The (1)H and (17)O NMR relaxometric properties of two cationic complexes formed by Gd(III) with a macrocyclic heptadentate triamide ligand, L(1), and its Nmethylated analogue, L(2), have been investigated in aqueous media as a function of pH, temperature and magnetic field strength. The complexes possess two water molecules in their inner coordination sphere for which the rate of exchange has been found to be sensibly faster for the Nmethylated derivative and explained in terms of electronic effects (decrease of the charge density at the metal center) and perturbation of the network of hydrogen-bonded water molecules in the outer hydration sphere. The proton relaxivity shows a marked dependence from pH and decreases of about six units in the pH range 6.5 to 9.0. This has been accounted for by the displacement of the two water molecules by dissolved carbonate which acts as a chelating anion. The formation of ternary complexes with lactate, malonate, citrate, acetate, fluoride and hydrogenphosphate has been monitored by (1)H NMR relaxometric titrations at 20 MHz and pH 6.3 and the value of the affinity constant, K, and of the relaxivity of the adducts could be obtained. Lactate, malonate and citrate interact strongly with the complexes (log K > or =3.7) and coordinate in a bidendate mode by displacing both water molecules. Larger affinity constants have been measured for GdL(2). Acetate, fluoride and hydrogenphosphate form monoaqua ternary complexes which were investigated in detail with regard to their relaxometric properties. The NMR dispersion (NMRD) profiles indicate a large contribution to the relaxivity of the adducts from water molecules belonging to the second hydration shell of the complexes and hydrogen-bonded to the anion. A VT (17)O NMR study has shown a marked increase of the rate of water exchange upon binding which is explained by coordination of the anion in an equatorial site, thus leaving the water molecule in an apical position, more accessible for interactions with the solvent molecules of the second hydration shell which facilitate the exchange process.

The synthesis and photophysical characterisation are reported of a series of cationic, neutral and anionic europium and terbium complexes based on structurally related, nonadentate ligands based on the cyclen macrocycle. Each complex incorporates a tetraazatriphenylene moiety and overall absolute emission quantum yields are in the range 15-40% in aerated aqueous media. Dynamic quenching of the lanthanide excited state occurs with electron-rich donors, e.g. iodide, ascorbate and urate, and a mechanistic interpretation is put forward involving an electron transfer process. The cationic lanthanide complexes are taken up by NlH/3T3 cells and tend to localise inside the cell nucleus.

The interaction of q = 0 delta- and lambda-Tb and Eu complexes with poly(dAdT), poly(dGdC) and calf-thymus DNA has been examined by absorption, emission and chiroptical spectroscopy and is sensitive to complex helicity, base-pair type and the nature of the lanthanide excited state.

Nonacoordinate delta- and lambda-Eu and Tb complexes have been tested as imaging and reactive probes in mouse fibroblast (NIH 3T3) cells. The uptake of these complexes by the cells was assessed by fluorescence microscopy. Complex-induced DNA damage was studied by gel electrophoresis and shown to be a function of complex chirality.

The binding of tetracationic Λand ∆-europium complexes of tetraamide and triamide ligands incorporating an N-methylphenanthridinium group to calf-thymus DNA, poly(dGdC) and super-coiled plasmid DNA has been monitored by absorption, luminescence and CD difference spectroscopy. With the tetraamide complexes, preferential binding to (CG) base-pairs was signalled by pronounced hypochromism, a small red shift and substantial fluorescence quenching with a limiting base-pair complex ratio of 2 : 1, consistent with an intercalative interaction and charge neutralisation. For the triamide Eu complex, a lower base-pair : complex ratio was found and changes in the form and polarisation of the Eu emission spectrum were consistent with coordination of a nucleobase phosphate group to the hydrated Eu centre.

In cationic nine-coordinate chiral terbium and europium complexes incorporating exciton-coupled naphthyl groups and a tetraazatriphenylene sensitising chromophore, efficient intramolecular energy transfer occurs leading to population of the naphthyl triplet state. With the terbium complex, the absolute quantum yield of singlet oxygen formation is 51% (lambda(exc) 355 nm), and for the Eu complex the intensity of metal-based emission increases by up to 350% on binding to poly(dGdC) or calf-thymus DNA, and was greater for the delta-isomer.

The interaction of ∆and Λ-Eu and Yb cationic complexes bearing an N-methylphenanthridinium chromophore with [(CG) 6 ] 2 , [(AT) 6 ] 2 and [CGCGAATTCGCG] 2 has been interrogated by ESMS, 1 H NMR, absorption, difference circular dichroism, fluorescence quenching and Ln luminescence emission spectroscopy. Stepwise complexation occurs with up to 3 : 1 limiting stoichiometry for [(CG) 6 ] 2 and 2 : 1 for [CGCGAATTCGCG] 2 , as indicated by absorption measurements and direct ESMS observation of the non-covalent duplex adducts. Binding to [(CG) 6 ] 2 occurred with an affinity of 8.7 × 10 6 M Ϫ1 duplex Ϫ1 for the ∆-Eu isomer which was 50 times greater than to [(AT) 6 ] 2 . A primary component of the free energy of binding has been linked to an intercalative interaction, supported by absorption, ICD and fluorescence quenching characteristics. The lanthanide coordination environment and local helicity remain unchanged but the oligonucleotide underwent distinctive changes in local helicity and pitch which were sensitive to the handedness of the Ln complex and in certain cases to the nature of the Ln ion (Yb vs. Eu). With [CGCGAATTCGCG] 2 1 H NMR TOCSY and NOESY analysis in the presence of increasing concentrations of the Gd analogues revealed that the most avid complex binding site was located in the centre of the oligonucleotide, with the ∆-isomer binding more strongly.