Thermal stability of gels

EXPERIMENT 12 Activity and Thermal Stability of Gel-immobilized Peroxidase 389... 

The formation of bilayer vesicles was also observed for dialkyldimethylammonium bromide 33 in ether-containing ionic liquids 26, 27 (Figure 24) [124]. Ionic amphiphiles intrinsically possess solvophilic (or ionophilic) groups and electrostatic repulsions between them are highly screened in ionic liquids. In addition, the presence of ether-linkages in ionic liquids increases their net polarity. These factors contribute to enhance the association force of ammonium amphiphiles in ionic liquids and concurrently increase the thermal stability of gel(crystalline) state bilayers [124]. 

Methods for removing water from solids depends on the thermal stability of the solids or the time available. The safest way is to dry in a vacuum desiccator over concentrated sulfuric acid, phosphorus pentoxide, silica gel, calcium chloride, or some other desiccant. Where substances are stable in air and melt above 100°, drying in an air oven may be adequate. In other cases, use of an Abderhalden pistol may be satisfactory. 

In a current rheological study [296], the galactoxyloglucan from Hymenia courbaril was mixed with starch containing 66% amylose and with waxy corn starch (amylopectin). The gel mixtures showed, under static rheological conditions, an increase in paste viscosity compared to those of the polysaccharides alone. Dynamic rheometry indicated that the interactions resulted in increased thermal stability of the gel formed in comparison to that of the starch alone. 

In the present investigation, we have found that significant improvement of the hydro-thermal stability of MCM-41 can be achieved by simply adding additional tetraalkylammonium or sodium ions to the synthesis gel. 

Immobilized enzymes are becoming increasingly important in commercial processes. In this experiment, students will trap molecules of the enzyme horseradish peroxidase within a polyacrylamide gel matrix. The reaction kinetics and thermal stability of the immobilized enzyme will be measured. This experiment introduces students to the use of enzymes in biotechnology. 

In this section, the thermal stability of acrylamide gel-immobilized peroxidase will be compared to that of the free enzyme. The free enzyme is assayed in the following manner Dilute 1 mL of the stock horseradish peroxidase (0.1 mg/mL, 15 units/mL) with 299 mL of glass-distilled water. Add 1.0 mL of this diluted enzyme to each of two test tubes. Place one of the tubes in a 60°C water bath for exactly 4 minutes. Allow the other tube to sit at room temperature for the same time interval. Cool the higher-temperature tube to room temperature by placing in a water bath. To each tube add 2.0 mL of the aminoantipyrine-phenol stock solution and 2.0 mL of the H202 solution and mix well. Allow the tubes to sit at room temperature for exactly 3 minutes then immediately read the sl5l0 for each. Record the results in your notebook. 

Other properties which have contributed to the attractiveness and versatility of the sol-gel doping approach are the chemical, photochemical and electrochemical inertness as well as the thermal stability of the matrix the ability to induce electrical conductivity16 the richness of ways to modify chemically the matrix and its surface as well as the above-mentioned controllability of matrix structural properties the enhanced stability of the entrapped molecule1,17 the ability of employing the chromatographic properties of the matrix for enhanced selectivity and sensitivity of reactions with the dopant4 the simplicity of the entrapment procedure the ability to obtain the doped sol-gel material in any desired shape (powders, monoliths, films, fibers) and the ability to miniaturize it18,19. 

Auschra C, Stadler R (1993) Thermal-stability of poly(styrene-b-methyl methacrylate) and poly(styrene-b-ethylene-co-l-butene-b-methyl methacrylate) - a gel-permation. Polym Bull 30 305-311... 

---