A model for isotropic,nematic, and columnar ordering in a self-assembling system - comparison with the phase behavior of 2,3,6,7,10,11-hexa-(1,4,7-trioxaoctyl)-triphenylene in water

Many amphiphilic molecules in aqueous solution spontaneously self-assemble into labile anisotropic aggregates. At large enough concentration, this shape anisotropy may lead to complex liquid-crystalline mesophases. Here we compare the results of a recent excluded volume model for reversible assembling flexible linear aggregates to a corresponding experimental amphiphilic system, 2,3,6,7,10,11-hexa-(1,4,7-trioxaoctyl)-triphenylene, in water. Our comparison emphasizes the importance of including aggregate flexibility into theories of micellar assembly.     

The structure and dynamic properties of mixed adsorption and penetration layers of α-dipalmitoylphosphatidylcholine/β-lactoglobulin at water/fluid interfaces

The interfacial tensions of mixed α-dipalmitoylphosphatidylcholine (DPPC)/β-lactoglobulin layers at the chloroform/water interface have been measured by the pendent drop and drop volume techniques. In certain intervals, the adsorption kinetics of these mixed layers was strongly influenced by the concentrations of both protein and DPPC. However, at low protein concentration, C_{β-lactoglobulin}=0.1 mg l⁻¹, the adsorption rate of mixed interfacial layers was mainly controlled by the variation of the DPPC concentration. As C_{β-lactoglobulin} was increased to 0.8 mg l⁻¹, the interfacial activity was abruptly increased, and within the concentration range of C_DPPC=10⁻⁴–10⁻⁵ mol l⁻¹, the DPPC has very little effect on the whole adsorption process. In this case, the adsorption rate of mixed layers was mainly dominated by the protein adsorption. This phenomenon also happened as the protein concentration was further increased to 3.6 mg l⁻¹. When C_DPPC>3 · 10^–5 mol l⁻¹, the adsorption behaviour was very similar to that of the pure DPPC although the protein concentration was changed. The equilibrium interfacial tensions of the mixed layers are dramatically effected by the lipid as compared to the pure protein adsorption at the same concentration. It reveals the estimation of which composition of lipid and protein decreases the interfacial tension. The combination of Brewster angle microscopy (BAM) with a conventional LB trough was applied to investigate the morphology of the mixed DPPC/β-lactoglobulin layers at the air/water interface. The mixed insoluble monolayers were produced by spreading the lipid at the water surface and the protein adsorbed from the aqueous buffer subphase. The BAM images allow to visualise the protein penetration and distribution into the DPPC monolayer on compression of the complex film. It is shown that a homogeneous distribution of β-lactoglobulin in lipid layers preferentially happens in the liquid fluid state of the monolayer while the protein can be squeezed out at higher surface pressures.     

A novel method for the determination of a PCB sum value by enzyme immunoassay to overcome the cross-reactivity problem

Many attempts have been made to detect polychlorinated biphenyls (PCBs) by enzyme immunoassay (ELISA). All known ELISAs to PCBs show characteristic cross-reactivity problems. Without any prior information about the composition of the sample, no quantification of the total PCB content is possible. A chemical approach is shown to solve the cross-reactivity problem by the quantitative dechlorination of all PCB congeners to the single compound biphenyl. For the reductive dechlorination palladium on barium sulfate and ammonium formate were used. The dechlorination procedure was optimized to be performed at room temperature in methanol without the exclusion of oxygen or water. For the development of polyclonal biphenyl-antibodies the synthesis of the hapten biphenylhexanoic acid via Grignard cross-coupling is described and an immunization protocol is given. The purity of the used immunological reagents proved to be very crucial. The whole procedure was tested with spiked soil samples. The detection limit for PCBs (Clophen A50) in soil was 1 mg/kg (3.1 μmol/kg). This corresponds to a biphenyl concentration in methanol of 0.1 mg/L (0.6 μmol/L). Received: 25 September 1998 / Revised: 1 December 1998 / Accepted: 4 December 1998     

Routine analysis of vinicultural relevant fungicides, insecticides and herbicides in soil samples using enhanced solvent extraction (ESE)

