Thermostability testing

The Fig. 2 shows a scheme of the test equipment. The sample is placed in a thermostated test chamber which is filled with the swelling agent of a constant pH. The sample is clamped on one side. The sample can be loaded with a constant force... 

The effect tends to increase with reduced system lengths (capillary system) and is probably caused by isomerization of the -isomer of silicomolybdic acid. Temperatures of ships laboratories often are notoriously variable. If the ambient temperature varies by more than about 3 K within a calibration interval, the manifold should be thermostatically controlled. This may be done by either using a thermostated test-tube as a coil core for the mixing and reaction coils (shaded rectangle in Fig. 10-12) or deploying the coils in a water bath. 

At low temperature, nonionic surfactants are water-soluble but at high temperatures the surfactant s solubUity in water is extremely smaU. At some intermediate temperature, the hydrophile—Hpophile balance (HLB) temperature (24) or the phase inversion temperature (PIT) (22), a third isotropic Hquid phase (25), appears between the oil and the water (Fig. 11). The emulsification is done at this temperature and the emulsifier is selected in the foUowing manner. Equal amounts of the oil and the aqueous phases with aU the components of the formulation pre-added are mixed with 4% of the emulsifiers to be tested in a series of samples. For the case of an o/w emulsion, the samples are left thermostated at 55°C to separate. The emulsifiers giving separation into three layers are then used for emulsification in order to find which one gives the most stable emulsion. 

The long term tests in the SASOL plant as well as in the Schwechat plant were run with outlet temperatures of 450°C, but both plants were also operated with higher loads that caused reactor outlet temperatures of 470°C or even higher. In comparison with the test run at 450°C, only a slight increase in deactivation rate was detectable which demonstrates the thermostability of the catalyst. From the aspect of thermostability, outlet temperatures of 450°-470°C are acceptable. Further considerations including the possibility of overload operation, the SNG specification to be achieved in final methanation, end-of-run conditions, and cost of reactor material will affect the selection of optimum outlet temperature. 

These tests were performed to establish the limits in flexibility and operability of a methanation scheme. The two demonstration plants have been operated in order to determine the optimum design parameters as well as the possible variation range which can be tolerated without an effect on catalyst life and SNG specification. Using a recycle methanation system, the requirements for the synthesis gas concerning H2/CO ratio, C02 content, and higher hydrocarbon content are not fixed to a small range only the content of poisons should be kept to a minimum. The catalyst has proved thermostability and resistance to high steam content with a resultant expected life of more than 16,000 hrs. 

Before starting any experiment, the potential of the test electrode Ej is measured with reference to a saturated calomel electrode which is connected to the experimental cell through a bridge containing the same supporting electrolyte solution. Such measurements are taken whenever the concentration of the metal ion is changed. The cell is kept immersed in a thermostated bath maintained at a known temperature. 

Different types of CE instruments have different thermostating systems, have different detectors, use capillary of different lengths, have detection windows at different distances from the injection point, and have different injectors. Thus, additional tests may be required after a method transfer. 

The cell-bound amylopullulanase was solubilized with detergent and lipase. It was then purified to homogeneity by treatment with streptomycin sulfate and ammonium sulfate, and by DEAE-Sephacel, octyl-Sepharose and puUulan-Sepharose column chromatography (12). The final enzyme solution was purified 3511-fold over the crude enzyme extract with an overall recovery of 42% and had a specific activity of 481 units/mg protein. The average molecular weight of the enzyme was 136,500 determined by gel filtration on Sephacryl S-200 and SDS-PAGE, and it had an isoelectric point at pH 5.9. It was rich in acidic and hydrophobic amino acids. The purified enzyme was quite thermostable in the absence of substrate even up to 90°C with essentially no loss of activity in 30 min. However, the enzyme lost about 40% of its original activity at 95 C tested for 30 min. The optimum tenq)erature for the action of the purified enzyme on pullulan was 90°C. However, the enzyme activity rapidly decreased on incubation at 95°C to only 38% of the maximal 30 min. The enzyme was stable at pH 3.0-5.0 and was optimally active at pH 5.5. It produced only maltotriose and no panose or isopanose from pullulan. 

