Search

The Gd(iii)-complexes of three novel HP-DO3A-like ligands have been investigated to assess the relationship between relaxometry and intramolecular catalysis of the proton exchange. The structures of these ligands differ from the parent HP-DO3A because the methyl group of the hydroxy-propyl arm has been replaced by -Ph-OH, -Ph-NH2 and -Ph-COOH, respectively. The phenol, amine and carboxylate functionalities display an intramolecular H-bonding with the coordinated hydroxyl moiety that affects either the pK values of the involved functionalities and the rate of the proton exchange process.

Kinetic inertness is a key property for a Gd-based contrast agent. The Gd(III) complex of a cyclohexyl-fused AAZTA derivative shows the highest kinetic inertness for non-macrocyclic bis hydrated (q = 2) Gd(III)-complexes with a dissociation half-life of 91 years under physiological conditions, very close to that of macrocyclic clinically approved contrast agents. It also shows optimal relaxometric performance (r1 = 8.3 mM(-1) s(-1) at 20 MHz and 25 °C) due to the presence of two inner sphere water molecules in fast exchange with bulk water and not displaced by endogenous anions.

The rate of axial water exchange in well-defined series of lanthanide complexes depends on the extent of second sphere hydration which is determined by complex hydrophobicity and the nature of the lanthanide ion and its counter-ion.

The reaction of Ru3(CO)6(μ-CO)(μ3∶η2 ∶η3∶η5-C12H 8) (physisorbed on SiO2) with CO in the solid state leads to Ru3(CO)12 and acenaphthylene in quantitative yields; the Ru3(CO)12 generated in situ is highly mobile leading to a reduced chemical shielding anisotropy.

A heterodinuclear macrocyclic complex containing both Yb3+ and Na+ ions has been synthesized and characterized by X-ray crystallography and 1H and 23Na solution NMR; at room temperature the coordinated Na+ ion is in slow chemical exchange with free Na+ ions and its NMR resonance is strongly shifted.

Novel sub-microsized graphitic carbon shells embedding nanometric Gd(III) oxidic phases feature thermal and chemical inertness with enhanced T2 relaxation in aqueous dispersions, thus representing potential candidates for dual diagnostic (magnetic resonance imaging) and therapeutic (neutron capture therapy) applications.

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.

The ability of the paramagnetic macromolecular complex (GdDO3ASQ)30-Orn114 to enhance the water proton relaxation rate has been found to be a function of pH; this behaviour is related to the structural changes occurring in the polypeptide upon protonation of the side-chain NH2 groups.

Spectroscopic studies of the reaction of [Os3(CO)11MeCN)] with para-thiocresol to form [Os3(µ-H)(CO)10(µ-SC6H4Me-p)] indicate that the reaction proceeds via a two-step consecutive process involving the intermediate [Os3(CO)11-(MeC6H4SH-p)], in which there is an agostic Os–H–S interaction.

Enhancement of the relaxivities of Gd-based MRI contrast agents is achieved by placing the metal ion at the barycentre of the molecular complex in order to improve motional coupling.

A gadolinium(III) paramagnetic complex bearing salicylate functionalities can be used to evaluate the OH˙ radical production by measuring water proton relaxation times.