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51.
Magnus Pauly Julia Krger Viola Duppel Corban Murphey James Cahoon Bettina V. Lotsch Paul A. Maggard 《Chemical science》2022,13(11):3187
The in-depth understanding of the reported photoelectrochemical properties of the layered carbon nitride, poly(triazine imide)/LiCl (PTI/LiCl), has been limited by the apparent disorder of the Li/H atoms within its framework. To understand and resolve the current structural ambiguities, an optimized one-step flux synthesis (470 °C, 36 h, LiCl/KCl flux) was used to prepare PTI/LiCl and deuterated-PTI/LiCl in high purity. Its structure was characterized by a combination of neutron/X-ray diffraction and transmission electron microscopy. The range of possible Li/H atomic configurations was enumerated for the first time and, combined with total energy calculations, reveals a more complex energetic landscape than previously considered. Experimental data were fitted against all possible structural models, exhibiting the most consistency with a new orthorhombic model (Sp. Grp. Ama2) that also has the lowest total energy. In addition, a new Cu(i)-containing PTI (PTI/CuCl) was prepared with the more strongly scattering Cu(i) cations in place of Li, and most closely matching with the partially-disorder structure in Cmc21. Thus, a complex configurational landscape of PTI is revealed to consist of a number of ordered crystalline structures that are new potential synthetic targets, such as with the use of metal-exchange reactions.The layered carbon nitride, poly(triazine imide), exhibits a complex configurational landscape for the coordination of cations within its intralayer cavities that has been elucidated for the first time. 相似文献
52.
An on-line method for the determination of airborne organophosphate esters based on dynamic sonication-assisted solvent extraction and large-volume injection (LVI) gas chromatography with nitrogen-phosphorous detection is introduced. The LVI is performed with a programmed-temperature vaporizer. The entire extracted fraction of 800 microl (hexane-methyl-tert.-butyl ether, 7:3, v/v) is introduced directly into the GC system without any clean-up step following extraction. The extraction and analysis step were completed in less than 15 min. The limit of detection of the investigated organophosphate esters was established to be in the range of 5-32 pg/filter. The correlation coefficients (r2) were investigated in the linear range study of the entire system and established to be approximately 0.9900 for all the investigated organophosphates esters. Applications of the method was demonstrated with the extraction of air samples collected onto glass fiber filters from different indoor environments. Six organophosphate esters were found at the levels 0.4-138 ng/m3. 相似文献
53.
Córdova A Ibrahem I Casas J Sundén H Engqvist M Reyes E 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(16):4772-4784
Hexose sugars play a fundamental role in vital biochemical processes and their biosynthesis is achieved through enzyme-catalyzed pathways. Herein we disclose the ability of amino acids to catalyze the asymmetric neogenesis of carbohydrates by sequential cross-aldol reactions. The amino acids mediate the asymmetric de novo synthesis of natural L- and D-hexoses and their analogues with excellent stereoselectivity in organic solvents. In some cases, the four new stereocenters are assembled with almost absolute stereocontrol. The unique feature of these results is that, when an amino acid is employed as the catalyst, a single reaction sequence can convert a protected glycol aldehyde into a hexose in one step. For example, proline and its derivatives catalyze the asymmetric neogenesis of allose with >99 % ee in one chemical manipulation. Furthermore, all amino acids tested catalyzed the asymmetric formation of natural sugars under prebiotic conditions, with alanine being the smallest catalyst. The inherent simplicity of this catalytic process suggests that a catalytic prebiotic "gluconeogenesis" may occur, in which amino acids transfer their stereochemical information to sugars. In addition, the amino acid catalyzed stereoselective sequential cross-aldol reactions were performed as a two-step procedure with different aldehydes as acceptors and nucleophiles. The employment of two different amino acids as catalysts for the iterative direct aldol reactions enabled the asymmetric synthesis of deoxysugars with >99 % ee. In addition, the direct amino acid catalyzed C(2)+C(2)+C(2) methodology is a new entry for the short, highly enantioselective de novo synthesis of carbohydrate derivatives, isotope-labeled sugars, and polyketide natural products. The one-pot asymmetric de novo syntheses of deoxy and polyketide carbohydrates involved a novel dynamic kinetic asymmetric transformation (DYKAT) mediated by an amino acid. 相似文献
54.
The cytochrome P450 (P450) enzymes are mainly localized to the endoplasmic reticulum (ER), where they function within catalytic
complexes metabolizing xenobiotics and some endogenous substrates. However, certain members of families 1–3 were also found
in other subcellular compartments, such as mitochondria, plasma membrane, and lysosomes. The physiological function of these
enzymes in non-ER locations is not known, although plasma-membrane-associated P450s have been described to be catalytically
active and to participate in immune-mediated reactions with autoantibody formation that can trigger drug-induced hepatitis.
