Toshiyuki Moriuchi

Anisotropic Electron Transport Properties in Sumanene Crystal

The high electron mobility with large anisotropy was attained in the needle-like single crystal of sumanene, which was indicated by time-resolved microwave conductivity (TRMC) measurement.

Design of Ferrocene-Dipeptide Bioorganometallic Conjugates To Induce Chirality-Organized Structures

The highly ordered molecular assemblies in proteins can have a variety of functions, as observed in enzymes, receptors, and the like. Synthetic scientists are constructing bioinspired systems by harnessing the self-assembling properties of short peptides. Secondary structures such as alpha-helices, beta-sheets, and beta-turns are important in protein folding, which is mostly directed and stabilized by hydrogen bonding and the hydrophobic interactions of side chains. The design of secondary structure mimics that are composed of short peptides has attracted much attention, both for gaining fundamental insight into the factors affecting protein folding and for developing pharmacologically useful compounds, artificial receptors, asymmetric catalysts, and new materials. Ferrocenes are an organometallic scaffold with a central reverse-turn unit based on the inter-ring spacing of about 3.3 A, which is a suitable distance for hydrogen bonding between attached peptide strands. The conjugation of organometallic compounds with biomolecules such as amino acids, peptides, and DNA should provide novel systems that reflect properties of both the ferrocene and the biologically derived moieties. In this Account, we focus on recent advances in the design of ferrocene-peptide bioconjugates, which help illustrate the peptidomimetic basis for protein folding and the means of constructing highly ordered molecular assemblies. Ferrocene-peptide bioconjugates are constructed to form chirality-organized structures in both solid and solution states. The ferrocene serves as a reliable organometallic scaffold for the construction of protein secondary structures via intramolecular hydrogen bonding: the attached dipeptide strands are constrained within the appropriate dimensions. The introduction of the chiral dipeptide chains into the ferrocene scaffold induces the conformational enantiomerization of the ferrocenyl moiety; the chirality-organized structure results from intramolecular hydrogen bonding. The configuration and sequence of the amino acids are instrumental in the process. Regulation of the directionality and specificity of hydrogen bonding is a key component in the design of various molecular assemblies. Ferrocene-peptide bioconjugates also have a strong tendency to self-assemble through the contributions of available hydrogen-bonding donors in the solid state. Some ferrocene-peptide bioconjugates bearing only one dipeptide chain exhibit a helically ordered molecular assembly through a network of intermolecular (rather than intramolecular) hydrogen bonds. The propensity to form the chiral helicity appears to be controlled by the chirality of the dipeptide chains. Organization of host molecules is a useful strategy for forming artificial receptors. The conformationally regulated ferrocene-peptide bioconjugate provides the chirality-organized binding site for size-selective and chiral recognition of dicarboxylic acids through multipoint hydrogen bonds. Metal ions serve a variety of purposes in proteins, including structural stabilization for biological function. The complexation of ferrocene-peptide bioconjugates with palladium(II) compounds not only stabilizes the chirality conformational regulation but also induces conformational regulation of the dipeptide chain through complexation and intramolecular chirality organization. Construction of the chirality-organized ferrocene-peptide bioconjugates is also achieved by metal-directed assembly. These varied examples amply demonstrate the value of ferrocene-peptide bioconjugates in asserting architectural control over highly ordered molecular assemblies.

Highly ordered structures of peptides by using molecular scaffolds

Protein secondary structures such as alpha-helices, beta-sheets, and beta-turns are important in inducing the three-dimensional structure and biological activity of proteins. Designing secondary structure mimics composed of short peptides has attracted much attention not only to gain fundamental insight into the factors affecting protein folding but also to develop pharmacologically useful compounds, artificial receptors, asymmetric catalysts, and new materials. In this tutorial review, we focus on molecular scaffolds employed to induce beta-sheet-like structure in attached peptide chains, thereby creating highly ordered molecular structures, and discuss the versatility of these molecular scaffolds to regulate the attached peptide strands in the appropriate dimensions.

Characterization of ferrocene derivatives bearing podand dipeptide chains (-l-Ala-l-Pro-OR)

Ferrocene derivatives bearing podand dipeptide chains (-l-Ala-l-Pro-OR; R=Me, Et, Pr, CH2Ph) were synthesized and characterized by spectroscopy and X-ray crystallography. The ferrocenes exhibited Cotton effects in the CD spectra to indicate an ordered conformation, which is considered to depend on the intramolecular hydrogen bonds between CO (Ala) and NH (Ala of another strand). The X-ray structural analysis also revealed that such identical intramolecular hydrogen bonding is present in the solid state to orient the podand dipeptide chains in the same direction. A helical molecular arrangement in the crystal packing was observed in the case of the methyl and ethyl esters to form the ferrocenic and hydrophobic columns.

