A mathematical evaluation of dose-dependent PpIX fluorescence kinetics in vivo

The in vivo pharmacokinetics of protoporphyrin IX (PpIX) after administration of 5-aminolevulinic acid (ALA) cannot be described accurately by mathematical models using first-order rate processes. We have replaced first-order reaction rates by dose-dependent (Michaelis-Menten [MM]) reaction rates in a mathematical compartment model. Different combinations of first-order and dose-dependent reaction rates were evaluated to see which one would improve the goodness-of-fit to experimentally determined in vivo PpIX fluorescence kinetics as a function of concentration. The mathematical models that were evaluated are all based on a three-compartment model for drug distribution, conversion to PpIX and subsequent conversion to heme. Implementation of dose-dependent reaction rates improved the goodness-of-fit and enabled interpolation to other drug doses. For most data sets the time constant for delivery to the target cells turned out to be dose dependent. For all data sets the use of MM rates for the conversion of ALA to PpIX yielded better fits. The clearance of PpIX turned out to be a first-order process for all doses and types of administration. Fluorescence curves measured on a specific tissue type but obtained in different studies with different measurement techniques could be described with a single set of parameters.     

Facile chemoselective synthesis of dehydroalanine-containing peptides

Useful methodology is described for the synthesis of dehydroalanine residues (II) within peptides. The unnatural amino acid (Se)-phenylselenocysteine (I) can be incorporated into growing peptide chains via standard peptide synthesis procedures. Subsequent oxidative elimination affords a dehydroalanine at the desired position. The oxidation conditions are mild and tolerate functionalities commonly found in peptides, including variously protected cysteine residues. To illustrate its utility, cyclic lanthionines have been synthesized by this method.     

A ten-residue fragment of an antibody (mini-antibody) directed against lysozyme as ligand in immunoaffinity chromatography

The interaction between an antibody molecule and a protein antigen is an example of "natural" protein modelling. Amino acids of the antigen-binding site consisting of three hypervariable segments (L1, L2, L3) of the light (L) and three (H1, H2, H3) of the heavy (H) chain of an antibody molecule interact with amino acids present in an epitope of a protein. A ten-residue peptide was synthesized with an amino acid sequence analogous to the hypervariable L3 segment of a monoclonal antibody directed against lysozyme. The peptide was immobilized on CH-Sepharose 4B and the affinity adsorbent was used to purify lysozyme added to a detergent extract of insect cells infected with a recombinant baculovirus. This methodology may also be applicable to other antigen-antibody combinations, in immunoaffinity chromatography for selective purification of a protein or in an immunosensor for detection of a protein.     

Time-dependent pump-probe spectra of NeBr2

Time- and frequency-resolved pump-probe measurements on NeBr2 have been performed to better characterize its fragmentation dynamics on the B electronic state for vibrational levels in the energy region of the transition from direct vibrational predissociation to intramolecular vibrational relaxation dynamics. Above nu'=20 of the Br2 stretching mode, it was observed that the dependence of lifetime on the vibrational quantum number deviates from the energy-gap law by leveling off in the range of 10 psE transitions of the complex. These transitions are shifted 20 cm(-1) to lower energy from the free Br2 resonances, indicating an E state Ne-Br2 bond energy of 82 cm(-1). Measurements of NeBr2 vibrational predissociation via the delta nu=-2 channel were also performed for nu'=27, 28, and 29. The closing of the delta nu=-1 channel leads to an increase in the lifetimes of these vibrational levels. A new Nd:yttrium aluminum garnet pumped dual optical parametric oscillator/optical parametric amplifier system is described that allows us to conveniently record time-delayed pump-probe spectra with 2-cm(-1) spectral resolution and 15-ps time resolution.     

STRUCTURE AND PHOTOBIOLOGICAL ACTIVITY OF 7-CHLORO-1,4-BENZODIAZEPINES. STUDIES ON THE PHOTOTOXIC EFFECTS OF CHLORDIAZEPOXIDE, DESMETHYLCHLORDIAZEPOXIDE AND DEMOXEPAM USING A BACTERIAL INDICATOR SYSTEM

