Degradation of magnetite nanoparticles in biomimetic media

Magnetic nanoparticles (NPs) of magnetite Fe₃O₄ obtained by coprecipitation (COP), thermal decomposition (DT), and commercial sample (CM) have been degraded in similar conditions to physiological medium at pH 4.7 and in simulated body fluid (SBF) at pH 7.4. The formation of the nanoparticles was confirmed by FTIR spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). In view of medical and environmental applications, the stability of the particles was measured with dynamic light scattering. The degradation processes were followed with atomic absorption spectroscopy (EAA) and TEM. Magnetic measurements were carried out using vibrating sample magnetometry (VSM). Our results revealed that the structural and magnetic properties of the remaining nanoparticles after the degradation process were significantly different to those of the initial suspension. The degradation kinetics is affected by the pH, the coating, and the average particle size of the nanoparticles.     

Drift estimation for a periodic mean reversion process

In this paper we propose a periodic, mean-reverting Ornstein–Uhlenbeck process of the form

Light‐Controlled Conformational Switch of an Aromatic Oligoamide Foldamer

An aromatic oligoamide sequence composed of a light‐responsive diazaanthracene‐based aromatic β‐sheet flanked by two variable diameter helical segments was prepared. Structural investigations revealed that such oligomers adopt two distinct conformations: a canonical symmetrical conformation with the two helices stacked above and below the sheet, and an unanticipated unsymmetrical conformation in which one helix has flipped to directly stack with the first helix. Photoirradiation of the foldamer led to the quantitative, and thermally reversible, formation of a single photoproduct resulting from the [4+4] cycloaddition of two diazaanthracenes within the aromatic β‐sheet. NMR and crystallographic studies revealed a parallel arrangement of the diazaanthracene photoproduct and a complete conversion into a symmetrical conformation requiring a rearrangement of all unsymmetrical conformers. These results highlight the potential of foldamers, with structures more complex than isolated helices, for the design of photoswitches showing nontrivial nanometer scale shape changes.     

Expanding the carbo‐Benzene Chemical Space for Electron‐Accepting Ability: Trifluorotolyl/Tertiobutyl Substitution Balance

With the view to altering the lipophilicity and electron accepting ability of the tetraphenyl‐carbo‐benzene scaffold, peripheral fluorination of the C₁₈ ring through aromatic linkers was envisaged from the C₁₈Ph₆ and o‐^tBu₂C₁₈Ph₄ references, by replacement of two Ph substituents with two p‐CF₃‐C₆H₄ counterparts (^FTol). The synthesis relied on a [8+10] macrocyclization involving a common bis(trifluorotolyl)‐tetraynedione, followed by reductive aromatization of the resulting [6]pericyclynediols. While p‐^FTol₂C₁₈Ph₄ proved to be hardly tractable due to an extremely low solubility, p‐^FTol₂‐o‐^tBu₂C₁₈Ph₂ could be extensively studied by X‐ray crystallography, NMR and UV/Vis spectroscopy, voltammetry, STM imaging of monolayers, and AFM imaging of binary films with P3HT or PC₇₁BM fabricated by spin‐coating for organic photovoltaic cells and J?V curve measurement thereof. The electronic and polarity properties are correlated with moderate but consistent electron‐withdrawing effects of the CF₃ groups, in agreement with the DFT‐calculated frontier orbitals and multipole moments. The results provide guidelines for optimization of fluorinated carbo‐benzene targets.     

Measurement of the rate of nu(e) + d --> p + p + e(-) interactions produced by (8)B solar neutrinos at the Sudbury Neutrino Observatory

Solar neutrinos from (8)B decay have been detected at the Sudbury Neutrino Observatory via the charged current (CC) reaction on deuterium and the elastic scattering (ES) of electrons. The flux of nu(e)'s is measured by the CC reaction rate to be straight phi(CC)(nu(e)) = 1.75 +/- 0.07(stat)(+0.12)(-0.11)(syst) +/- 0.05(theor) x 10(6) cm(-2) s(-1). Comparison of straight phi(CC)(nu(e)) to the Super-Kamiokande Collaboration's precision value of the flux inferred from the ES reaction yields a 3.3 sigma difference, assuming the systematic uncertainties are normally distributed, providing evidence of an active non- nu(e) component in the solar flux. The total flux of active 8B neutrinos is determined to be 5.44+/-0.99 x 10(6) cm(-2) s(-1).     

Supramolecular Recognition: Protonmotive‐Driven Switches or Motors?

A dicationic molecular receptor bearing two cofacially disposed terpyridyl-Pd-Cl units forms stable 1:1 host-guest complexes with planar, neutral platinum(II) complexes. When the guest is modified to incorporate a pyridine group, the now basic guest is protonated by trifluoroacetic acid in acetonitrile solutions. The basic yellow guest forms a stable, deep red 1:1 host-guest complex with the yellow palladium receptor. Addition of trifluoroacetic acid to this host-guest complex leads to the displacement of the guest from the receptor. It is proposed that the dissociation of the guest is caused by electrostatic repulsion between the dicationic receptor and the positively charged protonated guest. Addition of base restores the host-guest complex. This protonmotive translocation of the guest from the host to the solution is discussed in terms of the mechanisms that drive molecular motors, the power stroke and the Brownian ratchet. It is concluded that the system is best described as a molecular switch that operates by the same mechanism as one stroke of a molecular motor     

Constraints on nucleon decay via invisible modes from the Sudbury Neutrino Observatory

Data from the Sudbury Neutrino Observatory have been used to constrain the lifetime for nucleon decay to "invisible" modes, such as n-->3nu. The analysis was based on a search for gamma rays from the deexcitation of the residual nucleus that would result from the disappearance of either a proton or neutron from 16O. A limit of tau(inv)>2 x 10(29) yr is obtained at 90% confidence for either neutron- or proton-decay modes. This is about an order of magnitude more stringent than previous constraints on invisible proton-decay modes and 400 times more stringent than similar neutron modes.