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Although enzymes of thermophilic organisms are often very resistant to thermal denaturation, they are usually less active than their mesophilic or psychrophilic homologues at moderate or low temperatures. To explore the structural features that would improve the activity of a thermophilic enzyme at less than optimal temperatures, we randomly mutated the DNA of single-site mutants of the thermostable Thermus thermophilus 3-isopropylmalate dehydrogenase that already had improved low-temperature activity and selected for additional improved low-temperature activity. A mutant (Ile279 → Val) with improved low-temperature activity contained a residue that directly interacts with the adenine of the coenzyme NAD(+), suggesting that modulation of the coenzyme-binding pocket's volume can enhance low-temperature activity. This idea was further supported by a saturation mutagenesis study of the two codons of two other residues that interact with the adenine. Furthermore, a similar type of amino acid substitution also improved the catalytic efficiency of another thermophilic dehydrogenase, T. thermophilus lactate dehydrogenase. Steady-state kinetic experiments showed that the mutations all favorably affected the catalytic turnover numbers. Thermal stability measurements demonstrated that the mutants remain very resistant to heat. Calculation of the energetic contributions to catalysis indicated that the increased turnover numbers are the result of destabilized enzyme-substrate-coenzyme complexes. Therefore, small changes in the side chain volumes of coenzyme-binding residues improved the catalytic efficiencies of two thermophilic dehydrogenases while preserving their high thermal stabilities and may be a way to improve low-temperature activities of dehydrogenases in general.

The structure of membrane lipids in Archaea is different from those of Bacteria and Eucarya in many ways including the chirality of the glycerol backbone. Until now, heterochiral membranes were believed to be unstable; thus, no cellular organism could have existed before the separation of the groups of life. In this study, we tested the formation of heterochiral hybrid membrane made of Bacterial sn-glycerol-3-phosphate-type polar lipid and Archaeal sn-glycerol-1-phosphate-type polar lipid using the fluorescence probe. The stability of the hybrid liposomes made of phosphatidylethanolamines or phosphatidylcholines or polar lipids of thermophilic Bacteria and polar lipids of Archaea were investigated. The hybrid liposomes are all stable compared with homochiral liposome made of dimyristoylphosphatidylethanolamine and dipalmitoylphosphatidylcholine. However, the stability was drastically changed with increasing carbon chain length. Accordingly, "chirality" may not be but chain length is important. From these results, we suggest that the heterochiral hybrid membrane could be used as the membrane lipid for the last universal common ancestor (Commonote) before the emergence of Archaea and Bacteria.

A thin film of trimethylammonium-exchanged perovskite-type niobate ((CH3)3NHSr2Nb3O10) was prepared by casting its exfoliated aqueous dispersion onto a glass substrate. The electric conductivity of a film (3−9 μm thick) was measured in vacuum under the illumination of light (280∼450 nm). Photocurrent raised and decayed slowly in the time range of 103 seconds in response to the on-and-off of an incident light. Atmospheric oxygen accelerated the decay rate of current in the dark. In the absence of oxygen, the decay curve obeyed the equation of stretched exponential relaxation (ip = ip(0) exp(−(t/τ)β). From the dependence of the photocurrent on various parameters such as film thickness, light wavelength, and temperature, the observed persistent phenomena were interpreted according to the following mechanisms: (1) a free electron was photogenerated under the illumination of light most effectively when photon energy corresponded to the edge of a band gap transition; (2) the generated electrons were trapped at...

Electrical conductivity of titania nanosheets was investigated for a single-layered Langmuir-Blodgett (LB) film deposited onto a comb-type electrode (5 or 10 microm (electrode spacing) x 8 mm (electrode width)). The photoresponsive electrical properties of the film were investigated by irradiating with a Xe lamp under various atmospheric conditions. The atmosphere was controlled by introducing either oxygen or nitrogen gases containing different amounts of water vapor. As a result, the LB film behaved as an insulator with little photoresponse under dry atmospheric conditions. It became conductive on illuminating with a Xe lamp under a wet oxygen atmosphere. Conductivity increased with the increase of irradiation time (0-30 min) to attain a stationary value in 1 h. The highest conductive state thus attained lasted for several hours in the dark. The impedance of the film was measured over the frequency range of 1 MHz to 50 Hz by varying the relative humidity of an atmosphere from 0 to 100%. The results were analyzed by assuming an equivalent circuit consisting of one resistance (R) with constant Warburg component (W) and one capacitance (C) in parallel. The R component depended remarkably on the relative humidity, while the C component stayed nearly at the constant value. The dependence of R on water vapor (PH2O) was expressed by R = A[PH2O]n with A = constant and n = -2.9. The results were rationalized in terms of the surface modification of titania nanosheets to hydrophilic nature under the illumination of UV light.

