Untersuchung der Struktur und Assemblierung des Lichtsammelkomplexes II höherer Pflanzen mittels elektronenparamagnetischer Resonanz (EPR)

Der Haupt-Lichtsammelkomplex (LHCII) des Photosyntheseapparates höherer Pflanzen gehört zu den häufigsten Membranproteinen der Erde. Seine Kristallstruktur ist bekannt. Das Apoprotein kann rekombinant in Escherichia coli überexprimiert und somit molekularbiologisch vielfältig verändert werden. In Detergenzlösung besitzt das denaturierte Protein die erstaunliche Fähigkeit, sich spontan zu funktionalen Protein-Pigment-Komplexen zu organisieren, welche strukturell nahezu identisch sind mit nativem LHCII. Der Faltungsprozess findet in vitro im Zeitbereich von Sekunden bis Minuten statt und ist abhängig von der Bindung der Cofaktoren Chlorophyll a und b sowie verschiedenen Carotinoiden.rn Diese Eigenschaften machen LHCII besonders geeignet für Strukturuntersuchungen mittels der elektronenparamagnetischen Resonanz (EPR)-Spektrokopie. Diese setzt eine punktspezifische Spinmarkierung des LHCII voraus, die in dieser Arbeit zunächst optimiert wurde. Einschließlich der Beiträge Anderer stand eine breite Auswahl von über 40 spinmarkierten Mutanten des LHCII bereit, einen N-terminalen „Cys walk“ eingeschlossen. Weder der hierfür notwendige Austausch einzelner Aminosäuren noch die Anknüpfung des Spinmarkers beeinträchtigten die Funktion des LHCII. Zudem konnte ein Protokoll zur Präparation heterogen spinmarkierter LHCII-Trimere entwickelt werden, also von Trimeren, die jeweils nur ein Monomer mit einer Spinmarkierung enthalten.rn Spinmarkierte Proben des Detergenz-solubilisierten LHCII wurden unter Verwendung verschiedener EPR-Techniken strukturell analysiert. Als besonders aussagekräftig erwies sich die Messung der Wasserzugänglichkeit einzelner Aminosäurepositionen anhand der Electron Spin Echo Envelope Modulation (ESEEM). In Kombination mit der etablierten Double Electron-Electron Resonance (DEER)-Technik zur Detektion von Abständen zwischen zwei Spinmarkern wurde der membranständige Kernbereich des LHCII in Lösung eingehend untersucht und strukturell der Kristallstruktur für sehr ähnlich befunden. Die Vermessung kristallographisch nicht erfasster Bereiche nahe dem N-Terminus offenbarte die schon früher detektierte Strukturdynamik der Domäne in Abhängigkeit des Oligomerisierungsgrades. Der neue, noch zu vervollständigende Datensatz aus Abstandsverteilungen und ESEEM-Wasserzugänglichkeiten monomerer wie trimerer Proben sollte in naher Zukunft die sehr genaue Modellierung der N-terminalen Domäne des LHCII ermöglichen.rn In einem weiteren Abschnitt der Arbeit wurde die Faltung des LHCII-Apoproteins bei der LHCII-Assemblierung in vitro untersucht. Vorausgegangene fluoreszenzspektroskopi-sche Arbeiten hatten gezeigt, dass die Bindung von Chlorophyll a und b in aufeinanderfolgenden Schritten im Zeitbereich von weniger als einer Minute bzw. mehreren Minuten erfolgten. Sowohl die Wasserzugänglichkeit einzelner Aminosäurepositionen als auch Spin-Spin-Abstände änderten sich in ähnlichen Zeitbereichen. Die Daten deuten darauf hin, dass die Ausbildung der mittleren Transmembran-Helix mit der schnelleren Chlorophyll-a-Bindung einhergeht, während sich die Superhelix aus den beiden anderen Transmembranhelices erst im langsameren Schritt, zusammen mit der Chlorophyll-b-Bindung, ausbildet.rn

