Sandra Mazerat

Magnetic Bistability of Individual Single-Molecule Magnets Grafted on Single-Wall Carbon Nanotubes†

A POM to remember: Hexanuclear Fe(III) polyoxometalate (POM) single-molecule magnets (see structure) can be noncovalently assembled on the surface of single-wall carbon nanotubes. Complementary characterization techniques (see TEM image and magnetic hysteresis loops) demonstrate the integrity and bistability of the individual molecules, which could be used to construct single-molecule memory devices.

Insights into the mechanism of the gas-phase purification of HiPco SWNTs through a comprehensive multi-technique study

While the purification of carbon nanotubes may be considered as an already sorted matter, their use in some highly demanding fields such as electrochemistry, biological studies or magnetism may be precluded by the remaining catalyst and carbonaceous impurities. For these purposes, the widely-used purification methods need to be improved. In this paper, a comprehensive study of the well-known gas-phase purification procedure of single wall nanotubes (SWNTs) is performed, which aims at depicting the nature and the amount of the remaining impurities, of both the catalyst and carbon types, and at getting insights into its mechanism. This has been achieved by cross-referencing data emerging from transmission electron microscopy (TEM), electron energy loss spectroscopy (EELS), electron diffraction, magnetization measurements, X-ray diffraction (XRD) and Raman spectroscopy. We demonstrate that this method can lead to the elimination of the largest part of the impurities while maintaining fairly good yields. According to the mechanistic picture we have drawn, we suggest some possible improvement to the procedure that should lead to fully purified SWNTs with limited subsequent losses.

Amyloid Assemblies of Influenza A Virus PB1-F2 Protein Damage Membrane and Induce Cytotoxicity

PB1-F2 is a small accessory protein encoded by an alternative open reading frame in PB1 segments of most influenza A virus. PB1-F2 is involved in virulence by inducing mitochondria-mediated immune cells apoptosis, increasing inflammation, and enhancing predisposition to secondary bacterial infections. Using biophysical approaches we characterized membrane disruptive activity of the full-length PB1-F2 (90 amino acids), its N-terminal domain (52 amino acids), expressed by currently circulating H1N1 viruses, and its C-terminal domain (38 amino acids). Both full-length and N-terminal domain of PB1-F2 are soluble at pH values ≤6, whereas the C-terminal fragment was found soluble only at pH ≤ 3. All three peptides are intrinsically disordered. At pH ≥ 7, the C-terminal part of PB1-F2 spontaneously switches to amyloid oligomers, whereas full-length and the N-terminal domain of PB1-F2 aggregate to amorphous structures. When incubated with anionic liposomes at pH 5, full-length and the C-terminal part of PB1-F2 assemble into amyloid structures and disrupt membrane at nanomolar concentrations. PB1-F2 and its C-terminal exhibit no significant antimicrobial activity. When added in the culture medium of mammalian cells, PB1-F2 amorphous aggregates show no cytotoxicity, whereas PB1-F2 pre-assembled into amyloid oligomers or fragmented nanoscaled fibrils was highly cytotoxic. Furthermore, the formation of PB1-F2 amyloid oligomers in infected cells was directly reflected by membrane disruption and cell death as observed in U937 and A549 cells. Altogether our results demonstrate that membrane-lytic activity of PB1-F2 is closely linked to supramolecular organization of the protein.

Towards bottom-up nanopatterning of Prussian blue analogues

Summary Ordered nanoperforated TiO2 monolayers fabricated through sol–gel chemistry were used to grow isolated particles of Prussian blue analogues (PBA). The elaboration of the TiO2/CoFe PBA nanocomposites involves five steps. The samples were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), infrared spectroscopy and X-ray photoelectron spectroscopy (XPS) all along the synthesis process. Selected physico-chemical parameters have been varied in order to determine the key steps of the synthesis process and to optimize it. This study is an important step towards the full control of the fabrication process.

Sequential growth of bistable copper-molybdenum coordination nanolayers on inorganic surfaces.

Sequential growth in solution is a powerful tool to control the growth of coordination networks on surfaces. We used this approach to prepare nanolayers of the bistable copper-molybdenum cyanide-bridged network. The nanolayers were grown on functionalized silicon and on bare platinum surfaces. The use of platinum dots organized on silicon oxide led to the growth of isolated and organized coordination objects. The bistable properties, characteristic of the bulk, have been evidenced for the nanolayers using infrared spectroscopy.

Surface initiated supplemental activator and reducing agent atom transfer radical polymerization (SI-SARA-ATRP) of 4-vinylpyridine on poly(ethylene terephthalate)

Poly(ethylene terephthalate) (PET) substrates were modified by means of surface-initiated supplemental activator and reducing agent atom transfer radical polymerization (SI-SARA-ATRP) of 4-vinylpyridine (4VP). Substrates were pretreated in order to graft chloromethylbenzene (CMB) units capable of initiating the radical polymerization reaction of 4VP units. Surface characterization techniques, including Water Contact Angle (WCA), Attenuated Total Reflection (ATR), X-ray photoelectron spectroscopy (XPS), Atomic Force Microscopy (AFM) and Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) showed a successful grafting of a stable, smooth and homogenous layer of p4VP. This process offers the advantages of a rapid, simplified and low cost strategy to chemically modify polymer substrates with covalently bonded layer of the pH responsive p4VP for different applications. Moreover, by using TOF-SIMS profiling, we were able to track a density gradient along the z-axis generated by the interpenetrating phases of the different layers of the final modified surface. Fact that we correlated to the various positions of initiation sites within the polyethylenimine (PEI) used for PET aminolysis prior to CMB grafting. Our strategy will be used in future work to graft other polymers for different applications where industrial scale viable options are needed.

