A Microgel Construction Kit for Bioorthogonal Encapsulation and pH‐Controlled Release of Living Cells

pH‐Cleavable cell‐laden microgels with excellent long‐term viabilities were fabricated by combining bioorthogonal strain‐promoted azide–alkyne cycloaddition (SPAAC) and droplet‐based microfluidics. Poly(ethylene glycol)dicyclooctyne and dendritic poly(glycerol azide) served as bioinert hydrogel precursors. Azide conjugation was performed using different substituted acid‐labile benzacetal linkers that allowed precise control of the microgel degradation kinetics in the interesting pH range between 4.5 and 7.4. By this means, a pH‐controlled release of the encapsulated cells was achieved upon demand with no effect on cell viability and spreading. As a result, the microgel particles can be used for temporary cell encapsulation, allowing the cells to be studied and manipulated during the encapsulation and then be isolated and harvested by decomposition of the microgel scaffolds.     

Regioselective Arene Functionalization: Simple Substitution of Carboxylate by Alkyl Groups

Arenes with various alkyl side‐chains were synthesized in high yields and excellent regioselectivities. Starting from toluic and naphthoic acids, the carboxylate group was conveniently substituted by alkyl halides by Birch reduction and subsequent decarbonylation. The method is characterized by inexpensive starting materials and reagents, and methylation of arenes was realized. Besides simple alkyl substituents, the scope of arene functionalization was extended by benzyl, fluoro, amino, and ester groups. We were able to control the alkylation of 1‐naphthoic acid during Birch reduction by the addition of tert‐butanol. This allowed the regioselective synthesis of mono and bis‐substituted naphthalenes from the same starting material.     

The sdfem on Shishkin meshes for linear convection-diffusion problems

Summary. We consider singularly perturbed linear elliptic problems in two dimensions. The solutions of such problems typically exhibit layers and are difficult to solve numerically. The streamline diffusion finite element method (SDFEM) has been proved to produce accurate solutions away from any layers on uniform meshes, but fails to compute the boundary layers precisely. Our modified SDFEM is implemented with piecewise linear functions on a Shishkin mesh that resolves boundary layers, and we prove that it yields an accurate approximation of the solution both inside and outside these layers. The analysis is complicated by the severe nonuniformity of the mesh. We give local error estimates that hold true uniformly in the perturbation parameter , provided only that , where mesh points are used. Numerical experiments support these theoretical results. Received February 19, 1999 / Revised version received January 27, 2000 / Published online August 2, 2000     

Two types of limit cycles of a resonant converter modelled by a three-dimensional system

In this paper, the long-run dynamics of a resonant converter is studied. The modelling of the resonant converter can be done using various approximations and the long-run dynamics of the two dimensional cases were earlier analysed. In this paper, we discuss results that can be extended to the three dimensional case. It seems that limit cycles describe the long-run dynamics in important situations in the three dimensional case, too. Our objective is to relate the limit cycles found previously in the two-dimensional case to those found now in the three dimensional approximation.     

Photometrische Messung der Konzentration und Dispersität in kolloiden Lösungen. I. Lichtschwächungsmessung

Ohne Zusammenfassung     

Synthesis of rigid photoswitchable hemithioindigo ω-amino acids

The synthesis of novel N-Boc- and N-Fmoc protected hemithioindigo-based ω-amino acids is described. An approach to modulate the thermal stability of a hemithioindigo subunit is presented. Placing the amino-group in the stilbene part from the para- to meta-position leads to an increase of the half-life of the thermally labile E-form from 19 h to 47 h.     

Nondestructive three-dimensional analysis of layered polymer structures with chemical imaging

Three-dimensional (3D) chemical information was obtained by means of a combination of two-dimensional attenuated total reflection Fourier transform infrared (ATR-FT-IR) imaging with a focal plane array detector and variable angle depth profiling. Since the penetration depth of the evanescent wave in ATR spectroscopy is not limited by diffraction, it was possible to resolve thin sandwiched polymer layers nondestructively within a stack of polymer layers. Chemical images were obtained from layers of different thickness of the laminate by moving a custom-made aperture to specific positions on the condenser lens of the ATR accessory. Sequences of absorption images detect the successive appearance of thin, buried layers of polybutylmethacrylate (d(PBMA) = 400 nm) and polycarbonate (d(TMPC) = 300 nm) in different depths of the stack of polymer layers. The depth resolution of variable-angle ATR-FT-IR imaging is sufficiently high to detect surface roughness at the interface between different polymer layers. Two different stacks of polymers with reordered sandwich-layers were imaged simultaneously, demonstrating the potential of variable angle ATR-FT-IR for 3D-imaging of a sample with xyz-heterogeneity, which can be a powerful analytical technique for materials science and biomedical research.