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Direct Monitoring (direct + monitoring)
Selected AbstractsDirect monitoring of molecular recognition processes using fluorescence enhancement at colloid-coated microplatesJOURNAL OF MOLECULAR RECOGNITION, Issue 4 2001Ch. Lobmaier Abstract Direct monitoring of recognition processes at the molecular level is a valuable tool for studying reaction kinetics to assess affinity constants (e.g. drugs to receptors) and for designing rapid single step immunoassays. Methods currently used to gain information about binding processes predominantly depend on surface plasmon resonance. These systems use excitation with coherent light in attenuated total reflection geometry to obtain discrimination between surface-bound and free molecules in solution. Therefore labeling of the compounds is not necessary, but due to the complexity of the measuring setup the method is rather costly. In this contribution we present a simple method for performing kinetic single step biorecognition assays with fluorophore labeled compounds using the fluorescence enhancement properties of surface bound silver colloids. Silver colloids are bound to standard microplates via silanization of the plastic surface. Fluorophores close to this colloid coated surface show a significant gain in fluorescence compared to fluorophores farther away in the bulk solution. Therefore discrimination between surface bound and free fluorophores is possible and the binding of, for example, fluorophore labeled antibodies to antigens immobilized on the colloid surface results in increasing fluorescence intensity. Utilization of standard microplates makes this method fully compatible with conventional microplate processing and reading devices. Neither excitation with coherent laser light nor ATR geometry is required, the measurement is performed in a standard fluorescence microplate reader in front face geometry with a xenon flash lamp as excitation source. Methods for the preparation of colloid-coated microplates and fluorescence-enhanced biorecognition assays are presented. Additionally the dependence of the system performance on the structure and properties of the metal colloid coated surface is described. A two-component biorecognition model system shows a detection limit in the subnanomolar range. The ease of colloid-surface preparation and the high sensitivity makes fluorescence enhancement at colloid-coated microplates a valuable tool for studying reaction kinetics and performing rapid single-step immunoassays. Copyright © 2001 John Wiley & Sons, Ltd. [source] Direct monitoring of coronary artery motion with cardiac fat navigator echoesMAGNETIC RESONANCE IN MEDICINE, Issue 2 2003Thanh D. Nguyen Abstract Navigator echoes (NAVs) provide an effective means of monitoring physiological motion in magnetic resonance imaging (MRI). Motion artifacts can be suppressed by adjusting the data acquisition accordingly. The standard pencil-beam NAV has been used to detect diaphragm motion; however, it does not monitor cardiac motion effectively. Here we report a navigator approach that directly measures coronary artery motion by exciting the surrounding epicardial fat and sampling the signal with a k -space trajectory sensitized to various motion parameters. The present preliminary human study demonstrates that superior-inferior (SI) respiratory motion of the coronary arteries detected by the cardiac fat NAV highly correlates with SI diaphragmatic motion detected by the pencil-beam NAV. In addition, the cardiac fat navigator gating is slightly more effective than the diaphragmatic navigator gating in suppressing motion artifacts in free-breathing 3D coronary MR angiography (MRA). Magn Reson Med 50:235,241, 2003. © 2003 Wiley-Liss, Inc. [source] High-altitude migration of the diamondback moth Plutella xylostella to the U.K.: a study using radar, aerial netting, and ground trappingECOLOGICAL ENTOMOLOGY, Issue 6 2002Jason W. Chapman Abstract 1. The high-altitude wind-borne migration of the diamondback moth Plutella xylostella in the U.K. in 2000 was investigated (a) by direct monitoring of insect flight by vertical-looking radar and by aerial netting, and (b) through evidence of temporal variation in P. xylostella abundance deduced from a network of light traps. 2. Migrating P. xylostella were identified by a unique combination of size and shape data derived from the continuously operating vertical-looking radar. 3. Radar-detected migratory overflights correlated significantly with associated peaks in abundance of P. xylostella estimated by catches in a U.K.-wide light trap network; however the correlation was stronger when light trap catches were lagged by 1 day. 4. The first notable catches of P. xylostella in the U.K. occurred in early May, and were accompanied by migrations over the radar from the east. 5. Radar data and back-tracking indicated that a major wind-borne migration of P. xylostella from The Netherlands to southern England took place in early May, and that this was responsible for the establishment of the U.K. population. 6. The origin of early-season P. xylostella occurring in Britain is discussed. [source] Magnetic, 57Fe Mössbauer, and IR Monitoring of the Thermal Spin Transition in a New Family of Iron(II) Spin-Transition ComplexesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 12 2003Arno F. Stassen Abstract A new family of iron(II) tetrafluoroborate and perchlorate spin-crossover compounds has been synthesised and is discussed. The iron(II) ion is surrounded by six 1-ethyltetrazole ligands, which are halogen-substituted on the C2 atom of the ethyl group. The spin-crossover temperatures T1/2 are high compared to the unsubstituted (1-alkyltetrazole)iron(II) complexes. The shape of the spin-transition curve (i.e. ,HS vs. T) varies largely over the different complexes and appears to be influenced neither by the crystal packing, nor by the electronic effects. The temperature-dependent spin-transition behaviour has been studied by magnetic susceptibility and by 57Fe-Mössbauer spectroscopy. These data have been supported by temperature-dependent mid-range infrared spectroscopy: the thermally induced spin transition has been observed by direct monitoring of the aromatic C,H stretching frequency. