A new approach to generating supramolecular architectures, based on inexpensive and easy-to-prepare imine ligands, is described together with its application to the self-assembly of supramolecular triple-helicates.

Metalation of 2,6-diphenylpyridine (1) by potassium tetrachloroplatinate in acetic acid gives a monocyclometalated chloride-bridged dimer 4. This dimer is split with CO to give a kinetic product 9t with the incoming CO trans to the orthometalated carbon. The kinetic product of cleavage is shown to be 16 kJ mol -1 higher in energy than the thermodynamic product 9c, which has the CO trans to the pyridine nitrogen. The isomerization of 9t to 9c is shown not to take place via an associative mechanism and, with analogue 11, is effectively suppressed when excess chloride is added, implying that it takes place via a chloride dissociation. The monocyclometalated 9 undergoes a second cyclometalation to give the C∧N∧C dicyclometalated complex 15 in high yield. This second cyclometalation is brought about by the simple expedient of adding water to the monocyclometalated precursor. The addition of water is rationalized on the basis of needing to ionize the HCl byproduct of the reaction. Using a substituted pyridine (5) analogous chemistry is observed. Single-crystal X-ray structures of one of the intermediates (6) and one of the final products (15) have been solved. Density functional theory calculations are used to rationalize the isomerizations of the monocyclometalated intermediates and the need to ionize HCl in the second cyclometalation.

The non-structural protein 3 (NS3) of hepatitis C virus (HCV) possesses three activities which are likely to be essential for virus replication ; a serine protease located in the N terminus and helicase and NTPase activities located in the C terminus. Sequence analysis of the helicase/NTPase domain has identified motifs indicative of the DEAD-box family of helicases. Here we present the characterization of the helicase and NTPase activities of full-length NS3, expressed as a His-tagged fusion protein in E. coli, and make comparisons with published data of NS3 helicase domain alone. The helicase and NTPase activities of full-length NS3 have been demonstrated and we have characterized the effects of amino acid substitutions on conserved motifs of NS3 helicase. Helicase and NTPase activities were dependent on Mg 2M and ATP and inhibited by monovalent cations. NS3 was able to hydrolyse all four NTPs and dNTPs to drive DNA duplex unwinding but with differing abilities. NTPase activity was stimulated by all polynucleotides tested, with poly(U) having the greatest effect. Mutational analysis of conserved motifs of NS3 helicase showed all conserved residues to be required for optimal activity. These results are in accord with a recently proposed model for NS3 helicase activity.

Facile reaction of the model urease complex [Ni2(OAc)3(urea)(tmen)2][OTf] (A) with acetohydroxamic acid (AHA) gives the monobridged hydroxamate complex (I) [Ni2(OAc)2(AA)(urea)(tmen)2][OTf] with a Ni−Ni distance of 3.434(1) Å compared to that of 3.5 Å in urease (OAc, CH3COO-; tmen, N,N,N‘,N‘-tetramethylethylenediamine; OTf, CF3SO3; AHA, acetohydroxamic acid; AA, acetohydroxamate anion). I is a close model of one proposed mode of urease inhibition by hydroxamic acids, recently observed in the acetohydroxamate-inhibited C319A variant of Klebsiella aerogenes urease. Reaction of [Ni2(OH2)(OAc)4(tmen)2] (B) with AHA gives the dibridged hydroxamate complex (II) [Ni2(OAc)(AA)2(tmen)2][OAc] with a Ni−Ni distance of 3.005(1) Å. Infrared spectroscopic studies provide evidence for the bridging acetate groups undergoing carboxylate shifts thereby assisting replacement of acetate by hydroxamate. Both I and II show ferromagnetic exchange coupling.