Oscillations in solvent fraction of polyelectrolyte multilayers driven by the charge of the terminating layer

We have investigated polyelectrolyte multilayers of poly(styrene sulfonate) (PSS) and poly(allylamine hydrochloride) in contact with D2O by neutron reflectometry. The study particularly focuses on the changes in the solvent fraction of the system upon addition of a layer. When the layers are deposited at a low salt concentration (0.25 M NaCl), no significant changes in the solvent fraction are detected. In contrast, at a larger salt concentration (1 M NaCl), oscillations in the solvent fraction are detected when a new layer is deposited. In this case, addition of PSS systematically increases the solvent volume fraction, and addition of PAH decreases the solvent fraction. The results suggest that one of the parameters driving the oscillations in solvent fraction is the uncompensated charges present in the layers. This study opens new perspectives on results previously published by other authors: in addition to polymer desorption, water uptake or release might contribute to the different regimes of multilayer growth reported in the literature (linear, asymmetric, or exponential growth). In addition, comparison to NMR results previously reported allows for conclusions about the mobility of the solvent in the multilayers: the average rotational correlation time of the water molecules in the polyelectrolyte layers decreases upon addition of PSS and increases upon addition of PAH.     

Interactions of Pb2+ with fulvic acid by electrophoretically mediated on-capillary microanalysis

Studies of yessotoxin involving confirmation of fragmentation processes using a high-resolution orthogonal hybrid quadrupole time-of-flight (QqTOF) mass spectrometer and nanoLC hybrid quadrupole TOF MS have been undertaken. The fragmentation of YTX was studied in negative mode using nano electrospray (nanoESI) QqTOF mass spectrometry. Three major molecule-related ions were observed, [M - 2Na + H]-, [M - Na]- and [M - 2Na]2-, and fragmentation of the latter was studied in detail. This showed that product ions were formed as a consequence of charge-remote fragmentation processes that included a strong directional cleavage of the polyether rings of YTX. NanoLC coupled with QqTOF MS was used to determine YTX in small samples of the phytoplankton, Protoceratium reticulatum, by monitoring the [M - 2Na]2- ion at m/z 570. A PepMap C18 nanoLC column (75 microm x 10 cm, 100 A, 3 microm, LC Packings) was used and the solvent was acetonitrile/water (90:10 (v/v)) containing 1 mM ammonium acetate, at a flow rate of 400 nl/min, for 30 min. Calibrations obtained with YTX standard solutions were linear over four orders of magnitude, 0.75-250 ng/ml; r2 = 0.9947-0.9998. Phytoplankton cells (ca. 100-300) were picked, extracted with methanol/water (40:60), and the YTX concentration was determined over the range 0.011-0.020 ng/cell. The detection limit (3 x S/N) of this method was ca. 0.5 pg YTX on-column.     

Triplet-triplet annihilation in dilute,solid solutions of aromatic polymers

Summary The triplet-triplet annihilation of mass fractionatedPVCA (M=3.6·10³–1.4·10⁶) in toluene glasses was studied by phosphorescence, for glasses ofPVCA andP2VN (order of M=10⁶) inMTHF the intensity of phosphorescence and delayed fluorescence were studied as a function of the excitation intensity. A survey of T-T annihilation in solid solutions of aromatic polymers is given and requirements for a theory explaining low dimensional energy transport and exciton-exciton annihilation are pointed out.Presented at the ACS-Symposium Polymer Photophysics: Fundamentals and Applications. ACS-Spring Meeting 1992, San Francisco, April 5–10, 1992     

Equilibrium study of selected divalent d-electron metals adsorption on A-type zeolite

The objective of the presented study was to investigate the adsorption of Cu, Co, Mn, Zn, Cd and Mn on A-type zeolite. The isotherms for adsorption of metals from their nitrates were registered. The following adsorption constants K of metals were found: 162,890, 124,260, 69,025, 16,035, 10,254, and 151 [M(-1)] for Cu, Co, Mn, Zn, Cd, and Ni, respectively, for the concentration range 10(-4)-10(-3) M. On the other hand, the investigation of pH influence on the distribution constants of metals showed that the adsorption of metals proceeds essentially through an ion-exchange process, surface hydrolysis, and surface complexation. The supplementary results from DRIFT, scanning electron microscopy, and X-ray diffraction methods confirmed the presumption about the possible connection between the electronic structure of divalent ions and their adsorption behavior, showing that ions with d5 and d10 configurations such as Mn2+, Zn2+, Cd2+, with much weaker hydrolytic properties than Cu2+ and Ni2+, strongly interact with the zeolite framework and therefore their affinity to the zeolite phase is much stronger when compared with that of the Ni2+ ion, but at the same time not as strong as the affinity of the Cu2+ ion, the latter forming a new phase during the interaction with zeolite framework. For Zn2+, during inspection of the correlation between the proton concentration H/Al and zinc concentration Zn/Al on the zeolite surface, the formation of the surface complex [triple bond]S-OZn(OH) was proposed. A correlation between the heterogeneity of proton concentrations H/Al on Me-zeolite surfaces and the hydrolysis constants pKh of Me2+ ions was found.     

