Supramolecular chemistry in water is a constantly growing research area because noncovalent interactions in aqueous media are important for obtaining a better understanding and control of the major processes in nature. This Review offers an overview of recent advances in the area of water-soluble synthetic receptors as well as self-assembly and molecular recognition in water, through consideration of the functionalities that are used to increase the water solubility, as well as the supramolecular interactions and approaches used for effective recognition of a guest and self-assembly in water. The special features and applications of supramolecular entities in aqueous media are also described.

Supramolecular Chemistry in Water

Anion–arene adducts: C–H hydrogen bonding, anion–π interaction, and carbon bonding motifs

Neutral anion receptors (LH) form stable 1 : 1 H-bond [LH⋯X]− complexes with carboxylates, halides and phosphate (X−). Some of the [LH⋯X]− complexes, in presence of an excess of X−, release an HX fragment, with formation of [HX2]− and the deprotonated receptor L−. The tendency towards deprotonation increases with the acidity of the receptor and with the stability of the [HX2]− self-complex. Thus, the more acidic thiourea containing receptor deprotonates in the presence all the investigated anions except chloride, whereas the less acidic urea containing receptor undergoes deprotonation only in the presence of fluoride, due to the high stability of [HF2]−.

Urea vs. thiourea in anion recognition

This paper refines the nature of the interactions between electron-deficient arenes and halide anions. Conclusions are based on (i) new crystal structures containing alkali halide salts with 1,2,4,5-tetracyanobenzene (TCB) and 18-crown-6, (ii) evaluation of crystal structures found in the Cambridge Structural Database, and (iii) MP2/aug-cc-pVDZ calculations of F-, Cl-, and Br- complexes with TCB, 1,3,5-tricyanobenzene, triazine, and hexafluorobenzene. When the halide lies above the plane of the π system, the results establish that three distinctly different types of complexes are possible:  strongly covalent σ complexes, weakly covalent donor−π-acceptor complexes, and noncovalent anion−π complexes. When aryl C−H groups are present, a fourth type of interaction leads to C−H · · · X- hydrogen bonding. Characterization of the different geometries encountered with the four possible binding motifs provides criteria needed to design host architectures containing electron-deficient arenes.

Structural criteria for the design of anion receptors: the interaction of halides with electron-deficient arenes.

Anion coordination chemistry in aqueous solution of polyammonium receptors

Synthetic receptors for carboxylic acids and carboxylates

Synthetic Receptors for Carboxylic Acids and Carboxylates

The title compound, C11H8N4S, is found to have a symmetrical resonance structure in which both pyridyl-N atoms interact with the S atom forming hemi-bonds. This also results in the formation of a delocalized di­imine region and disturbance of the aromaticity in the pyridyl rings.

2-(2-Pyridylimino)-2H-1,2,4-thiadiazolo[2,3-a]pyridine

Compounds (I), C14H20N2O4S, and (II), C12H14N2O3S2, are two minor products of the same reaction Both structures contain identical ester functionalities in similar orientations Both independent mol­ecules of (I) contain an ethoxy­carbo­thio­yl­amine moiety, whilst (II) possesses a novel exocyclic thione system fused with a pyridine ring

David Douheret

Papers

Synthetic receptors for carboxylic acids and carboxylates

Synthetic Receptors for Carboxylic Acids and Carboxylates

2-(2-Pyridylimino)-2H-1,2,4-thiadiazolo[2,3-a]pyridine

tert‐Butyl 2‐[2‐(ethoxycarbothioylamino)‐3‐pyridyloxy]acetate and tert‐butyl 2‐(3‐thioxopyrido[2,1‐c][1,2,4]thiadiazol‐8‐yloxy)acetate

2-(2-Pyridylimino)-2H-1,2,4-thiadiazolo[2,3-a]pyridine.

David Douheret

Papers

Synthetic receptors for carboxylic acids and carboxylates

Synthetic Receptors for Carboxylic Acids and Carboxylates

2-(2-Pyridylimino)-2H-1,2,4-thiadiazolo[2,3-a]pyridine

tert‐Butyl 2‐[2‐(ethoxy­carbo­thio­yl­amino)‐3‐pyridyl­oxy]acetate and tert‐butyl 2‐(3‐thio­xopyrido­[2,1‐c][1,2,4]thia­diazol‐8‐yl­oxy)­acetate

2-(2-Pyridylimino)-2H-1,2,4-thiadiazolo[2,3-a]pyridine.

tert‐Butyl 2‐[2‐(ethoxycarbothioylamino)‐3‐pyridyloxy]acetate and tert‐butyl 2‐(3‐thioxopyrido[2,1‐c][1,2,4]thiadiazol‐8‐yloxy)acetate