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81.
82.
The results of proton and carbon magnetic resonance studies on pleiadiene (1) are reported. Data are discussed with respect to the structure of 1. Proton resonance studies indicate for 1 a rather planar configuration. Bonding phenomena in the two six-membered rings are only small affected by the 1,8 bridging of the naphthalene. As nonalternant 14 π-electron system 1 shows a carbon-13 spectrum typical for such compounds. The carbon-13 chemical shifts are discussed in comparison to related hydrocarbons. 相似文献
83.
84.
The interactions between gelatin and two anionic surfactants (sodium di-sec-butylnaphthalenesulfonate and sodium dodecylbenzenesulfonate, respectively) were investigated using rheological methods, charge and surface tension measurements. Upon the addition of surfactants, the viscosity of aqueous gelatin solutions increases at pH values higher than the isoelectric point (IEP) of the gelatin, provided that a distinct surfactant concentration is exceeded. The increase in viscosity depends on the structure of the hydrophobic moiety of the surfactant. Surface tension measurements suggest the formation of gelatin-surfactant-complexes. If the surfactant is added in high concentration, the viscosity does not further increase, and free micelles are formed in the solution. Directly at the IEP and at pH values below, the addition of surfactants leads to flocculation because of electrostatic interactions. At all surfactant concentrations, the flow behaviour was strictly Newtonian. As a model of the structure of the complex, a modified bead and necklace-model is suggested. This model proposes the nucleation of micelles at the hydrophobic gelatin regions (micellar surfactant-gelatin complexes). The number of micelle moieties per gelatin chain could be estimated to be about three. The complex stability is dependent on the extent of hydrophobic interaction.The gelation behaviour of gelatin is strongly affected by the addition of the surfactant. The ratio between the attainable linear storage and loss moduli,G andG, decreases strongly. Gelation is generally hindered, but the effect is stronger at pH values below the IEP than above. 相似文献
85.
Merino G Méndez-Rojas MA Beltrán HI Corminboeuf C Heine T Vela A 《Journal of the American Chemical Society》2004,126(49):16160-16169
A series of molecules, based on the smallest carbon cluster with one planar tetracoordinate carbon atom, C5(2-), are presented. To gain a better understanding about which electronic factors contribute to their stabilization, several global reactivity indexes, molecular scalar fields, and magnetic responses were calculated. The optimized bond lengths and the topological analysis of the electron density show that the central carbon atom in the parent dianion C5(2-) has a planar local environment, and it is coordinated to four other carbon atoms. The bonding of the parent dianion with the metal cations is highly ionic. The magnetic properties show that the C5(2-) derivatives are strongly diatropic and have a remarkable transferability of structural and electronic features from the anion to the salts. The theoretical analysis suggests that the lithium salt, C5Li2, is the most plausible candidate for experimental detection. 相似文献
86.
Replacement of Water Molecules in a Phosphate Binding Site by Furanoside‐Appended lin‐Benzoguanine Ligands of tRNA‐Guanine Transglycosylase (TGT) 下载免费PDF全文
Dr. Luzi J. Barandun Frederik R. Ehrmann Daniel Zimmerli Dr. Florian Immekus Maude Giroud Claudio Grünenfelder Dr. W. Bernd Schweizer Dr. Bruno Bernet Michael Betz Prof. Dr. Andreas Heine Prof. Dr. Gerhard Klebe Prof. Dr. François Diederich 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(1):126-135
The enzyme tRNA‐guanine transglycosylase has been identified as a drug target for the foodborne illness shigellosis. A key challenge in structure‐based design for this enzyme is the filling of the polar ribose‐34 pocket. Herein, we describe a novel series of ligands consisting of furanoside‐appended lin‐benzoguanines. They were designed to replace a conserved water cluster and differ by the functional groups at C(2) and C(3) of the furanosyl moiety being either OH or OMe. The unfavorable desolvation of Asp102 and Asp280, which are located close to the ribose‐34 pocket, had a significant impact on binding affinity. While the enzyme has tRNA as its natural substrate, X‐ray co‐crystal structures revealed that the furanosyl moieties of the ligands are not accommodated in the tRNA ribose‐34 site, but at the location of the adjacent phosphate group. A remarkable similarity of the position of the oxygen atoms in these two structures suggests furanosides as a potential phosphate isoster. 相似文献
87.
88.
Rudolf Heine 《Mathematische Annalen》1938,115(1):115-129
Ohne ZusammenfassungAuszug aus einer von der philosophischen Fakultät der Universität Greifswald angenommenen Dissertation. 相似文献
89.
Heinrich Heine 《Fresenius' Journal of Analytical Chemistry》1883,22(1):61-62
Ohne Zusammenfassung 相似文献
90.
A new theory of the origin of SiC polytypes is presented in which the observed polytypes are stabilised as equilibrium phases at the high temperatures of growth, the structures becoming frozen in on cooling. Results of first principles pseudopotential total energy calculations show that the SiC polytypes containing only bands of width 2 and 3 are nearly degenerate in energy while all other polytypes have higher energies. We develop an inter-layer interaction model to describe the energies of the polytypes. Calculations of the phonon free energies of several SiC polytypes using the valence overlap shell model are described. These calculations show that the phonon free energy gives rise to effectively long ranged interactions between the SiC layers which can stabilise a large number of ordered polytypes as equilibrium phases. 相似文献