N-Heterocyclic carbene complexes of rhodium: structures, dynamics and catalysis

A series of imidazolium salts of the type [BocNHCH2CH2ImR]X (Boc = t-Bu carbamates; Im = imidazole) (R = Me, X = I, 1a; R = Bn, X = Br, 1b; R = Trityl, X = Cl, 1c) and [BnImR’]X (R’ = Me, X = Br, 1d; R’ = Bn, X = Br, 1e; R’ = Trityl, X = Cl, 1g; R’ = tBu, X = Br, 1h) bearing increasingly bulky substituents were synthetized and characterized. Subsequently, these precursors were employed in the synthesis of silver(I)-N-heterocyclic (NHC) complexes as transmetallating reagents for the preparation of rhodium(I) complexes [RhX(NBD)(NHC)] (NHC = 1-(2-NHBoc-ethyl)-3-R-imidazolin-2-ylidene; X = Cl; R = Me, 4a; R = Bn, 4b; R = Trityl, 4c; X = I, R = Me, 5a; NHC = 1-Bn-3-R’-imidazolin-2-ylidene; X = Cl; R’ = Me, 4d, R’ = Bn, 4e, R’ = Trityl, 4g; R’ = tBu, 4h). VT NMR studies of these complexes revealed a restricted rotation barriers about the metal-carbene bond. While the rotation barriers calculated for the complexes in which R = Me, Bn (4a,b,d,e and 5a) matched the experimental values, this was not true for the complexes 4c,g, bearing a trityl group for which the values are much smaller than the calculated ones. Energy barriers for 4c,g, derived from a line shape simulation, showed a strong dependence on the temperature while for 4h the rotational energy barrier is stopped at room temperature. The catalytic activity of the new rhodium compounds was investigated in the hydrosilylation of terminal alkynes and in the addition of phenylboronic acid to benzaldehyde. The imidazolium salts 1d,e were also employed in the synthesis of new iron(II)-NHC complexes. Finally, during a six-months stay at the University of York a new ligand derived from Norharman was prepared and employed in palladium-mediated cross-coupling.

Modellkomplexe zur Untersuchung der Radikal-Metall-Wechselwirkung innerhalb des wasseroxidierenden Zentrums im Photosystem II

Im Rahmen dieser Arbeit wurden zweikernige Modellkomplexe zur Untersuchung der Radikal-Metallwechselwirkung innerhalb des wasseroxidierenden Zentrums des Photo¬systems II synthetisiert und eine magneto-strukturelle Korrelation dieser Komplexe erstellt. Als Liganden wurden diverse sechs- bis siebenzähnige Chelatliganden verwendet, welche über zwei Koordinationstaschen und eine verbrückende Phenolatgruppe verfügen. Zwei daran gebundene Manganionen liegen in einer wohl definierten Umgebung nicht koordinativ gesättigt vor. An die freien Koordinationsstellen können weitere ein bis zwei Brückenliganden binden, bei denen es sich in dieser Arbeit hauptsächlich um Carboxylate handelt. Durch die Verwendung eines diamagnetischen Brückenliganden konnte die magnetische Spin-Spin-Austauschwechselwirkung zwischen den spintragenden Manganionen über die verbrücken¬de Phenolatgruppe bestimmt werden. Komplexe, welche über Manganionen in den gleichen Oxidationsstufen, aber über unterschiedliche Carboxylatbrückenliganden verfügen, weisen ähnliche magnetische Austauschwechselwirkungen zwischen den Metallzentren auf. Diese Beobachtung konnte durch eine strukturelle Ähnlichkeit dieser Komplexe erklärt werden. Mittels Aufsummieren der Bindungslängen der verbrückenden Phenolateinheit zu beiden Zentralionen kann innerhalb dieser Komplexe jeweils die Länge des Wechselwirkungspfades erhalten werden, welcher die magnetische Austauschwechselwirkung maßgeblich beein¬flusst. Je länger der Wechselwirkungspfad ist, desto kleiner ist die Austausch¬wechsel¬wirkung. Durch Austausch der diamagnetischen Carboxylate durch paramagnetische benzoat¬substituierte Nitronyl Nitroxid Radikale wurden den Komplexen ein bis zwei weitere Spinzentren hinzugefügt, welche mit den Spins der Zentralionen wechselwirken können. Simulationen der magnetischen Suszeptibilitätsmessungen liefern Werte für die magneti¬schen Austausch¬wechselwirkungen zwischen den Nitronyl Nitroxid Radikalen und den Manganionen, die in allen Fällen schwach ferromagnetisch zwischen 0 und 4,7 cm-1 sind. In einer Auftragung dieser Austauschwechselwirkungen gegen die Mangan-Carboxylat-Bindungs¬längen von strukturell charakterisierten äquivalenten acetatverbrückten Komplexen, kann eine lineare Abhängigkeit gezeigt werden.

