Scientific publications

Films of NiO-TiO2 with Ni concentration of 100, 90, 87, 83, 75, 66, 50 and 33 mol% have been obtained via the sol-gel route by dip coating technique and sintered in air between 250 and 500°C using ethanolic sols of nickel acetate tetrahydrate (Ni(CH3COO)2∙4H2O) and titanium n-propoxide (Ti(O-CH(CH3)2)4) precursors. Xerogels obtained by drying the sols have been studied up to 900°C by thermal analysis (DTA/TG) coupled to mass and IR spectroscopy. The crystalline structure and morphology of the layers in the as deposited, bleached and colored states were determined by X-ray diffractometry, scanning electron microscopy and transmission electron microscopy. Their electrochromic properties have been studied in 1 M KOH aqueous electrolyte as a function of the layer composition, thickness and sintering temperature. Deep brown colour with reversible transmittance changes have been obtained using cycling voltammetry and chronoamperometry processes. The best composition to get stable sols, a high reversible transmittance change and fast switching times (< 10 s) was obtained with double NiO-TiO2 layers 160 nm thick having 75% Ni molar concentration, and sintered between 300 and 350°C. The mechanism of coloration and morphology transformation of the layer during cycling are discussed in terms of an activation and degradation period. The results are in agreement with the accepted Bode model.

Brown coloring electrochromic 5 x 10 cm2 windows with the configuration K-glass/NiO-TiO2/electrolyte/CeO2-TiO2/K-glass have been prepared and characterized by optoelectrochemical techniques (cyclic voltammetry, chronoamperometry and galvanostatic measurements). The electrochromic layers have been prepared by the sol-gel technique. As electrolyte either a 1 M aqueous KOH solution or a newly developed starch-based gel impregnated with KOH have been used. The CeO2-TiO2 sol gel layers sintered at 550°C have been previously characterized in 1 M aqueous KOH electrolyte as a function of the thickness up to 2000 cycles and showed a highly reversible behavior without any corrosion effect. The NiO-TiO2 sol-gel layers sintered at 300°C have been extensively characterized in the same electrolyte up to about 7000 cycles. All windows present a deep brown color characteristic of the presence of Ni3+ (NiOOH) species, that is fully reversible for several thousands of cycles with a rather-fast kinetics (< 30 s). The transmittance of the bleached state however slowly decreases with cycling (permanent coloration). The full-bleached condition can be nevertheless recovered by applying a negative potential for a long duration. Deeper coloration is usually obtained by cycling the windows galvanostatically with a current density of 20 µA/cm2. The lifetime of the windows is however limited because of the degradation of the NiO-based layers due to the not fully reversible exchange of OH- that turns the layers mechanically fragile and leads eventually to their complete removal from the substrate. Windows working satisfactorily up to 7000 and 17 000 cycles have been obtained using aqueous KOH electrolyte and starch KOH gel electrolyte, respectively. Memory tests showed that the devices bleach at the open circuit potential from T=39% (colored state) to about T=50% in 60 min.

Pure anatase-TiO2 nanoparticles with 8 nm average crystallite size was synthesized hydrothermally at 200°C in 2 h. The structural and physicochemical properties of nano-TiO2 were determined by powder XRD, FT-IR, BET and SEM analyses. The behavior of anatase nano-TiO2 in catalytic degradation of Rhodamine B (RB) dye in transparent nano-TiO2 sol under UV-light was examined as a function of irradiation power of UV-Iight, irradiation time, amount of nano-TiO2 and initial RB concentration in the sol. Rhodamine B was fully degraded with the catalysis of the nano-TiO2 in a short time as low as 60 min. Photocatalytic activity of the nano-TiO2 for degradation of RB was compared with Degussa P-25 at optimum catalysis conditions determined for the nano-TiO2. It was found that, when compared to Degussa P-25, the nano-TiO2 could be repeatedly used with increasing photocatalytic activity. It was found that the photodegradation obeys the pseudo first-order reaction kinetics with the rate constant of 0.0658 min-1, and the half period t1/2 was 10.53 min.

