Karl Grubmayr

Beiträge zur Chemie der Pyrrolpigmente, 18. Mitt.: Pyrromethenone—Partialstrukturen von Gallenpigmenten: Struktur und Eigenschaften in Lösung

Depending on solvent polarity and concentration a monomer—dimer equilibrium for pyrromethenones was deduced by means of absorption and fluorescence spectroscopy and measurement of a colligative property. The monomer could be characterized as asyn-(Z) form with a dihedral angle at the methine single bond of about fourty degrees using the lanthanide shift technique and nuclearOverhauser effect studies. Two types of dimer geometry with differing bond strengths were found by comparingPPP calculation results with the measured absorption spectra and the liquid crystal induced circular dichroism.The (Z) isomers can be transformed to the corresponding (E) isomers by means of a photoreaction. The latter is thermally stable but rather sensitive against oxygen, light and protons, an effect which varies strongly with the substitution pattern of the pyrrole fragment thus enabling isolation in certain cases only.

Beiträge zur Chemie der Pyrrolpigmente, 25. Mitt. Die diastereomeren (geometrisch isomeren) Biliverdindimethylester—Struktur, Konfiguration und Konformation

Photoisomerization of the symmetrically substituted bilatrienes-abc1 and2 adsorbed on aluminum oxide yields the photoisomers1′ and2′, whereas the biliverdindimethylester (3) gives rise to two isomers3′ and3″. By X-ray photoelectron spectrometry of the N1s-level all these diastereomers were shown to have a bislactam structure. From1H-NMR experiments (chemical shifts, Lanthanide induced shifts, double resonance experiments) the configurations (Z,Z,Z) at the methin positions were assigned to the educts—the photoisomers1′ and2′ having the configurations (Z,Z,E). The configurations (Z,Z,E) and (E,Z,Z) could be assigned to the diastereomers3′ and3″. The conformational aspects within these series are discussed and on the basis of several studies asyn-syn-syn-helical arrangement is deduced for the systems of configuration (Z,Z,Z). For the (Z,Z,E) isomers in the region of (Z)-configuration a conformation resembling the (Z,Z,Z)-systems is reasonable, but in the region of configuration (E) a stronger twisting at the methin single bond due to steric crowding should be favoured.

Beiträge zur Chemie der Pyrrolpigmente, 16. Mitt.: 5-[5-Methyliden-(5H-pyrrolyl-2-methyliden)]-3-pyrrolin-2-on — eine Partialstruktur von Gallenpigmenten

By investigation of model systems related to 5-[5-methylidene-(5H-pyrrolyl-2-methylidene)]-3-pyrrolin-2-one by means of pK- and Lanthanide induced shift measurements (usingPDIGM-calculations),1H-NMR-, IR-, and UV-spectroscopy andPPP-calculations an intramolecular hydrogen bond has been shown to be characteristic of this bile pigment partial structure. As a consequence of this bond the system is coplanar (in solution) in contrast to the recently studied pyrromethenones and arylmethylidenepyrrolinones which have a twisted conformation at the methine single bond.

Beiträge zur Chemie der Pyrrolpigmente, 27. Mitt.

Pyrromethenones are isomerized into their diastereomers at the exocyclic double bond by light, whereas dipyrromethenes and methylenepyrrolylmethyllenepyrrolinones as well as integral bile pigments containing these two partial structures (biliviolines, biliverdines) are not. The reason for this dichotomy was shown by investigation of model compounds to be neither the thermodynamically and kinetically instable product nor the availability of low states of lone pair character. Instead the very efficient radiationless decay of the excited singlet proceeds via a desactivation process being a tunneling between excited and ground state potential surfaces. Calculations according to this theory ofFormosinho affords quantitative results which are in excellent agreement with experimental data. Another desactivation mode comes from the crossing of the potential surfaces of the ground state of one tautomeric form with those of the excited state of another, leading to a proton transfer process. The molecular basis of these processes is shown to be inter—as well as intramolecular hydrogen bonding.

Beiträge zur Chemie der Pyrrolpigmente, 9. Mitt.: Bildung, Struktur und Konfiguration vonZ- undE-Arylmethyliden-3,4-dimethyl-3-pyrrolin-2-onen

The condensation of 3.4-dimethyl-3-pyrrolin-2-one with p-methyl-, p-chloro-benzaldehyde and ferrocenealdehyde yields theZ-andE-isomers of the corresponding condensates. Due to kinetic control theZ-isomers are obtained almost exclusively in this reaction. TheE-isomers of the two firstmentioned products can be produced by photochemical isomerization. The structures (tautomeric forms) and configurations of the isomers were established by the Lanthanide-induced-shift-technique and by evaluating the Nuclear-Overhauser-Effect.The condensation of 3.4-dimethyl-3-pyrrolin-2-one with p-methyl-, p-chloro-benzaldehyde and ferrocenealdehyde yields theZ-andE-isomers of the corresponding condensates. Due to kinetic control theZ-isomers are obtained almost exclusively in this reaction. TheE-isomers of the two firstmentioned products can be produced by photochemical isomerization. The structures (tautomeric forms) and configurations of the isomers were established by the Lanthanide-induced-shift-technique and by evaluating the Nuclear-Overhauser-Effect.

