  We extend the Bell forced dissociation rate model to take account into
dynamic disorder. The motivation of the present work is from the recent forced
dissociation experiments of the adhesive receptor-ligand complexes, in which
some complexes were found to increase their mean lifetimes (catch bonds) when
they are stretched by mechanical force, while the force increases beyond some
thresholds their lifetimes decrease (slip bonds). Different from our previous
model of force modulating dynamic disorder, in present work we allow that the
projection of force onto the direction from the bound to the transition state
of complex could be negative. Our quantitative description is based on a
one-dimension diffusion-assisted reaction model. We find that, although the
model can well describe the catch-slip transitions observed in the single bond
P-selctin glycoprotein ligand 1(PSGL-1)-P- and L-selectin forced dissociation
experiments, it might be physically unacceptable because the model predicts a
slip-catch bond transitions when the conformational diffusion coefficient tends
to zero.
