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41.
Stephan Tillmann 《Topology》2005,44(1):203-216
The A-polynomial of a manifold whose boundary consists of a single torus is generalised to an eigenvalue variety of a manifold whose boundary consists of a finite number of tori, and the set of strongly detected boundary curves is determined by Bergman's logarithmic limit set, which describes the exponential behaviour of the eigenvalue variety at infinity. This enables one to read off the detected boundary curves of a multi-cusped manifold in a similar way to the 1-cusped case, where the slopes are encoded in the Newton polygon of the A-polynomial. 相似文献
42.
Phycotoxins produced by various species of toxigenic microalgae occurring in the plankton are a global threat to the security
of seafood resources and the health of humans and coastal marine ecosystems. This has necessitated the development and application
of advanced methods in liquid chromatography coupled to mass spectrometry (LC-MS) for monitoring of these compounds, particularly
in plankton and shellfish. Most such chemical analyses are conducted in land-based laboratories on stored samples, and thus
much information on the near real-time biogeographical distribution and dynamics of phycotoxins in the plankton is unavailable.
To resolve this problem, we conducted ship-board analysis of a broad spectrum of phycotoxins collected directly from the water
column on an oceanographic cruise along the North Sea coast of Scotland, Norway, and Denmark. We equipped the ship with a
triple-quadrupole linear ion-trap hybrid LC-MS-MS system for detection and quantitative analysis of toxins, such as domoic
acid, gymnodimine, spirolides, dinophysistoxins, okadaic acid, pectenotoxins, yessotoxins, and azaspiracids (AZAs). We focused
particular attention on the detection of AZAs, a group of potent nitrogenous polyether toxins, because the culprit species
associated with the occurrence of these toxins in shellfish has been controversial. Marine toxins were analyzed directly from
size-fractionated plankton net tows (20 μm mesh size) and Niskin bottle samples from discrete depths, after rapid methanolic
extraction but without any further clean-up. Almost all expected phycotoxins were detected in North Sea plankton samples,
with domoic acid and 20-methylspirolide G being most abundant. Although AZA was the least abundant of these toxins, the high
sensitivity of the LC-MS-MS enabled detailed quantification, indicating that the highest amounts of AZA-1 were present in
the southern Skagerrak in the 3–20 μm size-fraction. The direct on-board toxin measurements enabled isolation of plankton
from stations with high AZA-1 levels and from the most suspicious size-fraction, i.e. most likely to contain the AZA-producer.
A large number (>100) of crude cultures were established by serial dilution and later screened for the presence of AZAs after
several weeks growth. From one crude culture containing AZA, a small dinoflagellate was subsequently isolated and brought
into pure culture. We have thus proved that even sophisticated mass spectrometers can be operated in ship laboratories without
any limitation caused by vibrations of the ship’s engine or by wave movement during heavy seas at wind forces up to nine Beaufort.
On-board LC–MS–MS is a valuable method for near real-time analysis of phycotoxins in plankton for studies on bloom dynamics
and the fate of toxins in the food web, and for characterization and isolation of putatively toxigenic organisms. 相似文献
43.
Dr. Jayanta Ghosh Mirali Gheibi Dr. Tillmann Kalas Cristian Sarpe Bastian Zielinski Ramela Ciobotea Christoph Burghard Morscher Dr. Ingo Koehne Prof. Dr. Rudolf Pietschnig Dr. Arne Senftleben Prof. Dr. Thomas Baumert Dr. Hendrike Braun 《Chemphyschem》2023,24(12):e202300001
Temporally delayed, phase-locked coherent pairs of near IR femtosecond laser pulses were employed to study electronic coherences in molecular Nd3+-complexes at room temperature. Dissolved and solid complexes were studied under a confocal microscope set-up with fluorescence detection. The observed electronic coherence on a few hundred femtoseconds time scale is modulated by additional coherent wave packet dynamics, which we attribute mainly to be vibrational in nature. In future, the complexes may serve as prototypes for possible applications in quantum information technology. 相似文献
44.
