The adsorption and decomposition of carbon monoxide on Ni(100) and the oxidation of the surface carbide by oxygen

The interaction of carbon monoxide with Ni(100) has been studied by ellipsometry and Auger electron spectroscopy. Bombardment by electrons of a relatively high energy (2500 eV) leads to the disproportionation of the adsorbed CO (2 COad → Cad + CO2g ). The rate of oxidation of this surface carbide is , where hc is the carbon 272 eV Auger peak height, n=0.5 and the apparent activation energy Eact =13.3 kcal/mole. This relation is valid at 200–400°C and at oxygen pressures of 5 × 10−9−8 × 10−7 Torr

Sulfonation of Polyvinylidene fluoride: Investigation of the Microstructure by {¹H, ¹³C, ¹⁹F} NMR Spectroscopy and Mechanisms

The cycle between the preparation of sulfonated polyvinylidene fluoride (PVDF) membranes and the study of their properties allows several groups to make critical observations that lead to a hypothesis-driven process for sulfonation optimization. To facilitate this previously poorly understood process, we studied an example of PVDF sulfonation by chlorosulfonic acid (ClSO3H). We prepared sulfonated polyvinylidene fluoride (S-PVDF_X) samples with different sulfonation reaction times (X = 3, 5, and 16 h) and confirmed the sulfonation by means of Fourier transform infrared spectroscopy, differential scanning calorimetry, thermogravimetric analysis and NMR spectroscopy. The microstructure of the sulfonated sample S-PVDF_5 h was determined using a multinuclear {1H, 13C, 19F} NMR study. The results obtained allowed, for the first time, highlighting the dehydrofluorination of the PVDF chain in a super acidic medium and the formation of a sequence due to the esterification reaction between the alcoholic and acidic chain ends. In addition, we identified the two primary grafting sites of the sulfonic acid groups in the S-PVDF chain and demonstrated the importance of the head-to-head and tail-to-tail defects in the dehydrofluorination and sulfonation mechanisms

Structure of the Mixed Aggregates between a Chiral Lithium Amide and Phenyllithium or Vinyllithium

The structures, in THF, of 1:1 mixed aggregates of phenyllithium or vinyllithium with a chiral lithium amide derived from a 3-aminopyrrolidine are proposed on the basis of a multinuclear (¹H, ⁶Li, ¹³C) NMR spectroscopic and DFT theoretical studies. In both cases, the lithium amide adopts an azanorbornyl-like folding and establishes stable coordinations with the C sp² reactants, leading to rigid complexes that are expected to be at the origin of the inductions observed for the alcohols resulting from the condensation of these mixed aggregates on <i>ortho</i>-tolualdehyde

Enantioselective Alkynylation of Aldehydes by Mixed Aggregates of 3‑Aminopyrrolidine Lithium Amides and Lithium Acetylides

Lithium acetylides form, with 3-aminopyrrolidine lithium amides, noncovalent 1/1 mixed aggregates that have been characterized by 1D and 2D multinuclear NMR spectroscopy and DFT computations. The results show that the complex adopts a structure organized around a N–Li–C–Li core and that the acetylide appendage lies within the plane of this quadrilateral, midway between the two lithium cations. These complexes have been employed for the enantioselective alkynylation of a series of aromatic aldehydes and provided the expected propargylic alcohols in ee values up to 85% in THF at −78 °C

Organocatalyzed Multicomponent Synthesis of Isoxazolidin-5-ones

An unprecedented multicomponent organocatalyzed Knoevenagel–aza-Michael–cyclocondensation reaction between Meldrum’s acid, hydroxylamines, and aldehydes afforded a straightforward entry to a large array of racemic and <i>syn</i>-diastereoenriched isoxazolidinones as synthetically useful scaffolds. This process revealed a markedly facile aza-Michael–cyclocondensation sequence as a key domino reaction between RCO₂NHOH and transient alkylidene Meldrum’s acid upon Brønsted base catalysis

Alkyllithium Mixed Aggregates: Dynamic Behavior and Comprehensive Analysis of NMR ²<i>J</i>_{⁷Li–⁷Li} Spin–Spin Coupling

