Structural data, ’*-core complexes

SiH3)2C6H4 (H2L) leads to the nickel(iv) complex Ni(dmpe-P,.f, )(L-6V,6V )2. 31P NMR spectroscopic studies of the reaction indicate the presence of the intermediates Ni(dmpe-.P,.P )(dmpe-P)(L-Structural data have confirmed the unusual Ni2Si2 core. Starting from Ni(depe)2 (depe = l,2-bis(diethylphosphino)ethane), reaction with... 

The above described data have been summarized by different laboratories into structural models. In Fig. 2 the most recent proposals are shown. They all agree on the point that the minor pigment-proteins should be located in a pericentral position between the core complex and the major LHCII. Major differences are encountered in the monomeric (B) or dimeric (A, C, D) organization of the core, the stoichiometry between the core complex and LHC proteins (model in panel D uses the same stoichiometry as the one in panel A) and, finally, the possibility that CP29 and CP24 belong to the same subcomplex (A, C), as previously suggested [9, 10, 63], or are independently connected to the core complex (B, D). 

Several methods for the isolation of PBS have been established [81,104,105,138]. Principally they are based on the observation that PBS are only stable in solutions of high ionic strength, e.g. 0.75-0.9 M potassium phosphate. The PBS are detached from the membranes with 2% Triton X-100. The function of the intact PBS is tested by fluorescence emission spectra at 680 nm upon excitation at 550-650 nm. Most of the structural data describing the PBS originate from the hemidis-coidal type, as reviewed in Refs. 1,77 and 79-86. The complex architecture of the PBS rods and core is best described for the PBS of the cyanobacterium Synechococcus 6301 (a cyanobacterium which contains C-PC but neither PEC nor C-PE in the rods) with a bicylindrical core and for the PBS of the cyanobacterium Syne-chocystis 6701 (which contains C-PC and C-PE in the rods) with a tricylindrical core (reviewed in Refs. 1, 139 and 140). Each cylinder in the core is formed by four complexes of APC trimers with linker polypeptides cylinder A,... 

In PS I, as in PS II, there are a number of Chi alb protein complexes having lightharvesting and energy-transfer functions. Such complexes most probably exist in direct contact with the RC (part of the core complex), and certainly exist as peripheral LHC I antenna complexes further removed from the RC. A native PS I complex (80-180 Chi per RC, 100 kDa) with at least 6 polypeptides was isolated by solubilization of the thylakoid membrane with nonionic detergents (for example, Triton X-100) [177,178]. With further detergent treatment, the PS I complex dissociated into the core complex (CC I with the RC) and the peripheral antenna complex (LHC I) (spinach, barley, pea, Chlamydomonas reinhardtii [179-183]. The peripheral antenna complex (pea, spinach Chi alb ratio 4.0 1, typical fluorescence at 730 nm) contains 3-4 antenna polypeptides (19-25 kDa) [181,184,185]. This complex was also dissociated into two different antenna complexes - LHC la (2 polypeptides of 22 and 23 kDa) and LHC Ib (1 polypeptide, 20 kDa) - which differ in their fluorescence characteristics (680 nm and 730 nm) [184]. No structural data on these polypeptides are available at present. It was postulated that in C. reinhardtii, in addition to the peripheral antenna complex, an antenna system (with 4 polypeptides) exists, which connects the peripheral antenna energetically with the core complex CC 1 [183]. 

In 1991 the first Ti11 porphyrin complexes Ti(OEP)(//2-PhCCPh) (103) and Ti(TTP)(//2-PhCCPh) (OEP = octaethylporphyrinato, TTP = me o-tetra-/ -tolyl-porphyrinato) were made and characterized by Woo et a/.1019 The syntheses involved reduction of TiCl2-porphyrin complexes by LiAlH4 in the presence of PhCCPh. Structural data confirmed a nearly planar porphyrin core for Ti(OEP)( 72-PhCCPh). 

The tetrameric Zr complexes [Zr(0H)2(H20)2L]4X8 (L = bipyridyl, phenanthroline, various Schiff-bases X = Cl, NCS) were the presumed products from the reaction of ZrOCl2 with various heterocyclic bidentate ligands.336 The interaction of H20 with Zr0(C104)2 or Zr0(N03)2 was probed by NMR spectroscopy.337,338 In the latter case, the cation [Zr4(0H)8(H20)i6]8+ (80) was proposed as the product.338 The related trimer [Zr02Ci2H8(/u2-0H)]3(//3-0)Li5(THF)g(H20)5 (81) was isolated from the hydrolysis product of an organometallic precursor. X-ray structural data confirmed the planarity of the six-membered Zr3(/r2-OH)3 core.339 In related work, protometric studies of Zr hydroxide complexes have probed thermodynamic stability,340 while FT IR and theoretical investigations have addressed the details of laser-ablated group IV metal atoms that... 

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