Selective internal manipulation of a single molecule by scanning tunneling microscopy

We have studied the adsorption of the polyaromatic molecule 1,4"-paratriphenyldimethylacetone, which we have nicknamed Trima. The originality of this linear molecule is that it was designed and synthesized to have two functionalities. First, chemisorb itself to the surface by its two ends rather like a bridge. Second, the central part of the molecule could then be rotated by injecting electrons with the tip of the scanning tunneling microscope (STM). The length of the molecule corresponds exactly to the spacing between five dimers in a row on the Si(100)-2 x 1 surface. We found that the molecule adsorbs as expected on the clean silicon surface by using complementary STM and synchrotron radiation studies. Manipulation of individual molecules with the STM tip showed selective internal modifications that were highly voltage dependent. These manipulations were found to be compatible with an electronic excitation of the pi-pi* transition of the molecule.     

Planar chromatographic separation of petroleum residues and coal-derived liquids

Vacuum distillation residues from two petroleum crudes, a coal liquefaction extract and a coal tar pitch have been fractionated by planar chromatography (PC) using two solvent sequences: pyridine–acetonitrile and tetrahydrofuran (THF)–toluene. Fractions recovered from PC were examined by UV-fluorescence spectroscopy (UV-F), size-exclusion chromatography (SEC). UV-F and SEC of the whole samples showed differences in aromatic cluster size and molecular mass (MM) ranges which could be related to the different origins of the samples. The MM ranges indicated by SEC were greater for the vacuum residues than for coal-derived materials. However, the UV-F spectra of the fractions indicated that the petroleum residue fractions contained similar aromatic types, whereas the fractions from coal liquids contained significantly different aromatic types. SEC profiles of the fractions indicated a separation of coal-derived samples by increasing molecular size with increasing immobility in PC, whereas for petroleum fractions, the same trend was not apparent. MALDI-mass spectra of the set of original samples showed broadly similar ranges of MM distributions but additional work is necessary to identify appropriate matrices and procedures in order to improve the MALDI spectra.     

A convergence result for a vibro-impact problem with a general inertia operator

Nonlinear Dynamics - We consider a mechanical system with a finite number of degrees of freedom and non-trivial inertia matrix, submitted to a single perfect unilateral constraint. We assume that...     

Is high‐resolution magic angle spinning NMR a practical speciation tool for cheese samples? Parmigiano Reggiano as a case study

High-resolution magic angle spinning (HRMAS) NMR is probably the most apt NMR method to analyze complex materials involving a solid phase, e.g. foodstuffs. We present here an HRMAS analysis of grated cheese (Parmigiano Reggiano). A full NMR characterization of this cheese allows the identification of the presence of fatty acids (saturated and unsaturated), amino acids and other small organic molecules. Since the presence and relative concentration of these molecules have previously been shown to correlate with organoleptic, origin and age characterization, HRMAS NMR of cheese is likely to provide a good complimentary tool for the analysis of this food material.     

Hydrogenolysis of hexane on supported rhodium catalysts

Hexane was reacted in mixtures with excess hydrogen on 5% Rh on different supports: Al₂O₃ and SiO₂, the latter catalyst in two states: after reduction at 603 K (LT) and after a prereduction at 1253 K (HT). The main reaction was hydrogenolysis. The catalysts were characterized with the fragment composition at different temperatures and hydrogen pressures. Two surface states could be distinguished: one with more hydrogen favored single rupture, the other with less hydrogen preferred multiple fragmentation. The transition between these states could be rather abrupt, as the surface hydrogen availability changed. The tendency to produce multiple fragments increased in the order Rh/Al₂O₃< Rh/SiO₂-LT < Rh/SiO₂-HT.     

A Tris(triazolate) Ligand for a Highly Active and Magnetically Recoverable Palladium Catalyst of Selective Alcohol Oxidation Using Air at Atmospheric Pressure

High efficiency and selectivity, easy magnetic recovery and recycling, and use of air as the oxidant at atmospheric pressure are major objectives for oxidation catalysis in terms of sustainable and green processes. A tris(triazolyl) ligand, so far only used in copper‐catalyzed alkyne azide cycloadditions, was found to be extremely efficient in SiO₂/γ‐Fe₂O₃‐immobilized palladium complexes. It was characterized by inductively coupled plasma (ICP) analysis, transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), energy‐dispersive X‐ray spectroscopy (EDX), and X‐ray photoelectron spectra (XPS) and found to fulfill the combined conditions for the selective oxidation of alcohols to aldehydes and ketones.     

Near-Surface Structure of Plasma Polymer Films Affects Surface Behavior in Water and its Interaction with Proteins

Using low pressure plasma polymerization, nano-scaled oxygen-rich plasma polymer films (CO) were deposited onto pristine silicon wafers as well as on nitrogen-containing plasma polymer (CN) model surfaces. We investigate the influence of the nature of the substrate as well as a potential sub-surface effect emerging from the buried CO/CN interface, just nanometers below the surface. X-ray Photoelectron Spectroscopy and Time-of-Flight Secondary Ion Mass Spectrometry revealed two important phenomena that occurred during the deposition of the terminal CO layer: (1) a strong degree of oxidation, already for 1 nm nominal thickness, and (2) a gradual transition in chemical composition between the two layers, clearly indicating that effectively a vertical chemical gradient results, even when a two-step coating process was applied. Such terminal gradient film structures were used to study film stability in aqueous environments. Molecular rearrangements were scrutinized in the top-surface in contact with water and we found that the top-surface chemistry and wetting properties of the oxygen-rich termination layer matched those of thick CO reference coatings. Nevertheless, the adsorption of green fluorescent protein (GFP) was observed to be sensitive to the CO terminal layer thickness. Namely, an enhanced protein adsorption was observed for 1–2 nm thick CO layers on CN, whereas a significantly reduced protein adsorption was seen on ≥?3 nm thick CO terminal layers. We conclude that both, surface and sub-surface conditions significantly affect protein adsorption as opposed to the traditional consideration of surface properties alone.     

Rational design of lanthanide binding peptides

Lanthanide-binding peptides are very attractive for the design of bioprobes. Indeed, they combine the amazing properties of lanthanide ions, such as their time-resolved luminescence (Eu, Tb) or electronic relaxation (Gd) to the characteristics of the peptide scaffold, such as large solubility in water and ability to recognize biological substrates. Peptides derived from natural amino acids are reviewed in a first section. Some of their lanthanide complexes have already demonstrated their efficiency in determining protein structures and functions. Then, we will show how insertion of chelating unnatural amino acids modulates peptide-lanthanide complexes properties, such as luminescence and stability.