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Artificial metal enzymes that combine proteins with synthesized unnatural metal complexes as cofactors are attracting attention. The preparation of artificial metal enzymes not only clarifies the behavior of metal ions in biology, but also leads to the development of synthetic chemistry fields such as the discovery of new catalytic reactivity and substrate selectivity that are not observed in nature. In addition, a certain Schiff base zinc (II) complex is known to exhibit antioxidant and anticancer activity, too. Therefore, in this study, we investigated a rapid synthesis method of two known amino acid Schiff base zinc (II) complexes using microwave method and the complexation of zinc (II) complex with chicken egg white lysozyme, which is a relatively low molecular weight protein. Furthermore, investigation of weakly non-covalent intermolecular interaction features between the zinc (II) complexes and lysozyme was also carried out using some spectroscopic measurements.

Based on the potential redox and catalytic ability of oxovanadium complexes, our goal was to characterize the physical properties of two such complexes to be used as mediators for laccase. Computational studies, TD-DFT calculations and docking simulations were performed to elucidate the interaction between laccase and the two anionic complexes (aquabis(oxalato)oxidovanadate(IV) (1) and bis(oxalato)dioxidovanadate(V)) (2), respectively. Electrochemical measurements carried out on anion complexes of 1 and 2 docked into laccase were compared to laccase alone, showing changes in oxidation-reduction potential and current value, especially with the oxovanadium anion of 2. Since both internal tiny magnetic fields of ferromagnetic catalysts and external applied magnetic fields were found in previous investigations to constitute effective ways to improve the oxygen transfer rate, the magnetic susceptibility was measured. A valence change proneness was confirmed with higher valence for the oxovanadium anion of 2, which is in accordance with the electrochemical results.

Single crystals of two achiral and planar heterocyclic compounds, C9H8H3O(CA1) and C8H5NO2 (CA4), recrystallized from ethanol, were characterized by single crystal X-ray analysis, respectively, and chiral crystallization was observed only for CA1 as P212121 (# 19), whereas it was not observed for CA4 P21/c (# 14). In CA1, as a monohydrate, the hydrogen bonds were pronounced around the water of crystallization (O4), and the planar cyclic sites were arranged in parallel to slightly tilted positions. On the other hand, an anhydride CA4 formed a dimer by hydrogen bonds between adjacent molecules in the crystal, which were aggregated by van der Waals forces and placed in parallel planar cyclic sites.

Induced chirality (achiral target in chiral matrix such as proteins) sometimes play a useful role in evaluating supramolecular systems involving biomolecules. Enzymatic fuel cells, which generate electricity via enzymatic redox reactions at electrodes hold a significant potential for sustainable power. Bacterial laccase, a multi-copper oxidase, was used in the cathodic compartment of the enzymatic biofuel cells because of its low redox potential. Three new salen Cu(II) complexes were designed and investigated as mediators. The Schiff base ligands consisted of both a redox-active (anthraquinone) and a photochromic (azobenzene) moiety. The interaction between laccase and a mediator was examined with induced circular dichroism (CD) and the docking tool to observe in which of the laccase domains the mediators bind as well as study the photo-induced tuning of both the cis-trans photoisomerization and orientation by the Weigert effect. Both the electrochemical and photochromic properties are also discussed and compared using density functional theory (DFT), time-dependent (TD)-DFT, and docking simulations.

Metal–organic frameworks (MOFs) have been of particular interest to researchers because of their structural designability, robustness, and rich science arising from uniform porosity. Among them, Hofmann-type MOFs, which are one of the earliest examples of a MOF, have been intensively studied. For the bulk state of Hofmann-type MOFs, their spin transition behavior induced by guest molecules and external stimuli has long been discussed as a key subject. On the other hand, the use of Hofmann-type MOFs as a nanoscale architecture has recently attracted significant attention toward future practical applications, such as stimuli-responsive sensors and switching devices. In this review, we present an overview of the recent development of fabrication of crystalline architectures at the nanoscale including thin films and nanoparticles utilizing Hofmann-type MOFs.

