Time-resolved refractive index and absorption mapping of light-plasma filaments in water

By means of a quantitative shadowgraphic method, we performed a space-time characterization of the refractive index variation and transient absorption induced by a light-plasma filament generated by a 120 fs laser pulse in water. The formation and evolution of the plasma channel in the proximity of the nonlinear focus were observed with a 23 fs time resolution.     

Molecular ion yield enhancement induced by gold deposition in static secondary ion mass spectrometry

Static ToF-SIMS was used to evaluate the effect of gold condensation as a sample treatment prior to analysis. The experiments were carried out with a model molecular layer (Triacontane M = 422.4 Da), upon atomic (In⁺) and polyatomic (Bi₃⁺) projectile bombardment. The results indicate that the effect of molecular ion yield improvement using gold metallization exists only under atomic projectile impact. While the quasi-molecular ion (M+Au)⁺ signal can become two orders of magnitude larger than that of the deprotonated molecular ion from the pristine sample under In⁺ bombardment, it barely reaches the initial intensity of (M−H)⁺ when Bi₃⁺ projectiles are used. The differences observed for mono- and polyatomic primary ion bombardment might be explained by differences in near-surface energy deposition, which influences the sputtering and ionization processes.     

On the road to high-resolution 3D molecular imaging

This contribution reviews the state-of-the-art in the domains of molecular imaging and depth profiling, the two methodological platforms required for 3D molecular imaging by secondary ion mass spectrometric (SIMS). Using molecular dynamics calculations, it also describes some of the mechanisms that make cluster projectiles such as C₆₀ so different for organic sample analysis. The discussion addresses issues that deserve proper attention on the way to 3D molecular imaging in SIMS, such as ultimate lateral resolution, limited molecular yields, chemical effects and damage, and highlights solutions currently in embryo in the many research teams concerned by 3D molecular imaging.     

NMR observation of Tau in Xenopus oocytes

The observation by NMR spectroscopy of microinjected 15N-labelled proteins into Xenopus laevis oocytes might open the way to link structural and cellular biology. We show here that embedding the oocytes into a 20% Ficoll solution maintains their structural integrity over extended periods of time, allowing for the detection of nearly physiological protein concentrations. We use these novel conditions to study the neuronal Tau protein inside the oocytes. Spectral reproducibility and careful comparison of the spectra of Tau before and after cell homogenization is presented. When injecting Tau protein into immature oocytes, we show that both its microtubule association and different phosphorylation events can be detected.     

In‐Situ Nanostructuring and Stabilization of Polycrystalline Copper by an Organic Salt Additive Promotes Electrocatalytic CO2 Reduction to Ethylene

Bridging homogeneous molecular systems with heterogeneous catalysts is a promising approach for the development of new electrodes, combining the advantages of both approaches. In the context of CO₂ electroreduction, molecular enhancement of planar copper electrodes has enabled promising advancement towards high Faradaic efficiencies for multicarbon products. Besides, nanostructured copper electrodes have also demonstrated enhanced performance at comparatively low overpotentials. Herein, we report a novel and convenient method for nanostructuring copper electrodes using N,N′‐ethylene‐phenanthrolinium dibromide as molecular additive. Selectivities up to 70 % for C_≥2 products are observed for more than 40 h without significant change in the surface morphology. Mechanistic studies reveal several roles for the organic additive, including: the formation of cube‐like nanostructures by corrosion of the copper surface, the stabilization of these nanostructures during electrocatalysis by formation of a protective organic layer, and the promotion of C_≥2 products.     

Experimental Requirements for an Efficient Control of Free‐Radical Polymerizations via the Reversible Addition‐Fragmentation Chain Transfer (RAFT) Process

Summary: Reversible addition‐fragmentation chain transfer (RAFT) polymerization is a recent and very versatile controlled radical polymerization technique that has enabled the synthesis of a wide range of macromolecules with well‐defined structures, compositions, and functionalities. The RAFT process is based on a reversible addition‐fragmentation reaction mediated by thiocarbonylthio compounds used as chain transfer agents (CTAs). A great variety of CTAs have been designed and synthesized so far with different kinds of substituents. In this review, all of the CTAs encountered in the literature from 1998 to date are reported and classified according to several criteria : i) the structure of their substituents, ii) the various monomers that they have been polymerized with, and iii) the type of polymerization that has been performed (solution, dispersed media, surface initiated, and copolymerization). Moreover, the influence of various parameters is discussed, especially the CTA structure relative to the monomer and the experimental conditions (temperature, pressure, initiation, CTA/initiator ratio, concentration), in order to optimise the kinetics and the efficiency of the molecular‐weight‐distribution control.

Schematic of the RAFT polymerization.     

Rate-equation theory of sub-Poissonian laser light

Lasers essentially consist of single-mode optical cavities containing two-level atoms with a supply of energy called the pump and a sink of energy, perhaps an optical detector. The latter converts the light energy into a sequence of electrical pulses corresponding to photo-detection events. It was predicted in 1984 on the basis of Quantum Optics and verified experimentally shortly thereafter that when the pump is non-fluctuating the emitted light does not fluctuate much. Precisely, this means that the variance of the number of photo-detection events observed over a sufficiently long period of time is much smaller than the average number of events. Light having that property is said to be'sub-Poissonian'. The theory presented rests on the concept introduced by Einstein around 1905, asserting that matter may exchange energy with a wave at angular frequency only by multiples of . The optical field energy may only vary by integral multiples of as a result of matter quantization and conservation of energy. A number of important results relating to isolated optical cavities containing two-level atoms are first established on the basis of the laws of Statistical Mechanics. Next, the laser system with a pump and an absorber of radiation is treated. The expression of the photo-current spectral density found in that manner coincides with the Quantum Optics result. The concepts employed in this paper are intuitive and the algebra is elementary. The paper supplements a previous tutorial paper (J. Arnaud, Opt. Quantum. Electron., 27 1995) in establishing a connection between the theory of laser noise and Statistical Mechanics.     

Synthesis of novel C2-aryl pyrrolobenzodiazepines (PBDs) as potential antitumour agents

Three novel C2-aryl substituted pyrrolobenzodiazepines (PBDs) have been synthesised and evaluated in a number of cell lines revealing selective cytotoxicity at the sub-nanomolar level towards melanoma and ovarian cancer cell lines.     

Radiation force on multilayer media

It is shown that the force exerted by plane electromagnetic waves on multilayer media can be evaluated in terms of the changes in momentum flow that take place at the planes of discontinuity. The expression obtained is relevant to radiation pressure experiments.