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21.
The present work focuses on the development of an in‐operando technique based on the visible spectroscopic reflectometry (VSR) for simultaneous determination of the oxide film formation during anodizing. The establishment of the VSR as in‐operando technique requires an extensive validation by comparative in‐situ but non‐operando thickness measurements under aqueous conditions. The investigations were carried out on anodic oxide films on pure titanium. The authors demonstrate the VSR as a simple and robust method for measurement under electrolyte covering. Additionally, an empirical correction algorithm extends the limitation of the visible reflectometry in thin film thickness. Reliable film thickness values can be measured down to ≥5 nm. The in‐operando mode yields additional information about the film growth time resolved. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
22.
The dinucleoside phosphate ΠdpΠd ( 4 ) was synthesized from the monomers 1-(5′-O-monomethoxytrityl - 2′ - deoxy - β - D - ribofuranosyl) - 2 (1 H) - pyridone ((MeOTr) Πd, 2 ) and 1-(5′-O-phosphoryl-3′-O-acetyl-2′-deoxy-β-D -ribofuranosyl)-(1H)-pyridone (pΠd(Ac), 3 ). Its 6.4% hyperchromicity and an analysis of the 1H-NMR. spectra indicate that the conformation and the base-base interactions in 4 are similar to those in natural pyrimidine dinucleoside phosphates. 相似文献
23.
M. Schneider U. Langklotz A. Michaelis B. Arnold 《Surface and interface analysis : SIA》2010,42(4):281-286
Aluminium–steel friction welds (AlMgSi0.5/C35 and AlMgSi0.5/X5CrNi18‐10) were electrochemically investigated in a NaAc/HAc buffer (pH 5.9) and 0.1 mol/l NaCl using the microcapillary technique. This technique allows a lateral resolution of electrochemical measurements. However, microscopic investigations and scanning electron microscopy/energy dispersive X‐ray SEM/EDX measurements show that the reaction zone (RZ) and the heat affected zone (HAZ) of the welds are smaller than the microcapillary diameter. This paper discusses the advantages and limitations of the microcapillary technique in view of friction welds. Nevertheless, the electrochemical experiments allow a clear detection of the changing active surface area and the correlation to the microstructure (intermetallics). The application of microcapillary measurements on samples which were exposed in marine climate for 2 years shows a good correlation between the local potential measurements and the local corrosion phenomena. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
24.
Afif Ahmed Radenahmad Nikdalila Rahman Seikh Mohammad Habibur Torino Nico Saqib Muhammad Hossain Shahzad Park Jun-Young Azad Abul Kalam 《Journal of Solid State Electrochemistry》2022,26(1):111-120
Journal of Solid State Electrochemistry - Protonic ceramic fuel cells have become extremely interesting due to their high power output at the intermediate temperature range... 相似文献
25.
Gerhard Quinkert Stefan Scherer Dietmar Reichert Hans-Peter Nestler Helma Wennemers Andreas Ebel Klaus Urbahns Klaus Wagner Klaus-Peter Michaelis Gerhard Wiech Günter Prescher Bernd Bronstert Bernd-Jürgen Freitag Ilka Wicke Dietmar Lisch Pavel Belik Thorsten Crecelius Dirk Hrstermann Gottfried Zimmermann Jan W. Bats Gerd Dürner Dieter Rehm 《Helvetica chimica acta》1997,80(6):1683-1772
The two conformers of a cyclohexa-2, 4-dienone with different substituents at C(6) on irradiation are believed to undergo ring opening stereospecifically affording a mixture of two configurationally isomeric diene-ketenes (and descendents thereof)- Exceptions are generally found for those dienones with one C and one O substituent or even with two C substituents, if one of them carries a polar group at a site able to interact through space with the ring C?O group. In these cases, only one of the two anticipated diene-ketenes (and descendents thereof) is produced. A thorough investigation of the photochemistry of a series of structurally different cyclohexa-2, 4-dienones on analytical as well as on preparative scale extends our mechanistic knowledge of the various routes from diene-ketenes into a variety of compound classes. Novel compound classes accessible to diene-ketenes are seven-membered carbocycles (by intramolecular aldolization of the zwitterion of appropriately substituted, transiently formed diene-(N, O)-ketene acetals) and β-lactams (by Staudinger reaction). 相似文献
26.
Regio‐ and Enantio‐selective Chemo‐enzymatic C−H‐Lactonization of Decanoic Acid to (S)‐δ‐Decalactone
Jack Manning Michele Tavanti Joanne L. Porter Nico Kress Sam P. DeVisser Nicholas J. Turner Sabine L. Flitsch 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(17):5724-5727
The conversion of saturated fatty acids to high value chiral hydroxy‐acids and lactones poses a number of synthetic challenges: the activation of unreactive C?H bonds and the need for regio‐ and stereoselectivity. Here the first example of a wild‐type cytochrome P450 monooxygenase (CYP116B46 from Tepidiphilus thermophilus) capable of enantio‐ and regioselective C5 hydroxylation of decanoic acid 1 to (S)‐5‐hydroxydecanoic acid 2 is reported. Subsequent lactonization yields (S)‐δ‐decalactone 3 , a high value fragrance compound, with greater than 90 % ee. Docking studies provide a rationale for the high regio‐ and enantioselectivity of the reaction. 相似文献
27.
