Interactions between tetrahydrofolate and palladium(II) complexes

Interactions between folate derivatives and palladium(II) complexes are monitored in 1 : 1 molar ratio mixtures by circular dichroic spectra. The results are consistent with the following conclusions, i.e., tetrahydrofolate forms a chelate complex with palladium(II) through nitrogens 5 and 10 which is characterized by a unique circular dichroic spectrum. Mixtures of pallodium (II) complexes and dihydrofolate on methylenetetrahydrofolate could not be expected to, nor do they, give rise to similar circualr dichroic spectra for the following reasons: (1) The N5, N10 chelation site of tetrahydrofolate is blocked in methylenetetrahydrofolate, so coordination of a palladium(II) species must occur at some secondary site. (2) The N5, N10 chelation site is available but carbon six of the pteridine ring system is no longer asymmetric in dihydrofolate. Mixtures of dihdrofolate and palladium(II) complexes have no measurable circular dichroic spectra under the experimental conditions used.