Steric control of bacteriochlorophyll ligation

2006
journal article
article
dc.abstract.enThe axial coordination of central Mg(2+) ion in chlorophylls is of great structural and functional importance for virtually all photosynthetic chlorophyll proteins; however, little thermodynamic data are available on the ligand binding to these pigments. In the present study, spectral deconvolution of the bacteriochlorophyll Q(X) band serves to determine the ligand binding equilibria and relationships between thermodynamic parameters of ligand binding, ligand properties, and steric interactions occurring within the pigment. On the basis of the temperature effects on coordination, DeltaH degrees, DeltaS degrees, and DeltaG degrees of binding various types of ligands (acetone, dimethylformamide, imidazole, and pyridine) to diastereoisomeric bacteriochlorophylls were derived from respective van't Hoff's plots. At ambient temperatures, only ligation by imidazole and pyridine occurs spontaneously while DeltaG degrees becomes positive for ligation by acetone and dimethylformamide, due to a relatively large entropic effect, which is dominating when the energetic effects of ligation are small. It reflects, in quantitative terms, the control of the equatorial coordination of the Mg(2+) ion via the axial coordination: a "hard" free Mg(2+) ion is made into a softer center through the coordination of tetrapyrrole. Pigment structural features have comparable effects on the energetic and entropic contributions to the difference of ligation free energy between the diastereoisomers of bacteriochlorophyll. DeltaS degrees and DeltaH degrees values are consistently lower for the S epimer, most likely due to the steric crowding between bulky substituents. The two epimers show a 5 J.mol(-1).K(-1) difference in DeltaS degrees values, regardless of the ligand type, while the difference in DeltaH degrees amounts to 1.7 kJ.mol(-1), depending on the ligand. Such steric control of ligation would relate to the partial diastereoselectivity of chlorophyll self-assembly and, in particular, the very high diastereoselectivity of the ligation of chlorophylls in photosynthetic proteins.pl
dc.affiliationWydział Biochemii, Biofizyki i Biotechnologii : Zakład Fizjologii i Biochemii Roślinpl
dc.contributor.authorKania, Agnieszka - 128618 pl
dc.contributor.authorFiedor, Leszek - 127902 pl
dc.date.accessioned2014-12-16T12:03:28Z
dc.date.available2014-12-16T12:03:28Z
dc.date.issued2006pl
dc.description.number2pl
dc.description.physical454-458pl
dc.description.volume128pl
dc.identifier.doi10.1021/ja055537xpl
dc.identifier.eissn1520-5126pl
dc.identifier.eissn1943-2984pl
dc.identifier.issn0002-7863pl
dc.identifier.urihttp://ruj.uj.edu.pl/xmlui/handle/item/2308
dc.languageengpl
dc.language.containerengpl
dc.subtypeArticlepl
dc.titleSteric control of bacteriochlorophyll ligationpl
dc.title.journalJournal of the American Chemical Societypl
dc.typeJournalArticlepl
dspace.entity.typePublication
dc.abstract.enpl
The axial coordination of central Mg(2+) ion in chlorophylls is of great structural and functional importance for virtually all photosynthetic chlorophyll proteins; however, little thermodynamic data are available on the ligand binding to these pigments. In the present study, spectral deconvolution of the bacteriochlorophyll Q(X) band serves to determine the ligand binding equilibria and relationships between thermodynamic parameters of ligand binding, ligand properties, and steric interactions occurring within the pigment. On the basis of the temperature effects on coordination, DeltaH degrees, DeltaS degrees, and DeltaG degrees of binding various types of ligands (acetone, dimethylformamide, imidazole, and pyridine) to diastereoisomeric bacteriochlorophylls were derived from respective van't Hoff's plots. At ambient temperatures, only ligation by imidazole and pyridine occurs spontaneously while DeltaG degrees becomes positive for ligation by acetone and dimethylformamide, due to a relatively large entropic effect, which is dominating when the energetic effects of ligation are small. It reflects, in quantitative terms, the control of the equatorial coordination of the Mg(2+) ion via the axial coordination: a "hard" free Mg(2+) ion is made into a softer center through the coordination of tetrapyrrole. Pigment structural features have comparable effects on the energetic and entropic contributions to the difference of ligation free energy between the diastereoisomers of bacteriochlorophyll. DeltaS degrees and DeltaH degrees values are consistently lower for the S epimer, most likely due to the steric crowding between bulky substituents. The two epimers show a 5 J.mol(-1).K(-1) difference in DeltaS degrees values, regardless of the ligand type, while the difference in DeltaH degrees amounts to 1.7 kJ.mol(-1), depending on the ligand. Such steric control of ligation would relate to the partial diastereoselectivity of chlorophyll self-assembly and, in particular, the very high diastereoselectivity of the ligation of chlorophylls in photosynthetic proteins.
dc.affiliationpl
Wydział Biochemii, Biofizyki i Biotechnologii : Zakład Fizjologii i Biochemii Roślin
dc.contributor.authorpl
Kania, Agnieszka - 128618
dc.contributor.authorpl
Fiedor, Leszek - 127902
dc.date.accessioned
2014-12-16T12:03:28Z
dc.date.available
2014-12-16T12:03:28Z
dc.date.issuedpl
2006
dc.description.numberpl
2
dc.description.physicalpl
454-458
dc.description.volumepl
128
dc.identifier.doipl
10.1021/ja055537x
dc.identifier.eissnpl
1520-5126
dc.identifier.eissnpl
1943-2984
dc.identifier.issnpl
0002-7863
dc.identifier.uri
http://ruj.uj.edu.pl/xmlui/handle/item/2308
dc.languagepl
eng
dc.language.containerpl
eng
dc.subtypepl
Article
dc.titlepl
Steric control of bacteriochlorophyll ligation
dc.title.journalpl
Journal of the American Chemical Society
dc.typepl
JournalArticle
dspace.entity.type
Publication
Affiliations

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