Sonochemical nanosynthesis at the engineered interface of a cavitation microbubble

This work demonstrates the potential of sonochemistry to become a most valuable tool for nanotechnology if the underlying complex processes are understood and controlled. It is shown that control of cavitation requires controlling of interfaces at the microsec time scale and thus a diversity of phenomena are observed using different surfactants. By means of concrete examples it is shown that non-equilibrium nanostructures, e.g. Ru/Pt core-shell nanoparticles can be prepared. Hollow microbubbles with nanoparticles in the wall, which may contain gases over weeks, can be constructed by sonication of the corresponding colloid solutions.     

Adsorption of novel thermosensitive graft-copolymers: Core-shell particles prepared by polyelectrolyte multilayer self-assembly

The adsorption properties of thermosensitive graft-copolymers are investigated with the aim of developing self-assembled multilayers from these copolymers. The copolymers consist of a thermoreversible main chain of poly(N-isopropylacrylamid) and a weak polyelectrolyte, poly(2-vinylpyridine), as grafted side chains. Zeta-potential, single particle light scattering and adsorption isotherms monitor the adsorption of the thermoreversible copolymers to precoated colloidal particles. The results show a smaller surface coverage for a larger density of grafted chains. The surface coverage is discussed in terms of surface charge density in the adsorbed monolayer. Taking into account the monolayer adsorption properties, conditions are developed for the multilayer formation from these copolymers. A low pH provides a sufficient charge density of the grafted chains to achieve a surface charge reversal of the colloids upon adsorption. The charge reversal after each adsorbed layer is monitored by zeta-potential and the increase of the thickness is determined by light scattering. Stable and reproducible multilayers are obtained. The results imply that the conformation of the thermosensitive component in multilayers depends strongly on the grafting density, where the polymer with a higher grafting density adsorbs in a flat conformation while that with a lower grafting density adsorbs with more loops.     

Control of the water permeability of polyelectrolyte multilayers by deposition of charged paraffin particles

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.     

pH-responsive capsules derived from nanocrystal templating

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.     

Spontaneous deposition of horseradish peroxidase into polyelectrolyte multilayer capsules to improve its activity and stability

Horseradish peroxidase (HRP) was encapsulated in preformed polyelectrolyte multilayer (PEM) microcapsules by spontaneous deposition with remarkably improved stability and catalytic activity.     

Thermal behavior of polyelectrolyte multilayer microcapsules. 1. The effect of odd and even layer number

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.     

Electrophilic hydrogen-deuterium exchange of some deactivated pyrroles

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.     

Beitrag zur Kreatininbestimmung in Fleischextrakt und fleischextrakthaltigen Erzeugnissen

Zusammenfassung Die von Hadorn 1946 veröffentlichte Methode zur Bestimmung von Kreatinin in Erzeugnissen der Suppenindustrie wurde vereinfacht und gleichzeitig deren Genauigkeit verbessert.Durch Umwandlung des Kreatins in Kreatinin durch Kochen mit verd. Salzsäure am Rückfluß wird die Huminstoffbildung, die beim Eindampfen mit Salzsäure bis zur Trockne auftritt, vermieden oder stark zurückgedrängt.Das Ausäthern der bei der Farbreaktion mit Pikrinsäure störenden Substanzen wird durch Verwendung eines Magnetrührers verbessert. Die Anfärbung mit Pikrinsäure wird durch die Zugabe einer Pikratlösung an Stelle der getrennten Zugabe von Pikrinsäure und Natronlauge vereinfacht.Die Abhängigkeit der Farbstoffbildung von der Temperatur wird untersucht und die Möglichkeit der Stabilisierung des Farbstoffs aufgezeigt.

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Summary The method for the determination of creatinine in products of the soup industry, published by Hadorn in 1946, has been simplified and improved in its accuracy.By transformation of the creatine into creatinine by boiling with diluted hydrochloric acid under reflux, the formation of humic substances, which appear when evaporating with hydrochloric acid until dry, can be prevented or largely restrained. The ether-extraction of the substances disturbing the colour reaction with picric acid is improved by the application of a magnetic stirrer.The staining with picric acid is simplified by the addition of a picrate solution in place of the separate addition of picric acid and sodium hydroxide solution.The dependence of the colour reaction on temperature has been investigated and the possibility to stabilize the colouring substances is shown.

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Fräulein S. Künzel und Fräulein J. Pawlak danke ich für ihre wertvolle Mitarbeit.