As a matter of course, cation exchange membranes permit {HEAD ~ selective permeation} of {TAIL ~ cations} alone 
As a matter of course , cation exchange membranes permit { HEAD ~ selective permeation } of { TAIL ~ cations } alone
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL OTH