Receptor anionic

Ferrocene-based bisphosphanes, in hydrogenations, 10, 10 Ferrocene-based receptors anion receptors, 12, 476 cation receptors, 12, 466 for neutral guest species, 12, 483 Ferrocene-based sensors, screen-printed, in biosensing,... 

It is important to appreciate that these ditopic macrocycles contain a polyether moiety on one side and present a diamido motif on the other. Addition of a charged pyridinium cation to the substrate-free form of these macrocycles then generates a highly efficient receptor for chloride, presumably as the result of both template-induced organization and electrostatic effects. The further incorporation of hydro-quinone groups and polyether functionalities into the cyclic framework presumably contributes to the stabilization of the cationic pyridinium component within the final interpenetrated structure. Interestingly, while titration of the pyridinium cation building block alone revealed a preference for oxoanions, the final receptor-anion... 

Lewis acidic hosts (Section V.A) illustrated important theoretical concepts such as the chelate effect and binding cooperativity, which have now been shown to exist for anion as well as cation binding. This work has also resulted in the crystallographic determination of eye-catching solid state receptor-anion complexes, while heteroelement NMR has allowed an accurate means of probing the solution phase structure of these complexes. Already, multinuclear tin systems are being built into functioning anion selective electrodes. 

These characteristics are shared with subunits that form other ion channels/receptors and thus define a receptor superfamily, usually referred to as the nicotinic family. All members in this superfamily function as either cation- or anion-selective channels, thereby mediating fast excitatory or inhibitory synaptic transmission. In mammalian cells, the cation-selective members include nicotinic and 5HTg receptors, whereas the anion-selective members include GABA, GAB Ac, and glycine receptors. Anion-selective channels in this family are also found in invertebrates these channels are gated by glutamate, 5-HT, histidine, and acetylcholine (1). 

Mangani, S. and Ferraroni, M., Natural anion receptors anion recognition by proteins , in Supramolecular Chemistry of Anions, Bianchi, A., Bowman-James, K. and Garcia-Espana, E. (eds), Wiley New York, 1997, 63-78. 

Proton NMR titrations in DMSO-de/O.S water at 298 K were conducted to elucidate stability constants for a number of anions, added as their terabuty-lammonium salts. Fluoride affects the largest change on the proton resonance however an association constant was only calculated for 60a (>10 M ) therefore titrations were repeated in more competitive media (DMSO-d6/5% water). Both receptors showed selectivity for fluoride however 60a bound with a 1 1 binding stoichiometry (1360 M ) whereas the data for 60b could only be fitted to a 1 2 receptor/anion model (iCi = 940 andK2 = 21 M ). The crystal structures of 60a with chloride and fluoride are shown in Figs. 8 and 9 respectively. 

Row, Maitra and co-workers have linked two steroid subunits to synthesize macrocycle 66. The fluoride-binding properties of compoimd 66 were then investigated by a NMR titration experiment in CDCI3 at 22 °C, which found that the receptor bound fluoride with a 1 2 receptor/anion stoichiometry (a result confirmed by Job plot analysis) and stability constants of Ki = 1.8 ( 0.1) xlO M-i and K2 = 2.5 ( 0.35) xlO were found [79]. 

When a redox-active transition metal is used as the signalling imit of a receptor, anion binding is coupled to electron transfer, i.e. anion binding changes the redox potential (couple) of the transition metal. This electrochemical shift can be represented as A, the difference in redox potentials between the receptor anion complex and the receptor alone. Concomitantly, electron transfer at the redox centre also changes the affinity of the receptor for the guest species. These coupled processes are linked thermodynamically by Eq. 1, where Kred and Kox are the stability constants of the reduced and oxidised forms of the receptor anion complex respectively [7]. 

From a thermodynamic standpoint, the value of the shift in redox potential is determined by the ratio of Kox/-f red> instead of the absolute value of either Kox or Kted- As a consequence a receptor need not necessarily have a very high binding strength for the anion to be sensed. If electron transfer leads to a sufficiently large change in the stability of the receptor anion complex, a measurable change in redox potential can be observed. 

The novel series of ferrocene receptors 64-68, which incorporate thiobar-biturate anion binding/chromophore groups, have been shown to operate as UV-vis anion sensors in acetonitrile solution. Addition of basic anions such as cyanide, acetate and benzoate causes the attenuation of the absorption maximum at around 440 nm (due to a charge transfer transition between the amine and the thiobarbiturate group), with the simultaneous occurrence of a new band at 370 nm. In cases where the titration data could be fitted, 1 2 receptor anion binding stoichiometries were found [47]. 

