WO2003041095A1

WO2003041095A1 - Process of composites preparation between particulate materials and cyclodextrins and/or their derivatives products thereof

Info

Publication number: WO2003041095A1
Application number: PCT/BR2002/000155
Authority: WO
Inventors: Ruben Dario Sinisterra Millan; Alberto Bocanegra Diaz; Nelcy Della Santina Mohallem
Original assignee: Universidade Federal De Minas Gerais - Ufmg
Priority date: 2001-11-05
Filing date: 2002-11-05
Publication date: 2003-05-15
Also published as: BR0105499C1; BR0105499A; BRPI0105499B1; BR0105499F1

Abstract

The present process is characterized by the mixture of an aqueous solution of metallic salts of ferrites, hydroxide in aqueous solution and cyclodextrin and/or derivatives, which yield a magnetic solid after heating. The magnetic fluid obtained does not need to be either filtered or centrifuged, for the particle size is uniform in the range of 150 nm, ranging from 0.1 to 250 mg Fe/ml through a single-step process. An important characteristic of the composites obtained in the present invention is that as they present permanent magnetization they can be driven by the relatively weak magnetic field of a permanent magnet. The composites in the present invention are also characterized by the presence of the paramagnetic properties. The composites formed may be used as magnetic adhesives, magnetic plaints, lubricants, magnetic fluids, sealers, magnetic fluids, sealers, magnetic recording media, catalysts, magnetic refrigeration, magnetically targetable drug carriers and matrices for magnetically assisted biological isolation, among other applications.

Description

"Process of composites preparation between particulate materials and cyclodextrins and/or their derivatives products thereof Field of the Invention

The present invention is characterized by the process of composites preparation between particulate materials and cyclodextrins and/or their derivatives products thereof.

Background of the Invention

Particulate materials are formed by bodies of nanometric or microscopic dimensions and significative mass with specific properties. A composite can be defined as a material formed by two or mores distinct constituents with specific phases which offer properties that are not possible to obtain from their individual components [E. P. Giannelis, Adv. Mater., 8, 29

(1996)].

All substances found in nature have magnetic properties and interact with magnetic fields [Brailsford, F.; An introduction to Magnetic Properties of

Materials, p.1, Longmans, Green and Co. Ltd. 1958, Great Britain ]. Basically, the magnetic state of matter can be classified as diamagnetism, paramagnetism, ferro- and anti-ferromagnetism, ferrimagnetism, and superparamagnetism. Diamagnetism is a weak form of non-permanent magnetism which appears when an external field is applied. The magnitude of the magnetic momentum induced is extremely small and in opposite direction to that of the field applied.

Paramagnetism is a phenomenon which occurs in materials which have permanent magnetic momentum, even though isolated from each other. In the absence of an external field, paramagnetic materials have no magnetization.

The application of an external field produces a small magnetization in the direction of the field.

Ferromagnetism is a phenomenon which occurs only in metallic materials which have high permanent magnetic momentum, even in the absence of external magnetic fields. In antiferromagnetism, the materials present coupling of magnetic momentum, which results in an equal antiparallel alignment, leading to the cancellation of these momentums.

Ferrimagnetism occurs with materials which present ionic magnetic momentums with the tendency to align in antiparallel directions. Two sub networks are formed in the material, one with the orientation of the magnetic momentum and another with the opposite orientation. The two momentums are different in magnitude and the material has a permanent magnetic momentum. Metallic oxides with magnetic properties can only present ferrimagnetism (Valenzuela, R.; Magnetic Ceramics, p.121 , 1994, Cambridge University Press). The macroscopic magnetic characteristics of ferromagnetic and ferrimagnetic materials are similar, but are distinct due to the fact that ferromagnetic materials have parallel magnetic momentums. Superparamagnetism occurs in ferro or ferrimagnetic materials with particle size smaller than ca. 10 nm, leading a single magnetic domain to the particle (Kim and collaborators, J. Magn. Magn. Mat.;225;, 30-36; 2001). Superparamagnetic materials are characterized by the fact that they do not keep the magnetic momentum in the absence of an external magnetic field. Under an external magnetic field, they present magnetization similar to that of ferromagnetic materials [Bean and Livingston; J. Appl. Phys. Suppl to vol. 30, 1205; (1959)].

Particles with paramagnetic, superparamagnetic, ferromagnetic, and ferrimagnetic properties are henceforth referred to as magnetic particles. A magnetic fluid is a suspension of very thin magnetic particles dispersed in an appropriate solvent, being the dispersion maintained by Brownian movement of the particles. To prevent particle agglomeration due to Van der Waals attractive forces, the particles are coated in varied ways. When a magnetic field is applied, the magnetic force is transmitted to all the volume of the liquid and the magnetic fluid responds as a fluid, to say, the magnetic particles are not separated from the solvent [Zins and collaborators, J. Mol. Liq.,83, 217-232; (1999)]. Magnetic fluids are not found in nature and must therefore be synthesized [R. Perez-Castillejos and collaborators, Sensors and Aquators A, 84, 176-180 (2000)]. To synthesize magnetic fluids, ferrites are largely used due to their chemical stability and availability [Cabuil, Current. Opinion in Colloid and Interface Science, 5, 44-48 (2000)].

Magnetic fluids have several technological applications, such as magnetic adhesives, magnetic paints, lubricants, magnetic sealers, magnetic recording media, catalysts, magnetic refrigeration. Applications are also found in magnetically controlled drug delivery, and in the formulation of image magnetic resonance contrast, in the treatment of anemia, as therapeutic agents in the treatment of hyperthermia, and matrices for magnetically assisted biological isolation, among others.

