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Lippert, Bernhard; Gupta, Deepali
doi: 10.1039/b823087kpmid: 19513468
Metal binding to ligands with the potential of existing in different tautomeric structures can dramatically alter the tautomeric equilibrium by stabilizing a particular, frequently minor, tautomer. The assumption that metal complexation of a minor tautomer is chemically irrelevant because of its very low abundance is misleading and in many cases wrong. In fact, from available X-ray structural data on metal–nucleobase complexes it is evident that metal binding to rare, as opposed to preferred tautomers, is anything but an exception. This “promotion of rare tautomers” through metal coordination is of particular biological relevance in the case of nucleobases because any deviation from Watson–Crick base pairing is potentially mutagenic. In recent years models of “metal-stabilized rare nucleobase tautomers” have been characterized for all common DNA nucleobases, including by X-ray crystallography. Though metal binding causes relatively minor structural changes in the nucleobases, electronic changes as expressed by acid–base properties, for example, can be substantial. In this perspective article the biological consequences of the occupation of nucleobase sites by a metal entity and the altered acid–base chemistry of the nucleobase with regard to base mismatch formation, prevention of base pairing, and acid–base catalysis in nucleic acids are examined. Although not relevant to biology, the behaviour of the unsubstituted parent nucleobases is illuminating in this respect and therefore included.
doi: 10.1039/b902866hpmid: 19513469
Zinc(II) complexes of salen ligands, and particularly those of the salphen family of ligands, are extremely versatile synthons. This Frontier reviews the recent applications of these molecular building blocks in supramolecular chemistry, and their potential in various fields of material science.
Zhuang, Gui-Lin; Sun, Xiao-Jun; Long, La-Sheng; Huang, Rong-Bin; Zheng, Lan-Sun
doi: 10.1039/b823294fpmid: 19513470
A cage-shaped 3d–4f heterometallic ferromagnetic cluster, consisting of six Ni(ii) and three La(iii) ions, was synthesized by microwave irradiation. The magnetic susceptibilities of the cluster were fitted with the help of the program MAGPACK, revealing that the magnetic exchange in the cluster is closely related to the coordination mode and spatial distribution between the metal ions.
Camponeschi, Francesca; Gaggelli, Elena; Kozłowski, Henryk; Valensin, Daniela; Valensin, Gianni
doi: 10.1039/b907626npmid: 19513471
The interaction between Zn2+ and the single repeat of PrP-rel-2 of zebrafish at physiological pH was investigated by NMR spectroscopy; the chemical shift mapping and the proton–proton distances were used to obtain the structural model of the Zn2+ complex.
Luckay, R. C.; Sheng, X.; Strasser, C. E.; Raubenheimer, H. G.; Safin, D. A.; Babashkina, M. G.; Klein, A.
doi: 10.1039/b904114apmid: 19513472
Competitive transport experiments involving metal ions from an aqueous source phase through a chloroform membrane into an aqueous receiving phase have been carried out using a series of -(thio)phosphorylated (thio)amide and thiourea ligands as ionophores in the organic phase. The source phase contained equimolar concentrations of Co, Ni, Cu, Zn, Ag, Cd and Pb with the source and receiving phases being buffered at different pH. Good transport properties were observed for Ag in the case of . The best extraction properties have been shown by , , , and which contain an unsubstituted nitrogen atom at the CS groups ( and ), or a third nitrogen atom, capable of participating in additional coordination (, and ). Reaction of Cu(NO)·6HO with the potassium salt of the -thiophosphorylated thiourea NHC(S)NHP(S)(OPr) formed a new supramolecular Cu complex, [{()}{()}·] that contains both trinuclear and hexanuclear forms in its solid state structure, and in solution.
Sarkar, Biprajit; Hübner, Ralph; Pattacini, Roberto; Hartenbach, Ingo
doi: 10.1039/b902645bpmid: 19513473
Isomeric complexes of platinum, which contain two non-innocent ligands are reported. The built-in coordination asymmetry in the ligands makes it possible to separate two different positional isomers. Results from X-ray crystallography is used to invoke the popular structure oxidation state correlation in these complexes. The redox processes are discussed and interpreted with the help of UV-vis–NIR and EPR spectroelectrochemistry.
Silvério, Sara; Torres, Susana; Martins, André F.; Martins, José A.; André, João P.; Helm, Lothar; Prata, M. Isabel M.; Santos, Ana C.; Geraldes, Carlos F. G. C.
doi: 10.1039/b823402gpmid: 19513474
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A novel bis-hydroxymethyl-substituted DTTA chelator N′-Bz-C4,4′-(CH2OH)2-DTTA (1) and its DTPA analogue C4,4′-(CH2OH)2-DTPA (2) were synthesized and characterized. A variable-temperature 1H NMR spectroscopy study of the solution dynamics of their diamagnetic (La) and paramagnetic (Sm, Eu) Ln3+ complexes showed them to be rigid when compared with analogous Ln3+-DTTA and Ln3+-DTPA complexes, as a result of their C4,4′-(CH2OH)2 ligand backbone substitution. The parameters that govern the water 1H relaxivity of the [Gd(1)(H2O)2]− and [Gd(2)(H2O)]2− complexes were obtained by 17O and 1H NMR relaxometry. While the relaxometric behaviour of the [Gd(2)(H2O)]2− complex is very similar to the parent [Gd(DTPA)(H2O)]2− system, the [Gd(1)(H2O)2]− complex displays higher relaxivity, due to the presence of two inner sphere water molecules and an accelerated, near optimal water exchange rate. The [Gd(1)(H2O)2]− complex interacts weakly with human serum albumin (HSA), and its fully bound relaxivity is limited by slow water exchange, as monitored by 1H NMR relaxometry. This complex interacts weakly with phosphate, but does not form ternary complexes with bidentate bicarbonate and l-lactate anions, indicating that the two inner-sphere water molecules of the [Gd(1)(H2O)2]− complex are not located in adjacent positions in the coordination sphere of the Gd3+ ion. The transmetallation reaction rate of [Gd(1)(H2O)2]− with Zn2+ in phosphate buffer solution (pH 7.0) was measured to be similar to that of the backbone unsubstituted [Gd(DTTA-Me)(H2O)2]−, but twice faster than for [Gd(DTPA-BMA)(H2O)]. The in vivo biodistribution studies of the 153Sm3+-labelled ligand (1) in Wistar rats reveal slow blood elimination and short term fixation in various organs, indicating some dissociation. The bis-hydroxymethyl-substituted DTTA skeleton can be seen as a new lead for the synthesis of high relaxivity contrast agents, although its low thermodynamic and kinetic stability will limit its use to in vitro and animal studies.