Synthesis and Self‐Assembly of NCN‐Pincer Pd‐Complex‐Bound Norvalines |
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Authors: | Kazuki Ogata Daisuke Sasano Tomoya Yokoi Dr. Katsuhiro Isozaki Ryota Yoshida Dr. Toshio Takenaka Dr. Hirofumi Seike Dr. Tetsuya Ogawa Prof. Dr. Hiroki Kurata Dr. Nobuhiro Yasuda Prof. Dr. Hikaru Takaya Prof. Dr. Masaharu Nakamura |
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Affiliation: | 1. International Research Center for Elements Science, Institute for Chemical Research, Kyoto University, Uji, Kyoto, 611‐0011 (Japan), Fax: (+81)?774‐38‐3186;2. Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University, Nishikyo‐ku, Kyoto, 615‐8510 (Japan);3. CREST (Japan) Science and Technology (JST), Tokyo, 102‐3531 (Japan);4. Advanced Research Center for Beam Science, Institute for Chemical Research, Kyoto University, Uji, Kyoto, 611‐0011 (Japan);5. JASRI, SPring‐8, 1‐1‐1, Kouto, Sayo, Hyogo 679‐5198 (Japan) |
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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, R1COOH, or amines, R2NH2, to give the corresponding N‐/C‐functionalized norvalines R1‐D /L ‐[PdCl(dpb)]Nva‐R2 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. |
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Keywords: | metalated amino acid metalated peptide palladium self‐assembly supramolecular gel |
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