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Fwd: Suggesting CIF data item values

  • To: coredmg@iucr.org
  • Subject: Fwd: Suggesting CIF data item values
  • From: Brian McMahon <bm@iucr.org>
  • Date: Tue, 28 May 2019 11:58:32 +0100
  • In-Reply-To: <bf819614-0861-e955-66e8-c95c486c5b16@chemie.uni-hamburg.de>
  • References: <bf819614-0861-e955-66e8-c95c486c5b16@chemie.uni-hamburg.de>
Dear Core CIF Group members
I am forwarding a query I have received, and would be interested to hearyour thoughts on the proposal.

-------- Forwarded Message --------Subject: 	Suggesting CIF data item valuesDate: 	Mon, 27 May 2019 08:39:54 +0200From: 	Timo Stein <timo.stein@chemie.uni-hamburg.de>To: 	bm@iucr.org

Dear Mr. McMahon,

I'm writing you to kindly enquire about how to suggest new data values that are associated with CIF data items. I found the form 'Suggest a new CIF data item', but I'm not suggesting a new CIF data item, but only a single property for _chemical_absolute_configuration. The values listed within coreCIF 2.4.5 involve:
   * rm - the absolute configuration was assigned on the basis of a     reference molecule, e.g. a co-crystallized molecule of known     absolute configuration   * ad - the absolute configuration was established by anomalous dispersion   * rmad - rm + ad   * syn - absolute configuration of the compound in question is based on     the chiral information of its synthetical precursor and has not been     altered   * unk   * .
I suggest to add the property synad to emphasize that ad has been used to assign a particular absolute configuration _and_ the absolute configuration is known. As an example, one could think of a scXRD experiment using Cu irradiation on a crystal comprised of an /N/-functionalized L-amino acid in trigonal space group /P/32. While the Flack parameter /x/ should show preference for /P/32 over the enantiomorphic space group /P/31, its standard deviation might be too high if a crystal of only mediocre quality containing elements with /Z/ <= 8 is studied.
However, if the chemist can ensure that the stereoinformation on C(alpha) has not been altered during the process of synthesis, purification, and crystallization of the /N/-functionalized L-amino acid, _chemical_absolute_configuration synad would be the most appropriate description on how the absolute configuration was assigned. The absolute configuration 'was established by reference to an unchanging chiral centre in the synthetic procedure' (from syn) and 'confirmed by anomalous-dispersion effects in diffraction measurements on the crystal' (from rmad).
Thank you for consideration of this suggestion.

Yours sincerely
Timo Stein

-- Timo SteinAK Prof. Dr. Michael FröbaDepartment of ChemistryInstitute of Inorganic ChemistryUniversity of HamburgMartin-Luther-King-Platz 6D-20146 HamburgTel: +49-40-42838-6102Fax: +49-40-42838-6348
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