effecting hydrogen bonding between mutually complementary portions of {HEAD ~ the first and second series fragments} to form {TAIL ~ a double stranded structure}; and 
to form
effecting hydrogen bonding between mutually complementary portions of { HEAD ~ the first and second series fragments } to form { TAIL ~ a double stranded structure } ; and
OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH