  Here we show, combining a simulation and theoretical study, that
electrostatic correlations typical of multivalent ions can reverse the
selectivity of a biological nanochannel. Our results provide a physical
mechanism for a new, experimentally observed phenomenon, namely the inversion
of the selectivity of a bacterial porin (the E. Coli OmpF) in presence of
divalent and trivalent cations. Also, the differences and similarities between
the driving force for this phenomenon and other similar nano and micro-escale
electrokinetic effects (e.g. inversion of streaming current in silica
nanochannels) are explored.
