SINGLE-STRANDED NUCLEIC-ACIDS AS TEMPLATES FOR PORPHYRIN ASSEMBLY FORMATION

Resonance light scattering (RLS) and circular dichroism (CD) spectrosc opies have been used to investigate the interactions of several cation ic porphyrins with poly(dA) and poly(rA). Neither tetrakis(N-methylpyr idinium-4-yl)porphin nor its zinc(II) derivative (H(2)T4 and ZnT4) sho w any tendency to form extended porphyrin assemblies in the presence o f poly(dA). However, the poly(dA) complex of CuT4 involves considerabl e porphyrin self-stacking. In the presence of poly(rA), only ZnT4 of t hese three porphyrin derivatives, fails to assemble. Differences in th e interactions of rans-bis(N-methyl-pyridinium-4-yl)diphenylporphine ( t-H2Pagg) with these two single-stranded nucleic acid polymers are des cribed. Whereas the porphyrin is capable of forming extended assemblie s with either poly(dA) or poly(rA), increasing the salt concentration in the latter system results in a reversal of the induced circular dic hroism spectrum in the Soret region indicating a conformational change of the porphyrin assembly.