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221.
Alexei Antipov Dmitry Shchukin Yuri Fedutik Irina Zanaveskina Vera Klechkovskaya Gleb Sukhorukov Helmuth Mhwald 《Macromolecular rapid communications》2003,24(3):274-277
A new biomimetic approach for performing CaCO3 synthesis exclusively inside micron‐sized polyelectrolyte capsules, based on the fermentative formation of a precipitative agent (CO32− anion) by urease‐catalyzed urea hydrolysis, was developed. Precipitated CaCO3 completely fills the interior capsule volume and has a metastable vaterite phase.
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223.
Glinel K Prevot M Krustev R Sukhorukov GB Jonas AM Möhwald H 《Langmuir : the ACS journal of surfaces and colloids》2004,20(12):4898-4902
We present a new way to protect polyelectrolyte multilayers from water, consisting in the adsorption and subsequent fusing of charged wax particles atop a multilayer. The formation of the wax layer is demonstrated by different techniques such as ellipsometry, contact angle measurements, and atomic force microscopy. The diffusion of water in protected and unprotected multilayers is studied by in situ neutron reflectometry. Whereas a top layer of wax crystals already allows substantial reduction of the diffusion, the fusion of this top layer leads to the dominating exclusion of water from the multilayers when dipped in water. This method opens up new interesting avenues for polyelectrolyte multilayers in practical applications where permeability of water, ions, or hydrophilic drugs is an issue. 相似文献
224.
Helmuth M. Gilow Yoon H. Hong Paula L. Millirons Richard C. Snyder William J. Casteel 《Journal of heterocyclic chemistry》1986,23(5):1475-1480
The rate coefficients and partial rate factors for the hydrogen-deuterium exchange of some 1-substituted pyrroles (1-substituents = -COCH3, - COC6H5, -SO2CH3, -SO2CF3, -N(CH3)3, -NH(CH3)2, -SO2C6H5) in deuterated trifluoroacetic acid have been determined. In all cases the rate of exchange is faster at the 2-position. Similarly, the hydrogen-deuterium exchange of some pyrroles with electron withdrawing substituents in the 2-position indicate a relative reactivity of 4→ 5→ 3-position with the selectivity being greatest for the more electron withdrawing groups. A nitro group in the 3-position of pyrrole shows a relative reactivity of 5→2→4-position for the hydrogen-deuterium exchange in deuterated trifluoroacetic acid. A linear correlation is observed for the log of the rate coefficient of the hydrogen-deuterium exchange at the 4-position of some 2-substituted pyrroles and the difference in the calculated energy of formation of the pyrrole and the corresponding 4-deuterated cation. 相似文献
225.
Duan H Kuang M Zhang G Wang D Kurth DG Möhwald H 《Langmuir : the ACS journal of surfaces and colloids》2005,21(24):11495-11499
In the current work we demonstrate a facile and versatile way to create hydrophilic polymeric capsules by integration of Au nanocrystal templating, surface-initiated atom-transfer radical polymerization, and selective chemical cross-linking of polymer shells. Capsules of the homopolymer of 2-(dimethylamino)ethyl methacrylate and its copolymers with 2-(diethylamino)ethyl methacrylate and poly(ethylene glycol) methyl ether methacrylate were constructed. They swell at low pH and shrink at high pH. On the basis of the pH sensitivity of the resulting capsules, encapsulation and release of a drug model, rhodamine 6G, were realized. Furthermore, by cleaving Au-S bonds between Au cores and polymer shells, capsules containing free Au cores were generated, paving a simple pathway to introduce more functionality to the polymeric capsules. 相似文献
226.
Horseradish peroxidase (HRP) was encapsulated in preformed polyelectrolyte multilayer (PEM) microcapsules by spontaneous deposition with remarkably improved stability and catalytic activity. 相似文献
227.
228.
Köhler K Shchukin DG Möhwald H Sukhorukov GB 《The journal of physical chemistry. B》2005,109(39):18250-18259
The temperature-dependent behavior of hollow polyelectrolyte multilayer capsules consisting of poly(diallyldimethylammonium chloride) (PDADMAC) and poly(styrene sulfonate) (PSS) with a different number of layers was investigated in aqueous media using confocal laser scanning microscopy, scanning and transmission electron microscopy, atomic force microscopy, and elemental analysis. Capsules with an even number of layers exhibited a pronounced shrinking at elevated temperature resulting in a transition to a dense sphere, whereas capsules with an odd number of layers swelled during heating to 5-fold of their initial size followed by their rupture. This effect increases for odd layer numbers and decreases for even layer numbers with increasing layer number. According to elemental analysis, an excess of PDADMAC monomers exists within the multilayers of capsules with an odd number of layers leading to a repulsion between the positive charges, whereas shells with an even number of layers have a balanced ratio between the oppositely charged polyions, so that the temperature-dependent behavior is controlled by the different interactions between polyelectrolytes and the bulk water. At a certain temperature, the polyelectrolyte material softens thus facilitating any rearrangement. Besides incubation temperature, the duration of heating has an influence on the restructuring of the multilayers. 相似文献
229.
Richard Becker Helmuth Berger Mladen Prester Marko Miljak 《Journal of solid state chemistry》2006,179(3):836-842
The crystal structures of the two new synthetic compounds Co2TeO3Cl2 and Co2TeO3Br2 are described together with their magnetic properties. Co2TeO3Cl2 crystallize in the monoclinic space group P21/m with unit cell parameters a=5.0472(6) Å, b=6.6325(9) Å, c=8.3452(10) Å, β=105.43(1)°, Z=2. Co2TeO3Br2 crystallize in the orthorhombic space group Pccn with unit cell parameters a=10.5180(7) Å, b=15.8629(9) Å, c=7.7732(5) Å, Z=8. The crystal structures were solved from single crystal data, R=0.0328 and 0.0412, respectively. Both compounds are layered with only weak interactions in between the layers. The compound Co2TeO3Cl2 has [CoO4Cl2] and [CoO3Cl3] octahedra while Co2TeO3Br2 has [CoO2Br2] tetrahedra and [CoO4Br2] octahedra. The Te(IV) atoms are tetrahedrally [TeO3E] coordinated in both compounds taking the 5s2 lone electron pair E into account. The magnetic properties of the compounds are characterized predominantly by long-range antiferromagnetic ordering below 30 K. 相似文献
230.
Kubowicz S Thünemann AF Weberskirch R Möhwald H 《Langmuir : the ACS journal of surfaces and colloids》2005,21(16):7214-7219
Micelles of ABC block copolymers with varying degrees of polymerization of the B block (n) and constant lengths of the A and C blocks were investigated by small-angle X-ray scattering (SAXS), analytical ultracentrifugation (AUC), surface tension measurements, and isothermal titration calorimetry. The copolymers consisting of hydrophilic poly(N-acylethylene imine)s, end-capped with a hydrophobic fluorocarbon and a hydrocarbon block, are polymeric surfactants (gamma = 35 mN/m). They form cylindrical micelles with radii of 3.0 nm (n = 35), 3.8 nm (n = 57), and 4.0 nm (n = 72). Their lengths are about 20 nm. The micelles can be doped with 1,4-diiodoperfluorobutane for the polymers with n = 57 and 72 but not for n = 35. We assume that the doped micelles form distinct fluorocarbon domains, which are able to incorporate selectively the fluorocarbon dopant. The work presented here is a contribution to the development of multicompartment micelles. 相似文献