Ruthenium Olefin Metathesis Catalysts Featuring N-Heterocyclic Carbene Ligands Tagged with Isonicotinic and 4-(Dimethylamino)benzoic Acid Rests: Evaluation of a Modular Synthetic Strategy

A modular and flexible strategy towards the synthesis of N-heterocyclic carbene (NHC) ligands bearing Brønsted base tags has been proposed and then adopted in the preparation of two tagged NHC ligands bearing rests of isonicotinic and 4-(dimethylamino)benzoic acids. Such tagged NHC ligands represent an attractive starting point for the synthesis of olefin metathesis ruthenium catalysts tagged in non-dissociating ligands. The influence of the Brønsted basic tags on the activity of such obtained olefin metathesis catalysts has been studied.     

Antimicrobial Activity of Geranium Oil against Clinical Strains<em> </em>of <em>Staphylococcus aureus</em>

The aim of this work was to investigate the antibacterial properties of geranium oil obtained from Pelargonium graveolens Ait. (family Geraniaceae), against one standard S. aureus strain ATCC 433000 and seventy clinical S. aureus strains. The agar dilution method was used for assessment of bacterial growth inhibition at various concentrations of geranium oil. Susceptibility testing of the clinical strains to antibiotics was carried out using the disk-diffusion and E-test methods. The results of our experiment showed that the oil from P. graveolens has strong activity against all of the clinical S. aureus isolates-including multidrug resistant strains, MRSA strains and MLS_B-positive strains-exhibiting MIC values of 0.25-2.50 μL/mL.     

Temperature and Pressure Dependence Studies of the Motions of the +NH3 Radical Trapped in γ Irradiated Ammonium Perchlorate Single Crystal

The temperature and pressure dependences of the ⁺NH₃ coupling tensors have been investigated by ESR spectroscopy. The linear variation of the reduced correlation time of the “rotational diffusion” motion with reciprocal of the temperature is shown to be unrelated to the dilatation of the matrix. Comparison with ⁺ND₃ results gives the contribution to the nitrogen isotropic coupling constant of the out of plane vibration of the nitrogen atom.     

Cationic amino-containing N-isopropyl- acrylamide-styrene copolymer particles: 2-surface and colloidal characteristics

 In a previous paper [1], the synthesis of various polystyrene– poly[NIPAM] core–shell latexes bearing cationic amidino and/or amino charges has been described. Several colloidal properties of these cationic latexes have been charac-terized such as: particle size, surface charge density, electrophoretic mobility and finally colloidal stability. Due to the poly[NIPAM]-rich layer in the shell, it was found that temperature played a significant role on all these properties, a LCST around 33 °C being exhibited. In addition, ionic strength was also found to affect the colloidal behavior of these latexes, the largest effect being observed with latexes having both amidino and amino surface charges. The critical coagulation concentra-tions (CCC) of the various latexes above and below the LCST were determined, highlighting the contribution of electrostatic and steric repulsive forces to the stability of these particles. Received: 20 January 1998 Accepted: 8 June 1998     

Highly magnetic latexes from submicrometer oil in water ferrofluid emulsions

The synthesis of functionalized submicrometer magnetic latex particles is described as obtained from a preformed magnetic emulsion composed of organic ferrofluid droplets dispersed in water. Composite (polystyrene/γ‐Fe₂O₃) particles were prepared according to a two‐step procedure including the swelling of ferrofluid droplets with styrene and a crosslinking agent (divinyl benzene) followed by seeded emulsion polymerization with either an oil‐soluble [2,2′‐azobis(2‐isobutyronitrile)] or water‐soluble (potassium persulfate) initiator. Depending on the polymerization conditions, various particle morphologies were obtained, ranging from asymmetric structures, for which the polymer phase was separated from the inorganic magnetic phase, to regular core–shell morphologies showing a homogeneous encapsulation of the magnetic pigment by a crosslinked polymeric shell. The magnetic latexes were extensively characterized to determine their colloidal and magnetic properties. The desired core–shell structure was efficiently achieved with a given styrene/divinyl benzene ratio, potassium persulfate as the initiator, and an amphiphilic functional copolymer as the ferrofluid droplet stabilizer. Under these conditions, ferrofluid droplets were successfully turned into superparamagnetic polystyrene latex particles, about 200 nm in size, containing a large amount of iron oxide (60 wt %) and bearing carboxylic surface charges. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2642–2656, 2006     

Effect of thiol-containing monomer on the preparation of temperature-sensitive hydrogel microspheres

The main objective of this study is to prepare, thermally, sensitive microgel particles bearing thiol groups via precipitation polymerization of N-isopropylacrylamide (NIPAM), methylenebisacrylamide (MBA) and vinylbenzylisothiouronium chloride (VBIC) using 2-2′-azobis(2-amidinopropane)-dihydrochloride (V50) as initiator. The influence of various parameters has been investigated as a systematic study to point out the role of each reactant on polymerization conversion, and consequently, on particles and water-soluble polymer formation. The final microgel particles were characterized with respect to particle size and swelling ability. The aim of this paper is to complete our first short communication; Macromolecular symposia, 2000. 150: p. 283–290.     

