Equilibrium, 1H and 13C NMR spectroscopy,and X-ray diffraction studies on the complexes Bi(DOTA)- and Bi(DO3A-Bu)

Several Bi(III) complexes are used in medicine as drugs. Bi(DO3A-Bu) has recently been proposed as a nonionic contrast agent in X-ray imaging (H(3)DO3A-Bu = 10-[2,3-dihydroxy-(1-hydroxymethyl)propyl]-1,4,7,10-tetraazacyclododecane-1,4,7,-triacetic acid). The solution equilibria and NMR structure and dynamics of Bi(DO3A-Bu) and of the similar Bi(DOTA)(-) have been investigated (H(4)DOTA = 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid). The stability constants were determined with the study of the competition equilibria between Br(-) ions and the ligands DOTA or DO3A-Bu for the Bi(III) by spectrophotometry. The stability constants, obtained for Bi(DOTA)(-) and Bi(DO3A-Bu), are very high, log K = 30.3 and 26.8, respectively. Potentiometric titrations indicated the dissociation of one of the protons among the three alcoholic OH groups in Bi(DO3A-Bu). The dissociation constant is log K = 7.53 (0.09) indicating that at physiological pH about 50% of the species possess -1 charge. It was shown by (1)H and (13)C NMR spectroscopy that the OH group attached to the middle carbon atom of the "butriol" side chain is coordinated to the Bi(III) and starts to deprotonate at pH > 5.5. The crystal structure of NaBi(DOTA).H(2)O shows an octacoordinated arrangement of the donor atoms around the Bi(III), with no water in the inner sphere. The crystals belong to the centrosymmetric space group C2/c. The temperature dependent (1)H and (13)C NMR spectra indicate that both Bi(DOTA)(-) and Bi(DO3A-Bu)(-) complexes are fluxional. For Bi(DOTA), the Delta(deltadeltadeltadelta) right harpoon over left harpoon Lambda(lambdalambdalambdalambda) fluxionality was identified, and on the basis of the activation parameters, a synchronous motion was suggested for the fluxional motion resulting in the change of ring conformation and of the helicity of the complex. The transition state is supposed to be more symmetrical than the initial state. The deprotonated Bi(DO3A-Bu) has a highly asymmetric NMR structure in solution, and its fluxional motion is slower than that of Bi(DOTA)(-).     

Flow-rate variated HPLC-/EC-determination of phenols

Summary An HPLC-EC-method is proposed for the determination of phenol, alkylphenols, hydroxyphenols and chlorophenols. With the application of programmed flowrate variation good resolution within short analysis times could be reached; the eluent is usable for several times. An electrochemical dual-detector provides detection limits ranging from 55 pg for hydroquinone to 19 ng for pentachlorophenol (injection volume 20 l). The dual mode is used to increase selectivity and sensitivity. The method was successfully applied to the direct determination of phenols in waste and river water.     

A new approach to (-)-swainsonine by ruthenium-catalyzed ring rearrangement

A new enantioselective synthesis of the idolizidine alkaloid (-)-swainsonine 1 in 40% overall yield starting from the known oxazolidinone 6 is described. Throughout the synthesis, the high efficiency of metal-catalyzed reactions is illustrated. The key step is a new ruthenium-catalyzed metathesis rearrangement reaction. In this ring-closing/ring-opening tandem process, stereocenters are transferred from a ring to the olefinic side chain of the formed heterocycle. The metathesis precursor was obtained by palladium-catalyzed desymmetrization of cyclopentenediol. The synthesis was completed by functionalization of the terminal double bond, cyclization of the second ring, and diastereoselective dihydroxylation.     

An industrially viable catalyst system for palladium-catalyzed telomerizations of 1,3-butadiene with alcohols

The telomerization reaction of 1,3-butadiene with alcohols to give alkyl octadienyl ethers in the presence of palladium-carbene catalysts has been studied in detail. Unprecedented catalyst efficiency with turnover numbers (TON) up to 1,500,000 and turnover frequencies (TOF) up to 100,000 h(-1) have been obtained after optimization for the reaction of methanol in the presence of an excess of in situ generated carbene ligands. High yields (75-97 %) and catalyst productivities (TON 15,000-100,000) are observed for other aliphatic alcohols and phenols. For comparison five carbene-palladium(0) complexes have been synthesized and characterized by X-ray crystallography. Both electronic and steric effects on the stability and reactivity of the catalysts have been discussed on the basis of density functional theory calculations.     