Beiträge zur Chemie der Pyrrolpigmente, 13. Mitt. Die thermische Stabilität der geometrischen Isomeren von Arylmethylidenpyrrolinonen

From kinetic studies and the investigation of several model compounds it has been deduced that the interconversion of (E)- and (Z)-arylmethylidenepyrrolinones proceeds via a thermal accessible dipolar (singlet) state thus being analogous to the many known thermal (Z)—(E)-isomerizations. There is a pronounced dependence of this reaction on the solvent and the substitution of the aryl part of the molecule; the equilibrium position between (Z)- and (E)-isomers is determined by the substituent in position “4” of the pyrrolinone ring.

Beiträge zur Chemie der Pyrrolpigmente, 11. Mitt.: Die Lichtabsorption geometrisch isomerer Arylmethyliden-pyrrolinone —Konformationsanalytische Studien

By investigation of the geometrical isomers of several substituted arylmethylidene-pyrrolinones using lanthanide induced shift experiments in connection with a computer program, the ring current model,PPP—SCF—LCAO—MO—CI calculations and UV spectroscopy the following conclusions could be drawn: The light absorptions ofZ- andE-isomers vary only in the case of different dihedral angles at the arylmethine bond. The dihedral angles in theE-isomers are determined by the substituent in 4-position of the lactam ring. Hydrogen makes no difference whereas methyl leads to a more twistedE-structure which therefore shows a marked hypsochromic shift of the intense long wavelength absorption band, as compared to the correspondingZ-isomer.By investigation of the geometrical isomers of several substituted arylmethylidene-pyrrolinones using lanthanide induced shift experiments in connection with a computer program, the ring current model,PPP—SCF—LCAO—MO—CI calculations and UV spectroscopy the following conclusions could be drawn: The light absorptions ofZ- andE-isomers vary only in the case of different dihedral angles at the arylmethine bond. The dihedral angles in theE-isomers are determined by the substituent in 4-position of the lactam ring. Hydrogen makes no difference whereas methyl leads to a more twistedE-structure which therefore shows a marked hypsochromic shift of the intense long wavelength absorption band, as compared to the correspondingZ-isomer.

Beiträge zur Chemie der Pyrrolpigmente, 28. Mitt.: Die thermische Stabilität der geometrischen Isomeren von Bilatrienen-abc

In the equilibrium between the two diastereomeric (Z, Z, Z) and (E, Z, Z) forms of aetiobiliverdine-IV-γ the former is preferred by about 20kJ/mol. For the thermal isomerization a barrier of 108kJ/mol has to be surmounted—as measured for the latter isomer. A value of 12.4 for the logarithm of the preexponential factor leads to a polar singlet mechanism, which was deduced previously for pyrromethenones and arylmethylenepyrrolinones, but a much more positive activation entropy for the verdinoid system indicates a pronounced delocalisation of charge over the entire conjugated system in the corresponding transition state.

Beiträge zur Chemie der Pyrrolpigmente, 22. Mitt.: Die Selektivität photochemischer Isomerisierungen bifunktioneller und bichromophorer Verbindungen mit geometrischer Isomerie — Studien an Gallenpigmentstrukturmodellsystemen

Bifunctional molecules of structural type5 and6 (resembling bilatrienes-abc) containing double bonds show a strong selectivity toward photochemical isomerization: Starting from the (Z,Z)-isomer the (Z,E)-isomer, is obtained but none of the (E,E)-isomer. The reason for this selectivity could be established by conformational analysis,PPP-calculations and the photochemical behaviour of N-methylated derivatives (8 and9). The configuration, (Z) at a particular double bond induces a certain amount of twisting at the attached, single bond on steric reasons. This twisting is smaller than the twisting observed for the double-single-bond system of configuration (E). It is this differrential twist which causes the observed selectivity.On the other hand bichromophoric systems like2 or4 give no selectivity on photochemical isomerization.Based on the experimental data an energy scheme for the singlet isomerization paths for bichromophoric and bifunctional systems was deduced.

Beiträge zur Chemie der Pyrrolpigmente, 32. Mitt.: Zum diagnostischen Wert der13C-Kernresonaz-spektroskopie bei diastereomeren Bilatrienen-abc

All13C-NMR signals of (Z, Z, Z)-Aetiobiliverdin-IV-γ could be assigned to the corresponding positions of the molecular framework using double resonance experiments. In the (Z, Z, E)-isomer the methine carbon signals of the terminal moieties are shifted in a dramatically different manner. Thus they represent an ideal tool for labelling experiments aiming at an experimental support of the photoisomerization hypothesis of the photoreaction of phytochrome.