Recognition halide anions

As a part of our program to develop new adjuvants for the into-cell delivery of phosphorylated nucleotide-type antiviral agents (see Section 3 of this chapter), we became interested in developing a sapphyrin-based approach to phosphate anion chelation. As proved true for halide anion recognition, important initial support for the idea that sapphyrins could function as phosphate anion receptors came from single crystal X-ray diffraction studies. In fact, to date, five X-ray structures of sapphyrin-phosphate complexes have been obtained. ... 

The simplest recognition process is that of spherical substrates these are either positively charged metal cations (alkali, alkaline-earth and lanthanide cations) or the negative halide anions (see Chapt. 3). 

Linear recognition is displayed by the hexaprotonated form of the ellipsoidal cryptand bis-tren 33, which binds various monoatomic and polyatomic anions and extends the recognition of anionic substrates beyond the spherical halides [3.11, 3.12]. The crystal structures of four such anion cryptates [3.11b] provide a unique series of anion coordination patterns (Fig. 4). The strong and selective binding of the linear, triatomic anion N3" results from its size, shape and site complementarity to the receptor 33-6H+. In the [N3 pyramidal arrays of +N-H "N- hydrogen bonds, each of which binds one of the two terminal nitrogens of N3-. 

Chaumont, A., Wipff, G., Halide anion solvation and recognition by a macrotricyclic tetraammonium host in an ionic liquid a molecular dynamics study. New J. Chem. 2006, 30, 537-545. 

Dipolar electrostatic interactions have also been manipulated for the purposes of anion binding. Macrocyclic receptor 10 was shown to be capable of binding halide anions through interactions with the positive ends of the S = O and P = O dipoles (54). Evidence was also provided for the simultaneous binding of primary alkyl ammonium cations (to the oxygen atoms) and halide anions (to the dipoles). This topic of simultaneous cation and anion recognition is of considerable current interest. Further examples will be encountered during this chapter. 

Halide anion recognition by calix[4]pyrrole a quantum chemical study, F. Pichierri,... 

In this study, the recognition of halide anions X" (X = Cl, Br, I) is clearly established by the isolation and X-ray structure determination of a series of well-defined complexes containing the hahde salt and the admixed aromatic... 

Pierre. P. Schurhammer, R. Wipff G. Halide anion recognition in water 1 a hexaprotonated octaaza-crypt-and A molecular dynamics investigation. Chem. Eur. J. 2000. 6 (23). 4257-4264. 

J Structural Studies. As was true in the case of the halide anion recognition, important support for the proposed phosphate anion binding interaction has come from single crystal X-ray diffraction analyses. As shown in Figures 6 and 7, respectively, the diprotonated form of sapphyrin binds the monobasic forms of both phosphoric and phenylphosphoric acid. While, at least from the perspective of the coordinated atoms, these two structures bear a striking resemblance to those of the mono- and dihydrochloride salts alluded to above, in both cases it is of interest to note that in each relevant comparison pair, the phosphate oxyanion is far closer to sapphyrin plane. Specifically, in the case of the H2P04 structure, this chelated atom is found to reside 0.83 A (only ) above the macrocylic plane. Similarly, in the case of the 1 2 complex formed between diprotonated sapphyrin and... 

In order to further develop the coordination chemistry of anions and to extend recognition of anionic substrates beyond the spherical halides, an ellipsoidal macro-bicyclic cryptand Bis-Tren (14) was designed, whose hexaprotonated form was expected to bind various anions [9, 10]. Indeed, potentiometric and spectroscopic measurements showed that (14)-6H complexes a number of monovalent and polyvalent anions. The strong and selective binding observed for the linear triatomic anion NJ may be attributed to its complementarity to the molecular cavity of (14)-6H . As confirmed by crystal structure determination, NJ forms the cryptate [N c (14)-6H ] (15), in which the substrate is bound inside the cavity by two pyramidal arrays of three hydrogen bonds, which hold the two terminal... 

Sessler et al. introduced the anion-recognition ability of calix[4]pyrrole (1.11). 1.11 has the ability to bind halide anions efficiently through hydrogen-bonding interactions between pyrrolic NHs and the anions when the macrocyclic is fixed in the cone conformation. Counter cations are encapsulated at the same time in the opposite side of the bowlshaped calix[4]pyrrole cavity because of the electron-rich pyrrole cavity (Figure 1.9). 

COMPUTATIONAL STUDIES OF THE MOLECULAR RECOGNITION OF HALIDE ANIONS BY CALK[4]AROMATICS... 

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],... 

The development of fluorescent probes for anion recognition has been very limited so far in comparison with those for cations. Most of the presently available methods of detection of anions based on fluorescence involve quenching, redox reactions, substitution reactions, ternary complex formation(15) and thus cannot be considered as recognition methods. For instance, the fluorescent sensors that are used for the determination of chloride anions in living cells are based on collisional quenching of a dye by halide ions 6-methoxy-iV-(sulfopropyl)quinoliniuni and... 

ArmentroutPB (1999) Gas-Phase Organometallic Chemistry. 4 1-45 Astruc D, Daniel M-C, Ruiz J (2006) Metallodendritic Exo-Receptors for the Redox Recognition of Oxo-Anions and Halides. 20 121-148 Aubert C, Fensterbank L, Gandon V, MalacriaM (2006) Complex Polycyclic Molecules from Acyclic Precursors via Transition Metal-Catalyzed Cascade Reactions. 19 259-294... 

Polyphenylene and polyfluorene have been extensively used as fluorescence-based sensors, and several chromogenic forms of these polymers have been reported. Incorporation of monomers with additional coordination sites into these polymers has led to the development of a variety of different anion sensors, mostly for halide ions (Lee et al. 2004 Zhou et al. 2005 Vetrichelvan et al. 2006 Kim et al. 2007). Extension of these materials toward recognition of more complex analytes should be possible. 

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