Partial Oxidation as a Rational Approach to Kinetic Control in Bioinspired Magnetite Synthesis

Abstract

Biological systems show impressive control over the shape, size and organization of mineral structures, which often leads to advanced physical properties that are tuned to the function of these materials. Such control is also found in magnetotactic bacteria, which produce-in aqueous medium and at room temperature-magnetite nanoparticles with precisely controlled morphologies and sizes that are generally only accessible in synthetic systems with the use of organic solvents and/or the use of high-temperature methods. The synthesis of magnetite under biomimetic conditions, that is, in water and at room temperature and using polymeric additives as control agents, is of interest as a green production method for magnetic nanoparticles. Inspired by the process of magnetite biomineralization, a rational approach is taken by the use of a solid precursor for the synthesis of magnetite nanoparticles. The conversion of a ferrous hydroxide precursor, which we demonstrate with cryo-TEM and low-dose electron diffraction, is used to achieve control over the solution supersaturation such that crystal growth can be regulated through the interaction with poly-(α,β)-dl-aspartic acid, a soluble, negatively charged polymer. In this way, stable suspensions of nanocrystals are achieved that show remanence and coercivity at the size limit of superparamagnetism, and which are able to align their magnetic moments forming strings in solution as is demonstrated by cryo-electron tomography.

Control of magnetite nanocrystal morphology in magnetotactic bacteria by regulation of mms7 gene expression

“…By means of organic molecules, organisms produce finely tuned inorganic materials, even nanoscale structures 1 2 3 4 . The relevant bioprocesses, collectively called biomineralization, are especially attractive to materials scientists because these processes also may facilitate the development of technologies for production of a wide variety of inorganic materials under mild conditions and in aqueous environments 5 6 7 8 9 10 11 . In recent comprehensive molecular studies, proteins and the corresponding genes that are involved in biomineralization have been characterized in various biological systems 12 13 14 .…”

Bioinspired magnetite synthesis via solid precursor phases

“…7c and d ). 102 Time-resolved cryo-TEM indicated that this reaction gave well-crystallized 34 ± 11 nm particles, which for 65% had an octahedral morphology according to cryo-TEM and cryo-electron tomography (cryo-ET, 3D cryo-TEM). Also in this study the slow recrystallization kinetics from a solid precursor phase to magnetite allowed polymeric additives to tweak the properties of the obtained nanoparticles.…”

“…In most cases, the reaction is carried out at elevated temperatures (typically 90 °C), although it has been demonstrated that complete conversion to magnetite can also be achieved at ambient temperatures. 100 – 102 …”

Biomineralization of Magnetosomes: Billion-Year Evolution Shaping Modern Nanotools

“…This is an example of naturally occurring partial oxidation of ferrous ion. Partial oxidation is also used to obtain artificial, biomimetic magnetite [78]. In this case, the ferrous cation is precipitated to form ferrous hydroxide (Fe(OH) 2 ).…”

“…In this case, the ferrous cation is precipitated to form ferrous hydroxide (Fe(OH) 2 ). After that, a strong oxidizing agent, usually nitrate, partially transform Fe 2+ to Fe 3+ , leading to magnetite: While coprecipitation leads to nanoparticles of an irregular shape, partial oxidation magnetite has a well-defined faceted morphology and a larger size [78]. Due to its low solubility, Fe(OH) 2 tends to form larger precipitates.…”