Scientific publications

We present a method to characterize surface-chemical properties of gold nanocrystals. Spherical, 60 run gold nanocrystals were immobilized on quartz substrates by a coupling agent and cleaned in a hydrogen plasma. The nanocrystals were then functionalized with alkanethiol self-assembled monolayers (SAM) of varying chain lengths by adsorption from the gas phase, and localized surface plasmon resonance (LSPR) spectroscopy was performed on the samples. Depending on the alkane thiol chain length, the adsorption of the SAM redshifted the LSPR to different extents, in accordance with Mie theory. SAM thickness differences below 1 nm could be easily resolved. Our results demonstrate that LSPR spectroscopy can be applied to characterize thin organic layers on dry supported gold particles with high sensitivity.

Drug-dependent dissociation or association of cellular receptors represents a potent pharmacologic mode of action for regulating cell fate and function. Transferring the knowledge of pharmacologically triggered protein-protein interactions to materials science will enable novel design concepts for stimuli-sensing smart hydrogels. Here, we show the design and validation of an antibiotic-sensing hydrogel for the trigger-inducible release of human vascular endothelial growth factor. Genetically engineered bacterial gyrase subunit B (GyrB) (ref. 4) coupled to polyacrylamide was dimerized by the addition of the aminocoumarin antibiotic coumermycin, resulting in hydrogel formation. Addition of increasing concentrations of clinically validated novobiocin (Albamycin) dissociated the GyrB subunits, thereby resulting in dissociation of the hydrogel and dose- and time-dependent liberation of the entrapped protein pharmaceutical VEGF 121 for triggering proliferation of human umbilical vein endothelial cells. Pharmacologically controlled hydrogels have the potential to fulfil the promises of stimuli-sensing materials as smart devices for spatiotemporally controlled delivery of drugs within the patient. © 2008 Macmillan Publishers Limited. All rights reserved.

Synthetic biology provides insight into natural gene-network dynamics and enables assembly of engineered transcription circuitries for production of difficult-to-access therapeutic molecules. In Mycobacterium tuberculosis EthR binds to a specific operator (OethR) thereby repressing ethA and preventing EthA-catalyzed conversion of the prodrug ethionamide, which increases the resistance of the pathogen to this last-line-of-defense treatment. We have designed a synthetic mammalian gene circuit that senses the EthR-O ethR interaction in human cells and produces a quantitative reporter gene expression readout. Challenging of the synthetic network with compounds of a rationally designed chemical library revealed 2-phenylethyl-butyrate as a nontoxic substance that abolished EthR's repressor function inside human cells, in mice, and within M. tuberculosis where it triggered derepression of ethA and increased the sensitivity of this pathogen to ethionamide. The discovery of antituberculosis compounds by using synthetic mammalian gene circuits may establish a new line of defense against multidrug-resistant M. tuberculosis. © 2008 by The National Academy of Sciences of the USA.

The syntheses and structural details of tetraisopropoxyaluminates and tetra-tert-butoxyaluminates of nickel(II), copper-(I), and copper(II) are reported. Within the nickel series, either Ni[Al(OiPr)4]2∙2HOiPr, with nickel(II) in a distorted octahedral oxygen environment, or Ni[Al(OiPr)4]2∙py, with nickel(II) in a square-pyramidal O4N coordination sphere, or Ni[(iPrO)(tBuO)3Al]2, with Ni(II) in a quasi-tetrahedral oxygen coordination, has been obtained. Another isolated complex is Ni[(iPrO)3AlOAl(OiPr)3]∙3py (with nickel(II) being sixfold-coordinated), which may also be described as a "NiO" species trapped by two Al(OiPr)3 Lewis acid-base systems stabilized at nickel by three pyridine donors. Copper(l) compounds have been isolated in three forms: [(iPrO)4Al]Cu∙2py, [(tBuO)4Al]Cu∙2py, and Cu2[(tBuO)4Al]2, In all of these compounds, the aluminate moiety behaves as a bidentate unit, creating a tetrahedrally distorted N2O2 copper environment in the pyridine adducts. In the base-free copper(I) tert-butoxyaluminate, a dicopper dumbbell [Cu-Cu 2.687(1) Å] is present with two oxygen contacts on each of the copper atoms. Copper(II) alkoxyaluminates have been characterized either as Cu[(tBuO)4Al]2, {Cu(iPrO)[(iPrO)4Al]}2, and Cu[(tBuO)3(iPrO)Al]2 (copper being tetracoordinated by oxygen) or as [(iPrO)4Al]2Cu∙py (pentacoordinated copper similar to the nickel derivative). Finally, a copper(II) hydroxyaluminate has been isolated, displaying pentacoordinate copper (O4N coordination sphere) by dimerization, with the formula {[(tBuO)4Al]Cu(OH)∙py}2. The formation of all of these isolated products is not always straightforward because some of these compounds in solution are subject to decomposition or are involved in equilibria. Besides NMR [copper(I) compounds], UV absorptions and magnetic moments are used to characterize the compounds.

Core/shell nanowires of Al/Al2O3 are obtained by decomposition of tert-butoxyalane on metal, silicon or glass substrates heated up to 650 °C without use of a noble metal seed. These biphasic nanowires are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), scanning energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM) and high-resolution TEM. They have uniform diameters of about 20-30 nm, are composed of an inner aluminium wire, wrapped up by aluminium oxide at a constant molar ratio, and have lengths of several micrometers. As the temperatures approach the melting point of Al (660.4 °C), we propose a growth mechanism for the nanowires which resembles to vapour-liquid-solid (VLS) growth of ceramic nanowires with a liquid metal phase catalyst seed which in this case is aluminium. The biphasic nature of the wires is due to the disproportionation of aluminium in the transient AlO and to Ostwald ripening.

