Triiodothyronine: The 3'-Iodine Is Proximal to the α-Ring in Crystal Structure Conformation

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Science  18 Feb 1972:
Vol. 175, Issue 4023, pp. 764-766
DOI: 10.1126/science.175.4023.764


The crystal and molecular structure of the thyroid hormone L-triiodothyronine has been determined by x-ray diffraction. The two phenyl rings are almost perpendicular to each other, the acute angle between their normals being 82 degrees. The 3'-iodine is situated proximal to the α-ring, rather than distal as inferred from chemical studies. Theoretical calculations indicate this proximal conformation to be energetically favored over the distal one.