Synthesis and the Unique Crystal Structure of [(H2O)⊂(DB18C6)(μ2‐H2O)2/2][(H3O)⊂(DB18C6)(μ2‐H2O)2/2]I3 (DB18C6 = dibenzo‐18‐crown‐6)

In the title compound 1 , the macrocylic ligand DB18C6 arranges to build two types of channels in which either only water or water and H₃O⁺ molecules are stacked to linear polymers. The counter ions, I₃^—, also form chains and fill in the spaces left between the parallel stacks of the crown ethers. Compound 1 should therefore possess interesting conducting properties and might as well serve as model for biological water channels.     

Computational exploration of rearrangements related to the vitamin B12-dependent ethanolamine ammonia lyase catalyzed transformation

DFT (B3LYP/6-31G) and ab initio molecular orbital theory (QCISD/cc-pVDZ) are used to investigate several possible mechanisms involving free radical intermediates as well as their protonated forms for processes related to the coenzyme B(12)-dependent rearrangement catalyzed by ethanolamine ammonia lyase. Two major types of rearrangements are discussed in detail, intramolecular migration and dissociation of the amine/ammonia groups, for both of which several scenarios are considered. According to the calculations, the complete dissociation of the migrating group and its subsequent association constitute an unlikely route for both the protonated and the unprotonated reactant because of the high-energy barriers (more than 23 kcal/mol) involved in these steps. Direct migration of the protonated amine group is far more favorable (10.4 kcal/mol) and therefore presents the most likely candidate for the actual enzymatic reaction. The calculations further imply that the direct loss of an ammonium cation (10.6 kcal/mol) represents a feasible pathway as well. Comparing the rearrangements for the aminoethanol radical and its protonated counterpart, in line with previous findings reported by Golding, Radom, and co-workers, we find that the migration of a protonated group is in general associated with lower energy barriers, suggesting that the actual enzyme substrate quite likely corresponds to (partially) protonated aminoethanol. As the extent of the substrate protonation/deprotonation by the active site of the enzyme may vary, the actual energy barriers are expected to range between the values calculated for the two extreme cases of a substrate, that is, the aminoethanol radical 2 and its fully protonated form 6.     

The Solid-state Structures of a Non-hydrated Yttrium Carboxylate and a Yttrium Carboxylate Hemihydrate Obtained by Reaction of Yttrium Alkoxides with Carboxylic Acids

The yttrium carboxylates Y(methacrylate)₃ and Y(acetate)₃·0.5 H₂O were prepared by reaction of Y(OCH₂CH₂OMe)₃ with methacrylic or acetic acid and characterized by X-ray structure analyses. Both carboxylates have chain structures with both bridging and chelating-bridging carboxylate ligands. In Y(acetate)₃·0.5 H₂O, every second yttrium atom is nine-coordinate due to the additional coordination of a water molecule.     

Vinyliden-Übergangsmetallkomplexe XXVI. Synthese und struktur kationischer Carbonyl-, Alken-, Vinyliden-, Alkinyl- und Alkin-Rhodiumkomplexe mit der Baueinheit trans-[Rh(PPr3)2]