We report the fabrication and characterization of the first example of a tetracyanonickelate-based two-dimensional-layered metal–organic framework, {Fe(py)2Ni(CN)4} (py = pyridine), thin film. To fabricate a nanometer-sized thin film, we utilized the layer-by-layer method, whereby a substrate was alternately soaked in solutions of the structural components. Surface X-ray studies revealed that the fabricated film was crystalline with well-controlled growth directions both parallel and perpendicular to the substrate. In addition, lattice parameter analysis indicated that the crystal system is found to be close to higher symmetry by being downsized to a thin film.

A salen-type Schiff base Zn(II) complex included in human serum albumin (HSA) protein was examined by UV-Vis, circular dichroism (CD), and fluorescence (PL) spectra. The formation of the composite material was also estimated by a GOLD program of ligand&ndash, protein docking simulation. A composite cast film of HSA and Zn(II) complex was prepared, and the effects of the docking of the metal complex on the degradation of protein molecules by mid-infrared free electron laser (IR-FEL) were investigated. The optimum wavelengths of IR-FEL irradiation to be used were based on experimental FT-IR spectra and vibrational analysis. Using TD-DFT results with 6-31G(d,p) and B3LYP, the IR spectrum of Zn(II) complex could be reasonably assigned. The respective wavelengths were 1652 cm&minus, 1 (HSA amide I), 1537 cm&minus, 1 (HSA amide II), and 1622 cm&minus, 1 (Zn(II) complex C=N). Degradation of HSA based on FT-IR microscope (IRM) analysis and protein secondary structure analysis program (IR-SSE) revealed that the composite material was degraded more than pure HSA or Zn(II) complex, the inclusion of Zn(II) complex enhanced destabilization of folding of HSA.

The title compound is composed of a benzene ring linked to an indazole unit by an N=N bond and has high planarity. The diazenyl group adopts a trans (E) conformation., The title azo compound, C16H16N4, was synthesized from 2,6-di­methyl­aniline. The diazenyl group adopts a trans (E) conformation, with an N=N bond length of 1.265 (4) Å. The pyrazole ring is approximately planar. In the crystal, zigzag chains along the b-axis direction with a C(3) is graph-set motif are formed by N—H⋯N hydrogen bonds involving the pyrazole moiety.

The planar achiral title compound has C 2v symmetry and crystallizes in the chiral space group P21., The title compound, C10H10O4, was synthesized from tetra­methyl-1,4-benzo­quinone. In the crystal, the almost planar mol­ecule (r.m.s. deviation = 0.024 Å) forms intra­molecular hydrogen bonds between the aldehyde and hy­droxy groups and exhibits C 2v symmetry. This achiral mol­ecule crystallizes in the chiral space group P21 with inter­molecular O—H⋯O and C—H⋯O hydrogen bonding and C—H⋯π and C=O⋯π inter­actions stabilizing the crystal packing.

In this study, we report the synthesis, characterization, and chiroptical properties of azo-group-containing chiral salen type Schiff base Ni(II), Cu(II), and Zn(II) complexes absorbed on gold nanoparticles (AuNPs) of 10 nm diameters. Induced circular dichroism (CD) around the plasmon region from the chiral species weakly adsorbed on the surface of AuNP were observed when there were appropriate dipole&ndash, dipole interactions at the initial states. Spectral changes were also observed by not only cis-trans photoisomerization of azo-groups but also changes of orientation due to Weigert effect of azo-dyes after linearly polarized UV light irradiation. Spatial features were discussed based on dipole-dipole interactions mainly within an exciton framework.

Chiral crystals were discovered due to spontaneous resolution when enantiomers of 4-phenyldiazenyl-2-[(R or S)-(1-phenylethyl)-iminomethyl]phenol and its racemic mixture were prepared. Using two ligands per molecule, optically active R,R and S,S enantiomers and meso R,S diastereomer of Cu(II) complexes were prepared. Strong chiral recognition was expected for them. Laccase has attracted attention as a catalyst that reduces oxygen to water in a cathode of biofuel cells, which can be effectively mediated by metal complexes. Furthermore, azobenzene can align perpendicularly to the polarization direction of irradiating linearly polarized ultraviolet light (Weigert effect) as well as to the conventional cis-trans photoisomerization accompanying the shift of redox potential. Thus, we also studied the photo-induced control of cis-trans forms and the alignment of these Cu(II) complexes as a mediator to fit laccase appropriately. We discuss photo-induced control on not only electronically but also sterically-favored redox conditions. The meso(R,S)-form of the Cu(II) complex in cis-form was found to be the best at increasing the current of cyclic voltammetry (CV) among the three R,R and S,S enantiomers and the R,S diastereomer of the Cu(II) complexes.

