Book reviews

Ohne Zusammenfassung

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Book reviews

     

Evidence against the S-meson

Measurements are reported of p?p total cross sections from 388 to 599 MeV/c in small momentum steps. Statistical errors are typically ±0.4%and the normalisation uncertainty is ±0.7%. There is no evidence for the “S-meson”.     

Study on the aggregation of teicoplanin

The aggregation of teicoplanin was studied in four solutions: 0.06 M phosphate buffers pH 4.3 and 6.3, both with and without 10% (v/v) of acetonitrile. Conductometry, capillary electrophoresis, cyclic voltammetry, and static light scattering were employed to determine the critical micelle concentration (CMC) of teicoplanin. Dynamic light scattering was used to give an additional information on the size and the size distribution of the particles formed. While the CMC was found in solutions without acetonitrile, attempts to detect any CMC failed in solutions containing acetonitrile. The results point out to different solvating mechanism in solutions with and without acetonitrile, leading to two different schemes of association.     

Suppression of Different Phases of Systemic Contact Hypersensitivity by Urocanic Acid Oxidation Productsfn1

On exposure to UV‐B, the epidermal component trans‐urocanic acid (UCA) is not only photoisomerized into cis‐ UCA but will also, at least in part, be photooxidized into UCA oxidation products (UOPs). We hypothesized that UOPs can mimic UV‐induced systemic immunosuppression comparable to the suppressive properties already established for cis‐UCA. A crude mixture of UOPs showed a significant suppression of the sensitization phase of the systemic contact hypersensitivity (CHS) response to picryl chloride (PCI). Three of the UOPs were selected for this study: imidazole‐4‐carboxylic acid (ImCOOH), immidazole‐4‐carboxaldehyde (ImCHO) and imidazole‐4‐acetic acid (ImAc). Effects on the sensitization, elicitation and postelicitation phases of CHS to PCI in BALB/c mice were studied and compared with the effects of cis‐UCA. ImCHO was equally effective at suppressing the sensitization phase as cis‐UCA. The triplet combination of the imidazoles (1:1:1) showed more pronounced suppression than that induced by cis‐UCA. The most effective compounds for the suppression of the elicitation phase appeared to be ImAc and cis‐UCA. Significant suppression of the postelicitation phase was only obtained with the triplet combination of ImCHO, ImCOOH and ImAc, the combination that appeared to be effective at all three tested phases. Because these three UOPs are present in UV‐B‐exposed human stratum corvneum, these compounds may play a role in UV‐B‐induced immunosuppression.     

Characterization of cyclofructan-based chiral stationary phases by linear free energy relationship

Cyclofructans (CFs), a new class of chiral selectors, have been recently introduced for application in liquid chromatography and capillary electrophoresis. So far, derivatized CFs have performed interesting separation possibilities for a variety of compounds. The current work is focused on characterization of three different CF-based chiral stationary phases (CF-based CSPs), i.e. isopropyl carbamate cyclofructan 6 (IP-CF6), R-naphthylethyl carbamate cyclofructan 6 (RN-CF6) and dimethylphenyl carbamate cyclofructan 7 (DMP-CF7). The linear free energy relationship (LFER) model was used to reveal the dominant interactions participating in the complex retention mechanism. A set of 44 different test solutes, with known solvation parameters, was used to determine the regression coefficients of the LFER equation under two mobile-phase compositions in normal separation mode. The LFER results showed that hydrogen bond acidity, hydrophobicity and dipolarity/polarizibility mostly affect the retention and separation process on the CF-based columns in the studied separation systems.     

Toughness of polymeric networks: The limited importance of crosslink density

Four series of polymeric model networks were prepared with bimodal chain length distribution between crosslink points and two types of dangling chains as network defects. In the last series the crosslink density was changed without a large change in the chemical composition. The fracture toughness of those networks were compared with that of the defect–free networks. The fracture toughness of the various networks is surprisingly little influenced by the introduction of defects. Neither bimodality, nor dangling chains, nor a high sol fraction alters the toughness of the network. A good correlation between K_Ic and the weight fraction of polyether is observed. A much smaller dependence of K_Ic on the strand density can be deduced. The yield stress is high and approximately invariant for all systems studied. It is concluded that the toughness of a polymeric network does not seem to be influenced by its perfection and only to a small extent by its degree of crosslinking.