Loeb, Gale and co-workers have used Pt(II) as a structural template for the self-assembly of a series of anion receptors. Receptors 129-132 were found to bind a variety of anions in DMSO-d solution [92,93]. Even the simple tetrapyridine receptor 129 has an affinity for anions due to its electrostatic charge. The addition of pyrrole hydrogen-bond donors increases the stability of the receptor anion complexes by more than five-fold in 130, but in 131... 

Keywords Anion-n interactions Anion coordination Anion receptors Anions Host-guest systems Supramolecular chemistry... 

More recently, some simple and yet highly effective amide-cleft-based anion receptors were synthesized by Crabtree and coworkers. Receptors 10-14 are based upon benzene or pyridine rings that are substituted in the 1- and 3-positions, or in the case of pyridine 2- and 6-positions, with either amide or sulfonamide groups. Proton NMR titrations in dichIoromethane-fi 2 were used to determine the association constants of the receptors with halide anions and acetate. All the receptors displayed solely 1 1 receptor anion complex stoichiometry in solution. except receptor 13 that showed behavior consistent... 

Kubo and coworkers synthesized a 7M-thiourea functionalized dibenzo-diaza-30-crown-10 51 that wraps around potassium cations, so bringing the two thiourea groups into close proximity, forming an anion binding site. NMR titration experiments with (Ph0)2P(0)0 anions (which form both 1 1 and 1 2 receptor anion complexes with 51) in acetonitrile-r/j solution in the absence and presence of potassium cations show an increase in Ki from 490 to 9200 M upon addition of three equivalents of potassium cations. 

Becher, J. A pyiTolo-tetrathiafulvalene cage Synthesis and X-ray crystal structure. Org. Lett. 2802. 4. 4189-4192. Bartoli, S. Roelens. S. Binding acetylcholine and tetra-methylammonium to a cyclophane receptor Anion s contribution to the cation-jt interaction. J. Am. Chem. Soc. 2002. 124. 8307-8315. 

Figure 2. NMR anion coordination studies (a) H NMR titration curve for compound 1 and fluoride anions in dichloromethane-c/2 and (b) molar ratio ()ob) plot of compound 1 with fluoride anions indicating a 1 1 receptor/anion stoichiometry.

In the solid state, a series of anion receptors may assemble in various assembling modes in the forms of receptor-anion complexes by combination with counter cations. jS-Unsubstituted lb afforded a planar [1 -1- l]-type pentacoordi-nated CF complex Ib CF that involved the pyrrole NH, the bridging CH, and phenyl ortho-CH units (Fig. 9.3a). Planar anion Ib CF stacked with tetrapropy-lammonium cations (TPA" ) to form a charge-by-charge columnar structure with a Cl -Cl distance of 8.54 A, and a separation of 7.29 A between the Ib CF units... 

Y. Haketa, S. Sasaki, N. Ohta, H. Masunaga, H. Ogawa, N. Mizuno, F. Araoka, H. Takezoe, H. Maeda, Oriented salts dimension-controlled charge-by-chaige assemblies from planar receptor-anion complexes. Angew. Chem. Int Ed. 49, 10079-10083 (2010)... 

B. Dong, Y. Terashima, Y. Haketa, H. Maeda, Charge-based assemblies comprising planar receptor-anion complexes with bulky alkylammonium cations. Chem. Eur. J. 18, 3460-3463 (2012)... 

B. Dong, T. Sakurai, Y. Honsho, S. Seki, H. Maeda, Cation modules as building blocks forming supramolecular assemblies with planar receptor-anion complexes. J. Am. Chem. Soc. 135, 1284-1287 (2013)... 

Excess toxicity of varying extents occurs for acetylcholinesterase (AChE) inhibitors such as organophosphorous compounds (Bruijn and Hermens, 1991a,b). Acetylcholine serves as a neurotransmitter in the central as well as in the peripheral nervous systems of various vertebrates and invertebrates (Corbett, Wright and Baillie, 1984 Fukuto, 1990). When an efferent impulse reaches the nerve ending, acetylcholine is released into the synaptic cleft and diffuses to receptors located in the postsynaptic membrane, causing stimulation of the nerve fibre or the muscle. The quaternary ammonium of the acetylcholine binds by electrostatic interactions to the receptors anionic centre... 

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