Structural and biochemical studies of Sporosarcina pasteurii UreE: a nickel-chaperone involved in the urease activation process

Urease is a nickel-dependent enzyme that catalyzes hydrolysis of urea in the last step of organic nitrogen mineralization. Its active site contains a dinuclear center for Ni(II) ions that must be inserted into the apo-enzyme through the action of four accessory proteins (UreD, UreE, UreF, UreG) leading to activation of urease. UreE, acting as a metallo-chaperone, delivers Ni(II) to the preformed complex of apo-urease-UreDFG and has the capability to enhance the GTPase activity of UreG. This study, focused on characterization of UreE from Sporosarcina pasteurii (SpUreE), represents a piece of information on the structure/mobility-function relationships that control nickel binding by SpUreE and its interaction with SpUreG. A calorimetric analysis revealed the occurrence of a binding event between these proteins with positive cooperativity and a stoichiometry consistent with the formation of the (UreE)2-(UreG)2 hetero-oligomer complex. Chemical Shift Perturbations induced by the protein-protein interaction were analyzed using high-resolution NMR spectroscopy, which allowed to characterize the molecular details of the protein surface of SpUreE involved in the complex formation with SpUreG. Moreover, backbone dynamic properties of SpUreE, determined using 15N relaxation analysis, revealed a general mobility in the nanoseconds time-scale, with the fastest motions observed at the C-termini. The latter analysis made it possible for the first time to characterize of the C-terminal portions, known to contain key residues for metal ion binding, that were not observed in the crystal structure of UreE because of disorder. The residues belonging to this portion of SpUreE feature large CSPs upon addition of SpUreG, showing that their chemical environment is directly affected by protein-protein interaction. Metal ion selectivity and affinity of SpUreE for cognate Ni(II) and non cognate Zn(II) metal ions were determined, and the ability of the protein to select Ni(II) over Zn(II), in consistency with the proposed role in Ni(II) cations transport, was established.

Detektion von Nickel- und Cobaltspezies in einzelnen lebenden Zellen mit hoher lateraler Auflösung

