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131.
Jan Bornholdt Dr. Jakob Felding Dr. Rasmus P. Clausen Dr. Jesper L. Kristensen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(41):12474-12480
The pyrimidine‐2‐sulfonyl (pymisyl) group is introduced as a new protecting group that can be used to activate aziridines towards ring opening. It is readily introduced and removed under mild conditions. Regioselective ring opening of pymisyl‐protected 2‐methyl‐aziridine with organocuprates gives the corresponding sulfonamides in high yields, and the pymisyl group can subsequently be removed upon treatment with a thiolate. The versatility of this new nitrogen protecting group is illustrated with a new synthesis of Selegiline, a monoamine oxidase‐B inhibitor marketed for the treatment of Parkinson’s disease. 相似文献
132.
133.
Gonzalo Angulo Dr. Jakob Grilj Eric Vauthey Prof. Luis Serrano‐Andrés Prof. Òscar Rubio‐Pons Dr. Patrice Jacques Prof. 《Chemphyschem》2010,11(2):480-488
The experimental ultrafast photophysics of thioxanthone in several aprotic organic solvents at room temperature is presented, measured using femtosecond transient absorption together with high‐level ab initio CASPT2 calculations of the singlet‐ and triplet‐state manifolds in the gas phase, including computed state minima and conical intersections, transition energies, oscillator strengths, and spin–orbit coupling terms. The initially populated singlet ππ* state is shown to decay through internal conversion and intersystem crossing processes via intermediate nπ* singlet and triplet states, respectively. Two easily accessible conical intersections explain the favorable internal conversion rates and low fluorescence quantum yields in nonpolar media. The presence of a singlet–triplet crossing near the singlet ππ* minimum and the large spin–orbit coupling terms also rationalize the high intersystem crossing rates. A phenomenological kinetic scheme is proposed that accounts for the decrease in internal conversion and intersystem crossing (i.e. the very large experimental crescendo of the fluorescence quantum yield) with the increase of solvent polarity. 相似文献
134.
A broadly useful acid-labile traceless azido linker for the solid-phase synthesis of NH-1,2,3-triazoles is presented. A variety of alkynes were efficiently immobilized on a range of polymeric supports by Cu(I)-mediated azide-alkyne cycloadditions. Supported triazoles showed excellent compatibility with subsequent peptide chemistry. Release of pure material (typically >95%) from the solid support was readily achieved by treatment with aqueous TFA. 相似文献
135.
Divalent dipeptides have been introduced as counter ions in aqueous CZE. The dipeptides form ion pairs with amino alcohols in the BGE and facilitate the separation of amino alcohols. High concentrations of dipeptide caused reversed effective mobility for the analytes. The net charge of the dipeptide can be controlled using a buffer or a strong base, and regulates the interaction between the dipeptide and the amino alcohol. A stronger interaction and higher selectivity of amino alcohols was observed when the dipeptides were used as divalent counter ions, than in monovalent or uncharged form. Association constants for ion pairs between divalent dipeptides and amino alcohols can be used to enhance selectivity for amino alcohols in CZE. No chiral separation of amino alcohols was observed when using the dipeptides as ion‐pairing chiral selectors in aqueous BGE, but addition of methanol to the BGE promoted enantioselectivity. 相似文献
136.
Philipp Wachter Christian Schreiner Hans-Georg Schweiger Heiner Jakob Gores 《The Journal of chemical thermodynamics》2010,42(7):900-903
The determination of phase transition points of nine different ionic liquids (ILs) was performed by thermal analysis with simultaneous recording of conductivity. Conductivity of electrolyte solutions and ILs drastically changes during phase transitions and thus is an additional and very sensitive indicator for measuring phase transition points. Evaluation of temperature–time functions and conductivity–time functions with our computer-coupled automated equipment enabled the determination of melting temperatures with high accuracy and reliability. This claim is based on large samples, low temperature change rates and by regularly repeated measurements, i.e. at least seven measurements per IL. The melting temperatures of 1-butyl-1-methylpyrrolidinium trifluoromethanesulfonate, 1-butyl-1-methylpyrrolidinium tris(penta-fluoroethyl)trifluorophosphate, and 1-methyl-3-propylimidazolium iodide were, to our knowledge, determined for the first time. The melting temperatures of the other 1-butyl-1-methylpyrrolidinium-, 1-ethyl-3-methylimidazolium-, 1-hexyl-3-methylimidazolium-, and trimethylsulfonium-based ILs showed either a very good accordance with values published in literature or were distinctly higher. 相似文献
137.