In the area of image diagnosis such as X-ray, ultra-sound, and MRI, for example, it is largely accepted the use of substances which enhance the contrast between healthy and sick tissues. Such substances are called contrast agents. In MRI for example, the contrast agent normally acts by modifying the characteristic relaxation times (Ti and T₂ ) of the nucleus of protons of water molecules, thus generating the resulting image. When they are injected into a living organism, materials with paramagnetic, superparamagnetic, ferromagnetic and ferrimagnetic can lead to the reduction of the relaxation times Ti and T₂ [Gunther WO PS 97/25073]. To use magnetic fluids in magnetically assisted biologic isolation, the particles must present some special characteristics. They must be biocompatible, biodegradable, stable, preferably spherical and uniform in size. In addition, they must also undergo surface modifications (hydrophobic/hydrophilic) leading to the adsorption of special molecules (Grϋttner and collaborators; J. Magn. Magn. Maf.,_225, 1-7, 2001).

For example, particles coated with polystyrenes present spherical shape and excellent size distribution, which is an advantage, but their surfaces are hydrophobic and therefore their surfaces (they do) not bind to large quantities of non-specific proteins, which is a disadvantage. Similar behavior is observed with poly-lactic acid coating.

Coating magnetic particles with polysaccharides has the advantage of their biocompatibility and selectivity for adsorption of biomolecules on the surface, but their are too sensitive to mechanical stress. The biocompatibility of magnetic fluids and toxicity seem to be determined by the nature of the substance of the magnetic matrix and/or the nature of the coating.

There are many patents of art related to obtaining the magnetic fluids described next. All processes in the state of the art here described are extremely complex and expensive in comparison to the present invention.

Thakur and collaborators [US 5,240,626 (1993)] obtained an aqueous magnetic fluid based on magnetite by coating the particles with functional carboxy- polymers like polymethyl methacrylate. The component particles of the fluid were between 2-20 nm in size and presented a magnetic momentum of 30 A m²/Kg.

Raj and collaborators [ US 5,958,282 (1999)] mixed a non-magnetic iron oxide (α- Fe₂O₃) with water and a commercial surfactant ("Westvaco Reax 88B") in a ball mill under stirring at 3500 RPM for 4 hours. The mixture was heated to 70 °C. A magnetic fluid made up of magnetite particles with size in the order of 10 nm was obtained. The magnetic fluid presented magnetization saturation in the range of 108 - 178 Gauss (approximately 8500 A/m).

Ziolo and collaborators [US 6,048,920 (2000)] used an ionic exchange resin to capture iron sulfide particles after oxidation with an appropriate base to obtain magnetite nanoparticles bonded to the resin. The particles obtained are in the range of 20-120 nm and present magnetization saturation equal to 16.1 A/m. Kovac and collaborators [US 3,990,981 (1976) and US 4,107,063 ( 1978)] described obtaining magnetic fluids to be used as magnetic printing paints by mixing magnetite and polyethylenglycol. After coating the magnetic particles with organic sulfides, sulfonates, carboxylates or organic amines. Magnetic particle size was in the range 5-30 nm and presented a magnetic momentum of 20-25 A m/Kg.

Sambucetti and collaborators [US 4,026,713 (1997)] mixed magnetite, glycerol, alkyl ethylene glycol monoether and polyethylene diol with low molecular weight, 200g/mol, to obtain a magnetic fluid formed by particles with size between 5 and 30 nm and magnetic momentum in the range 25-30 A m/Kg. Due to the presence of different highly toxic substances in the magnetic fluids obtained through the processes cited above, they have limited use in medical or pharmaceutical areas. Yu and collaborators ( Mat. Chem. Phys ;66, 6-9, 2000) obtained a magnetic fluid formed by magnetite nanoparticles by precipitating iron oxide under a nitrogen atmosphere in the presence of oleic acid and sodium oleate. Magnetic fluid particle size was 8-10 nm and presented spontaneous magnetization of 69.4 A m²/kg in a field of 0.6 Tesla. Zins and collaborators (J. Mol. Liq.; 83; 217-232, 1999) formed NiZn nanoparticles suspended in water by treating particle surface with ferric nitrate. The particle size obtained was in the range of 14 nm and presented saturation magnetization of 70 A/m.

Shen and collaborators (J. Magn. Magn. Mat; 194, 37-44, 1999) obtained an aqueous magnetic fluid stabilized by a double layer of fatty acids with particle size between 3-6 nm and saturation magnetization of 2 A/m in a magnetic field of 0.2 Tesla. The material was obtained by co-precipitation of an aqueous solution of Fe(ll) and Fe(lll) in the presence of dodecanoic acid (C₁₀). The resulting particles were coated with a second surfactant (n alkanoic acid, n=9- 13). Kim and collaborators ( J. Magn. Magn. Mat; 225, 30-36, 2001) formed magnetite with nanometric size from the mixture of solutions of FeCI₃ and FeCI₂ and NaOH under gaseous nitrogen atmosphere to minimize the size of the particles obtained. It was obtained a magnetic fluid with nanoparticles with 6 nm in diameter. The magnetization of the fluid obtained was 42.1 A m²/kg at 300K in a magnetic field of 1 Tesla. Most processes for obtaining magnetic fluids are a modification of the called "Molday Process" (Molday, US 4,452,773). This process is based on the precipitation of iron oxides in an alkaline solution containing a water-soluble polysaccharide, preferably dextran. The particles of the composite of colloidal size comprise iron oxide crystals coated with dextran. Iron oxide crystals normally present maghemite or magnetite structure. Iron oxide particle size obtained by Molday method is heterogeneous, being this the great disadvantage observed in the present state of the art. Groman and collaborators [US 4,951 ,675 (1990)] obtained a biodegradable magnetic fluid by making some modifications to the Molday ^'s method. By using dextran with molecular weight of 75,000 daltons or albumin from bovine serum as coating materials, they prepared magnetic particles with size between 1 and 500 nm. The use of centrifugation (1500 g / 15 min), dialyses (380 L of distilled water for 3 days changing water daily for every 80 mL of magnetic fluid, and ultra filtration allowed obtaining a magnetic fluid with particle size of ca. 150 nm. The incorporation of dextran of high molecular weight as used by Molday, 500,000 daltons, onto magnetic particles can cause adverse effects when these complexes are administered parenterally. Thus, low molecular weight dextran was used, 1000-5000 daltons, to coat magnetite aiming to improve the biocompatibility of the magnetic fluid [Groman and collaborators, US 5,248,492 ( 1993)]. Aiming to overcome the difficulties observed in the Molday and similar methods, Gunther [WO 25073 (1997)] proposed a process to produce composites with magnetic particles inside a hydrophilic organic compound. The posterior break of the polymer generates particles in the range of 1 to 300 nm containing 0.1- 250 mg Fe/mL. However, the process described by Gunther is extremely complex and the use of chemical agents in the oxidation process can generate chemical contamination.

