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101.
Pawel Dziedzic 《Tetrahedron letters》2009,50(52):7242-7245
Inorganic ammonium salts catalyze the direct aldol reaction between unmodified ketones and aldehydes to furnish the corresponding β-hydroxy ketones in aqueous media. The reactions are highly chemoselective and operationally simple. 相似文献
102.
Nico Fleck Caspar A. Heubach Tobias Hett Florian R. Haege Pawel P. Bawol Helmut Baltruschat Olav Schiemann 《Angewandte Chemie (International ed. in English)》2020,59(24):9767-9772
The understanding of biomolecular function is coupled to knowledge about the structure and dynamics of these biomolecules, preferably acquired under native conditions. In this regard, pulsed dipolar EPR spectroscopy (PDS) in conjunction with site‐directed spin labeling (SDSL) is an important method in the toolbox of biophysical chemistry. However, the currently available spin labels have diverse deficiencies for in‐cell applications, for example, low radical stability or long bioconjugation linkers. In this work, a synthesis strategy is introduced for the derivatization of trityl radicals with a maleimide‐functionalized methylene group. The resulting trityl spin label, called SLIM, yields narrow distance distributions, enables highly sensitive distance measurements down to concentrations of 90 nm , and shows high stability against reduction. Using this label, the guanine‐nucleotide dissociation inhibitor (GDI) domain of Yersinia outer protein O (YopO) is shown to change its conformation within eukaryotic cells. 相似文献
103.
Density functional theory has been applied to a series of unsubstituted planar metalloporphyrins (MPs) to elucidate how geometry and frequencies correlate with the metal-nitrogen distance, referred to as the core size. Different transition metals can invoke expansion or contraction of the porphyrin core due to electronic effects resulting from the amount of d-electron pairing as well as occupancy of the d(x(2)(-y(2))) orbital. A full vibrational analysis consisting of all in-plane and out-of-plane frequencies was carried out, and the resulting modes were plotted against core size for a linear analysis and grouped within symmetry blocks. The modes were separated according to planarity, and all modes with a large slope and best fit greater than 0.8 were considered sensitive to metal-nitrogen distances. All planar skeletal modes above 1450 cm(-1), including the pyrolle ring deformations, are found to be core-size sensitive. The most significant out-of-plane modes sensitive to core size are gamma(8) and gamma(9), which are infrared active and grouped within the A(2u) symmetry block. The present work also opens possible quantitative applications for the correlation of spectroscopic properties of MPs and heme proteins with actual structural parameters. 相似文献
104.
Pawel G. Parzuchowski Martyna Grabowska Michal Jaroch Monika Kusznerczuk 《Journal of polymer science. Part A, Polymer chemistry》2009,47(15):3860-3868
This article describes the synthesis of a new glycerol‐based AB2 type monomer—ethyl{3‐[2‐hydroxy‐1‐(hydroxymethyl)ethoxy]propyl}thioacetate ( 4 ) and its application for the preparation of hyperbranched polyesters. The polycondensation of 4 has been performed over a wide range of catalysts and reaction conditions leading to polymers containing solely primary hydroxyl groups. The polycondensation progress has been monitored by means of 1H NMR. The degree of branching of the polymers showed to be in the range of 0.5 ± 0.03. The obtained polyesters easily undergo hydrolysis or alcoholysis and may be of interest as recycled materials. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3860–3868, 2009 相似文献
105.
In this paper we investigate the performance of a linear wavelet-type deconvolution estimator for weakly dependent data. We
show that the rates of convergence which are optimal in the case of i.i.d. data are also (almost) attained for strongly mixing
observations, provided the mixing coefficients decay fast enough. The results are applied to a discretely observed continuous-time
stochastic volatility model. 相似文献
106.
Masitas CA Kumar M Mashuta MS Kozlowski PM Grapperhaus CA 《Inorganic chemistry》2010,49(23):10875-10881
The ruthenium(II) dithiolate complex (bmmp-TASN)RuPPh(3) (1) reacts with O(2) under limiting conditions to yield isolable sulfur oxygenated derivatives as a function of reaction time. With this approach, a family of sulfur-oxygenates has been prepared and isolated without the need for O-atom transfer agents or column chromatography. Addition of 5 equiv of O(2) to 1 yields the thiolato/sulfinato complex (bmmp-O(2)-TASN)RuPPh(3) (2) in 70% yield within 5 min. Increasing the reaction time to 12 h yields the sulfenato/sulfinato derivative (bmmp-O(3)-TASN)RuPPh(3) (3) in 82% yield. Longer reaction times and/or additional O(2) exposure yield the bis-sulfinato complex (bmmp-O(4)-TASN)RuPPh(3) (4). All products remain in the Ru(II) oxidation state under the conditions employed. Stoichiometric hydrolysis of acetonitrile to acetamide by 2 and 3 is observed in mixed acetonitrile, methanol, PIPES buffer (pH = 7.0) mixtures. The Ru(III)/(II) reduction potential of -0.85 V (versus ferrocenium/ferrocene) for 1 shifts to -0.39 and -0.26 V for 2 and 3, respectively, because of the decreased donor ability of sulfur upon oxygenation. X-ray diffraction studies reveal a decrease in Ru-S bond distances upon oxygenation by 0.045(1) and 0.158(1) ? for the sulfenato and sulfinato donors, respectively. Conversely, sulfur-oxygenation increases the Ru-P bond distance by 0.061(1) ? from 1 to 2 and an additional 0.027(1) ? from 2 to 3. Density functional theory investigations using the BP86 and B3LYP functionals with a LANL2DZ basis set for Ru and the 6-31G(d) basis set for all other atoms reveal a direct correlation between the oxygenation level and the Ru-P distance with an increase of 0.031 ? per O-atom. 相似文献
107.
A highly enantioselective catalytic route to carbamate- and benzoate-protected β-amino aldehydes and β-amino acids is presented. The amino acid-catalyzed one-pot asymmetric reaction between unmodified aldehydes and α-amido sulfones gives the corresponding β-amino compounds with up to 95:5 dr and 97->99% ee. 相似文献
108.
Nambu Y Zhao LL Morosan E Kim K Kotliar G Zajdel P Green MA Ratcliff W Rodriguez-Rivera JA Broholm C 《Physical review letters》2011,106(3):037201
Magnetism in the orthorhombic metal CaFe(4)As(3) was examined through neutron diffraction for powder and single crystalline samples. Incommensurate [q(m) ≈ (0.37-0.39) × b*] and predominantly longitudinally (|| b) modulated order develops through a 2nd order phase transition at TN = 89.63(6) K with a 3D Heisenberg-like critical exponent β = 0.365(6). A 1st order transition at T2 = 25.6(9) K is associated with the development of a transverse component, locking q(m) to 0.375(2)b*, and increasing the moments from 2.1(1) to 2.2(3) μ B for Fe2+ and from 1.3(3) to 2.4(4) μB for Fe+. The ab initio Fermi surface is consistent with a nesting instability in cross-linked FeAs strips. 相似文献
109.
Pawel Sosna 《Applied Categorical Structures》2014,22(1):211-227
Given a triangulated category ${{\mathcal T}}$ over a field K and a field extension L/K, we investigate how one can construct a triangulated category ${{\mathcal T}}_L$ over L. Our approach produces the derived category of the base change scheme X L if ${{\mathcal T}}$ is the bounded derived category of a smooth projective variety over K and the field extension is finite and Galois. We also investigate how the dimension of a triangulated category behaves under scalar extensions. 相似文献
110.