Sulfinylimine: Wichtige neue Bausteine zur Entwicklung der Chemie der Polysulfanmono- und -disulfonsäuren

Sulfinylimines: Important Building Blocks for Developing the Polysulfanemonoand -disulfonic Acid Chemistry Besides hydrolysis of perfluoroorganosulfanesulfinylimines in closed systems, reactions of R_fS_xCl with K₂S₂O₅ or M₂S₂O₃ are also productive methods for the preparation of perfluoroorganosulfanemonosulfonates. The free acid CF₃SSSO₃H is made by treating the potassium salt with a strong acidic cation resin. It is unstable and shows a pK_s-value of approx. –0,5 providing an acidity comparable with polyphosphoric acids. Metathetical reactions of the potassium salts with [(C₆H₅)₄M]Cl (M = P, As) or [R₄N][ClO₄] (R = n-C₃H₇, n-C₄H₉) respectively lead to well crystallized salts. Single crystals are used for x-ray structure analysis. These prove the polysulfanesulfon-moiety to be present in these molecules. Sulfur-sulfur-bonds can also be evidenced by chlorolysis reactions. Not only with Cl₂ but also with SCl₂ R_fS_xCl or R_fS_x+1Cl and ClSO₂OM are formed respectively. In this way CF₃SSSCl is prepared for the first time. The reaction of CF₃SeBr and K₂S₂O₅ provides K[CF₃SeSO₃] which is unstable and decomposes to CF₃SeSeCF₃, K₂S₂O₆, SO₂ and KBr. When S₂Cl₂ is reacted with (CH₃)₃SiNSO besides the main product S₂(NSO)₂ also minor amounts of S_x(NSO)₂ (x = 3, 4, 5) are formed. While hydrolysis of S₂(NSO)₂ leads quantitively to (NH₄)₂S₄O₆, a mixture of ammoniumpolysulfanedisulfonates are obtained from S_x(NSO)₂ which could not be separated. It is demonstrated that chemical reactivity is dominated by disproportionation of S₂(NSO)₂ into S(NSO)₂ and sulfur. Additonal sulfinylimines are obtained by metathesis of XNSO (X = Cl, Br) and AgSCN or AgSeCN respectively. The structures of S₂(NSO)₂ and OSNSCN are established by x-ray methods. By spectroscopical evidence it is shown that OSNSeCN is isostructured with OSNSCN.     

Desorption of hydrogen from an electrode surface under influence of an external magnetic field – In-situ microscopic observations

The effect of a magnetic field in the perpendicular-to-electrode configuration on the hydrogen evolution reaction (HER) was investigated during the deposition of Co. An enhanced desorption of hydrogen in the form of numerous small bubbles was found by combining potentiostatic investigations, coupled with an electrochemical quartz crystal microbalance (EQCM), and simultaneous microscopic observations of the electrode surface. The results are consistent with the recently proposed qualitative model [J.A. Koza, M. Uhlemann, A. Gebert, L. Schultz, Electrochem. Commun. 10 (2008) 1330].     

Automated sample preparation by pressurized liquid extraction-solid-phase extraction for the liquid chromatographic-mass spectrometric investigation of polyphenols in the brewing process

The analysis of polyphenols from solid plant or food samples usually requires laborious sample preparation. The liquid extraction of these compounds from the sample is compromised by apolar matrix interferences, an excess of which has to be eliminated prior to subsequent purification and separation. Applying pressurized liquid extraction to the extraction of polyphenols from hops, the use of different solvents sequentially can partly overcome these problems. Initial extraction with pentane eliminates hydrophobic compounds like hop resins and oils and enables the straightforward automated on-line solid-phase extraction as part of an optimized LC-MS analysis.     

