Scientific publications

Time-delay circuitries in which a transcription factor processes independent input parameters can modulate NF-κB activation, manage quorum-sensing cross-talk, and control the circadian clock. We have constructed a synthetic mammalian gene network that processes four different input signals to control either immediate or time-delayed transcription of specific target genes. BirA-mediated ligation of biotin to a biotinylation signal-containing VP16 transactivation domain triggers heterodimerization of chimeric VP16 to a streptavidin-linked tetracycline represser (TetR). At increasing biotin concentrations up to 20 nM, TetR-specific promoters are gradually activated (off to on, input signal 1), are maximally induced at concentrations between 20 nM and 10 μM, and are adjustably shut off at biotin levels exceeding 10 μM (on to off, input signal 2). These specific expression characteristics with a discrete biotin concentration window emulate a biotin-triggered bandpass filter. Removal of biotin from the culture environment (input signal 3) results in time-delayed transgene expression until the intracellular biotinylated VP16 pool is degraded. Because the TetR component of the chimeric transactivator retains its tetracycline responsiveness, addition of this antibiotic (input signal 4) overrides biotin control and immediately shuts off target gene expression. Biotin-responsive immediate, bandpass filter, and time-delay transcription characteristics were predicted by a computational model and have been validated in standard cultivation settings or biopharmaceutical manufacturing scenarios using trangenic CHO-K1 cell derivatives and have been confirmed in mice. Synthetic gene circuitries provide insight into structure-function correlations of native signaling networks and foster advances in gene therapy and biopharmaceutical manufacturing. © 2007 by The National Academy of Sciences of the USA.

We describe an efficient inducible gene expression system in HEK.EBNA cells, a well-established cell system for the rapid transient expression of research-tool proteins. The transgene control system of choice is the novel acetaldehyde-inducible regulation (AIR) technology, which has been shown to modulate transgene levels following exposure of cells to acetaldehyde. For application in HEK.EBNA cells, AlcR transactivator plasmids were constructed and co-expressed with the secreted alkaline phosphatase (SEAP) gene under the control of a chimeric mammalian promoter (PAIR) for acetaldehyde-regulated expression. Several highly inducible transactivator cell lines were established. Adjustable transgene induction by gaseous acetaldehyde led to high induction levels and tight repression in transient expression trials and in stably transfected HEK.EBNA cell lines. Thus, the AIR technology can be used for inducible expression of any desired recombinant protein in HEK.EBNA cells. A possible application for inducible gene expression is a controlled proliferation strategy. Clonal HEK.EBNA cell lines, expressing the fungal transactivator protein AlcR, were engineered for gas-adjustable expression of the cell-cycle regulator p27Kip1. We show that expression of p27 Kip1 via transient or stable transfection led to a G1-phase specific growth arrest of HEK.EBNA cells. Furthermore, production pools engineered for gas-adjustable expression of p27Kip1 and constitutive expression of SEAP showed enhanced productive capacity. © 2006 Wiley Periodicals, Inc.

When Si8R*6 (R* = Si(tBu)3) is reacted with mild halogenation reagents like carbon tetrachloride, carbon tetrabromide, tin tetrachloride and iodine, new compounds are formed which besides the Si(tBu)3 groups have halide ligands and a silicon-silicon backbone which is either cyclic, bicyclic or polycyclic. We here report on the molecular and crystal structures of four derivatives: Si5R*3Cl5 (9), Si4R*3Br5 (10), Si8R*4Cl6 (11) and Si8R*3I11 (12). The molecule 9 has a bicyclic silicon back-bone with a three- and four-membered cycle sharing one edge, 10 is monocyclic with four membered silicon-silicon-ring, 11 is polycyclic and can be derived from a Si8-cube and 12 is bicyclic with a four- and five-membered silicon ring sharing one edge. We also propose some possible reaction mechanisms which follow from observations found during our experiments.

When the polycyclic alumosiloxane [Ph2SiO]8[AlO(OH)]4 is allowed to react with either cyclopentadienyl sodium in tetrahydrofuran or with dimethyl zinc in diethyl ether the organic ligands on the metal elements are eliminated as cyclopentadiene or methane and the metals are bonded to oxygen atoms in the alumosiloxane forming [Ph2SiO]8[AlO2(Na)]4∙5(THF) or [Ph2SiO]8[AlO(OH)]2[AlO2]2[Zn(OH)]2∙2(OEt2), respectively. X-ray structure determinations reveal that in the sodium derivative the original polycycle rests almost unchanged while in the zinc derivative the inner skeleton is rearranged.