Investigation of 2-[2-(4-Methoxy-phenylamino)-vinyl]-1,3,3-trimethyl-3H-indolium Chloride as a New Reagent for the Determination of Chromium(VI)

 The complex formation and extraction of chromium(VI) with 2-[2-(4-methoxy-phenylamino)-vinyl]-1,3,3-trimethyl-3H-indolium chloride reagent was studied by means of spectrophotometry. The influence of medium acidity, the concentration of chloride ions and dye reagent, the nature of the extractant and some other factors (time of extraction, stability of color, interference, etc.) on the absorbance of colored extracts were studied. The optimum conditions were found to be 0.02–0.1 M H₂SO₄, 1.0–1.5 M NaCl, (2.0–2.5) × 10⁻⁴ M of reagent. The absorbance of the colored extracts obeys Beer’s Law in the range of 0.26–7.28 mg L⁻¹. The procedure of Cr(VI) extraction and spectrophotometric determination was examined. Author for correspondence. E-mail: andruch@kosice.upjs.sk Received November 19, 2002; accepted March 10, 2003 Published online June 13, 2003     

On-line coupling of capillary isotachophoresis and capillary zone electrophoresis for the determination of flavonoids in methanolic extracts of Hypericum perforatum leaves or flowers

Five flavonoids (hyperoside, isoquercitrin, quercitrin, quercetin and rutin) were separated and determined in extracts of Hypericum perforatum leaves or flowers by capillary zone electrophoresis (CZE) with isotachophoretic (ITP) sample pre-treatment using on-line column coupling configuration. The background electrolyte (BGE) used in the CZE step was different from the leading and terminating ITP electrolytes but all the electrolytes contained 20% (v/v) of methanol. The optimal leading electrolyte was 10 mM HCl of pH* approximately 7.2 (adjusted with Tris) and the terminating electrolyte was 50 mM H3BO3 of pH* approximately 8.2 (adjusted with barium hydroxide). This operational system allowed to concentrate and pre-separate selectively the flavonoid fraction from other plant constituents before the introduction of the flavonoids into the CZE capillary. The BGE for the CZE step was 50 mM Tris buffer of pH* approximately 8.75 containing 25 mM N-[tris(hydroxymethyl)methyl]-3-aminopropanesulfonic acid as co-ion and 55 mM H3BO3 as complex-forming agent. The ITP-CZE method with spectrophotometric detection at 254 nm was suitable for the quantitation of the flavonoids in real natural samples; kaempferol was used as internal standard. The limit of detection for quercetin-3-O-glycosides was 100 ng ml(-1) and calibration curves were rectilinear in the range 1-10 microg ml (-1) for most of the analytes. The RSD values ranged between 0.9 and 2.7% (n=3) when determining approximately 0.07-1.2% of the individual flavonoids in dried medicinal plants.     

Synthesis of alpha-amino acids via asymmetric phase transfer-catalyzed alkylation of achiral nickel(II) complexes of glycine-derived Schiff bases

Achiral, diamagnetic Ni(II) complexes 1 and 3 have been synthesized from Ni(II) salts and the Schiff bases, generated from glycine and PBP (7) and PBA (11), respectively, in MeONa/MeOH solutions. The requisite carbonyl-derivatizing agents pyridine-2-carboxylic acid(2-benzoyl-phenyl)-amide 7 (PBP) and pyridine-2-carboxylic acid(2-formyl-phenyl)-amide 11 (PBA) were readily prepared from picolinic acid and o-aminobenzophenone or picolinic acid and methyl o-anthranilate, respectively. The structure of 1 was established by X-ray crystallography. Complexes 1 and 3 were found to undergo C-alkylation with alkyl halides under PTC conditions in the presence of beta-naphthol or benzyltriethylammonium bromide as catalysts to give mono- and bis-alkylated products, respectively. Decomposition of the complexes with aqueous HCl under mild conditions gave the required amino acids, and PBP and PBA were recovered. Alkylation of 1 with highly reactive alkyl halides, carried out under the PTC conditions in the presence of 10% mol of (S)- or (R)-2-hydroxy-2'-amino-1,1'-binaphthyl 31a (NOBIN) and/or its N-acyl derivatives and by (S)- or (R)-2-hydroxy-8'-amino-1,1'-binaphthyl 32a (iso-NOBIN) and its N-acyl derivatives, respectively, gave rise to alpha-amino acids with high enantioselectivities (90-98.5% ee) in good-to-excellent chemical yields at room temperature within several minutes. An unusually large positive nonlinear effect was observed in these reactions. The Michael addition of acrylic derivatives 37 to 1 was conducted under similar conditions with up to 96% ee. The (1)H NMR and IR spectra of a mixture of the sodium salt of NOBIN and 1 indicated formation of a complex between the two components. Implications of the association and self-association of NOBIN for the observed sense of asymmetric induction and nonlinear effects are discussed.     

Dendrimers based on [1,3,5]‐triazines

A comprehensive and chronological account of dendrimers based on [1,3,5]‐triazines is provided. Synthetic strategies to install the triazine through cycloaddition, cyclotrimerization, and nucleophilic aromatic substitution of cyanuric chloride are discussed. Motivations and applications of these architectures are surveyed, including the preparation of supramolecular assemblies in the solution and solid states and their use in medicines, advanced materials, and separations when anchored to solid supports. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3411–3433, 2006     

Kinetics of oxidative degradation of pantothenic acid by cerium(IV) in aqueous perchloric acid

The kinetics of oxidation of pantothenic acid (PA), Me₂C(CH₂OH)CH(OH)C(O)NHCH₂CH₂CO₂H, by cerium(IV) in aqueous HClO₄ medium at constant ionic strength, 2.0 mol dm^–3, has been studied spectrophotometrically. The reaction showed first-order kinetics in Ce^IV concentration, an apparent less than unit order dependence in [PA] and an inverse fractional order in [H⁺]. Initial addition of products had no significant effect on the rate of the reaction. A possible mechanism is proposed, and the reaction constants involved in the mechanism have been computed. There is good agreement between the observed and calculated rate constants under different experimental conditions. The activation parameters were calculated with respect to the slow step of the proposed mechanism.