Shape-tunable polymer nodules grown from liposomes via ring-opening metathesis polymerization

A new inisurf (acting as surfactant and initiator) molecule for ring-opening metathesis polymerization (ROMP) was synthesized and used in aqueous solution in order to control the size and shape of polymer nodules grown from liposomes. Nodules were observed to grow in size with conversion of monomer, and depending on the monomer used, they adopted either a spherical or comet-like shape. Here, we investigate polymer production from a liposome surface. We use a hydrophobic derivative of the Grubbs catalyst positioned at the liposome surface to allow for ROMP of monomers dissolved in the aqueous outer phase. We obtain nodules of polymer that can grow up to tens of micrometers, unveiling new efficient possibilities of polymerization from a membrane in an aqueous solution.     

Importance of REP values when comparing the CALUX bioassay results with chemoanalyses results Example with spiked vegetable oils

Differences between chemical activated luciferase gene expression (CALUX) bioassay and chemoanalyses results are observed.This paper shows that calculations of the TEQ values using REP values instead of WHO TEF values give different results. The REP values do affect the results obtained by the CALUX technique. These differences are more marked for the dioxin like PCB compounds (CALUX TEQ values are lower than WHO TEQ values) than for the dioxin compounds (CALUX TEQ values are higher than WHO TEQ values).The CALUX results were compared with the concentrations of the congeners’ spiked into the oil.     

Electroactive ligands: the first metal complexes of tetrathiafulvenyl-acetylacetonate

The reaction of tris(alkylthio)tetrathiafulvalene thiolates with 3-chloro-2,4-pentanedione affords tetrathiafulvalene (TTF) moieties substituted by the acetylacetone function (TTFSacacH), precursors of novel redox-active ligands: the acetylacetonate ions (TTFSacac). These TTFSacacHs have been characterized by X-ray diffraction analyses, and similar trends have been observed, such as a TTF core almost planar and the acetylacetone substituent located in a plane almost perpendicular to the plane formed by the TTF core. Their chelating ability has been demonstrated by the formation of the corresponding M(TTFSacac)2(pyridine)2 complexes in the presence of M(II)(OAc)2.H2O (M = Ni2+, Zn2+). These complexes with TTFSacac moieties, Ni(TTFSacac)2(pyridine)2, 6b, and Zn(TTFSacac)2(pyridine)2, 7b, have been characterized by X-ray diffraction analyses, showing in all structures the metal(II) center chelated by two TTFacac units in the equatorial plane and the octahedral coordination geometry around the metal completed by two axial pyridine ligands. Cyclic voltammetry and UV-visible-near infrared spectroscopic measurements have evidenced a sizable interaction between the two electroactive ligands and the stabilization of a mixed-valence state in the one-electron oxidized complexes.     

Quantum trajectories in atom-surface scattering with single adsorbates: the role of quantum vortices

In this work, a full quantum study of the scattering of He atoms off single CO molecules, adsorbed onto the Pt(111) surface, is presented within the formalism of quantum trajectories provided by Bohmian mechanics. By means of this theory, it is shown that the underlying dynamics is strongly dominated by the existence of a transient vortitial trapping with measurable effects on the whole diffraction pattern. This kind of trapping emphasizes the key role played by quantum vortices in this scattering. Moreover, an analysis of the surface rainbow effect caused by the local corrugation that the CO molecule induces on the surface, and its manifestation in the corresponding intensity pattern, is also presented and discussed.     

Structure and Dynamics of Methyl-substituted Beryllocene: [Be(C5Me5)2]

In this paper we study theoretically the molecular structure of [Be(C₅Me₅)₂], with special interest in similarities and differences found in the computed geometric parameters, depending on the treatment of the electron correlation used. Given the low energy differences found between the different configurations studied (less than 4 kcal mol⁻¹), and the high fluxionality found in experimental studies for this compound, we analyzed the dynamics of the system by means of first principles molecular dynamics calculations. A complex dynamics is found and analyzed in terms of two molecular rearrangement processes: 1,2-sigmatropic intraring rearrangement and a ring inversion mechanism that interchanges the roles (with regard to their coordination to the central Be atom) of the two rings.Dedicated to Dr. Jeal Paul Malrieu on occasion of his 65th birthday.     

Synthesis of (-)-Vulcanolide by enantioselective protonation

Two efficient enantioselective syntheses of the more active (S,S)-enantiomer of the powerful musk odorant Vulcanolide are described. In both syntheses, the key step is an enantioselective protonation of a ketone enolate. A third enantioselective protonation, of a thiol ester enolate, was applied for the determination of the absolute configuration of Vulcanolide by comparison with a known compound.     

