Michaela Wilhelm

Protein adsorption on colloidal alumina particles functionalized with amino, carboxyl, sulfonate and phosphate groups.

Colloidal oxide particles in biomedical or biotechnological applications immediately become coated with proteins of the biological medium, a process which is strongly influenced by the surface characteristics of the particles. Fundamental correlations between surface characteristics and the, so far mainly uncontrollable, protein adsorption are still not clear. In this study the surface of colloidal alumina particles (d(50)=179 ± 8 nm) was systematically adjusted with NH(2), COOH, SO(3)H and PO(3)H(2) functional groups to investigate the influence on the adsorption of the three model proteins, bovine serum albumin (BSA), lysozyme (LSZ) and trypsin (TRY). The surface functionalization is characterized and discussed in detail with regard to the morphology, isoelectric point, zeta potential, hydrophilic/hydrophobic properties, functional group density and stability. Protein-particle interaction was then assessed by evaluating the amount of protein adsorbed and the zeta potentials of protein-particle conjugates. Protein adsorption was found to be influenced by the type of functional group as well as the expected electrostatic forces under the given experimental conditions. The level of protein adsorption might, hence, be specifically controlled by the type of surface functionalization. Possible adsorption modes of BSA, LSZ and TRY on the particles are suggested by considering the spatial surface potential distribution of the proteins calculated from the protein database file. The particles presented provide an excellent prerequisite for further investigation of fundamental particle-protein interactions and the design of functionally graded materials for biomedical and biotechnological applications, e.g. as drug carriers or for protein purification.

Development of a Novel Zinc/Air Fuel Cell with a Zn Foam Anode, a PVA/KOH Membrane and a MnO

A new type of zinc/air fuel cell comprising a Hg/Pb free Zn foam anode, a PVA/KOH electrolyte membrane and a MnO2/SiOC-based cathode was developed in this work. The electrochemical activity of the zinc foam and air electrode was investigated in 6 M KOH under half-cell conditions. The pristine ZnO layer of the foam matrix favoured direct oxidation of the zinc particles to zinc oxide in 6 M KOH. In the laboratory cell, a specific energy of about 500 mWh g(-1) zinc was measured at 5 mA discharging current with a zinc foam, a PVA/KOH/H2O membrane and a MnO2+ Vulcan/carbon paper cathode. A correlation between cell performances and porosity of the zinc foam was found. However, stability of the Zn foam and SiOC GDL materials towards KOH should be improved.

Detection of Homogeneous Distribution of Functional Groups in Mesoporous Silica by Small Angle Neutron Scattering and in Situ Adsorption of Nitrogen or Water

The distribution of SO(3)H-functional groups attached to the ordered inner pore walls of mesoporous Si-MCM-41 materials based on SiO(2) was investigated by gas adsorption combined with in situ small angle neutron scattering (SANS). The functionalization was performed by two different methods, (i) grafting and (ii) co-condensation. The adsorbates N(2) at 77 K or a H(2)O/D(2)O mixture of 42:58 at 298 K possess neutron scattering length densities (SLD) similar to that of SiO(2) and therefore quench the diffraction signals of the nonmodified silica. SANS measurements show that N(2) matches completely not only with the pristine mesoporous Si-MCM-41 but also with Si-MCM-41-SO(3)H functionalized by grafting. Thus, full access of adsorbate into the entire length of the pores is proven. For the analysis of the distribution of functional groups within the pores in dependence on the used functionalization method, grafting or co-condensation, however, the more specific adsorbate H(2)O/D(2)O (42:58) is necessary, because it reacts more sensitively toward small changes in the SLD of the host material. For grafted Si-MCM-41-SO(3)H materials, an incomplete quenching was observed, indicating that only some regions, probably the pore mouths, have been modified. For a sample functionalized by co-condensation, almost no quenching of the neutron diffraction was found, indicating a very homogeneous distribution of the functional groups along the entire pores.

