Polyelectrolyte complexes of poly(methacryloxyethyl trimethylammonium chloride) and poly(ethylene oxide)-block-poly(sodium methacrylate) studied by asymmetrical flow field-flow fractionation and dynamic light scattering

Polyelectrolyte complex (PEC) formation between cationic poly(methacryloxyethyl trimethylammonium chloride) (PMOTAC) and anionic poly(ethylene oxide)-block-poly(sodium methacrylate) (PEO-b-PMANa) was studied by asymmetrical flow field-flow fractionation and dynamic light scattering. The influence of ionic strength and mixing ratios of the charged units of the polyelectrolytes on the complex formation was evaluated. The diffusion coefficients and the hydrodynamic diameter distributions of the free and complexed polyelectrolytes were measured. In the absence of salt, the weight averaged hydrodynamic diameters were 48 and 28 nm for PMOTAC and PEO-b-PMANa, respectively. In the presence of salt, the particles were smaller, with weight averaged hydrodynamic diameters of 44-45 and 8-10 nm, respectively. In salt-free solution, at 1:1 mixing ratio of the charged monomer units of PMOTAC and PEO-b-PMANa, polydisperse particles with diameters of 2000-4000 nm were formed. In the presence of 20, 80, and 160 mM of sodium chloride, the 1:1 complexes were relatively monodisperse particles with weight averaged hydrodynamic diameters of 93, 124, and 120 nm, respectively.     

Dérivés de l'hydroxyméthyl-5 furfural. I. Synthése de dérivés du di- et terfuranne

Addition of α, β-unsaturated sulfones or ketones to 5-hydroxmethyl-furaldehyde or related furanaldehydes in the presence of a thiazolium salt gives di or tetraketonic furan compounds. Dehydrative cyclizationled to di- and terfuryl derivatives.     

FiD: a software for ab initio structural identification of product ions from tandem mass spectrometric data

We present FiD (Fragment iDentificator), a software tool for the structural identification of product ions produced with tandem mass spectrometric measurement of low molecular weight organic compounds. Tandem mass spectrometry (MS/MS) has proven to be an indispensable tool in modern, cell-wide metabolomics and fluxomics studies. In such studies, the structural information of the MS(n) product ions is usually needed in the downstream analysis of the measurement data. The manual identification of the structures of MS(n) product ions is, however, a nontrivial task requiring expertise, and calls for computer assistance. Commercial software tools, such as Mass Frontier and ACD/MS Fragmenter, rely on fragmentation rule databases for the identification of MS(n) product ions. FiD, on the other hand, conducts a combinatorial search over all possible fragmentation paths and outputs a ranked list of alternative structures. This gives the user an advantage in situations where the MS/MS data of compounds with less well-known fragmentation mechanisms are processed. FiD software implements two fragmentation models, the single-step model that ignores intermediate fragmentation states and the multi-step model, which allows for complex fragmentation pathways. The software works for MS/MS data produced both in positive- and negative-ion modes. The software has an easy-to-use graphical interface with built-in visualization capabilities for structures of product ions and fragmentation pathways. In our experiments involving amino acids and sugar-phosphates, often found, e.g., in the central carbon metabolism of yeasts, FiD software correctly predicted the structures of product ions on average in 85% of the cases. The FiD software is free for academic use and is available for download from www.cs.helsinki.fi/group/sysfys/software/fragid. Copyright (c) 2008 John Wiley & Sons, Ltd.     

