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111.
Stephan Schmidt Michael Zeiser Thomas Hellweg Claus Duschl Andreas Fery Helmuth Möhwald 《Advanced functional materials》2010,20(19)
Thermoresponsive poly(N‐isopropylacrylamide) (PNIPAM) microgel films are shown to allow controlled detachment of adsorbed cells via temperature stimuli. Cell response occurs on the timescale of several minutes, is reversible, and allows for harvesting of cells in a mild fashion. The fact that microgels are attached non‐covalently allows using them on a broad variety of (charged) surfaces and is a major advantage as compared to approaches relying on covalent attachment of active films. In the following, the microgels’ physico‐chemical parameters in the adsorbed state and their changes upon temperature variation are studied in order to gain a deeper understanding of the involved phenomena. By means of atomic force microscopy (AFM), the water content, mechanical properties, and adhesion forces of the microgel films are studied as a function of temperature. The analysis shows that these properties change drastically when crossing the critical temperature of the polymer film, which is the basis of the fast cell response upon temperature changes. Furthermore, nanoscale mechanical analysis shows that the films posses a nanoscopic gradient in mechanical properties. 相似文献
112.
Alexey M. Yashchenok Daniil N. Bratashov Dmitry A. Gorin Maria V. Lomova Anton M. Pavlov Andrei V. Sapelkin Bong Sup Shim Gennady B. Khomutov Nicholas A. Kotov Gleb B. Sukhorukov Helmuth Möhwald Andre G. Skirtach 《Advanced functional materials》2010,20(18):3136-3142
Single‐wall carbon nanotubes modified by anionic polyelectrolyte molecules are embedded into the shells of microcapsules. Carbon nanotubes serve as rigid rods in a softer polymeric capsule, which forms a free‐standing shell upon treatment with glutaraldehyde and subsequent drying. The embedded carbon nanotubes exhibit a broad absorption in the UV–near‐infrared part of the spectrum, and that allows point‐wise activation and opening of the microcapsules by laser. Raman signal analysis shows changes of carbon‐nanotube‐specific lines after high‐power laser irradiation, which is characteristic of the formation of disordered carbonlike structures. These polyelectrolyte/carbon nanotube composite capsules represent a novel light‐addressable type of microcontainers. 相似文献
113.
114.
Michelle Prevot Christophe Déjugnat Helmuth M?hwald Gleb B Sukhorukov 《Chemphyschem》2006,7(12):2497-2502
Layer-by-layer assembled polyelectrolyte microcapsules are of great interest because they can possibly be used as microcontainers and they show interesting stimuli-responsive properties, which have been recently investigated. Here, we exploit capsules which are made temperature-sensitive by encapsulating poly(N-isopropylacrylamide) (PNIPAM). PNIPAM has a cloud point in water at about 32 degrees C, above which it collapses and is insoluble in water. Further this temperature responsiveness can be tuned by addition of various ions at various concentrations. Here, we present the encapsulation of PNIPAM inside polyelectrolyte microcapsules, and describe the dependence of the lower critical solution temperature (LCST) on the nature and the amount of different salts added. With this information, we demonstrate the ability to tune and finely control the collapse of encapsulated PNIPAM. In this light, this system could be used as a microsensor or drug- delivery system. 相似文献
115.
Ulrich Mayer Helmuth Hoffmann Robert Kellner 《Monatshefte für Chemie / Chemical Monthly》1988,119(11):1207-1221
A systematic study has been carried out on the solvent and concentration dependence of the P=O stretching vibrationv(PO) of the model compoundEt
3PO in various aprotic and several CH-acidic solvents. Evidence has been found for the existence of dipole-dipole complexes in concentrated solutions ofEt
3PO in solvents of low acceptor numbers. In dilute solutions, however, the P=O stretching band generally occurs as a single symmetrical peak which shows that only one kind of solvate species is present in solution. In CH-acidic solventsEt
3PO is present in the form of hydrogen bonded complexes. Informations about the structure of these complexes have been obtained by means of spectrophotometric titrations. It has been shown that the wavenumbersv°(PO) obtained by extrapolation ofv(PO) values to zero concentration are linearly related to the acceptor numbers of the solvents, previously derived from31P-chemical shift measurements. The existence of this linear relationships proves that both parameters are linearly related to the strength of the intermolecular interactions and are virtually free from unspecific contributions such as magnetic anisotropy or vibrational coupling effects. The results of the present study show that the P=O stretching vibration ofEt
3PO represents an ideal probe for the investigation of solvent effects and solvation mechanisms.
