This critical review focuses on the development of anion sensors, being either fluorescent and/or colorimetric, based on the use of the 1,8-naphthalimide structure; a highly versatile building unit that absorbs and emits at long wavelengths. The review commences with a short description of the most commonly used design principles employed in chemosensors, followed by a discussion on the photophysical properties of the 4-amino-1,8-naphthalimide structure which has been most commonly employed in both cation and anion sensing to date. This is followed by a review of the current state of the art in naphthalimide-based anion sensing, where systems using ureas, thioureas and amides as hydrogen-bonding receptors, as well as charged receptors have been used for anion sensing in both organic and aqueous solutions, or within various polymeric networks, such as hydrogels. The review concludes with some current and future perspectives including the use of the naphthalimides for sensing small biomolecules, such as amino acids, as well as probes for incorporation and binding to proteins; and for the recognition/sensing of polyanions such as DNA, and their potential use as novel therapeutic and diagnostic agents (95 references).

/pdf/colorimetric-and-fluorescent-anion-sensors-an-overview-of-34leqpwx5y.pdf

Colorimetric and fluorescent anion sensors: an overview of recent developments in the use of 1,8-naphthalimide-based chemosensors

Halogen Bonding in Supramolecular Chemistry.

Applications of Supramolecular Anion Recognition

The present critical review outlines the close relationship and mutual interplay between molecular recognition, active site considerations in enzyme catalysis involving anions, and organocatalysis utilizing explicit hydrogen bonding. These interconnections are generally not made although, as we demonstrate, they are quite apparent as exemplified with pertinent examples in the field of (thio)urea organocatalysis. Indeed, the concepts of anion binding or binding with negatively (partially) charged heteroatoms is key for designing new organocatalytic transformations. Utilizing anions through recognition with hydrogen-bonding organocatalysts is still in its infancy but bears great potential. In turn, the discovery and mechanistic elucidation of such reactions is likely to improve the understanding of enzyme active sites (108 references).

(Thio)urea organocatalysis—What can be learnt from anion recognition?

This critical review includes advances in anion complexation in the year 2007. The review covers anion receptors that employ amides and thioamides, pyrroles and indoles, ureas and thioureas, guanidinium, ammonium, and imidazolium groups and receptors containing hydroxyl groups. In addition, receptors containing metal ions or Lewis acids are discussed along with anion–π interactions and the membrane transport of anionic species by synthetic transporters and channels (204 references).

Anion receptor chemistry: highlights from 2007

Anions cannot diffuse passively through biological membranes and membrane-bound proteins mainly govern the transmembrane movement of these charged species. The use of synthetic compounds that are able to facilitate the transmembrane transport of anions is a fascinating and burgeoning topic. The study of facilitated anion transport across lipid bilayers is an emerging field in supramolecular and bioorganic chemistry. In this critical review we describe the recent research progress in this area, focusing on literature published during the years 2007–2009. An overview of the assays that are used in the transmembrane transport of anions is also included (158 references).

Recent advances in the transmembrane transport of anions

Bicarbonate is involved in a wide range of biological processes, which include respiration, regulation of intracellular pH and fertilization. In this study we use a combination of NMR spectroscopy and ion-selective electrode techniques to show that the natural product prodigiosin, a tripyrrolic molecule produced by microorganisms such as Streptomyces and Serratia, facilitates chloride/bicarbonate exchange (antiport) across liposomal membranes. Higher concentrations of simple synthetic molecules based on a 4,6-dihydroxyisophthalamide core are also shown to facilitate this antiport process. Although it is well known that proteins regulate Cl-/HCO3- exchange in cells, these results suggest that small molecules may also be able to regulate the concentration of these anions in biological systems.

/pdf/using-small-molecules-to-facilitate-exchange-of-bicarbonate-5ga2n9ltpb.pdf

Using small molecules to facilitate exchange of bicarbonate and chloride anions across liposomal membranes

Membrane-active calixarenes: toward 'gating' transmembrane anion transport

A transmembrane anion transporter selective for nitrate over chloride

Synthetic receptors have been developed for anions such as chloride, phosphate, sulphate and carboxylate. Development of selective receptors for nitrate has, however, been more difficult. Theoretical calculations show that a six-coordinate geometry is the ideal geometry for coordinating NO3 − . Crystallographic data show, however, that NO3 −  usually adopts a two- or three-coordinate geometry when interacting with receptors. In this review, we briefly discuss the role of NO3 −  in human health and its physical properties. We discuss how proteins and synthetic compounds bind NO3 − , with an emphasis on crystal structures and calculations. Synthetic compounds that best mimic proteins in their types of non-covalent interactions are generally the most effective for binding NO3 − .

Oluyomi A. Okunola

Papers

Recent advances in the transmembrane transport of anions

Using small molecules to facilitate exchange of bicarbonate and chloride anions across liposomal membranes

Membrane-active calixarenes: toward 'gating' transmembrane anion transport

A transmembrane anion transporter selective for nitrate over chloride

Natural and Synthetic Receptors for Nitrate Anion