Comparison of infrared-excited up-converting phosphors and europium nanoparticles as labels in a two-site immunoassay

Research in the field of immunoassays and labels used in the detection has been recently focused on particulate reporters, which possess very high specific activity that excludes the label as a sensitivity limiting factor. However, the large size and shape of the particulate labels may produce additional problems to immunoassay performance. The aim of this work was to study with two identical non-competitive two-site immunoassays whether up-converting phosphor (UCP) particles are comparable in performance with europium(III) chelate-dyed nanoparticles as particulate labels. In addition we strived to verify the common assumption of the photostability of up-converting phosphor particles supporting their potential applicability in imaging. Detection limits in two-site immunoassay for free prostate-specific antigen (free-PSA) were 0.53 ng L⁻¹ and 1.3 ng L⁻¹ using two different up-converting phosphors and 0.16 ng L⁻¹ using europium(III) nanoparticle. Large size distribution and non-specific binding of up-converting phosphor particles caused assay variation in low analyte concentrations and limited the analytical detection limit. The non-specific binding was the major factor limiting the analytical sensitivity of the immunoassay. The results suggests the need for nanoscaled and uniformely sized UCP-particles to increace the sensitivity and applicability of up-converting phosphor particles. Anti-Stokes photoluminescence of up-converting phosphor particles did not photobleach when measured repeatedly, on the contrary, the time-resolved fluorescence of europium nanoparticles photobleached relatively rapidly.     

Rotation of methyl radicals in a solid argon matrix

Electron spin resonance (ESR) measurements were carried out to study the rotation of methyl radicals (CH3) in a solid argon matrix at 14-35 K temperatures. The radicals were produced by dissociating methane by plasma bursts generated either by a focused 193 nm laser radiation or a radio frequency discharge device during the gas condensation on the substrate. The ESR spectrum exhibits axial symmetry at the lowest temperature and is ascribed to ground state molecules with symmetric total nuclear spin function I=3/2. The hyperfine anisotropy (Aparallel)-Aperpendicular) was found to be -0.01 mT, whereas that of the g value was 2.5x10(-5). The anisotropy is observed for the first time in Ar and is manifested by the splitting of the low-field transition. Elevation of temperature leads reversibly to the appearance of excited state contribution having antisymmetric I=1/2. As a function of the sample temperature, the relative intensities of symmetric and antisymmetric spin states corresponding to ground and excited rotor states, respectively, proton hyperfine and electron g-tensor components, and spin-lattice relaxation rates were determined by a numerical fitting procedure. The experimental observations were interpreted in terms of a free rotation about the C3 axis and a thermal activation of the C2-type rotations above 15 K. The ground and excited rotational state energy levels were found to be separated by 11.2 cm-1 and to exhibit significantly different spin-lattice coupling. A crystal field model has been applied to evaluate the energy levels of the hindered rotor in the matrix, and crystal field parameter varepsilon4=-200 cm-1, corresponding to a 60 cm-1 effective potential barrier for rotation of the C3 axis, was obtained.     

Unexpected Isomerization of Hexa-tert-butyl-octaphosphane

Octaphosphane {cyclo-(P₄tBu₃)}₂ ( 1 ) undergoes an unexpected isomerization reaction to the constitutional isomer 2,2′,2′′,2′′′,3,3′-hexa-tert-butyl-bicyclo[3.3.0]octaphosphane ( 2 ) in the presence of Lewis acidic metal salts. The mechanism of this reaction is discussed and elucidated with DFT calculations. The results underline the fascinating similarity between phosphorus-rich and isolobal carbon compounds. The new bicyclic octaphosphane 2 shows a dynamic behavior in solution and reacts with [AuCl(tht)] (tht=tetrahydrothiophene) to give a mono- ([AuCl( 2 -κP³)], 3 ) and a dinuclear complex ([(AuCl)₂( 2 -κP³,κP^3′)], 4 ). With cis-[PdCl₂(cod)] (cod=1,5-cyclooctadiene), the chelate complex ([PdCl₂( 2 -κ²P²,P^2′)], 5 ) with a different coordination mode of the ligand was obtained.     

Self assembly of Janus ellipsoids

We propose a primitive model of Janus ellipsoids that represents particles with an ellipsoidal core and two semisurfaces coded with dissimilar properties, for example, hydrophobicity and hydrophilicity, respectively. We investigate the effects of the aspect ratio on the self-assembly morphology and aggregation processes using Monte Carlo simulations. We also discuss certain differences between our results and those of earlier results for Janus spheres. In particular, we find that the size and structure of the aggregate can be controlled by the aspect ratio.