Grϋttner and collaborators (J. Magn. Magn. Mat, 225. 1-7, 2001) developed hybrid magnetic particles of polystyrene with polysaccharides, polyethylene with silicon, polysaccharides with polyalkylcianoacrylate and polysaccharides with poly-latic acid. In the process to obtain hybrid magnetic particles of Grϋttner and collaborators, it is necessary to form magnetic particles, coat first them with a layer of polymer or silicon, depending on the case, and clean them with organic solvents. The particles obtained present a smaller tendency of adhesion to the plastic wall, higher resistance to mechanical stress, and new possibilities of incorporation or adsorption of drugs, presenting potential as magnetically controlled drug carriers. Grϋttner's process to obtain fluid iron is potentially dangerous due to the use of a series of solvents and chemical substances, which may result in toxic effects in the final product.

According to Yang and collaborators (Hyperfme Interactions, 7Q, 1129-1132, 1992) when the surface of magnetite nanoparticles (Fe3θ_ is coated with organic surfactants, occurs an important modification to their magnetic properties.

There are innumerable methods for the synthesis and stabilization of ferrites in the state of art, however, they are not applicable to pharmacological purposes, mainly due to their non-aqueous nature and the toxicity of the coatings and the surfactants used in their synthesis.

For intravenous use, particles size and size distribution and the chemical nature of the surface of the composites are of great importance in the determination of the efficient action of the magnetic fluids, the resident time in the blood stream, and biodistribution. The size of the particles for intravenous use is of great importance for their distribution through the organism. To circulate through capillaries of smaller diameter, the particles must be smaller than 5 μm, but only particles smaller than 200 nm can be filtered through vessels. Submicroscopic particles are rapidly phagocyted by cells in the reticule endothelial system [Gref and collaborators; Advan.Drug Deliv. Rev.; 16; 215-233; (1995)].

Particles coated with polystyrene and with diameter close to 60 nm are removed from the blood within minutes by the reticule endothelial system. Similarly, particles coated with albumin, poly-lactic acid, poly-latic-co-glycolic acid, poly cyanoacrylate or polyacrylic amide present an average blood stream life equally short. However, the particles can be camouflaged from the reticule endothelial system. Particles with hydrophilic surface in which water molecules may be adsorbed present an extended blood stream average life. Particles with neuter surface seem to be more appropriate in relation to the increase in blood stream half life [Gref and collaborators; Adv.Drug Deliv. Rev.; 16; 215-233; (1995)]. Pilgrim proposed in US 5,160,725 and WO 21240 (1994) that magnetic particles can be kept longer in the blood stream without being attacked by the reticulo- endothelial system when they have stabilizing particles bonded to their surfaces. Examples of materials that can be used as stabilizers include oligosaccharides and polysaccharides. Magnetic particles thus stabilized characterize a magnetic fluid.

Hafeli and collaborators ( J. Magn. Magn. Mat; 194. 76-82, 1999) studied the factors that determine biocompatibility and toxicity of magnetic fluids. Particles of Fe-C and magnetic and non-magnetic fluids coated with polylactic acid, polystyrene or dextran were used in the study. The study showed that the particles, magnetic or otherwise, presented biocompatibility in acceptable therapeutic concentrations (less than 150 mg/kg). The toxic effects can be associated to the presence of detergents, polymers and/or monomers derived from the fluid preparation.

Liberti and collaborators [US 6,120,856 (2000)] use a thermal treatment to coat magnetic particles. The coating is formed typically by a polypeptide, a protein or an antibody. However, the intravenous use of this type of coating has been harshly criticized by Bogdanov and collaborators (Adv. Drug. Deliv. Rew.; 16; 335-348; 1995), among others. These authors point out that the use of serum albumins and other proteins such as inmunoglobulins as coating material for magnetic particles for intravenous human use presents a high risk of virus contamination such as HIV or hepatitis. Many ferrofluids using water as solvent have been proposed, for example: Kovac [US 3,990,981(1976) 4,107.063(1978)]; Sambucetti [US 4,026,713(1977)]; Thakur [US 5,240,626 (1993)]; Groman [US 5,248,492 (1993); WO 25073 (1997)]. They all are obtained by means of complex processes which raise costs and the possibility of product contamination. Among other applications of particulate materials with magnetic properties are magnetically targetable drug carriers. This strategy allows vectoring and concentrating anti-cancer chemotherapeutical agents around the tumor for maximum efficiency. Bergemann and collaborators (J. Magn. Magn. Mat; 194. 45-52, 1999) obtained a targetable carrier coating iron oxide magnetic particles with polysaccharides or polymeric derivatives. The coating was sterilized with sulfide-, phosphate and/or carboxylate groups or derivatives. Later, it was possible to bind a drug ionically, such as anthracylin, epirubicin derivative. Paclitaxel, a commercial drug from epirubicin has demonstrated great therapeutic potential in the treatment of head and neck cancer. Using the device obtained by Bergemann and collaborators, it was possible to concentrate large quantities of drugs around the tumors, thus reducing their side effects.

