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91.
A method is proposed for calculating the melting temperature (T 0) of a pure substance by combining cryoscopic measurements of melting temperature (T m ) of various impure samples with differential calorimetric values of temperature differencesT 0-T m for the same samples. The proposed expression is: $$T_0 = \frac{{\mathop \Sigma \limits_1^n T_m }}{n} + \frac{{\mathop \Sigma \limits_1^n (T_0 - T_m )}}{n}$$ where the right-side term denotes the average value of a sufficiently high number of experiments (n). The value ofT 0 determined in such a way, may be much more reliable than that obtained by using graphical methods or preparing an extremely pure sample. 相似文献
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Akpa Eric Jacques Philippe Wathelet Bernard Paquot Michel Fuchs Regine Budzikiewicz Herbert Thonart Philippe 《Applied biochemistry and biotechnology》2001,91(1-9):551-561
Bacillus subtilis produces various families of lipopeptides with different homologous compounds. To produce “new molecules” with improved activities
and to select strains that produced a reduced number of homologs or isomers, we studied the effects of different media on
the nature of the synthesis of fatty acid chains for each lipopeptide family. This study focused on two B. subtilis strains cultivated in flasks. Optimized medium for lipopeptide production and Landymedium modified by replacing glutamic
acid with other α-amino acids were used. We found that the intensity of production of homologous compounds depends on the
strain and the culture medium. Analysis of these lipopeptides by high-performance liquid chromatography showed that the strain
B. subtilis NT02 yielded various homologous compounds when cultivated in Landy medium (L-Glu), but primarily one homologous product in
high relative amounts when cultivated in the optimized medium. Mass spectrometric analysis and determination of the amino
acid composition of this molecule enabled us to identify it as Bacillomycine L c15. 相似文献
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Introducing a Hydrogen‐Bond Donor into a Weakly Nucleophilic Brønsted Base: Alkali Metal Hexamethyldisilazides (MHMDS,M=Li,Na, K,Rb and Cs) with Ammonia 下载免费PDF全文
Dr. Roman Neufeld Reent Michel Dr. Regine Herbst‐Irmer Ralf Schöne Prof. Dr. Dietmar Stalke 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(35):12340-12346
Alkali metal 1,1,1,3,3,3‐hexamethyldisilazide (MHMDSs) are one of the most utilised weakly nucleophilic Brønsted bases in synthetic chemistry and especially in natural product synthesis. Like lithium organics, they aggregate depending on the employed donor solvents. Thus, they show different reactivity and selectivity as a function of their aggregation and solvation state. To date, monomeric LiHMDS with monodentate donor bases was only characterised in solution. Since the first preparation of LiHMDS in 1959 by Wannagat and Niederprüm, all efforts to crystallise monomeric LiHMDS in the absence of chelating ligands failed. Herein, we present ammonia adducts of LiHMDS, NaHMDS, KHMDS, RbHMDS and CsHMDS with unprecedented aggregation motifs: 1) The hitherto missing monomeric key compound in the LiHMDS aggregation architectures. Monomeric crystal structures of trisolvated LiHMDS ( 1 ) and NaHMDS ( 2 ), showing unique intermolecular hydrogen bonds, 2) the unprecedented tetrasolvated KHMDS ( 3 ) and RbHMDS ( 4 ) dimers and 3) the disolvated CsHMDS ( 5 ) dimer with very close intermolecular Si?CH3???Cs s‐block “agostic” interactions have been prepared and characterised by single‐crystal X‐ray structure analysis. 相似文献
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The impact of the cononsolvency effect on poly (N-isopropylacrylamide) based microgels at interfaces
Marcel Richter Melanie Hunnenmörder Regine V. Klitzing 《Colloid and polymer science》2014,292(10):2439-2452
The paper addresses the effect of solid interfaces on the cononsolvency effect for poly(N-iso propylacrylamide) based microgels containing different contents of the co-monomer allyl acetic acid (AAA). The cononsolvency effect is studied by dynamic light scattering (DLS) in solution and with atomic force microscopy (AFM) at surfaces against different mixtures of water and organic solvent (ethanol, iso-propanol, and tetrahydrofuran). For the studies at interfaces, the microgels are spin coated on silicon wafers that are precoated with poly(allylamine hydrochloride) (PAH). The minimum in particle volume due to cononsolvency shows a pronounced shift from 10–20 % of organic solvent to 40–50 % after deposition at the Si/PAH wafer. The strong shift indicates an increase of water to organic solvent ratio within the gel at the surface with respect to the bulk solution. In order to understand the increase of water to organic solvent ratio, shrinking/reswelling AFM experiments for different spin-coating conditions and under ambient conditions are carried out. Spin coating from water instead from different solvent mixtures has no effect on the cononsolvency. In ambient conditions, the cononsolvency effect disappears 相似文献
100.
Komatsu K L'Hôte D Nakamae S Mosser V Konczykowski M Dubois E Dupuis V Perzynski R 《Physical review letters》2011,106(15):150603
We present the experimental observation of the fluctuation-dissipation theorem violation in an assembly of interacting magnetic nanoparticles in the low temperature superspin-glass phase. The magnetic noise is measured with a two-dimension electron gas Hall probe and compared to the out of phase ac susceptibility of the same ferrofluid. For "intermediate" aging times of the order of 1 h, the ratio of the effective temperature T(eff) to the bath temperature T grows from 1 to 6.5 when T is lowered from T(g) to 0.3 T(g), regardless of the noise frequency. These values are comparable to those measured in an atomic spin glass as well as those calculated for a Heisenberg spin glass. 相似文献