Entwurf zur Bodenanalyse

Ohne ZusammenfassungBegutachtet von den Commissionsmitgliedern: Dr. Bretschneider, Dr. Grouven, Professor Dr. Knop, Dr. Peters, Dr. Stohmann und Dr. Zöller.Bei der ersten Wanderversammlung deutscher Agriculturchemiker, welche im Mai 1863 zu Leipzig gehalten wurde, sind zum Behufe der Ausarbeitung gemeinsam zu befolgender Methoden und Untersuchungssysteme Commissionen ernannt worden. Als erste Frucht von deren Arbeiten ist in den Landw. Versuchs-Stationen, dem Organ für wissenschaftliche Forschungen auf dem Gebiete der Landwirthschaft, herausgegeben von Dr. Fr. Nobbe, Band VI, der Entwurf zurBodenanalyse von Dr. Emil Wolff, begutachtet von den andern Commissionsmitgliedern, veröffentlicht worden. Ich theile denselben im Einverständniss mit dem Herrn Verfasser auch an dieser Stelle mit, einerseits um den löblichen Zweck, welchen die Wanderversammlung der deutschen Agriculturchemiker im Auge hat, nach Kräften zu fördern, andererseits die mancherlei neuen Methoden, welche bei agriculturchemischen Untersuchungen in Gebrauch gekommen sind, auch in den Kreisen zu verbreiten, welchen die speciell agriculturchemischen Schriften nicht zu Gesicht kommen. Ich füge hinzu, dass die kleine Modification auf S. 94, sowie die Anmerkungen ebendaselbst in Folge brieflicher Mittheilung des Herrn Prof. Wolff aufgenommen worden sind. Dem Wunsche desselben, dass ich meinerseits Bemerkungen zufügen möchte, werde ich gerne entsprechen, so bald ich Zeit finde, betreffende Experimentaluntersuchungen vorzunehmen. R. F.     

On the interpretation of fluorescence anisotropy decays from probe molecules in lipid vesicle systems

Measurements of fluorescence depolarization decays are widely used to obtain information about the molecular order and rotational dynamics of fluorescent probe molecules in membrane systems. This information is obtained by least-squares fits of the experimental data to the predictions of physical models for motion. Here we present a critical review of the ways and means of the data analysis and address the question how and why totally different models such as Brownian rotational diffusion and wobble-in-cone provide such convincing fits to the fluorescence anistropy decay curves. We show that while these models are useful for investigating the general trends in the behavior of the probe molecules, they fail to describe the underlying motional processes. We propose to remedy this situation with a model in which the probe molecules undergo fast, though restricted local motions within a slowly rotating cage in the lipid bilayer structure. The cage may be envisaged as a free volume cavity between the lipid molecules, so that its position and orientation change with the internal conformational motions of the lipid chains. This approach may be considered to be a synthesis of the wobble-in-cone and Brownian rotational diffusion models. Importantly, this compound motion model appears to provide a consistent picture of fluorescent probe behavior in both oriented lipid bilayers and lipid vesicle systems.     

NMR Fourier zeugmatography

A new technique of forming two- or three-dimensional images of a macroscopic sample by means of NMR is described. It is based on the application of a sequence of pulsed magnetic field gradients during a series of free induction decays. The image formation can be achieved by a straightforward two- or three-dimensional Fourier transformation. The method has the advantage of high sensitivity combined with experimental and computational simplicity.     

Framework and extra-framework aluminium in wet ion exchanged Fe-ZSM5 and the effect of steam during the decomposition of N2O

The role of extra-framework and framework aluminium in wet-ion exchanged Fe-ZSM5 has been studied using ²⁹Si NMR and ²⁷Al triple quantum magic angle spinning (3QMAS) NMR. A series of samples were studied, the parent material, the wet ion exchanged Fe-ZSM5 and Fe-ZSM5 that has been used in the decomposition of N₂O with varying reaction conditions. Various framework and extra-framework aluminium species have been identified. It was found that cationic Fe species prefer to replace the Brønsted acid protons in their charge balancing role at those aluminium sites associated with the largest quadrupolar product. The framework aluminium atoms that pertain to the smaller quadrupolar product, which are either charge balanced by extra-framework aluminium or a proton, are much less prone to exchange. In the catalytic decomposition of N₂O it seemed that water present in small amounts enhances the catalytic activity. However, water also decreases the long term stability and performance by dealuminating the zeolite framework. With a high amount of water present, Fe-ZSM5 was destabilised and catalytically inferior.