Specific Fluoride Receptors

The CPK model of an X-ray structure of [Cp Ir(Ll)]3 liF provides an explanation for this selectivity (Fig. 10.20). The fluoride ion was found to be positioned at the opening of the cavity, closely surrounded by the three Cp ligands. As a result, the four very short CH F contacts between the Cp ligands and F could be observed (CH - - F = 2.15-2.28 A). This very tight encapsulation of the fluoride ion was expected to contribute to the overall stability of the host-guest complex and prevented the coordination of larger anions. 

The modular nature of these assemblies makes it possible to incorporate many structural variations of these organometaUamacrocyclic complexes. Given the exceptional performance of these organometaUamacrocyclic receptors when compared with classical ionophores, such as crown ethers and cryptands, various applications can be envisioned in the future, including studies in water [6,12e]. 

Roberts, J. D. Watson, Molecular Biology of the Cell, pp. 481-612, Garland Publishing, New York, 1989  

de Mendoza, ). Rebek )r., Angeiv. Chem. Int. Ed. Engl. 1992, 31, 61 and references therein  

Cabestaing, I. Laios, G. Leclercq, C. Peovot, G. Jaouen, /. Organomet. Chem. 2001, 639, 500. 

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Scheme 4 Schematic representation of a specific fluoride receptor based on a Li containing metallamacrocycle...

The above results served to demonstrate the validity of considering the protonated sapphyrins as both specific fluoride binding agents [162-166] and as novel members of an increasingly large class of anion receptors [167-172]. This is of considerable interest since protonated porphyrins, with a core diameter of approximately 4 A, are too small to bind anions centrally, let alone accommodate the needed two extra protons within the macrocyclic core [173-176]. 

The mechanism of action of adenyl cyclase stimulators or inhibitors is unclear except for fluoride, which stimulates purified preparations of the enzyme. All other known inhibitors or stimulators are inactive on the purified enzyme, but they can modulate its activity when the enzyme is in the particulate form. Therefore, investigators have proposed that binding to specific membrane receptors modifies the configuration of membrane-bound adenyl cyclase. The existence of receptors specific for the various lipolytic hormones has been demonstrated on the fat cell membrane. All such receptors (except those for epinephrine) are destroyed by treatment with trypsin, which suggests that they are proteins. The specificity of the... 

Aryltriazenes can also be decomposed by hydrogen fluoride in organic solution after extraction from their aqueous mother phase. In this case, hydrogen fluoride can be used in small excess but the nature of the solvent is crucial for example, tetrahydrofuran gives complex mixtures, dichloromethane promotes radical reactions (dimerizations, reductions) and acetic acid favors triazene decomposition before fluorination. Aromatic and haloaromatic compounds seem to be the best solvents.283 Such a technique, especially suited for the rapid introduction of an 18F atom, has been employed to produce [ 8F]haloperidol (3), the specific receptors of which have been localized in the brain by positron emission transaxial tomography.298... 

NCB-20 cells. A schematic representation of these proteins within the lipid bilayer of the plasma membrane is shown in Figure 8.27. The arrowed solid lines represent the normal points of interaction between the proteins. Activation of the catalytic subunit E may be effected, in the absence of a specific agonist for surface receptors (R), by stimulation of the G-protein complex with fluoride ions. F ions probably produce their effect by facilitating dissociation of from G py, and G is then free to complex with E. This association is an essential step in the activation of adenylate cyclase. The possibility that desensitization of PGI2 receptors of NCB-20 cells might be... 

It should be pointed out that a specific modification of Ti(0)Pc 1 (R = -H) in organic polymers is the most widely used photoconductor in bilayer photoreceptor copiers and laser printers [19]. A thin film containing ethylene-bridged silicon phthalocyanine polymer dispersed in poly(vinylidene fluoride) (1 4 by weight) obtained by casting from a DMF slurry on quartz was orientated in an electrical field [20], A double-layered receptor device for measuring the... 

General Concepts - Hormone-sensitive adenyl cyclase systems are located principally, if not exclusively, in the surface membrane of the cell. . Isolated fat cells contain in their surface membrane an adenyl cyclase which is activated by catecholamines, five different peptide hormones, and fluoride ion. , . . fter incubation with trypsin, these cells no longer respond to the peptide hormones but do respond to epinephrine and to fluoride ion . However, after incubation of "ghosts", the hypotonic lysate of isolated fat cells, with trypsin, all adenyl cyclase activity is lost. These results have been interpreted to indicate a difference in accessibility of the proteolytic enzyme to the outer and inner surfaces of the plasma membrane of the intact cell and ghosts. All six hormones stimulate the same adenyl cyclase activity, but several lines of evidence indicate that they do so through distinct, specific receptors , . 

NHNP-NBE inactivates irreversibly the hormone-dependent adenylate cyclase activity, whereas the fluoride-stimulated activity remains intact. Bromoacetic acid as well as bromoacetamide causes enzyme inactivation at concentrations two orders of magnitude higher than those obtained with NHNP-NBE. Other bromoacetyl derivatives of propranolol, e.g., BHNPK (Fig. 2), - which do not react specifically with the /J-receptor, were similar in behavior to bromoacetic acid (see below) and bromoacetamide. Specific binding of [ H] propranolol to the /8-receptor was inhibited irreversibly by the compound NHNP-NBE. ... 

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