Studies of lanthanide interactions with polyoxometalates: Evaluation as magnetic resonance imaging agents.

摘要

A series of lacunary (XM{dollar}sb{lcub}11{rcub}{dollar}O{dollar}sb{lcub}39{rcub}sp{lcub}rm n-{rcub}{dollar} and P{dollar}sb2{dollar}M{dollar}sb{lcub}11{rcub}{dollar}O{dollar}sb{lcub}61{rcub}sp{lcub}10-{rcub}{dollar}) and plenary (SiW{dollar}sb{lcub}12{rcub}{dollar}O{dollar}sb{lcub}40{rcub}sp{lcub}4-{rcub}{dollar} and P{dollar}sb2{dollar}M{dollar}sb{lcub}18{rcub}{dollar}O{dollar}sb{lcub}62{rcub}sp{lcub}6-{rcub}{dollar}) polyoxometalates (POM) were synthesized, analyzed and their solution chemistry with lanthanide cations was studied by a variety of physical methods. These lanthanide complexes are evaluated with regard to potential applications as magnetic resonance imaging agents.; For elemental analysis of POM, quantitative methods were developed using ICP-AES for the determination of B, Si, Ge, P and Mo and atomic absorption spectroscopy for Na. The two-step procedure minimizes interelement interferences using matrix matching of sample and standard solutions, offering comparable precision to classical methods. The FTIR spectra of POM in D{dollar}sb2{dollar}O and in KBr demonstrated their aqueous stability, and provided evidence of similarities between the solution and solid state structures.; The thermodynamics parameters of complexation ({dollar}Delta{dollar}G, {dollar}Delta{dollar}H, and {dollar}Delta{dollar}S) of Eu(III) with POM were studied at 1 M ionic strength. pK{dollar}sb{lcub}rm a{rcub}{dollar} values for the lacunary POM indicate weak basicity with two protonations between pcH 7 and 2. {dollar}sp7{dollar}F{dollar}sb0 to sp5{dollar}D{dollar}sb0{dollar} Selective excitation spectra coupled with the computer program, SQUAD, were used to determine 1:1 and 1:2 stability constants and to calculate {dollar}Delta{dollar}G{dollar}sb{lcub}rm 10n{rcub}{dollar} (n = 1,2). The stability constants are discussed in terms of statistical, electrostatic and geometrical effects. The enthalpies of complexation, {dollar}Delta{dollar}H{dollar}sb{lcub}rm 10n{rcub}{dollar} (n = 1,2), were determined for the formation of the 1:1 and 1:2 complexes of Eu(III) by titration calorimetry. The entropies of complexation, {dollar}Delta{dollar}S{dollar}sb{lcub}rm 10n{rcub}{dollar} (n = 1,2), were calculated from {dollar}Delta{dollar}G{dollar}sb{lcub}rm 10n{rcub}{dollar} (n = 1,2) and {dollar}Delta{dollar}H{dollar}sb{lcub}rm 10n{rcub}{dollar} (n = 1,2) values.; In addition, the {dollar}sp7{dollar}F{dollar}sb0 to sp5rm Dsb0{dollar} selective excitation spectra of Eu(III)-polyoxometalate complexes were evaluated qualitatively. Based on the number of peaks, the number of inner sphere H{dollar}sb2{dollar}O molecules and the known structures, binding sites were proposed for 1:1 and 1:2 complexes.; The Gd(POM){dollar}sb2{dollar} complexes were kinetically unstable in Sprague-Dawley rat serum. In vitro challenges to Gd(POM){dollar}sb2{dollar} by metal cations, DTPA, and DTPA-doped serum suggest instability in serum is due primarily to a transmetalation mechanism.