Interactions of Guanine Derivatives with Ethylenediamine and Diethylenetriamine Complexes of Palladium(II) in Solution: Pd Binding Sites of the Guanine Ring and Formation of a Cyclic Adduct, [{Pd(en) (guanine ring)}₄]

Interactions of guanine derivatives with ethylenediamine (en) and diethylenetriamine (dien) complexes of Pd(II) in aqueous solution were investigated by Raman, IR, CD, and NMR (¹⁵N,¹H,³¹P) spectroscopy and by chromatography. The Raman and IR spectra varied with the molar ratio r of Pd to G, and two types (A and B) of coordination of G to Pd were found. Detailed analysis of the Raman and IR spectra including those of ^l8O=C(6)-substituted guanosine showed that N(7) is the binding site in adduct A and both N(7) and deprotonated N(l) are bound to different Pd atoms in the adduct of Pd(dien) at r = 2 (Bl) and the adduct of Pd(en) at r = 1 (B2).¹⁵N NMR spectra supported the binding at N(7) and deprotonated N(l) in the Bl and B2 adducts. Gel chromatography and HPLC suggested that Bl consists of two Pd(dien) molecules and one guanine ring, while B2 is an n/n adduct of Pd(en) and G. ¹H NMR spectra of B2 and its analogues formed with mixtures of guanosine 5'-monophosphate and inosine 5'-monophosphate can be interpreted as being due to a 4/4 cyclic adduct with C₄ symmetry in the G ring configuration. Reflecting the fixed configuration of the G rings, strong CD bands are observed for this adduct.³¹P NMR and vibrational spectra suggested that the phosphate group of guanosine 5'-monophosphate is hydrogen bonded from the amino group of Pd(en), and this hydrogen bonding stabilizes the 4/4 cyclic adduct.