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1.
Matthew J. Hills Irmgard Kiewitt Kumar D. Mukherjee 《Applied biochemistry and biotechnology》1991,27(2):123-129
Lipase from rape (Brassica napus L., immobilized onto celite, catalyzes esterification and transesterification reactions in hexane. The activity of the lipase is stimulated up to 35 fold by the addition of water (1.3% w/v). The activity of the lipase in hydrolysis is about 8 times higher than in the esterification reactions in hexane. Interesteri-fication reactions between mono- and diacylglycerols and transesterification reactions of mono- and diacylglycerols with alcohols were also catalyzed at relatively high rates but transesterification/esterification of these acylglycerols with fatty acids was comparatively slow. In transesterification reactions, triacylglycerols reacted rather slowly. 相似文献
2.
Irmgard Heber 《Colloid and polymer science》1967,215(2):145-149
Zusammenfassung Steigert man für das Poly?thylen die Kristallisationstemperatur, so findet man Kristallformen in der folgenden Reihenfolge:
rautenf?rmige Einkristalle— rautenf?rmige Einkristalle mit abgeschnittenen spitzen Ecken (“truncated lozenge crystals”)-l?ngliche
sechseckf?rmige Einkristalle, bei denen die kristallographische b-Achse der orthorhombischen Elementarzelle in Richtung der l?ngsten Ausdehnung des Kristalls liegt. Diese l?nglichen Sechsecke
lagern sich zu Sph?rolithen zusammen, und zwar so, da? die kristallographische b-Achse radial liegt, wie es auch bei den aus der Schmelze gewachsenen Sph?rolithen der Fall ist. Damit sind für das Poly?thylen
übergangsformen zwischen den Einkristallen und Sph?rolithen aufgezeigt.
Sph?rolithe, die aus der L?sung gewachsen sind, zeigen im Polarisationsmikroskop nur dann ein konzentrisches Ringsystem, wenn
bei der Bildung der Sph?rolithe ein Mindestangebot an Substanz vorhanden ist. Die Ringbreite nimmt dann mit steigender Kristallisationstemperatur
zu. Bei aus der Schmelze gewachsenen Poly?thylen-Sph?rolithen ist mit der Bildung von nicht-kristallographischen Verzweigungen
eine Drehung der Indikatrix verbunden. Vermutlich wird also auch bei aus der L?sung gewachsenen Sph?rolithen das Ringsystem
auf dem Auftreten von Verzweigungen infolge hohen Angebotes von kristallisierender Substanz beruhen.
Summary With increasing temperature of crystallization polyethylene crystallizes from solution as lozenge single crystals, truncated lozenge crystals and longish hexagonal crystals, with the crystallographic b-axis along the long diagonal. In the solutions longish hexagonal crystal plates are able to cluster and to form spherulites, in which their crystallographic b-axes are oriented radially like the b-axes in spherulites grown from the melt. Various transition species have been observed. In polarised light the spherulites grown from solution show a concentric ring-system only, if during the crystallization a sufficient quantity of polyethylene is present. The ring-width increases with increasing crystallization temperature. Further it is shown that in polyethylene spherulites grown from the melt the rotation of the indicatrix is connected with a non-crystallographic branching. We suppose, that also for the solution-grown spherulites the ring-system depends on branching.相似文献
3.
Armin Presser Olaf Kunert Irmgard P?tschger 《Monatshefte für Chemie / Chemical Monthly》2006,26(1):365-374
Several improved approaches for the preparation of tetra-O-benzyl-α-D-glucopyranosyl bromide and tetra-O-pivaloyl-α-D-glucopyranosyl bromide are discussed. The importance of these compounds, which are useful glycosyl donors, was demonstrated
by successful preparation of cholesteryl glucopyranosides in an almost neutral medium without the formation of orthoesters.
In addition, accurate 1H and 13C NMR resonance assignments of the synthesized cholesteryl glycosides were performed by 2D NMR spectroscopy. 相似文献
4.
Nikolaus von der Heydt Irmgard von der Heydt 《Zeitschrift für Physik B Condensed Matter》1980,37(3):249-264
The driven system of conducting channels in a nerve membrane is investigated. A current flow generates a coupling between the channels: the current through a channel is influenced by the presence of other conducting channels via the deformation of the equipotential surfaces within the media adjacent to the membrane. We derive an integral equation for the membrane voltageV(s) (s in the membrane plane) and solve it for different membrane conductance distributions(s) including models for stochastic distributions of conducting channels.V(s) is a nonlinear functional of(s). The system of coupled channels is compared with an Ising model. The system exhibits a multi-channel interaction which can be characterized by two different rangesd
int andD
1. For a mean channel distanced
0d
int interaction effects are negligible, and ford
0D
1 all channel-voltages are equal and thus represent a mean-field for the channels. Increasing conductivity of the medium decreasesd
int and increasesD
1. With experimental data on sodium channels in nerve membranes we find:d
intd
0, i.e. a 50% decrease of the channel-voltages by the interaction, andD
1103104
d
0, which indicates mean-field behaviour of the channels. In a subsequent paper we shall treat the statistics of channels which open and close stochastically under the influence of the local membrane voltage. 相似文献
5.