Infrarotspektroskopische Untersuchungen über Substrat-Lösungsmittel-Wechselwirkungen. Teil 1: Solvatation von Triethylphosphinoxid in aprotischen und CH-aciden Lösungsmitteln
Zusammenfassung Es wurde die Konzentrations- und Lösungsmittelabhängigkeit der P=O-Valenzschwingungv(PO) der ModellverbindungEt 3PO in verschiedenen aprotischen und CH-aciden Lösungsmitteln systematisch untersucht. In hinreichend verdünnten Lösungen tritt die P=O-Valenzschwingung als einzelne symmetrische Bande auf, was beweist, daß nur eine einzige Solvatform vorliegt. In Lösungsmitteln niedriger Akzeptorzahl konnte bei höheren Konzentrationen die Existenz von Dipol-Dipol-Komplexen nachgewiesen werden. In CH-aciden Lösungsmitteln liegtEt 3PO in Form von Wasserstoffbrückenkomplexen vor. Aussagen über die Struktur dieser Komplexe konnten mit Hilfe spektrophotometrischer Titrationen erhalten werden. Die durch Extrapolation auf Konzentration null erhaltenen Wellenzahlenv° (PO) hängen linear von den aus den31P-chemischen Verschiebungen vonEt 3PO bereits früher bestimmten Akzeptorzahlen der Lösungsmittel ab. Die Existenz dieser linearen Beziehung beweist, daß beide Parameter frei von störenden Einflußfaktoren (magnetische Anisotropie- und Schwingungskopp-lungseffekte) sind und tatsächlich linear mit der Stärke der intermolekularen Wechselwirkung variieren. Die Ergebnisse der vorliegenden Studie zeigen, daß die P=O-Valenzschwingung vonEt 3PO eine hervorragende Sonde zur Untersuchung von Lösungsmitteleffekten und Solvatationsmechanismen darstellt.相似文献
116.
Multilayer microcapsules showing unique charge-controlled permeability have been successfully fabricated by employing poly(styrene sulfonate) (PSS)-doped CaCO3 particles as templates. Encapsulation of the PSS molecules is thus achieved after core removal. Scanning force microscopy (SFM), UV-vis, Raman spectroscopy, and zeta-potential confirm the existence of the PSS molecules in the CaCO3 particles and the resultant microcapsules, which are initially incorporated during the core fabrication process. A part of these additionally introduced PSS molecules interacts with PAH molecules residing on the inner surface of the multilayer wall to form a stable complex, while the other part is intertwined in the capsule wall or in a free state. Capsules with this structure possess many special features, such as highly sensitive permeability tuned by probe charge and environmentally controlled gating. They can completely reject negatively charged probes, but attract positively charged species to form a higher concentration in the capsule interior, as evidenced by confocal microscopy. For example, the capsules completely exclude dextran labeled with fluorescein isothiocyanate (FITC-dextran), but are permeable for dextran labeled with tetramethylrhodamine isothiocyanate (TRITC-dextran) having similar molecular mass (from 4 to 70 kDa), although there are only few charged dyes in a dextran chain. By reversing the charge of the probes through pH change, or by suppressing charge repulsion through salt addition, the permeation can be readily switched for proteins such as albumin or small dyes such as fluorescein sodium salt. 相似文献
117.
By reaction of [Ir(COD)Cl]2 (COD = 1,5-cyclooctadiene) with i-C3H7MgBr in the presence of cyclic dienes, complexes of the type [IrH(COD)L] (L = 1,3-cyclohexadiene, 2-methyl-],3-cyclohexadiene, 5-ethyl-1,3-cyclohexadiene, 1,3-cycloheptadiene) are obtained. The system IrCl3/i-C3H7MgBr/1,3-C6H8 yields [IrH(1,3-C6H8)2]. According to NMR spectroscopic investigations the pure hydrido forms exist in solution only at low temperatures while at room temperature dynamic H-addition—elimination equilibria of the type [IrH(η4-diene)(COD)] ? [Ir(η3-enyl)(COD)] and [IrH(η4-1,3-C6H8)2] ? [Ir(η3-C6H9)-(η4-1,3-C6H8)], respectively, are observed; the hydrogen at the iridium atom is thereby transferred to the endo positions of the diene ligands. 相似文献
118.
Wang X Zheng S He Q Brezesinski G Möhwald H Li J 《Langmuir : the ACS journal of surfaces and colloids》2005,21(3):1051-1054
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. 相似文献
119.
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. 相似文献
120.
Christina M. Standfest-Hauser Thomas Lummerstorfer Roland Schmid Karl Kirchner Helmuth Hoffmann Michael Puchberger 《Monatshefte für Chemie / Chemical Monthly》2003,134(9):1167-1175
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 相似文献