It angered me that the EPA used such poor judgment in trying to ram an amendment through hurriedly while they had the questionable favor of former President Bill Clinton. This was just further evidence of their lack of integrity.

System Suitability
I read with much interest the article published in the September 2001 issue of Today’s Chemist at Work, “Getting the Peaks Perfect: System Suitability for HPLC” [p 38]. As I am working with GC analysis (capillary gas chromatography), I would be interested to know whether there are plans for publication on system suitability for GC. I would be particularly interested in SST criteria for the GC part. I am currently involved in establishing a general validation plan for our laboratory and I think it would be useful to integrate such tests as the SST into it.

Author’s Reply:

System suitability testing is typically for HPLC testing in the pharmaceutical industry under Good Manufacturing Practices. However, the concept can be useful for other industries as well. Thanks for you letter.

Electron Mix-Up
The statements indicating that electron holes move more slowly than electrons, and that hole transport layers are thicker than electron transport layers in “Thinner, Lighter, Better, Brighter” in the November 2001 issue of Today’s Chemist at Work are incorrect. In organic materials, hole mobility is typically much larger than electron mobility and therefore it is the hole transporting layer that is made thicker. Organic materials conduct holes via 1-electron oxidations, and in the case of tertiary amines, this involves a radical cation state. This essentially is the absence of an electron from the HOMO (highest occupied molecular orbital). In the case of electron mobility, an electron is injected into the LUMO (lowest unoccupied molecular orbital) of the material, resulting in an anionic excited state. The propagation of the radical cation state in whole transporting compounds is typically much more facile than the propagation to the anionic excited state. In fact, many researchers use an anode modification layer such as CuPc or other material as a buffer layer on top of the ITO to balance the injection of charge into an OLED.

Author’s Reply:

Thank you for your e-mail to correct the error. I transposed the mobility differences when I was writing the article, and the thickness of the transport layers is shown correctly in the image. Corrections to this and other errors have been made to the Web version of the article.

Mass Spectrometry
I found your article on TOF-MS [“Proteins on Mass (Spectrometry, That Is)”, October 2001, p 30] very interesting, as these instruments seem to be gaining in popularity for protein research. I do have some question as to their ultimate usefulness in drug discovery and was curious about your opinion. Most “small molecule” drugs work by receptor interaction. The molecular dimensions of these receptors are key in deducing correct “key in lock” fit to produce adequate efficacy. How do you envision these ionic analyzers revealing the tertiary in vivo conformation of the target proteins?

Author’s Reply:

You have indeed put your finger on the most pressing limitation in proteomics—that of translating primary sequence information into useful knowledge of final protein geometry. As you well recognize, this is the key to determining the kind of molecular interactions that occur with drugs. A host of researchers in bioinformatics, crystallography, and protein chemistry are working to determine how and to what extent predictions of final structure can be made from the “linear” knowledge of the primary structural pieces. Currently, there are some useful rules of thumb, but no magic Rosetta stone for translating knowledge of the component parts into three-dimensional biological structures. But, of course, without the kind of structural knowledge MS and other sequencing techniques provide, the attempts can’t even begin. For a good discussion of this very issue you can visit the ACS website to read an article in our sister magazine, Modern Drug Discovery: http://pubs.acs.org/subscribe/journals/mdd/v03/i09/html/willis.html.