title: Cyclic tetranuclear and hexanuclear palladium(II) complexes and their host-guest chemistry.
abstract: Cyclic tetrameric complexes have been prepared by the reaction of Pd(en)Cl2 or Pd(dapol)Cl2, or their nitrato analogues, with Na2(5'GMP) in aqueous solution, where en=1,2-diaminoethane, dapol=1,3-diamino-2-propanol, and 5'GMP=guanosine 5'-monophosphate. Addition of certain small molecules containing hydrophobic groups resulted in the expansion of the tetramer to a cyclic hexamer with strong bonding of one guest per hexameric host. At pH 5-6, the guest molecule can be a cation, anion, or neutral, and those species containing trimetylsilyl and t-butyl groups bonded the most strongly. The size of the central cavity of the [Pd(en)(5'GMP)]6 host has been estimated to be 5.2 A. Formation of the host-guest complex caused a large upfield shift (Deltadelta) of 2.5-2.9 ppm in the 1H NMR spectrum of the most highly affected guest protons, which were those in closest proximity to the guanine nucleobases. NOESY spectra were used to determine the interaction sites between the host and the guest. Apparent association constants determined at 26 degrees C and pD 5.4 for the [Pd(en)(5'GMP)]6-DSS and [Pd(en)(5'GMP)]6-t-butanol systems, where DSS is 3-(trimethylsilyl)-1-propanesulfonate anion, were 1.36+/-0.11x10(4) and 2.74+/-0.95x10(4) M(-3/2), respectively. The Pd(dapol)-5'GMP system forms hexameric host-guest complexes, similar in nature to those of the Pd(en)-5'GMP system. The molecular and crystal structures of Pd(dapol)Cl2 are also reported.
authors.affiliation: Department of Chemistry, The University of Texas at San Antonio, One UTSA Circle, San Antonio, Texas 78249, USA. judith.walmsley@utsa.edu
authors.forename: Judith A
authors.initials: JA
authors.lastname: Walmsley
authors.forename: Shourong
authors.initials: S
authors.lastname: Zhu
authors.forename: Antonio
authors.initials: A
authors.lastname: Matilla
authors.forename: Tiffanee G
authors.initials: TG
authors.lastname: Donowick
authors.forename: Jessica E
authors.initials: JE
authors.lastname: Cramp
authors.forename: Jose Manuel
authors.initials: JM
authors.lastname: Tercero
authors.forename: Tatyana
authors.initials: T
authors.lastname: Dalrymple
mesh_terms: D003461:Crystallography; D006157:Guanosine Monophosphate / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D010165:Palladium / Q000737:chemistry*
chemical_list: D010165:Palladium; D006157:Guanosine Monophosphate