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Automated ultrasound-assisted method for the determination of the oxidative stability of virgin olive oilEUROPEAN JOURNAL OF LIPID SCIENCE AND TECHNOLOGY, Issue 2 2007José Platero-López Abstract A fast and automated method is proposed for determining the oxidative stability of virgin olive oil by using ultrasound. The ultrasound microprobe (3,mm in diameter) was directly immersed into the olive oil sample contained in a test tube. The most influential variables in the oxidation process, namely pulse amplitude, duty cycle, irradiation time, and sample amount, were optimized. The oil absorbance at 270,nm was continuously monitored by oil recirculation through a 0.1-mm path length flow cell connected to a fiber optic microspectrometer. This short path length allowed the direct monitoring of absorbance without needing any sample dilution. The ultrasound energy was applied during 35,min, and the resulting increase in absorbance was continuously monitored. The difference between the final and the initial absorbance at 270,nm of a set of virgin olive oil samples was closely correlated with their oxidative stability calculated by the Rancimat method (R2,=,0.9915). The resulting equation enabled the prediction of the oxidative stability of virgin olive oil in a short period of time (35,min), by using a simple, inexpensive, automatic and easy-to-use system. [source] Chromogranins as regulators of exocytosisJOURNAL OF NEUROCHEMISTRY, Issue 2 2010Ricardo Borges J. Neurochem. (2010) 114, 335,343. Abstract Chromogranins (Cgs) constitute the main protein component in the vesicular matrix of large dense core vesicles (LDCV). These acidic proteins have been implicated in several physiological processes such as vesicle sorting, the generation of bioactive peptides and the accumulation of soluble species inside LDCV. This latter feature of Cgs accounts for the ability of vesicles to concentrate catecholamines and Ca2+. Indeed, the low affinity and high capacity of Cgs to bind solutes at the low pH of the LDCV lumen seems to be behind the delay in the neurotransmitter exit towards the extracellular milieu after vesicle fusion. The availability of new mouse strains lacking Cgs in combination with the arrival of several techniques for the direct monitoring of exocytosis (like amperometry, patch-amperometry and intracellular electrochemistry), have helped advance our understanding of how these granins concentrate catecholamines and Ca2+ in LDCV, and how they influence the kinetics of exocytosis. In this review, we will discuss the roles of Cgs A and B in maintaining the intravesicular environment of secretory vesicles and in exocytosis, bringing together the most recent findings from adrenal chromaffin cells. [source] Role of grafting in the emulsion polymerization of vinyl acetate with poly(vinyl alcohol) as an emulsifier.JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 20 2001Abstract The role of grafting in particle nucleation during the emulsion polymerization of vinyl acetate with partially hydrolyzed poly(vinyl alcohol) (PVA) as an emulsifier and potassium persulfate as an initiator was investigated. The polymerizations were carried out in batch with a low solids (10%) recipe. An automated reaction calorimeter (Mettler RC1) was used for the direct monitoring of the kinetics of emulsion polymerizations with three medium molecular weight PVAs differing in their degrees of blockiness (Poval 217EE > 217E > 217). Smith,Ewart case 1 kinetics (average number of free radicals per particle < 0.5) were followed in all cases, and no constant rate in interval II was observed. Contrary to what was expected, a nonlinear relationship was observed between the rate of polymerization (Rp) and the number of particles (Np). At Rp max,Np (217E) > Np (217EE) > Np (217), and the final Np was independent of the degree of blockiness of PVA. The particle size distributions were broad (particle diameter = 20,100 nm) and bimodal. On the basis of these data, we concluded that particle nucleation was continuous and was accompanied by extensive limited aggregation during the particle growth stages. The evolution of the amounts of grafted PVA and poly(vinyl acetate) (PVAc) were determined in polymerizations employing the two PVAs differing the most in blockiness (Poval 217EE and 217). The grafted PVAc followed similar profiles, increasing with conversion, particularly near the end of the two reactions. The amounts of grafted PVAc were about the same in the final latexes (37,39%). In contrast, the grafting of PVA was nearly complete by the time monomer droplets had disappeared in each reaction (25% conversion). However, the extent of grafting differed significantly, with the blockier PVA having about one-third the grafting of the more random PVA (,10% vs ,30%). In these low solids recipes, grafting appeared to be primarily a solution event, occurring predominantly in the aqueous phase and not at the particle/water interface, as was previously speculated. The PVAc grafts grew until the molecules became water-insoluble and precipitated, forming polymer particles. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3633,3654, 2001 [source] Scale sensitivity of synthetic long-term vegetation time series derived through overlay of short-term field recordsJOURNAL OF VEGETATION SCIENCE, Issue 4 2007Otto Wildi Abstract Questions: Is change in cover of dominant species driving the velocity of succession or is it species turnover (1)? Is the length of the time-step chosen in sampling affecting our recognition of the long-term rate of change (2)1 Location: 74 permanent plots located in the Swiss National Park, SE Switzerland, ca. 1900 m a.s.l. Methods: We superimpose several time-series from permanent plots to one single series solely based on compositional dissimilarity. As shown earlier (Wildi & Schütz 2000) this results in a synthetic series covering about 400 to 650 yr length. Continuous power transformation of cover-percentage scores is used to test if the dominance or the presence-absence of species is governing secondary succession from pasture to forest. The effect of time step length is tested by sub-samples of the time series. Results: Altering the weight of presence-absence versus dominance of species affects the emerging time frame, while altering time step length is uncritical. Where species turnover is fast, different performance scales yield similar results. When cover change in dominant species prevails, the solutions vary considerably. Ordinations reveal that the synthetic time series seek for shortest paths of the temporal pattern whereas in the real system longer lasting alternatives exist. Conclusions: Superimposing time series differs from the classical space-for-time substitution approach. It is a computation-based method to investigate temporal patterns of hundreds of years fitting between direct monitoring (usually limited to decades) and the analysis of proxy-data (for time spans of thousands of years and more). [source] | |||||||||||||