Selective chemical shift assignment of B800 and B850 bacteriochlorophylls in uniformly [13C,15N]-labeled light-harvesting complexes by solid-state NMR spectroscopy at ultra-high magnetic field.

The electronic ground states of the bacteriochlorophyll a type B800 and type B850 in the light-harvesting 2 complex of Rhodopseudomonas acidophila strain 10050 have been characterized by magic angle spinning (MAS) dipolar (13)C-(13)C correlation NMR spectroscopy. Uniformly [(13)C,(15)N] enriched light-harvesting 2 (LH2) complexes were prepared biosynthetically, while [(13)C,(15)N]-B800 LH2 complexes were obtained after reconstitution of apoprotein with uniformly [(13)C,(15)N]-enriched bacteriochlorophyll cofactors. Extensive sets of isotropic (13)C NMR chemical shifts were obtained for each bacteriochlorin ring species in the LH2 protein. (13)C isotropic shifts in the protein have been compared to the corresponding shifts of monomeric BChl a dissolved in acetone-d(6). Density functional theory calculations were performed to estimate ring current effects induced by adjacent cofactors. By correction for the ring current shifts, the (13)C shift effects due to the interactions with the protein matrix were resolved. The chemical shift changes provide a clear evidence for a global electronic effect on the B800 and B850 macrocycles, which is attributed to the dielectrics of the protein environment, in contrast with local effects due to interaction with specific amino acid residues. Considerable shifts of -6.2 < Deltasigma < +5.8 ppm are detected for (13)C nuclei in both the B800 and the B850 bacteriochlorin rings. Because the shift effects for the B800 and B850 are similar, the polarization of the electronic ground states induced by the protein environment is comparable for both cofactors and corresponds with a red shift of approximately 30 nm relative to the monomeric BChl dissolved in acetone-d(6). The electronic coupling between the B850 cofactors due to macrocycle overlap is the predominant mechanism behind the additional red shift in the B850.

Synthetic analogues of the histidine-chlorophyll complex: a NMR study to mimic structural features of the photosynthetic reaction center and the light-harvesting complex.

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.

Formation of Dinuclear Copper(II) Complexes from a Macrocycle with Built-in Pyrazole Groups.

The 22-membered macrocycle, containing four endocyclic pyrazole groups and two exocyclic pyridine groups, viz. (9,22-di(pyridin-2-ylmethyl)-1,4,9,14,17,22,27,28,29,30-decaaza-5,13,18,26-tetramethyl)pentacyclo[24.2.1.1(4,7).1(11,14).1(17,20)]triacontane-5,7(28),11(29),12,18,20(30),24(27),25-octaene (MePy22Pz), has been synthesized in an eleven-step procedure. Two dinuclear copper(II) compounds, viz. [Cu(2)(MePy22Pz)(NO(3))(4)](MeOH)(2) (A) and [Cu(2)(MePy22Pz)(CF(3)SO(3))(2)(H(2)O)(2)](CF(3)SO(3))(2)(MeOH)(2) (B), were prepared with this macrocycle. In both compounds the copper(II) ions are in a square pyramidal N(3)O(2) environment involving a pyrazole nitrogen, a pyridine nitrogen, and a tertiairy amine nitrogen and two oxygen atoms, which stem from two different nitrate anions in compound A and from a triflate anion and a water molecule in compound B. Two of the four pyrazole groups of the macrocycle do not participate in the coordination. The pendent pyridine groups protrude on opposite sides of the macrocycle. Consequently, the copper ions are on different sides of the macrocyclic ring and quite far apart with Cu-Cu distances of 8.668(4) Å in A and 6.814(1) Å in B.