Übergangsmetallen wie Nickel und Cobalt kommt meist eine große Bedeutung als Cofaktor in Enzymen oder Metallkomplexen im Metabolismus von Lebewesen zu. Da eine sehr geringe Konzentration dieser Übergangsmetalle in einer Zelle für deren Funktionalität ausreicht, ist eine konstante Konzentration der Spurenelemente in einer Zelle angestrebt. Durch meist anthropogene Einflüsse sind Pflanzen und Menschen zunehmend hohen Konzentrationen von Übergangsmetallen ausgesetzt, die in Abhängigkeit von ihrer Spezies, der Konzentration und der Lokalisation unterschiedliche Toxizitäten aufweisen können. Die Speziation von Metallen wurde bisher mittels gängiger Analyseverfahren, wie der ICP-MS und ähnlicher Verfahren, anhand von bulk-Material durchgeführt. Durch die Entwicklung von optischen Sensoren für Metallionen war es möglich, diese Metalle auch in lebenden Zellen mittels Fluoreszenzmikroskopie zu lokalisieren. Ke und Kollegen (2006, 2007) nutzten einen solchen optischen Sensor - Newport Green DCF, um die Aufnahme von Nickel in humane A543 Lungenbronchialepithelzellen nach Inkubation mit dem wasserlöslichen NiCl2 (0,5 mM und 1 mM) sowie den wasserunlöslichen Verbindungen Ni3S2 (0,5 µg/cm2 und 1 µg/cm2) und NiS (2,5 µg/cm2) nachzuweisen und zu lokalisieren und konnten damit eine Akkumulation von Nickel im Zytoplasma und im Zellkern aufzeigen. Dabei war bei wasserlöslichen und wasserunlöslichen Nickelverbindungen Nickel nach 24 h im Zytoplasma und erst nach 48 h im Zellkern zu beobachten.rnrnDa Nickel und Cobalt keine detektierbare Eigenfluoreszenz unter den gegebenen Bedingungen zeigten, wurde für den optischen Nachweis von Nickel und Cobalt mit dem konfokalen Laser-Raster Mikroskop (CLSM) nach der Zugabe der verschiedenen wasserlöslichen und wasserunlöslichen Metallverbindungen NiCl2, NiSO4, Ni3S2 und CoCl2 in einzelnen lebenden humanen Gingiva-Fibroblasten, sowie in Pflanzenzellen in dieser Arbeit ebenfalls der optische Sensor Newport Green DCF genutzt. Korrespondierend zu den Ergebnissen früherer Arbeiten von Ke et al. (2006, 2007), in denen die Nickelaufnahme bei Konzentrationen von >0,5 mM NiCl2 bzw. >0,5 µg/cm2 Ni3S2 gezeigt wurde, wurde Nickel in Fibroblasten in Abhängigkeit von der Spezies mit steigender Metallkonzentration von 100 µM bis 500 µM nach 16 h im Zytoplasma und zunehmend nach 24 h bis 48 h im Zellkern detektiert. Bei der wasserunlöslichen Verbindung Ni3S2 war der Nachweis von Nickel im Zellkern bereits nach 16 h bis 24 h erfolgreich. Zusätzlich wurden weitere Strukturen wie das Endoplasmatische Retikulum, die Mitochondrien und die Nukleoli durch eine starke Fluoreszenz des optischen Sensors bei Colokalisationsexperimenten mit Organell-spezifischen Fluoreszenzfarbstoffen als target für die Nickelbindung vermutet. Die Lokalisation von Cobalt in den Fibroblasten entsprach weitgehend der Lokalisation von Nickel. Im Zellkern war die Cobaltlokalisation jedoch auf die Nukleoli beschränkt. Weiterführende Versuche an humanen Gingiva-Fibroblasten zeigten, dass die Aufnahme der Metalle in die Fibroblasten pH-Wert abhängig war. Niedrige pH-Werte im sauren pH-Bereich verringerten die Aufnahme der Metalle in die Zellen, wobei ein pH-Wert im basischen Bereich keinen bedeutenden Unterschied zum neutralen pH-Bereich aufwies. Im Vergleich zu den Fibroblasten war in Pflanzenzellen zu jedem Zeitpunkt, auch bei geringen Konzentrationen der Metallverbindungen sowie des optischen Sensors, Nickel und Cobalt in den Zellkernen detektierbar. Durch die Eigenschaft der Pflanzenzellen eine Vakuole zu besitzen, war Nickel und Cobalt hauptsächlich in den Vakuolen lokalisiert. Weitere Strukturen wie das Endoplasmatische Retikulum, die Mitochondrien oder auch die Zellwand kamen bei Pflanzenzellen als target in Frage.rnrnDie Fluoreszenz und Lokalisation der Metalle in den Fibroblasten waren unabhängig von der Spezies sehr ähnlich, sodass in den Zellen die Spezies anhand der fluoreszenzmikroskopischen Aufnahmen kaum unterschieden werden konnten. Lambda-Scans in verschiedenen regions of interest (ROI) wurden durchgeführt, um durch die Fluoreszenzspektren Hinweise auf eine charakteristische Beeinflussung der Bindungspartner von Nickel und Cobalt oder dieser Metalle selbst in den Zellen auf den optischen Sensor zu bekommen und diese dadurch identifizieren zu können. Das Ziel der parallelen Detektion bzw. Lokalisation und gleichzeitigen Speziation bestimmter Nickel- und Cobaltpezies in einzelnen lebenden Zellen konnte in dieser Arbeit durch den optischen Sensor Newport Green DCF nicht erreicht werden.

