47 research outputs found
NMR conformational study of the lanthanide(III) complexes of DOTA in aqueous solution
No full textMarques, M.P.M. ; Geraldes, C.F.G.C. ; Sherry, A.D. ; Merbach, A.E. ; Powell, H. ; Pubanz, D. ; Aime, S. ; Botta, M
Metal Complexes as MRI Contrast Enhancement Agents
No full textMagnetic resonance imaging is one of the most efficient diagnostic modalities in clinical radiology and biomedical research. To enhance image contrast, paramagnetic complexes, mainly Gd3+ chelates, are used. Today, around one third of all medical MR images are generated with the use of a contrast medium and this number is expected to increase with the development of new applications and new agents. Recently, molecular imaging has emerged as a new area aiming at non-invasive visualisation of expression and function of bioactive molecules at the cellular level. Since any molecular imaging application requires a specific imaging probe, new chemical approaches become increasingly important. In this chapter, we discuss first proton relaxivity, the parameter that directly translates to the effectiveness of an MRI contrast agent. Many microscopic factors, including the hydration number, the water exchange rate, the rotational dynamics, as well as the electron spin relaxation, influence proton relaxivity for Gd3+ complexes. We show how the structure, the charge or the size of the chelate affects these factors. We also review the different strategies derived to obtain high-relaxivity probes. Non-toxicity of these agents is primordial for their application; therefore we also address the main physico-chemical aspects related to the in vivo stability of Gd3+-based agents, such as thermodynamic stability and kinetic inertness. The second part of the chapter is devoted to new-generation MRI contrast media, such as smart or responsive contrast agents that are capable of reporting on the physico-chemical environment in tissues. Among the huge number of systems reported in the field of smart MRI probes, we focus only on sensing of pH, redox state and metal ions. Many pathologies, such as stroke, infections, kidney disease and cancer are associated with significant pH variations. Accurate, high resolution, in vivo MRI pH mapping would be of great interest not only for diagnostic purposes but also for monitoring disease progression, choice and response to therapy. The partial oxygen pressure, pO2, is also significant in metabolic processes of cells, and its variation from normal values often indicates pathologies (ischemic diseases, strokes, tumors). As for metal ions, several of them play a crucial role in biological processes, whereas others are toxic. Alteration of the metal concentration in the body can often be correlated to disease states. Our objective here is to illustrate, via a few selected examples of Gd3+-based or Paramagnetic Chemical Exchange Saturation Transfer (PARACEST) agents, the major design principles in coordination chemistry to derive smart MRI probes using lanthanide complexes.LCI
Raman and infrared study of hexamethylphosphoramide complexes of lanthanide perchlorates
No full textAdducts of tin(IV) tetrahalides with neutral Lewis bases. II. Quantitative study of the Cis-Trans equilibria by NMR
No full textAdducts of tin(IV) tetrahalides with neutral Lewis bases. II. Quantitative study of the Cis-trans equilibria by NMR
No full text
A PCP-Pincer RuII-Terpyridine Building Block as a Potential "Antenna Unit" for Intramolecular Sensitization
No full textThe redox- and photoactive mononuclear complex [Ru(PCP)(tpy-DTTANa4)]Cl {PCP = [C6H3(CH2PPh2)2-2,6]-; tpy-DTTA4- = 4'-(2,2':6',2''-terpyridine)-diethylenetriamine-N,N,N",N"-tetraacetate} possesses an externally directed, vacant N3O4 polyaminocarboxylate-type binding site that coordinates to lanthanide(III) ions to give the neutral heterodinuclear RuII-LnIII complexes [Ru(PCP)(tpy-DTTA)Ln(H2O)2] (Ln = Gd3+, Eu3+). The photophysical properties of solutions of the mononuclear complex [Ru(PCP)(tpy-DTTANa4)]Cl were investigated in MeOH/EtOH (1:4) and compared to those of the solutions of heterodinuclear complexes [Ru(PCP)(tpy-DTTA)Ln(H2O)2] (Ln = Gd3+, Eu3+). Rigid matrix excitation at 77 K of the ππ* level of the ruthenium chromophore in the [Ru(PCP)(tpy-DTTA)Eu(H2O)2] complex results in a weak europium(III) emission pointing to a transfer of energy from RuEu as a result of the metal-to-ligand charge-transfer (MLCT) excited state of the ruthenium component to the luminescent lanthanide ion. The excited state lifetime of the europium complex is 0.2 ms in methanol solution. In deuterated solvents, the lifetime increases to 0.4 ms, which indicates that the process is solvent-dependent as a result of the strongly coordinated molecules of water that are responsible for the quenching in nondeuterated solvents
Coordination chemistry of amide-functionalised tetraazamacrocycles: structural, relaxometric and cytotoxicity studies
No full text25/09/2012MEB. Author version attached, OK to publis
