Homogeneous N doping of thick polyacetylene films by chemical way

The kinetics of reduction (n doping) of fibrillar films of polyacetylene (PA) by a large excess of organoalkaline electron donors in solution was studied. The doping rate is proportional to dopant concentration and inversely proportional to the square of film thickness (in a range 100–1000 microns). This means that the kinetics of reduction is entirely controlled, in these experiments, by the interfibrillar diffusion of dopants, leading to macroscopic doping inhomogeneity if the reaction is stopped before completion. The maximum doping level achieved at the end of the reaction is mainly controlled by the redox potential of the dopant. Homogeneously doped thick films, at various doping levels, were prepared using a suitable set of dopants in various solvents.     

Synthesis of di‐ and tetra‐adducts by addition of polystyrene macroradicals onto fullerene C60

Br‐terminated polystyrenes of controlled molar masses and low polydispersities prepared by atom transfer radical polymerization (ATRP) can be converted to macroradicals using an appropriate catalytic complex (CuBr/bipyridine/100 °C). The addition of this macroradicals PS° to 6–6 bonds of C₆₀ follows a specific atom transfer radical addition mechanism that favors the grafting of even number of chains onto the fullerene core. This peculiar mechanism, resulting from the properties of C₆₀, offers an easy synthetic route toward well‐defined di‐ and tetra‐adducts. In these adducts the disturbance of the electronic structure of the fullerene is kept at its minimum, as only one double bond needs to be opened on the C₆₀ to add two PS chains and only two double bonds are converted to single bonds in the tetra‐adduct. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3456–3463, 2004     

In situ synchrotron far infrared micro-spectroelectrochemistry with a grazing angle objective

We demonstrate the use of a grazing angle objective attachment to carry out in situ far infrared micro-spectroelectrochemistry at a copper electrode on a nano-scale. A thin-layer spectrochemical cell made out of Teflon was used, fitted with a 20-μm thick Mylar window; the working electrode was 500 μm in diameter. Measurements were carried out in 0.1 M NaOH solution as a function of applied potential between –1.4 and 0 V vs a Hg/Hg₂SO₄ reference electrode. Spectra were obtained with excellent signal to noise ratio for the surface oxide film, formed on copper electrochemically with less than 1 nL of active solution volume. The surface film at 0 V was about 130 nm thick and consisted mainly of CuO, with possibly some Cu(OH)₂ also present. This interpretation is consistent with previous works and thermodynamic calculations. The technique should be useful in other investigations and the further development of electrochemical surface science.     

Hétérocycles contenant du phosphore: XXVII—Etude par Résonance Magnétique Nucléaire de quelques dérivés des dioxa-et dithiaphospholanes-1,3,2 monosubstitués en 4

The ¹H n.m.r. spectra of some derivatives of 4-methyl (or 4-phenyl) 1,3,2-dioxa- and 1,3,2-dithiaphospholanes are analysed. The configurational study of the compounds has been investigated. The torsional angle of the C₄? C₅ fragment is calculated and the ring conformation in solution is discussed.     

Homogeneous Phosphodiesterase and Hybridization Assays Using Europium Cryptate: Oligonucleotide Conjugates

Upon conjugation to single-stranded oligonucleotides, a europium cryptate (Eu³⁺ tris-bipyridine) showed a marked increase in its fluorescence lifetime and was much less sensitive to fluorescence quenching by uric acid. This behavior was shown to be moderately dependent on the length and sequence of the oligonucleotide and all the single-stranded oligonucleotides studied displayed similar behavior. In contrast, a cryptate moiety attached to a double-stranded oligonucleotide did not display such an increase in its fluorescence lifetime and was quenched in presence of uric acid. Taking advantage of this unique behavior characterizing single-stranded K-ODN conjugates, a new concept of dosage based on the modulation of the cryptate fluorescence by a quencher was set up. This fluorescence quenching assay involving a single fluorescent label was applied to the monitoring of hybridization reactions and detection of a phosphodiesterase activity.     

Josephson plasma resonance and phonon anomalies in trilayer Bi2Sr2Ca2Cu3O10

The far-infrared (FIR) c axis conductivity of a Bi2223 crystal has been measured by ellipsometry. Below T(c) a strong absorption band develops near 500 cm(-1), corresponding to a transverse Josephson plasmon. The related increase in FIR spectral weight leads to a giant violation of the Ferrell-Glover-Tinkham sum rule. The gain in c axis kinetic energy accounts for a sizable part of the condensation energy. We also observe phonon anomalies which suggest that the Josephson currents lead to a drastic variation of the local electric field within the block of closely spaced CuO2 planes.     

A new kind of CNOT-gate implementation for information processing with trapped ions

A sequence of laser pulses is presented to implement a new kind of CNOT-gate in an linear arrangement of trapped ions. This type of quantum gate enables the designer of quantum algorithms to “send information into the phonon bus” controlled by the information stored in one of the ions. Some simulation results are given to show the dynamics of the system during the gate implementation. The simulation gives information about the leakage and the gate accuracy. Received: 11 July 2000 / Revised version: 20 October 2000 / Published online: 6 December 2000     

Cyclopropenylmethyl Cation: A Concealed Intermediate in Gold(I)‐Catalyzed Reactions

The last years have witnessed many gold‐catalyzed reactions of alkynes. One of the most prominent species in the reaction of two alkyne units is the vinyl‐substituted gold vinylidene intermediate. Here, we were able to show that the reaction of a haloacetylene and an alkyne proceeds via a hitherto overlooked intermediate, namely the cyclopropenylmethyl cation. The existence and relative stability of this concealed intermediate is verified by quantum chemical calculations and ¹³C‐labeling experiments. A comparison between the cyclopropenylmethyl cation and the well‐known vinylidene intermediate reveals that the latter is more stable only for smaller cycles. However, this stability reverses in larger cycles. In the case of the smallest representative of both species, the vinylidene cation is the transition state en route to the cyclopropenylmethyl cation. The discovery of this intermediate should help to get a deeper understanding for gold‐catalyzed carbon–carbon bond‐forming reactions of alkynes. Furthermore, since enynes can be formed from the cyclopropenylmethyl cation, the inclusion of this intermediate should enable the development of new synthetic methods for the construction of larger cyclic halogenated and non‐halogenated conjugated enyne systems.     

Modeling binary alloy solidification by a random projection method

This paper addresses the numerical modeling of the solidification of a binary alloy that obeys a liquidus–solidus phase diagram. In order to capture the moving melting front, we introduce a Lagrange projection scheme based on a random sampling projection. Using a finite volume formulation, we define accurate numerical fluxes for the temperature and concentration fields which guarantee the sharp treatment of the boundary conditions at the moving front, especially the jump of the concentration according to the liquidus–solidus diagram. We provide some numerical illustrations which assess the good behavior of the method: maximum principle, stability under CFL condition, numerical convergence toward self‐similar solutions, ability to handle two melting fronts.