Optical rotation gelation

It has been known for many years that the gelation of gelatin is accompanied by a large increase of the optical rotation in the levo direction. Smith (17) determined the final or equilibrium values of the specific rotation by setting the gel at a temperature several degrees below the temperature of interest. After a time, the temperature was raised to the temperature of interest and when the optical rotation became constant, it was recorded. This equilibrium value of the specific rotation was almost independent of the concentration above 30° C. and below 17° C. and increased as the temperature was decreased... 

Gelation and liquefaction of these polysaccharides may be readily monitored by observation of the optical rotation.183 A typical graph of... 

The interaction of agarose with two heavily substituted P1,4-1 inked D -xylans was studied. Using the same gelation and optical rotation criteria, the heavily substituted xylans... 

Cheetham, N. W. H. and Mashimba, E. N. M. Comfomiational aspects of xanthan-galactomannan gelation-Fuither evidence from optical-rotation studies. Carbohydr. Polym., 14,17-21 (1990). 

Busnell et al. [478] investigated the prematuring effect on the gelation behaviour of gelatin solutions with the aid of viscodastic experiments combined with differ tial scaiming calorimetry and optical rotation experiments also... 

This work mainly concerns with the question, if there is a correlation in gelation kinetics between network formation and the increasing helical content of the mixture. For this reason we have examined the time dependence of the mechanical parameters G and G" and the specific optical rotation during the gelation process, which has been induced by a temperature jump from 313 K to 293 K. The physical values G, G" and are plotted versus the time for a gelatin/water mixture of... 

The gelation of gelatin is accompanied by a change in optical rotation (see page 37), and this follows a course with time very similar to that described for the rigidity. When a solution is cooled from 36 to 16 C. 

In any case, the absorption of heat over a considerable temperature range agrees with conclusions from Optical rotation and rigidity measurements that gelation involves an equilibrium which can be progressively shifted by changing the temperature. 

Opticcd Rotation. The change in optical rotation with time during gelation has already been mentioned (page 22). The equilibrium value... 

Dependence of Optical Rotation on Other Added Substances. Katz and Wienhoven (1933) have reported the effects on optical rotation of a wide variety of substances. Those which diminished the numerical value of the specific rotation at 15° were observed qualitatively to lower the rigidity, and some of them prevented gelation at 15°. The latter compounds have already been mentioned under melting points. Others which caused a substantial numerical decrease in specific rotation at a concentration of 1 Jlf were thioacetamide, iodoethanol, sodium heptylate, sodium caprylate, and sodium isophthalate. The effectiveness of large anions is apparent, as in the depression of the melting point. 

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