The photobiological activity of chlordiazepoxide, an active ingredient of the drug Librium, which is known to induce phototoxic effects, and two of its metabolites, desmethylchlordiazepoxide and demoxepam, was investigated. Upon irradiation of these biologically active compounds with longwave UV light, the main decomposition product formed is an oxaziridine. Using a strain of Salmonella typhimurium as a test organism for cytotoxicity, it could be demonstrated that not only the drug itself, but also the major mammalian metabolites are phototoxic and, furthermore, that the respective oxaziridines are responsible for the toxic effects found upon irradiation. A close relationship appears to exist between the phototoxicity of the nitrones and the toxicity in the dark of their respective oxaziridines. Investigations of the photobiological activity of a few closely structurally related benzodiazepines could establish that a 4-oxide moiety in the benzodiazepine nucleus is the structural characteristic responsible for the appearance of phototoxicity; in those compounds which contain a 4-oxide in the benzodiazepine nucleus, photo-decomposition to a toxic oxaziridine is observed, while the analogues lacking the 4-oxide moiety do not show this characteristic and, therefore, no phototoxic effects can be observed. Finally, mutagenicity tests performed with the same bacterial indicator as used for phototoxic studies, and including chlorpromazine as a positive reference compound, indicate that under the present experimental conditions photoproducts formed upon irradiation of chlordiazepoxide and its metabolites with longwave UV light do not exert a mutagenic effect.     

Unique structural properties of the Mg-Al hydrotalcite solid base catalyst: an in situ study using Mg and Al K-edge XAFS during calcination and rehydration

The changes in the layered structure of Mg-Al hydrotalcite (Mg/ Al = 2) during heat treatment have been investigated by using in situ XAFS simultaneously at the Mg and Al K-edges. The development of unique in situ instrumentation allowed the coordination environments at both the Mg and Al centers to be monitored as a function of the temperature and heat treatment. The results of this study show that the hydrotalcite structure is highly flexible, and should lead to the further development of hydrotalcites as new solid basic catalysts. Moreover, the Mg and Al cations in the cation layers show different behavior as a function of temperature. The coordination of some octahedral Al ions decreases already at a temperature of 425 K, whereas the coordination about Mg does not show any modification at this temperature. However, hydrotalcite treated at 425 K, followed by cooling down to room temperature resulted in a complete reversal to the original octahedral Al coordination. It is proposed that Al-OH bond breakage occurs at 425 K, without the evolution of H2O. This bond is restored after cooling to room temperature. The actual dehydroxylation of hydrotalcite commences between 425 and 475 K, as indicated by a change in coordination of both the Mg and Al centers. This is accompanied by the evolution of H2O molecules and the changes are hence irreversible without the presence of excess water. Heat treatment at 725 K leads to the development of an MgO-like phase (octahedral Mg) and a mixed octahedral/tetrahedral Al phase. A subsequent rehydration at room temperature entirely restores the original coordination about the Al and Mg centers of hydrotalcite to a distance of 15 A, to which XAFS spectroscopy is sensitive.     

Effect of pressure on free-radical copolymerization kinetics. I. A concept of additivity of partial molar volumes of activation

A short review of the effect of pressure on copolymerization kinetics shows the necessity of simple models for a better understanding of activation volumes. Therefore, a simple concept, possibly generally valid for free-radical polymerization, is proposed, based on the assumption that molar volumes of activation can be expressed as an addition of a characteristic radical and a monomer contribution, regardless of the combination involved. The scheme may facilitate the visualization of the transition state and contribute to the understanding of reaction mechanisms of radical polymerizations. Ethylene–vinyl acetate copolymerization at 62°C with tert-butyl alcohol as solvent agrees with the proposed scheme, appearing from the pressure independence of the product of reactivity ratios at the different levels (35,600, and 1200 kg/cm²). Implicitly it can be shown that an ethylene monomer contributes about 2 cm³/mole more to the activation volumes of the propagation reactions than does the vinyl acetate monomer, whereas for the radicals the difference of the respective contributions to the activation volumes is opposite in sign.     

über Katalysatoren- und Fermentmodelle (1)

Ohne Zusammenfassung Die Arbeit wurde aus Mitteln des Marshall-Planes (ERP-Mittel) und mit Spenden aus dem „Fonds Chemie“ ausgeführt. Wir sprechen den zust?ndigen Stellen für die Gew?hrung der Beihilfe unseren verbindlichsten Dank aus. Der Deutschen Forschungsgemeinschaft danken wir für die überlassung einer Ultrazentrifuge, den Behring-Werken für die uns zur Verfügung gestellten Serumalbumin- und -globulin-Pr?parate.