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[sdpd] Re: SDPD stagnation

>With respect to the following data, has any attempt been
>made to compare the following with year by year - 
>numbers of a) protein and b) small molecule structure
>solutions?

No protein at all in the SDPD-Database, but we may try
a classification as :
        O = Organic
        OM = Organo metallic
        I = Inorganic
Note that O + OM = the CSD database
and I = the ICSD database

              Year  Total  I    OM    O          ICSD    CSD
             1999    56    25    17    14            25        31
             1998    61    32    19    10            32        29
             1997    55    28    15    12            28        27
             1996    49    20    20     9             20        29
             1995    59    40    14     5             40        19
             1994    46    32    13     1             32        14
             1993    28    12    14     2             12        16
             1992    34    23     6      5             23        11

One may possibly conclude that the trend is at increasing SDPD
of organic compounds. But nothing similar to the 4:1 ratio
of single crystal structures in CSD and ICSD.

>It may not just be due to available powder diffraction software/
>methods (though looking at the numbers below - none of the yearly
>figures are all that large?) - but also the availability of 
>single crystal CCDs and microCrystal synchrotron systems such 
>as the Siemens/Bruker CCD SMART system on Beamline 9.8 at Daresbury.  
>What % of "powder problems" can now be handled as single crystal
>problems using CCDs?

Alternative to SDPD is also electronic diffraction.

A good recent example of synchrotron radiation diffraction data
on a microscopic single crystal (dimensions 12 x 10 x 2 mu m) is :
"The single-crystal structure of the organic superconductor
beta(co)-(BEDT-TTF)(2)I-3 from a powder grain."
Madsen D.  Burghammer M.  Fiedler S.  Muller H.,
Acta Crystallogr. B55 (1999) 601-606. 

You can say that 90% maybe of those old SDPD could now
be realized from one microscopic single crystal. But this
consideration must take account of the difficulty to access
to these "facilities". Nevertheless, SDPD will be more and 
more clearly defined as "small science" as opposed to
synchrotron "big science". I don't know the percentage
of scientists having hardly access to synchrotron, or even to
CCD single crystal, but those scientists may continue for
a while to perform SDPDs from laboratory powder
diffractometers. Unfortunately for the commercial
programs, they have also limited budgets.

Best,


Armel Le Bail - Universite du Maine, Laboratoire des Fluorures,
CNRS ESA 6010, Av. O. Messiaen, 72085 Le Mans Cedex 9, France
http://www.cristal.org/