Iodine-starch inclusion compounds

Iodine-starch inclusion compounds la 46 Iodine-starch complex lb 195 Iodine substitution under the influence of light la 47... 

Iodine starch inclusion compounds 46 Iodine vapor reagent 46, 64, 78 2-Iodoestrone 66 Ipecacuanha alkaloids 46, 263 Ipecacuanhae radix extract 263 Iron cadons 144, 217, 311 Iron(IIl) chloride reagent 170,216,314 Iron(III) thiocyanate reagent 170 Isoascorbic acid 376 Isoleucine 246,247... 

Detection of Organic Iodine Gomjpounds, The most specific possible detection of organically bound iodine is of particular interest. According to Stahl and Peeiele [228] this is possible directly on a silica gel-starch layer by means of photochemical deiodination. The liberated iodine yields the blue-violet starch inclusion compound and amounts down to 0.5 [xg may be thus visualised. 

If it is desired to stabilize slightly yellow-colored iodine-containing chromatograms this is best done by treating them with dilute starch solution. This produces the well-known blue iodine inclusion compounds and these are stable over a long period. 

Documentation is carried out as soon as the iodine-colored chromatogram zones can be readily recognized. Then the adsorbed iodine can be allowed to evaporate in the fume cupboard or vacuum desiccator, so that the same chromatograms can be subjected to further reactions and separation steps (e. g. SRS techniques, 2-D separations, coupling techniques such as TLC/GC etc.). The chromatogram zones can also be stabilized by spraying with 0.5 to 1 percent starch solution [4, 5] the well-known blue clathrates that are formed (starch-iodine inclusion compounds) remain stable for months. 

The reaction between starch and iodine (or iodine-iodide mixtures) to form an inclusion compound was first reported in 1814 by Colin and de Claubry 131) and has since become familiar to all chemists through its applications in analytical chemistry. Its deep blue colour (kmax 620 nm) has been known for years to result from a linear arrangement of polyiodide within a canal formed by a helical coil of amylose. The helical amylose structure will trap other molecules 132,1331 and other hosts will stabilise polyatomic iodide guests134> 135). 

Thus, despite all the work carried out on starch-iodine, the exact nature of the guest iodine atoms is still not totally resolved. Teitelbaum, Ruby and Marks 156) have examined the compound using Raman and 129I Mossbauer spectroscopy and concluded that the pentaiodide ion 1 was the major chromophore present. However work based on iodine compounds of cyclodextrins 3-134 135) has shown that a variety of polyiodide species is possible, and the starch-iodine inclusion compound could conceivably involve I2 If, I2 I- I2, or I5 species 157). The anhydrous amylose-iodine compound has recently been found to exhibit semiconductor behaviour 158). 

It should be noted that the different structures of amylose and amylopectin confer distinctive properties to these polysaccharides (Table II). The linear nature of amylose is responsible for its ability to form complexes with fatty acids, low-molecular-weight alcohols, and iodine these complexes are called clathrates or helical inclusion compounds. This property is the basis for the separation of amylose from amylopectin when starch is solubilized with alkali or with dimethylsulfoxide, amylose can be precipitated by adding 1-butanol and amylopectin remains in solution. 

Thus the blue inclusion complex becomes visible only when all the hydrogen sulfite has been consumed. According to studies by / . C. Teitelbaum, S. L. Ruby and T. ]. Marks the blue inclusion compound consists of the amylose component of the starch and the polyhalogenide anion Is", this was established by comparing the Raman and I Mofibauer spectra of the blue-black amylose-iodine complex with those of the adduct between trimesic acid hydrate and H Is , the structure of which is known (see figures). 

Amylose. A component (20-30%) of starch surrounded by amylopectin. A. is a linear a-l,4-glucan, Mr 50000-200000 (see figure at starch). Crystalline A. occurs in various polymorphic forms (A, B, C, and V-A.), that differ in conformation and crystal packing. A. is soluble in water and gives the characteristic blue color with iodine-potassium iodide solution (Lugol s solution) (formation of inclusion compounds, traces of iodide ions are necessary for occurrence of the blue color, formation of I5 ions I -1 I I -1). Because of its predominately unbranched structure, A. can be degraded to oligosaccharides both by a- and by /S-amylase. The screw-like (helical) conformation also allows the formation of inclusion compounds with alcohols. 

Amylopectin a component of starch (the other is amylose). A. is a branched, water-insoluble polysaccharide (A/, 500,000-1,000,000) consisting of a main chain of a-l,4-linked D-glucose units with side chains (15-25 D-glucose units) attached a-1,6 to every 8th or 9th glucose. A. forms violet to red-violet inclusion compounds with iodine. It swells in water, and upon heating it forms a paste. 

Iodine-metal alginate compound... Sodium alginate reacts with iodine and under acid gives a blue stained adduct like a starch-iodine inclusion complex. In this paper results for film form metal alginate are presented. The effect of pH on the formation of a blue stained adduct is shown in Figure 4A. At about pH 1 the formation reaches the maximum. The amount of the adduct shows an increase with iodine concentration and... 

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... 

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