Diffusion coefficient, polyacrylamide gels

J. Lunney, A. Chrambach, and D. Rodbard, Anal. Biochem., 40 158-173 (1971). Factors Affecting Resolution, Bandwidth, Number of Theoretical Plates and Apparent Diffusion Coefficients in Polyacrylamide Gel Electrophoresis. 

Fan studied the transport properties of three ferrocene derivatives carrying different types of charge inside two gels of polyacrylamide and polyacrylate (55). The latter gel formed a passivation layer by electrophoresis, which behaved as a cation-exchange membrane. Chronoamperometry was applied while penetrating the film and revealed diffusion coefficients slightly below those inside the solution. From this, the author concluded that the transport occurs via water-filled domains. 

Figure 3. The ratio jx/Mo can be obtained from the ratio of the apparent diffusion coefficients measured on cylindrical and spherical gels. The theoretical curve is obtained from equation 12. The two experimental points correspond to a polyacrylamide gel in water (circle) and a polydimethylsiloxane gel in toluene (box). The temperature was 22 °C.

Figure 6. Variation of the diffusion coefficient of polyacrylamide gels on a double logarithmic scale as a function of their concentration at swelling equilibrium. The temperature was 22 C. The slope was 0.74 and agreed with the exponent predicted by equation 21.

The ratio d of the diffusion coefficients of the inhibitor and the activator d = cio / r value very close to one. Typically a value ofd = 1.07 is chosen in simulations, which appears to represent a situation rather unfavorable for the formation of Turing patterns. This view is too simple, however it overlooks the role of starch in the reaction. As discussed in Sect. 1.4.9, the activator 1 reacts with iodine, I2, to form triiodide ion 13 , which gets trapped by the starch molecules embedded in the gel or by iodide-binding sites of the gel. (Polyacrylamide binds polyiodide ions even in the absence of starch as does poly(vinyl alcohol), used as a... 

Wave refraction and reflection are ubiquitous in conservative media [29] however, until recently they had not been studied in excitable reaction-diffusion systems. Refraction was studied theoretically by Momev [30] in a reaction-diffusion system consisting of two regions with different diffusion coefficients and identical local chemical kinetics. Refraction of chemical waves was observed for the first time by Agladze and De Kepper [31] in the ferroin-catalyzed BZ system at the boundary between solution and polyacrylamide gel. In their experiments the jump in wave velocity produced by the difference in diffusion coefficients was small, and the authors were unable to make quantitative measurements. 

Chen, B.. Chrambach, A. Rodbard, D. (1979). Continuous optical scanning in polyacrylamide gel electrophoresis Estimation of the apparent diffusion coefficient of P-lactoglobulin. Analytical Biochemistry, 97,120-130. 

To check the predicted power law of the diffusion coefficient (Eq. (D-17)), experiments on polyacrylamide-water gels were carried out. It has been found that the exponent X0 lies between 0.65 and 0.75, and that these values are not too far firom the predicted value 0.75 . However, the system studied is polar and a polyelectrolyte behaviour due to partial hydrolysis of the amide group cannot be excluded. ... 

---