Spectroscopic and structural characterization of pure and FeCl<Subscript>3</Subscript>-containing tri-<Emphasis Type="Italic">n</Emphasis>-butyl phosphate

The spectroscopic properties and liquid structure of pure tri-n-butyl phosphate (TBP) and FeCl₃/TBP solutions have been investigated by Uv–Vis and Raman spectroscopies, X-ray diffraction and conductometry. Uv–Vis and Raman spectra, supported by conductometric measurements, consistently indicate that the solubilized salt is present mostly as TBP _n [FeCl_3???n ] ⁿ⁺ and FeCl₄ ^? complex ions due to specific interaction with the TBP phosphate group. Thanks to this interaction, a high amount of salt (up to 13 % w/w) can be dissolved despite the relatively low dielectric constant of TBP. The X-ray diffractogram of pure TBP has been interpreted in terms of three main contributions which can be attributed to spatial pair correlations between atoms of interacting TBP molecules. In the presence of increasing FeCl₃ amounts, it has been observed a progressive structuring effect, exerted by the dissolved salt, on the layers of opportunely oriented TBP molecules due to the formation of the complex ionic species. By simple treatment with NaBH₄, the synthesis of Fe nanoparticles has been achieved. The absence of water, the easiness of preparation, the high amount of salt which can be suspended and the peculiar physico-chemical properties of such systems are all elements worth of note for the fields of nanoparticle synthesis and for specialized technological applications.     

Electrospun poly(ethylene oxide)/chitosan nanofibers with cellulose nanocrystals as support for cell culture of 3T3 fibroblasts

Chitosan/poly(ethylene oxide) (PEO) (5:1) nanofibers with cellulose nanocrystals (CNCs) were produced using an electrospinning technique. The addition of CNCs to the chitosan/PEO solutions allowed the production of uniform fibers (without beads) with a high proportion of chitosan. The fiber diameters were influenced by the concentration of CNCs in the chitosan/PEO solutions. The solutions containing 10% (w/w) of CNCs produced thinner fibers compared to solutions containing 5% (w/w) of CNCs. Thermogravimetric analysis indicated that the nanofibers were thermally stable, despite the CNCs having an effect on the PEO decomposition. Results from the cell assay in cultures of 3T3 fibroblasts indicated that the chitosan/PEO nanofibers (with 10% CNCs) promoted cell attachment with changes in the cytoskeletal organization. The results obtained in this work highlight the favorable effect of CNCs in electrospinning of chitosan/PEO. As expected, the influence of nanofibers on 3T3 fibroblasts F-actin and β-tubulin network revealed alterations in cytoskeleton, leading to changes in cell morphology and spreading.     

Combining size-exclusion chromatography and fully automated chip-based nanoelectrospray quadrupole time-of-flight tandem mass spectrometry for structural analysis of chondroitin/dermatan sulfate in human decorin

Chondroitin/dermatan sulfate (CS/DS) chain of decorin (DCN) from human skin fibroblasts (HSk) was released by reductive β-elimination reaction and digested with chondroitin AC I lyase. Enzymatic hydrolysis mixture of CS/DS chains was separated by size-exclusion chromatography (SEC). Collected octasaccharide fraction was subjected to fully automated chip-based nanoelectrospray (nanoESI) quadrupole time-of-flight (QTOF) MS and tandem MS (MS/MS). MS of human skin fibroblasts DCN CS/DS displayed a high complexity due to the large variety of glycoforms, which under chip-nanoESI MS readily ionized to form multiply charged ions. Except for the regularly tetrasulfated octasaccharide, the investigated fraction contained four additional octasaccharides of atypical sulfation status. Two new oversulfated glycoforms and two undersulfated species were identified. Remarkably, the series of decasaccharides discovered in the same SEC pool was found to encompass a trisulfated and a novel hexasulfated [4,5-Δ-GlcAGalNAc(IdoAGalNAc)?] species. MS/MS by collision-induced dissociation (CID) on the [M-4H]? ion corresponding to the previously not reported [4,5-Δ-GlcAGalNAc(IdoAGalNAc)?](5S) corroborated for a novel motif in which three N-acetylgalactosamine (GalNAc) moieties are monosulfated, 4,5-Δ-GlcA and the first IdoA from the non-reducing end bear one sulfate group each, while the second N-acetylgalactosamine from the reducing end is unsulfated.     

Uranium(VI) sequestration by polyacrylic and fulvic acids in aqueous solution

Stability data on the formation of dioxouranium(VI) species with polyacrylic (PAA) and fulvic acids (FA) are reported with the aim to define quantitatively the sequestering capacity of these high molecular weight synthetic and naturally occurring ligands toward uranium(VI), in aqueous solution. Investigations were carried out at t = 25 °C in NaCl medium at different ionic strengths and in absence of supporting electrolyte for uranyl–fulvate ( \textUO₂²⁺ {{\text{UO}}_{2}}^{2+} –FA) and uranyl–polyacrylate ( \textUO ₂ ²⁺ {{\text{UO}}_{ 2}}^{ 2+ } –PAA, PAA MW 2 kDa) systems, respectively. The experimental data are consistent with the following speciation models for the two systems investigated: (i) UO₂(FA₁), UO₂(FA₁)(FA₂), UO₂(FA₁)(FA₂)(H) for \textUO ₂ ²⁺ {{\text{UO}}_{ 2}}^{ 2+ } –fulvate (where FA₁ and FA₂ represent the carboxylic and phenolic fractions, respectively, both present in the structure of FA), and (ii) UO₂(PAA), UO₂(PAA)(OH), (UO₂)₂(PAA)(OH)₂ for \textUO ₂ ²⁺ {{\text{UO}}_{ 2}}^{ 2+ } –polyacrylate. By using the stability data obtained for all the complex species formed, the uranium(VI) sequestration by PAA and FA was expressed by the pL₅₀ parameter [i.e. the −log(total ligand concentration) necessary to bind 50% of uranyl ion] at different pH values. A comparison between pL₅₀ values of FA and PAA and some low molecular weight carboxylic ligands toward uranyl ion is also given.     