Activated carbon from sewage sludge for removal of sodium diclofenac and nimesulide from aqueous solutions

Sludge based activated carbons (ACs) were used to remove selected pharmaceuticals such as diclofenac (DCF) and nimesulide (NM) from aqueous solutions. The powered sewage sludge was mixed with different proportions of ZnCl2. The mixture was pyrolyzed in a conventional oven using three different temperatures under inert atmosphere. Afterwards, in order to increase the specific surface area and uptake capacity the carbonized materials were acidified with 6mol L−1 HCl under reflux at 80 °C for 3 hours. The characterization of ACs was achieved by scanning electron microscopy, FTIR, TGA, hydrophobicity index by water, n-heptane vapor adsorption and nitrogen adsorption/desorption curves. The specific surface area (SBET) of adsorbents varied between 21.2 and 679.3m2g−1. According to the water and n-heptane analysis data all ACs had hydrophobic surface. Experimental variables such as pH, mass of adsorbent and temperature on the adsorption capacities were studied. The optimum pH, mass of adsorbent and temperature for adsorption of DCF and NM onto ACs were found to be 7.0 (DCF) and 10.0 (NM), 30mg and 25 °C, respectively. The kinetic adsorption was investigated using general-order, pseudo-first order and pseudo-second order kinetic models, while the general-order model described the adsorption process most suitably. The maximum amounts of DCF and NM adsorbed were 156.7 and 66.4mg g−1 for sample 1(500-15-0.5), respectively.

Coordination chemistry of lipoic acid and related compounds.

N-(1-Adamantyl)lipoamide (2) has been prepared from racemic lipoic acid and reacted with hydrogen chloride in chloroform to afford [H(2)2]Cl·xCHCl3 (3). 1H and 13C NMR spectra of 3 in CDCl3 show that 2 is protonated at the carbonyl oxygen atom. There are no indications of protonation at the amide N atom or the 1,2-dithiolane S atoms. X-Ray crystal structure analysis of 3 revealed the presence of the O-protonated dimer [H(2)2]+. The central part of this proton complex consists of a CO⋯H+⋯OC hydrogen bridge with a short O⋯O distance of 2.439(4) A. The CO bonds [1.273(5) and 1.282(5) A] are significantly lengthened and the (O)C–N bonds [1.313(5) and 1.311(5) A] are shortened compared to the typical bond lengths in non-protonated secondary amides. The chloride ions interconnect the [H(2)2]+ complexes into infinite chains via N–H⋯Cl−⋯H–N bridges [N⋯Cl 3.222(3) and 3.229(3) A] and bind the solvent molecules via Cl3CH⋯Cl− hydrogen bonds [C⋯Cl 3.361(6) and 3.386(7) A]. Theoretical DFT and MP2 investigations on the model complex [H(4)2]+, where 4 is N-methylacetamide, indicate that the central proton is highly dynamic. It can almost freely shift within a ±0.1 A range around the center of the O⋯O separation.

Adapted MR velocimetry of slow liquid flow in porous media

MR velocimetry of liquid flow in opaque porous filters may play an important role in better understanding the mechanisms of deep bed filtration. With this knowledge, the efficiency of separating the suspended solid particles from the vertically flowing liquid can be improved, and thus a wide range of industrial applications such as wastewater treatment and desalination can be optimized. However, MR velocimetry is challenging for such studies due to the low velocities, the severe B0 inhomogeneity in porous structures, and the demand for high spatial resolution and an appropriate total measurement time during which the particle deposition will change velocities only marginally. In this work, a modified RARE-based MR velocimetry method is proposed to address these issues for velocity mapping on a deep bed filtration cell. A dedicated RF coil with a high filling factor is constructed considering the limited space available for the vertical cell in a horizontal MR magnet. Several means are applied to optimize the phase contrast RARE MRI pulse sequence for accurately measuring the phase contrast in a long echo train, even in the case of a low B1 homogeneity. Two means are of particular importance. One uses data acquired with zero flow to correct the phase contrast offsets from gradient imperfections, and the other combines the phase contrast from signals of both odd and even echoes. Results obtained on a 7T preclinical MR scanner indicate that the low velocities in the heterogeneous system can be correctly quantified with high spatial resolution and an adequate total measurement time, enabling future studies on flow during the filtration process.

