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81.
Guangrong Meng Michal Szostak 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2015,127(48):14726-14730
Metal‐catalyzed reactions of amides proceeding via metal insertion into the N CO bond are severely underdeveloped due to resonance stabilization of the amide bond. Herein we report the first Heck reaction of amides proceeding via highly chemoselective N CO cleavage catalyzed by Pd0 utilizing amide bond ground‐state destabilization. Conceptually, this transformation provides access to a myriad of metal‐catalyzed transformations of amides via metal insertion/decarbonylation. 相似文献
82.
83.
Medium-bridged twisted lactams, in which a non-planar amide bond is achieved by incorporating the nitrogen atom at the bridgehead position in a medium-sized heterocycle, offer an attractive setting in which to study the properties of distorted amide linkages. This Emerging Area article will describe progress in the preparation and study of these compounds. This work shows that compounds containing an even moderately distorted amide bond display useful and unusual chemical properties while retaining a measure of stability that enables their study. 相似文献
84.
Komsta Ł Czarnik-Matusewicz H Szostak R Gumieniczek A Pietraś R Skibiński R Inglot T 《Journal of AOAC International》2011,94(3):743-749
This paper presents and discusses the building of discriminant models from attenuated total reflectance (ATR)-FTIR and Raman spectra that were constructed to detect the presence of acetaminophen in over-the-counter pharmaceutical formulations. The datasets, containing 11 spectra of pure substances and 21 spectra of various formulations, were processed by partial least squares (PLS) discriminant analysis. The models found in the present study coped greatly with the discrimination, and their quality parameters were acceptable. A root mean square error of cross-validation was in the 0.14-0.35 range, while a root mean square error of prediction was in the 0.20-0.56 range. It was found that standard normal variate preprocessing had a negligible influence on the quality of ATR-FTIR; in the Raman case, it lowered the prediction error by 2. The influence of variable selection with the uninformative variable elimination by PLS method was studied, and no further model improvement was found. 相似文献
85.
L. N. Puntus V. F. Zolin V. A. Kudryashova V. I. Tsaryuk J. Legendziewicz P. Gawryszewska R. Szostak 《Physics of the Solid State》2002,44(8):1440-1444
A ligand-cation charge transfer band was observed in the region of 360–400 nm in the Eu3+ luminescence excitation spectrum of europium 3,4-pyridine-dicarboxylates, but was absent in the spectra of europium 2,6-and 2,3-pyridine-dicarboxylates. This band is due to noticeable energy transfer through a charge-transfer state formed owing to the high polarizability of the ligand in the former compound. Energy transfer through the excited ligand-lanthanide charge-transfer state can explain the well-known effect of luminescence quenching by redox-sensitive lanthanide ions. 相似文献
86.
General Olefin Synthesis by the Palladium‐Catalyzed Heck Reaction of Amides: Sterically Controlled Chemoselective NC Activation
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Guangrong Meng Prof. Dr. Michal Szostak 《Angewandte Chemie (International ed. in English)》2015,54(48):14518-14522
Metal‐catalyzed reactions of amides proceeding via metal insertion into the N? CO bond are severely underdeveloped due to resonance stabilization of the amide bond. Herein we report the first Heck reaction of amides proceeding via highly chemoselective N? CO cleavage catalyzed by Pd0 utilizing amide bond ground‐state destabilization. Conceptually, this transformation provides access to a myriad of metal‐catalyzed transformations of amides via metal insertion/decarbonylation. 相似文献
87.
A. S. Aynacioglu G. v. Oppen W. -D. Perschmann D. Szostak 《Zeitschrift für Physik A Hadrons and Nuclei》1981,303(2):97-102
He atoms have been excited by Ne+ ion impact and the depolarization of the fluorescence lines at 668 nm and 492 nm by magnetic and electric fields has been studied. The Ne+ ion energy could be chosen such that pure cascade level crossing signals were observed. From the widths of magnetic depolarization signals the radiative lifetimes τ(1s4f 1 F)=74(2) ns and τ(1s5f 1 F)=133(5) ns have been determined. By investigating the electric field splitting of the magnetic depolarization signals the tensor polarizabilities ¦α ten(1s4f 1 F)¦=0.58(1) kHz/(V/cm)2 and ¦α ten(1s5f 1 F)¦=4.2(1) kHz/(V/cm)2 have been deduced. From the latter value a mean frequencyv(1s5g?1s5f)=14.4 GHz of the transitions between the levels of the 1s5f configuration and those of the 1s5g configuration has been derived.α ten(1s4f 1 F) depends sensitively on the singlet-triplet mixing in the 1s4f configuration and thus a mixing coefficient could be deduced for this configuration. 相似文献
88.
G. v. Oppen W. -D. Perschmann D. Szostak 《Zeitschrift für Physik A Hadrons and Nuclei》1978,286(3):243-247
He-atoms have been excited using 35 keV-He+-ion-He-atom-collisions. Investigating the electric and magnetic depolarization of fluorescence light, cascade-free lifetime measurements on the 1s 3d 1 D and3 D-levels of He I have been performed. From our measurements we deduced:τ(31 D)=(15.3±0.3)ns,τ(33 D)=(14.2±0.6)ns. 相似文献
89.
Reactions proceeding through open-shell, single-electron pathways offer attractive alternative outcomes to those proceeding through closed-shell, two-electron mechanisms. In this context, samarium diiodide (SmI(2) ) has emerged as one of the most important and convenient-to-use electron-transfer reagents available in the laboratory. Recently, significant progress has been made in the reductive chemistry of other divalent lanthanides which for many years had been considered too reactive to be of value to synthetic chemists. Herein, we illustrate how new samarium(II) complexes and nonclassical lanthanide(II) reagents are changing the landscape of modern reductive chemistry. 相似文献
90.
Carothers JM Oestreich SC Davis JH Szostak JW 《Journal of the American Chemical Society》2004,126(16):5130-5137
Very little is known about the distribution of functional DNA, RNA, and protein molecules in sequence space. The question of how the number and complexity of distinct solutions to a particular biochemical problem varies with activity is an important aspect of this general problem. Here we present a comparison of the structures and activities of eleven distinct GTP-binding RNAs (aptamers). By experimentally measuring the amount of information required to specify each optimal binding structure, we show that defining a structure capable of 10-fold tighter binding requires approximately 10 additional bits of information. This increase in information content is equivalent to specifying the identity of five additional nucleotide positions and corresponds to an approximately 1000-fold decrease in abundance in a sample of random sequences. We observe a similar relationship between structural complexity and activity in a comparison of two catalytic RNAs (ribozyme ligases), raising the possibility of a general relationship between the complexity of RNA structures and their functional activity. Describing how information varies with activity in other heteropolymers, both biological and synthetic, may lead to an objective means of comparing their functional properties. This approach could be useful in predicting the functional utility of novel heteropolymers. 相似文献