Stabilities of duplexes and triplexes of dA19 + dT19 with alternating methylphosphonate and phosphodiester linkages.

Results from UV thermal melting, polyacrylamide gel electrophoresis and circular dichroism (CD) experimetns are used to compare stabilities of complexes formed from 1:1 and 1:2 molar ratio mixtures of dA19 or dAP19 (alternating phosphodiester and methylphosphonate linkages on the A chain) with dT19 or dTP19 (alternating phosphodiester and methylphosphonate linkages on the T chain). Complexes formed from 1:1 and 1:2 molar ratio mixtures of dAP19 with dT19 are more stable than the respective unmodified 'parent' complexes, but less stable than complexes of dA19 (17 methylphosphonates on the A chain) + dT19. At 0.1 M Na+ complexes containing dTP19 are less stable than those with dT19, yet more stable than complexes containing the highly modified dT19 (17 methylphosphonates on the T chain). A value of 2.6 kcal/mol base triplets is calculated for delta H of dA19.2dT19-->dA19.dT19+dT19.