The complex trans-[Rh(CO)(NH₃)(PiPr₃)₂]PF₆ (2) was prepared from [(η³-C₃H₅)Rh(PⁱPr₃)₂] (1), NH₄PF₆ and CO or from 1 and NH₄PF₆ in presence of an excess of methanol. With an excess of CO, the dicarbonyl and tricarbonyl compounds trans-[Rh(CO)₂(PⁱPr₃)₂]PF₆ (3) and [Rh(CO)₃(PⁱPr₃)₂]PF₆ (4) were obtained. Displacement of one CO ligand in 3 by pyridine and acetone led to the formation of trans-[Rh(CO)(py)PⁱPr₃)₂]PF₆ (5a) and trans-[Rh(CO) (O=CMe₂(PⁱPr₃)₂]PF₆ (6), respectively. Treatment of 1 with [pyH]BF₄ and pyridine gave trans-[Rh(py)₂(PⁱPr₃)₂]BF₄ (7); in presence of H₂ the dihydrido complex [RhH₂(py)₂(PⁱPr₃)₂]BF₄ (8) was formed. The reaction of 1 with NH₄PF₆ and ethylene produced trans [Rh(C₂H₄(NH₃(PⁱPr₃)₂]PF₆(9) whereas with methylvinylketone and acetophenone the octahedral hydridorhodium(III) complexes [RhH(η²-CH=CHC(=O)CH₃ (NH₃(PⁱPr₃)₂]PF₆(11) and [RhH(η2-C₆H₄C(=O)CH₃(NH₃(Pⁱpr₃)₂]PF₆ (13) were obtained. The synthesis of the cationic vinylidenerhodium(I) compounds trans-[Rh(=C=CHR)(py)(PⁱPr₃)₂]BF₄ (14–16) and trans-[Rh(=C=CHR)(NH₃)(PⁱPr₃) ₂]PF6 (17–19) was achieved either on treatment of 1 with [pyH]BF₄ or NH₄PF₆ in presence of 1-alkynes or by ethylene displacement from 9 by HCCR. With tert-butylacetylene as substrate, the alkinyl(hydrido)rhodium(III) complex [RhH(CC^tBu)(NH₃)(O=CMe₂)(PⁱPr₃) ₂]PF₆ (20) was isolated which in CH₂Cl₂ solution smoothly reacted to give 19 (R =^tBu). The cationic but-2-yne compound trans-[Rh(MeCCMe)(NH₃)(Pⁱ Pr₃)₂]PF₆ (21) was prepared from 1, NH₄PF₆ and C₂Me₂. The molecular structures of 3 and 14 were determined by X-ray crystallography; in both cases the square-planar coordination around the metal and the trans disposition of the phosphine ligands was confirmed.

Abstract

Der Komplex trans-[Rh(CO)(NH₃)(PⁱPr₃)₂]PF₆ (2) wurde aus [(η³-C₃H₅)Rh(PⁱPr₃)₂] (1), NH₄PF₆ und CO oder aus 1, NH₄PF₆ und Methanol hergestellt. In Gegenwart von überschüssigem CO wurden die Dicarbonyl- und Tricarbonyl-Verbindungen trans-[Rh(CO)₂(PⁱPr₃)₂]PF₆ (3) und [Rh(CO)₃(PⁱPr₃)₂]PF₆ (4) erhalten. Die Verdrängung eines CO-Liganden in 3 durch Pyridin oder Aceton führte zur Bildung von trans-[Rh(CO)(py)(PⁱPr₃)₂]PF₆ (5a) bzw. trans-[Rh(CO)(O=CMe₂)(PⁱPr₃)₂]PF₆ (6). Bei Einwirkung von [pyH]BF₄ und Pyridin auf 1 entstand trans-[Rh(py)₂(PⁱPr₃)₂]BF₄ (7); in Gegenwart von H₂ bildete sich der Dihydrido-Komplex [RhH₂(py)₂(PⁱPr₃) ₂]BF₄ (8). Die Reaktion von 1 mit NH₄PF₆ und Ethen lieferte trans-[Rh(C₂H₄)(NH₃)(PⁱPr₃)₂] PF₆ (9) während mit Methylvinylketon und Acetophenon die oktaedrischen Hydridorhodium(III)-Komplexe [RhH(η²-CH=CHC(=O)CH₃ (NH₃)-(PⁱPr₃)₂]PF₆ (11) und [RhH(η-²-C₆H₄C(=O)CH₃(NH₃)(PⁱPr₃)₂)₂]PF₆ (13) erhalten wurden. Die Synthese der kationischen Vinyli-denrhodium(I)-Verbindungen trans-[Rh(=C=CHR(py)(PⁱPr₃)₂]BF₄ (14–16) und trans-[Rh(=C=CHR)(NH₃)(PⁱPr₃)₂]PF₆ (17–19) gelang durch Einwirkung von [pyH]BF₄ bzw. NH₄PF₆ auf 1 in Gegenwart von 1-Alkinen oder durch Ethen-Verdrängung aus 9 mit HCCR. Mit tert-Butylacetylen als Reaktionspartner wurde der Alkinyl(hydrido)rhodium(III)-Komplex [RhH(CC^tBu)(NH₃(O=CMe₂)(PⁱPr₃)₂]PF₆ (20) isoliert, der in CH₂Cl₂-Lösung sofort zu 19 (R =^tBu) reagiert. Die kationische 2-Butin-Verbindung trans -[Rh(MeCCMe)(NH₃)PⁱPr₃)₂]PF₆ (21) wurde aus 1, NH₄PF₆ und C₂Me₂ hergestellt. Die Strukturen von 3 und 14 wurden kristallographisch bestimmt; in beiden Fa len ließ sich die quadratisch-planare Koordination des Metalls und die trans-Anordnung der Phosphanliganden bestätigen.     

