Synthesis of 6-Heterocyclically Appended Tri- O-methyl Protected 6-Desmethyl Emodin Derivatives

A convenient synthesis of several 6-heterocyclically appended tri-O-methyl 6-desmethyl emodin derivatives including the tetrazolyl, oxazolyl, oxazolinyl, benzimidazolyl, benzoxazolyl, and benzothiazolyl derivatives of potential biological and medicinal interest was achieved starting from the tri-O-methyl protected emodin aldehyde or nitrile. In addition, these derivatives could serve as synthons for heterocyclic hypericin derivatives.     

Three-dimensional structure of the actinomycins.

Many complicated three-dimensional structures can be formulated for the actinomycins, red chromopeptide antibiotics distinguished by pronounced antineoplastic activity, because of their unique constitutional type. Since these structures largely determine the specific activity of the actinomycin molecules in the host cells, knowledge of the structural forms occurring naturally in solution is a decisive prerequisite for detailed insight into the mode of biological action of the actinomycins. Investigations by several methods have shown that, in spite of their deviating primary structures, all important actinomycins assume only one very characteristic, pseudo-C₂-symmetrical, and remarkably stable three-dimensional structural type.     

Pragmatic Studies on Protein-Resistant Self-Assembled Monolayers

Summary. The present study describes new synthetic routes to oligo(ethylene glycol)-terminated alkanethiols (OEG-ATs), starting from α,ω-dibromoalkanes, which are reacted either with OEG or with trityl mercaptan in the first step. In addition to these ether conjugates of OEG and AT, analogous ester and amide conjugates were prepared by established procedures. All thiols were used to form self-assembled monolayers (SAMs) on cleaned gold surfaces and these were stored for 1–2 weeks under water at 4°C before the extent of nonspecific protein adsorption was tested with IgG, BSA, and lysozyme at 1 mg cm⁻³ protein concentration in phosphate-buffered saline. Under these practice-oriented testing conditions, SAMs with tri(ethylene glycol) chains (EG ₃) exhibited nonsatisfactory protein resistance, in sharp contrast to EG ₄ or longer OEG chains. The effectiveness of EG ₃ was partially restored when they were linked to a long acyl chain (16-mercaptohexadecanoic acid) instead of 12-mercaptododecane or 11-mercaptoundecane. Furthermore it was found that (i) SAM formation at 20 μM thiol versus 500 μM OEG-AT gave identical results, (ii) gel-filtered proteins were much less adsorbed than the unpurified commercial products, and (iii) the method for gold-precleaning was very critical. In conclusion, this study offers convenient synthetic routes to OEG-AT and helps to choose molecules and procedures for reliable preparation of protein-resitant SAMs with prolonged stability during storage.     

In situ investigation of laser-induced ignition and the early stages of methane-air combustion at high pressures using a rapidly tuned diode laser at 2.55 microm

The laser-induced ignition of methane/air-mixtures at elevated pressures was investigated by an absorption spectroscopic technique. A room temperature continuous wave InGaAsSb/AlGaAsSb quantum well ridge diode laser was wavelength tuned around 2.55 mum by periodically modulating the injection current from 0 to 174 mA at a 5 kHz repetition rate. The laser heat sink temperature was fixed at 291 K. The infrared laser beam was sent through the pressurized combustion vessel perpendicularly to the igniting laser beam (Nd:YAG laser, 10 ns pulse duration, 20 mJ) at the position of the ignition spark. Fuel-rich to fuel-lean mixtures of methane/air (air equivalence ratio 0.89, 1.06, 1.42, 2.50) were investigated at initial pressures of up to 3 MPa. The initial temperature was 473 K, the volume of the combustion vessel 0.9x10(-3) m(3). The formation of water vapor in the vicinity of the laser spark was tracked by the diode laser. The time resolution of the measurements was 0.2 ms for a total continuous measurement time of up to 1 s. In this way, the laser-induced ignition and its accompanying effects could be investigated on a time scale spanning four orders of magnitude. Apart from the absorbance of water vapor which could be determined semi-quantitatively (due to the effects of severe pressure broadening at high pressures and the ignorance of the exact temperature distribution after ignition), the emissions from the flame (broadband, 1-10 mum) and a gas inhomogeneity index were recorded. The gas inhomogeneity index was obtained by extracting a frequency variable from the time-dependent fluctuations of the transmitted laser intensities and calculating its derivation. The absorbance of water vapor, the emissions from the flame and the gas inhomogeneity index were found to be a powerful tool to characterize laser-induced ignition. Major implications of in situ species concentration measurements at high pressures for the design and development of high-load combustors are presented.     

The Effect of Styrene-Butadiene-Styrene Modification on the Characteristics and Performance of Bitumen

Summary. In order to cover the effect of styrene-butadiene-styrene (SBS) modification on the characteristics of bitumen, two types of bitumen, one plain bitumen, and one polymer modified bitumen produced with the plain bitumen as base material were characterized in terms of chemical composition, microstructure, micromechanical properties, and thermoanalytical behavior. In order to determine the complex chemical composition of bitumen, elemental analysis, gel permeation chromatography, and the Iatroscan method were employed. Microstructure and micromechanical properties were determined using an environmental scanning electron microscope and the nanoindentation technique. Modulated differential scanning calorimetry was used to determine phase-change temperatures and endo/exotherms associated with molecular movement. The addition of SBS leads to different rheological behavior over the whole service temperature range. This is reflected in bitumen chemistry by differences in elemental composition and molecular weight distribution with much higher M _w values for the modified bitumen. Accordingly, the polymer leads to a shift in molecular fractions. Electron microscopy reveals two distinct phases building up the bitumen microstructure. The chosen mode of quantification leads to similar material parameters for both bitumens, which is explained by the use of the same base material. In contrast, nanoindentation delivers viscosities in the micro-range corresponding to large-scale rheological properties. Modulated differential scanning calorimetry indicates two glass transitions corresponding with two material phases also confirmed by other experiments. Due to modification, these glass transitions depart from each other and the amount of the two material phases changes, correlating with the shift in molecular fractions observed in Iatroscan analyses.     

A Route to Amino Functionalized Hypericin Derivatives and their Chemical and Photochemical Properties Pertaining to Photodynamic Therapy

Syntheses of amino functionalized hypericin derivatives could be achieved starting from the recently prepared emodin derived 1,3,8-trimethoxy-6-amino-9,10-anthraquinone. Our strategies for the preparation of 10,11-didemethyl-10,11-diaminohypericin, 10,11-didemethyl-10,11-di(acetylamino) hypericin, and its hypericinoidic diazepine derivative include synthetical modifications on the levels of the anthraquinone, anthron, and the phenanthroperylenequinone system itself. The chemical as well as photochemical properties of these unique hypericin derivatives, which might constitute new photodynamic therapy agents, are reported.