The need to bind a drug to the carrier covalently or ionically is a limiting factor to the use of the system proposed by Bergemann and collaborators. Many biologically active chemical substances loose their pharmacological capacity when submitted to inappropriate reaction conditions. In contrast, it is not always possible to bind the drug to the carrier covalently or ionically.

Kuznetsov and collaborators (J. Magn. Magn. Mat; 194. 83-89, 1999) consider that injections of biocompatible magnetic solutions do not produce toxic compounds during their metabolism in the organism, but that the toxicity derive from the mechanical effects and the damages caused to the blood vessels in vital organs by the magnetic particles of the fluids. Magnetic particles with superficial coating can form monolayers on the surface of the aortas yielding agglomerates in the blood vessels and stopping the blood supply and finally leading to death by choking. The use of less hydrophobic materials to coat the particles in magnetic fluids could be an alternative strategy to overcome particle buildup on blood vessel walls when it is necessary to use the magnetic fluids intravenously.

Polysaccharides are polymers which present numerous spaced OH groups on the surface and that can interact easily with the surface of the magnetic particles and stabilize them. However, the poor homogeneity of oligosaccharides and polysaccharides as coatings is considered a source of heterogeneity for particle size in the magnetic fluid.

There are highly homogeneous polysaccharides and with exceptional characteristics which can be used to coat magnetic particles. These polysaccharides are the cyclodextrins. Cyclodextrins belong to the cyclic oligosaccharide family, which includes six, seven or eight glucopyranose units. Due to steric interactions, cyclodextrins, CDs, form a cyclic structure in the shape of a truncated cone with an internal apolar cavity. These compounds are chemically stable and can be modified regioselectively. Cyclodextrins (hosts) form complexes with several hydrophobic molecules (guests) including them partially or completely into the cavity. Cyclodextrins are cyclic oligosaccharides formed by glucose units with α bonds (1-4) to each other. The number of glucose units can vary up to 12, however, molecules of 6, 7 and 8 units, called α, β and γ-cyclodextrin, respectively, stand out as object of study. Cyclodextrins can be chemically modified to improve their physical-chemical characteristics. CDs have been used to solubilize and encapsulate drugs, perfumes and flavors as described by [Szejtli, J., Chemical Reviews, (1998), 98, 1743-1753. Szejtli, J., J. Mater. Chem., (1997), 7, 575-587]. According to detailed studies by Rajewski, R.A. and Stella, V., [J. Pharmaceutical Sciences, (1996), 85, 1142- 1169] cyclodextrins present either low or no toxicity, mutagenecity, teratogenecity and carcinogenecity. Detailed toxicity studies, in special of hydroxypropyl-β-cyclodextrin, except for high concentrations of some derivatives which provoke damage to erythrocytes, demonstrate that these products in general do not bear risk to health. The use of cyclodextrins as food additives has been authorized in countries like Japan and Hungary, and for more specific uses in France and Denmark. Furthermore, CDs are obtained from a renewable source through the degradation of starch. All these characteristics are additional reasons to seek new applications. The structure of the CD molecule is similar to that of a truncated cone with symmetry close to Cι. The primary hydroxyls are located on the narrower end of the cone, and the secondary hydroxyls on the broader end. Despite the stability lent to the cone by the hydrogen intramolecular bonds, it is flexible enough to allow a considerable shift of its regular shape.

CDs are moderately soluble in water, methanol, and ethanol and readily soluble in aprotic polar solvents like dimethyl sulfur oxide, dimethylformamide, N,N- dimethylacetamide and pyridine. There are innumerous works in literature on the effects of the increase in water solubility of guests using cyclodextrins via inclusion compounds, as well as on the stability of inclusion compounds. Their physical-chemical characteristics are well described in [Szejtli, J., Chemical Reviews, (1998), 98, 1743-1753. Szejtli, J., J. Mater. Chem., (1997), 7, 575-587].

Cyclodextrins do not present superficial activity and generally exert a degradation effect on colloidal suspensions [J. Szejtli,, Cyclodextrin Technology, Kluwer Academic Publishers, 1988, pg. 140-141].

The cyclodextrins used in this invention can be selected from the group made up of hydroxyalkylated cyclodextrins (e.g.: hydroxypropyl β cyclodextrin), methylated cyclodextrins (e.g.: 2,6-di-O-methyl β cyclodextrin), branched cyclodextrins (e.g.: 6-O-Glucosil β-cyclodextrin), α-cyclodextrin, β-cyclodextrin, γ-cyclodextrin or their mixtures.

Due to the hydrophilic characteristics of the exterior of cyclodextrin, supramolecular structures can also be formed with guest molecules in aqueous solution. When the guest is inside the cyclodextrin cavity, an inclusion complex is formed and when it stays outside the cyclodextrin cavity, it is called association compound.

Klaveness and collaborators [US 5,928,626 (1999)] used a physical mixture of cyclodextrin, iron oxide and inert gases as ultra-sound contrast agents. In the microparticles obtained by Klaveness and collaborators, cyclodextrins serve as a contrast agent. In contrast, in this work, the inventors consider that the iron oxide does not present superficial activity and but serve only as a structural reinforcement.

