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Chlorobis(triphenylphosphine)nickel(I) tetrahydrofuran solvate and an unsolvated trigonal phase of chlorotris(triphenylphosphine)nickel(I)
In [NiCl(C(18)H(15)P)(2)].C(4)H(8)O, the Ni atom is coordinated by three ligands in a distorted trigonal-planar configuration, with a P-Ni-P angle of 111.52 (2) degrees. In [NiCl(C(18)H(15)P)(3)], there are three independent molecules in the asymmetric unit, with each Ni-Cl bond on a crystallographic threefold rotation axis. Each Ni centre is tetrahedrally bound. The Ni atoms in both compounds have a d(9) configuration and a formal oxidation state of Ni(I). A comparison is made between the form of [NiCl(PPh(3))(3)] presented here and that of a known toluene solvate.
Chlorobis(triphenylphosphine)nickel(I).
Crystals of the title compound, [NiCl(C(18)H(15)P)(2)], contain one molecule per asymmetric unit with no short intermolecular interactions. This is noteworthy since previous studies have reported that the formally 15-electron species oligomerizes in the solid state. The nickel(I) centre has a distorted trigonal-planar coordination geometry, the origin of which is suggested to be electronic in nature.
Transition metal complexes with thiosemicarbazide-based ligands. XLIII. Chlorobis(3-methylisoemicarbazide-kappa(2)N(1),N(4))zinc(II) chloride.
In the title compound, [ZnCl(C(2)H(7)N(3)S)(2)]Cl, the Zn(II) ion is five-coordinated in a distorted trigonal-bipyramidal arrangement, with the hydrazine N atoms located in the apical positions. The structure is stabilized by N[bond]H...Cl hydrogen bonds, which involve both the Cl atoms and all the hydrogen donors, except for one of the two thioamide N atoms. A comparison of the geometry of thiosemicarbazide and S-methylisothiosemicarbazide complexes with Zn(II), Cu(II) and Ni(II) shows the pronounced influence of the hydrogen-bond network on the coordination geometry of Zn(II) compounds.
Chlorobis(thiourea-kappa S)copper(I) bis(4,5-diazafluoren-9-one) monohydrate.
The title compound, [CuCl(CH(4)N(2)S)(2)] x 2C(11)H(6)N(2)O x H(2)O, consists of molecules of a Cu(I)-thiourea complex, free 4,5-diazafluoren-9-one (dafone) and crystalline water. The planar complex molecule has trigonal coordination geometry around the Cu(I) atom. The dafone and water molecules, which are hydrogen bonded to the Cu(I) complex, are approximately coplanar with this complex. The crystal displays a sheet structure and pi-pi stacking is observed between neighbouring sheets.
Structure of chlorobis(dicyclohexylphenylphosphine)gold(I).
[AuCl[C6H11)2(C6H5)P]2], Mr = 781.2, monoclinic, P2(1), a = 11.117 (4), b = 13.606 (5), c = 12.284 (4) A, beta = 109.59 (3) degrees, V = 1753 (2) A3, Z = 2, D chi = 1.48 g cm-3, lambda(Mo K alpha) = 0.71073 A, mu = 43.8 cm-1, F(000) = 792, T = 296 K, final R = 0.024 for 3239 unique observed reflections. The formation of complexes of the type LnAuX, where L is a phosphine, and X is halide or pseudohalide, shows considerable dependence on the nature of the phosphine. When L = Ph3P, three- and four-coordinated complexes are very easily prepared. However, for L = Cy3P, only linearly coordinated complexes could be isolated. The geometry of the title complex, with L = CyPhP, is best described as distorted trigonal planar. The P-Au-P angle is 158.24 (5) degrees while the P-Au-Cl angles are 92.63 (6) and 108.71 (6) degrees. Au-P distances are 2.300 (1) and 2.324 (1) A while Au-Cl is 2.744 (2) A.
Synthesis and Resolution of Quinazolinone Atropisomeric Phosphine Ligands(,).
The syntheses of 2-methyl-3-[2'-(diphenylphosphino)phenyl]-4(3H)-quinazolinone (MPQ, 1a) and methyl-substituted analogues were achieved in good yield by coupling N-acetylanthranilic acid with the corresponding phosphinoanilines. Resolution of ligand 1bwas achieved using (-)-di-&mgr;-chlorobis[(S)-dimethyl-(1-phenylethyl)aminato-C(2),N]dipalladium(II) (5). The resulting crystalline complex (S,R)-6 served to unambiguously assign the absolute configuration of antipode (R)-(-)-1b. A practical resolution of this series of ligands 1a-c was accomplished using the (benzenesulfonyl)hydrazone derivative of camphorsulfonic acid (7) as a resolving agent.