We report a step-by-step route to fabricate the first example of a crystalline oriented metal–organic framework thin film having an anionic inorganic pillar ligand, {Cu(4,4′-bipyridyl)2(SiF6)}. X-ray study and sorption analysis revealed its high crystallinity and porous character.

We have prepared supramolecular systems of chiral Schiff base Ni(II), Cu(II), Zn(II) complexes and colloidal gold nanoparticles (AuNP) of 10 nm diameters. They demonstrated that direct adsorption of chiral Schiff base metal complex on the surface of AuNP owing to observation of clear induced CD spectra for the first time. We observed and discussed induced CD bands on AuNP from chiral Schiff base Ni(II), Cu(II), Zn(II) complexes.

Fabrication of thin films made of metal–organic frameworks (MOFs) has been intensively pursued for practical applications that use the structural response of MOFs. However, to date, only physisorption-induced structural response has been studied in these films. Chemisorption can be expected to provide a remarkable structural response because of the formation of bonds between guest molecules and reactive metal sites in host MOFs. Here, we report that chemisorption-induced two-way structural transformation in a nanometer-sized MOF thin film. We prepared a two-dimensional layered-type MOF Fe[Pt(CN)4] thin film using a step-by-step approach. Although the as-synthesized film showed poor crystallinity, the dehydrated form of this thin film had a highly oriented crystalline nature (Film-D) as confirmed by synchrotron X-ray diffraction (XRD). Surprisingly, under water and pyridine vapors, Film-D showed chemisorption-induced dynamic structural transformations to Fe(L)2[Pt(CN)4] thin films [L = H2O (Film-H), pyridi...

The crystal structures of two azobenzene derivative Schiff base metal complexes (new C44H40CuN6O2 of P-1 and known C44H38MnN6O7 of P21/c abbreviated as Cu and Mn, respectively) were (re-)determined experimentally using conventional X-ray analysis to obtain electron density using a PLATON program. Cu affords a four-coordinated square planar geometry, while Mn affords a hexa-coordinated distorted octahedral geometry whose apical sites are occupied by an acetate ion and water ligands, which are associated with hydrogen bonds. The π-π or CH-π and hydrogen bonding intermolecular interactions were found in both crystals, which were also analyzed using a Hirshfeld surface analysis program. To compare these results with experimental results, a density functional theory (DFT) calculation was also carried out based on the crystal structures to obtain calculated electron density using a conventional Gaussian program. These results revealed that the axial Mn-O coordination bonds of Mn were relatively weaker than the in-plane M-N or M-O coordination bonds.

As resource- and time-saving and environmentally friendly synthetic methods than conventional one in a solution, microwave, and wet mechanochemical synthesis are tested for l -amino acid derivative Schiff base copper(II) complexes. Herein, we systematically compared efficiency (low-temperature, time, and yield (if possible to detect)) for both conventional solution method and microwave or mechanochemical methods. The wet mechanochemical synthesis promoted fast reaction (typically 20 ​min by mechanochemical vs 4 ​h by conventional) by a little amount of solvent for preparations of amino acid derivative Schiff base copper(II) complexes. New crystal structure of a five-coordinated square pyramidal copper(II) complex as one of the products of microwave method was also reported.

The oxygen reduction efficiency of a laccase-modified electrode was found to depend on the chirality of the oligopeptide linker used to bind the enzyme to the surface. At the same time, the electron transfer between the cathode electrode and the enzyme is improved by using a copper(II) complex with amino-acid derivative Schiff base ligand with/without azobenzene moiety as a mediator. The increased electrochemical current under both O2 and N2 proves that both the mediators are active towards the enzyme.

