This page has been superceded by the Virtual Museum of Minerals and Molecules, by the newly formed Minerals & Molecules Project. --P. Barak, 6 Jun 1998
EDDHA, commonly known as ethylenediaminedi(o-hydroxyphenylacetic) acid, or EHPG (N,N'-ethylenebis-2-(o-hydroxyphenyl) glycine). This molecule offers two amine nitrogens, two carboxylic oxygens, and two phenolic oxygens to satisfy octahedral coordination requirements. Because of the strong bonds between phenolic groups and Fe(III), chelates of this type are much stronger than purely carboxylic chelates. The phenol-Fe(III) bond gives a red to purple color to the ferrated chelate. Because it has two asymmetric carbons, organic synthesis yields three stereoisomers--meso and a racemic mix of the other two, modeled below.
Fe-rac-EDDHA, ball and stick model:
CPK Color Key: white, hydrogen; gray, carbon; red, oxygen; blue, nitrogen; purple, iron
This model shows the near-perfect octahedral coordination of the central Fe atom (purple), with two carboxylate oxygens, two phenolate oxygens, and two amine nitrogens as the apices of the octahedron. The symmetry of the central Fe atom with its nearest neighbors is one of the key factors in chelate stability.
Rotate the model to examine symmetry and to identify the functional groups: ethylenediamine (H2NCH2CH2NH2), phenol (C6H6OH), and acetic acid (CH2COOH).
(Full window model.)
Fe-rac-EDDHA, space-filling model:
This model show that the central Fe atom (purple) is nearly completely concealed by coordinating oxygens and nitrogens. No coordination by additional water (H2O) or hydroxide (OH-) is permitted in this structure, which adds to the stability of this chelate.
Rotate the model to see if there is any opportunity to squeeze another water or hydroxide into coordination with the Fe. (Both water and hydroxide are a little larger than the oxygens in the model.)
(Full window model.)
Virtual reality modeling language, VRML (pronounced ver' mal), is a 3-D mark up language stored in ascii files (as *.wrl, sometimes gzipped for compression) and interpreted by VRML-enabled browsers to render 3-D images. VRML files are generally small and the computational labor of rendering a 2-D image from the 3-D model is done locally on the user's computer, thereby making VRML a web-standard for 3-D.
Advantages are obvious: a 3-D space filling model of FeEDDHA took 280kb of bandwidth as a 35-frame animated GIF, and more as an AVI. In VRML format, the 3-D model is 8kb in size, and the user can manipulate in any manner desired.
More information is available on line at the FAQ of the newsgroup comp.lang.vrml and more VRML "worlds" are available at the VRML Repository. Those interested specifically in chemical models may check out the listing at VRML Repository/Chemistry and other models.
VRML was introduced in 1994 and has gone from v1.0 to 2.0. Browsers/plugins such as Live3D are available for PCs and PowerMacs for v1.0 and many are in beta development for 2.0. Some issues of compatibility will undoubtedly arise. Patience...
-Phillip Barak
This page was last modified by Phillip Barak, Univ. of Wisconsin, on 30 Nov 1997. All rights to text and images reserved.