Catalytic asymmetric rearrangement of allylic N-aryl trifluoroacetimidates. A useful method for transforming prochiral allylic alcohols to chiral allylic amines.
[reaction: see text] A useful method for the conversion of prochiral allylic alcohols to chiral allylic amines of high enantiopurity is reported. N-(4-Methoxyphenyl)trifluoroacetimidates are excellent substrates for the palladium(II)-catalyzed allylic imidate rearrangement as the allylic trifluoroacetamide products can be deprotected in two steps to provide chiral nonracemic allylic amines. Di-mu-chlorobis[(eta(5)-(S)-(pR)-2-(2'-(4'-isopropyl))oxazolinylcyclopentadienyl,1-C,3'-N))(eta(4)-tetraphenylcyclobutadiene)cobalt]dipalladium (6a, COP-Cl) is a superior catalyst because it does not require activation with silver salts and provides rearranged allylic trifluoroacetamides in good yields and high enantiomeric purities.
Atmospheric pressure chemical ionisation liquid chromatography/mass spectrometry of bacteriochlorophylls from Chlorobiaceae: characteristic fragmentations.
Atmospheric pressure chemical ionisation liquid chromatography/mass spectrometry/mass spectrometry (APCI-LC/MS/MS) has been applied to the study of bacteriochlorophylls c, d, and e of phototrophic prokaryotes. Cultures of Chlorobiaceae containing bacteriochlorophyll c, d or e were examined using a high-resolution high-performance liquid chromatography (HPLC) method and APCI-LC/MS/MS employing post-column addition of formic acid. The results reveal complex distributions of bacteriochlorophyll homologues, with some closely eluting species giving isobaric protonated molecules. On-line LC/MS/MS studies reveal characteristic fragment ions for bacteriochlorophylls c, d, and e. Fragmentations involving loss of the extended alkyl substituents that are unique to bacteriochlorophylls c, d and e and their derivatives have been rationalised by studying the phaeophorbides and the results applied to the direct study of the bacteriochlorophylls.
Crystal structure of the bacteriochlorophyll a protein from Chlorobium tepidum.
The bacteriochlorophyll (BChl) a protein from Chlorobium tepidum, which participates in energy transfer in green photosynthetic bacteria, has been crystallized using the sitting drop method of vapor diffusion. X-ray diffraction data collected from these crystals indicate that the crystals belong to the cubic space group P4132 with cell dimensions of a=b=c=169.5 A. A native X-ray diffraction data set has been collected to a resolution of 2.2 A. The initial solution was determined by using the molecular replacement method using the structure of the previously solved BChl a protein from Prosthecochloris aestuarii. A unique rotation and translation solution was obtained for two monomers in the asymmetric unit giving a pseudo-body centered packing. After rebuilding and refinement the model yields an R factor of 19.0%, a free R-factor of 28.3%, and good geometry with root-mean-square deviations of 0.013 A and 2.1 degrees for the bond lengths and angles, respectively. The structure of the BChl a protein from C. tepidum consists of three identical subunits related by a 3-fold axis of crystallographic symmetry. In each subunit the polypeptide backbone forms large beta-sheets and encloses a central core of seven BChl a molecules. The distances between neighboring bacteriochlorin systems within a subunit range between 4 A to 11 A and that between two bacteriochlorins from different subunits is more than 20 A. The overall structure is comparable with that of P. aestuarii but significant differences are observed for the individual bacteriochlorophyll structures. The surface of the trimer has a hydrophobic region that is modeled as the complex being a peripheral membrane protein partially embedded in the membrane. A general model is presented for the membrane organization with two of the bacteriochlorophyll structures in the membrane and transferring energy to the reaction center complex. In this model these two bacteriochlorophyll structures serve a similar role to the cofactors of integral membrane light-harvesting complexes although the protein structure surrounding the cofactors is significantly different for the BChl a protein compared with the integral membrane complexes.
The reaction center complex from the green sulfur bacterium Chlorobium tepidum: a structural analysis by scanning transmission electron microscopy.