Exploratory studies on coordination chemistry of a redox-active bridging ligand: synthesis, properties and solid state structures of the complexes

The explorative coordination chemistry of the bridging ligand TTF-PPB is presented. Its strong binding ability to Co(II) and then to Ni(II) or Cu(II) in the presence of hexafluoroacetylacetonate (hfac(-)), forming new mono-and dinuclear complexes 1-3, is described. X-ray crystallographic studies have been conducted in the case of the free ligand TTF-PPB as well as its complexes [Co(TTF-PPB)(hfac)(2)] (1) and [Co(hfac)(2)(mu-TTF-PPB)Ni(hfac)(2)] (2). Each metal ion is bonded to two bidentate hfac-anions through their oxygen atoms and two nitrogen atoms of the PPB moiety with a distorted octahedral coordination geometry. Specifically, nitrogen donor atoms of TTF-PPB adopt a cis-coordination but not in the equatorial plane, which is quite rare. Electronic absorption, photoinduced intraligand charge transfer ((1)ILCT), and electrochemical behaviour of 1-3 have been investigated. UV-Vis spectroscopy shows very strong bands in the UV region consistent with ligand centred pi-pi* transitions and an intense broad band in the visible region corresponding to a spin-allowed pi-pi* (1)ILCT transition. Upon coordination, the (1)ILCT band is bathochromically shifted by 3100, 6100 and 5900 cm(-1) on going from 1 to 3. The electrochemical studies reveal that all of them undergo two reversible oxidation and one reversible reduction processes, ascribed to the successive oxidations of the TTF moiety and the reduction of the PPB unit, respectively.

Syntheses and structures of molybdenum and tungsten complexes capable of epoxidaton and copper coordination polymers and dendrimers

We are interested in the syntheses of new complexes and in their characterization by single crystal X-ray diffraction techniques. Once we understand the structures, studies aimed at understanding uses of these complexes in the field of catalytic epoxidation using complexes soluble in water and syntheses of thin films (not assessed) were conducted. The syntheses, characterization and catalytic properties of a series of mononuclear, dinuclear and tetranuclear molybdenum and tungsten oxo complexes are described. The syntheses and structural characterization of two copper coordination polymers with 3,5-dihydroxylbenzoate ligand, and five paddlewheel shaped copper dendrimers coordinated with Fréchet-type dendrons are also detailed. The background of this dissertation is outlined in Chapter 1. Chapter 2 describes the syntheses, and characterization of two new mononuclear molybdenum(VI) and tungsten(VI) oxo complexes, MoO2Cl2(OPPh2CH2OH)2, and WO2Cl2(OPPh2CH2OH)2, bearing hydrophilic phosphine oxide ligand. The catalytic properties of these complexes for the epoxidation of cis-cyclooctene were also studied. Two new dinuclear molybdenum(VI) and tungsten(VI) oxo complexes Mo2O4Cl2[(HOCH2)PhPOO]2, and (CH3O)2(O)W(μ-O)(μ-O2PPh2)2W(O)(CH3O)2, bearing organophosphinate ligand are described in Chapter 3 and 4. Chapter 4 and 5 describes the syntheses and characterization of tetranuclear molybdenum(V) oxo complexes bearing various organophosphinate ligands. The catalytic abilities of these complexes for the epoxidation of cis-cyclooctene in the presence of hydrogen peroxide as oxidant were explored as well. Various spectroscopic methods, such as IR, UV-vis, and NMR are used to characterize the nature of these complexes. Crystal structures of compounds MoO2Cl2(OPPh2CH2OH)2, WO2Cl2(OPPh2CH2OH)2, Mo2O4Cl2[(HOCH2)PhPOO]2, (CH3O)2(O)W(μ-O)(μ-O2PPh2)2W(O)(CH3O)2, and Mo4(µ3-O)4(µ-O2PR2)4O4 (R=Ph, Me, ClCH2, o-C6H4(CH2)2) are also presented. The syntheses, and structural characterization of three copper(II) coordination polymers bearing 3,5-dihydroxybenzoate ligand are described in Chapter 6. Two copper(II) coordination polymers, [Cu2(3,5-dhb)2(pyridine)4]n, and [Cu2(3,5-dhb)4]n were afforded based on different amount of pyridine used in the reaction. The structures of these complexes are further built into 2D or 3D networks via inter or intra hydrogen bonds. The syntheses and structural characterization of the zinc(II) monomer, Zn(3,5-dhb)2(pyridine)2 is also described in this Chapter. Chapter 7 describes the syntheses, and characterization of five dendronized dicopper complexes bearing different generations of Fréchet-type dendrons. The structures of 3,5- bis(benzoyloxl)benzoic acid, 3,5-(PhCOO)2PhCOOH (G1), Cu2(3,5-dhb)4(THF)2, Cu2(G1)4(pyridine)2, and Cu2(G1)4(CH3OH)2 were characterized unambiguously by single X-ray diffraction. In addition, all compounds were characterized by FT-IR, UV-vis spectroscopy and elemental analyses.

