Amylose iodine interaction

The amylose-iodine interaction has a dipolar nature, as deduced from a distinct difference between the molecular coefficient of iodine in starch and in nonpolar solvents.123 The additional stabilization may result from the formation of resonating polyiodine chains at high dipolar interactions. The composition of the total energy of stabilization is shown5 in Table VI. 

Helix formation probably arises from a co-operative action of amylose and iodine partners. Different models have been proposed despite extensive investigation the nature of the interaction producing the intense visible absorption spectrum of the amylose-iodine complex is by no means clear. (For review see (8,16,22)). 

In order to examine whether interaction between chains also leads to an increase of the Cotton effect we studied amylose-iodine solutions under aggregating conditions. In experiments using iodine solutions of different 1 content we observed at standard amylose concentration (0.4 g/1) a considerable tendency towards aggregation with the initially 1 free iodine solution and with solution containing a large excess of 1 (1 12/55 I ). 

We have reported a novel reversible interaction of amylose-iodine-complex with proteins, which is closely associated with the coil— helix transition of amylose chain, and the high adsorptive capacity of this complex appears to be due to hydrophobic Interactions (1 6). 

Molecular Interactions. Various polysaccharides readily associate with other substances, including bile acids and cholesterol, proteins, small organic molecules, inorganic salts, and ions. Anionic polysaccharides form salts and chelate complexes with cations some neutral polysaccharides form complexes with inorganic salts and some interactions are stmcture specific. Starch amylose and the linear branches of amylopectin form inclusion complexes with several classes of polar molecules, including fatty acids, glycerides, alcohols, esters, ketones, and iodine/iodide. The absorbed molecule occupies the cavity of the amylose helix, which has the capacity to expand somewhat to accommodate larger molecules. The starch—Hpid complex is important in food systems. Whether similar inclusion complexes can form with any of the dietary fiber components is not known. 

Although the dipolar and resonating nature of the interaction of amylose and iodine is well established, Schlamowitz173 regards the iodine in a starch complex as being in a predominantly non-polar form, and Meyer and Bern-feld174 refute the helix theory and consider that adsorption of iodine occurs on colloidal micelles in amylose solutions. Most of the experimental facts which Meyer presents can, however, be satisfactorily explained on the helical model. 

Amylopectin Amylopectin is similar to amylose except that the glucose chain has branches. These branches involve linkages at the -CH2OH position ( 6), which makes them a 1 —> 6 linkages. Amylopectin is water-soluble it also interacts with iodine to form a reddish-purple complex. Typically, amylopectin is ten times the size of an amylose molecule. Digestion requires (3-amylase (1 4 linkages) and a second... 

Thus, randomly coiled amylose binds I3 ions, and this interaction is responsible for the helical structure of amylose. Helical amylose arrests iodine and further I3 anions, a process which is cooperative. If the filling of one helix commences, then the filling of another helix proceeds once the former helix is full. The longest available helix has priority in the uptake... 

The interaction of iodine and amylose involves formation of inclusion complexes in which iodine molecules are arranged, endwise and axially, inside a series of helices of a-(l 4)-linked n-glucose residues each helix... 

The parallel between the cyloamyloses and V-amyloses helped to explain the well-known blue colour of starch-iodine complexes a series of intensely coloured complexes of cyclohexaamylose, iodine and metal iodides had chains of iodine atoms in the central cavity of stacks of cyclohexaamyloses. The blue colour was thought to arise from charge transfer interactions amongst the I2 molecules and the linear and ions trapped in the central cavity. 

Some dyes have a specific interaction with certain polysaccharides e.g. Congo red interacts with (l->4) P-D, (l->3) P-D and (l->3)(l->4) p-D glucans and (l->4) p-D xylans (11, 12). Upon flooding the plate with the dye-solution, undegraded polysaccharide will be stained by the dye whereas degradation zones will remain uncoloured. Congo red was also applied directly in the medium with CMC (13). Another classical example is the blue coloured complex that is formed between intact amylose and Lugol s iodine solution. 

The Interaction of Sodium Dodecyl Sulfate, a Competing Ligand, with Iodine Complexes of Amylose and Amylopectin... 

Amylose and amylopectin are the Isotactlc homo-polymers of oc-D-glucose which interact with iodine (13) in aqueous systems to give the characteristic blue coloured complexes. 

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