title: Pi-pi stacking assisted binding of aromatic amino acids by copper(II)-aromatic diimine complexes. Effects of ring substituents on ternary complex stability.
abstract: Ternary Cu(ii) complexes containing an aromatic diimine (DA = di(2-pyridylmethyl)amine (dpa), 4,4'-disubstituted 2,2'-bipyridine (Y(2)bpy; Y = H (bpy), Me, Cl, N(Et)(2), CONH(2) or COOEt) or 2,2'-bipyrimidine) and an aromatic amino acid (AA = l-phenylalanine (Phe), p-substituted phenylalanine (XPhe; X = NH(2), NO(2), F, Cl or Br), l-tyrosine (Tyr), l-tryptophan (Trp) or l-alanine (Ala)) were characterized by X-ray diffraction, spectroscopic and potentiometric measurements. The structures of [Cu(dpa)(Trp)]ClO(4).2H(2)O and [Cu((CONH(2))(2)bpy)(Phe)]ClO(4).H(2)O in the solid state were revealed to have intramolecular pi-pi interactions between the Cu(ii)-coordinated aromatic ring moiety, Cu(DA) (Mpi), and the side chain aromatic ring of the AA (Lpi). The intensities of Mpi-Lpi interactions were evaluated by the stability constants of the ternary Cu(ii) complexes determined at 25 degrees C and I = 0.1 M (KNO(3)), which revealed that the stability enhancement of the Cu(DA)(AA) systems due to the interactions is in the order (CONH(2))(2)bpy < bpy < Me(2)bpy < (Et(2)N)(2)bpy with respect to DA. The results indicate that the electron density of coordinated aromatic diimines influences the intensities of the stacking interactions in the Cu(DA)(AA) systems. The Mpi-Lpi interactions are also influenced by the substituents, X, of Lpi and are in linear relationship with their Hammett sigma(p) values with the exception of X = Cl and Br.
authors.affiliation: Unit of Chemistry, Faculty of Engineering, Kansai University, Suita, Osaka 564-8680, Japan.
authors.forename: Tatsuo
authors.initials: T
authors.lastname: Yajima
authors.forename: Reiko
authors.initials: R
authors.lastname: Takamido
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Shimazaki
authors.forename: Akira
authors.initials: A
authors.lastname: Odani
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Nakabayashi
authors.forename: Osamu
authors.initials: O
authors.lastname: Yamauchi
mesh_terms: D024322:Amino Acids, Aromatic / Q000737:chemistry*; D003300:Copper / Q000737:chemistry*; D007097:Imines / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D013056:Spectrophotometry, Ultraviolet; D014961:X-Ray Diffraction
chemical_list: D024322:Amino Acids, Aromatic; D007097:Imines; D003300:Copper