Magnetic iron oxide fine particles, and magnetic particle-containing water dispersion and process for producing the same

Abstract

The present invention relates to a magnetic particle-containing water dispersion wherein the magnetic particles have a primary particle diameter of 5 to 15 nm and an average secondary particle diameter of 10 to 60 nm, and the water dispersion has a zeta potential of not more than −20 mV when a pH value of the water dispersion lies within the range of 6 to 8, and further a surface of the respective magnetic particles is coated with a carboxyl group-containing polymer. The magnetic particle-containing water dispersion is produced by heating an aqueous solution in which the carboxyl group-containing polymer is dissolved, to a temperature of 90 to 100° C. in a nitrogen atmosphere; adding a solution of a ferrous (II) salt and a ferric (III) salt and an alkali solution to the aqueous solution to react with each other at the same temperature; adding ethanol to the solution to obtain a precipitate; and removing a supernatant liquid from the solution, and then dispersing the precipitate in water and subjecting the resulting dispersion to dialysis. The magnetic particle-containing water dispersion is useful as a magnetic particle-containing water dispersion capable of producing magnetic particle-containing drugs for diagnosis and therapies which can exhibit a uniform functionality, with a good reproducibility.

1 . Magnetic iron oxide fine particles having a primary particle diameter of 5 to 15 nm and an average secondary particle diameter of 10 to 60 nm,
 a surface of the respective magnetic iron oxide fine particles being coated with a carboxyl group-containing polymer.   
     
     
         2 . A magnetic particle-containing water dispersion comprising water and magnetic iron oxide fine particles dispersed in the water, which magnetic iron oxide fine particles have an average primary particle diameter of 5 to 15 nm and an average secondary particle diameter of 10 to 60 nm,
 a surface of the respective magnetic iron oxide fine particles being coated with a carboxyl group-containing polymer.   
     
     
         3 . A magnetic particle-containing water dispersion according to  claim 2 , wherein the water dispersion has a zeta potential of not more than −20 mV when a pH value of the water dispersion lies within the range of 6 to 8. 
     
     
         4 . A magnetic particle-containing water dispersion according to  claim 2 , wherein the carboxyl group-containing polymer is a polyacrylic acid having a molecular weight of 1500 to 10000. 
     
     
         5 . A process for producing the magnetic iron oxide fine particles as defined in  claim 1 , comprising the steps of:
 heating an aqueous solution in which the carboxyl group-containing polymer is dissolved, to a temperature of 90 to 100° C. in a nitrogen atmosphere;   adding a solution of a ferrous (II) salt and a ferric (III) salt and an alkali solution to the aqueous solution to react with each other at the same temperature;   adding ethanol to the resulting solution to obtain a precipitate;   removing a supernatant liquid from the solution, and then dispersing the precipitate in water and subjecting the resulting dispersion to dialysis to obtain a water dispersion comprising the magnetic iron oxide fine particles whose surface is coated with the carboxyl group-containing polymer; and   freeze-drying the water dispersion to obtain the magnetic iron oxide fine particles.   
     
     
         6 . A process for producing the magnetic particle-containing water dispersion as defined in  claim 2 , comprising the steps of:
 heating an aqueous solution in which the carboxyl group-containing polymer is dissolved, to a temperature of 90 to 100° C. in a nitrogen atmosphere;   adding a solution of a ferrous (II) salt and a ferric (III) salt and an alkali solution to the aqueous solution to react with each other at the same temperature;   cooling the resulting solution to room temperature and then adding ethanol to the solution to obtain a precipitate; and   removing a supernatant liquid from the solution, and then dispersing the precipitate in water and subjecting the resulting dispersion to dialysis to obtain a water dispersion comprising the magnetic iron oxide fine particles whose surface is coated with the carboxyl group-containing polymer.   
     
     
         7 . A process for producing the magnetic particle-containing water dispersion according to  claim 5 , wherein a molar ratio of a carboxyl group (COON) to whole iron (Fe) (COOH/Fe) upon the reaction is 0.3 to 3.