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How Large Can We Build a Cyclic Assembly? Impact of Ring Size on Chelate Cooperativity in Noncovalent Macrocyclizations
Author(s) -
MontoroGarcía Carlos,
Mayoral María J.,
Chamorro Raquel,
GonzálezRodríguez David
Publication year - 2017
Publication title -
angewandte chemie
Language(s) - English
Resource type - Journals
eISSN - 1521-3757
pISSN - 0044-8249
DOI - 10.1002/ange.201709563
Subject(s) - cooperativity , ring size , intramolecular force , monomer , cytidine , chemistry , conjugated system , bond length , non covalent interactions , ring (chemistry) , crystallography , molecule , polymer , stereochemistry , hydrogen bond , crystal structure , organic chemistry , enzyme , biochemistry
Self‐assembled systems rely on intramolecular cooperative effects to control their growth and regulate their shape, thus yielding discrete, well‐defined structures. However, as the size of the system increases, cooperative effects tend to dissipate. We analyze here this situation by studying a set of oligomers of different lengths capped with guanosine and cytidine nucleosides, which associate in cyclic tetramers by complementary Watson–Crick H‐bonding interactions. As the monomer length increases, and thus the number of C(sp)–C(sp 2 ) σ ‐bonds in the π‐conjugated skeleton, the macrocycle stability decreases due to a notable reduction in effective molarity (EM), which has a clear entropic origin. We determined the relationship between EM or ΔS and the number of σ‐bonds, which allowed us to predict the maximum monomer lengths at which cyclic species would still assemble quantitatively, or whether the cyclic species would not able to compete at all with linear oligomers over the whole concentration range.