ISSN:0021-2148    

DOI:10.1002/ijch.198300022

出版商:WILEY‐VCH Verlag    

年代:1983

数据来源: WILEY

摘要:

AbstractThe results of X‐ray structural analyses of open‐chain polypyrrolic compounds are reviewed. Particular emphasis is placed on bilirubin and biliverdin derivatives and on the relevance of their observed conformations to the biological function and properties of natural bile pigments. Typical for bilirubin derivatives is a ridge‐tile conformation stabilised by six intramolecular hydrogen bonds, in which the individual pyrromethenone units areZ‐synperiplanar. Macrocyclic helical conformations are adopted by biliverdin derivatives and model bilatrienes‐abc. The bonding pattern and degree of bond delocalisation within the tetrapyrrole skeleton are discussed in comparison to the molecular geometries of model bi‐ and tripyrrolic compounds. The results indicate that the methine bridge at C5 may demonstrate considerable conformational flexibility in bilatrienes‐abc, whereas a marked degree of bond delocalisation is observed for the B, C and D rings. Protonation or metal complexation leads to pronounced changes in the degrees of stretch and widening of the helix and to corresponding changes in the electr

ISSN:0021-2148    

DOI:10.1002/ijch.198300023

出版商:WILEY‐VCH Verlag    

年代:1983

数据来源: WILEY

摘要:

AbstractThe methodology of bile pigment synthesis including oxidative ring cleavage of porphin derivatives, total syntheses from pyrrole precursors and mutual transformation of bile pigments has been critically reviewed.

ISSN:0021-2148    

DOI:10.1002/ijch.198300024

出版商:WILEY‐VCH Verlag    

年代:1983

数据来源: WILEY

摘要:

AbstractAcid treatment of a mixture of bilirubin IXα (1) and octaethyl‐10,23‐dihydro‐21H,24H‐bilin‐1,19‐dione (7), followed by dehydrogenation and esterification gives biliverdin IXα, biliverdin XIIIα and biliverdin IIIα (as the dimethyl esters,2, 3, 4, respectively), and octaethylbilindione (8), together with two minor verdins of intermediate polarity. These are identified as the products of the crossed pyrrole exchange reaction, which are 8‐carboxyethyl‐12,13,17,18‐tetraethyl‐2, 7‐dimethyl‐3‐vinyl‐21H,24H‐bilin‐1,19‐dione methyl ester (9) and 8‐carboxyethyl‐12,13,17,18‐tetra‐ethyl‐3,7‐dimethyl‐2‐vinyl‐21H,24H‐bilin‐1,19‐dione methyl ester (10). An improved preparation of bilirubin XIIIα (5) and bilirubin IIIα (6) is described and the products are crystallised and characterised. The NMR spectra of bilirubin XIIIα and IIIα are recorded in a polar aprotic solvent

ISSN:0021-2148    

DOI:10.1002/ijch.198300025

出版商:WILEY‐VCH Verlag    

年代:1983

数据来源: WILEY

摘要:

AbstractLiterature NMR data of bilirubin and related compounds and their interpretation in terms of structure, solution conformation and dynamic properties have been reviewed.1H‐spectrum assignments as well as solvent and temperature dependencies of the chemical shifts are described. Proton exchange rates, longitudinal relaxation times and nuclear Overhauser enhancements are surveyed. NMR is shown to provide knowledge on the basic structure, conformation, tautomerism, hydrogen bonding, acidity constants, segmental motion of side‐chains, interconversion between enantiomers and aggregation—disaggregation of these compounds in sol

ISSN:0021-2148    

DOI:10.1002/ijch.198300026

出版商:WILEY‐VCH Verlag    

年代:1983

数据来源: WILEY

摘要:

