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141.
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143.
Conrad T. Pfeiffer Justin D. Northrup Jae Eun Cheong Melody A. Pham Matthew F.L. Parker Christian E. Schafmeister 《Tetrahedron letters》2018,59(30):2884-2888
Spiroligomers are a class of peptidomimetics that connect interchangeable, stereochemically pure, cyclic monomers through pairs of amide bonds to form diketopiperazines between the monomers. This enables them to adopt predictable and programmable structure due to the rigidity of the final molecule. We present a new method for the solid phase synthesis of highly functionalized spiroligomers that incorporates the use of the p-nitrobenzyloxycarbonyl (pNZ) as a temporary amine protecting group and the pentafluorophenyl ester for monomer activation. This new method allows for the synthesis of spiroligomers with higher purity and increased yields when compared to previous methods. This improved method of synthesis of functionalized spiroligomers will facilitate the development of applications as catalysts, therapeutics and membrane channels. 相似文献
144.
Fatemeh Mahmoodani Conrad O. Perera Grant Abernethy Bruno Fedrizzi David Greenwood Hong Chen 《Journal of the American Society for Mass Spectrometry》2018,29(7):1442-1455
In a successful fortification program, the stability of micronutrients added to the food is one of the most important factors. The added vitamin D3 is known to sometimes decline during storage of fortified milks, and oxidation through fatty acid lipoxidation could be suspected as the likely cause. Identification of vitamin D3 oxidation products (VDOPs) in natural foods is a challenge due to the low amount of their contents and their possible transformation to other compounds during analysis. The main objective of this study was to find a method to extract VDOPs in simulated whole milk powder and to identify these products using LTQ-ion trap, Q-Exactive Orbitrap and triple quadrupole mass spectrometry. The multistage mass spectrometry (MSn) spectra can help to propose plausible schemes for unknown compounds and their fragmentations. With the growth of combinatorial libraries, mass spectrometry (MS) has become an important analytical technique because of its speed of analysis, sensitivity, and accuracy. This study was focused on identifying the fragmentation rules for some VDOPs by incorporating MS data with in silico calculated MS fragmentation pathways. Diels–Alder derivatization was used to enhance the sensitivity and selectivity for the VDOPs’ identification. Finally, the confirmed PTAD-derivatized target compounds were separated and analyzed using ESI(+)-UHPLC-MS/MS in multiple reaction monitoring (MRM) mode. 相似文献
145.
M. Sc. Benjamin Scheibe Clemens Pietzonka M. Sc. Otto Mustonen Prof. Dr. Maarit Karppinen Prof. Dr. Antti J. Karttunen Prof. Dr. Mihail Atanasov Prof. Dr. Frank Neese Dr. Matthias Conrad Prof. Dr. Florian Kraus 《Angewandte Chemie (International ed. in English)》2018,57(11):2914-2918
The D2h‐symmetric dinuclear complex anion [U2F12]2? of pastel green Sr[U2F12] shows a hitherto unknown structural feature: The coordination polyhedra around the U atoms are edge‐linked monocapped trigonal prisms, the UV atoms are therefore seven‐coordinated. This leads to a U–U distance of 3.8913(6) Å. A weak UV–UV interaction is observed for the dinuclear [U2F12]2? complex and described by the antiferromagnetic exchange Jexp of circa ?29.9 cm?1. The crystalline compound can be easily prepared from SrF2 and β‐UF5 in anhydrous hydrogen fluoride (aHF) at room temperature. It was studied by means of single crystal X‐ray diffraction, IR, Raman and UV/VIS spectroscopy, magnetic measurements, and by molecular as well as by solid‐state quantum chemical calculations. 相似文献
146.
Asymmetric Catalytic Preparation of Polysubstituted Cyclopropanol and Cyclopropylamine Derivatives 下载免费PDF全文
Marwan Simaan Prof. Dr. Ilan Marek 《Angewandte Chemie (International ed. in English)》2018,57(6):1543-1546
The catalytic asymmetric carbometalation of cyclopropenes followed by either an electrophilic oxidation or amination reaction provides a unique approach to the formation of diastereomerically pure and enantiomerically enriched cyclopropanol and cyclopropylamine derivatives, respectively. 相似文献
147.
Zusammenfassung Zwei neue Tüpfelreaktionen für Vanadinum werden beschrieben.-Benzoinoxim gibt einen gelben Niederschlag in schwefelsauren Vanadatlösungen, der auf der Tüpfelplatte den Nachweis von 1 Vanadinum ermöglicht. Der Nachweis der durch Zusatz von Vanadylsalz zu Ferrichlorid gebildeten Ferroionen kann auf der Tüpfelplatte mit,-Dipyridyl oder mit o-Phenanthrolin durchgeführt werden. In beiden Fällen wird eine Erfassungsgrenze von 0,1 Vanadinum erreicht und nur wenige Ionen stören den Nachweis.Der Nachweis der Ferroionen mit Hilfe von Dimethylglyoxim (1 V) und auch der Vanadatnachweis durch die durch Wolframat erzeugte Gelbfärbung (0,3 V) wurden in bezug auf Störungen durch gleichzeitig anwesende Stoffe gründlich untersucht. Die Dimethylglyoximprobe wird durch Zusatz von Phosphat wesentlich verbessert.