We have attempted to control the helical pitch of a chiral nematic liquid crystal by the use of a photoresponsive chiral metal complex. For this purpose, a novel Ru(III) complex [Ru(acac)2(L)] was synthesized, where acac and L denote acetylacetonato and 1,3-bis-{4-[6-(4-phenylazo-phenoxy)-hexyloxy]-phenyl}-propane-1,3 -dionato, respectively. The complex underwent cis−trans photoisomerization in methanol when under UV (λmax = 360 nm) or visible (λmax = 450 nm) light illumination, respectively. When the complex was doped into a room-temperature nematic liquid crystal (ZLI-1132), it induced a chiral nematic phase. Under illumination with UV or visible light, the helical pitch of the chiral nematic phase could be changed reversibly by up to 50%. Corresponding to this change, the helical twisting power (HTP) of the complex varied between 34.0 and 22.0 μm-1, or between −43.9 and −26.6 μm-1 at 35.0 °C, where the positive and negative signs corresponded to the Λ- and Δ-enantiomers, respectively. This has been the...

The present work pursued a possibility that enantioselectivity was achieved through weak intermolecular interactions between a catalyst and a substrate. For that purpose, we studied the photooxidation of alpha-ethylbenzyl phenyl sulfide catalyzed by a polypyridyl ruthenium(II) complex as a chiral photosensitizer. No covalent bonding was formed between a catalyst and a substrate, because the complexes used ([Ru(phen)(3)](2+) or [Ru(bpy(3))(2+)]) were coordinatively saturated. Enantiomer excess (ee) was attained to be 30% when a chiral photosensitizer was immobilized on montmorillonite clay. It was even improved to 43% in the presence of an additional chiral auxiliary, dibenzoyl-D(+)-tartaric acid. Notably, no enantioselectivity was achieved when the reaction took place in homogeneous solutions. The ab initio calculations were performed on the stability of an associate composed of a catalyst (metal complex) and a product (sulfoxide) to obtain a clue to reaction mechanisms. The calculations suggest that chiral discrimination is achieved even through noncovalent interactions between a substrate and a chiral sensitizer when the attacking direction by a substrate toward a catalyst is limited sterically on a solid surface.

A high-power chiral dopant system involving 6-coordinate metal complexes was designed on the basis of a shape model. Accordingly, a series of mixed 1,3-diketonate complexes of Ru(III), [Ru(acac)2(L-n)], in which acac = acetylacetonate and L-n = dibenzoylmethanate substituted with n octyloxy groups (abbreviated as Ru-n hereafter), was prepared and optically resolved. Their performance as chiral dopants was evaluated in terms of helical twisting power (HTP) in a room-temperature nematic liquid crystal, N-(4-methoxybenzylidene)-4-n-butylaniline (MBBA), by measuring the helical pitch lengths and CD spectra for the induced chiral nematic phases. The Δ- and Λ-enantiomers induced macroscopic left-handed (M) and right-handed (P) helices, respectively, and the (absolute) values for HTP have proven to be remarkably large, e.g. βM = 1.8 × 102 μm-1 in the case of Λ-Ru-2. The induced CD spectra for the dilute MBBA* materials (the asterisk denotes in this paper that MBBA has been doped with a chiral substance) were fit...

Coadsorption studies of chiral tris(1,10-phenanthroline)ruthenium(II) ([Ru(phen)3]2+) and N-methylated cinchona alkaloid cation (MQN+) were conducted on a smectite clay by ion exchange reactions. Photoinduced energy transfer between these cations was confirmed by the photoluminescence spectra, indicating that the cations were co-intercalated in the interlayer space of a smectite. When a ternary ion-exchanged adduct of [Ru(phen)3]2+/MQN+/smectite was employed as a packing material for liquid chromatography, the column proved to resolve a racemic mixture of 1,1‘-binaphthol more effectively than the column packed with a binary adduct of [Ru(phen)3]2+/smectite. The results reflected the enhancement of the chiral discrimination ability through the cooperative interactions among two kinds of preadsorbed chiral cations.

