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21.
Christoph Englert Dr. Ivo Nischang Cornelia Bader Philipp Borchers Julien Alex Michael Pröhl Martin Hentschel Dr. Matthias Hartlieb Dr. Anja Traeger Prof. Dr. Georg Pohnert Dr. Stephanie Schubert Dr. Michael Gottschaldt Prof. Dr. Ulrich S. Schubert 《Angewandte Chemie (International ed. in English)》2018,57(9):2479-2482
A benzoin‐derived diol linker was synthesized and used to generate biocompatible polyesters that can be fully decomposed on demand upon UV irradiation. Extensive structural optimization of the linker unit was performed to enable the defined encapsulation of diverse organic compounds in the polymeric structures and allow for a well‐controllable polymer cleavage process. Selective tracking of the release kinetics of encapsulated model compounds from the polymeric nano‐ and microparticle containers was performed by confocal laser scanning microscopy in a proof‐of‐principle study. The physicochemical properties of the incorporated and released model compounds ranged from fully hydrophilic to fully hydrophobic. The demonstrated biocompatibility of the utilized polyesters and degradation products enables their use in advanced applications, for example, for the smart packaging of UV‐sensitive pharmaceuticals, nutritional components, or even in the area of spatially selective self‐healing processes. 相似文献
22.
The N‐Methylpyrrolidone (NMP) Effect in Iron‐Catalyzed Cross‐Coupling with Simple Ferric Salts and MeMgBr 下载免费PDF全文
Dr. Salvador B. Muñoz III Dr. Stephanie L. Daifuku Jeffrey D. Sears Tessa M. Baker Stephanie H. Carpenter Dr. William W. Brennessel Prof. Michael L. Neidig 《Angewandte Chemie (International ed. in English)》2018,57(22):6496-6500
The use of N‐methylpyrrolidone (NMP) as a co‐solvent in ferric salt catalyzed cross‐coupling reactions is crucial for achieving the highly selective, preparative scale formation of cross‐coupled product in reactions utilizing alkyl Grignard reagents. Despite the critical importance of NMP, the molecular level effect of NMP on in situ formed and reactive iron species that enables effective catalysis remains undefined. Herein, we report the isolation and characterization of a novel trimethyliron(II) ferrate species, [Mg(NMP)6][FeMe3]2 ( 1 ), which forms as the major iron species in situ in reactions of Fe(acac)3 and MeMgBr under catalytically relevant conditions where NMP is employed as a co‐solvent. Importantly, combined GC analysis and 57Fe Mössbauer spectroscopic studies identified 1 as a highly reactive iron species for the selective formation generating cross‐coupled product. These studies demonstrate that NMP does not directly interact with iron as a ligand in catalysis but, alternatively, interacts with the magnesium cations to preferentially stabilize the formation of 1 over [Fe8Me12]? cluster generation, which occurs in the absence of NMP. 相似文献
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24.
The single‐crystal X‐ray structure analysis of hexakis(2,4,6‐triisopropylphenyl)cyclotristannoxane, cyclo‐[(2,4,6‐i‐Pr3‐C6H2)2SnO]3 ( 1 ), is reported and reveals this compound to contain an almost planar six‐membered ring. Redistribution reactions of 1 with cyclo‐(t‐Bu2SnO)3 and t‐Bu2SiCl2, respectively, failed and indicate an unusual kinetic inertness of the Sn–O bonds in 1 as compared to related molecular diorganotin oxides containing less bulkier substituents. The redistribution reaction of cyclo‐(t‐Bu2SnO)3 with cyclo‐(t‐Bu2SnS)2 leads to an equilibrium involving the trimeric diorganotin oxysulphides cyclo‐t‐Bu2Sn(OSnt‐Bu2)2S ( 2 a ) and cyclo‐t‐Bu2Sn(SSnt‐Bu2)2O ( 2 b ). 相似文献
25.
Hesse-Ertelt S Witter R Ulrich AS Kondo T Heinze T 《Magnetic resonance in chemistry : MRC》2008,46(11):1030-1036
Solid-state (13)C-NMR spectroscopy was used to characterize native cellulose pellicles from two strains of Gluconacetobacter xylinus (ATCC 53582, ATCC 23769), which had been statically cultivated in Hestrin-Schramm (HS) medium containing fully (13)C-labeled beta-D-glucose-U-(13)C(6) as the sole source of carbon. For both samples, the (13)C-NMR chemical shifts were completely assigned for each (13)C-labeled site of cellulose I(alpha) with the aid of 2D refocused INADEQUATE NMR. To determine the principal chemical shift tensor components, a pulse sequence based on the recoupling of anisotropy information (RAI) was applied at 10 kHz MAS. The detailed (13)C tensors of cellulose I(alpha) from different bacterial celluloses are thus available now for the first time, and these results have been compared with previously published data of nonenriched material and with theoretical predictions. 相似文献
26.
Villano SM Eyet N Lineberger WC Bierbaum VM 《Journal of the American Chemical Society》2008,130(23):7214-7215
The gas-phase reactivity of the CHCl*- anion has been investigated with a series of halomethanes (CCl4, CHCl3, CH2Cl2, and CH3Cl) using a FA-SIFT instrument. Results show that this anion primarily reacts via substitution and by proton transfer. In addition, the reactions of CHCl*- with CHCl3 and CH2Cl2 form minor amounts of Cl2*- and Cl-. The isotopic distribution of these two products is consistent with an insertion-elimination mechanism, where the anion inserts into a C-Cl bond to form an unstable intermediate, which eliminates either Cl2*- or Cl- and Cl*. Neutral and cationic carbenes are known to insert into single bonds; however, this is the first observation of such reactivity for carbene anions. 相似文献
27.
