Recognition, anion

Dynamic anion recognition by macrocyclic polyamines in neutral pH aqueous solution 98CC1495. 

Beer PD, Timoshenko V, Maestri M et al (1999) Anion recognition and luminescent sensing by new ruthenium(II) and rhenium(I) bipyridyl calix[4]diquinone receptors. Chem Commun... 

There are a limited number of fluorescent sensors for anion recognition. An outstanding example is the diprotonated form of hexadecyltetramethylsapphyrin (A-7) that contains a pentaaza macrocydic core (Figure 10.31) the selectivity for fluoride ion was indeed found to be very high in methanol (stability constant of the complex 105) with respect to chloride and bromide (stability constants < 102). Such selectivity can be explained by the fact that F (ionic radius 1.19 A) can be accommodated within the sapphyrin cavity to form a 1 1 complex with the anion in the plane of the sapphyrin, whereas Cl and Br are too big (ionic radii 1.67 and 1.82 A, respectively) and form out-of-plane ion-paired complexes. A two-fold enhancement of the fluorescent intensity is observed upon addition of fluoride. Such enhancement can be explained by the fact that the presence of F reduces the quenching due to coupling of the inner protons with the solvent. 

Table 20 Electrochemical data" for [87] and its electrochemical anion recognition properties.

CV and SWV were used to investigate the electrochemical anion recognition properties of these species in acetonitrile and the results are summarized in Tables 21 and 22. With reference to the known electrochemical properties of [Ru(bipy)3][PF6]2, the respective reversible oxidation and reduction redox couples exhibited by the receptors can be assigned to the metal-centred... 

Nature uses globular protein domains to bind sulfate and phosphate anions using respectively 7 and 12 complementary anion-hydrogen bond arrangements. With this in mind we decided to construct new, neutral ferrocene derivatives that contain various hydrogen bond donor and acceptor sites for anion recognition. 

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... 

V-(6-methoxyquinolyl)acetic acid are examples of such probes.(48) Therefore, one cannot speak of anion recognition because the probe does not associate with the anion but only interacts in the excited state causing a decrease in fluorescence... 

Wilcox[102-104] A/,A/ -disubstitued (thio)urea derivatives studies on substituent effects in anion recognition and supramolecular chemistry... 

Currently, the only other monoprotonated sapphyrin-monoanion complex to be solved by X-ray diffraction analysis is that of 3-HN,. As expected, in this complex the azide counteranion is bound above the sapphyrin plane by a combination of anisotropic electrostatic interactions and oriented hydrogen bonds (Figure 4). As such, this structure supports the conclusion, reached in the case of 3-HCl, that a single positive charge on the sapphyrin is enough to effect anion recognition of anionic substrates, at least in the solid state. 

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. ... 

Despite the prominence of anion recognition chemistry in biological systems, the design of supramolecular anion receptors was slow to develop with respect to the analogous chemistry of cations, and this discrepancy may readily be traced to a number of inherent difficulties in anion binding ... 

These problems have been addressed in a wide variety of imaginative and novel ways and progress in anion complexation has been rapid in recent years " to the extent that it has now been described by Lehn as a full member of the field of supramolecular chemistry. It is important to note that the search for anion-selective receptors has not been limited to the mimicry of Mother Nature s approach. Indeed, a great number of the hosts developed are far from being biocompatible as the tools of the chemist are not limited to the building blocks of natural systems. This aspect of anion recognition chemistry lies at the heart of supramolecular chemistry, the interface between chemistry and biology. ... 

The application of anion receptors in sensing has been mentioned earlier. Dioxatetraazamacrocycles 381 were synthesized for the application in chiral anion recognition [43]. Mesoporous films by 382 were developed to be used as sensors for volatile organic compounds [44]. Receptors for anions were also studied to mimic their transport through membranes [45]. 

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