Die Molekulare Zusammensetzung von erstarrten Phosphor-Schwefel-Schmelzen und die Kristallstruktur von β-P4S6

The Molecular Composition of Solidified Phosphorus-Sulfur Melts and the Crystal Structure of β-P₄S₆ Phosphorus sulfur melts were annealed for one week at 673 K and then quenched in ice water. The solids were dissolved in CS₂ and the concentrations of phosphorus sulfides were determined by ³¹P NMR spectroscopy. Samples containing between 44 and 70 mol% sulfur dissolved completely in CS₂. Between 0 and 42 mol% remains an insoluble residue of red phosphorus. Above 72 mol% it consisted of sulfur chains linked by phosphorus atoms. The solutions contained mainly the congruently melting compounds P₄S₃, P₄S₇, and P₄S₁₀ having maximum concentrations at their stoichiometric compositions. Other compounds P₄S_n (n = 4–9) which decompose on heating, according to the phase diagram, were also found in surprisingly high concentrations. One of these was β-P₄S₆ which crystallizes in the monoclinic space group P2₁/c with the lattice parameters a = 702.4(2), b = 1 205.6(2), c = 1 148.9(6) pm and β = 103.4(2)°. Reaction of white phosphorus with sulfur was also investigated. In contrast to the results of previous authors, who described the system P₄–S₈ below 373 K as eutectic, we found that the elements reacted below this temperature.     

Evaluation of wet oxidation pretreatment for enzymatic hydrolysis of softwood

The wet oxidation pretreatment (water, oxygen, elevated temperature, and pressure) of softwood (Picea abies) was investigated for enhancing enzymatic hydrolysis. The pretreatment was preliminarily optimized. Six different combinations of reaction time, temperature, and pH were applied, and the compositions of solid and liquid fractions were analyzed. The solid fraction after wet oxidation contained 58–64% cellulose, 2–16% hemicellulose, and 24–30% lignin. The pretreatment series gave information about the roles of lignin and hemicellulose in the enzymatic hydrolysis. The temperature of the pretreatment, the residual hemicellulose content of the substrate, and the type of the commercial cellulase preparation used were the most important factors affecting the enzymatic hydrolysis. The highest sugar yield in a 72-h hydrolysis, 79% of theoretical, was obtained using a pretreatment of 200°C for 10 min at neutral pH.     

Analysis of Methylcitric Acid by Enantioselective Multidimensional Gas Chromatography-Mass Spectrometry

Methylcitric acid (2-hydroxybutane-1,2,3-tricarboxylic acid–MCA) is a structural analogue of citric acid, but due to an additional methyl group it is a chiral molecule with two stereogenic centers and thus four stereoisomers are conceivable. MCA occurs naturally as prominent metabolite in body fluids of patients with inherited metabolic diseases such as propionic acidemia, methylmalonic aciduria, or holocarboxylase synthetase deficiency. Therefore methylcitric acid is considered to be an important diagnostic marker for these diseases. MCA is most likely produced from accumulated propionyl-CoA in these diseases by the enzyme si-citrate synthase from the citric acid cycle; however, there are other enzymes known which could catalyze the same reaction with different stereoselectivity, such as re-citrate synthase or the more specific enzyme methylcitrate synthase, found in microorganisms. Almost all methods dealing with MCA in the literature are non-enantioselective. For that reason there is no information about occurrence of MCA enantiomers in healthy people, patients with propionic acidemia, methylmalonic aciduria, or holocarboxylase synthetase deficiency and about value of enantiomeric distribution for diagnosis and long-term treatment. The enantioselective analysis of MCA as corresponding trimethyl ester was achieved by enantioselective multidimensional gas chromatography coupled with mass spectrometry using heptakis-(2,3-di-O-methyl-6-O-tert-butyl-dimethylsilyl)-β-cyclodextrin as chiral stationary phase. The described method allows a reliable screening of MCA in complex matrices like urine without time consuming sample preparation and with mass selective detection. During this investigation urine samples from various patients and healthy controls were analyzed. As concluded, MCA is a good diagnostic marker and can be easily measured by the method presented. Only the two stereoisomers (2S,3R) and (2S,3S) were detectable in patients and healthy controls. The varying ratios of these stereoisomers cannot presently be correlated with the health status of patients, although there are some indications that this might be possible. However, the quantitative levels of MCA, determined as the ratio of MCA absolute peak area divided by 1,000 to the creatinine contents of urine samples in this investigation, showed a dependence on the state of health and MCA would thus also be a possible marker for long-term treatment. Such a substance is of major interest nowadays since there are different studies searching for such a long-term marker in propionic acidemia or methylmalonic aciduria.     

Synthesis of cyclobutylideneacetic esters via aluminum chloride promoted [2+2] cycloadditions of ethyl 2,3-butadienoate to olefins

In the presence of AlCl₃, ethyl 2,3-butadiemoate reacts with a variety of olefins, including simple unactivated cycloalkenes, to give cyclobutylideneacetic esters at room temperature. The cycloaddition is regioselective and stereoselective.     

Microarray technology as a universal tool for high-throughput analysis of biological systems

Over the last years microarray technology has become one of the principal platform technologies for the high-throughput analysis of biological systems. Starting with the construction of first DNA microarrays in the 1990s, microarray technology has flourished in the last years and many different new formats have been developed. Peptide and protein microarrays are now applied for the elucidation of interaction partners, modification sites and enzyme substrates. Antibody microarrays are envisaged to be of high importance for the high-throughput determination of protein abundances in translational profiling approaches. First cell microarrays have been constructed to transform microarray technology from an in vitro technology to an in vivo functional analysis tool. All of these approaches share a common prerequisite: the solid support on which they are generated. The demands on this solid support are thereby as manifold as the applications themselves. This review is aimed to display the recent developments in surface chemistry and derivatization, and to summarize the latest developments in the different application areas of microarray technology.