Iodine formation with amylose

Figure 16-6 (a) Schematic structure of the starch-iodine complex. The amylose chain forms a helix around l6 units. [Adapted from A T. Calabrese and A. Khan, "Amylose-lodine Complex Formation with Kl Evidence for Absence of Iodide Ions Within the Complex." J. Polymer Sci. 1999, A37,2711.] (fc>) View down the starch helix. Showing iodine inside the helix.8 [Figure kindly provided by R. D. Hancock, [rower Engineering, Sett Lake City.]... 

Lipid-complexed amylose chains interfere with amylose-iodine (If and If) complex formation. Therefore, extraction of complexed lipids with 75% n-propanol is necessary prior to determination of total amylose content. 

Both the amylose and amylopectin components of starch form complexes with iodine, but early studies showed that there is no connection between the iodine reaction and the reducibility of starch fractions.63 The complex of amylose is pure blue, whereas the complex of amylopectin is blue-violet.5864 Thus, the varying amylose-to-amylopectin ratio can be one of the factors responsible for the various shades of blue color exhibited by various varieties of starch. Amylopectin takes up less iodine than does amylose. Also the course of complex formation uptake is different, as is evident65 from Fig. 2. 

The iodine affinity is due to the formation of colored complexes with amylose. The color of this complex depends on both the concentration of the iodine in the solution and the kind of starch. Amylose binds 20% (v/v) of iodine, to develop a blue color, whereas amylopectin binds only O.S to 1% (v/v) of iodine to give a red-violet eolor. Starch which does not contain any amylose gives a red color with iodine. Thus, evaluation of the degree of dextrinization based on the observations of Komm and Martin needs standardization of the method and approach, because ofthe variability in the origin of the starch. Table XVI shows that methods in use to date are not equivalent to one another. The color-development characteristics are again dependent on the origin of the starch. ... 

Two methods were used one is the iodine method that was used to determine dextrinization or the ratio of hydrolysis of the starch, and the other is the phenolphifaalein method lhat was used to determine CD formation. Starch-dextrinizing activity was determined in accordance with Fuwa (19) and Pongasawasdi and Yagisawa (20) with slight modifications. The reaction mixture containing 100 (iL of diluted enzyme aliquot and 300 pL of 0.5% soluble starch prepared in 0.1 M acetate buffer, pH 5.5, was incubated at 55 °C for 10 min. The enzyme reaction was stopped by the addition of 4.0 mL of 0.2 M HCl solution. Then, 0.5 mL of iodine solution (0.3 g/L I2 and 3.0 g/L KI) was added to form an amylose-iodine complex with residual amylose. The final volume was adjusted to 10 mL with distilled water. The absorbance of the blue color of the amylose-iodine complex was measured by spectrophotometer at 700 nm, and a decrease in absorbance was verified, when compared to a control tube with heat-inactivated enzyme. One unit of enzyme activity was defined as the quantity of enzyme that reduces the blue color of the starch-iodine complex by 10% per minute. 

The enzymatic polymerization of G-l-P using 6 and 9 as primers was performed to produce the two types of amylose-grafted polyacetylenes (7) and (10) (Schemes 5a and b). The complex formation with iodine is a well-known characteristic property of amylose [23]. The colorless solutions of 7 and 10 in DMSO turned to violet after the addition of a standard iodine-iodide solution to the polymer solution, as the same color change in the complex formation of amylose with iodine. Values of the A-max of UV-Vis spectra of the iodine... 

Kobayashi, K., Kamiya, S. Enomoto, N. (1996). Amylose-carrying styrene macromonomer and its homo- and copolymers Synthesis via enzyme-catalyzed polymerization and complex formation with iodine. Macromolecules, 29, 8670-8676. 

The yield is higher in basic solution in the presence of an oxidizing agent. Iodine forms a blue complex with P-amylose in starch. A hnear array of I5 species consisting of I2 -1 - I2 units bound to the amylose hehx causes blue color formation. 

Amylose [9005-82-7] (CgHjoOsln (for use in iodine complex formation). Amylopectin was removed from impure amylose by dispersing in aqueous 15% pyridine at 80-90 (concn 0.6-0.7%) and leaving the soln stand at 44-45" for 7 days. The ppte was re-dispersed and recrystd during 5 days. After a further dispersion in 15% pyridine, it was cooled to 45°, allowed to stand at this temperature for 12hours, then cooled to 25° and left for a further lOhours. The combined ppte was dispersed in warm water, ppted with EtOH, washed with absolute EtOH, and vacuum dried [Foster and Paschall JACS 75 1181 7955]. 

I hen iodine is mixed with starch, I the amylose stTands coil around the iodine molecules, forming a starch-iodine complex that has a characteristic dark blue color. The more starch present in a solution, the deeper the blue. The formation of this color is used to identify the presence of starch. In this activity, you will use an iodine solution to test for the presence of amylose and the amylose-digesting action of your saliva. 

It was realized long ago that a number of organic compounds can obscure the blue reaction.97 This effect is caused by the formation of inclusion complexes by such compounds. Hence, the iodine reaction is widely used as the test for complexation of starch, mainly amylose, with many organic... 

Fio. 11.—Effect of pH and temperature (T) on the formation of the amylose-iodine complex, expressed as the change (in %) of the relative extinction of the band measured at 625 nm. (Reprinted with permission from J. Hollo and J. Szejtli, Przem. Spoz., (1957) 429-433.)... 

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