Interaction of Sapphyrin with Phosphorylated Species of Biological Interest

A model for the interaction of the water-soluble sapphyrin
derivative 1 with a variety of nucleic acid
species is presented. Three modes of interaction are described: 
The first mode, seen with all the nucleic acid species,
is that of “phosphate chelation”. This mode is exemplified by
a solid state structure of the complex formed between
the monobasic form of cAMP and the sapphyrin species
[2H·2]2+. It involves the specific
chelation of the oxyanion
of a phosphorylated nucleotide or nucleic acid species with the
protonated core of sapphyrin via Coulombic
interactions
that include H-bonding interactions. Spectroscopically, this
interaction is characterized by a visible absorption at
422 nm and corresponds to complexes formed between the dimeric form of
1 and phosphorylated nucleotides. In
the case of double-stranded DNA, this mode of binding shows a
preference for the more flexible copolymer [poly(dA-dT)]2 over [poly(dG-dC)]2.
The second mode involves a hydrophobic
interaction with the nucleobases present
in both monomeric and single-stranded polymeric nucleotides.
Spectroscopically, this nucleotide-dependent
interaction
is characterized by the absorption of the monomeric species of
1 at ca. 450 nm. The third mode involves the
highly
ordered aggregation of 1 on the surface of certain
double-stranded, helical nucleic acids at low phosphate ester
to
sapphyrin (P/S) ratios and is templated by the higher order structure
of these nucleic acid polymers. Spectroscopically,
this mode is characterized by a visible absorption at ca.
400 nm and a large, conservative induced CD signal for
1.