Pogorelsky I. V. Polyanskiy M. N. Babzien M. Yakimenko V. Dover N. P. Palmer C. A. J. Najmudin Z. Schreiber J. Shkolnikov P. Dudnikova G. 《Laser Physics》2011,21(7):1288-1294
A picosecond CO2 laser was used successfully in a number of experiments exploring advanced methods of particle acceleration [1]. Proton acceleration
from gas-jet plasma exemplifies another advantage of employing the increase in laser wavelength from the optical to the mid-IR
region. Recent theoretical- and experimental-studies of ion acceleration from laser-generated plasma point to better ways
to control the ion beam’s energy when plasma approaches the critical density. Studying this regime with solid-state lasers
is problematic due to the dearth of plasma sources at the critical electron density ∼1021 cm−3, corresponding to laser wavelength λ = 1 μm. CO2 laser offers a solution. The CO2 laser’s 10 μm wavelength shifts the critical plasma density to 1019 cm−3, a value attainable with gas jets. Capitalizing on this approach, we focused a circular polarized 1-TW CO2 laser beam onto a hydrogen gas jet and observed a monoenergetic proton beam in the 1–2 MeV range. Simultaneously, we optically
probed the laser/plasma interaction region with visible light, revealing holes bored by radiation pressure, as well as quasi-stationary
soliton-like plasma formations. Our findings from 2D PIC simulations agree with experimental results and aid in their interpretation. 相似文献
138.
P. P. Pershukevich D. V. Shabrov V. P. Osipov J. Schreiber V. A. Lapina 《Journal of Applied Spectroscopy》2011,78(4):524-533
This is a study of the luminescence properties of coatings formed on aluminum alloys by anodizing in electrolytic solutions
based on oxalic, sulfuric, and tartaric-sulfonic acids. At least two emission centers, with band maxima in the ranges of 390–410
and 470–510 nm, can be reliably identified in the photoluminescence spectra. The first type of center is characterized by
single-band photoluminescence excitation spectra and the second, by two-band spectra. An analysis of the two-band photoluminescence
excitation (PLE) spectra in the range of 470–510 nm shows that the position of the narrow short-wavelength PLE spectrum near
272 nm is independent of the type of acid used in the anodization process. The position and shape of the other PLE spectral
bands depend both on the type of acid used and on the processing of the alloy or alumina surfaces. It is assumed that defect-free
alumina centers are responsible for the 272 nm PLE band, while the other photoluminescence bands are caused primarily by different
divacancies of oxygen (F2+ {F_2^+} , F
2, and F2+2 {F_2^{+2}} centers) whose origin is governed by the type of electrolyte. 相似文献
139.
S. Thiem M. Schreiber 《The European Physical Journal B - Condensed Matter and Complex Systems》2011,83(4):415-421
From the quantum mechanical point of view, the electronic characteristics of
quasicrystals are determined by the nature of their eigenstates. A practicable way to
obtain information about the properties of these wave functions is studying the scaling
behavior of the generalized inverse participation numbers Zq ~ N - Dq (q - 1)Z_q \sim N - ^{D_q (q - 1)} with the system size N. In particular, we investigate
d-dimensional quasiperiodic models based on different metallic-mean
quasiperiodic sequences. We obtain the eigenstates of the one-dimensional metallic-mean
chains by numerical calculations for a tight-binding model. Higher dimensional solutions
of the associated generalized labyrinth tiling are then constructed by a product approach
from the one-dimensional solutions. Numerical results suggest that the relation D
q
dd = dD
q
1d holds for these models. Using the product structure of the labyrinth tiling we prove that
this relation is always satisfied for the silver-mean model and that the scaling exponents
approach this relation for large system sizes also for the other metallic-mean
systems. 相似文献
140.
M. Baumgartl B. Orta? T. Schreiber J. Limpert A. Tünnermann 《Applied physics. B, Lasers and optics》2011,104(3):523-536
Passive mode-locking in fiber lasers is investigated by numerical and experimental means. A non-distributed scalar model solving
the nonlinear Schr?dinger equation is implemented to study the starting behavior and intra-cavity dynamics numerically. Several
operation regimes at positive net-cavity dispersion are experimentally accessed and studied in different environmentally stable,
linear laser configurations. In particular, pulse formation and evolution in the chirped-pulse regime at highly positive cavity
dispersion is discussed. Based on the experimental results a route to highly energetic pulse solutions is shown in numerical
simulations. 相似文献