Several retention/retrieval mechanisms are active in the ER retention of the P450s and inverse integration of the translated
P450 into the ER membrane appears to be responsible for transport to the plasma membrane. Furthermore, hydrophilic motifs
in the NH2-terminal part have been suggested to be important for mitochondrial import. Phosphorylation of P450s has been described to
be important for increased rate of degradation as well as for targeting into mitochondria. It was also suggested that the
mitochondria-targeted P450s from families 1–3 could be active in drug metabolism using an alternative electron transport chain.
In this review we present an update of the field emphasizing studies concerning localization, posttranslational modification,
such as phosphorylation, and intracellular transport of microsomal P450s. 相似文献
55.
Use of a small particle solid‐core packing for improved efficiency and rapid measurement of sirolimus and everolimus by LC‐MS/MS
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Measurement of whole blood sirolimus and everolimus is required in order to optimize patient treatment following solid organ transplant. Assay by LC‐MS/MS is increasingly preferred; however efficient use of the instrument and short turnaround times are crucial. Use of a 1.6 µm solid‐core packing HPLC column (Cortecs) gave significant increases in efficiency, sensitivity and throughput compared with an existing method, following simple protein precipitation of small‐volume (20 μL) whole blood samples. Sirolimus, everolimus and the stable isotopic internal standard (13C2D4 – everolimus) eluted at around 0.8 min, and total analytical run time was 2.2 min, saving almost 4 min per sample compared with an existing method. Within‐assay imprecision (CV) was 3.3–8.5%, and between‐assay imprecision was 2.2–10.8%. Retrospective assay of external quality assurance samples and comparison of patient samples assayed in parallel showed only small differences (between +6.8 and ?1.9%) in results using the Cortecs column when compared with the existing method. No significant interferences or ion suppression were observed. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
56.
MaxwellD. Cummings Jimmy Lindberg Tse‐I Lin Herman deKock Oliver Lenz Elisabet Lilja Sara Fellnder Vera Baraznenok Susanne Nystrm Magnus Nilsson Lotta Vrang Michael Edlund sa Rosenquist Bertil Samuelsson Pierre Raboisson Kenneth Simmen 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2010,122(9):1552-1552
57.
Henning Osholm Srensen Magnus Magnussen Nicolai Stuhr‐Hansen 《Acta Crystallographica. Section C, Structural Chemistry》2005,61(8):o503-o505
The first crystal structure of a three‐terminal sulfur end‐capped oligophenylenevinylene, C36H30O3S3·0.5C7H8, has been determined at 122 (1) K. The molecular threefold symmetry is not utilized in the crystal structure. It is confirmed that the double bonds have been fully transformed into a trans configuration by iodine treatment. 相似文献
58.
59.
[reaction: see text] The synthesis of alpha-substituted alpha,beta-enones by a new metal iodide-promoted one-pot three-component reaction involving commercially available cyclopropyl ketones, aldehydes, and secondary amines followed by base treatment is described. 相似文献
60.
Prof. Dr. K. Magnus 《Archive of Applied Mechanics (Ingenieur Archiv)》1980,49(5-6):295-308
übersicht Aktive Elemente in Kreiselsystemen k?nnen sich in verschiedenartigen Effekten auswirken. Allgemeine Bewegungsgleichungen werden
abgeleitet. Mit ihrer Hilfe lassen sich globale Aussagen zum Stabilit?tsverhalten von Kreiselsystemen mit Rotorantrieb gewinnen:
1) Konservative Systeme bleiben auch dann quasi-konservativ, wenn eine ideal wirkende Antriebsregelung vorhanden ist, die
die relativen Geschwindigkeiten zwischen den Rotoren und ihren Geh?usen konstant h?lt. 2) Eigenstabile Asynchron-Antriebe
machen ein grenzstabiles Kreiselsystem asymptotisch stabil bezüglich der Geschwindigkeiten. 3) Entsprechendes gilt für eigenged?mpfte
Synchron-Antriebe; hier gilt die asymptotische Stabilit?t auch für die Rotorwinkel selbst. Am Beispiel einer motorangetriebenen
Zentrifuge werden diese Ergebnisse durch Untersuchen der Eigenwerte pr?zisiert. Zugleich wird gezeigt, da? bezüglich der Lagewinkel
Instabilit?t infolge kinetischer Auswanderung auftreten kann.
Hans Ziegler zum 70. Geburtstag gewidmet 相似文献
Summary Due to active elements in gyroscopic systems various effects may occur. For their examination quite general equations of motion are derived, which allow some globale statements concerning the stability of gyro-systems with motor-driven rotors: 1) Conservative systems will behave quasi-conservative, if ideal working controllers are installed, which keep the relative rotational velocities of the rotors constant. 2) Asynchronous driving motors, which are stable for themselves, turn a marginal stable system into a system, asymptotically stable with respect to the velocities. 3) The same is valid for systems, in which the rotors are driven by damped synchronous motors; here asymptotic stability exists for the rotor-angles as well. As an example a motor-driven centrifuge is examined. The general results are proved and extended by calculating the eigenvalues. Furthermore it is shown that unstable behaviour with respect to the attitude angles is possible due to effects of kinetic drift.
Hans Ziegler zum 70. Geburtstag gewidmet 相似文献