Among the innumerous applications of cyclodextrins, they might be considered perfect to coat magnetic particles to obtain ferrofluids with targetable magnetic drug carriers, contrast agents for MRI or vectors for biological separations, among others. The advantages of using cyclodextrins in this invention derive from the fact of their low toxicity, water solubility, good surfactant activity, capacity to include varied substances within theirs cavities, being obtainable from renewable sources, the ability to serve as targetable drug carriers when bound to magnetic particles, among others of interest as described in this report.

Pilgrimm [US 6,274,121 ( 2001)] obtained superparamagnetic iron oxides or ferrites coated with orthosilicon or their condensation products, phosphate groups containing metaphosphoric acid or orthophosphoric acid or their condensation products bound to organic substances such as cyclodextrins, for example. According to Pilgrimm, the magnetic particles were stabilized with the orthosilicon acid coating and the use of cyclodextrins modified with ortho- or metaphosphoric acid was only used to better adjust the magnetic particle properties desired.

The present invention enables obtaining magnetic monodispersed ferrofluids coated with cyclodextrins in a quick, simple and efficient way involving a single- step process. It also allows to obtain composites with magnetic behavior formed by particulate materials and monodispersed cyclodextrins and with size in the range of 150 nm containing 0.1-250 mg Fe/mL through a simple single-step process. The composites obtained in the present invention have the special characteristic that the coating is formed by a neuter hydrophilic material, which can increase the average life of the bioactive principles.

An important characteristic of the composites obtained in the present invention is that they present permanent magnetization, they can be driven by the relatively weak magnetic field of a permanent magnet rather than the strong magnetic fields used to control superparamagnetic particles. In the present invention, the magnetic fluid is obtained through the mixture of an aqueous cyclodextrin and hydroxide solution with a ferrite, slightly heated (40- 50°C). The fluid particles are uniform and can be obtained without the need of filtration or centrifugation. In the present invention, oxides such as cobalt ferrite (CoFe₂O₄), copper ferrite (CuFe₂O4), dysprosium iron garnet (DyFe0₃), erbium orthoferrite ( ErFe0₃), gadolinium iron garnets (Fe₅Gd3θi2), holmium iron garnet (Fe5Hθ3θi2), manganese-nickel-iron oxide (FeMnNiO4), gamma iron oxide (maghemite) (Fβ2θ3), ferrous-ferric oxide (magnetite)(Fe3θ₄), alpha iron oxide (hematite) (Fβ₂θ3), lanthanum ferrite (FeLaOs), magnesium ferrite (MgFβ₂θ4), manganese ferrite (Fe2MnO₄), nickel aluminum ferrite

nickel zinc ferrite (Fe₂Nio,5Zno,5), nickel zinc ferrite (Fe2Nio,4Zno,β), nickel zinc ferrite (Fe2Nio,8 no,2), nickel ferrite (Fβ₂Niθ₄), samarium iron garnet (FesO^Sms), silver lanthanum ferrite (Ago.sFe-^Lao.s O19), yttrium iron garnet (Fβ5θι₂Y3), yttrium orthoferrite (FeY0₃), which for the purposes of this invention will hence be called ferrites or magnetic particles. The fluids obtained with these ferrites have similar physical- chemical properties and varying magnetic properties according to each kind of ferrite used.

In this invention, particles of generic formula MOFe∑Os, where M represents a bivalent metallic ion chosen from the group Fe, Co, Ni, Mn, Be, Mg, Ca, Ba, Sr, Cu, Zn, Pt or their mixtures or oxides with formula Fβ₂θ3Me₂θ₃, where Me represents a trivalent metallic ion select from a group made up by Al, Cr, Bi, metals of rare earths and their mixtures, that for the purposes of this invention will hence be called ferrites and/or magnetic particles.

Ferrites can be obtained by means of some of the known state-of-art synthesis methods. It stands out in this invention that the composites obtained are soluble in water and do not form agglomerates under the magnetic field of a permanent magnet, but present permanent magnetization. This is possible when 2.8637g of β- cyclodextrin is mixed with 8 mL of ammonia hydroxide 30% in 15 mL of de- ionized water. For this mixture, 2.000g of the magnetite obtained is added depending on the state of the technique. The mixture is heated up to 50 °C under magnetic stirring until the solubilization of the magnetite (ca. 3 hours). The fluid presents permanent magnetization and final pH 7. Another characteristic of this invention is that the composites obtained are totally soluble in water and present paramagnetism when mixed with 0.9938 g of β-cyclodextrin with 5 mL of ammonia hydroxide 30% in 5 mL of de-ionized water and 0.1000g of Fe (SO₄)35H₂O. The mixture is heated up to 48°C under magnetic stirring for 4 hours, filtered and the solid part is discarded. The filtered liquid is stable under the magnetic field of a permanent magnet and presents paramagnetism and pH 7. The fluid obtained can be dried at 45^°C in air and a brown solid which can be easily dissolved again in water is obtained. In addition, in this invention, cyclodextrins are used to coat magnetic particles to reduce the fixation of proteins onto the particle surfaces, thus decreasing their risk of adhering to the walls of blood vessels and later forming thrombi, which happens with hydrophobic polymers and/or oily layers.

Another advantage which characterizes this invention is the use of cyclodextrins to form magnetically targetable drug carrier composites. One more advantage of the present invention is the fact that aged samples of the magnetic fluid stored at room temperature present stability for up to 2 months, while most magnetic fluids known at the present state of art require low storage temperatures. It stands out in this invention the simplicity of the method and not using conventional surfactants such as either detergents or electrolytes, which minimizes the risks of chemical contamination and reduces production costs. Furthermore, it is very important in the present invention the quality and the stability of the magnetic fluid obtained, the size of the particles, the size uniformity of the magnetic particle formed, and the low cost of both the synthesis materials and the raw materials used.

