Neutral anion receptors

Design and application of macroheterocycles as neutral anion receptors 98CC443. 

The complexation of various molecular anions by other types of macrocyclic ligands has been reported [3.1-3.4] in particular with cyclophane-type compounds. Two such receptors are represented by the protonated forms of the macropolycycles 40 [3.29] and 41 [3.30]. Quaternary polybipyridinium compounds also bind anionic substrates [3.31]. Progress is also being made towards the developments of neutral anion receptor molecules [3.32]. The thermodynamic and kinetic data for anion complexation by macrocyclic receptors have been reviewed [2.18c]. 

Kubik, S., Kirchner, R., Nolting, D., and Seidel, J. (2002) A molecular oyster A neutral anion receptor containing two cyclopeptide subunits with a remarkable sulfate affinity in aqueous solution, J. Am. Chem. Soc. 124, 12752-12760. 

Fig. 26 Neutral anion receptor consisting of two tetraamide macrocycles linked by two ethylenediamine spacers (15) [58] (a) crystal structure of uncomplexed 15 (b) crystal structure of the hydrogendifluoride complex [15—FHFI, in which each fluorine atom is bound to only two N-H fragments of the proximate tetraamide macrocycle (c) lateral and (d) top views, highlighting the interaction of HF2- with N-H fragments...

Figure 50 Neutral anion receptors with high selectivity for H2PO4 [71]...

Synthesis and complexation studies of neutral anion receptors, S. Valiyayeettil,... 

Antonisse, M. M. G. and Reinhoudt, D. N., Neutral anion receptors, design and application , Chem. Commun., 1998,443 48. 

Sessler and coworkers have prepared fluorinated calix[4]pyrroles (97 = 1) and expanded calixpyrroles (98 n = 2-5) by the condensation of 3,4-difluoropyrrole with acetone under acid catalysis (Fig. 3.47). The fluorinated dipyrrolylqumoxaline 99 was also synthesized from 3,4-difluoropyrrole. These were studied as neutral anion receptors that had higher affinity and greater selectivity relative to their nonfluorinated congeners. 

Anzenbacher, P., Jr. Try, A.C. Miyaji, H. Jursikova, K. Lynch, V.M. Marquez, M. Sessler, J.L. Fluorinated calix[4]pyrrole and dipyrrolylquinoxaline neutral anion receptors with augmented affinities and enhanced selectivities. J. Am. Chem. Soc. 2000, 122, 10268-10272, and references therein. 

Abstract This review article provides a broad overview to the area of anion coordination by synthetic organic receptors and includes examples of different functional groups used to bind anions. The first section examines neutral anion receptors containing amide-, sulfonamide-, urea- and thiourea-based receptors. Then aromatics such as pyrrole, car-bazole and indole are discussed before concluding the discussion of neutral systems with examples of hydroxy OH donors. A brief overview of charged systems is also provided. 

Antonisse. M.M.G. Reinhoudt. D.N. Neutral anion receptors Design and application. Chein. Cornmun. 1998, (4). 

H-binding sites like C(0)-NH fragments in a preorganized receptor molecule should increase the selectivity and efficiency of anion complexation. Using this approach a novel class of neutral anion receptors that contain a unique combination of an immobilized Lewis acidic binding site (U02 ) and the presence of additional amide C(0)-NH groups which can form a favorable H-bond with a coordinated anion guest, has been developed [ref 27 and 28]. 

The reaction of 3,4-difluoropyrrole 391 with aliphatic ketones 466 afforded fluorinated calix[n]pyrroles. Different fluorinated macrocyclic compounds of this type were prepared using this approach by careful variation of concentration, temperature, and reaction time. Calix[4]pyrrole 467 and calix[5]pyrroles 468 can be prepared as sole products. In contrast, calix[8]pyrrole 469 is always obtained as a mixture with calix[5]pyrrole 468. Calix[4]pyrroles 467 act as neutral anion receptors and were found to bind anions such as fluoride, chloride, or dihydrogen phosphate with an enhanced affinity compared to their non-fluorinated analogues [150,152],... 

Anzenbacher P, Try AC, Miyaji H, Jursicova K, Lynch VM, Marquez M, Sessler J (2000) Fluorinated cahx[4]pyrrole and dipyrrolylquinoxahne. Neutral anion receptors with augmented affinities and enhanced selectivities. J Am Chem Soc 2000(122) 10268-10272... 

Pyrrole contains a single NH H-bonding donor group and constitutes the basis for a wide variety of charged and neutral anion receptors. Pyrrole differs from urea discussed above as it does not contain an H-bond acceptor group. 

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