Porphyrin self-assembly as template for RNA?

The self-assembly of chiral porphyrin molecules HpD, (hematoporphyrin IX de rivative) has been shown to form helical fibers in low salt aqueous conditi ons. The spectroscopic (UV and circular dichroism (CD)), thermodynamic (Tm, differential scanning calorimetry (DSC)) and microscopic (light and scanni ng force microscopy (SFM)) examinations of the HpD properties were performe d individually and in the presence of nucleic acid double strands (15-60 de greesC, 0-50 mM NaCl). The asymmetric HpD molecules themselves at room temp erature show sharp positive or negative CD signals, which increase enormous ly with HpD concentration. The data show strong evidence for the external s elf-stacking interaction of HpD, pure and in the presence of polynucleotide s. At low salt concentration (< 40 mM NaCl, pH 7) the spectra change comple tely by increasing the temperature. At 35 to 40 degreesC RNA-similar spectr a of the pure HpD self-assemblies (without nucleic acids) occur. At higher temperatures the aggregates become unstable and break off. At room temperat ure the helical structure of the fibers could be visualized by SFM investig ations. Molecular modeling analysis offers dynamic arrangements of the self -assemblies from stacks to spiral-like superstructures with increasing temp erature. Hydrogen bonding, electron transferring and electrostatic interact ions determine the shape of the proposed highly flexible arrangements. More over, the interrelation between the HpD stacks and the helix of the polynuc leotides was studied. The calculated low transition energies indicate the i mportance of these structures as a crossing link. All data are discussed in favor of a hypothetical evolutionary matrix role in porphyrin self-assembl y for RNA. Copyright (C) 2001 John Wiley & Sons, Ltd.