Oksana Kasyutich

Self-assembly and optically triggered disassembly of hierarchical dendron–virus complexes

Nature offers a vast array of biological building blocks that can be combined with synthetic materials to generate a variety of hierarchical architectures. Viruses are particularly interesting in this respect because of their structure and the possibility of them functioning as scaffolds for the preparation of new biohybrid materials. We report here that cowpea chlorotic mottle virus particles can be assembled into well-defined micrometre-sized objects and then reconverted into individual viruses by application of a short optical stimulus. Assembly is achieved using photosensitive dendrons that bind on the virus surface through multivalent interactions and then act as a molecular glue between the virus particles. Optical triggering induces the controlled decomposition and charge switching of dendrons, which results in the loss of multivalent interactions and the release of virus particles. We demonstrate that the method is not limited to the virus particles alone, but can also be applied to other functional protein cages such as magnetoferritin.

Silver Ion Incorporation and Nanoparticle Formation Inside the Cavity of Pyrococcus Furiosus Ferritin: Structural and Size-Distribution Analyses.

Highly symmetrical protein cage architectures from three different iron storage proteins, heavy and light human ferritin chains (HuHFt and HuLFt) and ferritin from the hyperthemophilic bacterium Pyrococcus furiosus (PfFt), have been used as models for understanding the molecular basis of silver ion deposition and metal core formation inside the protein cavity. Biomineralization using protein cavities is an important issue for the fabrication of biometamaterials under mild synthetic conditions. Silver nanoparticles (AgNPs) were produced with high yields within PfFt but not within HuHFt and HuLFt. To explain the molecular basis of silver incorporation, the X-ray crystal structure of Ag-containing PfFt has been solved. This is the first structure of a silver containing ferritin reported to date, and it revealed the presence of specific binding and nucleation sites of Ag(I) that are not conserved in other ferritin templates. The AgNP encapsulated by PfFt were further characterized by the combined use of different physical-chemical techniques. These showed that the AgNPs are endowed with a narrow size distribution (2.1 +/- 0.4 nm), high stability in water solution at millimolar concentration, and high thermal stability. These properties make the AgNP obtained within PftFt exploitable for a range of applications, in fields as diverse as catalysis in water, preparation of metamaterials, and in vivo diagnosis and antibacterial or tumor therapy.

Hierarchical self-assembly and optical disassembly for controlled switching of magnetoferritin nanoparticle magnetism

Protein cages such as ferritin and viral capsids are interesting building blocks for nanotechnology due to their monodisperse structure and ability to encapsulate various functional moieties. Here we show that recombinant ferritin protein cages encapsulating Fe(3)O(4)-γ-Fe(2)O(3) iron oxide (magnetoferritin) nanoparticles and photodegradable Newkome-type dendrons self-assemble into micrometer-sized complexes with a face-centered-cubic (fcc) superstructure and a lattice constant of 13.1 nm. The magnetic properties of the magnetoferritin particles are affected directly by the hierarchical organization. Magnetoferritin nanoparticles dispersed in water exhibit typical magnetism of single domain noninteracting nanoparticles; however, the same nanoparticles organized into fcc superstructures show clearly the effects of the altered magnetostatic (e.g., dipole-dipole) interactions by exhibiting, for example, different hysteresis of the field-dependent magnetization. The magnetoferritin-dendron assemblies can be efficiently disassembled by a short optical stimulus resulting in release of free magnetoferritin particles. After the triggered release the nanomagnetic properties of the pristine magnetoferritin nanoparticles are regained.

Bioengineered magnetic crystals

In this paper we report on the successful application of a protein crystallization technique to fabricate a three-dimensionally ordered array of magnetic nanoparticles, i.e. a novel type of metamaterial with unique magnetic properties. We utilize ferritin protein cages for the template-constrained growth of superparamagnetic nanoparticles of magnetite/maghemite Fe3O4-γ-Fe2O3 (magnetoferritin), followed by thorough nanoparticle bioprocessing and purification, and finally by protein crystallization. Protein crystallization is driven by the natural response of proteins to the supersaturation of the electrolyte, which leads to spontaneous nucleation and 3D crystal growth. Within a short period of time (hours to days) we were able to grow functional crystals on the meso-scale, with sizes of the order of tens, up to a few hundred micrometres. We present initial magnetic and Raman spectroscopy characterization results for the obtained 3D arrays of magnetic nanoparticles.

Co-Ni-Cu/Cu Multilayers Electrodeposited Using a Channel Flow Cell

Co-Ni-Cu/Cu multilayers were electrodeposited from a single electrolyte using a flow cell with substrate and counter electrode facing each other across a 3 mm wide channel. Substrates were 25 nm Au/3 nm Cr sputtered on glass, and the electrolyte was sulfamate based. The multilayers exhibited giant magnetoresistance (GMR) of up to ∼7%, but only for Cu layer thicknesses ≥3 nm. Potentiostatic deposition gave higher GMR values than galvanostatic deposition. Both varying the flow rate and varying the Cu content of the electrolyte influenced the GMR, which decreased with increasing Cu deposition current. While the flow cell gives much improved control over mass transport, cells relying on natural convection give higher GMR.

