Thanks again for all the responses to my question about small-molecule
crystallography. I almost regret having sent the student to the
chemist. Trying this at home sounds like a fun afternoon.
On the ccp4 wiki, there was already a section describing how to solve a
small-molecule structure. I have now added a few points on data
collection based on the discussion here.
strucbio.biologie.uni-konstanz.de/ccp4wiki/index.php/Solve_a_small-molecule_structure
Andreas
On 24/03/2014 7:15, esse...@helix.nih.gov wrote:
Hi,
this depends on your equipment. You can mount a 0.1-0.2 mm xtal as if it was
a protein crystal onto a regular litho loop or better yet on a steel pin
that has a glass fibre glued into it. Use superglue to glue the crystal at
one end carefully to the glass fibre.
Then it is easy to mount the crystal as if it was a protein crystal.
Expect to move your detector as close as it is possible without bumping into
things. Hopefully you can get to about 1.4 A (or better but 1.4 is probably
the least resolution you need to get). Try different exposure times and or
x-ray generator currents so that you don't get overloads. Still use 1 deg
oscillation range. Not useful to go higher in my experience.
HKL2000 will work with the small molecule license but even the macro license
should work (but requires a bit more fiddling with some of the parameters).
Use direct methods in shelxs or shelxd(?). Keep in mind that the space group
may be centric or has mirror planes: P21/c is quite common but I would not go
so far as to suggest a space group without having seen some data.
Then use shelxs (or h) to refine the structure. You may find it useful to get
a copy of platon (Prof. Spek). http://www.cryst.chem.uu.nl/spek/platon/
Or wingx: http://www.chem.gla.ac.uk/~louis/software/wingx/
It's doable but takes a bit of time if you have no small molecule
crystallography background.
Ah and before you start, ask the student for elemental analysis results. If
the compound contains very heavy atoms, your CuKa radiation may not be useful.
In that case or perhaps in all cases if you need to switch to Mo radiation
(then resolution is not a problem as in the case of CuKa radiation).
Good luck.
Lothar
