For what it is worth, SHELXL sets the S-H distance to 1.20A. As with other
bonds to hydrogen, this allows for apparent shortening to fit the electron
distribution and also librational effects. An S-H distance determined by
neutron diffraction would be longer.
George
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
On Mon, 20 Aug 2007, Juergen J. Mueller wrote:
> Dear all,
> using refmac5 to provide H-atoms for a known protein structure the
> distance between CYS-CG and HG is defined to 1.34 Ang. in CYS.cif.
>
> This distance has been critisiced by a non-CCP4 program
> by
> * Poor covalent bond length of 1.33954 for hydrogen atom HG.
>
> In an other library-file CSH.cif the same distance is defined to 1.1 Ang.
> WHATIF uses 1.0 Ang. What is the most correct one?
> Could the CCP4-people comment on this?
>
> (Of course I know hydrogens will not be refined but they are neccessary for
> some
> modeling programs).
>
> Thank you,
> Juergen
>
>
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