Deep hydroxyl number

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 Ferric Chloride Phenol Test. —Many phenols give typical blue, green, purple, or red colors when a drop of ferric chloride is added to a dilute aqueous solution of the unknown. A number of phenols which do not give this test readily are found to respond when tested in alcoholic solution. Among the carboxy derivatives of phenol, those having the carboxyl group ortho to the phenolic hydroxyl, as in salicylic acid, respond with a typical deep purple color, but many compounds with the carboxyl group in the meta or para position fail to respond to the test. 

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