Functionalized Adamantane Tectons Used in the Design of Mixed-Ligand Copper(II) 1,2,4-Triazolyl/Carboxylate Metal–Organic Frameworks

Bistriazoles, 1,3-bis(1,2,4-triazol-4-yl)propane (tr2pr) and 1,3-bis(1,2,4-triazol-4-yl)adamantane (tr2ad), were examined in combination with the rigid tetratopic 1,3,5,7-adamantanetetracarboxylic acid (H4-adtc) platform for the construction of neutral heteroleptic copper(II) metal−organic frameworks. Two coordination polymers, [{Cu4(OH)2(H2O)2}{Cu4(OH)2}(tr2pr)2(H-adtc)4]·2H2O (1) and [Cu4(OH)2(tr2ad)2(H-adtc)2(H2O)2]·3H2O (2), were synthesized and structurally characterized. In complexes 1 and 2, the N1,N2-1,2,4-triazolyl (tr) and μ3-OH− groups serve as complementary bridges between adjacent metal centers supporting the tetranuclear dihydroxo clusters. The structure of 1 represents a unique association of two different kinds of centrosymmetrical {Cu4(OH)2} units in a tight 3D framework, while in compound 2, another configuration type of acentric tetranuclear metal clusters is organized in a layered 3,6-hexagonal motif. In both cases, the {Cu4(OH)2} secondary building block and trideprotonated carboxylate H-adtc3− can be viewed as covalently bound six- and three-connected nodes that define the net topology. The tr ligands, showing μ3- or μ4-binding patterns, introduce additional integrating links between the neighboring {Cu4(OH)2} fragments. A variable-temperature magnetic susceptibility study of 2 demonstrates strong antiferromagnetic intracluster coupling (J1 = −109 cm−1 and J2 = −21 cm−1), which combines for the bulk phase with a weak antiferromagnetic intercluster interaction (zj = −2.5 cm−1).

High-Spin Molecules: Synthesis, X-ray Characterization, and Magnetic Behavior of Two New Cyano-Bridged Ni II 9 Mo V 6 and Ni II 9 W V 6 Clusters with a S = 12 Ground State

The preparations, X-ray structures, and magnetic characterizations are presented for two new pentadecanuclear cluster compounds:  [NiII{NiII(MeOH)3}8(μ-CN)30{MV(CN)3}6]·xMeOH·yH2O (MV = MoV (1) with x = 17, y = 1; MV = WV (2) with x = 15, y = 0). Both compounds crystallize in the monoclinic space group C2/c, with cell dimensions of a = 28.4957(18) Å, b = 19.2583(10) Å, c = 32.4279(17) Å, β = 113.155(6)°, and Z = 4 for 1 and a = 28.5278(16) Å, b = 19.2008(18) Å, c = 32.4072(17) Å, β = 113.727(6)°, and Z = 4 for 2. The structures of 1 and 2 consist of neutral cluster complexes comprising 15 metal ions, 9 NiII and 6 MV, all linked by μ-cyano ligands. Magnetic susceptibilities and magnetization measurements of compounds 1 and 2 in the crystalline and dissolved state indicate that these clusters have a S = 12 ground state, originating from intracluster ferromagnetic exchange interactions between the μ-cyano-bridged metal ions of the type NiII−NC−MV. Indeed, these data show clearly that the cluster molecules stay intact in solution. Ac magnetic susceptibility measurements reveal that the cluster compounds exhibit magnetic susceptibility relaxation phenomena at low temperatures since, with nonzero dc fields, χ‘ ‘M has a nonzero value that is frequency dependent. However, there appears no out-of-phase (χ‘ ‘M) signal in zero dc field down to 1.8 K, which excludes the expected signature for a single molecule magnet. This finding is confirmed with the small uniaxial magnetic anisotropy value for D of 0.015 cm-1, deduced from the high-field, high-frequency EPR measurement, which distinctly reveals a positive sign in D. Obviously, the overall magnetic anisotropy of the compounds is too low, and this may be a consequence of a small single ion magnetic anisotropy combined with the highly symmetric arrangement of the metal ions in the cluster molecule.