Dr. Dinar Abdullin Dr. Hideto Matsuoka Dr. Maxim Yulikov Nico Fleck Dr. Christoph Klein Dr. Sebastian Spicher Dr. Gregor Hagelueken Prof. Dr. Stefan Grimme Prof. Dr. Arne Lützen Prof. Dr. Olav Schiemann 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(37):8820-8828
Pulsed EPR dipolar spectroscopy (PDS) offers several methods for measuring dipolar coupling and thus the distance between electron-spin centers. To date, PDS measurements to metal centers were limited to ions that adhere to the high-field approximation. Here, the PDS methodology is extended to cases where the high-field approximation breaks down on the example of the high-spin Fe3+/nitroxide spin-pair. First, the theory developed by Maryasov et al. (Appl. Magn. Reson. 2006 , 30, 683–702) was adapted to derive equations for the dipolar coupling constant, which revealed that the dipolar spectrum does not only depend on the length and orientation of the interspin distance vector with respect to the applied magnetic field but also on its orientation to the effective g-tensor of the Fe3+ ion. Then, it is shown on a model system and a heme protein that a PDS method called relaxation-induced dipolar modulation enhancement (RIDME) is well-suited to measuring such spectra and that the experimentally obtained dipolar spectra are in full agreement with the derived equations. Finally, a RIDME data analysis procedure was developed, which facilitates the determination of distance and angular distributions from the RIDME data. Thus, this study enables the application of PDS to for example, the highly relevant class of high-spin Fe3+ heme proteins. 相似文献
28.
Dr. Dinar Abdullin Nico Fleck Christoph Klein Philipp Brehm Sebastian Spicher Prof. Dr. Arne Lützen Prof. Dr. Stefan Grimme Prof. Dr. Olav Schiemann 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(10):2586-2596
Iron(III) porphyrins have the propensity to form μ2-oxo-dimers, the structures of which resemble two wheels on an axle. Whereas their crystal structure is known, their solution structure and internal dynamics is not. In the present work, the structure and dynamics of such dimers were studied by means of electron paramagnetic resonance (EPR) spectroscopy and quantum chemistry based molecular dynamics (MD) simulations by using the semiempirical tight-binding method (GFN-xTB). To enable EPR investigation of the dimers, a nitroxide was attached to each of the tetraphenylporphyrin cores through a linear and a bent linker. The inter-nitroxide distance distributions within the dimers were determined by continuous-wave (cw)-EPR and pulsed electron–electron double resonance (PELDOR or DEER) experiments and, with the help of MD, interpreted in terms of the rotation of the porphyrin planes with respect to each other around the Fe–O–Fe axis. It was found that such rotation is restricted to the four registers defined by the phenyl substituents. Within the registers, the rotation angle swings between 30° and 60° in the proximal and between 125° and 145° in the distal register. With EPR, all four angles were found to be equally populated, whereas the 30° and 145° angles are strongly favored to the expense of the 60° and 125° angles in the MD simulation. In either case, the internal dynamics of these dimers thus resemble the motion of a step motor. 相似文献
29.
30.
The bimolecular hydrogen-deuterium exchange behavior of protonated alkyl dipeptides in the gas phase
Erez H. Gur Leo J. de Koning Nico M. M. Nibbering 《Journal of the American Society for Mass Spectrometry》1995,6(6):466-477
As part of an ongoing characterization of the intrinsic chemical properties of peptides, thermal hydrogen-deuterium exchange has been studied for a series of fast-atom-bombardment-generated protonated alkyldipeptides and related model compounds in the reaction with D2O, CH3OD, and ND3 in a Fourier transform ion cyclotron resonance mass spectrometer. Despite the very large basicity difference between the dipeptides and the D2O and CH3OD exchange reagents, efficient exchange of all active hydrogen atoms occurs. From the kinetic data it appears that exchange of the amino, amide, and hydroxyl hydrogens proceeds with different efficiencies, which implies that the proton in thermal protonated dipeptides is immobile. The selectivity of the exchange at the different basic sites is governed by the nature of both the dipeptide and the exchange reagent. The results indicate that reversible proton transfer in the reaction complexes, which effectuates the deuterium incorporation, is assisted by formation of multiple hydrogen bonds between the reagents. Exchange is considered to proceed via the intermediacy of different competing intermediate complexes, each of which specifically leads to deuterium incorporation at different basic sites. The relative stabilization of the competing intermediate complexes can be related to the relative efficiencies of deuterium incorporation at different basic sites in the dipeptide. For all protonated dipeptides studied, the exchange in the reaction with ND3 proceeds with unit efficiency, whereas all active hydrogen atoms are exchanged equally efficiently. Evidently specific multiple hydrogen bond formations are far less important in the reversible proton transfers with the relatively basic ammonia, which allows effective randomization of all active hydrogen atoms in the reaction complexes. 相似文献