The three-dimensional (3D) structure of the reaction center (RC) complex isolated from the green sulfur bacterium Chlorobium tepidum was determined from projections of negatively stained preparations by angular reconstitution. The purified complex contained the PscA, PscC, PscB, PscD subunits and the Fenna-Matthews-Olson (FMO) protein. Its mass was found to be 454 kDa by scanning transmission electron microscopy (STEM), indicating the presence of two copies of the PscA subunit, one copy of the PscB and PscD subunits, three FMO proteins and at least one copy of the PscC subunit. An additional mass peak at 183 kDa suggested that FMO trimers copurify with the RC complexes. Images of negatively stained RC complexes were recorded by STEM and aligned and classified by multivariate statistical analysis. Averages of the major classes indicated that different morphologies of the elongated particles (length=19 nm, width=8 nm) resulted from a rotation around the long axis. The 3D map reconstructed from these projections allowed visualization of the RC complex associated with one FMO trimer. A second FMO trimer could be correspondingly accommodated to yield a symmetric complex, a structure observed in a small number of side views and proposed to be the intact form of the RC complex.
A motif for quinone binding sites in respiratory and photosynthetic systems.
Many of the membrane-bound protein complexes of respiratory and photosynthetic systems are reactive with quinones. To date, no clear structural relationship between sites that bind quinone has been defined, apart from that in the homologous family of "type II" photosynthetic reaction centres. We show here that a structural element containing a weak sequence motif is common to the Q(A) and Q(B) sites of bacterial reaction centres and the Q(i) site of the mitochondrial bc(1) complex. Analyses of sequence databases indicate that this element may also be present in the PsaA/B subunits of photosystem I, in the ND4 and ND5 subunits of complex I and, possibly, in the mitochondrial alternative quinol oxidase. This represents a first step in the structural classification of quinone binding sites.
Early evolution of cytochrome bc complexes.
Primary structures, functional characteristics and phylogenetic relationships of subunits of cytochrome bc complexes from phylogenetically diverse bacterial and archaeal species were analysed. A single case of lateral gene transfer, i.e. the import of an epsilon-proteobacterial cytochrome bc(1) complex into Aquificales, was identified. For the enzyme in the remainder of the species studied, the obtained phylogenies were globally in line with small subunit rRNA trees. The distribution of a few key phylogenetic markers, such as contiguousness of cytochrome b, nature of the c-type subunit or spacing between b-heme ligands, are discussed. A localised modification of previous tree topologies is proposed on the basis of the obtained data. The comparison of extant enzymes furthermore allowed us to define the minimal functional and evolutionary core of the enzyme. The data furthermore suggest that the ancestral enzyme was put together from subunits that previously had played a role in other electron transfer chains.
Crystal structure of auracyanin, a "blue" copper protein from the green thermophilic photosynthetic bacterium Chloroflexus aurantiacus.
Auracyanin B, one of two similar blue copper proteins produced by the thermophilic green non-sulfur photosynthetic bacterium Chloroflexus aurantiacus, crystallizes in space group P6(4)22 (a=b=115.7 A, c=54.6 A). The structure was solved using multiple wavelength anomalous dispersion data recorded about the CuK absorption edge, and was refined at 1.55 A resolution. The molecular model comprises 139 amino acid residues, one Cu, 247 H(2)O molecules, one Cl(-) and two SO(4)(2-). The final residual and estimated standard uncertainties are R=0.198, ESU=0.076 A for atomic coordinates and ESU=0.05 A for Cu---ligand bond lengths, respectively. The auracyanin B molecule has a standard cupredoxin fold. With the exception of an additional N-terminal strand, the molecule is very similar to that of the bacterial cupredoxin, azurin. As in other cupredoxins, one of the Cu ligands lies on strand 4 of the polypeptide, and the other three lie along a large loop between strands 7 and 8. The Cu site geometry is discussed with reference to the amino acid spacing between the latter three ligands. The crystallographically characterized Cu-binding domain of auracyanin B is probably tethered to the periplasmic side of the cytoplasmic membrane by an N-terminal tail that exhibits significant sequence identity with known tethers in several other membrane-associated electron-transfer proteins.
Chloroherpeton thalassium gen. nov. et spec. nov., a non-filamentous, flexing and gliding green sulfur bacterium.
A flexing and gliding green sulfur bacterium has been isolated from marine sources off the North East coast of the USA. Chloroherpeton thalassium is an obligate phototroph, and requires CO2 and S2 for growth; some organic acids can contribute to cell carbon, and N2 may be fixed. The cells contain typical chlorosomes, and gas vesicles may be present. Bacteriochlorophyll c is the main light harvesting pigment, and a small quantity of bacteriochlorophyll a is also present. Over 80% of the carotenoid is gamma-carotene. DNA base composition of the isolates ranges from 45.0-48.2 mol% G + C.
The microbial community at Laguna Figueroa, Baja California Mexico: from miles to microns.