Die konduktometrische F?llungstitration des Kaliums mit Natriumtetraphenyloborat Na[(C6H5)4B]

Zusammenfassung Trotz des geringeren Unterschiedes in der Ionenbeweglichkeit zwischen Natrium-Ionen und Kalium-Ionen als zwischen Lithium-Ionen und Kalium-Ionen eignet sich auch das Natriumtetraphenyloborat (Kalignost) für Leitfähigkeitstitrationen.Die Titrationen der wäßrigen Kaliumchloridlösungen sind bei Zimmertemperatur imph-Bereich 5–10 durchführbar.Die Ablesungen der Endleitfähigkeiten können 2 min nach Reagenszugabe erfolgen.Natrium-, Magnesium- oder Calcium-Ionen stören bis zu einem Äquivalenzverhältnis KCl : Fremdsalz=110 nicht, Eisen(III)-Ionen sind in etwa doppeltem Überschuß zulässig.Ammonium-Ionen werden quantitativ erfaßt. Wird Ammoniak mit Natronlauge ausgetrieben, dann ist die alkalische Lösung direkt zu titrieren.Es ist nicht erforderlich, Erdalkali-Ionen durch Natriumcarbonatzusatz auszufällen.Die Genauigkeit der Bestimmungen ist die gleiche wie bei konduktometrischen Fällungstitrationen im allgemeinen.Herrn Prof. Dr. A. Windaus zum 80. Geburtstag in Verehrung und Dankbarkeit gewidmet.Die vorstehend wiedergegebenen Untersuchungen wurden durch Bewilligung von ERP-Mitteln in großzügiger Weise gefördert.     

Polyarylenes on the Basis of Alkylpyrrole and Alkylcarbazole Derivatives and their Oligomeric Model Systems

The redox and spectroscopic properties of soluble poly- (9-decylcarbazole) derivatives and poly(1-decylpyrrole) were studied. The polymers were synthesized via the Yamamoto polycondensation method. Analyzing the electrochemical and optical properties of 3,6-linked poly(alkylcarbazole)s it is evident that the conjugation segment is the benzidine system and the overall properties of these polymers can be compared with meta linked poly(phenylene)s. In opposite, 2,7-linked poly(alkylcarbazole)s reveal an even longer conjugation segment comparable with para linked poly(phenylene)s. First observations in the case of poly(1-decylpyrrole) suggest a higher steric hinderance compared to poly- (1-methylpyrrole). Molecular modeling studies confirm this. © 1997 John Wiley & Sons, Ltd.     

Adsorption and displacement of beta-2-microglobulin at solid/liquid interfaces

Adsorption of beta-2-microglobulin from aqueous solution onto unmodified and methylated silicon wafers and subsequent displacement of the small globular protein by fibrinogen were studied by spectroscopic ellipsometry, immunosorbent assays and atomic force microscopy. The results provide evidence that hydrophobicity of the substrate increases the maximum adsorbed amount of beta-2-microglobulin and the resistance of the adsorbed protein to displacement from the interface by competing species, respectively. Further, the dynamics of beta-2-microglobulin adsorption was found to induce significant differences in the degree of displacement achieved at given conditions. The observed variations in displacement behavior of adsorbed beta-2-microglobulin were interpreted based on information on the layer structure gained by atomic force microscopy. More compact and relatively smooth protein layers were formed on the hydrophobic surface corresponding to lower displacement by fibrinogen.     

N–O-Bindungsspaltung in O-silylierten Oximen bei der Reaktion mit einem Titanocen-Alkin-Komplex

N–O Bond Cleavage in O-silylated Oximes by Reaction with a Titanocene-Alkyne Complex Cp₂Ti(Me₃SiC₂SiMe₃) 1 reacts with alicyclic and aliphatic O-silylated ketoximes of type R¹R²C=NOSiMe₃ ( 2 : R¹R² = (CH₂)₅; 3 : R¹ = R² = Me) under N–O bond breaking to the titanocene complexes Cp₂Ti(OSiMe₃)(N=CR¹R²) 6 (R¹R² = (CH₂)₅) and 7 (R¹ = R² = Me). The structure of 6 was obtained by X-ray crystal structure analysis ( 6 : triclinic, space group P1, Z = 2, a = 9.486(1), b = 9.865(1), c = 12.305(2) Å, α = 107.19(1), β = 96.08(1), γ = 111.08(1)°).