Surface modification of iron oxide nanoparticles by a phosphate‐based macromonomer and further encapsulation into submicrometer polystyrene particles by miniemulsion polymerization

A new strategy relying on the use of a phosphate‐based macromonomer (PAM200) to modify the surface of iron oxide nanoparticles was developed for the synthesis of submicrometer polystyrene (PS) magnetic particles. First, iron oxide nanoparticles were synthesized using the coprecipitation of ferrous and ferric salts in alkaline medium. Besides the classical oleic acid (OA)/octane‐based ferrofluid, styrene‐based ferrofluids were elaborated with either OA or PAM200 as the stabilizer. In all cases, maghemite (γ‐Fe₂O₃) was clearly identified, with nanoparticles rather spherical in shape but exhibiting broad particle size distribution (PSD). Both OA and PAM200 led to stable maghemite‐based ferrofluids showing superparamagnetic properties. Further use of these ferrofluids in styrene miniemulsion polymerization resulted in inhomogeneous distribution of maghemite among and inside the polymer particles with OA‐based ferrofluids, whereas PAM200/styrene‐based ferrofluids led to magnetic particles with homogeneous distribution of maghemite inside PS particles. Broad PSD and small nonmagnetic particles were however observed. The true mechanisms operating in these systems are still to elucidate, but this study validates PAM200 as an efficient compatibilizing agent between hydrophilic maghemite and hydrophobic PS. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 327–340, 2008     

Novel pyrrole C-nucleosides by nitrogen extrusion from pyridazine C-nucleosides

Pyridazine C-nucleosides have been synthesized by [4+2] cycloaddition of alkynyl C-nucleosides with substituted tetrazines. These pyridazines on extrusion of a nitrogen atom afforded novel pyrrole C-nucleosides with good yields. The results of electrochemical and chemical reduction are compared.     

Anomalous transition to turbulence in inert gases

It is found experimentally that the critical Reynolds numbers for the transition to turbulence are different for He, Ar, and Kr flows. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 7, 557–559 (10 October 1998)     

Synthesis and electronic properties of alternating alpha,alpha'-thiophene-phosphole oligomers

[structure: see text] Alternating thiophene-phosphole oligomers up to seven rings in length have been synthesized. A regular decrease of the HOMO-LUMO gap is observed upon increasing the length of the pi-conjugated system. The nature of the P-moieties dramatically influences the optical and electrochemical properties of these phosphole-based oligomers. Electro-oxidation of derivative 5a afforded an electroactive polymer exhibiting reversible p-doping.     

Synthetic applications of the nickel-catalyzed cyclization of alkynes combined with addition reactions in a domino process

Carbonickelations of alkynes and functionalization of the resulting vinylnickel moiety have been performed efficiently in a nickel-catalyzed domino cyclization-condensation process. This reaction, which does not require the preparation of any other organometallic reagent, proceeds only by exo-dig cyclization. This convenient and mild method constitutes a one-pot synthesis of substituted dihydrobenzofurans, chromans, isochromans, indoles, or indanes. Theses valuable products are generally obtained in good yields and high stereoselectivity. They are shown to be useful synthons for rapid access to functionalized polycyclic skeletons.     

A convenient synthesis of 5-arylamino-4H-pyran-4-ones using palladium-catalyzed amination

A concise approach to 5-arylamino-4H-pyran-4-ones is described via palladium-catalyzed amination reaction. The methodology involved in this Letter is based on protection/deprotection protocols and on manipulation of the 5-hydroxy group of readily available kojic acid. It would provide a new entry to a range of 5-arylamino-4H-pyran-4-ones via Buchwald-Hartwig-type amination reaction on 4H-pyran-4-one unit.     

Efficient New Synthesis of N‐Arylbenzo[b]furo[3,2‐d]pyrimidin‐4‐amines and Their Benzo[b]thieno[3,2‐d]pyrimidin‐4‐amine Analogues via a Microwave‐Assisted Dimroth Rearrangement

A useful and rapid access to libraries of N‐arylbenzo[b]furo[3,2‐d]pyrimidin‐4‐amines ( 1 ) and their novel benzo[b]thieno[3,2‐d]pyrimidin‐4‐amine analogues ( 2 ) was investigated for the first time. Title compounds were obtained via microwave‐accelerated condensation and Dimroth rearrangement of suitable anilines with N′‐(2‐cyanaryl)‐N,N‐dimethylformimidamides obtained by reaction of benzo[b]furane and benzo[b]thiophene precursors with N,N‐dimethylformamide dimethyl acetal. This work also demonstrates that well‐controlled parameters offer comfortable use of microwave technology and are both safe and beneficial to the environment. Some products obtained in this article exhibit interesting in vitro antiproliferative effects.     