Small-angle X-ray scattering studies on the X-ray induced aggregation of malate synthase II. Inactivation and aggregation experiments

The X-ray induced inactivation and aggregation of the enzyme malate synthase in aqueous solution were investigated by small-angle X-ray scattering and enzymic tests.Enzymic activity decreases about exponentially with increasing dose. The rate of inactivation depends linearly on the dose rate; the extrapolation to zero dose rate yielded a finite limiting value of the rate constant of inactivation. The inactivation doseD ₃₇ is a linear function of enzyme concentration.Enzymic tests and small-angle X-ray scattering on samples, which had been X-irradiated before the measurements, showed no direct relation between aggregation and inactivation. The substrates glyoxylate and acetyl-CoA and the substrate analogue pyruvate are able to protect the enzyme against radiation damage, however to a different extent against aggregation (pyruvate > glyoxylate > acetyl-CoA) or inactivation (glyoxylate > pyruvate acetyl-CoA; the latter showed no effect). These findings and the protective effect of dithiothreitol against aggregation and inactivation of the enzyme are discussed in context with the formation of hydrogen peroxide. A possible shielding of radiosensitive groups of the enzyme by the substrates and scavenging are also taken into consideration as explanations for the protective effects.While the novel application of small-angle X-ray scattering in the field of radiation biology delivers information on X-ray induced structural changes of biopolymers and on their kinetics, the occurrence of radiation damages in conventional small-angle X-ray scattering measurements on biopolymers can be reduced by a variety of precautions.

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Röntgenkleinwinkeluntersuchungen der durch Röntgenstrahlen induzierten Aggregation der Malatsynthase. II. Inaktivierungs- und Aggregationsexperimente

Zusammenfassung Die durch Röntgenbestrahlung in wäßriger Lösung induzierte Inaktivierung und Aggregation des Enzyms Malatsynthase wurden mit der Methode der Röntgenkleinwinkelstreuung und mit Enzymtests untersucht.Die Enzymaktivität nimmt mit zunehmender Dosis annähernd exponentiell ab. Die Inaktivierungsgeschwindigkeit hängt linear von der Dosisleistung ab; die Extrapolation auf Dosisleistung null ergab einen endlichen Grenzwert der Inaktivierungsgeschwindigkeitskonstante. Die InaktivierungsdosisD ₃₇ ist eine lineare Funktion der Enzymkonzentration.Enzymtests und Röntgenkleinwinkelstreuexperimente an Proben, welche vorher bereits bestrahlt worden waren, zeigten keinen direkten Zusammenhang zwischen Aggregation und Inaktivierung. Die Substrate Glyoxylat und Acetyl-CoA sowie das Substratanaloge Pyruvat vermögen das Enzym gegen Strahlenschäden zu schützen, jedoch in unterschiedlichem Ausmß gegen Aggregation (Pyruvat > Glyoxylat > Acetyl-CoA) oder Inaktivierung (Glyoxylat > Pyruvat Acetyl-CoA; letzteres zeigte keinen Effekt). Diese Befunde und die Schutzwirkung von Dithiothreitol gegen die Aggregation und Inaktivierung des Enzyms werden in Zusammenhang mit der Bildung von Wasserstoffperoxid diskutiert. Als weitere Erklärungen für die Schutzwirkungen werden die mögliche Abschirmung strahlenempfindlicher Gruppen des Enzyms durch die Substrate und der Einfang von Radikalen in Erwägung gezogen.Während die neuartige Anwendung der Röntgenkleinwinkelstreuung auf dem Gebiet der Radiobiologie Aufschluß über strahleninduzierte Strukturänderungen von Biopolymeren und deren Kinetik gibt, läßt sich das Auftreten von Strahlenschäden bei konventionellen Röntgenkleinwinkelmessungen an Biopolymeren durch verschiedene Vorkehrungen reduzieren.

