Actively mode-locked fiber laser using a deformable micromirror

We present what we believe to be the first fiber laser system that is actively mode-locked by a deformable micromirror. The micromirror device is placed within the laser cavity and performs a dual function of modulator and end-cavity mirror. The mode-locked laser provides ~1-ns-long pulses with 20 nJ/pulse energy at 5 MHz repetition rates.     

Direct Superacid-Promoted Difluoroethylation of Aromatics

Under superacid conditions, aromatic amines are directly and regioselectively 1,1-difluoroethylated. Low temperature in situ NMR studies confirmed the presence of benzylic α-fluoronium and α-chloronium ions as key intermediates in the reaction. This method has a wide substrate scope and can be applied to the late-stage functionalization of natural alkaloids and active pharmaceutical ingredients.     

Complementary Site-Selective Halogenation of Nitrogen-Containing (Hetero)Aromatics with Superacids

Site-selective functionalization of arenes that is complementary to classical aromatic substitution reactions remains a long-standing quest in organic synthesis. Exploiting the generation of halenium ion through oxidative process and the protonation of the nitrogen containing function in HF/SbF₅, the chlorination and iodination of classically inert Csp²−H bonds of aromatic amines occurs. Furthermore, the superacid-promoted (poly)protonation of the molecules acts as a protection, favoring the late-stage selective halogenation of natural alkaloids and active pharmaceutical ingredients     

Composition of lignocellulosic surfaces: comments on the interpretation of XPS spectra

The surface compositions of lignocellulosic materials are critical to their end use performance. X-ray photoelectron spectroscopy (XPS) measures the elemental composition sampling of a very thin surface layer, and has long been used to assess the surface composition of dry lignocellulosic materials. The method is based on the quantification of carbon and oxygen XPS peak sizes and shapes, but care is necessary to minimize the effects of surface contamination and degradation. We review the XPS method, and present a simplified approach to estimate the surface lignin content of extractive-free samples. The approach corrects for surface contamination and degradation by measuring the XPS signal of a cellulose standard under the same conditions as the lignin-containing samples. The method is illustrated using XPS results for a series of extracted softwood kraft pulps.     

Melting curve and fluid equation of state of carbon dioxide at high pressure and high temperature

The melting curve and fluid equation of state of carbon dioxide have been determined under high pressure in a resistively heated diamond anvil cell. The melting line was determined from room temperature up to 11.1+/-0.1 GPa and 800+/-5 K by visual observation of the solid-fluid equilibrium and in situ measurements of pressure and temperature. Raman spectroscopy was used to identify the solid phase in equilibrium with the melt, showing that solid I is the stable phase along the melting curve in the probed range. Interferometric and Brillouin scattering experiments were conducted to determine the refractive index and sound velocity of the fluid phase. A dispersion of the sound velocity between ultrasonic and Brillouin frequencies is evidenced and could be reproduced by postulating the presence of a thermal relaxation process. The Brillouin sound velocities were then transformed to thermodynamic values in order to calculate the equation of state of fluid CO2. An analytic formulation of the density with respect to pressure and temperature is proposed, suitable in the P-T range of 0.1-8 GPa and 300-700 K and accurate within 2%. Our results show that the fluid above 500 K is less compressible than predicted from various phenomenological models.     

Probing the structure and dynamics of end-grafted flexible polymer chain layers by combined atomic force-electrochemical microscopy. Cyclic voltammetry within nanometer-thick macromolecular poly(ethylene glycol) layers

The combined atomic force-electrochemical microscopy (AFM-SECM) technique was used in aqueous solution to determine both the static and dynamical properties of nanometer-thick monolayers of poly(ethylene glycol) (PEG) chains end-grafted to a gold substrate surface. Approach of a microelectrode tip from a redox end-labeled PEG layer triggered a tip-to-substrate cycling motion of the chains' free ends as a result of the redox heads' oxidation at the tip and re-reduction at the substrate surface. As few as approximately 200 chains at a time could be addressed in such a way. Quantitative analysis of the data, in the light of a simple model of elastic bounded diffusion SECM positive feedback, gave access to the end-tethered polymer layer thickness and the end-to-end diffusion coefficient of the chains. The thickness of the grafted PEG layer was shown to increase with the chain surface coverage, while the end-to-end diffusion coefficient was found to be constant and close to the one predicted by Rouse dynamics. At close tip-substrate separation, slowing of the chains' motion, as a consequence of their vertical confinement within the tip-substrate gap, was observed and quantitatively modeled.     

Mitochondrial activities in human cultured skin fibroblasts contaminated by <Emphasis Type="Italic">Mycoplasma hyorhinis</Emphasis>

Background  

Mycoplasma contaminations are a recurrent problem in the use of cultured cells, including human cells, especially as it has been shown to impede cell cycle, triggering cell death under various conditions. More specific consequences on cell metabolism are poorly known.     

3'-Ferrocene-labeled oligonucleotide chains end-tethered to gold electrode surfaces: novel model systems for exploring flexibility of short DNA using cyclic voltammetry

The flexibility of DNA is of central importance in biology, medicine, materials science, and mechanical engineering. In this study, we report an unprecedented electrochemical approach for investigating the flexibility of a short (typically 20-base), surface end-tethered single-stranded synthetic DNA oligonucleotide and of its postformed DNA duplex, taking as an example the homopolymer (dT)20 sequence in the regime of very high ionic strength ( approximately 1 M).