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.

Molecular recognition and fluorescent sensing of urethane in water

Molecular recognition and fluorescent sensing of Group 2A carcinogen-urethane was achieved in aqueous solution. The molecular sensors are the endo-functionalized molecular tubes with amide protons in the hydrophobic cavity.~1H NMR, fluorescence, and ITC titrations and single crystal X-ray crystallography reveal the binding stoichiometry, the binding affinities, and the driving forces. The binding is mainly driven by the hydrophobic effect through releasing the "high-energy" cavity water with minor contribution from hydrogen bonding. In addition, the syn-configured molecular tube was found to be a good fluorescent sensor for urethane in water(concentration range: 6.2–60 mmol/L) and in beer(concentration range: 22.9–60 mmol/L).

A phase-selective,bis-urea organogelator with a curved bis-naphthalene core

A phase-selective,bis-urea organogelator with a curved bis-naphthalene core was synthesized and characterized.This gelator is capable of gelating a variety of hydrocarbons and oils.The resulting gels have been characterized by rheology,SEM,and molecular modelling.The gelator can be applied in the powder form for the recovery of a thin layer of petrol oil spill in water.

Selective Recognition of Quaternary Ammonium Ions by Structurally Flexible Cages

The binding behaviors of three structurally similar and flexible cages to a series of quaternary ammonium ions have been systematically studied.The cage with phenyl sidewalls is new;moreover,its structure and conformational states have been characterized by NMR;2D NMR,and X-ray crystallography.The results reveal that the three cages show quite high binding affinities and selectivities to different guests.Enthalpy-entropy compensation was invoked to explain the different binding performance.Moreover,a six-component,high-fidelity self-sorting system was successfully constructed by using these cages and three guests.This suggests that conformationally flexible hosts may also achieve high binding affinities and selectivities,which is in contrast to the traditional point of view-only preorganized and rigid hosts are able to do so.This research advocates that conformational flexibility should also be seriously considered in host design.

Enantioselective Recognition of Neutral Molecules in Water by a Pair of Chiral Biomimetic Macrocyclic Receptors

Enantioselective recognition in water remains an ongoing challenge in supramolecular chemistry but is routine in nature.Herein,we report the first enantiopure pair of biomimetic macrocyclic receptors with hydrogen bonding donors in their deep hydrophobic cavities.The chiral naphthotubes can be efficiently synthesized through a chirality-directed macrocyclization strategy and are able to discriminate the enantiomers of neutral chiral molecules in water.Density functional theory calculations reveal that the“three-point contact”model effectively explains their enantioselectivity.The differential noncovalent interactions inside the hydrophobic cavity are responsible for the enantioselective recognition.Moreover,these chiral naphthotubes are both fluorescent and circular dichroism(CD)-active.In CD spectroscopy,they have been demonstrated to have the ability to detect nonchromophoric,achiral molecules in water.And,the use of fluorescence spectroscopy has aided in the determination of the enantiomeric excess(ee)values of chiral molecules.The results and conclusions obtained with these chiral biomimetic receptors can be used to better understand enantioselective recognition in biological systems.