Sites for Methane Activation on Lithium‐Doped Magnesium Oxide Surfaces

Density functional calculations yield energy barriers for H abstraction by oxygen radical sites in Li‐doped MgO that are much smaller (12±6 kJ mol^?1) than the barriers inferred from different experimental studies (80–160 kJ mol^?1). This raises further doubts that the Li⁺O^.? site is the active site as postulated by Lunsford. From temperature‐programmed oxidative coupling reactions of methane (OCM), we conclude that the same sites are responsible for the activation of CH₄ on both Li‐doped MgO and pure MgO catalysts. For a MgO catalyst prepared by sol–gel synthesis, the activity proved to be very different in the initial phase of the OCM reaction and in the steady state. This was accompanied by substantial morphological changes and restructuring of the terminations as transmission electron microscopy revealed. Further calculations on cluster models showed that CH₄ binds heterolytically on Mg²⁺O^2? sites at steps and corners, and that the homolytic release of methyl radicals into the gas phase will happen only in the presence of O₂.     

A Noble‐Metal‐Free System for Photocatalytic Hydrogen Production from Water

A series of heteroleptic copper(I) complexes with bidentate $\widehat{PP}$ and $\widehat{NN}$ chelate ligands was prepared and successfully applied as photosensitizers in the light‐driven production of hydrogen, by using [Fe₃(CO)₁₂] as a water‐reduction catalyst (WRC). These systems efficiently reduces protons from water/THF/triethylamine mixtures, in which the amine serves as a sacrificial electron donor (SR). Turnover numbers (for H) up to 1330 were obtained with these fully noble‐metal‐free systems. The new complexes were electrochemically and photophysically characterized. They exhibited a correlation between the lifetimes of the MLCT excited state and their efficiency as photosensitizers in proton‐reduction systems. Within these experiments, considerably long excited‐state lifetimes of up to 54 μs were observed. Quenching studies with the SR, in the presence and absence of the WRC, showed that intramolecular deactivation was more efficient in the former case, thus suggesting the predominance of an oxidative quenching pathway.     

The Synthesis of Magnetic Core‐Shell Nanoparticles by Surface‐Initiated Ring‐Opening Polymerization of ε‐Caprolactone

Summary: The synthesis of core‐shell particles with a poly(ε‐caprolactone) (PCL) shell and magnetite (Fe₃O₄) contents of between 10 wt.‐% and 41 wt.‐% proceeds by surface‐initiated ring‐opening polymerization of ε‐caprolactone to give surface‐immobilized oligomers with between 1 400 g · mol⁻¹ and 11 500 g · mol⁻¹. The particles are dispersable in good solvents for the PCL shell. Magnetization experiments on the resulting superparamagnetic ferrofluids give a core‐size distribution with an average diameter, d_v, of about 9.7 nm.

TEM image of Fe₃O₄/PCL core‐shell particles cast from CHCl₃ dispersion.     

Adsorption kinetics of n-nonyl-beta-D-glucopyranoside at the air-water interface studied by infrared reflection absorption spectroscopy

The adsorption of the surfactant n-nonyl-beta-D-glucopyranoside at the air-water interface after injection of the surfactant into the subphase was studied by infrared reflection absorption spectroscopy. In the first part, we investigated the equilibrium adsorption of n-nonyl-beta-D-glucopyranoside and the Gibbs adsorption isotherm was measured by applying the film balance technique. In the second part, the adsorption kinetics was followed by changes in the surface pressure and in the intensities of the OH band, which is related to the layer thickness, and the CH(2) antisymmetric stretching vibrational band. During an induction period, when the molecules are still highly diluted and the surface pressure is low, they are oriented parallel to the air-water interface. IR band simulations for the CH(2) antisymmetric stretching vibrational band support the idea of horizontally oriented molecules at the air-water interface. Later on, when more molecules are adsorbed to the air-water interface, they suddenly rearrange to an upright orientation as indicated by changes of the OH and the CH(2) bands. The observations are discussed in comparison to results obtained for the adsorption kinetics of n-decyl-beta-D-maltopyranoside, n-dodecyl-beta-D-maltopyranoside, and sodium dodecyl sulfate.     

Synthese,Kristallstruktur und Magnetismus von [(CH3)2NH2][PrCl4(H2O)2]

Preparation, Crystal Structure, and Magnetism of [(CH₃)₂NH₂][PrCl₄(H₂O)₂] The complex water containing chloride [(CH₃)₂NH₂][PrCl₄(H₂O)₂] has been prepared for the first time and the crystal structure has been determined from single crystal X‐ray diffraction data. The compound crystallizes orthorhombically in the space group Cmca (Z = 8) with a = 1796.6(2) pm, b = 940.7(1) pm, and c = 1238.4(2) pm. The anionic part of the structure is built up by chains of edge‐connected trigondodecahedra [PrCl₆(H₂O)₂]^3– according to [PrCl_4/2Cl₂(H₂O)₂]^–, which are held together by dimethylammonium cations ([(CH₃)₂NH₂]⁺). In order to study the interactions between the praseodymium cation (Pr³⁺) and the ligands magnetic measurements were carried out. The magnetic data were interpreted by ligand field calculations applying the angular overlap model.     

A Diazirine-Modified Membrane Lipid to Study Peptide/Lipid Interactions – Chances and Challenges

Although incorporation of photo-activatable lipids into membranes potentially opens up novel avenues for investigating interactions with proteins, the question of whether diazirine-modified lipids are suitable for such studies, remains under debate. Focusing on the potential for studying lipid/peptide interactions by cross-linking mass spectrometry (XL-MS), we developed a diazirine-modified lipid (DiazPC), and examined its behaviour in membranes incorporating the model α-helical peptide LAVA20. We observed an unexpected backfolding of the diazirine-containing stearoyl chain of the lipid. This surprising behaviour challenges the potential application of DiazPC for future XL-MS studies of peptide and protein/lipid interactions. The observations made for DiazPC most likely represent a general phenomenon for any type of membrane lipids with a polar moiety incorporated into the alkyl chain. Our finding is therefore of importance for future protein/lipid interaction studies relying on modified lipid probes.