Aluminium hydride oxide, HAlO, an Al-compound with hydrogen and oxygen directly bound to aluminium is produced by chemical vapour deposition (CVD). At higher process-temperatures a second material, Al-Al2O3, can be obtained. These materials differ not only in chemical composition, but also in surface morphology. While the first forms a smooth structural surface, the second builds up a highly chaotic surface composed of nanowires. The different behaviour of normal human dermal fibroblasts (NHDF) on these surfaces in terms of proliferation and differentiation was studied. NHDF have the possibility to differentiate into their contractile form, the myofibroblast (MF), as a response to the contact with a given surface or upon induction by growth factors. We were able to show, that cell compatibility and proliferation on HAlO and on Si-wafers are comparable, whereas NHDF do not proliferate on Al center dot Al2O3. MF differentiation could be seen on both, HAlO and Si-wafer, but not on Al center dot Al2O3.

The synthesis and structural characterization of rare earth alkoxides with thiophene-based substituents are presented. Monomeric metal thienylmethoxides have been prepared by aminolysis reactions between M[N(SiMe3)2]3 (M = Y3+, Nd3+, Er3+) and the structurally characterized tertiary alcohols HO-C(C4H3S)3 (1) or HO-C(C8H5S2)3 (2). The metal alkoxide derivatives of these thiophene-substituted alcohols have been isolated as air-sensitive base adducts, their molecular structures being investigated by single-crystal X-ray crystallography. The coordination spheres around the metal centres are distorted trigonal-bipyramidal for the yttrium thienylmethoxides Y[OC(C4H3S)3]3(thf)2 (3a), {Y[OC(C4H3S)3]3(thf)2}·toluene (3b), Y[OC(C4H3S)3]3(py)2 (4a), {Y[OC(C4H3S)3]3(py)2}·toluene (4b) and Y[OC(C8H5S2)3]3(thf)2 (5). An almost tetrahedral geometry has been detected for Er[OC(C8H5S2)3]3(thf) (9), whereas an approximately octahedral geometry was found for {Nd[OC(C4H3S)3]3(thf)3}·thf (6), {Nd[OC(C8H5S2)3]3(thf)3}·4thf (7) and Er[OC(C4H3S)3]3(thf)3 (8).

Gas-phase as well as sol-gel techniques can be used to access to materials which contain two sorts of solid phases, of which one is mostly acting as the matrix. The choice of the molecular precursor in both processing techniques is crucial to obtain the desired composite product. Single source precursors have advantages over multi source precursors, as they allow a simplified technique and often also lead to purer materials. Moreover, the same precursor may behave similarly in the gas phase or wet process or may behave very differently. In this review composite compounds are discussed with Al2O3 mostly acting as a matrix and with Ln2O3 (Ln = lanthanide element) acting as a second phase. Two processes for Nd:YAG materials are described in more detail as well as some new alcoholates of lanthanides derived from carbinol substituted by thiophenes.

The synthesis of nano-scaled materials using several variations of the single source precursor concept in sol-gel and chemical vapour deposition techniques is demonstrated. Mono- and biphasic ceramics and cermets (metallic phases incorporated in a metal oxide phase) are addressed. The materials prepared are all nanocrystalline in a range from 5 to 50nm. The ceramics belong inter alia to the spinel and perowskite-type. In the biphasic ceramic systems, especially NdAlO3 in Al2O3 is highlighted. In the cermet family Ge, Sn and Pb in either their oxide matrices or in perowskite matrices (M´MO3, M´ = Ca, Sr, Ba; M = Ge, Sn, Pb) and Al and Ga in Al2O3 or Ga2O3 matrices are discussed. Two general concepts are presented in more detail: 1) the arrangement of mutually dependent ligands in the precursor molecule, to facilitate intra-molecular cascade or domino reactions, and 2) the role of metastable phases for physical patterning. The temperature and pressure dependent formation of aluminum/aluminum oxide composites and their structural consequences leading to zero-dimensional ball-shape spheres or to one-dimensional nano-wires is shown as well as the core shell structures of such composites.

Zr(OPri)4∙(PriOH) reacts with N-phenylsalicylideneimine in anhydrous benzene in 1 : 2 molar ratio to afford [Zr{O(C6H4)CH=NPh}2{OPri}2] (1). Further reactions of 1 with various glycols yield heteroleptic complexes of the type [Zr{O(C6H4)CH=NPh}2{O-G-O}] [where-G-= (CH2)2 (2), (CH2CHCH3) (3), (CH3CHCHCH3) (4), (CH2CHC2H5) (5), (CH2)3 (6), (CH2CH2CHCH3) (7), and (CH2)6 (8)]. All new derivatives have been characterized by elemental analyses, FTIR and NMR (1H and 13C{1H}) studies. FAB mass spectra of 1 and 7 revealed the monomeric nature of these complexes. Complete hydrolyses and low temperature transformations of 1 and 7 using sol-gel technique formed tetragonal phase of ZrO2 at 700 °C, whereas transformation of tetragonal to monoclinic phase occurred at 900 ° C. SEM observations of these samples indicate formation of agglomerates of nanocrystalline zirconia (Scherer analysis).