SummaryHigh resolution He (Ia) and He (IIa) photoelectron spectra of cubane are reported. The assignments of the bands to different states of the cubane radical cation are made on the basis of ab initio STO-3G and MIND0/3 calculations, using geometries optimized within each treatment. The vibrational fine-structure observed supports the proposed assignment. An open shell MIND0/3 model for ground state cubane radical cation suggests that the Jahn-Teller distorted system fluctuates between twelve equivalent structures of C,,-symmetry. Localized molecular orbitals derived from the STO-3G model of cubane indicate that the major feature which discriminates this molecule with respect to other hydrocarbons is the large interaction matrix element between the opposed CC-o-orbitals of each face.
Nitric oxide is known as an inhibitor of soybean lipoxygenase-1. Investigating the interaction of a mammalian 15-lipoxygenase with nitric oxide, we found that this enzyme is also inhibited reversibly when incubated with nitric oxide for a short time period (5 s) under anaerobic conditions. This inhibition may be due to the formation of a dissociable lipoxygenase-nitric oxide complex. With longer incubation periods the ferrous lipoxygenase is oxidised to a ferric form. This oxidation renders the enzyme more susceptible to peroxide activation, causing a timedependent shortening of the kinetic lag phase.
ESRI has been shown to be a new and completely noninvasive method to monitor microacidity in different skin layers and on the skin surface. This nondestructive method allows serial measurements on skin samples to be performed without any preparatory steps.
Exothermal differential thermal analysis (DTA) effects for water release have been observed both for mechanically activated alumina gels, which may contain residual nitrate, and for strongly amorphisized AlO(OH) gels at comparably low temperatures (150-350 °C) under hydrogen. The observations are based on an investigation combining thermal analysis (TA), on-line coupled to mass spectrometry (MS), with ESR spectroscopy. This allowed the identification and quantification of trapped NO 2 molecules as well as to follow the mechanically and thermally induced changes of the Al-O-H matrix via the contained (or doped) Fe 3+ impurities. The appearance of the exothermal DTA effects is related not only to a strong mechanical activation and the access of hydrogen during the thermal treatment but also to the interaction of hydrogen with metallic platinum, for exampel, as crucible material or as metal powder. This interaction is discussed to be the origin of the chain start of the radical reaction between H 2 and NO 2 yielding H 2 O and NO. An experimental application of the observed phenomena is comparably simple and might promote a new kind of characterization of mechanically activated and highly reactive solid materials.
The purpose of the present paper is to describe p ossibilities and limitations for the determination of the rates of rotational diffusion and Heisenberg spin exchange, obtained from eontinuous-wave electron spin resonance (cw ESR) and ESR tomographic experiments. Model systems including nitroxides as paramagnetic reporter molecules have been examined in order to verify data, which have been obtained from cw ESR and ESR tomography. This has been done with particular emphasis on checking the influence of concentration, temperature, and viscosity on the spectral-spatial properties. These findings have been applied to the evaluation of penetration and permeation studies on human skin, The extracted full spectral information from ESR tomography allows the determination of the above mentioned dynamic parameters for model systems of definite geometry and for samples of human skin. It has been found that the signal-to-noise ratio is critical for all discussed applications.
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