AbstractA set of model compounds substituted with methyl groups in positions 7,8,12 and 13 were prepared to elucidate the tautomerism within the pyrromethene moiety of unsymmetrical bilatrienes and of 2,3‐dihydrobilatrienes‐abc. Configurational and1H‐NMR signal assignments were achieved using NOE difference spectra, coupling phenomena and comparison to the spectra of compounds substituted with ethyl groups in strategic positions. By application of resolution enhancement and the COSY‐technique a characteristic coupling pattern between the methyl groups of a pyrrole ring which is different from the one observed for the pyrrolenin ring could be documented using derivatives with fixed tautomeric structure (N‐methylation). All unsymmetrical bilatrienes and 2,3‐dihydrobilatrienes‐abcinvestigated are shown to be single tautomers — the position of the proton (N22, N23) obviously is governed by an optimisation of intramolecular h

ISSN:0021-2148    

DOI:10.1002/ijch.198300027

出版商:WILEY‐VCH Verlag    

年代:1983

数据来源: WILEY

摘要:

AbstractAbsorption and circular dichroism (CD) spectra are recorded for partially denatured phytochrome, Pfrchromopeptide as well as (ZZZ)‐ and (ZZE)‐configurated phycocyanin chromopeptides. Solvent induced circular dichroism (SICD) spectra are included for (ZZZ)‐ and (ZZE)‐octaethylbilindione. Irradiation of Prin 4 M urea yields a bleached chromophore with weak absorption and Δϵ values. On acidification in the dark it shows the known absorption and CD spectra of the Pfrchromophore. Subsequent irradiation of the acidified solution leads to absorption and CD spectra of the Prchromophore. The red shift of absorption and CD bands obtained during this Pfrŕ Prchromophore transformation is observed in both absorption and CD or SICD spectra of Pfrpeptides, (E)‐configurated phycocyanin peptides and (E)‐configurated octaethylbilindione during irradiation in acid solution. The shift may be coupled with inversion of the sign of CD or SICD bands, e.g., in fraction 5, phycocyanin peptide and octaethylbilindione. Several fractions of phycocyanin peptides with almost identical absorption spectra show significant differences in their CD spectra. Differences are also found in the pH dependency of CD or SICD spectra of the various fractions of phycocyanin peptides and of octae

ISSN:0021-2148    

DOI:10.1002/ijch.198300028

出版商:WILEY‐VCH Verlag    

年代:1983

数据来源: WILEY

ISSN:0021-2148    

DOI:10.1002/ijch.198300029

出版商:WILEY‐VCH Verlag    

年代:1983

数据来源: WILEY

摘要:

AbstractAnalysis of bilirubin and pyrromethenone N—H1H‐NMR chemical shifts indicates that in CDCl3solvent, where intermolecularly H‐bonded dimers or intramolecularly H‐bonded conformations are involved, the lactam N—H groups are more deshielded than the broader pyrrole N—H groups. Ind6‐DMSO, disaggregation and unfolding occurs with H‐bonding to the solvent and the sharper lactam N—H resonances becoming more shielded than the py

ISSN:0021-2148    

DOI:10.1002/ijch.198300030

出版商:WILEY‐VCH Verlag    

年代:1983

数据来源: WILEY

摘要:

AbstractThermal decomposition of 3‐(4‐methyl‐1‐naphthyl)‐propionic acid‐1,4‐endoperoxide at 34,7°C has been used to produce singlet oxygen in non‐photochemical conditions. Thus the reaction of bilirubin with singlet oxygen has been studied. A kinetic scheme is proposed taking into account physical and chemical quenching of singlet oxygen by bilirubin and quenching by the endoperoxide. From the lifetime, τ = 100 μs, of102in methylene chloride the following rate constants have been determined: for bilirubin:kphys quenching= 5.0 × 109M−1s−1,kchem quenching= 5.0 × 108M−1s−1and for the endoperoxide:k= 8.5 × 107M−1s−1. These same constants in the same order as above but in water (τ = 3μs) are: 4.9 × 109M−1s−1, 1.0 × 109M−1s−1and 9.0 × 108M−1's−1Moreover it has been shown that bilirubin is scarcely protected by albumin from singlet oxygenation. The protection in photochemical systems seems to be due to the lower a

ISSN:0021-2148    

DOI:10.1002/ijch.198300031

出版商:WILEY‐VCH Verlag    

年代:1983

数据来源: WILEY