Improving random mutagenesis by purification of the oligonucleotide variants

An oligonucleotide-based mutagenesis method is presented where, contrary to most classical mutagenic approaches, preselection of the variants is performed at the oligonucleotide level to avoid cloning of non-desired sequences. The method relies on the generation of differentially phosphate-protected oligonucleotides. Protection of the phosphates is accomplished by substoichiometric incorporation of an Fmoc-protected and n-propyl-protected trinucleotide phosphoramidite during ordinary oligonucleotide assembly. Instead of the alkali-labile beta-cyanoethyl group introduced in ordinary assembly, the trinucleotide introduces the alkali-stable n-propyl group. As a result, single mutants carry three ionic phosphates less than the wild-type sequence, double mutants carry six ionic phosphates less and so on. This difference in ionic ratio enables separation of the variants by conventional polyacrilamide gel electrophoresis. In the exemplified library described herein, two sub-populations containing mainly triple and quadruple mutants were selected out of five possible sub-populations.     

A fluoristatic method for the determination of alkaline phosphatase,sorbitol dehydrogenase,peroxidase and pseudocholinesterase

Instrumentation for fluoristatic procedures and several applications are described. The simple device is used to determine alkaline phosphatase (7–150 mU), sorbitol dehydrogenase (1–10 mU) and peroxidase (0.5–5 mU) with fluorescent substrates and pseudocholinesterase (10–100 mU) with a non-fluorescent substrate and erythrosine as fluorescence quencher. The method is of special interest for the determination of enzymes with low substrate concentrations.     

Eine thermometrisch-kinetische methode zur bestimmung von kupfer und cyanid mit hilfe der kupfer-katalysierten zersetzung von wasserstoffperoxid

The copper-catalyzed decomposition of hydrogen peroxide is retarded by cyanide. The oxidation of cyanide by hydrogen peroxide is likewise catalyzed by copper ions. The decomposition reaction of H₂O₂; can be followed thermometrically. Therefore, at a known copper concentration an unknown amount of cyanide can be determined from the retardation time; and an unknown amount of copper can be determined by adding a known amount of cyanide. Moreover, after the end of the retardation time, unknown copper concentrations can also be determined from the slope of the temperature curve (tana). Copper was determined in the range 4–40 μg, and cyanide in the ranges 3–30, 6–60 and 8–80 μg.     

Energetic mapping of Ni catalysts by detailed kinetic modeling

Temperature-programmed desorption (TPD) of CO has been performed on supported and unsupported nickel catalysts. The unsupported Ni catalyst consists of a Ni(14 13 13) single crystal which has been studied under ultrahigh vacuum conditions. The desorption energy for CO at low CO surface coverage was found to be 119 kJ/mol, and the binding energy of C to the Ni(111) surface of the crystal was 703 kJ/mol. The supported catalysts consist of nickel supported on hydrotalcite-like compounds with three different Mg2+/Al3+ ratios. The experimental results show that for the supported Ni catalysts TPD of CO leads to desorption of both CO and CO2, with the latter being dominant. Dissociation of CO takes place, and considerable amounts of residue C are left on the surface. The residue C is removed by temperature-programmed oxidation (TPO). The results show that a low Mg2+/Al3+ ratio in the hydrotalcite precursor seems to result in more steplike sites, kinks, and defects for carbon monoxide dissociation. A detailed kinetic modeling of the TPO results based on elementary reaction steps has been conducted to give an energetic map of supported Ni catalysts. Experimental results from the ideal Ni surface fit nicely with literature values, providing useful information for identifying active sites on supported Ni catalysts.     

Zur Darstellung unsymmetrisch substituierter Bis(organylamino) silane

The title compoundsR ₂Si(NHR ¹) (NHR ²) (B) were prepared according to Equ. (2) and (3) and via formerly unknown diphenyl-chloro-organylaminosilanes (A) as intermediates. The complex course of formation ofB in competition withR ₂Si (NHR ¹)₂ (C) andR ₂Si(NHR ²)₂ (D) (Scheme 1, Equ. (4)–(7), Table 2) was investigated in detail. Results of thermal rearrangement ofB are given in Table 5. Five novelA and six novelB compounds are confirmed by properties, elemental and structural data (Tables 1, 3 and 4).

Mit Auszügen aus der DissertationS. Klemke, Techn. Univ. Braunschweig 1978.     

On the Factors behind the Photocatalytic Activity of Graphene Quantum Dots for Organic Dye Degradation

Graphene quantum dots (GQD) are promising visible-light photocatalysts for organic dye degradation. Besides having improved visible-light activity compared with commercial TiO₂, GQD are versatile photocatalysts as their chemical composition and, consequently, optical properties can be tuned synthetically, with a direct impact on photoactivity. However, there is a lack of systematic comparative studies to benchmark GQD photocatalytic performance and relate it to their intrinsic properties. This is undertaken in this work for three types of GQD, which are prepared using well-established synthetic methods representative of top-down and bottom-up approaches using different precursors. Resulting GQD are similar in size but differ in chemical composition, crystallinity, bandgap (ranging from 2.63 to 3.63 eV) and visible-light absorptivity. Photoactivity measurements under comparable experimental conditions (visible-light illumination) reveal enormous activity differences for rhodamine B (RhB) degradation, with up to tenfold higher degradation yields at the same time for certain GQD types. The enormous influence of intrinsic and tunable GQD factors, like visible-light absorptivity and surface charge, on their photoactivity for the degradation of organic dyes is demonstrated, highlighting the importance of tailoring such parameters for enhanced photocatalytic performance. A plausible mechanism for GQD-catalyzed photodegradation of RhB is also proposed.     

Controlled Growth of SrxBa1−xNb2O6 Hopper- and Cube-Shaped Nanostructures by Hydrothermal Synthesis

Controlling the shape and size of nanostructured materials has been a topic of interest in the field of material science for decades. In this work, the ferroelectric material Sr_xBa_1−xNb₂O₆ (x=0.32–0.82, SBN) was prepared by hydrothermal synthesis, and the morphology is controllably changed from cube-shaped to hollow-ended structures based on a fundamental understanding of the precursor chemistry. Synchrotron X-ray total scattering and PDF analysis was used to reveal the structure of the Nb-acid precursor, showing Lindqvist-like motifs. The changing growth mechanism, from layer-by-layer growth forming cubes to hopper-growth giving hollow-ended structures, is attributed to differences in supersaturation. Transmission electron microscopy revealed an inhomogeneous composition along the length of the hollow-ended particles, which is explained by preferential formation of the high entropy composition, SBN33, at the initial stages of particle nucleation and growth.     

Untersuchungen zur Struktur des Triglycinsulfats mit Hilfe der hochauflösenden magnetischen Kernresonanzspektroskopie im Festkörper

Investigations of the Structure of Triglycinsulfate by High Resolution Magnetic Resonance in Solids Measurements were performed in the ferroelectric and paraelectric phase of TGS monocrystals with the aid of multiple pulse experiments for high resolution magnetic proton resonance in solids. The contributions to the spectra, which are to be expected theoretically from the different proton groups (NH₃, CH₂, OH), were calculated and compared with the corresponding experimental results. Splittings are discussed, which occur as a consequence of the ¹⁴N? ¹H-interaction and indicate changes at the phase transition point. The anisotropy of the effective chemical shift tensor caused by the rotation of NH₃-groups and the anisotropy of the chemical shift tensor of OH-groups were determined.