Synthesis and chemistry of N-benzoyl-O- [N'-benzoyl-l-phenylalanyl]-l-phenylalaninol,the major mycelial metabolite of penicillium canadense

The structure of the title compound was established by evidence including total and partial hydrolyses and a stereospecific synthesis. Debenzoylation using triethyloxonium fluoroborate was accompanied by rearrangement to the amidoalcohol 12 (desacetylasperglaucide).     

The application of modulated differential scanning calorimetry to the glass transition

The modulated differential scanning calorimetry (MDSC) technique superimposes upon the conventional DSC heating rate a sinusoidally varying modulation. The result of this modulation of the heating rate is a periodically varying heat flow, which can be analysed in various ways. In particular, MDSC yields two components (reversing and non reversing) of the heat flow, and a phase angle. These each show a characteristic behaviour in the glass transition region, but their interpretation has hitherto been unclear. The present work clarifies this situation by a theoretical analysis of the technique of MDSC, which introduces a kinetic response of the glass in the transition region. This analysis is able to describe all the usual features observed by MDSC in the glass transition region. In addition, the model is also able to predict the effects of the modulation variables, and some of these are discussed briefly.Financial support has been provided by the DGICYT (Project no.PB93/1241). J.M.H. wishes to acknowledge financial assistance for a sabbatical period from the Generalitat de Catalunya.     

Electrochemiluminescence enzyme immunoassay for TNT

Details of an electrochemiluminescence (ECL) enzyme immunoassay for TNT (2,4,6-trinitrotoluene) are reported. The design and construction of a computer controlled flow injection electrochemiluminometer in which the immunoassays are carried out is described. This system is used to select and pump solutions through a flow cell, which contains a gold working electrode as part of a three-electrode arrangement. The deposition of a re-usable immunosorbent dextran surface anchored to a gold surface in the flow cell by chemiadsorbed thiol groups is described. Antibodies are labeled with the enzyme glucose oxidase and used in competitive immunoassays in which the separation step is carried out by concentrating unbound antibodies on the immunosorbent surface. Hydrogen peroxide generated by the enzyme label when glucose is pumped through the flow cell is detected using luminol ECL. Light intensity was inversely proportional to the concentration of TNT in the sample in the range 0-100 ppb. The results are compared with colorimetric ELISA's carried out using the same reagents, and potential for developing a portable instrument for use in the field is discussed.     

A two-plasmid system for the glycosylation of polyketide antibiotics: bioconversion of -rhodomycinone to rhodomycin D

Background: The biological activity of many microbial products requires the presence of one or more deoxysugar molecules attached to agylcone. This is especially prevalent among polyketides and is an important reason that the antitumor anthracycline antibiotics are avid DNA-binding drugs. The ability to make different deoxyaminosugars and attach them to the same or different aglycones in vivo would facilitate the synthesis of new anthracyclines and the quest for antitumor drugs. This is feasible using the numerous bacterial genes for deoxysugar biosynthesis that are now available. Results: Production of thymidine diphospho (TDP)- -daunosamine (dnm), the aminodeoxysugar present in the anthracycline antitumor drugs daunorubicin (DNR) and doxorubicin (DXR), and its attachment to -rhodomycinone to generate rhodomycin D has been achieved by bioconversion with a strain of Streptomyces lividans that bears two plasmids. One contained the Streptomyces peucetius dnmJVUZTQS genes plus dnmW (previously named dpsH and considered to be a polyketide cyclase gene), dnrH, which is not required for the formation of rhodomycin D, and dnrl, a regulatory gene required for expression of the dnm and drr genes. The other plasmid had genes encoding glucose-1-phosphate thymidylyltransferase and TDP-glucose-4,6-dehydratase (dnmL and dnmM, respectively, or mtmDE, their homologs from Streptomyces agrillaceus) plus the drrAB DNR/DXR resistance genes. Conclusions: The high-yielding glycosylation of the aromatic polyketide -rhodomycinone using plasmid-borne deoxysugar biosynthesis genes proves that the minimal information for -daunosamine biosynthesis and attachment in the heterologous host is encoded by the dnmLMJVUTS genes. This is a general approach to making both known and new glycosides of anthracyclines, several of which have medically important antitumor activity.     

