Sequential and spatial organization of metal complexes inside a peptide duplex

Constructing multicomponent cooperative functional systems using metal complexes of short flexible peptides

The construction of cooperative systems comprising several units is an essential challenge for artificial systems toward the development of sophisticated functions comparable to those found in biological systems. Flexible frameworks possessing various functional groups that can form weak intra/intermolecular interactions similar to those observed in biological systems have promising design features for artificial systems used to control cooperative systems. However, it is difficult to construct multiple component systems >1 nm using these flexible units by controlling the arrangement of functional units, beginning with the precise control of the cooperative switching of multiple units. In general, it is difficult for oligopeptides to form stable conformations by themselves, although they have designability and structural features suitable for the development of cooperative systems. Increasing the number of coordination bonds in peptides, which are stronger than hydrogen bonds, can be used to control the assembled peptide structures and stabilize their structures owing to the variety of coordination bonds and selective binding affinity. Thus, metal complexes of artificial short peptides have great potential for the development of multicomponent cooperative systems. Based on this concept, we have developed a series of novel metal complexes of flexible peptides and have achieved, to date, cooperative systems, the formation of giant structures, and precise control over the functional units that are the essential bases for designable multifunctional systems that can be regarded as artificial enzymes. In this feature article, we summarize these results and discuss the principal/essential design of artificial systems.

Cyclic Heterometallic Interactions formed from a Flexible Tripeptide Complex Showing Effective Antiferromagnetic Spin Coupling

Developing tunable motifs for heterometallic interactions should be beneficial for fabricating functional materials based on cooperative electronic communications between metal centers. Reported here is the efficient formation of cyclic heterometallic interactions from a complex containing an artificial tripeptide with metal binding sites on its main chain and side chains. X-ray structural analysis and X-ray absorption spectroscopy revealed that the cyclic metal-metal arrangements arise from the amide groups connecting four square-planar Cu^II centers and four octahedral Ni^II centers in a cyclic manner. UV/Vis spectral studies suggested that this efficient formation was achieved by the selective formation of the square-planar Cu^II centers and a crystallization process. Magnetic measurements using SQUID clarified that the cyclic complex represented the S=2 spin state at low temperatures due to effective antiferromagnetic interactions between the Ni^II and Cu^II centers.

Programmable arrangement of metal ions in a cofacially stacked assembly of porphyrinoids toward molecular tags

Cofacial assemblies of metalloporphyrinoides represent a fascinating platform for the novel functional metal arrays to be molecular tags.

Intramolecular strong electronic coupling in a discretely H-aggregated phthalocyanine dimer connected with a rigid linker

This is the first example of a discrete dimer of phthalocyanines in an H-aggregate form. Intramolecular strong electronic coupling was observed between the phthalocyanines electrochemically.

Ligand effects on cooperative supramolecular polymerization of platinum(ii) acetylide complexes

Ligand substitutes exert significant impacts on supramolecular polymerization and macroscopic gelation behaviors of platinum(ii) acetylide monomers.

Dehydrogenative cyclization of N-acyl dipeptide esters for the synthesis of imidazolidin-4-ones

Dehydrogenative cyclization of N-acyl dipeptide esters was developed and imidazolidin-4-ones were obtained in moderate to good yields by using TBHP as oxidant and KI as catalyst under mild conditions.