Oriented attachment explains cobalt ferrite nanoparticle growth in bioinspired syntheses

Abstract

SummaryOriented attachment has created a great debate about the description of crystal growth throughout the last decade. This aggregation-based model has successfully described biomineralization processes as well as forms of inorganic crystal growth, which could not be explained by classical crystal growth theory. Understanding the nanoparticle growth is essential since physical properties, such as the magnetic behavior, are highly dependent on the microstructure, morphology and composition of the inorganic crystals. In this work, the underlying nanoparticle growth of cobalt ferrite nanoparticles in a bioinspired synthesis was studied. Bioinspired syntheses have sparked great interest in recent years due to their ability to influence and alter inorganic crystal growth and therefore tailor properties of nanoparticles. In this synthesis, a short synthetic version of the protein MMS6, involved in nanoparticle formation within magnetotactic bacteria, was used to alter the growth of cobalt ferrite. We demonstrate that the bioinspired nanoparticle growth can be described by the oriented attachment model. The intermediate stages proposed in the theoretical model, including primary-building-block-like substructures as well as mesocrystal-like structures, were observed in HRTEM measurements. These structures display regions of substantial orientation and possess the same shape and size as the resulting discs. An increase in orientation with time was observed in electron diffraction measurements. The change of particle diameter with time agrees with the recently proposed kinetic model for oriented attachment.

Size control of in vitro synthesized magnetite crystals by the MamC protein of Magnetococcus marinus strain MC-1

“…These types of interactions occur because the distance between charged amino acids is similar to the distance between atoms in the crystalline structure. This mechanism has been invoked to explain the control over size and morphology of magnetite nanocrystals by the C-terminal region of Mms6 (Arakaki et al 2003;Prozorov et al 2007;Wolff et al 2012Wolff et al , 2014. Since the structure of MamC remains unknown, to determine whether the observed effect of MamC correlates only with its net negative charge at the pH of the biomineralization experiments, or it is somehow more specific, we used several reference proteins of comparable molecular weight but different values of pI, so they will have a different net charge compared to that of MamC at the pH of the experiments.…”

“…A majority of the published studies thus far involved the Mms6 protein, with the effort focused on in vivo analysis of Δmms6 mutants (Tanaka et al 2006) and in vitro experiments carried out with the full-length Mms6 and its C-terminal peptide (Arakaki et al 2003(Arakaki et al , 2010Amemiya et al 2007;Prozorov et al 2007;Wolff et al 2012Wolff et al , 2014. Results from these studies showed that Mms6 affects the size and morphology of magnetite crystals and that magnetites formed from solutions containing recombinant Mms6 protein were uniform well-defined crystals of~30 nm in size.…”

“…While Mms6 seems to have an unstructured N-terminus followed by one transmembrane helix and α-helix structured C-terminus, MamC has two helicoidal transmembrane domains connected by an α-helix structured loop. It is also noteworthy that, while the acidic residues in Mms6 concentrate in the hydrophilic Cterminal region, which is believed to be the active site for iron binding and biomineralization (Arakaki et al 2003;Amemiya et al 2007;Prozorov et al 2007;Wolff et al 2012Wolff et al , 2014, such acidic residues in MamC are present in both the C-terminus and in the loop connecting the two transmembrane domains. These differences between MamC and Mms6 in structure, distribution of residues, and size (12.4 kDa MamC and 6 kDa Mms6) contribute to the interest in studying the effect of MamC on magnetite biomineralization process.…”

Correlative Electron and Fluorescence Microscopy of Magnetotactic Bacteria in Liquid: Toward In Vivo Imaging

“…Materials characterization techniques are typically aimed at direct observations of the magnetite nucleation and growth at high spatial resolution. High resolution TEM is often used to observe formation of magnetosomes in magnetotactic bacteria via cryogenic TEM (cryo-TEM) 4,[22][23][24][25][26][27][28][29] . This technique provides vital information about organization of the cellular structures and development of the magnetosomes 20,27 .…”

TEM and Associated Techniques

“…The "freeze and look" approach proved a very effective tool for evaluation of the complex synthetic pathways, notably the biomimetic formation of the nanoscale magnetite [165][166][167][168][170][171][172][173][174][175][176]. Importantly, the mechanism of biomimetic iron oxide formation remains unclear, largely because the analysis of the formed biomimetic solid is carried out either postsynthesis [6,21,22,34,44,78,177] or is performed on aliquots sampled during different stages of the growth process [165,166,171,173,[178][179][180][181][182]. Such an approach reveals the overall effect of the templating molecule and permits facile characterization of a biomimetic iron oxide; however, it generally lacks information about the dynamics of the material's formation.…”