Bis(hexamethyldisilazyl)tin(II) in excess reacts with the molecular alumosiloxane (Ph2SiO)8(AlO(OH))4 to yield the well known tin(II) derivative (Ph2SiO)8(AlO2)4Sn2 and the novel bicyclic [(Me3Si)2N]Sn[N(SiMe3)SiMe2CH2]2Sn[N(SiMe3)2] containing a tin-tin bond, which is formally related to the starting molecule by a missing hydrogen atom. From X-ray diffraction studies on single crystals it follows that the new compound has almost C2 point symmetry (the twofold axis intersecting the tin-tin bond) and that this tin-tin bond is the fusion edge of anellated fivefold Sn-Sn-N-Si-C rings. The bond connecting the almost tetrahedrally coordinated tin atoms (2.737(2) Å) is astonishingly very short. This feature is also reflected in the spectroscopic data (1H, 13C, 21Si, 119Sn-NMR) of the compound with a coupling constant 1J (117Sn/119Sn) of 9529 Hz.

This paper presents a high-stability, single-phase hybrid polyelectrolyte (SPHP) applied in a large EC device (5×10 cm2) using WO3 (electrochromic) and CeO2-TiO2 (counter-electrode-ion storage) electrodes, both produced by Leibniz-Institut of New Materials (Leibniz-INM, Germany). The electrochromic device exhibited excellent color and bleach reversibility, high coloration efficiency (>35 cm2/C) from the first cycle up to more than 60,000 CA cycles, and a maximum constant rate of deintercalation/intercalation (Oout/Qin=1). Its remarkable behavior and high stability render this material an excellent candidate for application in electrochromic devices.

In this paper, we discuss the high stability of a single-phase hybrid polyelectrolyte (SPHP) and nanocomposite hybrid polyelectrolyte (NHP) in a large electrochromic (EC) device (5 cm × 10 cm) mounted with different electrodes. The electrochromic device (K-glass/FTO/WO3/SPHP/CeO2-TiO2/FTO/K-glass—ECI,K-glass/FTO/WO3/NHP/CeO2-TiO2/FTO/K-glass—ECII,) exhibited excellent color and bleach reversibility, high coloration efficiency (CE) (>35 cm2/C) from the first cycle up to more than 60,000 CA cycles, and a maximum constant rate of deintercalation/intercalation (Oout/Qin = 1). Also, the life time of the EC device with Nb2O5:Mo (K-glass/FTO/Nb2O5:O/SPHP/CeO2-TiO2/FTO/K-glass—ECIII) was prolonged to up to more than 10,000 cycles with a fairly stable coloration efficiency (around 19 cm2/C) and Oout/Qin = 1. The SPHP and NHP were tested in a large EC device with different configurations to evaluate its successful performance. In conclusion, its remarkable behavior and high stability render this material an excellent candidate for application in EC devices.

Conclusion. Silica nanoparticles may serve as a nonviral delivery system to the sensory hair cells, spiral ganglion cells within the cochlea, and the vestibular organ, as well as the cochlear nucleus. Objectives. At present there are no targeted therapeutics for inner ear disease. A variety of viral vector systems have been tested in the inner ear with variable efficacy but they are still not regarded as safe systems for inner ear delivery. Nanoparticles are a nonviral method of delivering a variety of macromolecules that potentially can be used for delivery within the auditory system. In this study, we evaluated the distribution and safety of nanoparticles in the inner ear. Materials and methods. Cy3-labeled silica nanoparticles were placed on the round window membrane of adult mice. Hearing thresholds were determined after nanoparticle delivery by auditory brainstem responses (ABRs). Distribution of particles was determined by histological evaluation of the cochlea, vestibular organs, and brain stem. Results. Fluorescent microscopy demonstrated Cy3-labeled nanoparticles signals in the sensory hair cells and the spiral ganglion neurons of both the treated and contralateral inner ears. Additionally, the distal part of the central auditory pathway (dorsal cochlear nucleus, superior olivary complex) was found to be labeled with the Cy3-linked silica nanoparticles, indicating a retrograde axonal transport. No hearing loss or inflammation was noted in the treated cochlea.

Layers of the metastable, amorphous HAIO are synthesized by chemical vapor deposilion from he molecular compound tert-buloxyalane ([tBu-O-AlH2]2). At temperatures above 500 °C, these layers transform to biphasic Al center dot AlO3 due to the elimination of di-hydrogen. The interaction of HAIO films with short laser pulses causes partial transformation of amorphous HAIO into nano-crystalline Al∙Al2O3. Using an interference pattern of two coherent high-power Nd:YAG laser beams produces local and periodic heating, inducing crystallization at equally distant lines in the HAlO layer. Depending on the laser fluence, different morphologies and different amounts of crystalline phases are obtained. In this study, the surface morphology and the distribution of crystalline phases of the structured samples are analyzed using SEM, FIB and TEM. The two-dimensional structures consist of periodic variations of morphology, chemical composition, and phase identity with a well-defined long-range order. When bio-functionalized, the structured samples may be used as carriers for structurally controlled cell-cultivation.