Hirohiko Houjou

A new synthetic method for rotaxanes via tandem claisen rearrangement, diesterification, and aminolysis

A novel methodology to make rotaxanes via covalent bond formation has been developed. Rotaxanes composed of crownophanes having two phenolic hydroxy groups as a molecular rotor and an axle having diamide moieties were synthesized in moderate yields via three step processes: tandem Claisen rearrangement, intramolecular diesterification, and aminolysis.

Novel synthesis of macrocycles with chalcone moieties through mixed aldol reaction

Abstract 24-Membered novel macrocycles with chalcone structural moieties and isobutenyl ether linkages in the core have been prepared through mixed aldol reaction.

Twin Salphen: Asymmetric Heterodinuclear Complexes {MaMbL | Ma, Mb = Ni, Cu, Zn} of a Symmetrically Fused Salphen Ligand

Heterodinuclear complexes of a fully pi-conjugated salphen ligand were efficiently synthesized with arbitrary combinations of Ni(II), Cu(II), and Zn(II). The UV-vis spectra of the heterodinuclear complexes were approximately represented by a simple average of the spectra of the corresponding homodinuclear complexes. Systematic analysis of the spectra highlighted weak intracomplex interactions through the pi-conjugated system of the ligand.

Experimental and Theoretical Studies on Constitutional Isomers of 2,6-Dihydroxynaphthalene Carbaldehydes. Effects of Resonance-Assisted Hydrogen Bonding on the Electronic Absorption Spectra

We prepared and characterized a series of mono- and dicarbaldehydes of 2,6-dihydroxynaphthalene that bear potential resonance-assisted hydrogen bonding (RAHB) unit(s). X-ray crystal structures of selected compounds revealed that each salicylaldehyde moiety forms an intramolecular hydrogen bond and that the introduction of formyl groups into either the alpha- or beta-position causes a considerable difference in geometry, which was interpretative from a conventional scheme of resonance hybrids including ionic state. Analyses on NMR chemical shifts suggested that the compounds in solution are present as an equilibrium mixture between closed and open forms with respect to RAHB units. Ab initio calculations indicated that the formation of an intramolecular hydrogen bond strikingly influences the aromaticity of the individual local six-membered ring of naphthalene. The trend of the change in aromaticity was analyzed in connection with the extra stabilization energy of RAHB. In the UV-vis spectra, the beta-formyl derivatives specifically showed a substantial red shift compared to alpha-formyl derivatives. The absorption features were successfully reproduced by TD-DFT calculation, and those data were consistently explained from the effects of RAHB on electronic state of the naphthalenes pi-system. Finally, we pointed out a similarity in the electronic state between RAHB-bearing molecules and cata-condensed aromatic hydrocarbons.

The architecture of dinuclear Ni and Cu complexes: twisted and parallel forms controlled by the self-assembly of Schiff base ligands

Novel dinuclear complexes were synthesized through the self-assembly of macrocyclic Schiff base ligands and either nickel(II) or copper(II) ions. X-Ray structural analysis revealed that the complexes had either a double helix (twisted) structure in which each atom had a distorted square-planar coordination or a non-helical (parallel) structure in which the metals had octahedral coordination. The helical complexes were rather unusual in that their helicity originated not in the coordination centre, but mainly in the linker moieties in the ligand. Several factors influencing the formation of the helical structure are discussed.

Accurate evaluation of the absorption maxima of retinal proteins based on a hybrid QM/MM method

Here we improved our hybrid QM/MM methodology (Houjou et al. J Phys Chem B 2001, 105, 867) for evaluating the absorption maxima of photoreceptor proteins. The renewed method was applied to evaluation of the absorption maxima of several retinal proteins and photoactive yellow protein. The calculated absorption maxima were in good agreement with the corresponding experimental data with a computational error of <10 nm. In addition, our calculations reproduced the experimental gas‐phase absorption maxima of model chromophores (protonated all‐trans retinal Schiff base and deprotonated thiophenyl‐p‐coumarate) with the same accuracy. It is expected that our methodology allows for definitive interpretation of the spectral tuning mechanism of retinal proteins.

Interaction Force of Chitin-Binding Domains onto Chitin Surface

Interaction force of chitin-binding domains (ChBD1 and ChBD2) from a thermostable chitinase onto chitin surface was directly measured by atomic force microscopy (AFM) in a buffer solution. In the force curve measurement, multiple pull-off events were observed for the AFM tips functionalized with either ChBD1 or ChBD2, whereas the AFM tips terminated with nitrilotriacetic acid groups without ChBD showed no interaction peak, suggesting that the detected forces are derived from the binding functions of ChBDs onto the chitin surface. The force curve analyses indicate that the binding force of ChBD2 is stronger than that of ChBD1. This result suggests that ChBD1 and ChBD2 play different roles in adsorption onto chitin surface.

Facile Preparation of a Fully π‐Conjugated Metallopolymer Composed of Fused Salphen Complexes

Novel π-conjugated compounds composed of fused salphen groups as a repeating unit, embedded with four or an indefinite number of zinc nuclei have been synthesized. The solid-state absorption spectra, IR spectra, and powder XRD patterns of these compounds are investigated and compared with those of analogous oligomers. The presumptive polymer contains at least five units of the salphen complex and its assembly is highly ordered in the solid state.

Synthesis and characterization of dinuclear lanthanide(III) and yttrium(III) cryptates of a hexavalent anionic polydentate ligand

Abstract Reaction of tris(2-aminomethyl)amine with bis(hydroxybenzaldehyde) (1) in presence of M(CF3SO3)3 (M=Y, Gd, Tb, Dy, Ho, Er, Tm) in methanol yielded the dinuclear lanthanide(III) and yttrium(III) cryptates [M2L] (2). The structure of [Y2L] was established by X-ray crystallography. Each yttrium ion is in a seven-coordinate environment composed of three imine nitrogen atoms, one apical nitrogen atom, and three oxygen atoms. The dinuclear complexes were found to be a host for Rb+ and Cs+.

Spontaneous macrocyclization via recombination of a Schiff-base linkage

Abstract A macrocyclic compound that has two salenH 2 moieties was synthesized via recombination of an acyclic Schiff base in quite high yield, and was characterized by X-ray crystallography. The recombination occurred in a slow diffusion system of chloroform–methanol, where the starting material may spontaneously form a molecular assembly suitable for the subsequent reaction. This assumption was supported by the crystal structure of an analogue of the acyclic Schiff base.