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inverted chirality

Bill Ross bross at nas.nasa.gov
Fri Jun 7 20:52:58 EST 1996

AMBER also uses improper torsions to enforce chirality.

A definition from http://www.amber.ucsf.edu/amber/newparams.html:

 Improper torsions. 

   Improper torsions are so named because the atoms involved are not serially
   bonded; rather they are branched: 

                               / \
                              I   L

                         Improper I-J-K-L

   They are additionally used in the united-atom force field model when a
   carbon with an implicit hydrogen is a chiral center; in effect they keep the
   position from inverting (PN=3).

Is anyone still refining united-atom force fields?
My impression is that they may be 'old technology' now.

Bill Ross

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