Irmgard Kalf 《Journal of organometallic chemistry》2006,691(10):2277-2285
Enantiomerically pure cationic complexes were obtained via cyclopalladation of primary amines and subsequent addition of a chelating ethylendiamine ligand. No diastereomeric resolution was observed upon combining these cations with racemic mandelate or hydratropate anions, but four less popular products, namely three double salts and a solid solution, were obtained and structurally characterized. For one of the double salts, the alternative ionic compounds based on different stereoisomers of the same residues were synthesized independently: The conventional racemic solid and both diastereomeric salts formed by enantiopure cations and anions were studied by single crystal X-ray diffraction. Lattice energy calculations confirm that the diastereomeric salts differ significantly; formation of the partially racemic double salt, however, is energetically favourable and precludes resolution. 相似文献
6.
The use of additive correction schemes to obtain structures and vibrational frequencies of increasingly larger molecules is becoming more common. Such approaches, based on the cubic extrapolation formula applied directly to the quantity of interest, have been successfully validated only at the highest levels of computational accuracy: for coupled cluster methods with comparably large basis sets. Here, a systematic validation of geometries and vibrational frequencies is carried out, including more affordable and relevant levels of theory, such as the Møller-Plesset perturbation theory applied with smaller basis sets. Comparisons of such additive schemes against the more rigorous gradient-based extrapolation are presented. The cbs () routine of the open-source quantum-chemistry package Psi4 has been extended for this purpose. The results confirm that geometries and frequencies of covalently bound species obtained with additive correction schemes are in an excellent agreement with the results of gradient-based extrapolations. However, when applied to systems involving noncovalent interactions, the errors due to such schemes are significantly larger. In general, we propose the application of gradient-based extrapolations, as they incur no extra cost compared to additive schemes. 相似文献
7.
M. Sc. Florian Hofbauer Prof. Dr. Irmgard Frank 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(51):16332-16338
Previous single‐molecule atomic force microscopy (AFM) experiments showed a change in the reactivity of a bimolecular substitution reaction with a definite force acting on a protein containing disulfide bonds. Using Car–Parrinello molecular dynamics (CPMD) simulations, we analyse the relevant reaction pathways for the breaking of a disulfide bond in the presence of nucleophiles. 相似文献
8.
Manfred Meisel Annegrit Rabis Arnd-Rüdiger Grimmer Irmgard Hartwich Regina Bienert Dirk Wulff-molder 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1)
Abstract Previoudy we reported on the preparative use of donorstabilized monometaphosphates, Py.PO2Cl and Py.PS2Cl[1]. 3P MAS investigations as well as X-ray single crystal analysis have been carried out. The isotropic chemical shift of the sulfur compound shows the typical downfield shift (106 ppm) with respect to the oxygen compound The chemical shift anisotropy gives additional information. The relative large spans ω (Py.PO2Cl: 401 ppm, Py.PS2Cl: 461 ppm) [2] reveal strong deviations from tetrahedral symmetry (ω = 0 ppm) in agreement with the structural data. The values of the skew parametem K (0.64 and 0.71 resp.) reflect the trend to axial symmetry (k = ± l). X-ray diffraction and NMR data suggest a structural model corresponding to a concentration of double bond character on the two P-X bonds. This model is consistent with the extremely short P-X bond length (1.449 Å and 1.921 Å rasp.) as well as the large P-X-P bond angles (126.4°and 123.7° resp.). 相似文献
9.
Merfort I 《Journal of chromatography. A》2002,967(1):115-130
In this paper the analytical techniques of about the last 2 decades for sesquiterpenes including their lactones are reviewed. For sesquiterpenes, methods like GC, GC-EI-MS, GC-CI-MS, GC-MS-MS, GC-FT-IR, GC-UV, GC-AES, 13C-NMR, PY-GC-MS, HPLC, HPLC-TSP, SFE, SFC, SFC-UV are available, GC combined with MS is the most widespread. Sesquiterpene lactones can be analysed by HPLC, HPLC-TSP, HPLC-APCI, HPLC-ESI, HPLC-PB, HPLC-NMR, SFC, MEKC, GC, GC-MS, TLC and OPLC. Here HPLC is the method of choice. The usefulness of the individual methods are briefly discussed. 相似文献
10.