Rapid and Label-Free Electrochemical DNA Biosensor for Detecting Hepatitis A Virus

Diagnostic systems that can deliver highly specific and sensitive detection of hepatitis A virus (HAV) in food and water are of particular interest in many fields including food safety, biosecurity and control of outbreaks. Our aim was the development of an electrochemical method based on DNA hybridization to detect HAV. A ssDNA probe specific for HAV (capture probe) was designed and tested on DNAs from various viral and bacterial samples using Nested-Reverse Transcription Polymerase Chain Reaction (nRT-PCR). To develop the electrochemical device, a disposable gold electrode was functionalized with the specific capture probe and tested on complementary ssDNA and on HAV cDNA. The DNA hybridization on the electrode was measured through the monitoring of the oxidative peak potential of the indicator tripropylamine by cyclic voltammetry. To prevent non-specific binding the gold surface was treated with 3% BSA before detection. High resolution atomic force microscopy (AFM) confirmed the efficiency of electrode functionalization and on-electrode hybridization. The proposed device showed a limit of detection of 0.65pM for the complementary ssDNA and 6.94fg/µL for viral cDNA. For a comparison, nRT-PCR quantified the target HAV cDNA with a limit of detection of 6.4fg/µL. The DNA-sensor developed can be adapted to a portable format to be adopted as an easy-to- use and low cost method for screening HAV in contaminated food and water. In addition, it can be useful for rapid control of HAV infections as it takes only a few minutes to provide the results.

The disentangling of hysteretic spin transition, polymorphism and metastability in bistable thin films formed by sublimation of bis(scorpionate) Fe(II) molecules

We investigate the size-dependent bistability of a FeII[HB(3,5-(Me)2Pz)3]2 spin-transition compound in the form of thin films, the thickness of which varies from 130 to 8500 nm. From combined structural, magnetic and optical measurements, we demonstrate that the materials prepared by sublimation consist of crystalline grains of the triclinic phase exhibiting the first-order spin transition coexisting with those of a new high-spin metastable tetragonal polymorph in quite a large proportion (ca. 42%). Accordingly, we show that the as-sublimed thin-film of 130 nm thickness retains a remarkable 17 K width hysteresis (T1/2 = 152 K) while the spin transition becomes quantitative by the thermal annealing of the metastable phase at 373 K. The structural analysis based on single-crystal X-ray diffraction measurements provides evidence for a thermal hysteresis resulting from successive crystallographic phase transitions that is consistent with the calorimetric data. This accounts for the asymmetric shape of the hysteresis and the variation of cooperativity observed in the magnetic and optical data whatever the material dimension is.

N-terminal domain of PB1-F2 protein of influenza A virus can fold into amyloid-like oligomers and damage cholesterol and cardiolipid containing membranes.

PB1-F2 protein is a factor of virulence of influenza A viruses which increases the mortality and morbidity associated with infection. Most seasonal H1N1 Influenza A viruses express nowadays a truncated version of PB1-F2. Here we show that truncation of PB1-F2 modified supramolecular organization of the protein in a membrane-mimicking environment. In addition, full-length PB1-F2(1-90) and C-terminal PB1-F2 domain (53-90), efficiently permeabilized various anionic liposomes while N-terminal domain PB1-F2(1-52) only lysed cholesterol and cardiolipin containing lipid bilayers. These findings suggest that the truncation of PB1-F2 may impact the pathogenicity of a given virus strain.

Small-angle neutron scattering study of the short-range organization of dispersed CsNi[Cr(CN)6] nanoparticles

Prussian blue analogues magnetic nanoparticles (of radius R0 = 2.4–8.6 nm) embedded in PVP (polyvinylpyrrolidone) or CTA+ (cetyltrimethylammonium) matrices have been studied using neutron diffraction and small angle neutron scattering (SANS) at several concentrations. For the most diluted particles in neutral PVP, the SANS signal is fully accounted for by a “single-particle” spherical form factor with no structural correlations between the nanoparticles and with radii comparable to those inferred from neutron diffraction. For higher concentration in PVP, structural correlations modify the SANS signal with the appearance of a structure factor peak, which is described using an effective “mean-field” model. A new length scale R* ≈ 3R0, corresponding to an effective repulsive interaction radius, is evidenced in PVP samples. In CTA+, electrostatic interactions play a crucial role and lead to a dense layer of CTA+ around the nanoparticles, which considerably alter the SANS patterns as compared to PVP. The SANS ...