An artificial ionophore based on a polyhydroxylated steroid dimer

The Na+ transporting properties of the first member of a new class of artificial ionophores, based on a C2-symmetric polyhydroxylated steroid dimer, are described.     

Separation of benzene from alkanes by solvent extraction with 1-ethylpyridinium ethylsulfate ionic liquid

The (liquid + liquid) equilibrium (LLE) data for ternary mixtures {alkane + benzene + 1-ethylpyridinium ethylsulfate ([EPy][EtSO₄])} at T = (283.15 and 298.15) K and atmospheric pressure are presented. The alkanes used were hexane and heptane. The cloud point method was used to determinate the binodal curve, and the tie-line compositions were obtained by density measurements. The LLE data obtained were used to calculate distribution coefficients and selectivity values. The consistency of tie-line data was ascertained by applying the Othmer-Tobias and Hand equations. Correlation of the experimental tie-lines was conducted through the use of NRTL equation, which provides good correlation of the experimental data.The results show that [EPy][EtSO₄] can be used as an alternative solvent in liquid extraction processes for the removal of benzene from its mixtures with alkanes.     

Characterization of dendrimer properties by capillary electrophoresis and their use as pseudostationary phases

The general properties of dendrimers and in particular their electrolytic characteristics that are relevant in electrokinetic separations, are described. In order to confirm theoretical considerations on commercial dendrimer charge and hydrodynamic radius, several capillary zone electrophoresis (CZE) experiments were performed. Electrophoretic mobilities measured at different pH values indicated a sensible increase of dendrimer hydrodynamic radius at pH values lower than 2.5. This was probably due to the Coulombic repulsion of charged amine groups of the inner dendrimer shells. The principal reasons that should address the use of dendrimers as pseudostationary phases in micellar electrokinetic chromatography (MEKC) are discussed. Moreover, a survey of different separations performed utilizing dendrimers in MEKC as well as of several future plausible uses of various classes of dendrimers is presented.     

Magnetic structure of the europium fulleride ferromagnet Eu(6)C(60)

The powder neutron diffraction technique has been used for the direct observation of magnetic scattering below a Curie temperature of approximately 14 K in the fullerene-based molecular ferromagnet Eu6C60. Europium is in the divalent state with a magnetic moment of 7.1(3) muB per atom, and the configurational symmetry of the magnetic structure is body-centered cubic. Close contacts between Eu2+ and neighboring C60 units provide the signature of orbital hybridization, which can evidently account for the conducting and magnetic properties of the material.     

The oxidative addition of diphenylphosphine and monophenylphosphine to the electron-rich rhenium-rhenium triple bond. The isolation and characterization of compounds that contain the four-center Re(μ-X)(μ-PR2)Re cluster (X=halide)

Diphenylphosphine oxidatively adds to the ReRe bonds of Re₂ X ₄(-dppm)₂ (X=Cl or Br; dppm=Ph₂PCH₂PPh₂) and Re₂Cl₄(-dpam)₂ (dpam=Ph₂AsCH₂AsPh₂) to afford the dirhenium(III) complexes Re₂(-X)(-PPh₂)HX ₃(-LL)₂. The dppm complexes have also been prepared from the reactions of Re₂(-O₂CCH₃)X ₄(-dppm)₂ with Ph₂PH, and a similar strategy has been used to prepare Re₂(-Cl)(-PPh₂)HCl₃(-dmpm)₂ (dmpm=Me₂PCH₂PMe₂) from Re₂(-O₂CCH₃)Cl₄(dmpm)₂. Phenylphosphine likewise reacts with Re₂ X ₄(-dppm)₂ to give Re₂(-X)(-PHPh)HX ₃(-dppm)₂. An X-ray crystal structure determination on Re₂(-Cl)(-PPh₂)HCl₃(-dppm)₂ confirms its edge-shared bioctahedral structure. This complex crystallizes in the space group (No. 148) witha=21.699(3) Å, =84.50(4)°,V=10084(5) ų, andZ=6. The structure was refined toR=0.049 (R _w 0.069) for 5770 data withI>3.0(I). The Re-Re distance is 2.5918(7) Å. Oxidation of the bromide complex Re₂(-Br)(-PPh₂)HBr₃(-dppm)₂ with NOPF₆ produces the unusual dirhenium(III, II) cation [Re₂(-H)(-Br)[P(O)Ph₂]Br₂(NO)(-dppm)₂]⁺ which has been structurally characterized as its perrhenate salt, [Re₂(-H)(-Br)[P(O)Ph₂]Br₂(NO)(-dppm)₂]ReO₄ · 2CH₂Cl₂. This complex crystallizes in the space group (No. 2) witha=14.187(7) Å,b=16.419(5) Å,c=16.729(5) Å, =98.76(2)°, =110.11(3)°, =104.66(3)°,V=3414(6) ų,Z=2. The structure was refined toR=0.040 (R _w =0.051) for 5736 data withI>3.0(I). The presence of a phosphorus-bound [P(O)Ph₂]^– ligand, a linear nitrosyl and a bridging hydrido ligand has been confirmed. The Re-Re distance is 2.6273(8) Å.     

