Bipyridyl subunit

Crown compounds containing pyridyl or bipyridyl subunits.141... 

A reversible one-electron transfer at + 1.34 V was observed, assigned to the metal-centered Ru(II)/Ru(III) oxidation. The complex cathodic pattern of this species, comprising 10 successive reversible one-electron transfer, is the sum of that of its two subunits, the C60 core and the Ru(II) tris-bipyridyl complex, thus excluding any... 

It was originally assumed that in LADH the zinc existed in an octahedral form with six bonds available for coordination, until in 1967 Vallee and co-workers showed that the enzyme contained two different types of zinc atom.13773 Loss of two zinc atoms from the enzyme resulted in loss of catalytic activity but maintained the tertiary structure. It was postulated from this that one metal ion per subunit played a role maintaining the tertiary structure, while the other zinc functioned in a catalytic role. Only two of the zinc ions in the liver enzyme interact with the inhibitors 1,10-phenanthroline and 2,2 -bipyridyl, thus demonstrating the different chemical reactivities of the zinc ions.1378 It was also shown that one zinc per subunit could be selectively exchanged or removed by dialysis. This modified enzyme containing one zinc per subunit did not bind 1,10-phenanthroline, hence the catalytic zinc is removed first during dialysis.1379 The second zinc atom can be selectively removed in preference to the catalytic zinc, by carboxymethylation followed by dialysis.1377 ... 

A derivative of the (bpy.bpy.bpy) cryptand, obtained by modifying one of the chains, Lbpy, forms a di-protonated cryptate with EuCb in water at acidic pH, [EuCl3(H2Lbpy)]2+ in which the metal ion is coordinated to the four bipyridyl and two bridgehead nitrogen atoms, and to the three chlorine ions (Fig. 4.25). The polyamine chain is not involved in the metal ion coordination, due to the binding of the two acidic protons within this triamine subunit. In solution, when chlorides are replaced by perchlorate ions, two water molecules coordinate onto the Eu(III) ion at low pH and one at neutral pH, a pH at which de-protonation of the amine chain occurs, allowing it to coordinate to the metal ion. As a result, the intensity of the luminescence emitted by Eu(III) is pH dependent since water molecules deactivate the metal ion in a non-radiative way. Henceforth, this system can be used as a pH sensor. Several other europium cryptates have been developed as luminescent labels for microscopy. 

Hybrid systems have been constructed in which a metal complex is covalently linked to an organic species so as to produce a donor-acceptor dyad, with either subunit functioning as the chromophore. Thus, ruthenium(II) tris(2,2 -bipyridyl) complexes have been synthesized bearing appended anthraquinone or tyrosine functions. Both systems enter into intramolecular electron-transfer reactions. With an appended anthraquinone moiety, direct electron transfer occurs from the triplet excited state of the metal complex to the quinoid acceptor. This is not the case with tyrosine, which is an electron donor, but the metal complex can be photooxidized by illumination in the presence of an added acceptor. The bound tyrosine residue reduces the resultant ruthenium(III) tris(2,2 -bipyridyl) complex... 

Quite simultaneously, Swager and his coworkers [138] established that macrocycle (73) could be threaded onto a 2,2 -bipyridyl chelate (122) using either Zn(ll) or Cu(I) as template metals, affording prerotaxanes (123) and (124) respectively (Figure 40). The bipy moiety was substituted with bithiophenyl subunits at positions... 

The iron mineral is stable inside ferritin until the addition of reductant and/or chelators [48]. The rate at which the iron is released by reductive chelation (FMN/ NADH -I- bipyridyl) is relatively constant for recombinant H- and L-type ferritins [49] and for natural mixtures of subunits from different tissues, except when post-translationally modified [50, 51]. The site for iron release is unknown, but rates of release are similar in recombinant ferritins composed of all the ferritin subunit types currently known. 

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