[Ru-II(hedta)](-) complexes of 2,2 '-dipyridylamine (dpaH) and a bifunctional tethered analog, N,N,N ',N '-tetrakis(2-pyridyl)adipamide (tpada)

[Ru-II(hedta)L](-) complexes (hedta(3-) = N-hydroxyethylethylenediamine-N,N ,N'-triacetate); L = dpaH (2, 2'-dipyridylamine) and tpada (N,N,N',N'-tetra kis(2-pyridyl)adipamide)) have been studied by H-1 NMR and electrochemical methods in aqueous solution. The bidentate rings of dpaH and tpada are diff erentiated as shown by NMR upon coordination to Ru-II due to differences in the local environment. The dpa-R headgroup of each ligand binds 'in-plane' with the en backbone of hedta(3-) and with one pyridyl ring being nearer t he amine of hedta(3-) having the pendant glycinato group (matching the know n arrangement with bpy (2,2'-bipyridine)). Ru-II/III E-1/2 values follow th e order dpaH (0.32 V) < tpada (0.47 V) < bpy (0.54 V), showing that dpaH is a weaker pi-acceptor ligand than bpy, and that the withdrawing carbonyl fu nctionality enhances the K-acceptor capacity for the tpada ligand, approach ing the stability imparted by bpy. Only the 1:1 [Ru-II(hedta)(dpaH) complex forms even in the presence of excess dpaH. [Ru-II(hedta)(dpaH)] has a pK(a ) of the dipyridylamine proton of approximately 5.0 with [Ru-III(hedta)(dpa (-))] undergoing aquation (k(H2O) = 1.4 x 10(-2) s(-1)) and OH--assisted di ssociation (k(OH) = 1.33 x 10(4) M-1 s(-1)). The {[Ru-II-(hedta)](2)(tpada) }(2-) complex serves as a water-soluble model as to how {[ML'](2)(tpada)} c omplexes might act as an extended bridge betrveen two metal binding sites, potentially those of metalIo-derivatized DNA strands, or between one DNA st rand and a protein crosslink. In this model M represents an appropriate met al for DNA derivatization such as Ru-II, Pt-II or Pd-II and L' represents t he attachments to DNA nucleobase sites, aminocarboxylates/peptide coordinat ion for antitumor purposes. (C) 2000 Elsevier Science S.A. All rights reser ved.