The Utilization of Classical Spin Monte Carlo Methods to Simulate the Magnetic Behavior of Extended Three-Dimensional Cubic Networks Incorporating M(II) Ions with an S = 5/2 Ground State Spin

The numerical simulations of the magnetic properties of extended three-dimensional networks containing M(II) ions with an S = 5/2 ground-state spin have been carried out within the framework of the isotropic Heisenberg model. Analytical expressions fitting the numerical simulations for the primitive cubic, diamond, together with (10−3) cubic networks have all been derived. With these empirical formulas in hands, we can now extract the interaction between the magnetic ions from the experimental data for these networks. In the case of the primitive cubic network, these expressions are directly compared with those from the high-temperature expansions of the partition function. A fit of the experimental data for three complexes, namely [(N(CH3)4][Mn(N3)] 1, [Mn(CN4)]n 2, and [FeII(bipy)3][MnII2(ox)3] 3, has been carried out. The best fits were those obtained using the following parameters, J = −3.5 cm-1, g = 2.01 (1); J = −8.3 cm-1, g = 1.95 (2); and J = −2.0 cm-1, g = 1.95 (3).

Interaction of the Trinuclear Triangular Secondary Building Unit [Cu 3 (μ 3 -OH)(μ-pz) 3 ] 2+ with 4,4′-Bipyridine. Structural Characterizations of New Coordination Polymers and Hexanuclear Cu II Clusters. 2°

By reacting 4,4′-bipyridine (bpy) with selected trinuclear triangular CuII complexes, [Cu3(μ3-OH)(μ-pz)3(RCOO)2(LL′)] [pz = pyrazolate anion; R = CH3, CH3CH2, CH2═CH, CH2═C(CH3); L, L′ = Hpz, H2O, MeOH] in MeOH, the substitution of monotopic ligands by ditopic bpy was observed. Depending on the stoichiometric reaction ratios, different compounds were isolated and structurally characterized. One- and two-dimensional coordination polymers (CPs), as well as two hexanuclear CuII clusters were identified. One of the hexanuclear clusters self-assembles into a supramolecular three-dimensional structure, and its crystal packing shows the presence of two intersecting channels, one of which is almost completely occupied by guest bpy, while in the second one guest water molecules are present. This compound also shows a reversible, thermally induced, single-crystal-to-single-crystal transition.

