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41.
Acid hydrolysis of N(CH2CN)3 leads either nitrilotriacetamide, 1, and/or 3,5-dioxopiperazineacetamide, 4, in quantitative yield. 1 slowly and cleanly converts to 3,5-dioxopiperazineacetic acid, 5, in water, although ammonium salts prevent this reaction. 相似文献
42.
Eric R. Beckel Neil B. Cramer Adam W. Harant Christopher N. Bowman Corresponding author 《Liquid crystals》2013,40(11):1343-1350
Electro-optic properties of polymer stabilized ferroelectric liquid crystal (PSFLC) systems are examined as a function of varying concentrations of either a linear or crosslinked thiol-ene polymer. The thiol-ene method of polymer stabilization is a drastic change from previous studies designed to avert the problem of polymer phase separation. FLC rise time and tilt angle measurements were used to determine the effects of the polymer network on the optical properties of the system. The addition of monomer impurities to both systems demonstrated a reduction in tilt angle, which translated into decreased switching speeds in both systems prior to polymerization. The crosslinked thiol-ene system showed increased switching times due to the creation of polymer in the interlayer spacing of the FLC, but exhibited minimal increase in the rotational viscosity of the system. In addition, the crosslinked polymer systems resulted in an increase in the liquid crystalline order, which produced an increase in the contrast ratio of the system. The linear polymer system showed drastically different results as compared with the crosslinked system. The rise time and tilt angle measurements decreased upon polymerization of the linear thiol-ene and the rotational viscosity and contrast ratio values also decreased. We suggest that the linear thiol-ene polymer phase separation from the interlayer spacing leads to a microscopic misalignment of the FLC molecules, causing a decrease in the optical properties of the LC. 相似文献
43.
Tyrosine nitration of human ERK1 introduces an intra-hydrogen bond by molecular dynamics simulations
Xu Wu Zhang Yuanya Achi Oliver Y. Knierim Kathleen D. Hanks Justin G. Wang Yingchun 《Structural chemistry》2019,30(4):1459-1470
Structural Chemistry - ERK1 is an important kinase in Ras–Raf–MEK signaling. We have recently demonstrated by mass spectrometry that Tyr210 of ERK1 can be nitrated, and the nitration... 相似文献
44.
Saeed Kamali Hongxin Wang Devrani Mitra Hideaki Ogata Wolfgang Lubitz Brian C. Manor Thomas B. Rauchfuss Deborah Byrne Violaine Bonnefoy Francis E. Jenney Michael W. W. Adams Yoshitaka Yoda Ercan Alp Jiyong Zhao Stephen P. Cramer 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2013,125(2):752-756
45.
Influence of the degree of ionization on the growth mechanism of poly(diallyldimethylammonium)/poly(acrylic acid) multilayers 下载免费PDF全文
Dörte Bütergerds Christian Kateloe Cornelia Cramer Monika Schönhoff 《Journal of Polymer Science.Polymer Physics》2017,55(5):425-434
pH‐dependent growth laws of the mass coverage Γ(n) of poly(diallyldimethylammonium) chloride and poly(acrylic acid) (PAA) layer‐by‐layer films are analyzed by Quartz Crystal Microbalance‐D. (Attenuated Total Reflection)‐FTIR spectroscopy shows a degree of dissociation of acrylic acid groups in the films identical to that in solution. Apart from pH‐regimes of differently pronounced exponential and linear growth, the corresponding kinetics indicate pH‐dependent adsorption, reorganization, and diffusion processes. As the thickest films form with almost uncharged PAA (low pH), the results can only partly be explained by the dissociation degree of PAA in the film. For intermediate and high pH values chain interdiffusion as a mechanism for nonlinear growth is strongly dependent on the charge density of the PAA chains. However, at low pH other types of interactions, most likely ion–dipole interactions, play a major role in the multilayer growth. Furthermore, a change in the symmetry of growth can be observed in the low to intermediate pH range. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 425–434 相似文献
46.
Vincent J. Kalish Robert L. Shone Steven W. Kramer Paul W. Collins Kevin A. Babiak Kathleen T. McLaughlin 《合成通讯》2013,43(11):1641-1645
Hydrozirconation-iodination of a terminal acetylene followed by lithium-iodide exchange and finally dilithio cyanocuprate mediated conjugate addition to an appropriate cyclopentenone is reported as an efficient method for the synthesis of prostaglandin analogues. 相似文献
47.
