Re: [sdpd] Rietveld and Crystallography

[Armel Le Bail <alb...@cristal.org>]

>    Could somedy provide me some informations about Powder
>Diffraction and Rietveld Method usage in pharmaceutical area,
>or a website containing some informations about this application
>of powder diffraction techniques and analysis??

SDPD (Structure Determination by Powder diffractometry) is
more and more applied to pharmaceutical areas. Clues about
that can be seen at :

http://www.icdd.com/
Using the search option with "pharmaceutical" returns 44
entries among which you can find the PPXRD symposium.
This was a strong indication that ICDD felt recently more
concerned by pharmaceutical areas. If you intend to use
powder diffraction, the main ICDD product (the PDF) is for
you. However, be aware that among the 136895 powder
patterns in the PDF, there are only ~24000 organics. A very
curious fact, if you consider the number of organic and
organometallic crystal structures known (>220000).

http://www.cristal.org/iniref.html
In the SDPD database, you may look at the increasing
number of structures of pharmaceutical compounds
determined, as well as at the increasing number of methods
specific to organic compounds (molecule location by
grid-search, Monte Carlo, simulated annealing, genetic
algorithm...).

My opinion is that Powder Diffraction is a tool for identification
and characterization still insufficiently in use in pharmaceutical
areas, by wrong tradition (alternative like NMR is preferred).

Which was first of the egg or the chicken, according to your
answer, you may decide if this underdevelopment is due
to ICDD and the small number of powder patterns from organic
compounds, not allowing easy identification, or if it is because
of too few experts in organic compounds involved in powder
diffraction so that the PDF had no data to enter. A third
explanation is of course the old bad ICDD politics about not
including systematically calculated powder patterns. Improvements
are expected this century, may be...

Best wishes,

ALB

PS - Of course, if you only want to refine a known structure,
the SDPD reduces to the final step (the Rietveld method).


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