Preface: supramolecular chemistry of anionic species themed issue

Anions are key to many processes, both industrial and biological, playing crucial roles in both health and the environment. It is thus not surprising that their role, function and properties are at the heart of many scientific research programmes within the field of supramolecular chemistry. Over the past two decades, research in the supramolecular chemistry of anions has mapped out methods to achieve molecular recognition and sensing of anionic guests in organic solvent media. However, this is not the limit of the supramolecular chemistry of these species and more recent work has focussed on the syntheses of new selective receptors which function under competitive conditions in aqueous environments, the formation of sensor arrays of non-specific receptors that can be used to sense the presence of anionic species in complex mixtures using pattern recognition techniques and the development of highly selective anion transporters with the potential to become future therapeutics. More recently, there has been a growing interest in exploring their unique coordination requirements for use in crystal engineering and in the formation of supramolecular self-assemblies and materials. Hence, given the great interest that anions have attracted in our community, we felt that now was a golden opportunity to put together a dedicated issue for Chemical Society Reviews on the subject. With the view of trying to represent as much of the diverse function the anions have (or play) in supramolecular chemistry, we have collected a series of reviews covering many recent advances in the supramolecular chemistry of anions. Many of the authors of this collection will also present their latest results at a symposium on anion complexation and sensing that is to be held at Pacifichem 2010 in Honolulu in December 2010.

In this anion dedicated issue, Ben Hay (DOI: 10.1039/c0cs00075b) has written a tutorial review on the use of de novo structure-based design. For an example system designed to encapsulate sulfate please see Fig. 1. The early successes of computer based design auger well that this technique will become increasingly important in the future. Pablo Ballester (DOI: 10.1039/b926229f) discusses the complexation of anions in covalent and self-assembled molecular capsules. Antonella Dalla Cort, Paolo De Bernardin, Gianpiero Forte and Francesco Yafteh Mihan (DOI: 10.1039/b926222a) give an overview on the use of metal-salophen-based receptors for anions in which the anion is bound by coordination to metal centre. Two reviews cover the use of urea and thiourea as receptors for anions. From the inorganic community Valeria Amendola, Luigi Fabbrizzi and Lorenzo Mosca (DOI: 10.1039/b822552b) discuss a range of urea-based receptors whilst Ai-Fang Li, Jin-He Wang, Fang Wang and Yun-Bao Jiang (DOI: 10.1039/b926160p) discuss these systems from an organic chemistry perspective with a focus on sensing. Sung Ok Kang, José Llinares, Victor Day and Kristin Bowman-James (DOI: 10.1039/c0cs00083c) review the area of anion recognition and binding using cryptand-like anion receptors. Hemraj Juwarker and Kyu-Sung Jeong (DOI: 10.1039/b926162c) discuss in a tutorial review the roles that anions can play in directing the conformation of foldamer species containing hydrogen bond donor groups. The area of conformational control using anions is one of increasing importance and we expect this to become a significant area of activity in years to come. Stefan Kubik (DOI: 10.1039/b926166b) covers the important area of anion recognition in water—an area in which he has been a key player. Related to this is Thomas Rehm’s and Carsten Schmuck's review (DOI: 10.1039/b926223g) on ion-pair induced self-assembly in aqueous solvents. Carla Bazzicalupi, Andrea Bencini and Vito Lippolis (DOI: 10.1039/b926161n) discuss the use of cyclic polyamines for phosphate recognition—an important way of binding and discriminating between biologically important phosphate species. Darren Mercer and Steve Loeb (DOI: 10.1039/b926226c) discuss how metals can be used to template the formation of anion receptors from simple organic components and Gabriella Cavallo, Pierangelo Metrangolo, Tullio Pilati, Giuseppe Resnati, Maurizio Sansotera and Giancarlo Terraneo (DOI: 10.1039/b926232f) discuss the emerging area of receptors that employ halogen bonding to bind anionic guest species. A critical review from Sung Kuk Kim and Jonathan Sessler (DOI: 10.1039/c002694h) discusses systems that complex both components of an ion pair.

Fig. 1 An example of the use of computer-based design of a receptor to encapsulate sulfate.

In the sensing arena, Pavel Anzenbacher, Jr., Přemysl Lubal, Pavel Buček, Manuel A. Palacios and Maria E. Kozelkova (DOI: 10.1039/b926220m) provide a critical review on optical cross-reactive sensor arrays, while Ewan Galbraith and Tony James (DOI: 10.1039/b926165f) discuss anion sensors containing boron and Rebecca Duke, Emma Veale, Frederick Pfeffer, Paul Kruger and Thorfinnur Gunnlaugsson (DOI: 10.1039/b910560n) discuss recent advances in the area of colorimetric and fluorimetric anion sensing, focusing their review on using 1,8-naphthalimide based chemosensors. Calden Carroll, John Naleway, Mike Haley and Darren Johnson (DOI: 10.1039/b926231h) have written a critical review on the applications of arylethynyl-based receptors for anions and neutral molecules in cellular imaging.

Two reviews cover the transmembrane lipid-bilayer transport of anionic species. Jeff Davis, Yomi Okunola and Roberto Quesada (DOI: 10.1039/b926164h) give an update on advances in this area between 2007 and 2009 whilst Peter Brotherhood and Tony Davis (DOI: 10.1039/b926225n) highlight the use of steroids as scaffolds for the construction of membrane transport agents.

Franz Schmidtchen (DOI: 10.1039/c0cs00038h) discusses the important and fundamental topic of the thermodynamics of anion complexation in his critical review whilst the roles that anions can play in crystal engineering are discussed by Radu Custelcean (DOI: 10.1039/b926221k). Leo Joyce, Shagufta Shabbir and Eric Anslyn (DOI: 10.1039/b926224p) consider the roles that molecular recognition processes can play in the development of synthetic methodology whilst Jonathan Steed (DOI: 10.1039/b926219a) provides a tutorial on the roles that anions can play in controlling the formation and stability of low molecular weight gels. Phil Gale (DOI: 10.1039/c001871f) provides an overview of advances in anion receptor chemistry in the years 2008 and 2009.

We would like to thank all the authors and the Editor of Chemical Society Reviews, Dr Robert Eagling, for supporting this themed issue.

Footnote

† Part of a themed issue on the supramolecular chemistry of anionic species.

---