Parameters affecting the extraction efficiency of various pesticides from a native contaminated soil sample (C_org = 4.4%) using an enhanced solvent extraction (ESE) technique were investigated. The defined settings of temperature (50/150 °C), pressure (180/240 MPa), static and dynamic extraction time (5/15 min and 0/5 min, respectively) yielded results which did not differ significantly (RSD = 5.9–11.8%). In comparison to a classical shake-out extraction method the yielded quantities were on average 14% higher using ESE. The established method achieved a high precision (RSD = 2.8–9.1%) for the pesticides extracted from native contaminated soil samples. A significant influence of the sample matrix on accuracy was not observed. The RSDs of thirteen pesticides extracted from spiked sea sand varied in a similar range from 1.7 to 9.8% and the recoveries were between 83 and 112%. The method has been applied to soil samples from vineyards routinely. Received: 28 December 1998 / Revised: 8 March 1999 / Accepted: 11 March 1999     

Flexible V7O16 Layers as the Common Structural Element of Vanadium Oxide Nanotubes and a New Crystalline Vanadate

The walls of vanadium oxide nanotubes (VO_x‐NTs) are built up by vanadate layers between which the structure‐directing template, either a primary amine or a diamine with long alkyl chain, is located. The feasibility of various exchange reactions under preservation of the tubular morphology indicates a high structural flexibility of the VO_x‐NTs. The structure of the vanadate layers appears to be the same in all tubular vanadates, as revealed by the similarity of the diffraction patterns. Plate‐like crystals of a new crystalline phase, structurally closely related to the nanotubes, have now been prepared with ethylene diamine, applying a route that is analogous to the VO_x‐NT synthesis. The single crystal X‐ray structure determination showed that this new phase has the composition (en)V₇O₁₆ and crystallizes with triclinic symmetry. The structure is composed of V₇O₁₆ layers between which ethylene diamine mo le cules are embedded. The V₇O₁₆ layers comprise two sheets of square VO₅ pyramids and VO₄ tetrahedra that connect these sheets. The available experimental data establish that this V₇O₁₆ layer also is the basic element of the VO_x‐NT wall structure. The simulated X‐ray powder diffraction pattern calculated with a corresponding structural mode for VO_x‐NTs agrees well with the observed one.     

New Bifunctional Benzoxazaphosphorinanone Systems

The (CH₂)_n (n = 2, 3)‐bridged, PCl‐functional bis(benzoxazaphosphorinanone) derivatives, 3 a and 3 b , were prepared in high yield by the reaction of the salicylic acid amide derivatives, 2 a and 2 b , with phosphorus trichloride. Cyclocondensation of 3 a and 3 b with the bis(trimethylsilyl)ethers, 4 a – 4 c , furnished the symmetrical benzoxazaphosphorinanone derivatives, 5 a – 5 f , in moderate yield. 5 a – 5 f involve a nine‐membered ring, made up of carbon, nitrogen, phosphorus, and oxygen, as a central feature. Oxidation of  5 a – 5 f with the urea‐hydrogen peroxide adduct, (H₂N)₂C(:O) · H₂O₂, gave rise to the corresponding phosphoryl compounds, 6 a – 6 f . All new compounds were characterized by NMR spectroscopy, mass spectrometry, and elemental analysis. For compound 6 e an X‐ray crystal structure determination was conducted; the two formally identical halves of the molecule differ appreciably in the torsion angles in the region P–O–C (naphthyl).     

Synthesen und Strukturen von N‐Acylthioharnstoffkomplexen des Zinks und des Cadmiums

Synthesis and Structures of the Zinc‐ and Cadmium‐N‐Acylthiourea Complexes The synthesis and crystal structures of the N,N‐Diisobutyl‐N′‐benzoylthiourea complexes [Zn(Buⁱ₂btu)₂] and [Cd(Buⁱ₂btu)₂(HBuⁱ₂btu)] are reported. The complexes of Zn^II and Cd^II have different molecular structures. Whereas Zn^II forms a bischelate with tetrahedral coordination, three ligands coordinate in a trigonal‐bipyramidal manner in the Cd^II complex.     

