Identification of a source of size polydispersity and its solution in Brust-Schiffrin metal nanoparticle synthesis

The co-presence of thiol vs. disulfide in the well-known Brust-Schiffrin two-phase synthesis has been identified as a source of size polydispersity in nanoparticles synthesized and a procedure has been proposed to address this long outstanding issue.     

Controlled electrochemically-assisted deposition of sol-gel biocomposite on electrospun platinum nanofibers

The modification of platinum nanofibers by silica using the electrochemically-assisted deposition is reported here. Pt nanofibers are obtained by electrospinning and deposited on a glass substrate. The electrochemically-assisted deposition of the sol-gel material then gives the unique possibility to finely tune the silica film thickness around these nanofibers. It also allows the successful encapsulation of a biomolecule (glucose oxidase was chosen here as a model) while retaining its biological activity, as pointed out via the electrochemical monitoring of H(2)O(2) produced upon addition of glucose in the medium. This silica-glucose oxidase composite offers the possibility of comparing systematically the influence of the deposition time on the bioelectrode response and to compare it with the particular features of the deposits. It was found that the film first grew uniformly around the nanofibers and then started to deposit between them, covering the whole sample (fibers and glass substrate), and tended to fully embed the nanofibers for prolonged deposition. The thickness of the silica film is critical for the electroactivity of the biocomposite, the best response being obtained for a silica layer thickness in the range of the fiber diameter (～50 nm).     

Spontaneous electric fields in films of cis-methyl formate

A recent publication described a new group of spontaneously polarized materials in which electric fields in excess of 10(8) V m(-1) may be present. This phenomenon arises through dipole alignment in solid films formed by straightforward deposition from vapour and characterises a novel class of materials. Here we present further results for the properties of these materials, focusing on films of cis-methyl formate. These films are shown to display some notable new chemical physics. We find the novel result that the degree of dipole alignment and the corresponding electric field in films of cis-methyl formate can have a counter-intuitive temperature dependence, increasing six-fold between 80 K and 89 K, in sharp contrast to the pronounced and expected fall with deposition temperature seen both here between 50 K and 75 K and in numerous other species. A theoretical model demonstrates that the switch of gradient with rising temperature should be a general phenomenon and is associated with crossing of a singularity in the gradient occurring at a set of critical values of temperature and alignment.     

Estimates of a sum of Dirichlet series

We study the Dirichlet series with an arbitrary abscissa of absolute convergence. The lower and upper estimates for sums of these series are found. The above results allow us to establish some relations between the maximum modulus and the maximal term of Dirichlet series, especially to find conditions that ensure that the maximum modulus and the maximal term have the same many-term asymptotics.     

Parabolic contractions of semisimple Lie algebras and their invariants

Let $G$ be a connected semisimple algebraic group with Lie algebra $\mathfrak{g }$ and $P$ a parabolic subgroup of $G$ with $\mathrm{Lie\, }P=\mathfrak{p }$ . The parabolic contraction $\mathfrak{q }$ of $\mathfrak{g }$ is the semi-direct product of $\mathfrak{p }$ and a $\mathfrak{p }$ -module $\mathfrak{g }/\mathfrak{p }$ regarded as an abelian ideal. We are interested in the polynomial invariants of the adjoint and coadjoint representations of $\mathfrak{q }$ . In the adjoint case, the algebra of invariants is easily described and it turns out to be a graded polynomial algebra. The coadjoint case is more complicated. Here we found a connection between symmetric invariants of $\mathfrak{q }$ and symmetric invariants of centralisers $\mathfrak{g }_e\subset \mathfrak{g }$ , where $e\in \mathfrak{g }$ is a Richardson element with polarisation $\mathfrak{p }$ . Using this connection and results of Panyushev et al. (J Algebra 313:343–391, 2007), we prove that the algebra of symmetric invariants of $\mathfrak{q }$ is free for all parabolic subalgebras in types $\mathbf A$ and $\mathbf C$ and some parabolics in type $\mathbf B$ . This technique also applies to the minimal parabolic subalgebras in all types. For $\mathfrak{p }=\mathfrak{b }$ , a Borel subalgebra of $\mathfrak{g }$ , one gets a contraction of $\mathfrak{g }$ recently introduced by Feigin (Selecta Math 18:513–537, 2012) and studied from invariant-theoretic point of view in our previous paper (Panyushev and Yakimova in Ann Inst Fourier 62(6):2053–2068, 2012).     

Different mechanisms govern the two-phase Brust-Schiffrin dialkylditelluride syntheses of Ag and Au nanoparticles

Here we report the first unambiguous identification of the chemical structures of the precursor species involving metal (Au and Ag) ions and Te-containing ligands in the Brust-Schiffrin syntheses of the respective metal nanoparticles, through which the different reaction pathways involved are delineated.     

A FRET-Facilitated Photoswitching Using an Orange Fluorescent Protein with the Fast Photoconversion Kinetics

Fluorescent proteins photoswitchable with noncytotoxic light irradiation and spectrally distinct from multiple available photoconvertible green-to-red probes are in high demand. We have developed a monomeric fluorescent protein, called PSmOrange2, which is photoswitchable with blue light from an orange (ex./em. at 546 nm/561 nm) to a far-red (ex./em. at 619 nm/651 nm) form. Compared to another orange-to-far-red photoconvertable variant, PSmOrange2 has blue-shifted photoswitching action spectrum, 9-fold higher photoconversion contrast, and up to 10-fold faster photoswitching kinetics. This results in the 4-fold more PSmOrange2 molecules being photoconverted in mammalian cells. Compared to common orange fluorescent proteins, such as mOrange, the orange form of PSmOrange has substantially higher photostability allowing its use in multicolor imaging applications to track dynamics of multiple populations of intracellular objects. The PSmOrange2 photochemical properties allow its efficient photoswitching with common two-photon lasers and, moreover, via F?rster resonance energy transfer (FRET) from green fluorescent donors. We have termed the latter effect a FRET-facilitated photoswitching and demonstrated it using several sets of interacting proteins. The enhanced photoswitching properties of PSmOrange2 make it a superior photoconvertable protein tag for flow cytometry, conventional microscopy, and two-photon imaging of live cells.     

Thermodiffusion motion of electrically charged nanoparticles

The present work deals with experimental studies to examine the theoretical model of thermodiffusion of electrically charged nanoparticles. Three different ionic magnetic colloid samples have been synthesized and profoundly analyzed. The theoretical model is a classical one, based on the calculation of the temperature and the electric potential distribution around nanoparticles. The discrepancy between experimental data and theory turns out not to exceed 20%. We focus on applying different approximations between calculated electrical double layer in the theoretical model and experimental determination of the surface charge density of colloidal particles. We assume this is the main reason for obtained discrepancy.     

Parallel Microflow Photochemistry: Process Optimization, Scale-up, and Library Synthesis

A novel, multimicrocapillary flow reactor (MμCFR) was constructed and applied to a series of sensitized photoadditions involving 2(5H)-furanones. The reactor allowed for rapid and energy-, time-, and space-efficient sensitizer screening, process optimization, validation, scale-up, and library synthesis.