Patterns in the precision of quantitative data from multicomponent gas chromatographic or gas chromatographic-mass spectrometric analysis

The dispersion of the quantitative results in the analysis of volatile compounds from multicomponent mixtures by different fractionation techniques (solid-phase microextraction and direct thermal desorption) followed by GC or GC-MS presents nonrandom patterns related to the existence of different factors in the fractionation process or in the chromatographic separation which affect, to a different extent, the recovery of the sample components. Statistical techniques have been used to show the relative importance of these factors. The improvement in data precision achieved by using volatile compound concentration ratios is discussed.     

Simultaneous determination of arsenic, antimony and selenium by gas-phase diode array molecular absorption spectrometry, after preconcentration in a cryogenic trap

This paper describes a method for the simultaneous determination of As(III), Sb(III) and Se(IV) by combining hydride generation and gas phase molecular absorption spectrometry. A system for continuous hydride generation has been designed and developed, based on the use of a double process of gas-liquid separation, and optimal compromise operation conditions for the three compounds have been found. After generation, the hydrides are collected in a liquid nitrogen cryogenic trap, and then evaporated and driven to the flow cell of a diode array spectrophotometer, in which the transient signals over the 190–250 nm wavelength interval are measured. Under the recommended conditions (sample flow: 35 ml min⁻¹, 0.5 M HCl; reductor flow: 4 ml min⁻¹ of 4% NaBH₄, solution) linear response ranges above 50 μg 1⁻¹ for As(III), 30 μg 1⁻¹ for Sb(III) and 200 μg 1⁻¹ for Se(IV) are obtained with detection limits of 22 μg 1⁻¹, 15 μg 1⁻¹ and 65 μg 1⁻¹, respectively. Multiwavelength linear regression equations were used for the simultaneous determination of the three elements in different synthetic samples, with good precision and accuracy and to study simultaneously the interference from different chemical species for the three compounds. Results were similar to those obtained by other techniques using hydride generation.     

Synthesis and conformational analysis by 1H NMR and restrained molecular dynamics simulations of the cyclic decapeptide [Ser-Tyr-Ser-Met-Glu-His-Phe-Arg-Trp-Gly]

Summary The design of enzyme mimics with therapeutic and industrial applications has interested both experimental and computational chemists for several decades. Recent advances in the computational methodology of restrained molecular dynamics, used in conjunction with data obtained from two-dimensional ¹H NMR spectroscopy, make it a promising method to study peptide and protein structure and function. Several issues, however, need to be addressed in order to assess the validity of this method for its explanatory and predictive value. Among the issues addressed in this study are: the accuracy and generizability of the GROMOS peptide molecular mechanics force field; the effect of inclusion of solvent on the simulations; and the effect of different types of restraining algorithms on the computational results. The decapeptide Ser-Tyr-Ser-Met-Glu-His-Phe-Arg-Trp-Gly, which corresponds to the sequence of ACTH_1–10, has been synthesized, cyclized, and studied by two-dimensional ¹H NMR spectroscopy. Restrained molecular dynamics (RMD) and time-averaged restrained molecular dynamics (TARMD) simulations were carried out on four different distance-geometry starting structures in order to determine and contrast the behavior of cyclic ACTH_1–10 in vacuum and in solution. For the RMD simulations, the structures did not fit the NOE data well, even at high values of the restraining potential. The TARMD simulation method, however, was able to give structures that fit the NOE data at high values of the restraining potential. In both cases, inclusion of explicit solvent molecules in the simulation had little effect on the quality of the fit, although it was found to dampen the motion of the cyclic peptide. For both simulation techniques, the number and size of the NOE violations increased as the restraining potential approached zero. This is due, presumably, to inadequacies in the force field. Additional TARMD vacuum-phase simulations, run with a larger memory length or with a larger sampling size (16 additional distance-geometry structures), yielded no significantly different results. The computed data were then analyzed to help explain the sparse NOE data and poor chymotryptic activity of the cyclic peptide. Cyclic ACTH_1–10, which contains the functional moieties of the catalytic triad of chymotrypsin, was evaluated as a potential mimic of chymotrypsin by measurement of the rate of hydrolysis of esters of L-and d-phenylalanine. The poor rate of hydrolysis is attributed to the flexibility of the decapeptide, the motion of the side chains, which result in the absence of long-range NOEs, the small size of the macrocycle relative to that of the substrate, and the inappropriate orientation of the Gly, His, and Ser residues. The results demonstrate the utility of this method in computer-aided molecular design of cyclic peptides and suggest structural modifications for future work based on a larger and more rigid peptide framework.