Zur Chemie der Pyrrolpigmente, 56. Mitt.

From an investigation of the ICD of bilatrienes-abc and 2,3-dihydrobilatrienes-abc induced by mixtures of CCl₄ with (+)-cis-Pinane, (–)-lactic and (+)-tartaric acid esters it is concluded that specific interactions between chromophore and the chiral reagents afford a partial resolution of the labile racemate of helices. Attaching chiral residues covalently to the chromophore induces very low resolution of the same kind in case of apolar ligands like a cholesteryl-residue. However, with polar ligands as in the case ofBoc-lysyl derivatives enantiomeric excesses up to 90% are achieved depending on the solvent used.

Herrn Prof. Dr.Karl Schlögl zu seinem 60. Geburtstag gewidmet.     

Beiträge zur Chemie der Pyrrolpigmente, 59. Mitt.

By investigation of bilatrienes-abc possessing a rigid tautomeric structure within their pyrromethene fragment, using¹³C-NMR spectroscopy, a criterion for the fixation of tautomerism was deduced: if there is a signal in the otherwise unoccupied shift region between 157 and 170 ppm corresponding to an azomethine fragment, tautomerism is fixed. If there is no signal in this region there is a rapidly equilibrating system of the two possible tautomers. This criterion may be used as well for natural substitution patterns. Moreover, assignment of the¹³C-signals by correlation with the easily assigned¹H-NMR signals establishes the position of the fixed tautomeric system. The criterion is applied as well to the 2,3-dihydrobilatrienes-abc where it is in accord with the results gained from a coupling criterion reported earlier.

     

A linear dichroism study of pyrromethene-, pyrromethenone- and bilatriene-abc-derivatives

The linear dichroism of several pyrromethene, pyrromethenone and bilatriene-abc derivatives embedded in a polyethylene film and oriented by stretching is investigated. On dissolving these pigments in the polymer matrix no changes in their conformations are observed, as compared to solutions in apolar solvents. Polarisation of the absorption bands of the pigments is deduced from the polarisation spectra. To enhance the solubility and orientation in the polymer, a pyrromethenone and a bilatriene-abc bearing a C₁₈-alkyl chain were synthesised for the first time.

---

Zum Lineardichroismus von Pyrromethen-, Pyrromethenon- und Bilatrien-abc-Derivaten

Zusammenfassung Der Lineardichroismus einiger Pyrromethen-, Pyrromethenon- und Bilatrienabc-Derivate, die in eine Polyethylenfolie eingebettet vorliegen, wird untersucht. Bei der Lösung dieser Pigmente in der polymeren Matrix wird keine Veränderung der Konformation im Vergleich mit Lösungen in apolaren Lösungsmitteln beobachtet. Aus den Polarisationsspektren wird die Polarisation der Absorptionsbanden dieser Chromophore abgeleitet. Ein Pyrromethenon und ein Bilatrien-abc mit C₁₈-Alkylseitenkette wurden zur Verbesserung der Löslichkeit und Orientierung in der Polymerfolie erstmals dargestellt.

     

Beiträge zur Chemie der Pyrrolpigmente, 67. Mitt.

Bilatrienes-abc and 2,3-dihydrobilatrienes-abc are effectively solubilised by cationic, anionic and neutral surfactants, like cetyltrimethylammonium bromide, sodium dodecylsulfate and Triton-X-100. The absorption spectra of the solubilised pigments are comparable to those of solutions in common organic solvents. Accordingly, the configurations and conformations of the predominant populations remain unchanged in the micellar systems, compared to solutions. The apparent basicities and acidities of the pigments in micelles are different from those in aqueous solutions, however. This phenomenon may have implications for physiological systems. Two lipophilic pigments bearing long alkyl side chains are newly synthesised.

Herrn Prof. Dr.K. Komarek zum 60. Geburtstag gewidmet.     

Reactivity of pyrrole pigments. Part 10 MINDO/3 calculations on bile pigments

The applicability of the MINDO/3 method is evaluated for tetrapyrrolic bile pigments: geometries from already calculated dipyrrolic partial models have been used to reduce the calculation time. Net atomic charges and reactivity parameters obtained from the frontier orbital model, i.e. HOMO and LUMO distribution on the molecule, are reported for several conformations.

---

Reaktivität von Pyrrolpigmenten, 10. Mitt. MINDO/3-Rechnungen von Gallenpigmenten

Zusammenfassung Es wird der Einsatz von MINDO/3 für tetrapyrrolische Gallenpigmente beschrieben. Um die Rechenzeit herabzusetzen, wurden geometrische Daten verwendet, die vorher für dipyrrolische Partialstrukturen ermittelt worden waren. Für mehrere Konformationen werden Ladungsdichten und Reaktivitätsparameter nach dem Frontier-Orbital-Modell, nämlich HOMO- und LUMO-Verteilung, berichtet.