Résumé Deux nouvelles réactions à la touche sont décrites pour le vanadium. L'-benzoinoxime donne un précipité jaune en solution sulfurique de vanadate qui, sur la plaquette à touche, rend possible la recherche de 1 vanadium. La recherche des ions ferreux formés par addition d'un sel de vanadyle au chlorure ferrique peut être conduite sur plaquette avec l', -dipyridyle ou l'o-phénanthroline. Dans les deux cas, on atteint une limite de sensibilité de 0,1 de vanadium et quelques ions seulement gênent la recherche.Celle des ions ferreux au moyen de la diméthylglyoxime (1 de vanadium) et aussi la recherche des vanadates par la coloration jaune donnée avec un tungstate (0,3 de vanadium) furent expérimentées d'une manière approfondie en fonction des interférences par les substances simultanément présentes. L'essai à la diméthylglyoxime est essentiellement amélioré par addition de phosphate.相似文献
148.
Zhang Y Iwamoto T Radke G Kariya Y Suzuki K Conrad AH Tomich JM Conrad GW 《Journal of mass spectrometry : JMS》2008,43(6):765-772
In the present work, a rapid and novel method of on-target plate derivatization of keratan sulfate (KS) oligosaccharides for subsequent analysis by matrix-assisted laser desorption and ionization (MALDI) mass spectrometry is described. MALDI-(time-of-flight)-TOF spectra of labeled KS oligosaccharides revealed that significantly improved ionization can be accomplished through derivatization with pyrenebutyric acid hydrazide (PBH), and the most abundant peak in each spectrum corresponds to the singly charged molecular ion [M - H]- or [M + (n - 1)Na - nH]-, where n = the number of sulfates (n = 1, 2, 3...). The high-energy collision-induced dissociation (heCID) spectra of labeled KS oligosaccharides displayed fragments of compounds similar to those observed with laser-induced dissociation (LID) analysis, suggesting that both heCID and LID fragmentations can be used to analyze KS oligosaccharides. Moreover, fragmentation analysis of all labeled KS oligosaccharides was performed by MALDI-TOF/TOF-MS. With LID mode, sodium adducts showed fragmentation of glycosidic linkages with mainly Y/B/C ions, as well as various cross-ring cleavages providing exact information for the positions of sulfate groups along the KS oligosaccharide chains. This one-step on-target derivatization method makes MALDI-TOF/TOF-MS identification of KS fast, simple and highly throughput for trace amounts of biological samples. 相似文献
149.
Brian Conrad Keith Conrad Robert Gross 《Transactions of the American Mathematical Society》2008,360(6):2867-2908
For a prime polynomial , a classical conjecture predicts how often has prime values. For a finite field and a prime polynomial , the natural analogue of this conjecture (a prediction for how often takes prime values on ) is not generally true when is a polynomial in ( the characteristic of ). The explanation rests on a new global obstruction which can be measured by an appropriate average of the nonzero Möbius values as varies. We prove the surprising fact that this ``Möbius average,' which can be defined without reference to any conjectures, has a periodic behavior governed by the geometry of the plane curve .
The periodic Möbius average behavior implies in specific examples that a polynomial in does not take prime values as often as analogies with suggest, and it leads to a modified conjecture for how often prime values occur.
150.
One‐ or Two‐Electron Transfer? The Ambiguous Nature of the Discharge Products in Sodium–Oxygen Batteries 下载免费PDF全文
Dr. Conrad L. Bender Dr. Daniel Schröder Dr. Ricardo Pinedo Prof. Philipp Adelhelm Prof. Jürgen Janek 《Angewandte Chemie (International ed. in English)》2016,55(15):4640-4649
Rechargeable lithium–oxygen and sodium–oxygen cells have been considered as challenging concepts for next‐generation batteries, both scientifically and technologically. Whereas in the case of non‐aqueous Li/O2 batteries, the occurring cell reaction has been unequivocally determined (Li2O2 formation), the situation is much less clear in the case of non‐aqueous Na/O2 cells. Two discharge products, with almost equal free enthalpies of formation but different numbers of transferred electrons and completely different kinetics, appear to compete, namely NaO2 and Na2O2. Cells forming either the superoxide or the peroxide have been reported, but it is unclear how the cell reaction can be influenced for selective one‐ or two‐electron transfer to occur. In this Minireview, we summarize available data, discuss important control parameters, and offer perspectives for further research. Water and proton sources appear to play major roles. 相似文献