Mono‐ and Binuclear Rhodium and Platinum Complexes of 1, 3, 5‐Trimethyl‐1, 3, 5‐triaza‐2σ3λ3‐phosphorin‐4, 6‐dionyloxy‐substituted Calix[4]arenes

The reaction behaviour of 1, 3, 5‐triaza‐2σ³λ³‐phosphorin‐4, 6‐dionyloxy‐substituted calix[4]arenes towards mono‐ and binuclear rhodium and platinum complexes was investigated. Special attention was directed to structure and dynamic behaviour of the products in solution and in the solid state. Depending on the molar ratio of the reactands, the reaction of the tetrakis(triazaphosphorindionyloxy)‐substituted calix[4]arene ( 4 ) and its tert‐butyl‐derivative ( 1 ) with [(cod)RhCl]₂ yielded the mono‐ and disubstituted binuclear rhodium complexes 2 , 3 , and 5 . In all cases, a C₂‐symmetrical structure was proved in solution, apparently caused by a fast intramolecular exchange process between cone conformation and 1, 3‐alternating conformation. The X‐ray crystal structure determination of 5 confirmed [(calixarene)RhCl]₂‐coordination through two opposite phosphorus atoms with a P ⃜P separation of 345 pm. The complex displays crystallographic inversion symmetry, and the Rh₂Cl₂ core is thus exactly planar. Reaction of 1 and of the bis(triazaphosphorindionyloxy)‐bis(methoxy)‐substituted tert‐butyl‐calix‐[4]arene ( 7 ) with (cod)Rh(acac) in equimolar ratio and subsequent reaction with HBF₄ led to the expected cationic monorhodium complexes 5 and 8 , involving 1, 3‐alternating P‐Rh‐P‐coordination. The cone conformation in solution was proved by NMR spectroscopy and characteristic values of the ¹J(PRh) coupling constants in the ³¹P‐NMR‐spectra. Reaction of equimolar amounts of 4 with (cod)Rh(acac) or (nbd)Rh(acac) led, by substitution of the labile coordinated acetylacetonato and after addition of HBF₄, to the corresponding mononuclear cationic complexes 9 and 10 . Only two of the four phosphorus atoms in 9 and 10 are coordinated to the central metal atom. Displacement of either cycloocta‐1, 5‐diene or norbornadiene was not observed. For both compounds, the cone conformation was proved by NMR spectroscopy. Reaction of 4 with (cod)PtCl₂ led to the PtCl₂‐complex ( 11 ). As for all compounds mentioned above, only two phosphorus atoms of the ligand coordinate to platinum, while two phosphorus atoms remain uncoordinated (proved by δ³¹P and characteristic values of ¹J(PPt)). NMR‐spectroscopic evidence was found for the existence of the cone conformation in the cis‐configuration of 11 .     

Calix[4]arene‐based Bis‐phosphonites,Bis‐phosphites,and Bis‐O‐acyl‐phosphites as Ligands in the Rhodium(I)‐catalyzed Hydroformylation of 1‐Octene

New calix[4]arene‐based bis‐phosphonites, bis‐phosphites and bis‐O‐acylphosphites were synthesized and characterized. Treatment of these P‐ligands with selected rhodium and platinum precursors led to mononuclear complexes that were satisfactorily characterized. The solid state structure of the dirhodium(I) complex 14 has been determined by X‐ray diffraction. The two rhodium centres are bridged by two chloro ligands; one rhodium atom is further coordinated by calix[4]arene phosphorus atoms and the other by cyclooctadiene. The new calix[4]arene P‐ligands were tested in the Rh(I) catalyzed hydroformylation of 1‐octene. All Rh(I) complexes catalyzed the reaction leading to high chemoselectivity with regard to the formation of aldehydes. Yields and n/iso‐selectivities depended on the reaction conditions. Average yields of 80 % and n/iso‐ratios of about 1.3 to 1.5 were observed. High yields of aldehydes can be achieved using the methoxy substituted P‐ligands at low Rh:ligand ratios.