Surface radioactivity technique

By using a surface radioactivity technique, the penetration of the hydrophobic and flexible 1-14C-acetyl--casein and the rigid and globular 1-14C-acetyl-lysozyme molecules into phospholipid monolayers in different physical states was monitored. The adsorption of ff-casein to lecithin mono-layers is described by a model in which it is assumed that the protein condenses the lecithin molecules so that the degree of penetration is a function of the lateral compressibility of the phospholipid monolayer. The interaction of ff-casein with phospholipid monolayers is dominated by the hydrophobicity of the macromolecule, but lysozyme tends to accumulate mostly beneath phospholipid monolayers in this situation, electrostatic interactions between the lipid and protein are important. 

Monolayer Techniques. Surface tension and surface potential were measured by a torsion balance with the Wilhelmy plate and a radioactive (226Ra) air electrode (5, 20). 

The use of radioactive techniques to determine surface excesses was further extended in a series of elegant works, where the limited range (-1000 A) of a-recoiling atoms in water was utilized. Surface excesses of Bi-212 ions were determined - e.g. coadsorbed with dodecylsulfate - by collecting and counting the recoiling Tl-208 atoms above the surface. 

Surface Area. Overall catalyst surface area can be determined by the BET method mentioned eadier, but mote specific techniques are requited to determine a catalyst s active surface area. X-ray diffraction techniques can give data from which the average particle si2e and hence the active surface area may be calculated. Or, it may be necessary to find an appropriate gas or Hquid that will adsorb only on the active surface and to measure the extent of adsorption under controUed conditions. In some cases, it maybe possible to measure the products of reaction between a reactive adsorbent and the active site. Radioactively tagged materials are frequentiy usehil in this appHcation. Once a correlation has been estabHshed between either total or active surface area and catalyst performance (particulady activity), it may be possible to use the less costiy method for quaHty assurance purposes. 

Very few direct measurements of the reaction of surface silanol groups on quartz have been reported. This is apparently caused by the small effects due to the limited surface areas available. Adsorption of sodium ions on quartz was measured by radioactive tracer techniques by Gaudin et al. (293). Saturation was achieved at high pH (>10) and sodium ion concentrations above 0.07 Jlf. The calculated packing density of silanol groups was 4.25/100 A. Goates and Anderson (294) titrated quartz with aqueous sodium hydroxide and alcoholic sodium ethylate. The occurrence of two types of acidic groups was reported. 

Other techniques for the diffusion of gas through monolayers at the liquid interface have also been investigated (Blank, 1970). In these methods, the differential manometer system was used to measure the adsorption of gases such as C02 and 02 into aqueous solutions with and without the presence of monolayers. The Geiger-Mueller counter with a suitable sorbent and a radioactive tracer gas was used to measure the reduction of evolution of H2S and C02 from the surface solution when a monolayer was present. 

A recent report describes the radioactive labeled chromium (iii) ion adsorption on stearic acid LB films. The adsorption of chromium (iii) on a stearic acid monolayer on the surface of CrCl3 was described. Stearic acid monomolecular films on I0 3 M CaCl2 subsolutions were deposited in paraffin-coated microscope glass slides by the LB technique (pH range 2-9). 

Measurements of the quantities of glycolipids inserted into the membrane have also been reported by a technique based on the use of C-labeled lipid anchors. In this method, the carbohydrate (a-o-Man) was covalently coupled to the anchor at the surface of a pre-formed vesicle. Indeed, the liposome structure was shown to remain intact in the treatment. Nevertheless, the measurement of the incorporated mannose was performed after separation of bound and unbound material by centrifugation. The yields of coupling were shown to increase with the increase of the initial mannose/ C-anchor ratio, but non covalent insertions were displayed at high initial mannose concentrations. Therefore, the aforementioned method was not as accurate as could have been expected for the use of radioactive materials [142]. Radiolabeled phospholipids were also used for such determinations thus the amounts of glycosphingolipids incorporated into liposomes were quantified by the use of H-phospholipids whereas the amounts of glycolipids were determined by a sphingosine assay [143]. 

Actinide metal samples are characterized by chemical and structure analysis. Multielement analysis by spark source mass spectrometry (SSMS) or inductively coupled argon plasma (ICAP) emission spectroscopy have lowered the detection limit for metallic impurities by 10 within the last two decades. The analysis of O, N, H by vacuum fusion requires large sample, but does not distinguish between bulk and surface of the material. Advanced techniques for surface analysis are being adapted for investigation of radioactive samples (Fig. 11) ... 

Several practical aspects of the photoelectron technique will be discussed here. First, we shall concentrate upon the surface specificity of XPS and UPS. Then the sample preparation procedures will be reviewed. Thereafter, the charging effect, the energy calibration and the problems of handhng radioactive materials will be discussed. Lastly, a short review of similar topics applied to BIS will be given. 

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