FG Nanobiotechnologie
Refine
Document Type
Keywords
- Capacitive chemosensor (1)
- Enantioselective artificial receptors (1)
- Graphene (1)
- Layer-by-layer (1)
- Molecular architecture (1)
- Molecular recognition (1)
- Monolayers (1)
- Nanoparticle (1)
- Nanostructures (1)
- Palladium (1)
Institute
A composite material was prepared from graphene and palladium nanoparticles (PdNP) by layer-by-layer deposition on gold electrodes. The material was characterized by absorption spectroscopy, scanning electron microscopy, Raman spectroscopy and surface plasmon resonance. Cyclic voltammetry demonstrated the presence of electrocatalytic centers in the palladium decorated graphene. This material can serve as a sensor material for hydrogen at levels from 0.5 to 1% in synthetic air. Pure graphene is poorly sensitive to hydrogen, but incorporation of PdNPs increases its sensitivity by more than an order of magnitude. The effects of hydrogen, nitrogen dioxide and humidity were studied. Sensor regeneration is accelerated in humid air. The sensitivity of the nanocomposite depends on the number of bilayers of graphene–PdNPs.
In inflammatory lesions, sympathetic nerve fibers disappear soon after the start of inflammation. We identified sympathetic nerve repellents as possible causal agents in rheumatoid arthritis (RA). On nerve terminals, repellent factors bind to neuropilin-2 and its coreceptor. The aim of this study was to investigate the role of neuropilin-2 in the synovial tissue of patients with RA and patients with osteoarthritis (OA) and in experimental arthritis. The density of neuropilin-2–positive fibers and cells positive for semaphorin 3F (a sympathetic repellent) was investigated using immunofluorescence staining. Enzyme-linked immunosorbent assay was used to detect soluble neuropilin-2 in body fluids from patients with RA and patients with OA. An axon outgrowth assay and a neuropilin-2 Fc fusion construct (neuropilin-2Fc) were used to investigate semaphorin 3F–induced sympathetic nerve repulsion. In an animal model of type II collagen–induced arthritis, soluble neuropilin-2Fc was studied in vivo. The synovial density of neuropilin-2–positive sympathetic nerve fibers was lower in RA than in OA, but the density of cells positive for semaphorin 3F was similar. In synovial fluid, the level of soluble neuropilin-2 was markedly higher in RA compared with OA. Mouse sympathetic ganglia served as an excellent model with which to study semaphorin 3F–induced nerve fiber repulsion. Neuropilin-2 and its coreceptor were present on sympathetic neurons, and semaphorin 3F bound to neuropilin-2Fc (binding constant 96 nmoles/liter). Semaphorin 3F dose-dependently increased sympathetic nerve fiber repulsion (at a 50% maximum response concentration of 160–210 nmoles/liter). In contrast to our expectations, soluble neuropilin-2Fc did not inhibit repulsion but increased the repellent effect of semaphorin 3F. In experimental arthritis, therapy with neuropilin-2Fc aggravated arthritis. Soluble neuropilin-2 has no antirepellent activity but aggravates sympathetic nerve fiber repulsion and arthritis. Increased shedding of neuropilin-2 is probably an unfavorable sign in RA.
Monomolecular films of phthalocyanines: formation, characterisation and expelling by alkanethiols
(2007)
Adsorption of aluminum-2,3-naphthalocyanine (Al-PC) onto gold (111) substrate from the pure and mixed (with alkanethiols) solutions of the target molecules in ethanol was studied. The resulting films were characterized by X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure spectroscopy. The adsorption from the pure solution resulted in formation of an Al-PC monolayer composed of the strongly inclined molecules. However, a presence of only one molar percent of a thiolated compound (alkanethiol) in the primary solution led to the complete expelling of the Al-PC molecules from the substrate and formation of a one-component alkylthiolate monolayer. The results indicate that an equilibrium formation of mixed monolayers of rodlike thiolated molecules and relatively large planar-geometry molecules, whose interaction with the metal surface is mainly provided by the π-electron system, is difficult to achieve or is in most cases even impossible under equilibrium conditions and requires an introduction of additional anchor moieties (e.g., thiols) into these molecules, as has been demonstrated by successful coadsorption of hexadecanethiol and thiolated tetraphenylporphyrin.
Reduction on the spot: Planarly adsorbed thiolated porphyrin molecules (purple) incorporated in an insulating alkanethiol monolayer (blue) function as nanoelectrodes for the local reduction of metals (gray). This approach was applied for the in situ synthesis of nanoparticles of a predetermined size.
Chiroselective binding sites have been created on thin gold films by application of the spreader-bar approach.
Impedometric techniques and surface plasmon resonance were applied to detect binding. (R)-(+)-1,1 '-Binaphthyl-2,2 '-diol (R-BNOH) and (S)-(-)-1,1
'-binaphthyl-2,2'-diol (S-BNOH) were used as model analytes. The artificial receptors were prepared by co-adsorption of 16-mercaptohexadecane (matrix) with a thiol-modified chiral selector (template). The conjugates of d, l-thioctic acid and (R)-(+)- or (S)-(-)-1,1'-binaphthyl-2,2'-diamine were used as templates. Different concentration ratios of the matrix and template were tested. No chiral selectivity of surfaces formed by either the matrix or the template alone was observed. The use of alkylthiols shorter than 16-mercaptohexadecane led to the formation of surfaces with no chiral selectivity. The gold electrodes coated by the spreader-bar technique displayed an enantioselectivity of up to 4.76 or up to 2.55 as measured by the capacitive and SPR methods, espectively.
A spreader-bar approach to molecular architecture: formation of stable artificial chemoreceptors
(1999)
The destructive influence of lateral diffusion on nanostructured monolayers can be prevented by using the spreader-bar technique. This approach allows the formation of stable artificial receptors for barbituric acid by lateral structuring of a dodecanethiol monolayer with molecular spreader-bars from thiobarbituric acid without chemical polymerization (see schematic representation). The new technique may have applications in chemosensors, affinity chromatography, stereoselective catalysis, and molecular electronics.