DETERMINANTS OF THE SELECTIVE PHAGOCYTOSIS OF CARCINOGENIC PARTICULATE NICKEL COMPOUNDS

Certain inorganic nickel compounds such as crystalline NiS and Ni(,3)S(,2) are potent inducers of carcinogenesis and in vitro cell transformation, while several closely-related compounds such as amorphous NiS are essentially devoid of genotoxic activity. The phenomenon of selectivity of phagocytosis among such particulate nickel compounds has been hypothesized to account for their widely varying toxicological potency, yet the determinants of this selectivity have not been well characterized. Extracellular medium composition, particle dissolution, and particle surface charge were examined as potential determinants of selective phagocytosis for the carcinogenic crystalline and noncarcinogenic amorphous modifications of NiS. Selectivity and avidity of uptake of crystalline NiS by CHO cells was not dependent upon serum: phagocytosis of crystalline, but not amorphous NiS proceeded readily in a minimal salts/glucose medium at 37(DEGREES)C. The evolution of phagocytosis-inhibiting Ni(II) from the surface of amorphous NiS particles did not demonstrably contribute to the lower uptake of these noncarcinogenic particles despite their somewhat greater dissolution rate than the readily phagocytosed crystalline NiS particles. Significant differences in surface charge were noted between crystalline and amorphous NiS, the former being more negative in charge in distilled water suspension. Exposure of amorphous NiS particles to the vigorously reducing environment of a LiAlH(,4) solution under an inert atmosphere resulted in the particles' acquisition of a more negative surface charge. Amorphous NiS particles thus treated were phagocytosed by CHO cells to an extent similar to that of untreated crystalline NiS particles and likewise were shown to induce morphological transformation of primary Syrian hamster embryo cells with a similar potency. The potentiation of uptake characteristic of LiAlH(,4)-treated amorphous NiS was lost gradually upon storage of particles in ambient oxygenated atmosphere and was lost rapidly by apparent particle surface oxidation in aerated distilled water suspensions aged for up to 7 days. Concomitant with this loss of uptake there occurred a loss of negative surface charge. These results suggest the predominant role of particle surface charge rather than adsorbed serum components or particle dissolution as a determinant of selective phagocytosis among particulate nickel compounds. ^

Description and chemical composition of ferromanganese encrustations and deposits in the Atlantic Ocean from R/V Atlantis II cruises 20, 42, 60, 85; R/V Chain cruise 35; R/V Knorr cruise 61 and RRS Shackleton cruise 75/1 stations

Chemical and mineralogical compositions of ferromanganese oxide coatings on rocks dredged from the New England Seamounts, the Sierra Leone Rise and the Mid-Atlantic Ridge near the Equator have been determined in an investigation of regional differences in Atlantic ferromanganese deposits. Most encrustations are clearly of hydrogenous origin, consisting mainly of todorokite and delta MnO2, but several recovered from the equatorial fracture zones may be hydrothermal accumulations. Differences in the chemistry of the water column and in growth rates of the ferromanganese coatings may be important in producing this regional contrast in composition. Fine-scale changes in element abundances within the encrustations indicate that the nature of the substrate has little influence on compositional variations.

Geochemistry and isotopic ratios of samples from the Tiger gabbroic complex, Northern Victoria Land, Antarctica

Subduction related mafic/ultramafic complexes marking the suture between the Wilson Terrane and the Bowers Terrane in northern Victoria Land (Antarctica) are well-suited for evaluating the magmatic and structural evolu- tion at the Palaeo-Pacific continental margin of Gondwana. One of these intru- sions is the "Tiger Gabbro Complex" (TGC), which is located at the southern end of the island-arc type Bowers Terrane. The TGC is an early Palaeozoic island-arc related layered igneous complex characterized by extraordinarly fresh sequences of ultramafic, mafic and evolved lithologies and extensive development of high-temperature high-strain zones. The goal of the present study is to establish the kinematic, petrogenetic and temporal development of the TGC in order to evaluate the magmatic and structural evolution of the deep crustal roots of this Cambrian-aged island-arc. Fieldwork during GANOVEX X was carried out to provide insight into: (i) the spatial relations between the different igneous lithologies of the TGC, (ii) the nature of the contact between the TGC and Bowers Terrane, and (iii) the high-temperature shear zones exposed in parts of the TGC. Here, we report the results of detailed field and petrological observations combined with new geochronological data. Based on these new data, we tentatively propose a petrogenetic-kinematic model for the TGC, which involves a two-phase evolution during the Ross orogeny. These phases can be summarized as: (i) an early phase (maximum age c. 530 Ma) involving tectono-magmatic processes that were active at the deep crustal level represented by the TGC within the Bowers island arc and within a general NE-SW directed contractional regime and (ii) a late phase (maximum age c. 490 Ma) attributed to the late Ross orogenic intrusion of the TGC into the higher-crustal metasedimentary country rocks of the Bowers Terrane under NE-SW directed horizontal maximum stress and subsequent cooling.