     

Synthesis of a Fullerene Derivative of Benzo[18]crown-6 by Diels-Alder Reaction: Complexation Ability,Amphiphilic Properties,and X-Ray Crystal Structure of a Dimethoxy-1,9-(methano[1,2]benzenomethano)fullerene[60] Benzene Clathrate

A fullerene derivative 1 of benzo[18]crown-6 was obtained by Diels-Alder addition of fullerene[60](C₆₀) to the ortho-quinodimethane prepared in situ from 4,5-bis(bromomethyl)benzo[18]crown-6 ( 3 ) with Bu₄NI in toluene. Extraction experiments show that the complexation of K⁺ ions strongly increases the solubility of 1 in protic solvents like MeOH. Using Langmuir-Blodgett techniques, monolayers of the highly amphiphilic fullerene-derived crown ether 1 and its K⁺ ion complex were prepared. An X-ray crystal structure was obtained from a benzene clathrate of comparison compound 2 , synthesized by Diels-Alder reaction of C₆₀ with the ortho-quinodimethane derived from 1,2-bis(bromomethyl)-4,5-dimethoxybenzene ( 4 ). Both the fullerene molecule 2 and the benzene molecule are fully ordered in a crystal packing which is stabilized by intermolecular van-der-Waals contacts between the benzene ring and the C-spheres, intermolecular C…?C contacts between the C₆₀ moieties, and intermolecular O…?C contacts between the O-atoms of the veratrole moieties and fullerene C-atoms.     

Cu3AlCl6 und Cu2Al2Cl8, die Gaskomplexe im System CuCl/Al2Cl6

Cu₃AlCl₆ and Cu₂Al₂Cl₈, Gas Complexes in the System CuCl/Al₂Cl₆ Investigations by mass spectroscopy in the system CuCl_s/Al₂Cl_6,gestablished that only Cu₃AlCl₆ and Cu₂Al₂Cl₈ are observed as principal gas complexes. Results of flow measurements published by LAUGHLIN and Gregory (1976) which were attributed erroneously by these authors to the complex CuAlCl₄ may be described by the equilibria given in “Inhaltsübersicht”. The complexes cu₃AlCl₆ and Cu₂Al₂Cl₈ are supposed to have a cube type structure similar to Cu₄Cl₄.     

New multidentate potential ionophors of ether-amide type

The syntheses of acyclic compounds featuring ether-amide groups and different terminal substituents are presented. Three series of new multidentate potential ligands were obtained.

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Neue mehrzähnige potentielle Ionophore des Ether-Amid-Typs

Zusammenfassung Es wird die Synthese acyclischer Verbindungen mit Ether-Amid-Gruppen und verschiedenen endständigen Substituenten beschrieben. Es wurden drei Verbindungsreihen erhalten, die neue potentielle mehrzähnige Liganden repräsentieren.

     

Enantioselective Syntheses and Absolute Configurations of Viridiene and Aucantene,Two Constitutents of Algae Pheromone Bouquets

Viridiene ((+)- 6 ; (+)-(3R,4S)-3-((1Z)-1,3-butadienyl)-4-vinylcyclopentene) and aucantene ((+)- 18 ; (+)-(4R,5R)-4-((1E)-1-propenyl)-5-vinylcyclohexene) are constituents of the pheromone bouquets of several brown algae species. Key synthons to the title compounds are optically active γ-lactones with known or experimentally determined absolute configurations. Horse liver alcohol dehydrogenase, which catalyses the oxidation of meso- and racemic non-meso diols to chiral lactones, and pig-liver esterase, which catalyzes the saponification of meso-diesters to chiral half-esters, were utilized for the asymmetric synthesis of such precursors. The racemic non-meso diol rac- 1 is converted to the two stereoisomeric γ-lactones (+)- 2 and (+)- 3 which are readily separated. meso-Diol 12 is oxidized to the chiral γ-lactone (?)- 11 . Its enantiomer (+)- 11 is obtained by enantioselective saponification of the meso-diester 9 with pig-liver esterase. Appropriately designed syntheses lead from these chiral intermediates to both enantiomers (+)- and (?)- 6 of viridiene and (+)- and (?)- 18 of aucantene. In addition, kinetically controlled reduction of the racemic aldehydes rac- 5a and rac- 15 with horse liver alcohol dehydrogenase offers a convenient alternative to the enantioselective preparation of the enantiomers of the two hydrocarbons 6 and 18 . Chromatography of 6 on triacetylated cellulose as a stationary chiral phase confirms the enantiospecificity of the synthetic routes designed.