The molecular mechanism of the action of caffeine (CAF) as a complex-formin
g agent intercepting aromatic ligands that form intercalates with DNA is co
nsidered for the example of a typical ligand proflavine (PF, an acridine dy
e). Heteroassociation between CAF and PF was studied by one- and two-dimens
ional NMR spectroscopy (500 MHz), The concentration (at 298 and 308 K) and
temperature dependences of the proton chemical shifts of the molecules in a
n aqueous solution were studied with the use of a model taking into account
the formation of aggregates with infinite numbers of monomer units in both
self- and heteroassociation reactions, the equilibrium constants for heter
oassociation between CAF and PF were calculated, and the limiting proton ch
emical shifts of aromatic ligands incorporated into associates were determi
ned. The most probable structure of the 1 : 1 CAF-PF heterocomplex in an aq
ueous solution was calculated. Calculations were also performed to determin
e the relative contents of associates of various types in a mixed solution
containing CAF and PF. The special features of dynamic equilibrium between
CAF-PF heteroassociates were analyzed as depending on the concentration of
caffeine in mixed solutions and temperature. The heteroassociation between
CAF and PF molecules decreases the effective concentration and, accordingly
, the mutagenic activity of the acridine dye.