Photocatalytic performance of a hydrothermally synthesized pure anatase TiO2 with 8mm average crystalline size for decomposition of Reactive Red 141 was examined by investigating the effects of UV-light irradiation time, irradiation power, amount of TiO2 and initial dye concentration. Change in the UV absorbance of the dye during irradiation was monitored. One wt.% TiO2 in 30 mg/l Reactive Red 141 aqueous solution was found adequate for complete decolorization in 70 min at 770 W/m2 irradiation power. It was realized that, compared to Degussa P-25, the synthesized nano-TiO2 can be repeatedly used as a new catalyst. The results also proved that Reactive Red 141 is decomposed catalytically due to the pseudo first-order reaction kinetics.

The initial stages of diamond growth on treated Si(001) substrates were studied using various structural and spectroscopic characterization techniques. The nucleation behaviour across the substrate appeared to be inconsistent. Cross-sectional transmission electron microscopy (TEM) revealed the presence of localized amorphous carbon in areas between the Si substrate and the subsequently deposited polycrystalline diamond film, whereas diamond particles, apparently in direct contact with the Si substrate, were observed in other areas. Electron energy loss spectroscopy (EELS) revealed the presence of amorphous carbon in large pockets between polycrystalline diamond particles, as well as in some voids between the Si substrate and the diamond layer. Electron energy loss near edge structure (ELNES) results obtained from a small pocket of amorphous carbon between diamond particles showed a fine structure essentially similar to that of diamond; however, additional intensity was observed in the region of π-resonance, indicating mixed sp2/sp3 bonding. Although not detected by TEM or EELS, X-ray photo-spectroscopy revealed the emergence of a SIC layer during the early stages of growth.

Chitosan with a covalently attached anthrylunit is used as chemomechanical polymer, in which stacking and cation-pi interactions allow aromatic effector compounds with positively charged nitrogen centers to trigger macroscopic motions in aqueous surrounding. Thus, only protonated heterocycles such as imidazole or histamine lead at pH 5 to expansion, in contrast to toluenesulfonic acid, or pyrazole and pyrimidine. Inorganic salts and pH influence the polymer swelling, and must be taken into account for the calculation of net effects induced by organic effectors. Reversible volume expansions on the top of the swelling effect of water alone are observed as function of different effector, structures, showing, for example, 45% net effect with imidazole and 66% with benzimidazole. Aminoacids, for solubility reasons measured in the form of their methylesters, yield smaller expansions, showing, however, a regular and selective increase with, the lipophilicity of the residues. The kinetics of effector uptake, which relates to the velocity of expansion, are measured with histamine and follow first order, with t(1/2) = 2.7 min for 50% absorption.

We describe the design and detailed characterization of 6-hydroxy-nicotine (6HNic)-adjustable transgene expression (NICE) systems engineered for lentiviral transduction and in vivomodulation of angiogenic responses. Arthrobacter nicotinovorans pAO1 encodes a unique catabolic machinery on its plasmid pAO1, which enables this Gram-positive soil bacterium to use the tobacco alkaloid nicotine as the exclusive carbon source. The 6HNic-responsive repressor-operator (HdnoR-ONIC) interaction, controlling 6HNic oxidase production in A.nicotinovorans pAO1, was engineered for generic 6HNic-adjustable transgene expression in mammalian cells. HdnoR fused to different transactivation domains retained its ONIC-binding capacity in mammalian cells and reversibly adjusted transgene transcription from chimeric ONIC-containing promoters (PNIC; ONIC fused to a minimal eukaryotic promoter [Pmin]) in a 6HNic-responsive manner. The combination of transactivators containing various transactivation domains with promoters differing in the number of operator modules as well as in their relative inter-ONIC and/or ONIC-Pmin spacing revealed steric constraints influencing overall NICE regulation performance in mammalian cells. Mice implanted with microencapsulated cells engineered for NICE-controlled expression of the human glycoprotein secreted placental alkaline phosphatase (SEAP) showed high SEAP serum levels in the absence of regulating 6HNic. 6HNic was unable to modulate SEAP expression, suggesting that this nicotine derivative exhibits control-incompatible pharmacokinetics in mice. However, chicken embryos transduced with HIV-1-derived self-inactivating lentiviral particles transgenic for NICE-adjustable expression of the human vascular endothelial growth factor 121 (VEGF121) showed graded 6HNic response following administration of different 6HNic concentrations. Owing to the clinically inert and highly water-soluble compound 6HNic, NICE-adjustable transgene control systems may become a welcome alternative to available drug-responsive homologs in basic research, therapeutic cell engineering and biopharmaceutical manufacturing. © The Author 2005. Published by Oxford University Press. All rights reserved.

