Ether conjugate

A methanofullerene derivative possessing an ammonium subunit has been prepared and subsequently shown to form a supramolecular complex with a porphyrin-crown ether conjugate <06T1979>. The synthesis and study of these fullerene-containing supramolecular photoactive devices have also been reported <06CRC1022>. 

Transesterification of the fullerene crown ether conjugate (+)-89 allowed for the removal of the tether, leading to the D2fj-symmetrical bisadduct 94 (34%) [93], which is a very useful building block for further addition chemistry. 

A few other interesting molecular architectures exhibiting uncharacteristic electrochemical behavior have been constructed on the basis of the methanofullerene building block. These include two methanofullerene-substituted bipyridine ligands complexed to rhenium and ruthenium ((35) and (36) in Fig. 17), which were prepared as possible candidates for photoinduced electron transfer processes [138]. In addition, three fullerene crown ether conjugates ((38), (39), and (40) in Fig. 18) have... 

Electrochemical studies of fullerene crown ether conjugates (38), (39), and (40) yielded fascinating results. The three compounds differ only in the points of attachment of the tangential crown... 

Extending beyond alcohols and ethers, conjugate acids of carbonyl-based functional groups are known. Specifically referring to carboxylic acids and esters, the corresponding conjugate acids, illustrated in Scheme 3.7, have pKa values around 6. Furthermore, protonated aldehydes and ketones, illustrated in Scheme 3.8, have p/Ca values ranging from 7 to 9. 

On the other hand, protecting groups can be used to thwart heteroatom-assisted delivery. Reaction of the a,f -unsaturated sulfone 51.1 with trimethylsilylethynyl-lithium resulted in intramolecular delivery of the nucleophile to afford adduct 51.2 with a dr = 100 1 [Scheme 1.51].88 When the hydroxy group was protected as its trivnethylsilyl ether, conjugate addition took place from the opposite face to give the diastereoisomeric adduct 51.4, again with a dr = 100 l. 

This biosensor employs a potassium (K+) ion-selective electrode as the transducer, and chemical recognition involves the unh-digoxin antibody and a digoxin-crown ether conjugate. A diagram of the sensor is shown in Figure 7.5. 

In this device, a poly(vinyl chloride) (PVC) membrane separates an internal K+ solution from an external layer of digoxin antibody that is trapped at the sensor surface with a dialysis membrane. The digoxin-crown ether conjugate, which selectively binds K+, is present only in the PVC layer due to its hydrophobic properties. Competition between free digoxin (analyte) that freely crosses the... 

A similar procedure was used for antidigoxin antibody assay. Digoxin-benzo crown ether conjugates, rather than cortisol were entrapped in the PVC membrane of the K+ sensitive electrode. The detection limit was in the range of a few g/ml. The sensor was regenerated by a brief (<60 s) immersion in glycine-HCl buffer, pH 2.8. The membrane was stable for 1-2 weeks under conditions of routine use. 

A synthesis of a-azido ketones consists of the oxidation of triisopropylsilyl enol ethers in the presence of NaNj. Nitroalkanes act as aldol acceptors when their anions are exposed to CAN in the presence of silyl enol ethers. Conjugated ketones are obtained on subsequent treatment with triethylamine. 

Crown ethers conjugated to the ben-zofuranyl fluorophore (SBFl and PBFl), sodium green, CoroNa Red,... 

Bourgeois, J.-P. Echegoyen. L. Fibbioli, M. Pretsch, E. Diederich. F. Regioselective synthesis of trans-l fuller-ene i.v-adducts directed by a crown ether tether Alkali metal cation modulated redox properties of fullerene-crown ether conjugates. Angew. Chem. Int. Ed. 1998. 37. 2118-2121. 

Tsukube. H. Wada. M. Shinoda, S. Tarniaki, H. Porphyrinatoerbium-crown ether conjugate for synergistic binding and chirality sensing of zwitterionic amino acids. J. Chem. Soc., Chem. Commun. 1999, 1007-1008. 

Kidney hsdogenated hydrocaibcarbon tetrachloride), toluene, dioxane, diethylene glycol, ethylene glycol, glycol ethers, conjugates of trichloroethylene acute tubular necrosis, glomerular and tubular dysfunctions (e.g., albuminuria, proteinuria), glomerulonephritis, note modification of solvent effects caused by renal dysfunctions possible... 

Fig. 18. A self-assembled fullerene-crown ether conjugate monolayer.

A fullerene-crown ether conjugate, similar in structure to that used for building SAM associates, forms in solution a 1 1 complex with 3-aminomethyl-(2,2,5,5-tetramethylpyrrolindin-l-oxyl). Using visible light, which engages mainly with the fullerene core, a radical-triplet pah-in the quartet excited state has been recorded. Strong electronic interactions between the triplet excitations and an ammonium aminoxyl free radical are responsible for the radical-triplet character. 

Cooperative self-assembly and molecular binding behaviour of CD-crown ether conjugates mediated by alkali metal ions was characterised by 2D NMR/ ... 

Probe 34 (Fig. 28.8), a calix[4]biscrown-6 ether conjugated with BODIPY units, exhibits high selectivity for Cs" among several cations examined [62]. Substitution at the a-position of BODIPY improves the photophysical sensitivity. In the presence of Cs" ions, a hypsochromic shift was observed in the fluorescence and absorption spectra. This shift is due to binding of the crown ether to Cs", which decreased the electron-donating ability of the oxygen atoms. 

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