On the molecular structure of the phytochrome chromophore: X-ray analysis of two 2,3-dihydrobilatriene-abc derivatives

The molecular and crystal structures of the two 2,3-dihydrobilatrienes-abc1 and2, representing model compounds for the phytochrome chromophore, were determined by X-ray crystallography at 97 K. Crystals of the racemate1 contain disordered regions. Both molecules are found to be ofall-(Z) configuration, assuming a helical conformation. The acidic hydrogen atoms are localized at the nitrogen atoms of rings A, C and D. A summary of the geometries of unsaturated five-membered rings as observed in four accurate low-temperature crystal structures of bilatrienes-abc is given.Herrn Prof.Josef Schurz zum 60. Geburtstag gewidmet.     

An alternative analytic treatment of the Gutzwiller ansatz

An alternative analytic approach is formulated for treating Gutzwiller's variational ansatz. In contrast to the diagrammatic treatment recently published by Metzner and Vollhardt, our approach is purely algebraic and mainly based on expansions in terms of cluster integrals. The present theory is carried out for arbitrary dimension and band filling, but is applied here only to the Hubbard interaction term. In one dimension we find exact agreement between our results and those obtained by Metzner and Vollhardt.     

Some interlacing results for indefinite Hermitian matrices

A classical theorem of Cauchy states that the eigenvalues of a principal submatrix A₀ of a Hermitian matrix A interlace the eigenvalues of A. We consider the case of a matrix A which is Hermitian with respect to an indefinite inner product.     

Halochrome Molekeln. 7. Mitteilung. Synthese und acidobasisches Verhalten substituierter Heteroarenochinazoline

Halochromic Molecules. Synthesis and Acidobasic Properties of Substituted Heteroarenoquinazolines We have synthetized a series of substituted heteroarenoquinazolines. The 90-MHz FT ¹H-NMR spectra of starting and final products supported the postulated structures. Fragmentation in the mass spectra also were consistant with the assumed structures. With acid, the compounds partly from ring-opened, intensely coloured triphenylcarbenium salts of the Rhoduline-R type (C. I. 42565). UV/VIS spectra of the salts are discussed on the basis of VEPPP-CI calculations. The ?_pH* curves in buffered MeOH/H₂O solutions and the pK* values are determined. The title compounds undergo very complex protonation equilibria.