The vessel-stabilizing effect of angiopoietin-1 (Ang1)/ Tie2 receptor signaling is a potential target for pro-angiogenic therapies as well as anti-angiogenic inhibition of tumor growth. We explored the endothelial and vascular specific activities of the Ang1 monomer, i.e. dissociated from its state as an oligomer. A truncated monomeric Ang1 variant (i.e. ΔAng1) containing the isolated fibrinogen-like receptor-binding domain of Ang1 was created and recombinantly produced in insect cells. ΔAng1 ligated the Tie2 receptor without triggering its phosphorylation. Moreover, monomeric ΔAng1 was observed to bind α5β1 integrin with similar affinity compared with Tie2. Unexpectedly, in vitro treatment of endothelial cells with ΔAng1 showed some of the known effects of full-length Ang1, including inhibition of basal endothelial cell permeability and stimulation of cell adhesion as well as activation of MAPKs. Local treatment of the microvasculature of the developing chicken chorioallantoic membrane with the ΔAng1 protein led to profound reduction of the mean vascular length density, thinning of vessels, and reduction of the number of vessel branching points. Similar effects were observed in side-by-side experiments with the recombinant full-length Ang1 protein. These effects of simplification of the vessel branching pattern were confirmed through local gene transfer with lentiviral particles encoding ΔAng1 or full-length Ang1. Together, our findings suggest a potential use for exogenous Ang1 in reducing rather than increasing vascular density. Furthermore, we show that the isolated receptor-binding domain of Ang1 is capable of mediating some effects of full-length Ang1 independently of Tie2 phosphorylation, possibly through integrin ligation. © 2005 by The American Society for Biochemistry and Molecular Biology, Inc.

The dramatically increasing prevalence of multi-drug-resistant human pathogenic bacteria and related mortality requires two key actions: (i) decisive initiatives for the detection of novel antibiotics and (ii) a global ban for use of antibiotics as growth promotants in stock farming. Both key actions entail technology for precise, high-sensitive detection of antibiotic substances either to detect and validate novel anti-infective structures or to enforce the non-use of clinically relevant antibiotics. We have engineered prokaryotic antibiotic response regulators into a molecular biosensor configuration able to detect tetracycline, streptogramin, and macrolide antibiotics in spiked liquids including milk and serum at ng/mL concentrations and up to 2 orders of magnitude below current Swiss and EC threshold values. This broad-spectrum, class-specific, biosensor-based assay has been optimized for use in a storable ready-to-use and high-throughput-compatible ELISA-type format. At the center of the assay is an antibiotic sensor protein whose interaction with specific DNA fragments is responsive to a particular class of antibiotics. Binding of biosensor protein to the cognate DNA chemically linked to a solid surface is converted into an immuno-based colorimetric readout correlating with specific antibiotics concentrations. © 2004 Wiley Periodicals, Inc.

Background: Recent advances in functional genomics, gene therapy, tissue engineering, drug discovery and biopharmaceuticals production have been fostered by precise small-molecule-mediated fine-tuning of desired transgenes. Methods: Capitalizing on well-evolved quorum-sensing regulatory networks in Streptomyces coelicolor we have designed a mammalian regulation system inducible by the non-toxic butyrolactone SCB1. Fusion of the S. coelicolor SCB1 quorum-sensing receptor ScbR to the human Kox-1-derived transsilencing domain reconstituted a mammalian transsilencer (SCS) able to repress transcription from SCS-specific operator-containing promoters in a reverse SCB1-adjustable manner. Results: This quorum-sensing-derived mammalian transgene control system (Q-ON) enabled precise SCB1-specific fine-tuning of (i) desired transgene transcription in a variety of mammalian/human cell lines and human primary cells, (ii) small interfering RNA-mediated posttranscriptional knockdown (siRNA) in mammalian cells, and (iii) dosing of a human glycoprotein in mice. Conclusions: As exemplified by Q-ON technology, bacterial quorum-sensing regulons may represent a near-infinite source for the design of mammalian gene control systems compatible with molecular interventions relevant to future gene therapy and tissue engineering scenarios. Copyright © 2004 John Wiley & Sons, Ltd.