of multiple components into separate functional domains, and to precisely regulate assembly and dis-assembly over time, by taking advantage of competing catalytic pathways. We will show that these approaches are leading to the development of systems that share similarities with biological materials but that are much simpler in composition and design, and may incorporate biological, as well as non-biological synthetic components, thus opening up new applications ranging from nanotechnology to biomedicine.

This review highlights only some of the recent developments in the extremely active field of supramolecular materials science and has the goal to inspire researchers to focus on controlling spatial and temporal aspects of supramolecular materials design, ultimately giving rise to technologies and materials with properties that start to blur the living/nonliving materials divide toward a seamless interfacing of the biological and synthetic worlds. Certainly, supramolecular biomimicry is an increasingly important strategy to devise novel materials and the focus on controlling and designing spatial and temporal variability of these materials brings us closer to the aim of achieving a more seamless interface between living and non-living matter for medicine, biotechnology, food science, and environmental science.

Section snippets

Supramolecular design based on simple peptides and sugars

Life's macromolecules are complex polymers whose function is dictated by the precise sequence of long chains of hundreds or thousands of monomers (saccharides, amino acids, nucleotides). It has been recognized that much simpler combinations of monomers can also give rise to structure formation, providing opportunities to design building blocks for materials with designable/customizable properties. In this review, we focus on materials based on supramolecular assembly of amphiphiles derived from

Controlling order/disorder in self-assembly in shallow energy landscapes

While supramolecular materials research over the past few decades has typically focused on formation of thermodynamically stable structures [2], the emphasis is now shifting toward the production of dynamic structures where the emphasis is not necessarily on structure optimization, but instead on the ability to regulate order and disorder to achieve stimuli-responsiveness [18]. While thermodynamically stable structures are suited for materials applications where stability is sought, for dynamic

Co-assembly and self-separation to create hierarchical structures and nanoscale functional domains

The coordinated assembly of multiple components in one pot can give rise to several modes of interaction between these components: they can assemble orthogonally to form separate domains, they can disrupt each other's assembly or they can form co-assembled structures that are not accessible by either component alone [27].

Nature provides tremendous examples of supramolecular constructs which are reliant on coordinated assembly with tight control over micro-scopic and nano-scopic spatial

Active regulation of assembly/dis-assembly by catalytic reactions

Along with regulating supramolecular order/disorder and 3D spatial organization as discussed in the previous sections, biology regulates structures and functionality over time by taking advantage of metabolic pathways through competing build-up and break-down reactions. This requires accurate kinetic control over highly dynamic processes, which is essential to finely regulate homeostasis and, when needed, to adapt to changing environments. To this end, non-equilibrium conditions are key to

Future perspectives

It is clear that both thermodynamic and kinetic considerations are important in designing of supramolecular nanostructures with desired properties in terms of structure, function and, importantly, the ability to adapt or modify structures when required. It is likely that future research will include further functions, such as (adaptive) biomolecular recognition and (enzyme like) reactivity and catalysis [39]. While more traditional supramolecular approaches typically emphasize thermodynamic

References and recommended reading

Papers of particular interest, published within the period of review, have been highlighted as:

  • • of special interest

  • •• of outstanding interest

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