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Process Chemistry |
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Glucose Conversion to Gluconic Acid There are a number of applications in process chemistry where the Advanced Laser Polarimeter would find valuable use. Here, we have included an example where the detector is used to monitor the conversion of a chiral reactant of one specific rotation, into a chiral product with a different specific rotation. In this particular reaction, we monitor the conversion of glucose by the enzyme glucose oxidase. The figure below describes the glucose oxidase catalysis:
The specific rotation of the reactant, b -D-glucose, is 53 (deg. (g/ml)-1 dm-1) whereas the product, D-gluconic acid, has a specific rotation of 12.7 (deg. (g/ml)-1 dm-1). Thus, the reaction results in a net change in [ a] of approximately 30. This magnitude of change is easily measured by laser-based polarimetry. In this experiment, the reaction was actually carried out in the polarimetric detector flow cell.
Next, we will see how samples can be drawn from a reaction vessel at regular intervals and then analyzed by the polarimetric detection system. Of course, the natural extension of this application would be to use the detector as an online monitor for real-time control of a continuously operating reaction system. Overlaping Injections The data below shows how the PDR-Chiral Advanced Laser Polarimeter can be used with a flow injection analysis (FIA) system for sample introduction. Duplicate injections of a mixture of glucose and gluconic acid, were made approximately 40 seconds apart to verify the elution order and detector response for the two optically active compounds.
The b-D-glucose is the first to elute, showing a much greater response than the D-gluconic acid which elutes about 2 minutes later. This is in agreement with the [a] values reported in the literature. The degree of separation between the two peaks allows overlaping sample injections, significantly reducing the effective analysis time and giving us a fast, repetitive analysis of a reaction system. b-D-Glucose Response In the figure below, we show the polarimetric detector’s response as a function of the mole-fraction of b-D-glucose. The data presented here shows how a reaction could easily be followed using a polarimetric detector when a compound exhibiting one-chirality is converted into a compound with a different, or no, chirality.
A similar curve would be obtained when the mole-fraction of gluconic acid is plotted, only the slope would be less due to the smaller specific rotation of gluconic acid. Reaction Progress The final graph below shows a plot of collected data illustrating the potential for using in-process analysis and control to optimize a reaction involving chiral compounds. The conversion of glucose to gluconic acid was followed via polarimetric detection. Samples from the reaction vessel were introduced into the laser polarimeter using FIA. In this experiment, the reactions were followed for 50 minutes, however, other studies extended out as much as 12 hours. The enzyme itself is optically active, resulting in the difference in starting rotation of the reaction broth.
Clearly, we can see how increasing the amount of glucose oxidase catalyst (G.O.) significantly increases the reaction rate. It is also important to note that no separation was employed here. By using FIA, each sample took less than 3 minutes to analyze increasing the potential number of data points collected as compared with other techniques such as HPLC. Other Enzyme SystemsThe following table lists a number of medicinal and industrial enzyme systems that are suitable for monitoring with a polarimetric detector. Any of these systems would naturally benefit from process optimization using the PDR-Chiral Advanced Laser Polarimeter.
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