The title indole derivative, C11H11NO2, was synthesized from 1-methyl-1H-indole-3-carboxylic acid and methanol. The molecule is planar as it is situated on a mirror plane present in the space group Pbcm. In the crystal, molecules form three kinds of intermolecular C—H...O hydrogen bonds, resulting in a sheet structure in the ab plane. Parallel sheets interact by C—H...π stacking, stabilizing the crystal packing.

We have investigated linearly polarized UV light-induced molecular orientation due to Weigert effect of composite materials of new six binuclear nickel(II), copper(II), and zinc(II) complexes of two rigid Schiff base ring ligands (L1 and L2) composite materials with methyl orange (MO), an azo-dye, in polyvinylalchol (PVA) cast films. To compare the degree of molecular orientation, two ligands, namely flexible aliphatic cyclohexane (ML1: NiL1, CuL1, ZnL1) and rigid aromatic (ML2: NiL2, CuL2, ZnL2), were synthesized using amine moiety. We have also characterized these complexes by means of elemental analysis, IR, and UV-vis spectra, single crystal or powder X-ray diffraction (XRD) analysis, and so on. Composite materials of ML1 or ML2+MO+PVA were also prepared to separately disperse the solutes in a polymer matrix. For any metal complexes, optical anisotropy (represented as the R parameters) of ML2+MO+PVA was larger than ML1+MO+PVA because of the rigidness of the ligands.

Molecular orientation of dyes must be one of the important factors for designing dye-sensitized solar cells (DSSC). As model systems, we have prepared new hybrid materials composed of azobenzene (AZ) and chiral Schiff base Cu(II) complexes (pn(S)Cu and pn(R)Cu) in polymethyl methacrylate (PMMA) cast films. In addition to experimental results, in order to understand their behavior due to anisotropic alignment of them by linearly polarized UV light irradiation, the so-called Weigert effect, we treated theoretically and discussed based on computational chemistry and mathematical treatments (MD simulation and Bayesian statistics).

We describe the synthesis and sorption properties of a new metal-organic framework (MOF), Fe(H2O)2(bpy)[Pt(CN)4]·H2O (bpy = 4,4'-bipyridine), with a three-dimensional accordion-like structure. Although crystalline oriented MOF thin films reported to date have been mainly limited to a layer-type structure, we succeeded in the fabrication of its crystalline oriented thin film.

The title salt, K+·C13H9O2−·H2O, was synthesized from 5-bromosalicylaldehyde and a phenylboronic acid derivative using the Suzuki–Miyaura cross-coupling reaction (Miyaura & Suzuki, 1979). In addition to the intermolecular interactions between the charged species, two O—H...O hydrogen bonds involving the isolated water molecules further stabilize the crystal packing of the title salt leading to the formation of a three-dimensional framework structure.

The title chiral photochromic Schiff base compound, C21H19N3O2, was synthesized from (R)-(−)-2-phenylglycinol and salicylaldehyde of azobenzene derivative. The molecule exhibits the keto–amine tautomeric form and displays characteristic features of azobenzene derivatives. The diazenyl group adopts a trans (E) conformation, with N=N bond length of 1.260 (2) Å. The hydroxy group is involved in an intermolecular O—H...O hydrogen bond.

Three dinuclear metal complexes (comprised of six-coordinated nNi2L and five-coordinated nCu2L and nZn2L) were confirmed by means of elemental analysis, UV-vis and IR spectra, and single X-ray crystal structural analysis in a spectroscopic study. The stable structures of these nNi2L, nCu2L, and nZn2L complexes in poly(vinylalcohol) (PVA) films were analyzed using UV-vis spectra. The molecular orientation of hybrid PVA film materials after linearly polarized light irradiation was analyzed to obtain the polarized spectra and dichroic ratio. Among the three materials, nNi2L and nZn2L complexes indicated an increasing optical anisotropy that depended on the flexibility of the complexes. We have included a discussion on the formation of the pseudo-crystallographic symmetry of the components in a soft matter (PVA films).