Chemical Education Today
Letters The JCE Featured Molecules Editor replies The authors of this letter raise some valid points, although the quote from the Qur’an may be a little bit of overkill, or hubris—truth is a little more elusive than they suggest. The structures that are in the Featured Molecules section (1) are derived from extensive high-level calculations on isolated, nonsolvated molecules and are not derived from crystal or solution structures. The structures that are in the molecules collection are those obtained from a number of starting structures and show a marked similarity between bilirubin and biliverdin. It is clear from looking at the work of the authors of the letter that there are substantial differences between the gas-phase and solution structures. These differences include the spatial arrangement of the dipyrollic and propionate groups, intramolecular hydrogen bonding (or the lack thereof in the gas phase), and the degree of conjugation in the dipyrollic moieties. Calculations at the DFT BLY3P/6-31G(d) level on a model mono-dipyrollic methane shows that the pyrrole groups are non-planar and that there is no intramolecular hydrogen bonding as is the case in solutions.
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The issues raised in the letter provide us with a real teaching opportunity to illustrate the difference between structure in solution and in an isolated molecule, and we will supplement the material in the molecule collection with the results of solution calculations, and note in the Featured Molecules column when those additions have been made. The authors are correct that the (Z,Z)-biliverdin isomer is in fact (Z,Z,Z) and that change will be made on the Web site. Literature Cited
1. Coleman, W. F. J. Chem. Educ. 2006, 83, 1329.
Supporting JCE Online Material
http://www.jce.divched.org/Journal/Issues/2008/Feb/abs202.html Full text (HTML and PDF) with links to cited JCE article William F. Coleman Department of Chemistry Wellesley College Wellesley, MA 02481
[email protected] Journal of Chemical Education • Vol. 85 No. 2 February 2008 • www.JCE.DivCHED.org • © Division of Chemical Education
