ALPHA-DNA-X - ALPHA-TETRATHYMIDILATES AND BETA-TETRATHYMIDILATES COVALENTLY LINKED TO OXAZOLOPYRIDOCARBAZOLIUM (OPC) - COMPARATIVE STABILIZATION OF OLIGO BETA-[DT]-OLIGO BETA-[DA] AND OLIGO ALPHA-[DT]-OLIGO BETA-[DA] DUPLEXES BY THE INTERCALATING AGENT