A chiral sensing electrode has been prepared by coating an indium tin oxide (ITO) substrate with a hybrid film of metal complexes and a clay layer (montmorillonite). By applying the combined method of the Langmuir-Blodgett and self-assembly techniques, a monolayer of a water-soluble chiral metal complex (Lambda-[Os(phen)(3)](2+)), which acted as a mediator of oxidizing a target molecule, was fixed electrostatically onto a single-layered clay film. Chiral sensing was demonstrated by monitoring a photocurrent when the electrode was in contact with an aqueous NaClO(4) solution of 1,1'-2-binaphthol. As a result, the S-1,1'-2-binaphthol gave a photocurrent 1.8 times higher than the R-isomer at the applied potential of 700 mV (vs Ag|AgCl|KCl(sat)). Detection limit was determined to be 40 microM from the concentration dependence of a response current. Mechanisms for chiral sensing effect were explained in terms of the stereoselective binding of 1,1'-2-binaphthol with adsorbed Lambda-[Os(phen)(3)](2+) on a clay surface.

Myosin II molecules assemble and form filaments through their C-terminal rod region, and the dynamic filament assembly-disassembly process of nonmuscle myosin II molecules is important for cellular activities. To estimate the critical region for filament formation of vertebrate nonmuscle myosin II, we assessed the solubility of a series of truncated recombinant rod fragments of nonmuscle myosin IIB at various concentrations of NaCl. A C-terminal 248-residue rod fragment (Asp 1729-Glu 1976) was shown by its solubility behavior to retain native assembly features, and two regions within it were found to be necessary for assembly: 35 amino acid residues from Asp 1729 to Thr 1763 and 39 amino acid residues from Ala 1875 to Ala 1913, the latter containing a sequence similar to the assembly competence domain (ACD) of skeletal muscle myosin. Fragments lacking either of the two regions were soluble at any NaCl concentration. We referred to these two regions as nonmuscle myosin ACD1 (nACD1) and nACD2, respectively. In addition, we constructed an alpha-helical coiled-coil model of the rod fragment, and found that a remarkable negative charge cluster (termed N1) and a positive charge cluster (termed P2) were present within nACD1 and nACD2, respectively, besides another positive charge cluster (termed P1) in the amino-terminal vicinity of nACD2. From these results, we propose two major electrostatic interactions that are essential for filament formation of nonmuscle myosin II: the antiparallel interaction between P2 and N1 which is essential for the nucleation step and the parallel interaction between P1 and N1 which is important for the elongation step.

When a chloroform solution of a dicyano(diimine)platinum(II) complex, [Pt(CN)2(5,5‘-dinonyl-2,2‘-bipyridine)], was spread onto pure water, a reversible surface pressure−molecular area curve was obtained. The surface pressure began to increase steeply from 0 at a molecular area of 0.61 nm2 molecule-1. On further compression, the monolayer was stable at 0.2 nm2 molecule-1 and 30 mN m-1. In such a highly compressed state, the complex was thought to orient its planar ligand 2,2‘-bipyridine perpendicular to the water surface. The floating monolayer was vertically deposited onto a hydrophobic quartz substrate as an X-type film. The absorption spectra of the deposited films showed a broad peak at 480 nm, while that band was absent in the solution spectrum. The emission spectra of the films exhibited a broad band around 600 nm. The excitation spectra monitored at 600 nm coincided well with the absorption spectra. The results were interpreted in terms of the formation of the molecular aggregate, in which the plati...

Electric dichroism measurements have been performed on an aqueous dispersion of unilamellar titanium oxides produced by the exfoliation of the following three kinds of titanium oxides: (A) lepidoc...

