Mixtures of L-amino acids as reaction medium for formation of iron nanoparticles: The order of addition into a ferrous salt solution matters

Abstract

Owing to Mössbauer spectroscopy, an advanced characterization technique for iron-containing materials, the present study reveals previously unknown possibilities using L-amino acids for the generation of magnetic particles. Based on our results, a simple choice of the order of L-amino acids addition into a reaction mixture containing ferrous ions leads to either superparamagnetic ferric oxide/oxyhydroxide particles, or magnetically strong Fe0-Fe2O3/FeOOH core-shell particles after chemical reduction. Conversely, when ferric salts are employed with the addition of selected L-amino acids, only Fe0-Fe2O3/FeOOH core-shell particles are observed, regardless of the addition order. We explain this phenomenon by a specific transient/intermediate complex formation between Fe2+ and L-glutamic acid. This type of complexation prevents ferrous ions from spontaneous oxidation in solutions with full air access. Moreover, due to surface-enhanced Raman scattering spectroscopy we show that the functional groups of L-amino acids are not destroyed during the borohydride-induced reduction. These functionalities can be further exploited for (i) attachment of L-amino acids to the as-prepared magnetic particles, and (ii) for targeted bio- and/or environmental applications where the surface chemistry needs to be tailored and directed toward biocompatible species. © 2013 by the authors; licensee MDPI, Basel, Switzerland.