Shape-persistent linear, kinked, and cyclic oligo(phenylene-ethynylene-butadiynylene)s: self-assembled monolayers

Shape-persistent rigid phenylene-ethynylene-butadiynylenes form lamellar self-assembled monolayers (SAMs) at the HOPG/TCB interface, which were studied by scanning tunneling microscopy (STM) with submolecular resolution. Substitution of the terminating acetylene functions with polar cyanopropyldimethylsilyl groups leads to 2D phase separation and defined rod-rod interactions, which determine the packing distances between the rigid rods. The results stimulated the connection of rigid rods via septiarylene clamp units. They covalently link two rigid rod units and define the intramolecular rod-rod distance that matches the alkoxy substituent chain lengths. The systems can be described as half-ring structures of two rigid rods connected via a rotatable joint unit. These acetylene-terminated half-ring structures were also oligomerized under Cu and Pd catalysis to yield defined acyclic and cyclic oligomers. Detailed STM studies decoded the molecular origin of the surface patterning of such systems. The dodecyloxy side chains are adsorbed along the HOPG main axes and, together with the alkoxy backbone angle, determine the adsorption direction of the adlayers.     

Evaluation of the Standard Potential of the Ag/AgCl Electrode in a 50 wt-% Water–Ethanol Mixture

This paper deals with the evaluation of the standard potential of the Ag/AgCl electrode in a water–ethanol mixture (50 wt-%). A potentiometric method was applied using a cell without liquid junction. Mean activity coefficients of HCl in the same mixture have been also determined. The measurements were performed in the HCl molality range from 0.005 to 0.1 mol⋅kg⁻¹. The Debye–Hückel theory and Pitzer’s model, based on the interactions present in the solution, have been applied. Good agreement was found between the results obtained with the two approaches. Uncertainties of the Pitzer parameters and interionic forces are discussed based on the values found. The variation of the standard potential as a function of the temperature was used to calculate the transfer thermodynamic functions. The effects of the solvent composition on the thermodynamic properties of HCl allow to highlight structural changes in water–ethanol mixtures.     

Isopiestic Determination of the Osmotic and Activity Coefficients of K<Subscript>2</Subscript>HPO<Subscript>4</Subscript>(aq), Including Saturated and Supersaturated Solutions,at <Emphasis Type="Italic">T</Emphasis>=298.15 K

The osmotic coefficients of K₂HPO₄(aq) have been measured at T=298.15 K by the isopiestic vapor pressure method over the range of molalities from 1.3846 mol⋅kg⁻¹ to 13.939 mol⋅kg⁻¹ (oversaturation) with CaCl₂(aq) as the reference solution. The molalities and osmotic coefficients of saturated solutions in equilibrium with K₂HPO₄⋅xH₂O(cr) were measured simultaneously by the same method. Available literature osmotic coefficients of K₂HPO₄(aq) at T=298.15 K, and our new experimental data, were combined and modeled using an extended form of Pitzer’s equation and the Clegg-Pitzer-Brimblecombe equation based on the mole-fraction-composition scale. These equations were used to calculate the activity coefficients of K₂HPO₄(aq) at T=298.15 K.     

Synthesis, characterisation and application of iridium(III) photosensitisers for catalytic water reduction

The synthesis of novel, monocationic iridium(III) photosensitisers (Ir-PSs) with the general formula [Ir(III)(C^N)(2)(N^N)](+) (C^N: cyclometallating phenylpyridine ligand, N^N: neutral bidentate ligand) is described. The structures obtained were examined by cyclic voltammetry, UV/Vis and photoluminescence spectroscopy and X-ray analysis. All iridium complexes were tested for their ability as photosensitisers to promote homogeneously catalysed hydrogen generation from water. In the presence of [HNEt(3)][HFe(3)(CO)(11)] as a water-reduction catalyst (WRC) and triethylamine as a sacrificial reductant (SR), seven of the new iridium complexes showed activity. [Ir(6-iPr-bpy)(ppy)(2)]PF(6) (bpy: 2,2'-bipyridine, ppy: 2-phenylpyridine) turned out to be the most efficient photosensitiser. This complex was also tested in combination with other WRCs based on rhodium, platinum, cobalt and manganese. In all cases, significant hydrogen evolution took place. Maximum turnover numbers of 4550 for this Ir-PS and 2770 for the Fe WRC generated in situ from [HNEt(3)][HFe(3)(CO)(11)] and tris[3,5-bis(trifluoromethyl)phenyl]phosphine was obtained. These are the highest overall efficiencies for any Ir/Fe water-reduction system reported to date. The incident photon to hydrogen yield reaches 16.4% with the best system.