Molecular Design of Artificial Proteins Bearing Novel Structural Motif by Utilizing an Unnatural Amino Acid

本工作的目的是设计和合成人工蛋白质，其由含有非天然配位氨基酸5 '-氨基-2，2'-联吡啶-5-羧酸的肽组成。含有几个非天然氨基酸残基的肽有望与金属离子配位，从而提供具有独特结构基序的人工蛋白质。在多肽的合成中，二肽单元是单独制备的，被引入到常见的固相合成方法中;否则，由于其反应活性较低的氨基，合成困难。用此方法成功地合成了含有3个非天然氨基酸残基的21肽。此外，在吸收光谱中观察到通过肽与铁（II）离子反应形成铁（II）络合物，在541 nm处显示金属-配体电荷转移（MLCT）带。另一方面，如果使用钌（II）离子，则人工蛋白质具有钌三（联吡啶）型络合物作为核心，预期其将呈现光功能，例如发射、光催化和光诱导电子转移能力。由于钌三（5，5 ′-二取代-2，2 ′-联吡啶）配合物的研究较少，我们合成了各种非天然氨基酸衍生物和5，5 ′-二酰胺-2，2 ′-联吡啶的钌配合物，并研究了它们的光化学性质。特别是，这些配合物被发现作为传感器的各种阴离子的强烈结合与他们通过合作的氢键之间的酰胺氢（NH）在三个配体和阴离子。

The purpose of this work is to design and synthesize artificial proteins, which consist of peptides containing an unnatural and coordinating amino acid, 5'-amino-2,2'-bipyridine-5-carboxylic acid. The peptides containing a couple of residues of the unnatural amino acid are expected to coordinate with a metal ion, affording the artificial proteins with unique structural motifs. In the synthesis of peptides, the dipeptide units, which were separately prepared, were introduced into the common solid phase synthetic methods ; otherwise the synthesis was difficult due to its less reactive amino group. The 21-mer peptides with three residues of the unnatural amino acids were successfully synthesized by the methodology. Furthermore, formation of the iron(II) complexes by reacting the peptides with iron(II) ion was observed in absorption spectra, showing Metal-to-Ligand Charge Transfer (MLCT) band at 541 nm. On the other hand, if ruthenium(II) ion was used, the artificial proteins had ruthenium tris(bipyridine) type complexes as the core, which were expected to appear photo-functions, such as emission, photo-catalytic, and photo-induced electron transfer abilities. Since there are, however, few works on ruthenium tris(5,5'-disubstitueted-2,2'-bipyridine) complexes, we synthesized various ruthenium complexes of the unnatural amino acid derivatives and 5,5'-diamide-2,2'-bipyridines and investigated their photochemical properties. In particular, these complexes were found to act as sensors for a variety of anions by strongly binding with them via cooperative hydrogen bonding between the amide hydrogen (NH) in three the ligands and anions.