Janet M. Moloney

Ground and excited state chiroptical properties of enantiopure macrocyclic tetranaphthyl lanthanide complexes: controlled modulation of the frequency and polarisation of emitted light

Circular dichroism spectroscopy has revealed that strong exciton coupling occurs between adjacent pairs of 1-naphthyl chromophores in the chiral sodium, calcium and europium complexes of the macrocyclic tetraamide L1a/b. In constitutionally isomeric complexes involving a 2-naphthyl linkage, L2a/b, intramolecular excimer formation is observed by fluorescence emission spectroscopy as being strongest in the protonated ligand itself. The terbium and europium complexes show a well-defined circularly polarised luminescence that is independent of the nature of excitation: UV excitation at 300 nm via the proximate naphthyl antennae in [Tb.L1a]3+ and [Tb.L1b]3+ followed by intramolecular energy transfer results in mirror-image circularly polarised emission spectra. The lanthanide complex serves to modulate both the frequency and polarisation of the incident light in a controlled manner.

DEPENDENCE OF THE RELAXIVITY AND LUMINESCENCE OF GADOLINIUM AND EUROPIUM AMINO-ACID COMPLEXES ON HYDROGENCARBONATE AND PH

Reversible binding of hydrogencarbonate to a chiral di-aqua lanthanide complex occurs in the pH range 6.5–8.5, limiting the measured relaxivity in the gadolinium complex and enhancing the metal-based emission in the europium analogue.

Nuclear magnetic resonance, luminescence and structural studies of lanthanide complexes with octadentate macrocyclic ligands bearing benzylphosphinate groups

The solution and solid-state structures of lanthanide complexes of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetryltetramethylenetetra(benzylphosphinate), L1a, and of its o-, m- and p-methoxybenzyl analogues (L2, L3, L4) have been investigated by NMR, relaxometry, crystallographic and photophysical methods. It has been shown that the number of proximate water molecules is dependent on the size of the bound lanthanide ion: the complex [LaL1a]– is nine-co-ordinate and adopts a twisted square-antiprismatic structure with one bound water molecule. The analogous [YL1a]–, [YbL1a]–, [GdL1a]– and [EuL1a]– complexes also adopt a twisted square-antiprismatic geometry, but are eight-co-ordinate, with no metal-bound water. Relaxivity studies with the gadolinium complexes showed that they are purely ‘outer-sphere’ contrast agents, but they associate strongly with proteins leading to a pronounced relaxivity enhancement. Detailed biodistribution studies with [GdL1a]– revealed avid biliary uptake at low doses and a well defined tendency for the complex to be cleared more slowly from tumour tissue, allowing tissue differentiation.

Structure and dynamics of all of the stereoisomers of europium complexes of tetra(carboxyethyl) derivatives of dota: ring inversion is decoupled from cooperative arm rotation in the RRRR and RRRS isomers

The absolute configuration of the four stereoisomeric α-substituted derivatives of dota has been defined; in their Eu complexes, 2D-NMR methods have revealed that in solution ring inversion is independent of pendant arm rotation and the (RRRR)-[EuL1a] complex which in the solid state crystallises as a square antiprismatic structure.

Molecular structures of 1,12-B12H10(CO)2 and its dihydrate 1,12-B12H10[C(OH)2]2—a novel bis-carbene complex

Crystal structures of the dicarbonyl 1,12-B12H10(CO)2 and its hydrated form 1,12-B12H10(CO2H2)2·4H2O show little π-bond character in their B–C bonds but contain significant distortions from the regular B12 icosahedron geometry; the hydrate, until now thought to be a hydroxonium salt, contains dihydroxycarbene (‘protonated carboxylic acid’) ligands C(OH)2.

A short highly stereoselective synthesis of the fluorinated natural product (2S,3S)-4-fluorothreonine

A three step stereoselective route to the fluorinated natural product (2S,3S)-4-fluorothreonine is described; the route is amenable to the preparation of (2S,3S)-4-fluoro[3- 2 H]threonine and (2S,3R)-[4,4,4- 2 H 3 ]threonine.

Strong exciton coupling and circularly polarised luminescence in rigid complexes of chiral macrocyclic tetranaphthylamides

Strong exciton coupling occurs between adjacent pairs of naphthyl chromophores in the chiral sodium and europium complexes of L 1 ; in the constitutionally isomeric complexes of L 2 , intramolecular excimer formation is observed and both sets of Eu complexes give a well defined, metal-based circularly polarised emission.

Dimethylthiophosphoryl hydrazone ligands and their copper complexes: crystal structures and analysis of their solution complexation behaviour by electrospray mass spectrometry

Four new thiophosphoryl ligands containing NNPS or CNPS connectivities have been prepared and three of them characterised by single-crystal X-ray diffraction. The complexation of these ligands with salts of CuI, CuII, NiII and ZnII has been studied by electrospray mass spectrometry and uv-visible spectrophotometry in acetonitrile and methanol solution. Evidence for 1∶1 and 2∶1 complexation is presented. Two copper(I) complexes were isolated including a mixed chloride–bromide copper(I) complex in which a dimeric structure is adopted with a 22-membered metallacycle.

Chiroptical features and luminescence behaviour of macrocyclic tetra(4-quinolyl)-complexes: surprising absence of exciton coupling

The C4-symmetric (S)-tetra(4-quinolyl) tetraamide derivative of dota has been prepared. The sodium complex has been characterised by X-ray crystallography and although the quinolyl groups are appropriately oriented for exciton coupling in the solid-state, in solution no evidence for coupling was found for the free ligand nor its protonated, Na, Ca or Eu complexes. Instead, excimer formation was observed in emission consistent with a coplanar arrangement of the quinolyl groups.