Laguna Figueroa is a lagoonal complex on the Pacific coast of the Baja California penisula 200 km south of the Mexican-United States border. The hypersaline lagoon is 16 km long and 2-3 km wide with a salt marsh and evaporite flat and is separated from the ocean by a barrier dune and beach. At the salt marsh-evaporite flat interface a stratified microbial community dominated by Microcoleus chthonoplastes is depositing laminated sediments. Similar stratiform deposits with associated microbial mat communities have been found in cherts of the Fig Tree Group, South Africa which are 3.4 GE in age. Heavy rains in the winters of 1978-1979 and 1979-1980 flooded the evaporite flat with 1-3 meters of meteoric water and buried the laminated sediment under 5-10 cm of siliciclastic and clay sediment. These flooding events had a dramatic effect on the composition of the mat community. The Microcoleus dominated community, with species of Chloroflexus sp. and an Ectothiorhodospira-like filamentous purple phototroph, disappeared leaving a community dominated by the purple phototrophs Chromatium sp. and Thiocapsa sp. Recolonization of the surface by species of the cyanobacteria Oscillatoria sp. and Spirulina sp. preceded the return of the Microcoleus community. Field conditions were monitored by ground based observations and supplemented with LandSat and Skylab imagery. The microbial community was studied with light microscopy and transmission electron microscopy. The change in dominating microbial species was correlated with the episodes of flooding.
The evolution of glutathione metabolism in phototrophic microorganisms.
Of the many roles ascribed to glutathione (GSH) the one most clearly established is its role in the protection of higher eucaryotes against oxygen toxicity through destruction of thiol-reactive oxygen byproducts. If this is the primary function of GSH then GSH metabolism should have evolved during or after the evolution of oxygenic photosynthesis. That many bacteria do not produce GSH is consistent with this view. In the present study we have examined the low-molecular-weight thiol composition of a variety of phototrophic microorganisms to ascertain how evolution of GSH production is related to evolution of oxygenic photosynthesis. Cells were extracted in the presence of monobromobimane (mBBr) to convert thiols to fluorescent derivatives, which were analyzed by high-pressure liquid chromatography. Significant levels of GSH were not found in the green bacteria (Chlorobium thiosulfatophilum and Chloroflexus aurantiacus). Substantial levels of GSH were present in the purple bacteria (Chromatium vinosum, Rhodospirillum rubrum, Rhodobacter sphaeroides, and Rhodocyclus gelatinosa), the cyanobacteria [Anacystis nidulans, Microcoleus chthonoplastes S.G., Nostoc muscorum, Oscillatoria amphigranulata, Oscillatoria limnetica, Oscillatoria sp. (Stinky Spring, Utah), Oscillatoria terebriformis, Plectonema boryanum, and Synechococcus lividus], and eucaryotic algae (Chlorella pyrenoidsa, Chlorella vulgaris, Euglena gracilis, Scenedesmus obliquus, and Chlamydomonas reinhardtii). Other thiols measured included cysteine, gamma-glutamylcysteine, thiosulfate, coenzyme A, and sulfide; several unidentified thiols were also detected. Many of the organisms examined also exhibited a marked ability to reduce mBBr to syn-(methyl,methyl)bimane, an ability that was quenched by treatment with 2-pyridyl disulfide or 5,5'-bisdithio-(2-nitrobenzoic acid) prior to reaction with mBBr. These observations indicate the presence of a reducing system capable of electron transfer to mBBr and reduction of reactive disulfides. The distribution of GSH in phototrophic eubacteria indicates that GSH synthesis evolved at or around the time that oxygenic photosynthesis evolved.
Redox effects on the bacteriochlorophyll a-containing Fenna-Matthews-Olson protein from Chlorobium tepidum.
The BChl a-containing Fenna-Matthews-Olson (FMO) protein from the green sulfur bacterium Chlorobium tepidum was purified and characterized. Fluorescence spectra indicate that efficient excited state quenching occurs at neutral or oxidizing redox potentials. The major fluorescence lifetime at room temperature is approximately 60 ps in samples that are in neutral or oxidizing conditions, and approximately 2 ns in samples where the strong reductant sodium dithionite has been added. A similar change is observed in pump-probe picosecond absorbance difference experiments, where the long life time component increases after dithionite addition. A 16 Gauss wide EPR signal with g factor = 2.005 is observed in samples without dithionite. This signal largely disappears upon addition of dithionite. Dithionite induces large reversible changes in the 77 K absorbance spectra of the purified FMO protein and in whole cells. These results indicate that the FMO protein contains redox active groups, which may be involved in the regulation of energy transfer. Room temperature circular dichroism and low temperature absorption spectra show that dithionite also induces conformational or structural changes of the FMO protein complex.