Liquid chromatography at critical conditions in ternary mobile phases: Gradient elution along the critical line

In ternary mobile phases consisting of acetone, methanol, and water, the retention of PEG on reversed‐phase columns is independent on molar mass at certain compositions of the mobile phase. Along this critical adsorption line, the retention of polypropylene glycol varies quite strongly, which can be utilized in the separation of block copolymers. Gradient elution along the critical line allows a baseline separation of all oligomers in polypropylene glycol up to approximately 25 propylene oxide units. The same resolution can be achieved in the separation of ethylene oxide‐propylene oxide block copolymers, regardless of the length of the ethylene oxide block.     

Stereospecificity of the Au(I)-catalyzed reaction of 1-alkynyl-bicyclo[4.1.0]-heptan-2-ones with nucleophiles

The stereospecificity of the Au(I)-catalyzed reaction of 1-alkynyl-bicyclo[4.1.0]-heptan-2-ones with nucleophiles was investigated. The substrates were prepared in non-racemic form (up to 88% ee) through parallel kinetic resolution (CBS reduction) and reoxidation of the separated diastereomeric alcohols. The key Au-catalyzed reaction was then found to proceed without significant loss of absolute stereochemical information; this way, an achiral carbocationic intermediate could be excluded. Thus, a bicyclobutonium-type intermediate seems to be attacked in a S_N2-type fashion by the nucleophile in accordance with computational predictions.     

Deacetylation Regioselective De Glycals

ABSTRACT

Hydrazine acetate is shown to effect selective deacetylation on peracetylated glycals like D-xylal, D-glucal, D-galactal and L-rhamnal. It is demonstrated that the observed selectivity on the -4 position cannot be explained by acetyl migration during the reaction.     

Formation of Temporary Negative Ions and Their Subsequent Fragmentation upon Electron Attachment to CoQ0 and CoQ0H2

Ubiquinone molecules have a high biological relevance due to their action as electron carriers in the mitochondrial electron transport chain. Here, we studied the dissociative interaction of free electrons with CoQ₀, the smallest ubiquinone derivative with no isoprenyl units, and its fully reduced form, 2,3-dimethoxy-5-methylhydroquinone (CoQ₀H₂), an ubiquinol derivative. The anionic products produced upon dissociative electron attachment (DEA) were detected by quadrupole mass spectrometry and studied theoretically through quantum chemical and electron scattering calculations. Despite the structural similarity of the two studied molecules, remarkably only a few DEA reactions are present for both compounds, such as abstraction of a neutral hydrogen atom or the release of a negatively charged methyl group. While the loss of a neutral methyl group represents the most abundant reaction observed in DEA to CoQ₀, this pathway is not observed for CoQ₀H₂. Instead, the loss of a neutral OH radical from the CoQ₀H₂ temporary negative ion is observed as the most abundant reaction channel. Overall, this study gives insights into electron attachment properties of simple derivatives of more complex molecules found in biochemical pathways.     

Regulatory impact of environmental standards on the eco-efficiency of firms

In this paper, we propose an approach to implement environmental standards into Data Envelopment Analysis (DEA) and in this way to measure their regulatory impact on eco-efficiency of firms. One standard feature of basic DEA models lies in the exogeneity of inputs, desirable and undesirable outputs. Taking into account the environmental constraints, we therefore apply the bounded variable DEA model. The regulatory impact is assessed as difference in eco-efficiency scores before and after fictive introduction of an environmental standard. Furthermore, we distinguish between weak and strong disposability of undesirable outputs and develop corresponding models. Assessing the regulatory impact of environmental standards in advance provides support for environmental policymakers in choosing appropriate instruments and in adjusting the intensity of regulation.     

Thermally‐activated post‐growth dewetting of fullerene C60 on mica

Understanding and controlling the growth and stability of molecular thin films on solid surfaces is necessary to develop nanomaterials with well‐defined physical properties. As a prominent model system in organic electronics, we investigate the post‐growth dewetting kinetics of the fullerene C₆₀ on mica with real‐time and in situ X‐ray scattering. After layer‐by‐layer growth of C₆₀, we find a thermally‐activated post‐growth dewetting, where the smooth C₆₀‐layer breaks up into islands. This clearly shows that growth is kinetically limited before the system moves over an activation barrier into an energetically favored configuration. From the temperature‐dependent dewetting kinetics we find an effective activation barrier of 0.33 eV, which describes both the temperature‐dependent macroscopic changes in the surface morphology and the microscopic processes of inter‐ and intralayer diffusion during dewetting.