Supramolecular living polymers

Fluorescence is also a powerful tool for investigating the structure and dynamics of matter or living systems at a molecular or supramolecular level. Polymers, solutions of surfactants, solid surfaces, biological membranes, proteins, nucleic acids and living cells are well-known examples of systems in which estimates of local parameters such as polarity, fluidity, order, molecular mobility and electrical potential is possible by means of fluorescent molecules playing the role of probes. The latter can be intrinsic or introduced on purpose. The high sensitivity of fluo-rimetric methods in conjunction with the specificity of the response of probes to their microenvironment contribute towards the success of this approach. Another factor is the ability of probes to provide information on dynamics of fast phenomena and/or the structural parameters of the system under study. 

The term supramolecular polymer applies to any type of polymer-tike assembly that spontaneously forms by the reversible linear aggregation of one or more type of molecule in solution or in the melt. The crucial factor discriminating supramolecular from conventional or so-called dead polymers, is that for the former the monomeric and the polymeric states are in thermal equilibrium with each other, while for the latter this is not so (on the relevant experimental timescale). Examples of supramolecular polymers include the so-called giant surfactant micelles [1], peptide )3-sheet ribbons [2], self-assembled stacks of discotic molecules [3], protein fibers such as those formed by sickle cell hemoglobin [4], and so on. Chains of colloidal particles found in quite diverse contexts [5-8] and living polymers of chemically reactive species [9] also belong to the class of supramolecular polymers, if only in principle. 

The reattachment of two supramolecular polymers, such as that observed when a high concentration of sheared microtubules is permitted to incubate in vitro. End-to-end annealing of microtubules is an unlikely process in living cells, because (a) the viscosity of the cytoplasm is apt to reduce greatly the tumbling of these polymers and (b) the so-called minus ends of the microtubules are usually firmly attached to microtubule-organizing centers. 

Lohmeijer BGG, Schubert US (2004) Expanding the supramolecular polymer LEGO system nitroxide mediated living free radical polymerization for metallo-supramolecular block copolymers with a polystyrene block. J Polym Sci Part A Polym Chem 42 4016-4027... 

During the last two decades, chemists have become increasingly focused on how molecules interact, i.e. on supramolecular chemistry. Dynamic intermolecular processes provide opportunities for incorporation of control, adaptation and function in man-made materials, as observed in living systems. In biology, these processes are tightly controlled by the catalytic action of enzymes. In this chapter, we focus on enzymatically controlled supramolecular polymerisation, whereby self-recognising molecular building blocks assemble to form extended onedimensional (ID) structures, or supramolecular polymers, with unique adaptive features. 

Inspiration for development of dynamic supramolecular polymers comes from living systems, where enzyme-controlled formation and degradation of collagen fibrils, actin filaments and microtubules underlie vital cellular functions such as motility, differentiation, division, etc. (Fig. 1). 

Block co-polymers exhibit outstanding potential for a variety of applications as a result of their self-assembly into supramolecular structures (see Section 1.2.4). However, the exploration of organometallic multi-block materials was only begun in the early 1990s. Block co-polymers derived from the living anionic polymerization of vinylferrocene have been already briefly mentioned in Section 12.06.2.2.l.(i). In this section, side-chain metal-containing block co-polymers are surveyed. Examples of block co-polymers with metals in the main chain are discussed in Section 3.X. 

Percec, V. Schlueter. D. Mechanistic investigations on the formation of supramolecular cylindrical shaped oligomers and polymers by living ring opening metathesis polymerization of a 7-oxanorbornene monomer substituted with two tapered monodendrons. Macromolecules 4997. 30. 5783. 

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