title: Synthetic analogues of the histidine-chlorophyll complex: a NMR study to mimic structural features of the photosynthetic reaction center and the light-harvesting complex.
abstract: Mg(II)-porphyrin-ligand and (bacterio)chlorophyl-ligand coordination interactions have been studied by solution and solid-state MAS NMR spectroscopy. (1)H, (13)C and (15)N coordination shifts due to ring currents, electronic perturbations and structural effects are resolved for imidazole (Im) and 1-methylimidazole (1-MeIm) coordinated axially to Mg(II)-OEP and (B)Chl a. As a consequence of a single axial coordination of Im or 1-MeIm to the Mg(II) ion, 0.9-5.2 ppm (1)H, 0.2-5.5 ppm (13)C and 2.1-27.2 ppm (15)N coordination shifts were measured for selectively labeled [1,3-(15)N]-Im, [1,3-(15)N,2-(13)C]-Im and [1,3-(15)N,1,2-(13)C]-1-MeIm. The coordination shifts depend on the distance of the nuclei to the porphyrin plane and the perturbation of the electronic structure. The signal intensities in the (1)H NMR spectrum reveal a five-coordinated complex, and the isotropic chemical shift analysis shows a close analogy with the electronic structure of the BChl a-histidine in natural light harvesting 2 complexes. The line broadening of the ligand responses support the complementary IR data and provide evidence for a dynamic coordination bond in the complex.
authors.affiliation: Leiden Institute of Chemistry, Gorlaeus Laboratories, Leiden University, P.O. Box 9502, 2300 RA, Leiden, The Netherlands.
authors.forename: Adriaan J
authors.initials: AJ
authors.lastname: van Gammeren
authors.forename: Frans B
authors.initials: FB
authors.lastname: Hulsbergen
authors.forename: Cornelis
authors.initials: C
authors.lastname: Erkelens
authors.forename: Huub J M
authors.initials: HJ
authors.lastname: De Groot
mesh_terms: D025541:Bacteriochlorophyll A / Q000737:chemistry / Q000302:isolation & purification; D001429:Bacteriochlorophylls / Q000737:chemistry*; D002247:Carbon Isotopes; D002734:Chlorophyll / Q000737:chemistry / Q000302:isolation & purification; D000077194:Chlorophyll A; D006639:Histidine / Q000737:chemistry*; D007093:Imidazoles / Q000737:chemistry; D007553:Isotope Labeling; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry*; D008274:Magnesium / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D009587:Nitrogen Isotopes; D010788:Photosynthesis; D012242:Rhodobacter sphaeroides / Q000737:chemistry; D013055:Spectrophotometry, Infrared; D018724:Spinacia oleracea / Q000737:chemistry
chemical_list: D025541:Bacteriochlorophyll A; D001429:Bacteriochlorophylls; D002247:Carbon Isotopes; D007093:Imidazoles; D045342:Light-Harvesting Protein Complexes; D009587:Nitrogen Isotopes; D002734:Chlorophyll; D006639:Histidine; C037184:chlorophyll b; C029899:imidazole; D008274:Magnesium; C018100:1-methylimidazole; D000077194:Chlorophyll A