Surface‐Tuned Electron Transfer and Electrocatalysis of Hexameric Tyrosine‐Coordinated Heme Protein 下载免费PDF全文
Dr. Lei Peng Dr. Tillmann Utesch Dr. Aysu Yarman Dr. Jae‐Hun Jeoung Silke Steinborn Prof. Dr. Holger Dobbek Dr. Maria Andrea Mroginski Johannes Tanne Prof. Dr. Ulla Wollenberger Prof. Dr. Frieder W. Scheller 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(20):7596-7602
Molecular modeling, electrochemical methods, and quartz crystal microbalance were used to characterize immobilized hexameric tyrosine‐coordinated heme protein (HTHP) on bare carbon or on gold electrodes modified with positively and negatively charged self‐assembled monolayers (SAMs), respectively. HTHP binds to the positively charged surface but no direct electron transfer (DET) is found due to the long distance of the active sites from the electrode surfaces. At carboxyl‐terminated surfaces, the neutrally charged bottom of HTHP can bind to the SAM. For this “disc” orientation all six hemes are close to the electrode and their direct electron transfer should be efficient. HTHP on all negatively charged SAMs showed a quasi‐reversible redox behavior with rate constant ks values between 0.93 and 2.86 s?1 and apparent formal potentials ${E{{0{^{\prime }}\hfill \atop {\rm app}\hfill}}}$ between ‐131.1 and ‐249.1 mV. On the MUA/MU‐modified electrode, the maximum surface concentration corresponds to a complete monolayer of the hexameric HTHP in the disc orientation. HTHP electrostatically immobilized on negatively charged SAMs shows electrocatalysis of peroxide reduction and enzymatic oxidation of NADH. 相似文献
45.
Kleine T Bergander K Fröhlich R Wibbeling B Würthwein EU 《The Journal of organic chemistry》2011,76(7):1979-1991
2-Alkenylbenzylidene hydrazones 5a-m, which are accessible in good to excellent yields in a four-step synthesis, are converted into 1,2-diaza-4,5-benzoheptatrienyl metal compounds 1a-m by treatment with KO-t-Bu as base. These metal compounds undergo the various types of reactions in good yields and exclusively depending on the nature of substituents R(1) and R(3). Thus, metal compounds 1a-c carrying alkyl substituents R(1) and R(3) form 3H-benzodiazepines 6a-c after electrophilic quench of the intermediate cyclic anion 7 in a 7-endo-trig electrocyclic reaction with a mo?bius aromatic transition structure 1(-)-TS. Similarly, a benzothienyl derivative 5n is converted into diazepine 6d. Potassium compounds 1d-h, which are N-methyl and aryl substituted at R(3), form 1,2-dihydrophthalazines 8a-e in a predominantly charge-controlled 6-exo-trig cyclization reaction. In contrast, aryl-aryl-substituted systems 5i-m did not lead to cyclic products upon deprotonation, but the intermediate open-chain metal compounds 1i-m were trapped by acid chlorides at N1 to yield the hydrazides 10a-e. We interpret thermodynamics and kinetics of these reactions in the context of the Baldwin rules on the basis of quantum chemical calculations and discuss the transition structures considering the results of NICS and NBO-charge calculations. Examples of the products 6, 8, and 10 could be characterized by X-ray diffraction. 相似文献
46.
T Schwarze A Kelling H Müller M Trautmann T Klamroth O Baumann P Strauch HJ Holdt 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(34):10506-10510
Copper chemodosimeters: The copper(II)-promoted air oxidation of 1-3 to form 4-6 permits the highly selective colorimetric detection of Cu(2+) ions. The formation of copper(II) complexes of 4-6 proceeds rapidly, and the chemodosimeters 1-3 are viable at physiological pH. 相似文献
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Tetraarylethylenes from Diarylmethanones and Hexachlorodisilane: The “Sila‐McMurry” Reaction 下载免费PDF全文
Maximilian Moxter Dr. Jan Tillmann Matthias Füser Dr. Michael Bolte Dr. Hans‐Wolfram Lerner Prof. Dr. Matthias Wagner 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(45):16028-16031
Hexachlorodisilane reacts with diarylmethanones (aryl=C6H5, 4‐MeC6H4, 4‐tBuC6H4, 4‐ClC6H4, 4‐BrC6H4) to furnish the corresponding tetraarylethylenes in good yields. The reductive conversion requires temperatures of about 160 °C and reaction times of 60–72 h. In the initial step, the Lewis‐basic carbonyl groups likely generate low‐valent [SiCl2] as an analogue of [TiCl2] in the classical McMurry reaction. The coupling sequence further proceeds via benzopinacolones, which have been isolated as key intermediates. 相似文献