Functionalized mesoporous materials used as proton conductive additives for high temperature PEM fuel cell membranes

Abstract Mesoporous Si-MCM-41 has been functionalized with sulfonic acid groups (-SO 3 H). The modified powders were characterized by X-ray diffraction, adsorption measurements and infrared spectroscopy and studied upon proton conductivity by impedance spectroscopy. The powders exhibit high proton conductivities up to 10 –3 S cm –1 , and composite membranes with polysiloxanes and functionalized powders show good water management properties.

The influence of carbon nanotubes and graphene oxide sheets on the morphology, porosity, surface characteristics and thermal and electrical properties of polysiloxane derived ceramics

Graphene oxide (GO) and multi-walled carbon nanotubes (MWCNT) were incorporated into a SiOC composite ceramic matrix using a simple roll-mixing method followed by thermal cross-linking and pyrolysis. The structure, morphology, porosity, surface characteristics, and thermal properties of polysiloxane are analysed using scanning electron microscopy, BET specific surface area, mercury intrusion porosimetry, water vapour and n-heptane adsorption, and Raman spectroscopy, respectively. The electrical conductivity, conduction mechanism, and percolation behavior of the composite ceramics are investigated by electrical impedance spectroscopy in the temperature range of 25–250 °C. Free-rising composite ceramic foams are generated, incorporating both nanofillers into the SiOC ceramic matrix. Both nanofillers show a positive effect on the thermal stability of the SiOC ceramics. The room temperature DC conductivity value of pure SiOC ceramics shows ∼2.97 × 10−9 S cm−1, which increases by three to four orders of magnitude after the incorporation of 5 wt% conductive nanofillers (∼2.5 × 10−6 S cm−1 for 5 wt% GO and ∼2.08 × 10−5 S cm−1 for 5 wt% MWCNT). The calculated activation energy from the Arrhenius plot for composite ceramics is found to be lower (0.10 eV for 5 wt% GO and 0.07 eV for 5 wt% MWCNT) compared to the same SiOC ceramics without nanofillers (0.22 eV). The conduction mechanism studies of composite ceramics suggest a non-Debye type distribution of relaxation in SiOC. Thus the nanofiller-enhanced SiOC ceramics are highly promising materials for rechargeable batteries, high-temperature fuel cells, gas sensors, display devices etc.

Phenylmercury Chloride: Its Single-Crystal X-Ray Structure and Some Aspects of its Biological Chemistry

A single crystal of phenylmercury chloride (PhHgCl) was obtained by serendipity from a solution of diphenylmercury (HgPh2) and dihydrolipoic acid in tetrahydrofuran / carbon tetrachloride. The crystal structure of PhHgCl is pseudotetragonal. It is best described in the orthorhombic space group Cmma with a = 6.856(1), b = 6.882(1), c = 14.309(2) Å (at 193 K), and Z = 4. The Cl-Hg-C moiety of the PhHgCl molecule is exactly linear. The bond lengths at the Hg atom are Hg-Cl 2.345(2) and Hg-C 2.044(9) Å. In the crystal, the molecules are arranged in double layers parallel to the a,b plane. In a model medium for the gastric juice (0.1 M DCl in D2O / [D8]dioxan, 37 °C), HgPh2 reacts to form PhHgCl. HgCl2, which would result from complete dearylation, cannot be isolated from the reaction mixture. However, it appears that a small equilibrium concentration of HgCl2 may be present, because on addition of 1,4,7-trithiacyclononane (ttcn) and diethyl ether, the dichloride can be trapped as solid [Hg(ttcn)2][HgCl4]. We estimate that after oral uptake of HgPh2 20 -90% are transformed into PhHgCl in the stomach after 30 min

Crystal structure of 7-(p-toluenesulfonyl)-7-aza-1,4-dithiacyclononane (Ts[9]aneNS2), C13H19NO2S3

Abstract C13H19NO2S3, monoclinic, P21 (No. 4), a = 11.7973(9) Å, b = 5.6054(3) Å, c = 11.9380(9) Å, β = 107.977(9)°, V = 750.9 Å3, Z = 2, Rgt(F) = 0.032, wRref(F2) = 0.083, T = 193 K.