Dual complex of amylose with iodine and magnetite nano‐crystallites: Enhanced superparamagnetic and catalytic performance for synthesis of spiro‐oxindoles

Abstract

Mass magnetization of magnetite nanoparticles was enhanced by disassembling and encapsulating their building nano‐crystallites with water‐soluble starch. Incorporation of iodine into the as‐prepared nano‐conglomerate led to formation of a ternary nano‐complex and further enhancement of its superparamagnetic susceptibility. As an additional evidence for the anomalously heightened superparamagnetic property, the ternary nano‐complex showed lower magnetic remanence and coercivity than the pristine magnetite it was made from. These findings were ascribed to significant changes in, at least, size of the magnetite nano‐crystallites during formation of the nano‐composite. A significant enhancement was also observed in the catalytic efficiency of the nano‐composite, as was successfully exemplified in the synthesis of some novel spiro[oxindole‐dihydropyridine]s via a three‐component reaction between isatins, furan‐2,4(3H,5H)‐dione and aminouracils ‘on water’.