Self‐Assembling Hydrogels Crosslinked Solely by Receptor–Ligand Interactions: Tunability,Rationalization of Physical Properties,and 3D Cell Culture

We report a novel, noncovalent hydrogel system crosslinked solely by receptor–ligand interactions between biotin and avidin. The simple hydrogel synthesis and functionalization together with the widespread use of biotinylated ligands in biosciences make this versatile system suitable for many applications. The gels possess a range of tunable physical properties, including stiffness, lifetime, and swelling. The erosion rates, unexpectedly fast compared to the kinetic parameters for biotin–avidin, are explored in terms of stretching tensions on the polymers, a concept well‐known on the single‐molecule level, but largely unexplored in supramolecular systems. As proof of utility, the gels were functionalized with different peptide sequences to control human mesenchymal stromal cell morphology in 3D culture.     

Fe-lactate mediated formation of ZnO sols and self-organized nanorod assemblies

Hot ethanolic mixtures of hydrated Zn(II)- and Fe(II)-carboxylates (acetate and lactate) react to form yellow-orange colored Fe(III)_xZn_yO_zOH_w heteroclusters showing pronounced electronic resonances in the optical UV absorption spectra. On the addition of LiOH to these polymolecular sols, stable nanoparticulate Fe(III)–ZnO colloids are formed. During colloidal growth, 2–4 nm sized weakly crystallized Wurtzite nanoparticles are exclusively formed even in the presence of high Fe content up to 20 at.%. The presence of Fe(III) in the ZnO condensation process retards the nanoparticle growth and blocks the thermal crystallization and size enhancement up to 250 °C. The produced 0.5 M Fe(III)–ZnO sols are useful for film formation processes. From atomic force microscopy-AFM, scanning electron microscopy-SEM and X-ray diffraction-XRD studies, we note important differences in shape and morphology of the thermally annealed Fe(III)–ZnO layers depending on the iron carboxylate employed. Surprisingly, Fe(II)-lactate derived coatings are carrying vertically oriented cone-shaped aggregates composed of 60–120 nm long primary nanorods. Contrary, Fe(II)-acetate based synthesis gave sand-dune like film morphologies containing spherical 12 nm sized nanocrystallites. All film samples possess mesoporosity with pore size ranging between 5 and 20 nm.     

Conductance of alpha-helical peptides trapped within molecular junctions

Self-assembled monolayers of alpha-helical peptides on a gold surface were employed as model systems for the investigation of mediated electron transfer. The peptides contained 14, 15, 16, and 17 amino acid residues. The measurements of electron transmission through single molecules of helical peptides were performed using scanning tunneling spectroscopy (STS). The molecules were trapped between the gold tip and the substrate. Electrical contact between the molecule and the gold probe was achieved by the use of peptides containing thiol groups present at each end of the helix. The conductance behavior of the peptides was examined as a function of tip-substrate distance at fixed bias voltage. Measurements performed with peptides containing different numbers of amino acid residues indicate that the distance dependence of electron transmission through an alpha-helix is weaker than that through simple n-alkyl bridges.     

Kinetic studies on H+- and OH−-catalysed aquation of bis-aspartatochromium(III)

A potential synthetic biochromium source, bis-aspartatochromium(III) ion (where Asp is a tridentate N,O,O′-ligand, bonded via amine nitrogen and carboxylate oxygen atoms) has been obtained and characterized in aqueous solution. Kinetics of partial dechelation of the complex catalysed by H⁺ and OH^? ions has been studied spectrophotometrically within 0.1–1.0 M HClO₄ and 0.1–1.0 M NaOH ranges under first-order conditions. A linear dependence of the k _obs,H on [H⁺] and independence of the k _obs,OH on [OH^?] were established. The derived rate expression and identification of components of the reaction mixture provide evidence for a reaction mechanism, where the key role in the overall process is the formation of an intermediate species with bidentate N,O-bonded Asp via both spontaneous and H⁺(OH^?)-catalysed reaction paths. The intermediate is meta-stable and at pH 5–7 restores the substrate.     

Employing ultra high pressure liquid chromatography as the second dimension in a comprehensive two-dimensional system for analysis of Stevia rebaudiana extracts

Stevia rebaudiana extracts and plant materials are increasingly used as natural sweeteners. Polyphenolic and stevioside compounds contained in S. rebaudiana extracts were separated by comprehensive LC. A polyamine column operated in normal phase mode was used for the first dimension separation (D1), and a UHPLC C18 column operated in reversed phase mode was used for the second dimension separation (D2). The sub-2 μm column (2.1 mm × 30 mm, maintained at 70°C) and the UHPLC pump employed for D2 elution allowed a separation/cycle time of 20 s, with a backpressure oscillating between 805 and 922 bar at 3.4 mL/min. The reduced D2 cycle time allowed 3-12 D2 samplings for each peak eluted by D1. Polyphenolic and stevioside compounds were identified by combining the information coming from the position of the compounds in the 2D plot and UV spectra with that of reference materials.     

