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When I wrote SHELXL many years ago C-H...O hydrogen bonds had not yet
come into fashion, so I made no provision for them. Your suggestion of
using BIND to make an additional bond between the H and O should indeed
turn off the antibumping restraint, the only possible adverse
side-effect would be if you are also trying to place another hydrogen on
the oxygen (in which case the connectivitiy would be wrong). A safer
method would be to assign PART 1 to H and PART 2 to O, then they will
not 'see' each other and no antibumping restraint will be generated.
George
Artem Lyubimov wrote:
I am using SHELX to refine a protein structure where electron density
clearly shows what appears to be a rather strong CH - O hydrogen bond
between two residues (i.e. Met and Asp are within 2.5A of one
another). However, SHELX seems to interpret that as a steric clash and
the two residues are pushed apart (and out of density) in the
refinement. I'm trying different things to convince SHELX that those
atoms indeed belong this close together, but I'd like to ask the pros
for ideas, as well. I would prefer to avoid fixing the coordinates of
the residues, and using BIND to simulate covalent connectivity between
those atoms also seems like a misrepresentation of the situation. So,
is there a way to manually specify an individual hydrogen bond in
SHELX, rather than let the program find it? I can't find anything
about that in the manual. Alternatively, is there a way to selectively
turn off the anti-bumping restraints for a group of atoms? I seem to
remember a brief discussion on the matter in this forum, and the answer
appears to be "no", but I thought I'd ask anyway.
Thanks!
Art
--
Prof. George M. Sheldrick FRS
Dept. Structural Chemistry,
University of Goettingen,
Tammannstr. 4,
D37077 Goettingen, Germany
Tel. +49-551-39-3021 or -3068
Fax. +49-551-39-2582