The physical-chemical characteristics of the magnetic fluid in agreement with the process claimed in the present invention allows its use as a magnetically targetable drug carrier and a matrix for the magnetically assisted biological isolation, among other applications. This invention presents the added advantage that the fluid obtained through this technique can be suspended or solubilized in water or in organic salt solutions (e.g.: physiologic saline solution), or in monosaccharide solutions (e.g.: glucose or galactose), disaccharides (e.g.: lactose) or in aqueous solution of a mono or polyhydric alcohol physiologically tolerable (e.g.: ethanol, propanol, isopropanol, ethylene glycol, propylene glycol, glycerin or polyethylene glycol).

This invention is further explained by means of the following non-limiting examples.

EXAMPLE 1

Production of the magnetic fluid It is mixed 2.8637g of β-cyclodextrin and 8 mL of ammonia hydroxide 30% in 15 mL of de-ionized water. The mixture is heated up to 40 °C under magnetic stirring until the total dissolution of the β-cyclodextrin. To the mixture, 2.00G 3 of magnetite obtained through state-of-art technique is added. The mixture is heated up to 50^°C under magnetic stirring until the solubilization of the magnetite (ca. 3 hours). The fluid presents permanent magnetization and final pH 7. The particle size of the magnetic fluid was determined through light scattering technique. The average size was 150nm +/- 50nm. Measurement of particle size of the aged sample (15 and 30 days) shows that the size remains the same, which suggests the stability of the magnetic fluid and the non- aggregation of the particles. The spontaneous magnetization of the ferrofluid obtained was measured as being 15.7 A m²/kg. The fluid density measured at 20^°C was 0.9738 g/mL. 5 mL of the magnetic fluid obtained was dried at 50^°C and 0.0424 g of solid was obtained, which represents 8.48 mg of magnetite per mL of magnetic fluid. The spontaneous magnetization of the solid was 15.7 A m²/ kg. The composite obtained was physical-chemically characterized by elemental analysis, thermal analysis, infrared absorption spectroscopy, and X-ray diffraction through the powder method. The results of the elemental analysis of the complex are: Fe₃0₄ = 24.7% ; N=0.0% ; C= 34.75% ; H= 5.98%. According to the elemental analysis, for every ferrite unit there is one cyclodextrin unit in the composite. This result is confirmed by the thermal analysis, which presents two mass losses of 9% and 67% between 25-100^°C and 280-350^°C, respectively. These losses can be associated to the loss of 7 water molecules in the first event, and the fusion-decomposition of cyclodextrin in the second. The results of the thermal analysis suggest that the cyclodextrin cavity is free to carry guest molecules.

Additionally, infrared spectra of the composite exhibit bands characteristics of β- cyclodextriπ, i.e., bands in the region of 3500-2800 cm^"1 and 1400-1100 cm^"1, characteristic of O-H and C-O-C stretchings, respectively. One intense band also observed at 526 cm ^"1 can be attributed to M-0 bond stretching. This last band is (not observed for β-cyclodextrin, however, they are observed for iron ferrites (magnetite) at 530 cm ^~1. Another important observation is that the OH. symmetric stretchihg^band (3395 cm^"1) is broader in the composite spectrum in comparison to that of β-cyclodextrin and narrower in comparison to that observed in the ferrite spectrum. This observation can be interpreted as an evidence of the presence of a larger number of hydrogen bonds in the composite in comparison to cyclodextrin and ferrite. Moreover, the vibrational modes of the OH asymmetric deformation at 1408 and 1329 cm^"1 and the bands in the region of 1200 and 999 cm^"1 in the composite spectrum do not present significant changes in comparison to those of β-cyclodextrin in the same regions. These results suggest the formation of a superficial cyclodextrin layer on the magnetic particle without the formation of covalent bonds, besides the preservation of the ring structure of β-cyclodextrin after reaction.

The X-ray diffractogram of the composite presents peaks at 9, 13 and 23 degrees 2Θ characteristic of β-cyclodextrin and another peak at 36 degrees 2Θ, which is also observed in the magnetite diffractogram. Other characteristic peaks of iron ferrites and β-cyclodextrin were not observed. The set of results presented suggest that a magnetite-β-cyclodextrin complex system was obtained. The ferrite may be coated with one or several layers of cyclodextrin, possibly without covalent bonding among them, in the proportion of one magnetite unit per unit of cyclodextrin. The stability of the solid obtained suspended again in water held for 2 months. EXAMPLE 2

Production of magnetically targetable drug carrier It was mixed 0.2780g of FeSO -7H₂0 with 0.0657g of NiSO₄x7H₂0 and 0.0314g of ZnCO₃ in 25mL of water under magnetic stirring as suggested by Passos and collaborators (Macedo, C.V.; Passos, A. C; Silva, A.C.L.; Valente, G.C. and Mohallem, N.D.S.; Congresso Brasileiro de Electromagnetismo, UFSC; 322 - 324, 1995). To this suspension, 8.5q26g of solid β-cyclodextrin and 10mL of NH₄OH (11.0 M) was added. The resulting suspension was heated (60 °C) until it turned black. Heating was interrupted and the black suspension was kept under stirring for another 4 hours. In this way, a brown solid clinging to the stirring magnet was obtained. The solid was magnetically separated from the solution and washed until get the liquid neutrality. The solid formed presents permanent magnetization. The solid obtained was characterized by physical-chemical characteristics such as elemental analysis, thermal analysis (TG, DTG, DSC), infrared spectroscopy, and X-ray powder diffraction.

