Self-assembly with post-modification

Self-assembly can be divided into a number of classes 1. strict self-assembly, 2. irreversible self-assembly, 3. precursor modification followed by self-assembly, 4. self-assembly with post-modification, 5. assisted self-assembly, 6. directed self-assembly, 7. self-assembly with intermittent processing. 

Self-assembly with post-modification. The most common form of modification that is utilised in synthetic systems is the alteration of a system after the self-assembly step has taken place. Many common systems, such as rotaxanes and catenanes (Section 3.4), are formed from a self-assembled structure, held loosely together by non-covalent interactions, which are locked in place once the self-assembly process is complete by the formation of covalent bonds, much like tying off the ends of a knot. 

Self-assembly processes involving covalent modifications typically comprise one of the earlier classes of self-assembly followed by, preceded by, or intermixed with conventional covalent bond formation. In coordination chemistry, for example, self-assembly with precursor modification means synthesizing the component ligands and metal complexes before carrying out the reaction. Post-modification involves locking a self-assembled structure into a kinetically stable state. Self-assembly with intermittent processing involves combinations of both of these. 

One addition to the assembly lexicon added a layer of complexity to the above definition. Thus, one of the seven different classes of self-assembly originally proposed by Lindsey. — which are strict self-assembly processes (with or without a template) positioned in different chemical settings—is commonly known as "irreversible self-assembly." This term is used to describe two-step processes, whereby a strict self-assembly processes is followed by irreversible reactions that covalently knit together the array of subunits. As Whitesides noted, strictly speaking this term is a misnomer. Hence, along with other types of post-assembly modified self-assemblies, we categorize these processes as "self-assembly with covalent modification." Postmodification generally comes in the form of a series of covalent bond formation steps and is of less interest to us here. The crux of any self-assembly process is the self-assembly. 

Several types of self-assembly have been identified from the biological literature 7 (i) thermodynamic self-assembly (ii) irreversible self-assembly (iii) assisted and directed self-assembly and (iv) self-assembly with pre-, post-, or intermittent modification. 

In this case, the restriction of peptide self-assembly was both desired, and by design. More generally, when looking to modify peptides and retain their self-assembly, where modifications are incompatible with assembly, post-assembly strategies will be necessary. 

We can also mention the use of bio-sourced building blocks based on cellulose or dextran. Kadla et al. described value-added materials from naturally abundant polymers for system that may serve as a platform for the design and development of biosensors [197]. A hierarchically strucmred honeycomb film from dextran-ft-PS amphiphilic linear diblock copolymers has also been described by Chen et al. leading to ordered porous bio-hybrid films. [198] Honeycomb patterned surfaces functionalized with biomolecules for specific recognition of proteins or bacteria have been also achieved either by self-assembly of amphiphilic copolymers based on galactose moieties [155] or by post-modification with peptide sequences [199]. 

Fig. 10 Huisgen cycloaddition (top) is one method of post-self-assembly modification, providing a means to decorate an SCC with a variety of pendant groups (bottom)...

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