The measurement and assignment of scalar couplings in NMR spectra have, of course, been of interest to chemists for a long time because of the useful structural and dynamic information that can be provided. In the case of organolithium compounds, the magnitude of spin–spin coupling involving lithium strongly depends on the coupling partner, with fairly large values (>2 Hz) for ¹³C and ¹⁵N and small values (<1 Hz) for ¹H. However, the homonuclear scalar coupling between the ⁷Li nuclei interacting in mixed aggregates has never been measured experimentally. Several methods have been proposed to measure small scalar coupling constants in high-resolution NMR spectra, but all of them are not well suited for quadrupolar nuclei such as lithium 7. In this paper, we introduce a new tool to measure ⁷Li–⁷Li scalar couplings in unlabeled organolithium mixed aggregates based on 2D CT-COSY correlation spectroscopy. The obtained results on various alkyllithium mixed tetramers of <i>n</i>-BuLi/RLi (R = Me or <i>n</i>-BuO) show that in the absence of any exchange of the lithium nucleus a scalar coupling ²<i>J</i>_{⁷Li<i>–</i>⁷Li} = 0.586 Hz is expected between the ⁷Li nuclei, which decreases as the rate of lithium exchange increases. These experimental observations were theoretically rationalized by density functional theory calculations, with a particular emphasis on the elucidation of the physical nature of the involved interatomic interactions and on the accurate calculation of Li–Li coupling constants

Table_1_Characterization of Milkisin, a Novel Lipopeptide With Antimicrobial Properties Produced By Pseudomonas sp. UCMA 17988 Isolated From Bovine Raw Milk.docx

<p>Biosurfactants such as lipopeptides are amphiphilic compounds produced by microorganisms such as bacteria of the genera of Pseudomonas and Bacillus. Some of these molecules proved to have interesting antimicrobial, antiviral, insecticide, and/or tensioactive properties that are potentially useful for the agricultural, chemical, food, and pharmaceutical industries. Raw milk provides a physicochemical environment that is favorable to the multiplication of a broad spectrum of microorganisms. Among them, psychrotrophic bacterial species, especially members of the genus Pseudomonas, are predominant and colonize milk during cold storage and/or processing. We isolated the strain Pseudomonas sp. UCMA 17988 from raw cow milk, with antagonistic activity against Listeria monocytogenes, Staphylococcus aureus, and Salmonella enterica Newport. Antimicrobial molecules involved in the antagonistic activity of this strain were characterized. A mass spectrometry analysis highlighted the presence of four lipopeptides isoforms. The major isoform (1409 m/z), composed of 10 carbons in the lipidic chain, was named milkisin C. The three other isoforms detected at 1381, 1395, and 1423 m/z, that are concomitantly produced, were named milkisin A, B, and D, respectively. The structure of milkisin, as confirmed by nuclear magnetic resonance analyses, is closely related to amphisin family. Indeed, the peptidic chain was composed of 11 amino acids, 6 of which are conserved among the family. In conclusion, Pseudomonas sp. UCMA 17988 produces new members of the amphisin family which are responsible for the antagonistic activity of this strain.</p

Presentation_1_Characterization of Milkisin, a Novel Lipopeptide With Antimicrobial Properties Produced By Pseudomonas sp. UCMA 17988 Isolated From Bovine Raw Milk.pdf

<p>Biosurfactants such as lipopeptides are amphiphilic compounds produced by microorganisms such as bacteria of the genera of Pseudomonas and Bacillus. Some of these molecules proved to have interesting antimicrobial, antiviral, insecticide, and/or tensioactive properties that are potentially useful for the agricultural, chemical, food, and pharmaceutical industries. Raw milk provides a physicochemical environment that is favorable to the multiplication of a broad spectrum of microorganisms. Among them, psychrotrophic bacterial species, especially members of the genus Pseudomonas, are predominant and colonize milk during cold storage and/or processing. We isolated the strain Pseudomonas sp. UCMA 17988 from raw cow milk, with antagonistic activity against Listeria monocytogenes, Staphylococcus aureus, and Salmonella enterica Newport. Antimicrobial molecules involved in the antagonistic activity of this strain were characterized. A mass spectrometry analysis highlighted the presence of four lipopeptides isoforms. The major isoform (1409 m/z), composed of 10 carbons in the lipidic chain, was named milkisin C. The three other isoforms detected at 1381, 1395, and 1423 m/z, that are concomitantly produced, were named milkisin A, B, and D, respectively. The structure of milkisin, as confirmed by nuclear magnetic resonance analyses, is closely related to amphisin family. Indeed, the peptidic chain was composed of 11 amino acids, 6 of which are conserved among the family. In conclusion, Pseudomonas sp. UCMA 17988 produces new members of the amphisin family which are responsible for the antagonistic activity of this strain.</p

Conformation Control of Abiotic α‑Helical Foldamers

With the aim to find new protein–protein inhibitors, a three part methodology was applied to oligophenylpyridines. Theoretical ring twist angle predictions have been validated by X-ray diffraction and molecular dynamics simulations with NMR constraints. Careful choice of substituent and nitrogen positions in oligophenylpyridyl foldamer units opens the way to conformational control of the side chain distribution of this α-helix mimic

Stereoselective synthesis of functionalized vinyl ethers from allyl bromides activated by triethylamine

<p>An efficient coupling reaction of allyl bromides with various alcohols as nucleophiles activated by triethylamine, leading to functionalized vinyl ethers in good yields and with full stereoselectivity.</p