Polymerization nucleated supramolecular

Nucleated supramolecular polymerization, on the other hand, is a much more sensitive function of the external conditions. Indeed, a sharp polymerization point can be identified below which almost no material is in the polymerizated state and above which the self-assembled polymers exhibit a strong variation of their mean size with varying concentration, temperature, and so on. Nucleated equilibrium polymerization requires the existence of... 

If the conformational switching is that between high-molecular weight polymeric species, then the structural transition between them can be highly co-operative but the assembly remains by and large isodesmic. So, co-operativity is a required but not a sufficient condition for creating nucleated supramolecular polymerizations. 

The assembly models discussed in the preceding sections are presumably the simplest ones that one can set up for co-operative supramolecular polymerization. Their advantage is the relatively small number of adjustable parameters and conceptual simplicity. Disadvantage is the lack of a detailed description of the processes that actually led to the assembly becoming nucleated and that are system specific, that is, that depend on the details of the molecules involved and how precisely they interact. 

Zhao, D., and Moore, J.S. "Nucleation-elongation a mechanism for cooperative supramolecular polymerization". Org. Biomol. Chem. 1, 3471-3491 (2003). 

Rgure12 Schematic of helical supramolecular polymerization. Monomeric, nonhelical polymeric and helical polymeric states are in thermal equilibrium as indicated by the arrows. The equilibrium constants between the various species may differ greatly in magnitude. If helical polymers cannot form directly from the monomers, they need to be nucleated through the formation of nonhelical chains that may be energetically unfavorable. 

Figure 6 Examples of compounds that in selective solvents produce biomimetic supramolecular polymers that depending on the conditions exhibit a co-operature intramolecular ordering transition from random to highly ordered helical stacks or a nucleated polymerization transition from oligomeric prenuclei to very long, helical polymeric objects (ten Cate and Sijbesma, 2002 Dankers and Meijer, 2007 van Gorp et al., 2002 Brunsveld, 2001 Jonkheijm, 2005 Hirschberg, 2001).

Figure 10 Assembly diagram of compound 1 of Figure 6 in the solvent n-butanol (adapted from van Gestel, 2004a Weiss and Terech, 2005). Symbols represent results from UV-vis absorption, UV, fluorescence decay, FD, and circular dichroim spectroscopy, CD, and the drawn line the theoretical fits to the data. There are three types of transition I, isodesmic polymerization II, helical transition of long supramolecular polymers and III, nucleated helical assembly of the monomer units.

Fig. 11 Structures of the homochiral dendritic dipeptides (a), their CD blue) and UV red) spectra recorded during self-assembly in cyclohexane (b, c), the nucleation and growth mechanism of cooperative supramolecular helical polymerization and the structures of the supramolecular assemblies (d). Modified with permission from [114]. Cop3right 2011 American Chemical Society...

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