Solid supports gelatinous

The high specificity required for the analysis of physiological fluids often necessitates the incorporation of permselective membranes between the sample and the sensor. A typical configuration is presented in Fig. 7, where the membrane system comprises three distinct layers. The outer membrane. A, which encounters the sample solution is indicated by the dashed lines. It most commonly serves to eliminate high molecular weight interferences, such as other enzymes and proteins. The substrate, S, and other small molecules are allowed to enter the enzyme layer, B, which typically consist of a gelatinous material or a porous solid support. The immobilized enzyme catalyzes the conversion of substrate, S, to product, P. The substrate, product or a cofactor may be the species detected electrochemically. In many cases the electrochemical sensor may be prone to interferences and a permselective membrane, C, is required. The response time and sensitivity of the enzyme electrode will depend on the rate of permeation through layers A, B and C the kinetics of enzymatic conversion as well as the charac-... 

The most common solid supports in SPS are hydrophobic polystyrene (PS) resin beads (9), which are representatives of the class of so-called gelatinous solid supports. They consist of PS cross-linked with 1-2% divinylbenzene (DVB) and are described schematically in Fig. 1.1, which shows the appearance of a hydroxymethyl-grafted PS resin. 

In a similar vein, a series of papers published between 2002 and 2008 contains spectacular claims of highly enantioselective asymmetric additions of water to styrenes, unsaturated carboxylic acids, or simple terminal alkenes [34-Al]. The catalysts used are of the heterogeneous type and based on chiral biopolymers such as wool, gelatin, or chitosan as solid supports (sometimes in combination with silica or ion-exchange resins) that are doped with transition metal salts. This series of papers contains spectacular claims, insufficient experimental data, and erroneous chemical structures for the biopolymers used. As earlier work from the same group of authors on asymmetric catalysis on bio-polymeric supports is irreproducible [42], one is well advised to await independent confirmation of those results. 

In view of the fundamental importance of the Gibbs-Thomson formula, and the magnitude of the discrepancies between the figures calculated from it and the experimental results, it is of obvious interest to inquire to What causes the deviations may be due. The first point to be noticed is that the complex substances which exhibit them most markedly form, at least at higher concentrations, colloidal and not true solutions. It is, therefore, very probable that they may form gelatinous or semi-solid skins on the adsorbent surface, in which the concentration may be very great. There is a considerable amount of evidence to support this view. Thus Lewis finds that, if the thickness of the surface layer be taken as equal to the radius of molecular attraction, say 2 X io 7 cms., and the concentration calculated from the observed adsorption, it is found, for instance, for methyl orange, to be about 39%, whereas the solubility of the substance is only about 078%. The surface layer, therefore, cannot possibly consist of a more concentrated solution of the dye, which is the only case that can be dealt with theoretically, but must be formed of a semi-solid deposit. 

Natural media are those used on the basis of experience and not on the basis of exact knowledge of their composition and action. Natural or complex media usually contain peptones, beef extract, or yeast extract. When a solid medium is desired, a solidifying agent such as gelatin or agar may be incorporated into the medium. Examples of a relatively simple liquid and a solid medium that support the growth of many common heterotrophs are nutrient broth and nutrient agar. Their composition is as follows ... 

In summary, nuclear models of the crevice type consist essentially of gas phases stabilized in crevices in solid particles. While the crevice hypothesis represents a viable nuclear model, none of the existing mathematical treatments make predictions that are supported by the above-mentioned gelatin experiments (ref. 114). In addition to these problems with the mathematical devel-... 

Liquid and solid samples are placed in an opened cup while volatile samples are placed in a gelatine capsule and placed in the cup as for a normal sample. A suitable absorption solution is placed at the bottom of the bomb along with the prepared sample. It may be necessary to include an aid with combustion resistant samples as a support to combustion and such additives are low molecular weight paraffin oils, ammonium nitrates, benzoic acid, decalin, etc. 

A number of investigators have put forward the solid solution theory. Procter, investigating the swelling of gelatin gels, was, as early as 1914, the first who decided in favour of this theory and postulated a frame work of molecular dimensions, certainly an admirable achievement in those days. The solid solution theory was also supported by Katz in 1918. 

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