In situ UV-VIS detection of the association of water-soluble anionic porphyrin and aromatic bases in aqueous solution at high tempeatures using a capillary flow hydrothermal reactor system.

The association between anionic water-soluble porphyrin and aromatic heterocyclic bases has been investigated to demonstrate the usefulness of a new in situ UV-VIS monitoring method of hydrothermal reactions. Spectral and absorbance changes in the presence of bases were possible to be detected by the new method at temperatures up to 150 degrees C. The association constants (K(ass,1)) were determined from the absorbance-base concentration curves. The logarithmic values of K(ass,1) were proportional to the number of rings of the bases, but this relationship became ambiguous beyond 100 degrees C. This fact indicates that stacking between porphyrin and bases does indeed become weak at high temperatures.