Deep iodine number

Starch test Iodides are readily oxidized in acid solution to free iodine by a number of oxidizing agents the free iodine may then be identified by the deep-blue colouration produced with starch solution. The best oxidizing agent to employ in the spot test reaction is acidified potassium nitrite solution (cf. reaction 6) ... 

Analysis of the TBPA-Ti complex (39,40) indicates that the binding site for the hormone is located deep inside the channel. The hormone makes extensive interactions with the protein side chains that project into the channel. The 4 -hydroxyl of Ti interacts with a patch of hydroxy-amino acids of the protein while each of the iodines makes contact with a number of hydro-phobic protein residues. The T amino acid side chain functional groups are in appropriate positions to interact with glutamic acid and lysine residues. Thus, this channel provides a favorable environment for each of the characteristic substituents of the thyroid hormone (40). However, because of the Ti orientation disorder in the protein complex, this structural model is not a sensitive measure of the observed correlations between diphenyl ether conformations and binding affinity data. 

The ionization potential of iodine is sufficiently low for it to form a number of compounds in which it is electropositive. It forms I cations, for example, by reaction of solid silver nitrate with iodine solution, and such cations are sufficiently electrophilic to substitute aromatic compounds such as phenol. Iodine also exhibits the interesting property of forming solutions that are violet colored in non-donor type solvents, such as tetrachloromethane, but in donor solvents, such as ethanol or dioxan, there is a strong iodine-solvent interaction, which gives the solution a deep brown color. Even though iodine solutions were commonly used as antiseptic agents, the element is classified as toxic, and care should be taken to avoid eye intrusions or excessive skin contact. 

Iodides react with a number of oxidizing agents in acid solution to yield free iodine, which gives the familiar test with starch. The latter effect involves the production of a deep blue adsorption compound of iodine and starch. 1 When only small amounts of iodine are present, the insoluble blue starch-iodine compound remains in colloidal suspension. 

Carlyle (2001) lists a number of nineteenth century British terms indicating shade and/or soiuce variants of vermilion including Chinese v., carmine v., European v., pale v. deep v. and (Field s) orange v. as well as scarlet v. and extract of v. Typical adulterants of the period are given by Salter (1869) and Standage (1887) these include brickdust and orpiment as well as iron oxide, Persian red and iodine scarlet (qq.vl). Toch (1916) describes permanent v. as well as American quicksilver v. and Trieste v., the latter so called because it was foimd and made in the region. 

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