Amide naphthotubes:Biomimetic macrocycles for selective molecular recognition

Selective molecular recognition in water is routine for bioreceptors,but remains challenging for synthetic hosts.This is principally because noncovalent interactions are usually less efficient in aqueous environments.By mimicking the cavity feature of bioreceptors,Prof.Wei Jiang proposed and clarified the concept of“endo-functionalized cavity”.Through situating polar binding sites into a deep hydrophobic cavity,we designed and synthesized several macrocyclic hosts,among which amide naphthotubes are the most representative.The hosts can selectively recognize various polar molecules including organic micropollutants,drug molecules,and chiral molecules in water by employing the hydrophobic effect and shielded hydrogen bonding.In addition,these biomimetic hosts have been applied in spectroscopic analysis,adsorptive separation and self-assembly.In this review,we provide an overview of recent advances on amide naphthotubes with special emphasis on the efforts of Jiang's group.We are convinced that these biomimetic macrocycles will make further contributions to supramolecular chemistry and beyond.

Cucurbit[n]urils(n=7,8)can strongly bind neutral hydrophilic molecules in water

It is challenging to recognize neutral hydrophilic molecules in water.Effective use of hydrogen bonds in water is generally accepted to be the key to success.In contrast,hydrophobic cavity is usually considered to play an insignificant role or only to provide a nonpolar microenvironment for hydrogen bonds.Herein,we report that hydrophobic cavity alone can also strongly bind neutral,highly hydrophilic molecules in water.We found that cucurbit[n]urils(n=7,8)bind 1,4-dioxane,crown ethers and monosaccharides in water with remarkable affinities.The best binding constant reaches 10^(7) M^(−1) for cucurbit[8]uril,which is higher than its binding affinities to common organic cations.Density functional theory(DFT)calculations and control experiments reveal that the hydrophobic effect is the major contributor to the binding through releasing the cavity water and/or properly occupying the weakly hydrated cavity.However,hydrophobic cavity still prefers nonpolar guests over polar guests with similar size and shape.

Biomimetic Recognition-Based Bioorthogonal Host-Guest Pairs for Cell Targeting and Tissue Imaging in Living Animals

Bioconjugation methods offer very important tools in studying biological systems.Synthetic host-guest pairs provide an alternative and complementary conjugation method to bioorthogonal reactions and biological association pairs.Nevertheless,macrocyclic hosts that can be used for in situ capture are limited and often rely on extremely high binding affinities.Herein,we report an alternative bioorthogonal host-guest pair that relies on highly selective molecular recognition in water.The host,namely amide naphthotube,possesses a biomimetic cavity with inward-directing hydrogen bonding sites and shows selective and strong binding to the guest(2-phenyl pyrimidine)even in biological media.Through anchoring the tetraphenyl ethylene-modi fied hosts to cell surfaces,the bioorthogonal host-guest pair can be applied in cell surface recognition,cell-cell interactions,and tissue imaging in mice.The bioorthogonality is originated from the high binding selectivity of the biomimetic macrocyclic host,which is different from other known host-guest pairs that have been applied in biological systems.This research provides a new noncovalent bioconjugation tool and a new concept for designing bioorthogonal host-guest pairs for biological applications.