Showing papers by "Trevor Douglas published in 1994"

Magnetoferritin: characterization of a novel superparamagnetic MR contrast agent.

Abstract: A protein-encaged superparamagnetic iron oxide has been developed and characterized by using horse spleen apoferritin as a novel bioreactive environment. The roughly spherical magnetoferritin molecules, 120 A in diameter, are composed of a monocrystalline maghemite or magnetite core 73 A +/- 14 in diameter. Except for the additional presence of iron-rich molecules of higher molecular weight, the appearance and molecular weight (450 kd) of magnetoferritin are identical to that of natural ferritin; the molecules are externally indistinguishable from their precursor, with a pI (isoelectric point) in the range 4.3-4.6. The measured magnetic moment of the superparamagnetic cores is 13,200 Bohr magnetons per molecule, with T1 and T2 relaxivities (r1 and r2) of 8 and 175 L.mmol-1 (Fe).sec-1, respectively, at body temperature and clinical field strengths. The unusually high r2/r1 ratio of 22 is thought to arise from ideal core composition, with no evidence of crystalline paramagnetic inclusions. T2 relaxation enhancement can be well correlated to the field-dependent molecular magnetization, as given by the Langevin magnetization function, raised to a power in the range 1.4-1.6. With its nanodimensional biomimetic protein cage as a rigid, convenient matrix for complexing a plethora of bioactive substances, magnetoferritin may provide a novel template for specific targeting of selected cellular sites.

Magnetoferritin: Biomineralization as a novel molecular approach in the design of iron-oxide-based magnetic resonance contrast agents

Abstract: Bulte JWM, Douglas T, Mann S, Frankel RB, Moskowitz BM, Brooks RA, Baumgarner CD, Vymazal J, Frank JA. Magnetoferritin: biomineralization as a novel molecular approach in the design of iron-oxide-based magnetic resonance contrast agents. Invest Radiol 1994;29:S214–S216.

Further characterisation of forms of haemosiderin in iron-overloaded tissues.

Abstract: The biochemical and biophysical properties of isolated haemosiderins have been compared to that of another iron-containing protein, termed prehaemosiderin, which sediments through chaotropic potassium iodide only after 20 h of ultracentrifugation, in contrast to that of haemosiderin which is recovered after 2 h of ultracentrifugation. The iron/protein ratio and iron/phosphate ratio were less that that of the corresponding haemosiderin, while the elemental composition was also reduced in many of the prehaemosiderin samples. Mossbauer spectroscopy and electron diffraction identified the predominant presence of ferrihydrite in prehaemosiderin species even though the secondary haemochromatosis haemosiderin iron cores were essentially goethite-like. The majority of the prehaemosiderins isolated showed the presence of an additional peptide band at 17 kDa in addition to that at 21 kDa. Further Mossbauer studies of haemosiderin isolated from untreated secondary haemochromatosis patients showed that goethite was the predominant form of iron present, thereby indicating that the presence of this form of ferrihydrite was not wholly attributable to chelation therapy.

Mössbauer Spectroscopic and Magnetic Studies of Magnetoferritin

Abstract: Mossbauer spectroscopic and magnetic measurements have been made on a novel magnetic protein produced by the controlled reconstitution of ferritin. The data indicate that the predominant mineral form in the iron-containing cores is maghemite (γ-Fe2O3) rather than magnetite (Fe3O4).

Persistent oral contrast agent lining the intestine in severe mucosal disease: elucidation of radiographic appearance.

Abstract: Plain radiographs and computed tomographic scans obtained in a severely neutropenic patient with acute lymphoblastic leukemia and cytomegalovirus-associated enterocolitis revealed a pattern of prolonged mucosal adherence of oral contrast agent to the small bowel. This pattern was seen as long as 16 weeks after administration of contrast agent and has been seen previously only in patients who have received bone marrow transplants. Two sets of intestinal biopsy specimens contained crystals that coated denuded mucosa at the site of ulceration and later were trapped within the lamina propria. Electron diffraction and energy-dispersive radiographic analysis showed that these crystals were composed of barium sulfate.

Synthesis of iii-v semiconductor particles from organometallic precursors

Abstract: Reaction of the organometallic precursor molecules {[(CH3)3SiCH2]2In-P[Si(CH3)3]2}2 and {[(CH3)3SiCH2]2In-As[Si(CH3)3]2}2 with methanol yielded substantially pure precipitates of the III-V semiconductors InP and InAs. Addition of phenylphosphine or phenylarsine to the reaction mixtures effected “capping” of the growing semiconductor clusters, producing stable and soluble nanoclusters with organic surface groups, e.g. [(CH3)3SiCH2In] x[InP]y[PPh]z. Blue shifted absorption onsets in the optical spectra led to estimated cluster diameters of 55 A (InP) and 64 A (InAs). The nanoclusters as prepared were amorphous; however, they crystallized upon heating. Differential scanning calorimetry and X-ray diffraction have been used to characterize the crystallization process. Typical crystallization temperatures were close to 300°C and the associated activation energies ranged from 170 to 240 kJ/mol.