The elemental analysis shows the presence of 79 NiZn ferrite units per unit of β-cyclodextrin in the sample. This result is confirmed by thermal analysis, which presents a continuous decomposition profile between 25-750°C with a 30% mass loss in the same temperature range. This mass loss is associated to the dehydration of the sample and the decomposition of β-cyclodextrin. Infrared spectrum of the solid displays bands characteristic of β-cyclodextrin, i.e., in the 3500-2800-cm^"1 and 1100-cm^"1 regions, characteristic of O-H and C- O-C stretching, respectively. Two intense bands are also observed at 420 and 526 cm ^~\ which can be attributed to the asymmetric and symmetric stretchings of the M-O bond. These bands are not observed for β-cyclodextrin, however, they are observed for NiZn ferrites at 401 and 618 cm^"1. Another important observation is that the OH symmetric stretching band (3395 cm^"1) is broader in the solid spectrum in comparison to that of β-cyclodextrin and narrower in comparison to that observed in the ferrite spectrum. This observation could be interpreted as an evidence of the presence of a larger number of hydrogen bonds in the solid than in β-cyclodextrin and ferrite. It is observed that the O-H deformation bands at 1408 and 1329 cm^"1 for β- cyclodextrin are not observed in the solid spectrum. A possible explanation for this fact is that β-cyclodextrin may have formed a covalent bond of the M-O-β- cyclodextrin type with the ferrite. It is known that bulky reagents react preferentially with OH(6) primary hydroxyl groups of cyclodextrins. Moreover, the vibrational mode of the OH asymmetric deformation of β-cyclodextrin at 1408 and 1329 cm^"1 are not observed in the respective spectrum of the solid. The bands in the spectrum of the solid in the 1200 and 999 cm^"1 regions do not present significant changes in comparison to β-cyclodextrin in the same region. This result suggests the preservation of the ring structure of β-cyclodextrin after reaction. X-ray diffractograms of the solid present only two peaks at 57 and 36 degrees 2Θ, which are also observed in the β-cyclodextrin diffractogram. Other characteristic peaks of NiZn ferrites and of β-cyclodextrin were not observed. The set of results presented suggest that a complex ferrite-β-cyclodextrin system was obtained. The ferrite is in the outer cavity, possibly covalently bonded to the OH(6) primary hydroxyl oxygens of β-cyclodextrin. On the other hand, it may be concluded that the cavity is free to take in guest molecules, that it is a magnetically targetable drug carrier or a matrix for biological isolation. These applications are presented for the sake of example and do not limit the possible applications of the invention. EXAMPLE 3

Production of a paramagnetic fluid totally soluble in water A mixture of 0.9938 g of β-cyclodextrin with 5 mL of ammonia hydroxide 30% in 5 mL de-ionized water and 0.1000g Fβ2(S0₄)35H2O was made. The mixture was heated up to 48°C under magnetic stirring for 4 hours. The resulting mixture was filtered and the solid part was discarded. The filtered liquid was stable under the magnetic field of a permanent magnet and presented paramagnetism and pH 7. The fluid obtained was dried at 45°C in air and the brown solid obtained can be easily dissolved into water again. The solid obtained was characterized by physical-chemical techniques such as elemental analysis, thermal analysis (TG, DTG, DSC) infrared absorption spectroscopy, Mossbauer spectroscopy and powder X-ray diffraction. Elemental analysis results for the paramagnetic fluid were: Fe = 1.36 % ; C = 34.76 % ; N = 1.32 % ; H = 6.36 %. In agreement with elemental analysis results, the paramagnetic fluid can correspond to the following empirical formula: FeN4Ci23H27o, which could be reorganized as: [Fe(NH3)4(H O)2][(C 2H7oθ35) 7.4 H2θ]3, considering the reagents used.

TG / DTG curves of the complex present two events, one between 25-158 °C, and another between 167-500 °C. The first event occurs in the temperature range 25-158 °C accompanied by a weight loss of 11 %, equivalent to 435 g, which may represent 24 moles of water. The second event is made up of five integrated small events. Considered as a whole, the second event represents a loss of 86% of the total weight, equivalent to 3404 g, which may correspond to 3 moles of β-cyclodextrin. The five small events occur between 167-233 °C (14%), 233-291 °C (12%), 292-358 °C (19 %), 359-425 °C (19%) and 425-500 °C (22 %), respectively. The residue produced by heating the sample over 800^°C was 3% of the total weight, equivalent to 123.85g, which could correspond to 1 mol of Fe(NH3)4-

The DTA curve of the complex displays six events. The first event of endothermic character occurs in the range 25 - 169 °C, characterizing the formation of 24 moles of water, as observed in the TG/DTG curve. The second event, also with endothermic character, takes place in the range of 170-225 °C and might be considered as the fusion of the organic portion of the complex: β- cyclodextrin. The other four events characterize a large event between 225-580 °C, and may correspond to the events observed at the same temperature range in TG/DTG curves of the same compound. Mδssbauer effect spectrum of the solid measured between 4-300K (-269 and 25°C, respectively) presents a central duplet and four small satellites, without corresponding temperature changes. This occurs only for paramagnetic samples, which once more seems to confirm the chemical formula derived from elemental analysis. Infrared spectrum absorption of the paramagnetic fluid reveals an increase in the intensity of the band at 1420 cm^"1, in comparison to the same band of the β- cyclodextrin spectrum. This can be due to the angular asymmetric deformation of the H-N-H bond in the Fe(NH3)4 complex. The other bands corresponding to the organic part of the paramagnetic fluid (3200, 1158 e 600 cm^"1) can not be observed in IR spectrum, because they are superposed with stronger bands corresponding to β-cyclodextrin, which additionally are in larger proportion in the compound.

In the powder diffractogram, one can observe that the values of the angle 2Θ, interplanar distances and relative intensities for the complex are totally different from the corresponding values for β-cyclodextrin suggested by the formation of a new chemical species. The set of results presented suggest that a complex iron (III) tetraaminodiaquo- β-cyclodextrin complex was obtained, being the iron (III) complex interacting with the cavity, possibly without forming covalent bonds. In contrast, one can conclude that the cavity is free to take in guest molecules.