A Dynamically Inverting π‐Bowl Complex

The binding of metals to curved carbon p-surfaces has attracted continuous scientific interest since the discovery of metal complexes of buckminsterfullerene C60. [1–3] Molecules that consist of fragments of C60, that is, buckybowls, open geodesic polyarenes, or p bowls, possess curved carbon psurfaces; examples include corannulene (C20H10) and sumanene (1, C21H12; Figure 1a). [4, 5] From a coordination chemistry

Design and Redox Function of Conjugated Complexes with Polyanilines or Quinonediimines

Because of their potential application as new electrical materials that depend on their redox properties, π-conjugated polymers and oligomers have attracted much attention. Polyanilines, which are chemically stable, are one of the promising classes of conducting π-conjugated polymers. Polyanilines exist in three different discrete redox forms, which include the fully reduced leucoemeraldine, the semioxidized emeraldine, and the fully oxidized pernigraniline base form. The redox-active 1,4-phenylenediamine (PD) and 1,4-benzoquinonediimine, unit molecules of the emeraldine base form, can bind to transition metals to afford novel conjugated complexes. The introduction of metal centers into π-conjugated polymers is expected to dramatically change their functions. In this Account, we describe our ongoing research into the construction of conjugated complexes with redox-active π-conjugated polyanilines and 1,4-benzoquinonediimines. These systems can form architecturally controlled functionalized systems that depend on their dynamic redox properties, resulting in highly selective and versatile electron-transfer reactions and functionalized materials. Complexation with metals (Pd, V, Cu, etc.) occurred via the two nitrogen atoms of the quinonediimine moiety of the emeraldine base form of poly(o-toluidine) to afford the single-strand or cross-linked network conjugated complexes with d,π-conjugation. The complexation of the redox-active π-conjugated 1,4-benzoquinonediimines, unit molecules of the emeraldine base form, with palladium(II) compounds yielded a variety of conjugated complexes. Through regulation of the coordination mode of the quinonediimine moiety, we were able to architecturally control the formation of conjugated bimetallic, polymeric, or macrocyclic complexes. Complexation modulated the redox function of the quinonediimine moiety. Introduced metals act as a metallic dopant, and the complexed quinonediimine is stabilized as an electron sink. Furthermore, chirality could be induced into a π-conjugated backbone through complexation with optically active transition compounds, resulting in chiral d,π-conjugated complexes. We could also modulate the functional properties of conjugated complexes based on the redox states of the redox-active π-conjugated moieties. We also demonstrated how complexes with redox-active π-conjugated molecules can control the architecture of redox-functionalized systems through the metal imido bonds of these systems. Using the one-pot preparation of (arylimido)vanadium(V) compounds from the corresponding anilines, we synthesized binuclear complexes with axial chirality and trinuclear complexes with a tridendritic centrosymmetric structural motif. Such structures showed a strong tendency to self-assemble.

Synthesis of oxosumanenes through benzylic oxidation.

Oxosumanenes were synthesized through benzylic oxidation. The electronic and redox properties were revealed to exhibit the expanded π-conjugation compared to sumanene. Single-crystal X-ray analysis of monooxosumanene showed columnar π-stacking in a concave-convex fashion. Stereoselective trimethylation of the trioxo derivative was performed via 1,2-addition to the carbonyl groups.

A Novel Redox-Active Conjugated Palladium Homobimetallic Complex

The π-conjugated molecule N,N′-bis(4′-dimethylaminophenyl)-1,4-benzoquinone diimine (L2) was incorporated into the palladium(II) complex 1 bearing the N,N′-bis(2-phenylethyl)-2,6-pyridinedicarboxamide ligand, to afford the redox-active conjugated palladium(II) homobimetallic complex 2. An X-ray crystal structure determination of 2 reveals that two palladium complex units are bridged by the quinone diimine moiety to form the C2-symmetrical 2:1 complex with an anti configuration, and that the bridging π-conjugated spacer moieties are aligned along a straight line almost parallel to the a axis, to form the columns of the π-conjugated molecules in the molecular packing. Variable temperature 1H NMR studies of the conjugated complex 2 indicate that the syn configuration is enthalpically more favorable than the anti configuration in CD2Cl2 by 1.0 kcal/mol, but entropically less favorable by 4.5 cal/mol from the van’t Hoff plot. The redox function of the quinone diimine moiety is modulated by complexation with the palladium complex 1. The conjugated complex 2 shows three separate redox waves assignable to the successive one-electron reduction of the quinone diimine moiety and one-electron oxidation process of the two terminal dimethylamino groups. Chemical reduction of 2 in THF with CoCp2 resulted in the appearance of ESR signals with weak 105Pd coupling centered around g = 2.0041. The added electrons are considered to be delocalized over the PdII-quinone diimine d-π* system in the complex.

Hydrogen-bonding-directed molecular assembly of ferrocene bearing dipeptide chains (-l-Ala-l-Pro-NHPyMe) as an organometallic crystal architecture

Abstract The ferrocene 1 bearing the dipeptide chains, - l -Ala- l -Pro-NHPyMe, which was characterized by two intramolecular interchain hydrogen bondings between CO (Ala) and NH (another Ala) of each dipeptide chain to induce the chirality organized structure, was demonstrated to form a 1:2 complex with (1R,3S)-camphoric acid (CA). The single-crystal X-ray structure determination revealed a polymeric cocrystal composed of alternating units of 1 and two CA, which are linked by a network of hydrogen bonds to create the double-helical-like hydrogen-bonded molecular arrangement.

Structural characterization and complexation behavior of ferrocene bearing dipeptide chain (-L-Ala-L-Pro-NHPy)

Ferrocene 1 bearing dipeptide chain (-L-Ala-L-Pro-NHPy) was synthesized and characterized by spectroscopy and X-ray crystallography. The single-crystal X-ray structure determination of the ferrocene 1 revealed that a hydrogen-bonded network is formed in an antiparallel manner to give a highly organized assembly, wherein each molecule is connected to two neighboring molecules through N–H⋯N and N–H⋯O intermolecular hydrogen bonds, forming a seven-membered intermolecularly hydrogen-bonded ring. The ferrocene 1 served as a monodentate ligand to form the 2:1 trans -complex 2 with PdCl 2 (MeCN) 2 . The rotational barrier of the two pyridyl rings in the palladium(II) complex 2 was 10.1 kcal mol −1 .