Surface functionalization of silica nanoparticles supports colloidal stability in physiological media and facilitates internalization in cells

The influence of the surface functionalization of silica particles on their colloidal stability in physiological media is studied and correlated with their uptake in cells. The surface of 55 ± 2 nm diameter silica particles is functionalized by amino acids or amino- or poly(ethylene glycol) (PEG)-terminated alkoxysilanes to adjust the zeta potential from highly negative to positive values in ethanol. A transfer of the particles into water, physiological buffers, and cell culture media reduces the absolute value of the zeta potential and changes the colloidal stability. Particles stabilized by L-arginine, L-lysine, and amino silanes with short alkyl chains are only moderately stable in water and partially in PBS or TRIS buffer, but aggregate in cell culture media. Nonfunctionalized, N-(6-aminohexyl)-3-aminopropyltrimethoxy silane (AHAPS), and PEG-functionalized particles are stable in all media under study. The high colloidal stability of positively charged AHAPS-functionalized particles scales with the ionic strength of the media, indicating a mainly electrostatical stabilization. PEG-functionalized particles show, independently from the ionic strength, no or only minor aggregation due to additional steric stabilization. AHAPS stabilized particles are readily taken up by HeLa cells, likely as the positive zeta potential enhances the association with the negatively charged cell membrane. Positively charged particles stabilized by short alkyl chain aminosilanes adsorb on the cell membrane, but are weakly taken up, since aggregation inhibits their transport. Nonfunctionalized particles are barely taken up and PEG-stabilized particles are not taken up at all into HeLa cells, despite their high colloidal stability. The results indicate that a high colloidal stability of nanoparticles combined with an initial charge-driven adsorption on the cell membrane is essential for efficient cellular uptake.     

An implantable biofuel cell for a live insect

A biofuel cell incorporating a bienzymatic trehalase|glucose oxidase trehalose anode and a bilirubin oxidase dioxygen cathode using Os complexes grafted to a polymeric backbone as electron relays was designed and constructed. The specific power densities of the biofuel cell implanted in a female Blaberus discoidalis through incisions into its abdomen yielded maximum values of ca. 55 μW/cm(2) at 0.2 V that decreased by only ca. 5% after ca. 2.5 h of operation.     

Comparison of electron spin resonance probe and dielectric relaxation in physically and chemically crosslinked polymers

Dielectric relaxation spectroscopy in the frequency range from 10⁻² Hz to 10⁶ Hz and electron spin resonance (ESR) experiments are employed to study the dynamics in chemically and physically crosslinked networks. As examples for physically crosslinked networks ortho- and para-cresol novolacs were investigated. Dielectrically these materials show low-temperature β- and high-temperature α-relaxation. Both relaxation regions differ for both types of novolacs. This is also reflected by the ESR measurements and is discussed in terms of different hydrogen bonds found to be stronger in para-cresol novolac. For the chemically crosslinked poly(triallyl isocyanurate) only a β-peak is found by the dielectric measurements. Also in the ESR experiment the slow motion regime is characterized up to high temperatures. This means that the segmental motion is strongly suppressed by chemical crosslinking. Nevertheless the obtained change in the formal T_50G value can be used to characterize the glass transition in highly crosslinked systems by the ESR method.     

Mikrobieller Abbau organischer Fremdstoffe im Boden

Im Prinzip kann fast jede organische Industriechemikalie durch die Mikroorganismen des Bodens abgebaut werden.     

Assessing weak intramolecular donor-acceptor interactions using 1H-117Sn J-HMQC spectroscopy

It is demonstrated that long-range nJ(1H,117Sn) coupling constants down to 0.3 Hz, can be accurately quantified from non-linear fitting of the sine modulation of the associated 1H-117Sn correlation cross-peak intensities sampled as a function of the heteronuclear antiphase coherence preparation time in the 1H-117Sn J-HMQC pulse sequence. The contribution of additional, undesired modulations is illustrated and assessed using the product operator formalism, and is traced back to contributions that arise from miss-setting of the wandering 180 degrees pulse angle in the constant time period. The power of the method and its use in the characterization of weak intramolecular donor-acceptor interactions are illustrated by the determination of long-range nJ(1H,117Sn) coupling constants of bis[3-(dimethylamino)propyl]tin derivatives, [Me2N(CH2)3]2SnR2 (', R = Me; 3, R = Ph; 4, R = t-Bu). By comparing these with the values found for the corresponding bis(4-methylpentyl)tin derivatives, [Me2CH(CH2)3]2SnR2 (2', R = Me; 3', R = Ph), which lack such interactions, the use of long-range coupling constants to detect intramolecular donor-acceptor interactions is evaluated. It is concluded that nJ(1H,117Sn) couplings up to six bonds through an organic carbon chain can be quantified, whether donor-acceptor interactions are present or not. Furthermore, evidence is presented that, when two scalar coupling pathways co-exist, the pathway involving an intramolecular donor-acceptor interaction can have opposite sign, thus decreasing the overall coupling constant to a value smaller than that actually measured in the absence of a donor-acceptor interaction, where only one coupling pathway is active. There is nevertheless clear numerical value discrimination in the series of compounds investigated between long-range couplings in derivatives without weak intramolecular donor-acceptor interactions and those where such interactions can exist.