Claims

CLAIM

1. Process to obtain composites made up of cyclodextrins and/or cyclodextrin derivatives and particulated materials with magnetic behavior and/or derivative products characterized by a mixture of an aqueous solution of cyclodextrin, hydroxides and ferrites under magnetic stirring and at temperatures in the range 40-60°C.

2. Process to produce composites made up of cyclodextrins and/or cyclodextrin derivatives and particulated materials with magnetic behavior and/or derivative products characterized by the fact that the particulated materials are formed from an aqueous solution of metallic salts, hydroxide in aqueous solution and cyclodextrin, being the resulting mixture immediately heated between 50-90°C and kept under stirring during the time necessary to obtain particulated materials with magnetic behavior.

3. Process to obtain composites made up of cyclodextrins and/or cyclodextrin derivatives characterized by the mixture of an aqueous solution of cyclodextrin, hydroxides and metal salts under magnetic stirring at a temperature range 40-60°C, being the liquid obtained separated and dried at a temperature lower than 70°C.

4. Process in agreement with claims 1, 2 and 3, characterized by the fact that the hydroxide used can be selected from a group made up of alkaline hydroxides, alkaline earths and rare earths or their mixtures.

5. Process in agreement with claims 1, 2 and 3 characterized by the use of cyclodextrins, α-cyclodextrin, β-cyclodextrin and γ-cyclodextrin or their mixtures.

6. Process in agreement with claims 1, 2, 3 and 5, characterized by the use of cyclodextrins or cyclodextrin derivatives selected from the functional groups: alkyl, hydroxyalkyl, hydroxypropyl, and/or acyl or cyclodextrins with crosslinks or cyclodextrin polymers, branched cyclodextrins, or their mixtures.

7. Process in agreement with claims 1 , 2, and 3 characterized by the fact that the ferrite can be selected from the MOFβ2θ₃ group, where M represents a bivalent metallic ion selected from a group made up of Fe, Co, Ni, Mn, Be, Mg, Ca, Ba, Sr, Cu, Zn, Pt or their mixtures and/or oxides with the formula Fe₂θ₃Mβ₂θ₃, where Me represents a trivalent metallic ion selected from a group made up of Al, Cr, Bi, rare earth metals and/or their mixtures, cobalt ferrite (CoFe₂0₄), copper ferrite (CuFe₂O4), dysprosium iron garnet (DyFe0₃), erbium orthoferrite (ErFeOs), gadolinium iron garnet (Fe₅Gd3θι₂), holmium iron garnet (Fe₅Hθ₃θi₂), manganese-nickel iron ferrite (FeMnNi0 ), gamma-iron oxide (maghemite) (Fe₂O₃), ferric oxide (magnetite) (Fe₃O₄), alpha-iron oxide (hematite) (Fe₂θ₃), lanthanum ferrite (FeLaO₃), magnesium ferrite (MgFe2θ₄), manganese ferrite (Fe₂Mn0 ), nickel and aluminum ferrite

nickel zinc ferrite (Fe₂Nio,5Zno,5), nickel zinc ferrite

nickel zinc ferrite (Fe₂Ni_0l8Zn₀,2), nickel ferrite (Fe₂Ni0 ), samarium iron garnet (Fe₅Oi₂Sm₃), lanthanum silver ferrite (Ago,5Feι₂La₀,5 O19) yttrium iron garnet (Fe₅Oi₂Y₃), yttrium orthoferrite (FeYOβ) or their mixtures.

8. Process in agreement with claims 2, 3 and 7 characterized by the fact that the metal salts used can have the formula MgXb, M=Fe, Co, Ni, Mn, Be, Ca, Ba, Sr, Cu, Zn, Pt, Al, Cr, Bi, Dy, Er, Gd, Ho, Y, Sm, or La and X=CI^", NO3^", SO₄ ⁼, C0₃ ⁼, NH₄ ⁺, citrate, oxalate, gluconate, fumarate, phosphate, pyrophosphate, or their mixtures, _a can be equal or different from b, a and b can have any value greater than zero.

9. Process in agreement with claim 1 characterized by being a single-step process.

10. Process in agreement with claims 1, 2 and 3 characterized by not using either conventional surfactants, or electrolytes to solubilize the ferrites.

11. Process in agreement with claims 1 , 9 and 10 characterized by the fact of obtaining a magnetic fluid which presents permanent magnetization.

12. Product formed in agreement with claims 1 , 9, 10 and 11 characterized as a magnetic fluid, monodispersed, nanometric with permanent magnetization.

13. Process in agreement with claims 1 , 11 and 12 characterized by the fact the composites formed can be used as magnetic adhesives, magnetic paints, magnetic lubricants, magnetic sealing fluids, magnetic recording devices, catalysts, magnetic cooling, magnetically targetable drug carriers, and matrices for magnetically assisted biologic isolation, which are examples of use.

14. Product formed in agreement with claims 1 , 11 , 12, and 13 characterized by stability in water and/or aqueous buffer solutions and/or physiologic solutions at room temperature for as long as 2 months.

15. Process in agreement with claims 2, 5 and 6 characterized by the fact that cyclodextrin can be added as aqueous solution or as a solid.

16. Product formed in agreement with claims 2, 4, 8 and 9, characterized as magnetically targetable drug carrier and/or matrix for magnetically assisted biologic isolation, without limiting other possible applications of the invention.

17. Process in agreement with claim 3 characterized by the fact of obtaining a paramagnetic solid.

18. Product obtained in agreement with claims 3 and 17 characterized as a paramagnetic solid.

19. Product obtained in agreement with claims 3, 17, and 18, characterized as a water-soluble paramagnetic solid.