Amino acid-coated nano-sized magnetite particles prepared by two-step transformation

A series of amino acid-coated nano-sized magnetite (AA-NSM) particles such as leucine (Leu), arginine (Arg), cysteine (Cys), cystine, aspartate (Asp) and tyrosine (Tyr), were synthesized by a two-step transformation (TST) process. The TST process consists of the following steps: firstly preparing oxalate modified NSM (Ox-NSM) at pH 9 and secondly substituting AA for Ox to form AA-NSM at pH 5. Both the Ox- and AA-NSM particles were clearly confirmed by the FT-IR spectra and TGA curves. The content of each AA in the AA-NSM appeared different because of the difference in both the structure and isoelectric point of each AA molecule. It is noteworthy that Ox, as a template in the intermediate Ox-NSM, plays a key role in the formation of AA-NSM with free NH2 group inside. All of the AA-NSMs showed superparamagnetic property without hysteresis at room temperature and had strong saturated magnetization value (more than 50 emu/g), which may have potential applications in both biomedical and environmental areas.