  The authors use ab initio molecular dynamics and the density functional
theory+U (DFT+U) method to compute the hydration environment of the manganese
ion in manganese (II) and manganese (III) porphines (MnP) dispersed in liquid
water. These are intended as simple models for more complex water soluble
porphyrins, which have important physiological and electrochemical
applications. The manganese ion in Mn(II)P exhibits significant out-of-porphine
plane displacement and binds strongly to a single H2O molecule in liquid water.
The Mn in Mn(III)P is on average coplanar with the porphine plane and forms a
stable complex with two H2O molecules. The residence times of these water
molecules exceed 15 ps. The DFT+U method correctly predicts that water
displaces NO from Mn(III)P-NO, but yields an ambiguous spin state for the
MnP(II)-NO complex.
