Determination of Spin Concentrations in ESR Tomography as Applied for the Spatial Distribution of Spin Labels in Human Skin

The spectral–spatial electron spin resonance (ESR) imaging experiment provides information about the spatial and spectral properties of the examined sample, as well as the intensity distribution. Obtaining quantitative statements of the respective sample requires the usage of reference standards such as diphenylpicrylhydrazyl (DPPH) or charcoal. By means of ultraviolet-visible spectroscopy a DPPH sample has been quantified to become the reference DPPH standard for the following experiments. Moreover, charcoal together with DPPH serves as a standard to determine the spatial dimension. An ESR tomographic device has been modified concerning the sample shaping and arranging in a TE₁₀₂ resonator to allow the spatially resolved quantitative determination of spin concentrations of spin probes (S = 1/2) with an acceptable error. Only standard ESR equipment has been used except the additional gradient coils and their computer-aided controls for recording the tomogram. The presented results, i.e., the spatially resolved determination of spin concentrations, seem to be useful to describe, e.g., transport processes in biological objects. As a first application of the developed method, the spatial resolution of the effect of ultraviolet irradiation on the concentration of a spin probe in human skin could be determined. Altogether, the newly introduced method widens the field of applications of ESR spectroscopy and tomography. Authors' address: Werner Herrmann, Institute of Pharmacy, Free University Berlin, Kelchstrasse 31, 12169 Berlin, Germany     

Tetracyanoquinodimethane Reduction by Complexed Guanidinyl‐Functionalized Aromatic Compounds

In this work, we report on the reduction of tetracyanoquinodimethane (TCNQ) with dicationic complexes of guanidinyl‐functionalized aromatic (GFA) electron donors. In contrast to reduction with free GFAs, milder reduction conditions were achieved, and this led to semiconducting materials with extended TCNQ π stacking. The charge on the TCNQ units was estimated from the structural data obtained by single‐crystal X‐ray diffraction analysis and from IR spectroscopic data. The electrical conductivity was studied and the activation energy of the semiconducting materials was estimated from the temperature dependence of the conductivity.     

Rapid Autoxidation Forms Highly Oxidized RO2 Radicals in the Atmosphere

Gas‐phase oxidation routes of biogenic emissions, mainly isoprene and monoterpenes, in the atmosphere are still the subject of intensive research with special attention being paid to the formation of aerosol constituents. This laboratory study shows that the most abundant monoterpenes (limonene and α‐pinene) form highly oxidized RO₂ radicals with up to 12 O atoms, along with related closed‐shell products, within a few seconds after the initial attack of ozone or OH radicals. The overall process, an intramolecular ROO→QOOH reaction and subsequent O₂ addition generating a next R′OO radical, is similar to the well‐known autoxidation processes in the liquid phase (QOOH stands for a hydroperoxyalkyl radical). Field measurements show the relevance of this process to atmospheric chemistry. Thus, the well‐known reaction principle of autoxidation is also applicable to the atmospheric gas‐phase oxidation of hydrocarbons leading to extremely low‐volatility products which contribute to organic aerosol mass and hence influence the aerosol–cloud–climate system.     

Conceptual continuity as a mode of understanding complex systems: Applications to the dynamics sociopolitical systems

In complex biological systems, entities that are conceptually distinct but empirically related—such as sunlight and plant growth or antigene and immune response—are being explicitly linked through the identification of highly specific uninterrupted interaction sequences that take place between their macromolecular system components. These uninterrupted sequences of causation include common elements that are shared by the empirically related but conceptually distinct entities. Through the identification of specific shared elements, “conceptual continuity” is established between these entities. Examples are introduced to suggest that in sociopolitical systems, an analogous conceptual continuity can be established between distinct sociopolitical entities. The identification of specific shared elements, essential for the well being of each of the entities, can play a significant role in resolving conflicts between those separated by seemingly insurmountable obstacles such as race or religion or ideology. © 2006 Wiley Periodicals, Inc. Complexity 11:20–24, 2006     

Distribution and dimerization of some μ-imidodiphosphates

The distribution of chelate-forming reagents on a basis of arylimidodiphosphate between different organic solvents and 0.1 mol L⁻¹ HNO₃ has been studied by liquid-liquid extraction of ⁴⁶Sc. The values of dimerization constants K₂ in selected solvents, particularly on the chlorine and chlorine-fluorine hydrocarbon basis as well as distribution constants K_D(HA) have been determined.