Receptor-based sensing

T.D. James, K.R.A.S. Sandanayake, S. Shinkai, Saccharide sensing with molecular receptors based on boronic acid , Angew. Chem, Int. Ed. EngL 1996, 35, 1910-1922. 

Possible measures that are expected to improve the potentiometric selectivity are (1) use of hosts that form stronger complexes, (2) modification of the host to avoid ionophore self-association, and (3) an improved choice of the membrane solvent to avoid strong solvation of the hosts in the membrane. Evidence for the importance of (2) and (3) has been obtained from C NMR spectra of 12. While the properties of 1 1 host-guest complexes are very often of primary interest in supramolecular chemistry, the above results show that use of receptors for sensing purposes must be based on a receptor design that goes beyond this viewpoint. 

Anion receptors incorporating cobaltocenium have been studied extensively due to the combination of an accessible redox couple and potential favourable electrostatic interactions of the cationic organometallic metallocene complex with anions. The first anion receptor based on this species was reported by Beer and co-workers in 1989 [6]. The macrocyclic bis-cobaltocenium receptor 1 was shown to bind (via electrostatic interaction) and to electro chemically sense bromide in acetonitrile solvent media. 

Lhotak, P. (2005) Anion Receptors Based on Calixarenes" in Anion Sensing, (Topics in Current Chemistry) (ed. Stibor, J.), Springer, Heidelberg, 255, 65—95. 

Boronic acids RB(OH)2, boronic esters RB(OR)2, and triorganoboranes R3B have been studied extensively for the selective recognition of anions. " Moreover, arylboronic acids have proven highly useful for sensing of saccharides based on the facile formation of esters with diols, thus providing an excellent alternative to more commonly employed synthetic molecular receptors based on hydrogenbonding interactions. Absorption and fluorescence spectroscopy, circular dichroism, and cyclic voltammetry have all been successfiilly used as detection methods for organoboron sensors. 

Frank ME, Blizard DA (1999) Chorda tympani responses in two inbred strains of mice with different taste preferences. Physiol Behav 67 287-297 Fuller JL (1974) single-locus control of saccharin preference in mice. J Heredity 65 33-36 Galindo-Cuspinera V, Winnig M, Bufe B, Meyerhof W, Breslin PA (2006) A TAS1R receptor-based explanation of sweet water-taste . Nature 441 354-357 Glaser D, Tinti JM, Nofre C (1995) Evolution of the sweetness receptor in primates. I. Why does alitame taste sweet in all prosimians and simians, and aspartame only in Old World simians Chem Senses 20 573-584... 

An example will be reported here, based on nucleic acid receptors called aptamers, selected in vitro, which can be produced for a wide range of molecules [11] and represent now one of the frontiers of nucleic acid-based sensing. 

The advent of new receptors based on nucleic acids, called aptamers, is a new challenge in piezoelectric sensing, not based on the hybridization reaction. The development of aptasensors has analogies to the introduction of immunosensing almost two decades ago the direct detection of analytes in complex matrices by immobilizing an optimized receptor on the sensing surface. 

A receptor based on Co° (bpy)3 has been used by Sessler and coworkers for redox fluoride sensing [34]. In the cyclic voltammetry of 47 in DMSO solution addition of fluoride led to a complete disappearance of the Co(II)/(III) reduction wave. Addition of water to this solution restored this redox process, suggesting that the presence of a strongly bound fluoride anion renders the complex redox inactive. Chloride and dihydrogenphosphate produced cathodic shifts of 160 mV and 70 mV, respectively. It is proposed that... 

As we discussed in the introduction, the anion-jt interaction has potential application in the field of molecular recognition of anions. In this sense, several theoretical studies have proposed structures for novel receptors based... 

The cobaltocenium moiety was studied extensively in the context of redox-responsive anion receptors. " The first class of anion receptor based on this system was reported by Beer and Keefe in 1989. The ester functionalized hi 5-cobaltocenium maeroeyelie Reeeptor 1 bound and eleetroehemieally sensed bromide in acetonitrile via favorable electrostatic interactions. 

Because of their inherent stability, unique optical properties, and synthetic versatility, porphyrins and metalloporphyrins are excellent candidates for a variety of sensing-materials applications. Research in this area has focused on incorporation of synthetic porphyrins and metalloporphyrins into a variety of material matrices, such as polymers, glasses, and LB films. Substantial work has been done in the areas of solution and gas-phase. sensing, and highlights of both areas will be di.scussed. We will al.so briefly examine molecular recognition and receptor studies, becuase developments in these areas will further the development of porphyrin-based sensing materials. 

A new class of ferrocene (also cobaltocenium) receptors which sense anions both spectrally and electrochemically, is based upon attachment of metallocene moieties to a porphyrin skeleton. The porphyrin fragment can be simultaneously complexed by zinc [120]. 

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