title: Selective recognition of neutral guests in an aqueous medium by a biomimetic calix[6]cryptamide receptor.
abstract: The design of artificial receptors that can efficiently work in water is a challenging research area. A possible biomimetic approach for the elaboration of such receptors consists of associating a hydrophobic cavity with a polar polyfunctional binding site. On this basis, a hydrophilic calix[6]cryptamide decorated with oligo(ethylene glycol) units (i.e. 8) was synthesized through an efficient [1 + 1] macrocyclization reaction as the key-step. The complexation of neutral molecules was evaluated by NMR spectroscopy through competition experiments either in apolar or aqueous media. In both media, host 8 can bind neutral species that display H-bonding acceptor and donor groups such as amides or ureas. Interestingly, the most polar and acidic molecule is the best guest in chloroform and the worst one in an aqueous medium, highlighting the importance of the environment. As shown by NMR and X-ray diffraction data, the mode of recognition involves a complementary DAAAD-ADDDA quintuple H-bonding array between the binding partners as well as multiple CH-π interactions. A comparison of this calix[6]arene-based host-guest system with the binding site of biotin-binding proteins shows strong similarities. Besides, the acid-base control of the binding properties of receptor 8 in aqueous media is highly reminiscent of allosteric processes encountered in natural systems.
authors.affiliation: Laboratoire de Chimie Organique, Université libre de Bruxelles (ULB), Av. F. D. Roosevelt 50, CP160/06, B-1050 Brussels, Belgium. ijabin@ulb.ac.be.
authors.forename: Angélique
authors.initials: A
authors.lastname: Lascaux
authors.forename: Gaël De
authors.initials: G
authors.lastname: Leener
authors.forename: Luca
authors.initials: L
authors.lastname: Fusaro
authors.forename: Filip
authors.initials: F
authors.lastname: Topić
authors.forename: Kari
authors.initials: K
authors.lastname: Rissanen
authors.forename: Michel
authors.initials: M
authors.lastname: Luhmer
authors.forename: Ivan
authors.initials: I
authors.lastname: Jabin
mesh_terms: D000577:Amides / Q000737:chemistry*; D040761:Biomimetic Materials / Q000138:chemical synthesis / Q000737:chemistry*; D047250:Calixarenes / Q000138:chemical synthesis / Q000737:chemistry*; D018360:Crystallography, X-Ray; D003500:Cyclization; D019855:Ethylene Glycol / Q000737:chemistry; D006860:Hydrogen Bonding; D057927:Hydrophobic and Hydrophilic Interactions; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008968:Molecular Conformation; D014508:Urea / Q000737:chemistry*; D014867:Water / Q000737:chemistry
chemical_list: D000577:Amides; C000609232:calix(6)cryptamide; D014867:Water; D047250:Calixarenes; D014508:Urea; D019855:Ethylene Glycol