Sudarsanan Varaprath Mark Seaton Debra McNett Lin Cao Kathleen P. Plotzke 《International journal of environmental analytical chemistry》2013,93(3):203-219
Abstract A method was developed and validated to measure octamethylcyclotetrasiloxane (D4)? quantitatively by gas chromatography-mass spectrometry (GC-MS) at low level in extracts of several biological matrices that include plasma, liver, lung, feces and fat from rats. The key to the successful determination lay in the use of extracts dried with anhydrous magnesium sulfate. This was necessary in view of the propensity of the methyl siloxane based GC-stationary phase to generate D4 by its reaction with water present in the extracts. To enable quantiiation of D4 at parts per billion (μg/L) levels, the base ion m/z 281 resulting from the loss of a methyl group from the parent molecule was selected for monitoring by SIM mode in GC-MS. The recovery of D4 from any of the biological matrices was determined to be greater than 90% in three extractions. The D4 response for the standards in GC-MS was linear (R2 > 0.9900) and reproducible at concentrations ranging from 1—16,000 ng D4/g solvent. Precision was less than 5%. 相似文献
48.
The ionic liquid 1-ethyl-3-methylimidazolium acetate ([C2mim][OAc]) was successfully used as alternative solvent for native chemical ligation of peptide fragments to produce model peptide LYRAXCRANK (X = G, A, L, N, Q, K, and F). The commonly used buffer system including thiol additives such as thiophenol and benzyl mercaptan can be replaced by the nontoxic ionic liquid [C2mim][OAc]. In addition to improving the solubility of the peptides in [C2mim][OAc], yields and rates of the ligation reactions were found to be efficiently enhanced. 相似文献
49.
Laetitia Souillart Nicolai Cramer 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2014,126(36):9794-9798
The lactone motif is ubiquitous in natural products and pharmaceuticals. The Tishchenko disproportionation of two aldehydes, a carbonyl hydroacylation, is an efficient and atom‐economic access to lactones. However, these reaction types are limited to the transfer of a hydride to the accepting carbonyl group. The transfer of alkyl groups enabling the formation of C C bonds during the ester formation would be of significant interest. Reported herein is such asymmetric carbonyl carboacylation of aldehydes and ketones, thus affording complex bicyclic lactones in excellent enantioselectivities. The rhodium(I)‐catalyzed transformation is induced by an enantiotopic C C bond activation of a cyclobutanone and the formed rhodacyclic intermediate reacts with aldehyde or ketone groups to give highly functionalized lactones. 相似文献
50.
Margaret Rak Murielle Salome Susan G. W. Kaminskyj Kathleen M. Gough 《Analytical and bioanalytical chemistry》2014,406(12):2809-2816
We used synchrotron X-ray fluorescence to create the first semiquantitative, submicron resolution, element distribution maps of P, S, K, and Ca, in situ, in fungal samples. Data collection was performed at the European Synchrotron Radiation Facility beam line ID21, Grenoble, France. We studied developing hyphae, septa, and conidiophores in Aspergillus nidulans, comparing wild type and two cell wall biosynthesis gene deletion strains. The latter encode sequential enzymes for biosynthesis of galactofuranose, a minor wall carbohydrate. Each gene deletion caused hyphal morphogenesis defects, and reduced both colony growth and sporulation 500-fold. Elemental imaging has helped elucidate biochemical changes in the phenotype induced by the gene deletions that were not apparent from morphological examination. Here, we examined S as a proxy for protein content, P for nucleic acid content, as well as Ca and K, which also have important metabolic roles. Element distributions in wild-type fungi reflect biological aspects already known or expected from other types of analysis; however, the application of X-ray fluorescence (XRF) imaging reveals aspects of gene deletion phenotypes that were not previously available. We have demonstrated that deleting a dispensable gene involved in galactose metabolism (ugeA) and one involved in biosynthesis of a minor cell wall component (ugmA) led to changes in hyphal elemental distribution that may have resulted from compromised wall composition. 相似文献