  We present an analytical model for the role of hydrogen bonding on the
spin-orbit coupling of model DNA molecule. Here we analyze in detail the
electric fields due to the polarization of the Hydrogen bond on the DNA base
pairs and derive, within tight binding analytical band folding approach, an
intrinsic Rashba coupling which should dictate the order of the spin active
effects in the Chiral-Induced Spin Selectivity (CISS) effect. The coupling
found is ten times larger than the intrinsic coupling estimated previously and
points to the predominant role of hydrogen bonding in addition to chirality in
the case of biological molecules. We expect similar dominant effects in
oligopeptides, where the chiral structure is supported by hydrogen-bonding and
bears on orbital carrying transport electrons.
