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1.
2.
We show that there is a threshold in energy for the onset of chaos in cosmology for the Universe described as a dynamical system derived from the Einstein equations of General Relativity (GR). In the case of the mixmaster model (homogeneous and anisotropic cosmology with a Bianchi IX metric), the chaos occurs precisely at the prescribed necessary value H
vac=0 of the GR for the energy of the Universe while the system is found to be regular for H<0 and chaotic for H>0 with respect to its pure vacuum part. In the case of generalized scalar tensor theories within the Bianchi IX model, we show using the ADM formalism and a conformal transformation that the energy of the dynamical system as compared to vacuum lies below the zero energy threshold. The system is thus not exhibiting chaos and the conclusion still holds in the presence of ordinary matter as well. The suppression of chaos occurs in a similar way for stiff matter alone. 相似文献
3.
Summary A variety of bilipeptides has been synthesized and investigated by UV-VIS and CD spectroscopy to explore the conformational influence of peptide ligands on the covalently bound tetrapyrrol moiety. The results obtained are complemented by those reported previously. From the comprehensive data thus available several features of the peptidic chain regulating interactions with the bilatriene moiety have been elucidated. Accordingly, the presence of three amide linkages at the ligand is prerequiste for induction of pronounced conformational changes consisting either in a complete transition ofM intoP helical bilatriene species by inversion of all torsional angles, or in a stretching of the chromophore. The kind of conformational influence can be controlled by varying the position of the prolyl entity within a given peptide.Dedicated to Prof. Dr. Kurt Schaffner on occasion of his 60th birthday 相似文献
4.
Keller Hildegard Langer Elisabeth Lehner Harald Derflinger Gerhard 《Theoretical chemistry accounts》1978,49(2):93-100
The Algebraic Theory of Chirality Functions is derived by means of exclusively qualitative considerations. Hence, the significance of quantitative results is questionable. Moreover the construction of “Näherungsansätze” (”Approximation-Ansatz”), which may be interpreted as semiempirical methods, is achieved on the basis of plausibility and mathematical simplicity. Since physical arguments are not included, the consistency or inconsistency of “Näherungsansätze” with experimental results do not justify direct physical conclusions. 相似文献
5.
Silvia E. Braslavsky Alfred R. Holzwarth Harald Lehner Kurt Schaffner 《Helvetica chimica acta》1978,61(6):2219-2222
Freshly prepared solutions of biliverdin dimethyl ester ( 2 ) in ethanol showed fluorescence maxima at 710 and 770 nm [ΦF = 1.1. 10?4 (room temperature) and 5.0 10?4 (77 K)]. The maxima of monoprotonated 2 at 77 K were shifted to 725 and 806 nm and the quantum yield was increased to 2.6. 10?2. This acid effect was reversible by neutralization with base. When a neutral solution was kept standing in the dark at room temperature, or when an acidic solution was neutralized by base, an additional fluorescence maximum at 500 nm with a mirror image excitation spectrum with λmax = 470 nm developed, which disappeared on addition of acid and which is attributed to a chemical change of 2 . 相似文献
6.
Ewald Haidl Daniel Krois Harald Lehner 《Monatshefte für Chemie / Chemical Monthly》1985,116(1):119-131
Biliverdins undergo appreciable self association in acidic solutions especially if solvents like benzene or chloroform are employed. The population of aggregates further depends on the concentration of both the acid and the solute. In chloroform and benzene solutions at high acidity a doubly protonated species is formed. This is concluded from a combinatory evaluation of the CD and electronic absorption spectra of chiral optically active biliverdins (1–6) in benzene, chloroform, and ethanol solutions containing trifluoroacetic acid or hydrochloric acid. The aggregates formed at medium acid concentrations exhibit largeCotton effects in the long-wavelength absorption bands and thus dominate the CD spectra. Similarly, agrregates are the main contributors to theCotton effects of achiral, protonated biliverdins in (S)-(–)-ethyl lactate (SICD) at usual concentrations. The consequence and relevance of these findings with regard to the recent literature is briefly discussed.Dedicated to Prof. Dr.Karl Schlögl on occasion of his 60th birthday. 相似文献
7.
Heinz Falk Franz Lehner Marianne Rothböck 《Monatshefte für Chemie / Chemical Monthly》1985,116(11):1359-1361
Donors are added regioselectively to position 10 of 2,3-dihydrobilatrienes-abc in a reversible reaction, which is complicated in case of strongly basic donors due to the easy deprotonation of the partially saturated ring. Compared to the bilatrienes-abc the addition equilibrium is retarded by about two orders of magnitude. 相似文献
8.
Wolfhart Rüdiger Fritz Thümmler 《Angewandte Chemie (International ed. in English)》1991,30(10):1216-1228
Plants require light for photosynthesis. In order to adapt to the light conditions in their particular habitat, they have developed various photoreceptor systems. Of these, phytochrome allows even two-color vision in the red/far-red region. The photoreceptor phytochrome is of interest not only to botanists, but also to natural product chemists, photochemists, biochemists, photobiologists, and recently molecular biologists. Despite numerous studies, there are still considerable gaps in our knowledge of this photoreceptor. This article first describes the basic structural studies of the tetrapyrrole chromophore and its photochemical cis–trans isomerization, which is the source of the chromoprotein's photochromism. In the section on the protein moiety, beside other topics, the domain structure of phytochrome and the conformational changes during phototransformation are discussed. Finally, the known phytochrome genes are used to derive phylogenetic relationships, and possible structure–function relationships are discussed. 相似文献
9.
C. Glotzmann E. Langer H. Lehner Prof. Dr. K. Schlögl 《Monatshefte für Chemie / Chemical Monthly》1974,105(5):907-916
From racemization studies on optically active [2.2]metacyclophanes substituted in position 4, the parameters of activation for the inversion of the tenmembered ring were found to be: G
423
=31.5 kcal/mole, H
=27.5 kcal/mole and S
=–10 Cl/mole.Racemization does not occurvia bond forming or breaking; the value for the inversion barrier is not affected by substituents in position 4 and therefore corresponds to the value of unsubstituted [2.2]metacyclophane, whereas substituents in the bridge exert a distinct influence. These results can easily be explained on the basis of the isoconformational concept.
Mit 5 Abbildungen
Herrn Prof. Dr.O. Hoffmann-Ostenhof mit besten Wünschen zum 60. Geburtstag gewidmet. 相似文献
Mit 5 Abbildungen
Herrn Prof. Dr.O. Hoffmann-Ostenhof mit besten Wünschen zum 60. Geburtstag gewidmet. 相似文献
10.
Summary The imperfect mirror image relationship of the circular dichroism of (M) and (P) helical biliverdins bound to a homochiral entity (ICD) has been studied using the kinetically stable racemates (M+P)2 and (M+P)3. The phenomena associated with and eventual implications for the interpretation of ICD spectra of naturally occurring kinetically labile biliverdins in terms of chiral recognition are discussed.Dedicated to ProfessorKarl Schlögl on the occasion of his 70th birthday 相似文献