Salt Effects in the Cononsolvency of Poly(N‐isopropylacrylamide) Microgels

Poly(N‐isopropylacrylamide) (PNIPAM) is well known to exhibit reentrant behavior or cononsolvency in response to the composition of a mixed solvent consisting of water and a low‐chain alcohol. Since the solvent structure plays an important role in this phenomenon, the presence of structure‐breaking/structure‐making ions in solution is expected to have a dramatic effect on the cononsolvency of PNIPAM. The present work examines the way that the presence of different salts can modify the reentrant‐phase diagram displayed by a cationic PNIPAM microgel in the mixed ethanol/water solvent. The effects of four Hofmeister anions—SO₄^2?_, Cl^?, NO₃^? and SCN^?—with different abilities to modify the solvent structure are analyzed. The species with kosmotropic or structure‐making character show a clear competition with ethanol for the water molecules, intensifying the nonsolvency of the PNIPAM with the EtOH volume fraction (?_e). However, striking results are found with the most chaotropic or structure‐breaking anion, SCN^?. In contrast to what happens in water‐rich solutions, the presence of SCN^? in alcohol‐rich solvents enhances the solubility of the polymer, which macroscopically results in the microgel swelling. Moreover, this ion displays great stabilizing properties when ?_e> is 0.2. These results have been explained by considering how chaotropic or structure‐breaking ions interact with water and ethanol molecules.     

A fluorescent derivatization method of proteins for the detection of low‐level impurities by microchip capillary gel electrophoresis

A novel pre‐chip fluorescent derivatization method is presented for protein sizing and quantification by microchip CGE. The derivatization reaction employed a water‐soluble and stable fluorescent dye and was performed under conditions that favored the formation of homogeneous reaction products. The method delivered in terms of protein sizing similar results as microchip CGE with on‐chip staining but showed an extended linear dynamic range for protein quantification encompassing four orders of magnitude. The sensitivity of the method was similar to standard silver‐stained planar gels. The characterization of derivatization reaction products by MS and preparative isoelectric focusing indicated that a constant degree of dye molecule tagging was obtained over a broad range of protein/dye ratios. The method allowed detecting and quantifying an impurity spiked into an antibody preparation down to a level of 0.05%. Advantages of this method compared with CGE approaches with pre‐column derivatization include a shorter analysis time and an increased robustness and ease of use.     

Head-to-Tail Dimerization of N-Heterocyclic Diazoolefins

The head-to-tail dimerization of N-heterocyclic diazoolefins is described. The products of these formal (3+3) cycloaddition reactions are strongly reducing quinoidal tetrazines. Oxidation of the tetrazines occurs in a stepwise fashion, and we were able to isolate a stable radical cation and diamagnetic dications. The latter are also accessible by oxidative dimerization of diazoolefins.     

Composition and structure of iron oxidation surface layers produced in weak acidic solutions

Although oxidation/passivation of iron in basic solution has been extensively investigated, there is very little information on iron corrosion in weak acidic solutions. In this work, iron surface composition and structure, produced in aerobic aqueous solutions ranging from pH 2 to 5, were determined in detail by the use of infrared external reflection spectroscopy, X-ray photoelectron spectroscopy and scanning electron microscopy. The most striking observation is that at pH 2 and 3 almost all oxidized iron is dissolved in solution, whereas at pH 4 and 5 the product of iron oxidation is deposited on the iron surface in the form of lepidocrocite, gamma-FeOOH. Detailed iron surface and solution analyses allow the proposition of the following overall oxidation reactions: [EQUATION: SEE TEXT]. At pH 2 and 3, only a very thin surface layer consisting of FeO and Fe(OH)2 with polymeric structure is observed on the iron surface. The amounts of these surface species remain almost constant (2-5 nm) from the first minutes to a few hours of reaction, if pH is kept constant. Nevertheless, with time the akaganeite-like, beta-FeOOH structure is also detected. At pH 4 and 5, the amount of lepidocrocite deposited on the iron surface increases with reaction time. Detailed quantitative evaluation of the lepidocrocite produced at pH 5 and its surface distribution on iron was performed based on the comparison of infrared spectroscopic data with spectral simulation results of assumed surface structures. At pH 4 and 5 and a temperature of 40-50 degrees C, in addition to a very large amount of lepidocrocite other oxy-hydroxide surface species such as goethite (alpha-FeOOH) and feroxyhite (delta-FeOOH), were identified. Addition of Cl- ions to solution at 10(-3) M concentration at pH 5 increases the oxidation rate of iron by about 50%, and lepidocrocite remains the only oxidation product. Similarly, an addition of Fe2+ ions to solution at pH 5 very strongly enhances lepidocrocite formation as well as its conductivity. The latter finding is important for the possible application of metallic iron as a catalyst in redox reactions, for example, for decomposition of difficult-to-biodegrade water pollutants.