Analysis of charge transport in gels containing polyoxometallates using methods of different sensitivity to migration

Two methods have been used for examination of transport of charge in gels soaked with DMF and containing dissolved polyoxometallates. The first method is based on the analysis of both Cottrellian and steady-state currents and therefore is capable of giving the concentration of the electroactive redox centres and their transport (diffusion-type) coefficient. The second method provides the real diffusion coefficients, i.e. transport coefficients free of migrational influence, for both the substrate and the product of the electrode reaction. Several gels based on poly(methyl methacrylate), with charged (addition of 1-acrylamido-2-methyl-2-propanesulphonic acid to the polymerization mixture) and uncharged chains, have been used in the investigation. The ratio obtained for the diffusion coefficient (second method) and transport coefficient (first method) was smaller for the gels containing charged polymer chains than for the gels with uncharged chains. In part these changes could be explained by the contribution of migration to the transport of polyoxomatallates in the gels. However, the impact of the changes in the polymer-channel capacity at the electrode surface while the electrode process proceeds was also considered. These structural changes should affect differently the methods based on different time domains.     

Evaluation of physicochemical properties of a new group of SiO2/silane/POSS hybrid materials

Preparation of a new group of hybrid fillers, of SiO₂/silane/oligomeric silsesquioxane type, characterised by specific desirable physicochemical properties, was studied. Synthetic SiO₂ was precipitated by the emulsion method. At first, as a result of improved adhesion between SiO₂ and selected POSS compound, SiO₂ surface was functionalised with alkoxysilanes containing characteristics functional groups. Functionalised SiO₂ was used in the process of hybrid filler preparation according to hydrolytic condensation using methacryl POSS® mixture. To evaluate potential application of such fillers, SiO₂ systems, bifunctionalised using innovative method, were thoroughly characterised to determine their physicochemical properties as well as the effectiveness of functionalisation with silanes and POSS compound. Proposed method of SiO₂ surface modification using selected alkoxysilanes and oligosilsesquioxanes is innovative and gives very promising results. Bifunctionalisation of inorganic fillers with those compounds will substantially extended the range of their applications and probably will lead to improvement of mechanical properties of final polymer composites and reduction in the cost of their production which is the main feature of this research. Copyright © 2013 John Wiley & Sons, Ltd.     

Laccase–gold nanoparticle assisted bioelectrocatalytic reduction of oxygen

It was found that homogeneous activity of Trametes hirsuta laccase is considerably diminished in the presence of gold nanoparticles (Au-NPs). Heterogeneous electron transfer studies revealed that Au-NPs facilitate direct electron transfer (DET) between the T1 copper site of the laccase and the surface of Au-NP modified electrodes. DET was characterized by the standard heterogeneous ET constant of 0.5 ± 0.6 s^?1 at Au-NPs with an average diameter of 50 nm. As a consequence of this a well pronounced DET based bioelectrocatalytic oxygen reduction with current densities of 5–30 µA cm^?2 has been achieved at the laccase–Au-NP modified electrodes.     

Carbon‐Based Electrodes for Sensitive Electroanalytical Determination of Aminonaphthalenes

The electroanalytical performance of bare glassy carbon electrodes (GCE) for the determination of 1‐aminonaphthalene (1‐AN) and 2‐aminonaphthalene (2‐AN) was compared with GCE modified by a Nafion permselective membrane or multiwalled carbon nanotubes and with other types of carbon‐based materials, carbon film and boron doped diamond. Nafion‐modified GCE gave the highest sensitivity and lowest detection limit (0.4 µmol L^?1) for differential pulse voltammetric determination of 1‐AN. Electrochemical impedance spectroscopy gave information about the processes at the electrode surface. Simultaneous determination of 1‐AN and 2‐AN in a mixture at GCE and their determination in model samples of river water is presented.     

Coordination chemistry of H-spirophosphorane ligands towards pentacarbonylchlororhenium(I) – synthesis,structure and catalytic activity of complexes

Synthesis of a group of carbonyl rhenium coordination compounds with hydrospirophosphorane ligands was carried out and described. Different symmetrical HP(OCH₂CH₂NH)₂ L1 , HP(OCH₂CMe₂NH)₂ L2 , HP(OC₆H₄NH)₂ L3 , and unsymmetrical ligands HP (OCMe₂CMe₂O)(OC₆H₄NH) L4 were found to coordinate to the rhenium center as bidentate P,N donor ligands yielding fac-[ReCl (CO)₃ Ln ], where n = 1 – 4. Furthermore, monodentate coordination was also observed in some cases, as was clearly presented in the case of [ReCl(CO)₂( L4- κ²P,N)( L4- κP)] complex. All of the complexes were characterized using optical spectroscopy. Single-crystalX-ray diffraction was also performed in the case of fac-[ReCl(CO)₃ L3 ], fac-[ReCl(CO)₃ L4 ], [Re(CO)₂( L2 )₂]Cl and [ReCl (CO)₂( L4- κ²P,N)( L4- κP)] samples. Complexes [ReCl(CO)₃ L3 ] and [ReCl (CO)₃ L4 ], both bearing rings of conjugated double bonds within hydrospirophosphorane ligands, exhibited luminescence. Catalytic properties of rhenium complexes were assessed using the representative fac-[ReCl (CO)₃ L2 ] complex in the dimerization reaction of terminal alkynes. An efficient and selective procedure for synthesis of the E - enynes was developed. Coupling of (2-chlorophenyl)acetylene was mediated by [ReCl (CO)₃ L2 ]/TBAF system with a 100% conversion rate. Different substituents within aromatic alkynes were tolerated and the resulting products were dependent on the nature of the substituents.