The discrete plateau problem: Convergence results

We solve the problem of finding and justifying an optimal fully discrete finite element procedure for approximating minimal, including unstable, surfaces. In a previous paper we introduced the general framework and some preliminary estimates, developed the algorithm and give the numerical results. In this paper we prove the convergence estimate.

     

Developmental toxicity of benzotriazole in the protochordate Ciona intestinalis (Chordata, Ascidiae)

Benzotriazoles (BT) are applied as anticorrosive and de-icing agents and have been detected in a variety of aquatic ecosystems and municipal wastewater effluents. We have assessed the developmental effects of benzotriazole (CAS number 95-14-7) to the marine invertebrate Ciona intestinalis (Chordata, Ascidiae). At 15 ± 1 °C, the 24 h No-Observed Effect Concentration (NOEC) and Lowest Observed Effect Concentration (LOEC) values based on embryo morphological development were 100 and >100 mg L⁻¹, respectively (nominal concentration under static conditions). After 48 h, the NOEC and LOEC values were 10 and 32 mg L⁻¹, respectively. Light and electron microscopy studies on benzotriazole-exposed larva indicated that the primary target cells were the extra-embryonic test cells, which are known to play a significant apoptotic role during ascidian metamorphosis. The visible decline of test cells in benzotriazole-exposed larvae raises the possibility that the compound interferes with the regulation of embryo development in protochordates such as C. intestinalis. Further research is warranted to assess the potential longer term sublethal impacts of benzotriazole in aquatic organisms.     

Kalk

Ohne Zusammenfassung     

Isobaric thermal behavior of glasses during uniform cooling and heating. III. Predictions from the multiparameter KAHR model

The behavior of the multiparameter KAHR model (put forward by Kovacs, Aklonis, Hutchinson, and Ramos) has been investigated using a single-box retardation spectrum to describe the kinetics of volume and enthalpy recovery of glasses in three-step thermal cycles involving colling, isothermal annealing, and subsequent reheating. It has been shown that during the heating stage, the system may display up to three peaks in the expansion coefficient and the specific heat. The shifts of the peak temperatures T_p with respect to each of the four experimental variables Y_i defining the thermal history are analyzed systematically in terms of a set of reduced variables, scaled by two of the material constants of the system. These shifts, from which the various partial derivatives (?T_p/?Y_i)_j≠i are estimated, are determined for five values of another material parameter x, which characterizes the relative contributions (O ≤ x ≤ 1) of temperature and structure to the retardation times. the results show that the upper peak is always small and is insensitive to the characteristics of the spectrum and to the value of x, while the relevant peak temperature depens only slightly on the cooling and heating rates. On the Other hand, the magnitude and the shifts of the main peak depend on all the experimental variables and the material constants in a rather complex manner. It is shown, however, that in limiting situations, involving fast heating of well-stabilized glasses, the shifts of the relevant peak temperature T?all reduce to a linear function of x^?1. since this relationship is rather insensitive to the shape of the spectrum, the experimental determination of any one of the nonzero partial derivatives of T? provides a simple means for an independent estimate of the value of the important material constant x. Finally, the shifts of the upper and main peaks relative to each other will be analyzed in terms of the pertinent experimental variables and compared with actual data reported in the literature for polymer glasses.     

Quantitative test of thermal field theory for Bose-Einstein condensates

We present numerical results from a second-order quantum field theory of Bose-Einstein condensates applied to the 1997 JILA experiment [Phys. Rev. Lett. 78, 764 (1997)]]. Good agreement is found for the energies and decay rates for both the lowest-energy m=2 and m=0 modes. The anomalous behavior of the m=0 mode is due to experimental perturbation of the noncondensate. The theory is gapless and includes the coupled dynamics of the condensate and thermal cloud, the anomalous pair average, and all relevant finite size effects.     

A frequency-modulated quantum-cascade laser for spectroscopy of CH4 and N2O isotopomers

We report the development of a novel laser spectrometer for high-sensitivity detection of methane and nitrous oxide. The system relies on a quantum-cascade laser source emitting wavelength of around 8.06 microm, where strong fundamental absorption bands occur for the considered species and their isotopomers. The detection technique is based on audio-frequency and radio-frequency modulation of laser radiation. First experimental tests have been performed to estimate the achievable detection limits and the signal reproducibility levels in view of possible measurements of (13)C/(12)C, (18)O/(16)O, (17)O/(16)O and (15)N/(14)N isotope ratios.