A porphyrin, with four protruding ligands (two phenyl groups and two bromine atoms) called the limbs, is encompassed by a tricyclic octacationic cyclophane (suit) and rocks back and forth around 1000 times a second inside the suit.
Liu, W.; Stern, C. L.; Stoddart, J. F. Suitane. J. Am. Chem. Soc. 2020
The molecular receptor, XCage, encapsulates free-base and zinc porphyrins with subnanomolar binding affinities in water. The high affinities are sustained by the hydrophobic effect, large area [π···π] stacking and multiple [CH···π] interactions between the substrate porphyrins and the receptor. XCage acts as a proton-proof vest, resulting in ultrastable porphyrins that resist D/H exchange, protonation and solvolysis.
Liu, W.; Lin, C.; Weber, J. A.; Stern, C. L.; Young, R. M.; Wasielewski, M. R.; Stoddart, J. F. Cyclophane-Sustained Ultrastable Porphyrins. J. Am. Chem. Soc. 2020, 142, 8938–8945.
Squaraine / Croconaine Tetralactam Macrocycle
A tricyclic octacationic cyclophane, XCage, is designed and synthesized. The large and flat binding cavity of XCage covers 80% of the aromatic surface of perylene diimide through [π··· π] stacking, and there are in total eight [N ···O=C] ion-dipole interactions between these two partners, resulting in a picomolar binding affinity in water.
Liu, W.; Bobbala, S.; Stern, C. L.; Hornick, J.; Liu, Y.; Enciso, A. E.; Scott, E. A.; Stoddart, J. F. XCage: A Tricyclic Octacationic Receptor for Perylene Diimide with Picomolar Affinity in Water. J. Am. Chem. Soc. 2020, 142, 3165–3173.
An anthracene-based tetralactam macrocycle features an amphiphilic binding cavity where four polar NH bonds point convergently inside a nonpolar binding pocket. Sqaraine (left) and croconaine (right), two near infrared dyes, fit well inside the binding cavity, in which four H bond interactions and [π··· π] stacking are established. The shape complementarity demonstrated here leads to ultra-high binding affinities, which range from 10 to 10 M in water. Furthermore, the binding kinetics can be fine-tuned by slightly changing the N-substituted groups, covering the kinetic constants from 10 to 10 M s .
Liu, W.; Johnson, A.; Smith, B. D. Guest Back-Folding: A Molecular Design Strategy That Produces a Deep-Red Fluorescent Host/Guest Pair with Picomolar Affinity in Water. J. Am. Chem. Soc. 2018, 140, 3361–3370.
Liu, W.; Peck, E. M.; Smith, B. D. High Affinity Macrocycle Threading by a Near-Infrared Croconaine Dye with Flanking Polymer Chains. J. Phys. Chem. B 2016, 120, 995–1001.
Liu, W.; Peck, E. M.; Hendzel, K. D.; Smith, B. D. Sensitive Structural Control of Macrocycle Threading by a Fluorescent Squaraine Dye Flanked by Polymer Chains. Org. Lett. 2015, 17, 5268–5271.
Peck, E. M.; Liu, W.; Spence, G. T.; Shaw, S. K.; Davis, A. P.; Destecroix, H.; Smith, B. D. Rapid Macrocycle Threading by a Fluorescent Dye-Polymer Conjugate in Water with Nanomolar Affinity. J. Am. Chem. Soc. 2015, 137, 8668–8671.
Precious Metal Complexes Tetralactam Macrocycle
Precious metal (Au, Pd, Pt) coordination complexes with a squaraine planar geometry can be selectively recognized by two tetralactam macrocycles. Both receptors have a preorganized structure that is complementary to its precious metal guest. The receptors do not directly ligate the guest metal center but instead provide an array of arene π-electron donors that interact with the electropositive metal and hydrogen-bond donors that interact with the outer electronegative ligands.
Liu, W.; Oliver, A. G.; Smith, B. D. Macrocyclic Receptor for Precious Gold, Platinum, or Palladium Coordination Complexes. J. Am. Chem. Soc. 2018, 140, 6810–6813.
Anions Saddle Lactam Macrocycle
A small tetralactam macrocycle with four convergent NH bond donors was designed and synthesized as a receptor for anions (F , Cl , Br , AcO ). When complexed with these anions, this receptor adopts a saddle shape, after which we name it saddle lactam macrocycle. The fluoride complex of saddle lactam macrocycle self-assembles into a dimeric superstructure, where the two F ions are separated by 3.39 Å. The electrostatic penalty for this close proximity is compensated by attractive interactions provided by the surrounding saddle lactam molecules.
Liu, W.; Oliver, A. G.; Smith, B. D. Stabilization and Extraction of Fluoride Anion Using a Tetralactam Receptor. J. Org. Chem. 2019, 84, 4050–4057.