PARTNERSHIPS FOR RESEARCH AND EDUCATION IN MATERIALS
 
 
 
PROJECT 2. ENCODED ASSEMBLIES OF MAGNETIC IRON OXIDES AND FERRITES
seporator

II. Nanoparticles of Magnetic Iron Oxides and Ferrites as Prospective Imaging Agents

Faculty: Vladimir Kolesnichenko (Xavier)
Objective.  a)   Fundamental studies on magnetic metal oxide nanoparticles: nucleation and growth, surface and colloid chemistry, redox chemistry and the structure and magnetism relationship. b)  Developmental studies aiming novel MRI contrast agents.
Role of the Partner: Marc Walters’ group performed the relaxity NMR measurements.
Description of the research performed: The most water soluble and stable galactarates were obtained with iron(III).  The r1 relaxivity properties (spin-lattice relaxation) for two samples were tested by NMR and found 0.31 ± 0.02 mM-1 for NaFe3G(OH)4 and 0.29 ± 0.01 mM-1 for NaFe4G(OH)7.  These low numbers arise from the lack of exchange with the solvent, presumably because coordination sites of the metal centers are completely blocked by ligands.  The r2 values (spin-spin relaxation) were also found relatively small, what is presumably attributed to antiferromagnetic interaction of metal ion spins in these complexes. No further studies on galactarate complexes were conducted.
According to the original hypothesis, very small magnetic particles might be better r1 contrast agents than commonly known, larger USPIONs or SPION’s.  We studied how the relaxivity properties depend on (a) particle size and (b) particle spin state.  We performed systematic studies on 3.5 to 11 nm samples synthesized by the same chemical reactions, but under different reaction conditions.  Another set of samples was obtained by room-temperature oxidation of colloidal magnetite particles: 
4Fe3O4(H2deg) + O2 →  4Fe3O4(Hdeg) + 2H2O
The T1 relaxation is faster in water than in diethylene glycol; this can be attributed to high viscosity of the latter.  Chemically oxidized Fe3O4 particles were found to have only slightly weaker relaxivity than regular magnetite, but more stable and therefore potentially less toxic.

 

Preliminary results for r1 relaxivity of magnetite DEG and aqueous colloids are shown below.


Sample
Fe3O4

r1, mM-1
(CH2 protons of DEG)

r1, mM-1
(OH protons of DEG)

r1, mM-1
H2O

4.3 nm

2.95

3.23

 

5.3 nm

3.21

3.55

 

4.3 nm + O2

2.89

3.05

8.65

5.3 nm + O2

2.25

2.59

10.45

A series of samples have been studied by VSM variable-field magnetization method (L. Spinu, UNO) and Mössbauer spectroscopy (C. Johnson, University of Tennessee Space Institute).  The oxidized and smaller particles exhibited lower magnetic moments than larger unoxidized ones.
Samples of oleate-coated 4.3 nm magnetite particles were provided to Prof. Walters (NYU) for the development of magnetite-labeled lipid nanocapsules for delivery and imaging applications.
Future Plans. Synthesize the superparamagnetic iron oxide compounds with variable size, oxidation state and organic shell and study their colloid and surface chemistry, magnetic and relaxivity properties.

 
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