  For single-file translocations of a charged macromolecule through a narrow
pore, the crucial step of arrival of an end at the pore suffers from free
energy barriers, arising from changes in intrachain electrostatic interaction,
distribution of ionic clouds and solvent molecules, and conformational entropy
of the chain. All contributing factors to the barrier in the initial stage of
translocation are evaluated by using the self-consistent field theory for the
polyelectrolyte and the coupled Poisson-Boltzmann description for ions, without
radial symmetry. The barrier is found to be essentially entropic, due to
conformational changes. For moderate and high salt concentrations, the barriers
for the polyelectrolyte chain are quantitatively equivalent to that of
uncharged self-avoiding walks. Electrostatic effects are shown to increase the
free energy barriers, but only slightly. The degree of ionization,
electrostatic interaction strength, decreasing salt concentration and the
solvent quality all result in increases in the barrier.