Neverov AA Liu CT Bunn SE Edwards D White CJ Melnychuk SA Brown RS 《Journal of the American Chemical Society》2008,130(20):6639-6649
The di-Zn(II) complex of 1,3-bis[ N1, N1'-(1,5,9-triazacyclododecyl)]propane with an associated methoxide ( 3:Zn(II) 2: (-)OCH 3) was prepared and its catalysis of the methanolysis of a series of fourteen methyl aryl phosphate diesters ( 6) was studied at s (s)pH 9.8 in methanol at 25.0 +/- 0.1 degrees C. Plots of k obs vs [ 3:Zn(II) 2: (-)OCH 3] free for all members of 6 show saturation behavior from which K(M) and kcat (max) were determined. The second order rate constants for the catalyzed reactions (kcat (max)/K(M)) for each substrate are larger than the corresponding methoxide catalyzed reaction (k 2 (-OMe)) by 1.4 x 10(8) to 3 x 10 (9)-fold. The values of k cat (max) for all members of 6 are between 4 x 10(11) and 3 x 10(13) times larger than the solution reaction at s (s)pH 9.8, with the largest accelerations being given for substrates where the departing aryloxy unit contains ortho-NO 2 or C(O)OCH 3 groups. Based on the linear Br?nsted plots of k cat (max) vs s (s)pKa of the phenol, beta lg values of -0.57 and -0.34 are determined respectively for the catalyzed methanolysis of "regular" substrates that do not contain the ortho-NO 2 or C(O)OCH 3 groups, and those substrates that do. The data are consistent with a two step mechanism for the catalyzed reaction with rate limiting formation of a catalyst-coordinated phosphorane intermediate, followed by fast loss of the aryloxy leaving group. A detailed energetics calculation indicates that the catalyst binds the transition state comprising [CH 3O (-): 6], giving a hypothetical [ 3:Zn(II) 2:CH 3O (-): 6] complex, by -21.4 to -24.5 kcal/mol, with the strongest binding being for those substrates having the ortho-NO 2 or C(O)OCH 3 groups. 相似文献
28.
Stephanie Kaspar Diana Weier Winfriede Weschke Hans-Peter Mock Andrea Matros 《Analytical and bioanalytical chemistry》2010,398(7-8):2883-2893
Both the nucellar projection (NP) and endosperm transfer cells (ETC) of the developing barley grain (harvested 8 days after flowering) were isolated by laser capture micro-dissection combined with pressure catapulting. Protein extracts were analyzed by nanoUPLC separation combined with ESI-Q-TOF mass spectrometry. The majority of the ~160 proteins identified were involved in translation, protein synthesis, or protein destination. The NP proteome was enriched for stress defense molecules, while proteins involved in assimilate transport and the mobilization of nutrients were common to both the NP and the ETC. The combined qualitative and quantitative protein profiling allowed for the identification of several proteins showing tissue specificity in their expression, which underlines the distinct biological functions of these two tissues within the developing barley grain. 相似文献
29.
Benjamin A. DeGraff Mandy Hennip Julie M. Jones Carl Salter Stephanie A. Schaertel 《The Chemical Educator》2002,7(1):15-18
We describe an inexpensive modular Raman spectrometer system that can be assembled from commercial components for under $5000. Three typical applications are presented: a demonstration of a vibrational isotope effect, a Raman polarization experiment, and a resonance Raman experiment. This spectrometer system should make it easier to include the important topic of Raman spectroscopy in the undergraduate physical and analytical chemistry laboratory curricula. 相似文献
30.
Maria Lorna A. De Leoz Shuai Wu John S. Strum Milady R. Niñonuevo Stephanie C. Gaerlan Majid Mirmiran J. Bruce German David A. Mills Carlito B. Lebrilla Mark A. Underwood 《Analytical and bioanalytical chemistry》2013,405(12):4089-4105
Human milk oligosaccharides (HMOs), though non-nutritive to the infant, shape the intestinal microbiota and protect against pathogens during early growth and development. Infant formulas with added galacto-oligosaccharides have been developed to mimic the beneficial effects of HMOs. Premature infants have an immature immune system and a leaky gut and are thus highly susceptible to opportunistic infections. A method employing nanoflow liquid chromatography time-of-flight mass spectrometry (MS) is presented to simultaneously identify and quantify HMOs in the feces and urine of infants, of which 75 HMOs have previously been fully structurally elucidated. Matrix-assisted laser desorption/ionization Fourier transform ion cyclotron resonance MS was employed for high-resolution and rapid compositional profiling. To demonstrate this novel method, samples from mother–infant dyads as well as samples from infants receiving infant formula fortified with dietary galacto-oligosaccharides or probiotic bifidobacteria were analyzed. Ingested oligosaccharides are demonstrated in high abundance in the infant feces and urine. While the method was developed to examine specimens from preterm infants, it is of general utility and can be used to monitor oligosaccharide consumption and utilization in term infants, children, and adults. This method may therefore provide diagnostic and therapeutic opportunities. Figure
Quantification of human milk oligosacchairdes in the milk, feces, and urine of a mother-infant dyad by MALDI FT-ICR (spectra) and nano-LC MS (pie charts) 相似文献