Nucleation-elongation

The choice of starter sequences for a nucleation-elongation polymerization is very important. Starter sequences that can combine to form stable macrocycles (64 and 65) will result primarily in macrocycle formation (55), creating... 

The ultimate evidence for the nucleation-elongation mechanism is the effect of imbalanced stoichiometry on the MW of the polymerization. In standard step-growth polymerizations the MW is dependent upon the ratio of the monomer concentrations where almost exact 1 1 stoichiometry is necessary to bring about high MW [90]. An irreversible imine condensation of 67 and 68 was performed under imbalanced stoichiometry ([67]/[68]=0.5) and nonfolding conditions (Fig. 40) [93]. The starting material was completely consumed and... 

Zhao, D. Moore, J. S. Nucleation-elongation polymerization under imbalanced stoichiometry. J. Am. Chem. Soc. 2003,125,16294-16299. 

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

Figure 10.5 The equilibrium monomer concentration as a function of the total monomers for a nucleation-elongation protein polymerization process described by Equations (10.7) and (10.13). The constant K = k+ /K is the association constant of a monomer to the polymer [A ]eq is the equilibrium free monomer concentration and A is the total monomer concentration. The variable a = 1 — K /K depends on the difference in equilibrium constants between elongation and nucleation steps. At a = 0 there is no difference in equilibrium constants at er = l nucleation is highly unfavorable compared to elongation and there is infinite cooperativity in the polymerization process.

Assembly Mechanisms Nucleation/Elongation versus Polycondensation 185... 

Hybrid dynamic proteoids, containing alternating imine and acylhydrazone linkages, have been obtained by polycondensation of amphiphilic dialdehydes with amino acid hydrazides. The polymerization displays nucleation-elongation behavior driven by hydrophobic effects, resulting in the formation of globular particles reminiscent of folded proteins (Fig. 6) [89]. 

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