Novel gadolinium(III) polyaminocarboxylate macrocyclic complexes as potential magnetic resonance imaging contrast agents

A new heptadentate picolinate-based ligand and its corresponding Gd(iii) complex: the effect of pendant picolinate versus acetate on complex properties

Replacing one picolinate pendant by acetate group in H₄bpeda ligand, the synthesised bis(aquated) Gd(iii) complex of ligand H4peada showed better stability and r₁ relaxivity for its potential use as MRI contrast agent.

Preparation, spectroscopic and high field NMR relaxometry studies of gadolinium(III) complexes with the asymmetric tetraamine 1,4,7,11-tetraazaundecane

The reaction of Gd(III) with asymmetric tetramine 1,4,7,11-tetraazaundecane (2,2,3-tet, L(1)) ligand has been studied via NMR spectroscopy. The ligand proton longitudinal relaxation rates (R(1)) have been used to estimate the distances of these protons from the Gd(III) center, in Gd(III)-L(1) reaction solutions, in H(2)O/D(2)O 5/1 mixtures. Two Gd(III) complexes [Gd(III)(L(1))(NH(3))(H(2)O)(4)](CH(3)COO)(3)*2H(2)O (1) and [Gd(III)(L(1))(NH(3))(H(2)O)(2)]Cl(3)*EtOH (2) have been isolated and characterized by elemental analyses, TGA, IR, NMR and relaxometry measurements. The NMR relaxation measurements of 2 in aqueous solutions have been performed, under various temperature or concentration conditions, and compared with those of the commercial contrast agents Gd(III)-DTPA and Gd(III)-DTPA-BMA. It has also been studied the influence of (i) the Gd(III) inner-sphere water molecule number (q) alteration and (ii) the steric constraint enhancement on the metal site, over the relaxation rate values of the parent aqueous solution of Gd(III)-2,2,3-tet, and of the aqueous solutions of 2.

Template synthesis, spectroscopic studies and biological activities of macrocyclic complexes derived from thiocarbohydrazide and glyoxal

A novel series of complexes of the type [M(TML)X2]; where TML is Tetradentate Macrocyclic Ligand; M = Co(II), Ni(II), Cu(II), Zn(II)or Cd(II); X = Cl-, CH3COO- or NO3- have been synthesized by template condensation of glyoxal and thiocarbohydrazide in the presence of divalent metal salts in methanolic medium. The complexes have been characterized by elemental analyses, conductance measurements, molecular weight determination, magnetic measurements, electronic, NMR, infrared and far infrared spectral studies. Electronic spectra along with magnetic moments suggest a six coordinate octahedral geometry for these complexes. The low molar conductance values indicates them to be non-electrolytes. The biological activities of the metal complexes have been tested in vitro against a number of pathogenic bacteria to assess their inhibitory potential.

Lanthanides in magnetic resonance imaging

Magnetic Resonance Imaging is perhaps the most important and prominent technique in diagnostic clinical medicine and biomedical research. Its success and development as an imaging technique has been aided by the characteristics of contrast agents that enhance signal intensities and improve specificity. Gadolinium(iii) remains the dominant starting material for contrast agent design but other lanthanide ions (and other oxidation states i.e. +2) are also being increasingly investigated as alternatives to gadolinium(III) within laboratory conditions. This critical review provides a concise summary of the MRI-active gadolinium(III) complexes to date--their pros and cons, an outline of contrast agents based on other lanthanide ions (e.g. europium, dysprosium), and directs the reader to newer, more speculative areas of lanthanide-containing contrast agent design.