abstract
Aqueous suspensions of metal organic frameworks (MOF) containing different Ln(3+) ions, consisting of a series of layered Ln(3+) networks formulated as [Ln(H(2)cmp)(H2O) (where H(5)cmp is (carboxymethyl)iminodi(methylphosphonic acid), with a relatively Wide size distribution (400 nm to 1 mu m) were studied by relaxometry. The water H-1 longitudinal (r(1)) and transverse (r(2)) relaxivities were obtained for aqueous suspensions of these materials with different lanthanide ions. The values of r(1) are very small and varied only slightly with the effective magnetic moment (mu(eff)) of the lanthanide ions, while r(2) values are larger and proportional to the value of mu(2)(eff). The dependence of R-2 on tau(CP) (the time interval between two consecutive refocusing pulses in the train of 180 degrees pulses applied in a CPMG pulse sequence) was evaluated. The value of R-2 initially increases with tau(CP) and then saturates at higher tau(CP) at a value that is about 3 to 5 times lower than R-2p*. This can be explained by the static dephasing regime (SDR) theory, in which the diffusion effect is taken into account and where the condition tau(D) > Delta omega(r(p))(-1) holds (tau(D) = r(p)(2)/D, where D is the diffusion coefficient, rp is the radius of the particle, and Delta omega(r(p)) is the Larmor frequency shift at the particle's surface). Separation of the particles into two fractions With different particle sizes led to a significant enhancement of the r(2) relaxivity of the smaller particles with a narrow size distribution. Magnetometric measurements performed with the particles containing Dy(III), Ho(III), and Gd(III) showed a typical paramagnetic behavior from 4 to 100 K, used to determine the Curie constants.
keywords
GADOLINIUM OXIDE NANOPARTICLES; SUPERPARAMAGNETIC IRON-OXIDE; NMR TRANSVERSAL RELAXIVITY; COORDINATION POLYMER; MRI; SUSCEPTIBILITY; SUSPENSIONS; ADSORPTION; RELAXATION; PARTICLES
subject category
Chemistry
authors
Pereira, GA; Peters, JA; Paz, FAA; Rocha, J; Geraldes, CFGC
our authors
Filipe Alexandre Almeida Paz
Principal Researcher
João Rocha
Full ProfessorProjects
Nanostructured Photoluminescent rare-earth nanotubes and microporous silicates (PTDC/CTM/73243/2006)
acknowledgements
We thank Dr. Victor Amaral and Dr. Sonia Das (University of Aveiro) for the magnetic susceptibility measurements and data interpretation. This work was supported by the Foundation of Science and Technology (F.C.T.), Portugal (project PTDC/CTM/73243/2006 and Grant SFRH/BPD/35005/2007 to G.A.P.) and FEDER. This work was carried out in the frame of COST Action D38