Pyridyl‐Functionalised 3H‐1,2,3,4‐Triazaphospholes: Synthesis,Coordination Chemistry and Photophysical Properties of Low‐Coordinate Phosphorus Compounds

Novel conjugated, pyridyl‐functionalised triazaphospholes with either tBu or SiMe₃ substituents at the 5‐position of the N₃PC heterocycle have been prepared by a [3+2] cycloaddition reaction and compared with structurally related, triazole‐based systems. Photoexcitation of the 2‐pyridyl‐substituted triazaphosphole gives rise to a significant fluorescence emission with a quantum yield of up to 12 %. In contrast, the all‐nitrogen triazole analogue shows no emission at all. DFT calculations indicate that the 2‐pyridyl substituted systems have a more rigid and planar structure than their 3‐ and 4‐pyridyl isomers. Time‐dependent (TD) DFT calculations show that only the 2‐pyridyl‐substituted triazaphosphole exhibits similar planar geometry, with matching conformational arrangements in the lowest energy excited state and the ground state; this helps to explain the enhanced emission intensity. The chelating P,N‐hybrid ligand forms a Re^I complex of the type [(N^N)Re(CO)₃Br] through the coordination of nitrogen atom N² to the metal centre rather than through the phosphorus donor. Both structural and spectroscopic data indicate substantial π‐accepting character of the triazaphosphole, which is again in contrast to that of the all‐nitrogen‐containing triazoles. The synthesis and photophysical properties of a new class of phosphorus‐containing extended π systems are described.     

Shear-flow induced detachment of Saccharomyces cerevisiae from stainless steel: influence of yeast and solid surface properties

The present study focused on the shear-induced detachment of Saccharomyces cerevisiae in adhesive contact with a 316L stainless steel surface using a shear stress flow chamber, with a view to determining the respective influence of the yeast surface properties and the support characteristics. The effect of cultivation of S. cerevisiae yeast cells on their subsequent detachment from the solid surface was particularly investigated. In order to elucidate the role of stainless steel, non-metallic supports were used as control, covering a broad range of surface properties such as surface free energy and roughness: polypropylene (hydrophobic), polystyrene (mildly hydrophobic, similar to stainless steel) and glass (hydrophilic). All materials were very smooth with respect to the size of yeast. First, experiments were carried out on two types of yeast cells, just rehydrated in saline solution, a biological model widely used in the literature. The influence of the ionic strength (1.5 and 150 mM NaCl) on glass and stainless steel was evaluated. Unlike on glass, no clear evidence was found for electrostatic repulsion with stainless steel since high adhesion was observed whatever the ionic strength. A lack of correlation in adhesion results was also obtained when considering the surface physico-chemical characteristics of type I (hydrophilic) and type II (hydrophobic) rehydrated cells and those of both polymers. It was postulated that unavoidable “sticky” compounds were present on the cell wall, which could not be completely removed during the successive washings of the rehydrated cell suspension before use. This could dramatically alter the yeast surface properties and modify the adhesion strength, thus clearly demonstrating the necessity to work with yeast coming from fresh cultures. Biologically active yeast cells were then used. Once cultured, type I- and type II-yeast cells were shown to exhibit the same hydrophilic properties. Regardless of the material used, for the same ionic strength (150 mM NaCl), yeast adhesion was drastically reduced compared to rehydrated yeast cells. Among all the materials tested, the specificity of 316L stainless steel was clearly established. Indeed, for glass and polymers, cell adhesion was substratum-dependent and driven by the balance between the Lifshitz-van der Waals and Lewis acid/base interactions. Despite nearly identical surface free energies for polystyrene and stainless steel, the metallic surface promoted a totally distinct behaviour which was characterized by a strong – although highly variable – yeast adhesion.     

Tuning the Guest‐Binding Ability of a Helically Folded Capsule by In Situ Modification of the Aromatic Oligoamide Backbone

Starting from a previously described aromatic oligoamide helically folded capsule that binds tartaric acid with high affinity and diastereoselectivity, we demonstrate the feasibility of the direct in situ modification of the helix backbone, which results in a conformational change that reduces its affinity for guests by two orders of magnitude. Specifically, ring contraction of the central pyridazine unit into a pyrrole in the full helical sequence was investigated by using electrochemical and chemical processes. The sequence containing the pyrrole was synthesized independently in a convergent manner to ascertain its structure. The conformation of the pyrrolic folded capsule was elucidated in the solid state by X‐ray crystallography and in solution by using ¹H and ¹³C NMR spectroscopy. Solution studies revealed an unanticipated solvent‐dependent equilibrium between the anti–anti and syn–syn conformations of the pyrrole ring with respect to its two adjacent pyridine units. Titrations of the pyrrole‐containing sequence monitored by ¹H NMR spectroscopy confirmed the expected drop in affinity for tartaric acid and malic acid that arises from the conformation change in the backbone that follows the replacement of the pyridazine by a pyrrole. The reduction of the pyridazine to a pyrrole was characterized by cyclic voltammetry both on the entire sequence and on a shorter precursor. The lower cathodic potential of the precursor made its preparative‐scale electroreduction possible. Direct in situ modification of the pyridazine within the entire capsule sequence was achieved chemically by using zinc in acetic acid.