Compositions – Magnetic – Iron-oxygen compound containing
Patent
1997-01-03
1998-07-07
Bonner, Melissa
Compositions
Magnetic
Iron-oxygen compound containing
252 6256, 252 6254, 2523131, 436526, 427215, 427220, 428405, H01F 136, H01F 144, B03C 101, G01N 33543
Patent
active
057763607
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to magnetic particles comprising mixed oxides of divalent metals and iron(III) oxide having a particle diameter in the region of a few nanometers and a large surface area, to whose surface functional silanes are bound; a process for their preparation by simultaneous precipitation and silanization from aqueous solution; and their use as carrier material for the magnetic separation of substances immobilized therewith.
The term magnetic means that the particles have permanent magnetism, paramagnetism or superparamagnetism and react to magnetic fields.
Oxidic ferrites have long been known as magnetic materials. Such materials are described, for example, in Gmelins Handbuch der anorganischen Chemie, System No. 59, Verlag Chemie GmbH, Weinheim (1959), page 59 et seq. The most well known ferromagnetic materials are metal(II) ferrites, for example magnetite and .gamma.-Fe.sub.2 O.sub.3, which forms a continuous mixed series with ferrites. The ferrites may contain one or more metal(II) cations, and these themselves may be partly replaced by monovalent metal cations, for example lithium.
It has been known for a relatively long time that substances, particularly bioactive substances, for example drugs, cells, antibodies, oligo- and polynucleic acids, nucleotides, enzymes, vitamins, cofactors and proteins, can be immobilized on magnetic particles, for example magnetite, and can be separated off under the influence of magnetic fields for the analysis or diagnosis of admixed or undesired substances. Furthermore, highly disperse magnetic particles are also used as contrast media in visualizations by means of nuclear spin resonance methods (cf. WO 91/02811). In the case of in vivo applications, small particles are required in order to be able to pass through even very small pores. However, a small particle diameter is also desirable for achieving a high loading during immobilization.
U.S. Pat. No. 4,554,088 describes for this purpose magnetite particles which are functionally silanized at the surface and have particle diameters of about 50 nm and high diameters and a specific surface area of about 120 to 140 m.sup.2 /g. The particle diameter and the relatively small surface area are regarded as being too small for many applications, particularly in vivo applications.
In Journal of Colloid and Interface Science, Vol. 141, No. 2, pages 505 to 511, H. Kobayashi et al. describe microfine magnetite particles which are modified with aminosilanes and have diameters in the range of 10-15 nm but which only have specific surface areas of 77 to 99 m.sup.2 /g and are used for the immobilization of enzymes.
The modified magnetites are prepared by a two-stage process in which the magnetites are first formed by precipitation from aqueous metal salt solutions, and their surfaces are then modified in a second stage with functional silanes.
It has now surprisingly been found that magnetite particles which have diameters of 10 mm or less in combination with substantially larger specific surface areas and which can be loaded to a higher degree and are more suitable for separations and applications, particularly in vivo ones, are obtained if the silanization is carried out simultaneously with the precipitation of the mixed oxides. The mean size of the particles is surprisingly considerably smaller than in a process with the addition of silane. Furthermore, the crystallization of the magnetic particles is not adversely affected by the presence of the silane. Surprisingly, however, the silane is simultaneously bound to the mixed oxides in such a way that the functional groups at the surface are accessible to further reactions. It has also been found that these silanized magnetic particles have an extremely high dispersion stability and do not form any sediment over long periods.
The invention provides magnetic particles of mixed oxides from the group comprising the ferrites, which have a particle diameter of 1 to 10 nm and a specific surface area of 120 to 350 m.sup.2 /g and to whose surface functional silanes are
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Blackburn Robert P.
Bonner Melissa
Chiron Diagnostics Corporation
Morgenstern Arthur S.
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