A typical test loop includes a pump capable of pressure development to 1000 psig and sufficient valving and piping to permit multistation installation of fiber samples. Feed solutions are delivered from reservoirs which are thermostated and isolated in order to maintain constancy of temperature and composition. The facility is so established that both permeate and concentrate are returned continuously to the reservoir. 

These tests were performed by measuring the rate of dapiprazole release from gel vehicles 6 and 8 to an aqueous sink, through a non-porous membrane. For this purpose, a thin nylon membrane, which had been preconditioned by extraction with ethanol (1 h at 60°C) and overnight hydration in distilled water at room temperature, was positioned between the receiving (5 ml) and the donating (4 ml) compartment of a glass GH flow-through diffusion cell [5], thermostated at 30°... 

The polymerase chain reaction utilizes a thermostable DNA polymerase to amplify DNA through a series of temperature cycle steps. The key to the specificity of the reaction is the selection of oligonucleotide primers that hybridize to the opposite strands of the DNA being tested, about 400-2000 bp apart. If the sequence of the primers is unique within the genome, and the primers hybridize to the target DNA at a high enough temperature to avoid close matches (various... 

It was soon apparent that the new vitamin alone would not satisfy the dietary need of rats for the B factor. A second thermostable factor (B2) was required in addition to thiamin (B ), which was labile and easily destroyed by heating. When it became clear that factor B2 contained more than one component, it was called vitamin B complex. There was some confusion until relatively specific animal tests for each one of the members had been devised. 

Also he speculated that citrus juices contain two cloud-coagulating enzymes of different thermostabilities. One enzyme, most active at low pH and temperature, appeared to be destroyed by heating the juice at 65 to 70°C (149 to 158°F). The second enzyme, most active at pH 3.0 to 3.3 and about 35°C (95°F), appeared to require heating to 888C (191°F) for inactivation (12). Stevens (13) described a rapid test for pectic enzymes in citrus juice. It involved adding pectin under controlled conditions of temperature and sample preparation, and measuring the time required for flocculation. Stevens, and coworkers (14) further elaborated on the patent work (12, 13). They produced a trend curve of the... 

With the example of p-nitrophenyl esterase the Arnold group demonstrated that even the thermostability of an enzyme is amenable to directed evolution (Giver, 1998). As a test of thermostability the activity in standard conditions (pH 7.5, 0.25 mM p-nitrophenyl acetate) at 30 °C (AJ was compared with the activity in the standard assay at 30 °C (Ar) but after heating to Tm for 10 min (with subsequent cooling on ice and incubation for 30 min at room temperature). The results are shown in Figure 11.10. This work demonstrates that enhanced activity and enhanced stability need not be mutually exclusive. However, the improvements along one of the two axes sometimes tend to be minor, i.e., by a factor between 3 and 5. 

To ascertain the upper limit of protein thermostability and to evaluate the effect of additional disulfide bridges on the enhancement of protein thermostability, additional cysteine residues were introduced into several unrelated proteins by site-directed mutagenesis and deactivation behavior tested at 100°C (Volkin, 1987). All the proteins investigated underwent heat-induced beta-elimination of cystine residues in the pH 4—8 range with first-order kinetics and similar deactivation constants kj that just depended on pH 0.8 0.3 h-1 at pH 8.0 and 0.06 0.02 h 1 at pH 6.0. These results indicate that beta-elimination is independent of both primary amino acid sequence and the presence of secondary structure elements. Elimination of disulfides produces free thiols that cause yet another deleterious reaction in proteins, heat-induced disulfide interchange, which can be much faster than beta-elimination. 

Artificial membranes soaked in animal mucin dispersions or animal model mucosae are used as biological substrates. Another apparatus proposed for in vitro measurements of bioadhesive properties of liquid formulations (polymer solutions or pessaries upon melting) consists of a thermostated inclined plane over which a mucosal membrane or a mucin film is layered. This test measures, as a function of time, the amount of formulation that after contact with the biological substrate, drops on a microbalance placed under the inclined plane [86] (Figure 22.3). 

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