Sensing anions

Quaternary alkylammonium salts are generally water-soluble surfactants. The sol-gel-derived anion-sensing membranes encapsulating a quaternary alkylammonium salt, especially with high contents, are easy to deteriorate due to the exudation of the cationic site from the membrane to aqueous sample phases. Moreover, another issue concerning the dispersibility of ammonium salts in sol-gel-derived membranes may happen when high... 

Although non-covalent interactions of anions are one of the most actively explored areas of supramolecular chemistry [15], the anion sensing and recognition have up to now relied primarily on electrostatic binding or hydrogen bonding to the receptor [16,54-61]. However, recent UV-Vis and NMR spectral studies clearly reveal that complex formation takes place in the solutions between halides and neutral olefinic and aromatic it-acceptors such as those in Fig. 3 [23,62],... 

Beer PD, Bayly SR (2005) Anion Sensing by Metal-Based Receptors. 255 125-162 Bertini L, Bruschi M, de Gioia L, Fantucci P, Greco C, Zampella G (2007) Quantum Chemical Investigations of Reaction Paths of Metalloenzymes and Biomimetic Models - The Hydrogenase Example. 268 1-46 Bier FF, see Heise C (2005) 261 1-25... 

The study of anion coordination has implications for a number of areas in chemistry and biochemistry. These include analytical applications concerned with anion sensing or separation as well as model studies for anion-specific biochemical systems. With respect to the latter, it is of interest that the majority of enzymic systems so far characterized bind substrates which are anionic. 

A few examples were reported for the anion sensing by principle of quenching of fluorophores with anions such as I, Br, and Cl- as shown below ... 

An analogous system to the cation sensors is the use of optically nonactive anion ionophores together with a pH-sensitive chromophore for the anion sensing. In this system, simultaneous extraction of H+ and anion X- from the aqueous solution into an organic phase results in protonation of the chromophore anion C, e.g. 

E. Wang, C. Romero, D. Santiago and V. Syntilas, Optical anion sensing characteristics of indium-porphyrin and lipophilic dichlorofluorescein doped polymer films, Anal. Chim. Acta, 433 (2001) 89-95. 

Beer PD, Bayly SR (2005) Anion Sensing by Metal-Based Receptors. 255 125-162... 

Fig. 29 Protocol for anion sensing using mesoporous MCM-41-like solids (UVM-7) containing nanoscopic binding pockets and suitable dyes...

Anion sensing by complexes involving macrocyclic and calix[4]arene domains has been reviewed. The receptors [Ru(bpy)2(252)] + (in (252), R = Ph, 2-HOCeH4, 3-HOCeH4, 4-HOCeH4, Bu, or 4- BuC6H4) bind Cl, Br, and I hydrogen-bonded interactions that contribute to this process are discussed. All the complexes show the same anion selectivity CC > Br > The crystal... 

Figure 11.5 Schematic of anion sensing porphyrin Au MMPC. Reprinted with permission from Ref. 26.

Fig. 7 a Schematic representation for the monolayers of the anion-sensing library, b Relative fluorescence intensity of surfaces modified with different fluorophores and chemical functionalities in the presence of 1CT4 M solutions of HS04", NC>3", TbPCTf and AcCT as tetrabutylammonium salts in acetonitrile. The data have been normalized in the absence of anions the fluorescence emission at 585 and 575 nm for layers LO, L5-L8 and T0-T4, respectively, is set to 0... 

Metal-based receptors provide excellent frameworks for anion host organisation and can act as reporter groups in electrochemical and luminescent anions sensing applications. 

Figure 13.9 Electrochemical anion sensing by a dithiol SAM. Anion binding results in predictable cathodic perturbation of the SAM voltammetry. Anion binding affinities associated with such SAMs are, in some cases, orders of magnitude greater than those associated with the same receptors free in solution (reproduced by permission of The Royal Society of Chemistry).

P. D. B. thanks his postgraduate and postdoctoral co-workers for all their hard work and inspiration their names are cited in the references. A special thank you goes to Professor M. G. B. Drew for his numerous structure determinations and molecular modelling expertise and to my colleague Dr. Jason Davis for collaborative research on anion sensing SAMs and nanoparticles. P. D. B. gratefully acknowledges the financial support of EPSRC, AWE, Johnson Matthey and NSERC (Canada). 

Method A has been successfully applied in anion sensing. As mentioned previously, lanthanide ions can coordinate to anions such as acetate, fluoride, etc., which modulates the lanthanide luminescence. Examples of such systems will now be discussed. 

---