How Large Can We Build a Cyclic Assembly? Impact of Ring Size on Chelate Cooperativity in Noncovalent Macrocyclizations

• Published in: Angewandte Chemie Vol. 129; no. 49; pp. 15855 - 15859
• Main Authors: Montoro‐García, Carlos, Mayoral, María J., Chamorro, Raquel, González‐Rodríguez, David
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 04-12-2017
• Subjects: Chelateffekt; Chelates; Chemistry; Cooperative control; Effektive Molarität; Guanosine; Monomers; Nichtkovalente Synthesen; Nukleoside; Oligomers; Supramolekulare Chemie
• ISSN: 0044-8249; 1521-3757
• DOI: 10.1002/ange.201709563

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(sp2) 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.
Nach der Entschlüsselung der Beziehung zwischen Monomerlänge und Chelatkooperativität kann vorhergesagt werden, bis zu welcher Monomerlänge cyclische Spezies mit linearen Oligomeren in Ring‐Kette‐Selbstorganisationsprozessen konkurrieren.