title: Synthesis and self-assembly of NCN-pincer Pd-complex-bound norvalines.
abstract: The NCN-pincer Pd-complex-bound norvalines Boc-D/L-[PdCl(dpb)]Nva-OMe (1) were synthesized in multigram quantities. The molecular structure and absolute configuration of 1 were unequivocally determined by single-crystal X-ray structure analysis. The robustness of 1 under acidic/basic conditions provides a wide range of N-/C-terminus convertibility based on the related synthetic transformations. Installation of a variety of functional groups into the N-/C-terminus of 1 was readily carried out through N-Boc- or C-methyl ester deprotection and subsequent condensations with carboxylic acids, R(1)COOH, or amines, R(2)NH2 , to give the corresponding N-/C-functionalized norvalines R(1)-D/L-[PdCl(dpb)]Nva-R(2) 2-9. The dipeptide bearing two Pd units 10 was successfully synthesized through the condensation of C-free 1 with N-free 1. The robustness of these Pd-bound norvalines was adequately demonstrated by the preservation of the optical purity and Pd unit during the synthetic transformations. The lipophilic Pd-bound norvalines L-2, Boc-L-[PdCl(dpb)]Nva-NH-n-C11H23, and L-4, n-C4H9CO-L-[PdCl(dpb)]Nva-NH-n-C11H23, self-assembled in aromatic solvents to afford supramolecular gels. The assembled structures in a thermodynamically stable single crystal of L-2 and kinetically stable supramolecular aggregates of L-2 were precisely elucidated by cryo-TEM, WAX, SAXS, UV/Vis, IR analyses, and single-crystal X-ray crystallography. An antiparallel β-sheet-type aggregate consisting of an infinite one-dimensional hydrogen-bonding network of amide groups and π-stacking of PdCl(dpb) moieties was observed in the supramolecular gel fiber of L-2, even though discrete dimers are assembled through hydrogen bonding in the thermodynamically stable single crystal of L-2. The disparate DSC profiles of the single crystal and xerogel of L-2 indicate different thermodynamics of the molecular assembly process.
authors.affiliation: International Research Center for Elements Science, Institute for Chemical Research, Kyoto University, Uji, Kyoto, 611-0011 (Japan), Fax: (+81) 774-38-3186; Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto, 615-8510 (Japan).
authors.forename: Kazuki
authors.initials: K
authors.lastname: Ogata
authors.forename: Daisuke
authors.initials: D
authors.lastname: Sasano
authors.forename: Tomoya
authors.initials: T
authors.lastname: Yokoi
authors.forename: Katsuhiro
authors.initials: K
authors.lastname: Isozaki
authors.forename: Ryota
authors.initials: R
authors.lastname: Yoshida
authors.forename: Toshio
authors.initials: T
authors.lastname: Takenaka
authors.forename: Hirofumi
authors.initials: H
authors.lastname: Seike
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Ogawa
authors.forename: Hiroki
authors.initials: H
authors.lastname: Kurata
authors.forename: Nobuhiro
authors.initials: N
authors.lastname: Yasuda
authors.forename: Hikaru
authors.initials: H
authors.lastname: Takaya
authors.forename: Masaharu
authors.initials: M
authors.lastname: Nakamura
mesh_terms: D000596:Amino Acids / Q000737:chemistry*; D002264:Carboxylic Acids / Q000737:chemistry; D056831:Coordination Complexes / Q000138:chemical synthesis* / Q000737:chemistry*; D018360:Crystallography, X-Ray; D005782:Gels / Q000737:chemistry; D006860:Hydrogen Bonding; D008958:Models, Molecular; D015394:Molecular Structure; D010165:Palladium; D010455:Peptides / Q000737:chemistry*; D053838:Scattering, Small Angle; D013816:Thermodynamics; D014633:Valine / Q000031:analogs & derivatives* / Q000737:chemistry; D014961:X-Ray Diffraction
chemical_list: D000596:Amino Acids; D002264:Carboxylic Acids; D056831:Coordination Complexes; D005782:Gels; D010455:Peptides; D010165:Palladium; C005313:norvaline; D014633:Valine
keywords: metalated amino acid; metalated peptide; palladium; self-assembly; supramolecular gel