Photocrosslinking of Silicones. Part XV. Cationic Photocrosslinking of α, ω, 4-Terminated Disiloxanes

Abstract

The photoinduced cationic crosslinking of α, ω-terminated disiloxanes (epoxy, vinyl ether, propenyl ether) has been investigated by means of Real-Time IR spectroscopy. A lipophilic iodonium salt and three lipophilic sulfonium salts were used as photoinitiator. The crosslinking rate is influenced by the type of α, ω-terminated disiloxane used and differed by a factor of more than 100 from the aliphatic epoxy to the vinyl ether derivatives. Moreover, the sulfonium salts were found to have a lower initiation efficiency than the lipophilic iodonium salt in the various systems studied. These results are in good agreement with the quantum yield of proton formation in a hexamethyldisiloxane/dimethoxyethane mixture. The final degree of conversion is larger with the ene derivatives than with the epoxy derivatives. The application of a kinetic method allows us to estimate the rate constant of the termination step (k_t and for the propenyl derivative the rate constant of the propagation step kp. The termination step can be described by means of a first order reaction. k_t was found to depend on the light intensity and the type of initiators used, whereas k_p is independent of the initiator used.     

Porous Membranes Built Up from Hydrophilic Poly(ionic liquid)s

Porous polymer membranes made via electrostatic complexation are fabricated from a water‐soluble poly(ionic liquid) (PIL) for the first time. The porous structure is formed as a consequence of simultaneous phase separation of the PIL and ionic complexation with an acid, which occurred in a basic solution of a nonsolvent for the PIL. These membranes have a stimuli‐responsive porosity, with open and closed pores in isopropanol and in water, respectively. This property is quantitatively demonstrated in filtration experiments, where water is passing much slower through the membranes than isopropanol.

     

Self-assembled monolayers containing terminal mono-, bis-, and tris-nitrilotriacetic acid groups: characterization and application

We have undertaken a structural and functional study of self-assembled monolayers (SAMs) formed on gold from a series of alkylthiol compounds containing terminal multivalent chelators (MCHs) composed of mono-, bis-, and tris-nitrilotriacetic acid (NTA) moieties. SAMs were formed from single-component solutions of the mono-, bis-, and tris-NTA compounds, as well as from mixtures with a tri(ethylene glycol)-terminated alkylthiol (EG(3)). Contact angle goniometry, null ellipsometry, and infrared spectroscopy were used to explore the structural characteristics of the MCH SAMs. Ellipsometric measurements show that the amount of the MCH groups on surfaces increases with increasing mol % of the MCH thiols in the loading solution up to about 80 mol %. We also conclude that mixed SAMs, prepared in the solution composition regime 0-30 mol % of the MCH thiols, consist of a densely packed alkyl layer, an amorphous ethylene glycol layer, and an outermost layer of MCH groups exposed toward the ambient. Above 30 mol %, a significant degree of disorder is observed in the SAMs. Finally, functional evaluation of the three MCH SAMs prepared at 0-30 mol% reveals a consistent increase in binding strength with increasing multivalency. The tris-NTA SAM, in particular, is enabled for stable and functional immobilization of a His6-tagged extracellular receptor subunit, even at low chelator surface concentrations, which makes it suitable for applications when a low surface density of capturing sites is desirable, e.g., in kinetic analyses.     

CuO particles from ionic liquid/water mixtures: evidence for growth via Cu(OH)2 nanorod assembly and fusion

Tetrabutylammonium hydroxide/water mixtures are efficient reaction media for the fabrication of nanoscale metal oxides and hydroxides. Uniform CuO nanoplates, among others, can be grown on a large scale. This work shows that after 30 s at temperatures above 40 degrees C, CuO formation is already essentially complete. X-ray diffraction and transmission electron microscopy (TEM) show that the resulting plates form via a two-step process, where Cu(OH) 2 rods precipitate first. These rods aggregate and fuse into plates with a width/height ratio of about 1.9. High-resolution TEM and electron diffraction show that the plates are single crystals and exhibit only some defects, which most likely originate from the assembly and fusion of the primary rods.