The following six types of Ru(II) complexes were synthesized with an aim to develop a monolayer with chiral discrimination: 1 [Ru(bpy)2(4-C11bpy)](ClO4)2 (bpy = 2,2‘-bipyridine, 4-C11bpy= 4-methyl-4‘-undecyl-2,2‘-bipyridine); 2 [Ru(bpy)2(4,4‘-dC11bpy)](ClO4)2 (4,4‘-dC11bpy = 4,4‘-diundecyl-2,2‘ -bipyridine); 3 [Ru(bpy)2(5-C11bpy)](ClO4)2 (5-C11bpy= 5-methyl-5‘-undecyl-2,2‘-bipyridine); 4 [Ru(bpy)2(5,5‘-dC11bpy)](ClO4)2 (5,5‘-dC11bpy = 5,5‘-diundecyl-2,2‘-bipyridine); 5 [Ru(bpy)2(4-C18bpy)](ClO4)2 (4-C18bpy= 4-methyl-4‘-octadecyl-2,2‘-bipyridine); 6 [Ru(bpy)2(4,4‘-dC18bpy)](ClO4)2 (4,4‘-dC11bpy = 4,4‘-dioctadecyl-2,2‘-bipyridine). These complexes possess one or two alkyl chains at 4,4‘- or 5,5‘-positions of the 2,2‘-bipyridine ligand. A traditional amphiphile is a linear molecule with a polar head attached by one or two alkyl chains, whereas the present complexes cover both traditional (1, 2, 5, and 6) and nontraditional amphiphilic molecules (3 and 4). The monolayer behavior of these Ru(II) complexes on ...

Stacked and single-layered lepidocrocite-type titanium dioxides (hereafter denoted as single-layered and stacked TiO2's, respectively) have been investigated by using first-principles calculations within density functional theory. The crystal structures, electronic structures, dielectric properties, and mechanical properties have been studied. The validity of the present theory was confirmed by reproducing the experimental properties of known bulk TiO2 polymorphs (rutile and anatase). As for a single-layered lepidocrocite-type TiO2, the optimized structural parameters agree well with the reported data of an exfoliated nanosheet of Ti0.91O2 or Cs0.7Ti1.825O4□0.175 (□ = vacancy). Single-layered TiO2 is slightly less stable than rutile and anatase. The band gap of single-layered TiO2 is 3.15 eV, which is larger than those of rutile and anatase due to a quantum size effect in a two-dimensional structure with a thickness less than 1 nm. The dielectric constant of the single-layered lepidocrocite-type TiO2 is h...

This work aims at understanding the formation and stability of a layered structure of brucite mineral [Mg(OH)2] via density functional calculations. Because Mg−O−Mg bond formation from a hydrolyzed...

We have developed a novel method of modifying a solid surface with a single-layered film of anionic phyllosilicate as an anchor of cationic functional molecules. According to the method, a hybrid film of octadecylammonium and montmorillonite layer was deposited onto a Si substrate by the Langmuir−Blodgett method. Thereafter the Si substrate was immersed in methanol to remove an organic layer, leaving a single-layered montmorillonite film. As a final step, a cationic chiral molecule, Δ-[Ru(phen)3]2+ (phen = 1,10-phenanthroline), was self-assembled from its aqueous solution onto the single-layered montmorillonite film. The thickness of a single-layered montmorillonite film was estimated to be ca. 1.5−1.6 nm by atomic force microscopy observation. The thickness of the film increased to ca. 2.6−2.7 nm after the self-assembly treatment. The results were consistent with the analyses of interference oscillation patterns of specular X-ray reflectivity (SXR) curves. From the analyses of SXR curves, the thickness o...

Different spectroscopic and photoelectrochemical behaviors were observed when racemic and enantiomeric [Ru(bpy)3]2+ complexes were intercalated in the interlayer of K4Nb6O17, even for the same intercalation amount. The results are interpreted in terms of the stronger interaction between racemic [Ru(bpy)3]2+ molecules in the interlayer spaces of K4Nb6O17. The faster emission decay and lower photocurrent of the racemic [Ru(bpy)3]2+−K4Nb6O17 compound compared to the enantiomeric ones suggest that stronger concentration quenching exists between the racemic [Ru(bpy)3]2+ ions in the interlayer of K4Nb6O17. Combining the spectroscopic and photoelectrochemical results, the racemic [Ru(bpy)3]2+ ions are considered to intercalate more densely than the enantiomeric [Ru(bpy)3]2+ ions in the interlayer of K4Nb6O17, even for the same intercalation amount. Two cationic dyes were also directly intercalated into K4Nb6O17. The spectroscopic and photoelectrochemical behaviors of the dye−K4Nb6O17 compounds were investigated.

