Adsorbed layer fluorescence spectroscopy

For TIR fluorescence spectroscopy on water/oil interfaces, the choice of a probe molecule is of primary importance. For example, the penetration depth (dp) of an incident evanescent wave at a 1,2-dichloroethane (DCE, refractive index (n) n = 1.44)/water (m2 = 1.33)interface is calculated to be 94nm on the basisofEquation(13),whereX = 580 nm and 0 = 80°. It has been reported that the thickness of a sharp water/oil interface represented by water/DCE is 1 nm [9], so that dp of the incident evanescent wave is thicker than the thickness of the interfacial layer, and the fluorescence characteristics of a probe molecule in the bulk phase are superimposed, more or less, on those at the interface [2]. Therefore, a probe molecule should be highly surface-active and adsorb on the interface, so as to exclude fluorescence of the probe molecule from the bulk phase. In the present experiments, we employed xanthene dyes as fluorescence probes throughout... 

Among the other spectroscopies, either in the direct or reflection mode, fluorescence spectroscopy may be mentioned. A promising variant is Total Internal Reflection Fluorescence spectroscopy (TIRF). The decay rate of an excited fluorescing probe is usually Interpreted in terms of the local fluidity and polarity. The technique has been used to estimate the extent of ordering inside adsorbed surfactant layers, but this is not an absolute method because a fluorescent probe has to be inserted, and such probes themselves affect the local fluidity. More rigorous are fluorescence experiments with molecules that possess such a probe as an intrinsic part of their structure, such as tryptophans in... 

The chimney-sweeper cancer described by P. Pott in England as early as 1775, which is basically related to soot but not to carbon black, was the starting point of intensive research on analytical test methods for polycyclic aromatic hydrocarbons (PAH) in carbon blacks. Increasingly refined test methods have been developed (e.g., column, thin-layer, and paper chromatography, gas chromatography, UV and fluorescence spectrophotometry, and mass spectroscopy) to detect traces of such substances and to investigate the ability of carbon black surfaces to adsorb and to desorb PAHs. 

Techniques which allow one to monitor the boundary layer as a function of time, such as total internal reflection fluorescence (TIRF) spectroscopy 4 43), permit a quantitative evaluation of interfacial mass transport processes using, for example, fluorescently-tagged macromolecules which do not adsorb, such as fluorescein-labeled dextran 40 ... 

The sorption efficiency of MC was determined as the ratio of the quantity of the adsorbed substance to its initial amount (w / w), expressed in % for a certain ratio (w / w) of adsorbent to substance. Optimal ratios of adsorbent to substance equal 15-20 for barbiturates, 20 - 25 for cyanocobalamin and bilirubin, and 40 - 50 for hemoglobin. The initial concentration of absorbed substances was 100 - 200 pg/ml. The substances were incubated for lmin with MC either in physiological solution or in donor plasma and donor blood at room temperature (pH 7.4). The concentration of substances in the solutions was measured by differential visual and UV-spectroscopy. Concentrations of substances in blood and plasma and adsorption of total plasma proteins was determined by thin-layer chromatography with a fluorescent label. 

Spectroscopic methods, such as fluorescence recovery and quenching, Fourier-transform infrared spectroscopy (FT-IR), and light reflection technique have been used for studies of adsorbed proteins (for example Burghardt Axelrod 1981, Thompson et al. 1981, van Wagenen et al. 1982), and surfactant adsorption layers (for example Ldsche et al. 1983, L6sche Mohwald 1989, Daillant et al. 1991, Henon Meunier 1992, Mohwald 1993). Considerable progress has been made in recent years with respect to the sensitivity of detectors and the efficiency of computers, so that the power of these methods has increased remarkably. 

The recrystallization of S-layer proteins at phosphoethanolamine monolayers on aqueous subphases has been also studied on a mesoscopic scale by dual label fluorescence microscopy andFourier transform infrared spectroscopy (FTIR) [110]. It has been shown that the phase state of the lipid exerts a marked influence on the protein crystallization. When the surface monolayer is in the phase separated state between fluid and crystalline phase, the S-layer protein is preferentially adsorbed at the boundary line between the two coexisting phases and crystallization proceeded underneath the crystalline phase. Crystal growth is much slower under the fluid lipid and the entire interface is overgrown only after prolonged protein incubation. In turn, as indicated by characteristic frequency shifts of the methylene stretch vibrations on the lipids, protein crystallization affects the order of the alkane chains and drives the fluid lipid into a state of higher order. However, the protein does not interpenetrate the lipid monolayer as confirmed by x-ray reflectivity studies [105-107]. 

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