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Oxidatively stable, magnetic cobalt nanoparticles have been prepared by heating cobalt nanoparticles encapsulated in poly(styrene-b-4-vinylphenoxyphthalonitrile) block copolymers at elevated temperatures. The block copolymers were synthesized through the sequential anionic polymerization of styrene and tert-butyldimethylsilyloxystyrene. The silyl ether protecting groups on the second block were hydrolyzed under acidic conditions to afford poly(styrene-b-4-vinylphenol), and then the pendent phenols of the diblock copolymer were chemically modified with 4-nitrophthalonitrile to afford poly(styrene-b-4-vinylphenoxyphthalonitrile). Stable suspensions of ~8−10 nm diameter cobalt metal nanoparticles were formed by thermolysis of dicobalt octacarbonyl in solutions of toluene containing poly(styrene-b-4-vinylphenoxyphthalonitrile). The cobalt−polymer nanoparticle complexes were pyrolyzed under argon to afford highly magnetic cobalt nanoparticles encased in graphitic-like coatings. Magnetic susceptibility measurements indicate that the cobalt−graphitic particles are oxidatively stable and retain their high saturation magnetizations (~95−100 emu g^-1) for at least 1 year under ambient conditions.

Magnetic nanoparticles that display high saturation magnetization and high magnetic susceptibility are of great interest for medical applications. Magnetite nanoparticles display strong ferrimagnetic behavior and are less sensitive to oxidation than magnetic transition metal nanoparticles such as cobalt, iron, and nickel. For in vivo applications, well-defined organic coatings are needed to surround the magnetite nanoparticles and prevent any aggregation. The goal of this research was to develop complexes of magnetite nanoparticles coated with well-defined hydrophilic polymers so that they could be dispersed in aqueous fluids. Focal points have included the following:  (1) Investigations of polymer systems that bind irreversibly to magnetite at the physiological pH, (2) the design of block copolymers with anchor and tail blocks to enable dispersion in biological fluids, and (3) investigations of copolymer block lengths to maximize the concentration of bound magnetite. Hydrophilic triblock copolymers with controlled concentrations of pendent carboxylic acid binding groups were designed as steric stabilizers for magnetite nanoparticles. These copolymers were comprised of controlled molecular weight poly(ethylene oxide) tail blocks and a central, polyurethane anchor block containing carboxylic acids. Stoichiometric aqueous solutions of FeCl2 and FeCl3 were condensed by reaction with NH4OH to form magnetite nanoparticles, and then a dichloromethane solution of the block copolymer was added to adsorb the copolymer onto the magnetite surfaces. Stable magnetite dispersions were prepared with all of the triblock copolymers. The polymer−nanomagnetite conjugates described in this paper had a maximum saturation magnetization of 34 emu/g. Magnetization curves showed minimal hysteresis. Powder X-ray diffraction (XRD), selected area electron diffraction (SAED), and high-resolution electron microscopy (HREM) confirmed the magnetite crystal structure. Transmission electron microscopy (TEM) showed that the dispersions contained magnetite particles coated with the polymers with a mean diameter of 8.8 ± S.D. 2.7 nm.

The chemical composition of a suite of pigment gallstones obtained from patients suffering from β-thalassemia was studied using FTIR, FT-Raman, and Mössbauer spectroscopies with a view to gaining a better understanding of their complex composition and developing an effective characterization procedure. The combination of vibrational spectroscopic techniques such as FTIR and FT-Raman make it possible to identify the major chemical components of thalassemic pigment stones and to subcategorize them for further study. All but one sample had almost identical FTIR spectra where bands attributable to both cholesterol and various bilirubinate salts were observed. One sample, low in cholesterol, showed distinctive spectral peaks of calcitic CaCO3. This sample was sufficiently high in iron for Mössbauer spectroscopy, which showed, at room temperature, a quadrupole-split doublet consistent with the presence of iron (III). This concomitant presence of iron and a high CaCO3/low cholesterol content has, as far as we are aware, not been previously reported. When studied by FT-Raman, however, most of the stones gave spectra typical of previously characterized brown stones. Due to the limited number of stones available, in particular iron-rich samples, further work is required, but these preliminary results indicate that it may in fact be possible to unequivocally categorize thalassemic stones into different types using spectroscopic techniques. Together with FTIR and Raman microscopy of cut stones, such nondestructive spectroscopic techniques show promise in helping researchers gain an understanding of thalassemic stone formation and occurrence. In addition, the samples are maintained for further study, which is important considering the difficulty in establishing large suites of such special category stones. © 1997 John Wiley & Sons, Inc. Biospectroscopy 3: 409–416, 1997