Chemical Education Today
Letters The authors (Pillay and Salih) reply 1. The data in Table 1 of the main article (1) have not been corrected for errors in absorbance and sample preparation. Small changes in these parameters produce an error in the calculated extinction coefficient. For example, for item 1 in Table 1, a 2% drop in absorbance (2.35) and 5% error in sample preparation (42 µM) give a calculated extinction coefficient of 56. This is within the range of analytical and experimental error. The authors get 55, but have not stated what their error is. Another point to note is that extinction coefficient (molar absorptivity) is dependent on temperature and refractive index. We gave an approximate correction for absorbance for changes in temperature (by solar irradiation), but stated clearly that this aspect is unexplored. The absorbance data in Table 1 are uncorrected for slight changes in temperature. However, we indicated that the practitioner should consider this when conducting the experiment. 2. By their own admission, the authors declare that aqueous NaOH produces an absorption maximum at about 430 nm. Figure 1 in the main article shows an absorbance maximum at around 430 nm—so the work was conducted in NaOH. Spectrometers can be set at around 450 nm and adequate measurements can be made at this wavelength. Making a measurement near 450 nm does not imply that the maximum falls at this wavelength. 3. Figure 2 in the supplemental material was meant to be a facsimile of Figure 1 in the main article. We stated clearly that Figure 2S represents typical data for instructors—not for students. Instructors should have no problem in interpreting this figure, and should refer to the main article for further information. 4. Yes, we agree there is more than one photoproduct. The implication in the text is that biliverdin is the most commonly known product that results from photochemical oxidation of bilirubin. The implication is not that it is the only photoproduct. Low yields of biliverdin could be useful for microextraction and microsynthesis studies. 5. No, we disagree that dilute aqueous NaOH is not the best choice. The reason for using aqueous NaOH is that it is
robust, student-friendly, and eco-friendly. Under sound experimental conditions, the kinetics itself is not seriously affected by autoxidation and thermal effects during the experimentation period. 6. Material safety data sheets (MSDS) are widely used in chemical laboratories all over the world. In our case the MSDS state that bilirubin and biliverdin are eye and skin irritants. The authors say otherwise—perhaps; perhaps not. However, we certainly do not want our students to rub bilirubin or biliverdin into their eyes when doing an experiment of this nature. Better to be safe than sorry! 7. We chose bilirubin to demonstrate the practical nature of chemistry. Understandably, there are ongoing debates in clinical circles on the physiological function of bilirubin and biliverdin. We agree that up to date information is necessary and have provided references to satisfy this purpose. Literature Cited 1. Pillay, A. E.; Salih, F. M. J. Chem. Educ. 2006, 83, 1327–1329.
Supporting JCE Online Material
http://www.jce.divched.org/Journal/Issues/2008/Feb/abs201.html Full text (HTML and PDF) with links to cited JCE article A. E. Pillay Department of Chemistry The Petroleum Institute P.O. Box 2533 Abu Dhabi United Arab Emirates
[email protected] Fadhil M. Salih Department of Clinical and Biomedical Physics Sultan Qaboos University P.O. Box 35 Al Khoud 123 Oman
© Division of Chemical Education • www.JCE.DivCHED.org • Vol. 85 No. 2 February 2008 • Journal of Chemical Education
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