Synthesis of Iron Oxide Nanoparticles in Listeria innocua Dps (DNA‐Binding Protein from Starved Cells): A Study with the Wild‐Type Protein and a Catalytic Centre Mutant

A comparative analysis of the magnetic properties of iron oxide nanoparticles grown in the cavity of the DNA-binding protein from starved cells of the bacterium Listeria innocua, LiDps, and of its triple-mutant lacking the catalytic ferroxidase centre, LiDps-tm, is presented. TEM images and static and dynamic magnetic and electron magnetic resonance (EMR) measurements reveal that, under the applied preparation conditions, namely alkaline pH, high temperature (65 degrees C), exclusion of oxygen, and the presence of hydrogen peroxide, maghemite and/or magnetite nanoparticles with an average diameter of about 3 nm are mineralised inside the cavities of both LiDps and LiDps-tm. The magnetic nanoparticles (MNPs) thus formed show similar magnetic properties, with superparamagnetic behaviour above 4.5 K and a large magnetic anisotropy. Interestingly, in the EMR spectra an absorption at half-field is observed, which can be considered as a manifestation of the quantum behaviour of the MNPs. These results indicate that Dps proteins can be advantageously used for the production of nanomagnets at the interface between molecular clusters and traditional MNPs and that the presence of the ferroxidase centre, though increasing the efficiency of nanoparticle formation, does not affect the nature and fine structure of the MNPs. Importantly, the self-organisation of MNP-containing Dps on HRTEM grids suggests that Dps-enclosed MNPs can be deposited on surfaces in an ordered fashion.

Comparison of the Structure and Magnetotransport Properties of Co‐Ni‐Cu/Cu Multilayers Electrodeposited on n‐GaAs(001) and (111)

Co‐Ni‐Cu/Cu multilayers were electrodeposited directly onto n‐doped GaAs substrates with two different crystal orientations, (001) and (111), without the use of any seed layer. X‐ray diffraction and transmission electron microscopy showed that epitaxial growth occurred on GaAs(001), with either the {001} or {211} planes parallel to the substrate, but not on GaAs(111). On this substrate, the multilayers grow preferentially with the {111} planes parallel to the substrate, but the crystallites have no preferred orientation in‐plane. The presence of superlattice satellite peaks in the X‐ray data for the multilayers grown on GaAs(001) and their absence for those grown on GaAs(111) indicated that the latter had a less perfect layer structure. Multilayers grown on both substrates exhibited giant magnetoresistance (GMR). For small Cu layer thicknesses, , the GMR was suppressed for multilayers grown on both substrate orientations. For between ~20 and ~30 A, the GMR was much greater for the multilayers electrodeposited on GaAs(001) than for those on GaAs(111), while for larger layer thicknesses, the GMR for both substrate orientations was similar. This behavior can be explained qualitatively by the presence of different numbers of defects producing different degrees of ferromagnetic coupling in the two sets of multilayers.

Small angle x-ray and neutron scattering study of disordered and three dimensional–ordered magnetic protein arrays

The magnetic nanoparticles of Fe3O4-γ–Fe2O3 grown inside the cavity of globular proteins (apoferritin)-magnetoferritin proved to be a useful model system for studying the fundamental effects of magnetostatic interactions in nanoparticle assemblies. In this work the main focus is on structural characterization of such new nanocomposites by small angle x-ray scattering (SAXS) and small angle neutron scattering to evaluate interparticle separation (center to center) in two types of assemblies: three dimensional periodic arrays and disordered (amorphous) assemblies. Straightforward analysis of the face-centered cubic pattern of periodic arrays revealed that the interparticle spacing is 9.9 nm, whereas the SAXS pattern of disordered assembly reveals three correlation lengths, one of which is 10.5 nm and corresponds to the interparticle (center-to-center) nearest neighbor distance. The magnetic behaviors of the two systems are distinctly different. Given that the interparticle separation differs by only ∼0.6 nm...

The effect of dipolar interactions on the thermal relaxation of magnetoferritin

Magnetoferritin nanoparticles consist of ferrimagnetic magnetite?maghemite surrounded by a protein shell. Thermal relaxation data for both agglomerated and well-separated magnetoferritin show clear Tln(t/?0) scaling, thereby permitting a direct evaluation of the influence of magnetostatic interactions on the effective energy barrier distribution for magnetic reversal. For agglomerated magnetoferritin, the effect of the interactions is to broaden the distribution and shift its peak to lower energies, in contrast to the peak in the zero-field-cooled susceptibility, which moves to higher energies. Our result is in good agreement with earlier theoretical predictions (Iglesias and Labarta 2004 Phys.?Rev. B 70 144401).

A Study into Composite Laminators’ Motivation

Manufacture using advanced composite materials is a predominantly manual process. Despite recent advances in automation; the manufacture of complex panels such as those found in secondary aircraft structures, is usually carried out by highly skilled human operators. A requirement for increasing build rates of aircraft structures means that a formerly low production cycle technique must now be applied to much faster and larger production runs. This is further complicated by a desire to achieve higher quality at lower cost. Increased automation and laminator aids are being employed to achieve this goal. This paper presents an initial study into the current state of composite laminators’ motivation using Maslow’s Hierarchy of Needs. A series of semi-structured interviews were conducted with a variety of laminators from a range of industries. The principle aim is to generate a preliminary set of recommendations based on trends gained from this initial study, with a view to later widening the study to improve motivation and thus productivity and quality.