Hi,
I'm performing united atom simulations of sugars and lipids and
comparing calculated properties like C-H dipolar couplings and order
parameters with corresponding results from experiments. To do this I
need to calculate the hydrogen postitions of the hydrogens I'm
interested in, and have previously used the gromacs protonate tool for
this. Since some time this tool seems to be quite broken, so I've
written my own routines for the calculations.
Now to my concern. The gromacs tool seems to have used a fixed H-C-H
angle of 109.5 degrees when adding CH2-group hydrogens. I'm sure that
this is an approximation as good as anything, but shouldn't a better
approach be to let the H-C-H angle vary with the corresponding C-C-C or
C-C-O angle?
I've done some searching regarding this, and I've found these two articles
MASTRYUKOV, V.; OSINA, E. Journal of Molecular Structure. 1977, 36,
127-132.
Dakkouri, M. Journal of Molecular Structure. 1997, 413-414, 133-152.
stating the following empirical relationship between the angles (the
second article is citing the first) as an approximation of the angle
correlations fitted from diffraction data:
HCH=126.1-0.175*CCX
A C-C-O angle of 113 degrees would with this relation give a H-C-H angle
of 106.3 degrees.
Does anyone have any thoughts about this?
Regards
Jon Kapla
--
_____________________________________________________
Jon Kapla
Division of Physical Chemistry
Dpt. of Materials and Environmental Chemistry (MMK)
Arrhenius Laboratory
Stockholm University
SE-106 91 Stockholm
Pos: PhD Student
Phone: +46 8 16 11 79 (office)
Phone: +46 70 304 19 89 (cell)
E-mail: [email protected]
_____________________________________________________
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