Hydrolysis reaction analysis of L-alpha-distearoylphosphatidylcholine monolayer catalyzed by phospholipase A2 with polarization-modulated infrared reflection absorption spectroscopy

The hydrolysis reaction of L-alpha-distearoylphosphatidylcholine (DSPC) monolayers catalyzed by phospholipase A2 (PLA(2)) has been studied using polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS) with film balance measurements. The PM-IRRAS analysis provides quantitative information about the reaction efficiency at different surface pressures. It was found that the reaction efficiency of L-DSPC monolayer hydrolysis catalyzed by PLA(2) decreased with increasing surface pressure. At zero pressure (lift-off point), the hydrolysis reaction efficiency has the highest value of 45%. Increasing surface pressure leads to the decrease of the hydrolysis efficiency. Since the surface pressure is above 20 mN/m, the hydrolysis reaction nearly stopped. PM-IRRAS technique provides a powerful means to study the hydrolysis process catalyzed by phospholipase A2 at the air/water interface.     

Phospholipase A2 hydrolysis of mixed phospholipid vesicles formed on polyelectrolyte hollow capsules

Mixtures of the phospholipids L-alpha-dimyristoylphosphatidic acid (DMPA) and L-alpha-dipalmitoylphosphatidylcholine (DPPC) have been successfully adsorbed onto the charged surface of multilayer polyelectrolyte capsules to form a novel vesicle. Leaving such vesicles in phospholipase A(2) solution, we observed the hydrolysis reaction on the surface of the lipid/polymer vesicles and a permeability change before and after the reaction by confocal-laser scanning microscopy (CLSM). A capsule with adjustable permeability was constructed. This method may provide new features for drug-release vesicles.     

Immobilization, Characterization, and Preliminary Reactivity Studies of Halfsandwich Ruthenium Complexes on Silica

Summary. The complexes [RuCp(CH₃CN)₂(Ph₂PCH₂CH₂Si(OMe)₃)]PF₆ and [RuCp(CH₃CN) (Ph₂PCH₂CH₂Si(OMe)₃)₂]PF₆ were obtained in good yields by treatment of [RuCp(CH₃CN)₃]PF₆ with 1 and 2 equivs of Ph ₂PCH₂CH₂Si(OMe)₃. Both free Ph ₂PCH₂CH₂Si(OMe)₃ and the two complexes were grafted onto the surface of powdered silica. The surface coverage was determined independently by ³¹P solid state NMR and IR spectroscopy. IR data revealed that for Ph ₂PCH₂CH₂Si(OMe)₃ and the complexes 52, 52, and 18 molecules, respectively, were immobilized per 100nm² of SiO₂ surface. Similar values were obtained from ³¹P MAS NMR measurements. With the immobilized first complex the catalytic redox isomerization of allyl alcohol to propanal has been studied by means of IR spectroscopy and ¹H NMR spectroscopy showing the quantitative formation of aldehyde. While in the first cycle satisfactory turnover numbers were achieved, the subsequent cycles showed only low conversions to aldehyde presumably due to decomposition of the complex. The immobilized second complex was catalytically inactive.Received February 25, 2003; accepted March 24, 2003 Published online August 18, 2003     

Light‐Induced Water Splitting Causes High‐Amplitude Oscillation of pH‐Sensitive Layer‐by‐Layer Assemblies on TiO2

We introduce a simple concept of a light induced pH change, followed by high amplitude manipulation of the mechanical properties of an adjacent polymer film. Irradiation of a titania surface is known to cause water splitting, and this can be used to reduce the environmental pH to pH 4. The mechanical modulus of an adjacent pH sensitive polymer film can thus be changed by more than an order of magnitude. The changes can be localized, maintained for hours and repeated without material destruction.     

pH-responsive protein microcapsules fabricated via glutaraldehyde mediated covalent layer-by-layer assembly

Bovine serum albumin (BSA) hollow microcapsules were fabricated through glutaraldehyde (GA) mediated covalent layer-by-layer assembly. The GA cross-linking of the adsorbed BSA on the colloidal particles enabled their surfaces to be covered by reactive aldehyde groups, which reacted with BSA molecules to result in another covalently linked layer. Repeating of this cycle could then yield particles coated with BSA multilayers. Hollow microcapsules well dispersed in water were obtained after core removal. The good integrity and morphology of the BSA capsules were confirmed and characterized by confocal laser scanning microscopy, scanning electron microscopy and scanning force microscopy. The obtained BSA microcapsules possess reversible pH response, i.e., the capsules are permeable to macromolecules below pH 4 or above pH 10, while impermeable in between. The mechanisms of permeability transition were discussed. Using this property, dextran, with a molecular weight of ~155 kDa, was successfully loaded.     

Inducing spin crossover in metallo-supramolecular polyelectrolytes through an amphiphilic phase transition

A phase transition in an amphiphilic mesophase is explored to deliberately induce mechanical strain in an assembly of tightly coupled metal ion coordination centers. Melting of the alkyl chains in the amphiphilic mesophase causes distortion of the coordination geometry around the central transition metal ion. As a result, the crystal field splitting of the d-orbital subsets decreases resulting in a spin transition from a low-spin to a high-spin state. The diamagnetic-paramagnetic transition is reversible. This concept is demonstrated in a metallo-supramolecular coordination polyelectrolyte-amphiphile complex self-assembled from ditopic bis-terpyridines, Fe(II) as central transition metal, and dialkyl phosphates as amphiphiles. The magnetic properties are studied in a Langmuir-Blodgett multilayer. The modularity of this concept provides extensive control of structure and function from molecular to macroscopic length scales and gives access to a wide range of new molecular magnetic architectures such as nanostructures, thin films, and liquid crystals.     

Haltbare L?sungen von Eriochromschwarz T

Zusammenfassung Wäßrige Eriochromschwarzlösungen lassen sich durch Zugabe von Hydroxylammoniumsulfat und Isopropanol stabilisieren. Nach der angegebenen Vorschrift hergestellte Lösungen sind je nach Aufbewahrung 4 Wochen bis 1 Jahr beständig. Auch bei der Titration von Calcium und Magnesium in Gegenwart von Schwermetallen tritt keine Zersetzung des Indicators mehr ein.

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Summary Aqueous solutions of Eriochrome Black indicator can be stabilized by the addition of hydroxyl ammonium sulphate and isopropanol. Solutions prepared according to the instructions given in this paper are stable for four weeks to one year depending on type of storage. There is no longer any degradation of the indicator when titrating calcium and magnesium in the presence of heavy metals.

     

Single Polyelectrolyte Microcapsules Fabricated By Glutaraldehyde‐Mediated Covalent Layer‐By‐Layer Assembly

Summary: Single polyelectrolyte component microcapsules and multilayers, exemplified by poly(allylamine hydrochloride) (PAH), have been prepared using a method of glutaraldehyde (GA)‐mediated covalent layer‐by‐layer (LbL) assembly. The GA cross‐linking of the adsorbed PAH results in surfaces covered by reactive aldehyde groups, which can then react with PAH to result in another layer of covalently linked PAH. The repeated assembly of single polyelectrolyte in an LbL manner can be thus achieved. The PAH multilayers can grow linearly along with the layer number, and their thickness can be controlled at the nanometer scale, as verified by UV‐vis absorption spectrometry and ellipsometry. Single polyelectrolyte microcapsules are obtained after removal of the template cores at low pH. The morphology and integrity are confirmed by scanning force microscopy and confocal laser scanning microscopy.

Schematic illustration of the preparation of a single polyelectrolyte component microcapsule by GA‐mediated covalent LbL assembly.