The effect of a floating stearate monolayer on the formation of Mg−Al-hydrotalcite (Mg−Al-LDH) has been studied. A subphase was an aqueous solution of Mg(NO3)2·6H2O (1.6 × 10-3 M) and Al(NO3)3·6H2O (5.3 × 10-4 M) adjusted at pH = 10.5 by 1.0 M NaOH. Templating effects were studied in the following two ways. First, we spread a chloroform solution of stearic acid onto the above subphase and waited 6 h at zero surface pressure (0.51 nm2 molecule-1). After the surface was compressed to 20 mN m-1 (0.26 nm2 molecule-1), the floating film was deposited onto mica as a Z-type film (method 1). Second, we spread the same chloroform solution onto the subphase and started to compress the surface to the molecular area (0.40−0.20 nm2 molecule-1) after 30 min. The floating film was maintained at the constant surface pressure for 6 h. Thereafter, it was deposited onto mica as a Z-type film (method 2). From the atomic force microscope (AFM) images of the films, it was concluded that the largest thin crystals (ca. 3 × 10 μm...

Molecular dynamics (MD) simulations have been performed to study the flexibility of smectite clay minerals. We aim at the quantitative understanding of the mechanical behavior of a single clay layer in a completely exfoliated state. The repeating unit of a clay layer is taken to be ao = 0.52 nm and bo = 0.902 nm with formula of 2Na1/3 Al2[Si11/3Al1/3]O10(OH)2 which corresponds to that of beidellite. When the size of the basic cell (A = 9.3 nm, B = 2.6 nm, and C = 5 nm) (denoted by A-type cell) is reduced by 3−40% in the A-direction, the stationary structure of a clay layer is obtained as a curved sheet with a 2:1 smectite-type layer structure. In such a curved state, the layer experiences a stress of 0.5−0.7 GPa. The layer structure of a clay fractures when the size of the same basic cell is reduced by more than 40%. The bending constant is estimated for a curved layer by plotting the inverse of the average radius against stress. The similar calculations are performed by reducing the size of the basic cel...

Formation of hybrid monolayers of alkylammonium cations and clay particles at the air−water interface has been studied by surface pressure−molecular area (π−A) isotherm measurements, atomic force microscopy (AFM), and infrared (IR) spectroscopy. The π−A isotherm of a monolayer of octadecylammonium chloride (ODAH+Cl-: C18) on a clay suspension in a Langmuir−Blodgett trough approaches that of ODAH+Cl- on pure water when the amount of clay in the suspension decreases from 100 to 1 ppm. The AFM images of the films reveal hybrid monolayers with clay particles. At 0 mN m-1 the film is only partially covered with clay particles. As the molecular area decreases, the clay particles come closer and closer to each other in the film until they touch each other. Then the surface pressure increases. The IR spectra of multilayer films of ODAH+ and clay (3−10 layers) reveal a linear increase of the amount of the alkylammonium cations with the number of deposited layers. The area per ODAH+ cation in the film estimated fr...

Energy transfer from tris(4,7-diphenyl-1,10-phenanthroline)ruthenium(II) perchlorate (denoted by Ru(II)) to tris(4,7-diphenyl-1,10-phenanthroline)osmium(II) perchlorate (denoted by Os(II)) has been studied in cast and Langmuir−Blodgett (LB) films. The work is focused on the packing effects of chiral metal complexes on energy-transfer rates. Three kinds of films were prepared: a cast film of a 100:1 mixture of Λ-Ru(II) and Λ-Os(II) (or Δ-Os(II)) (sample 1), a Y-type LB film of a 100:1 mixture of Λ-Ru(II) and Λ-Os(II) (or Δ-Os(II)) (sample 2), and an alternative Y-type LB film of Λ-Ru(II) and Λ-Os(II) (or Δ-Os(II)) monolayers (sample 3). In all of these samples, stearic acid (SA) is added at a molecular ratio of [SA]/[Ru(II)] = 3 to stabilize a monolayer state. From the analyses of the decay curves of excited Os(II) (denoted by Os(II)*), the apparent unimolecular energy-transfer rate constant from excited Ru(II) (denoted by Ru(II)*) to Os(II), k2, is determined. As a result, k2 is found to be larger for Λ-...

Monolayer properties of a chiral amphiphilic ruthenium(II) complex, [Ru(phen)2L]2+ (phen, 1,10-phenanthroline; L, 4,4‘-dicarboxyl-2,2‘-bipyridyl didodecyl ester), have been investigated by measurin...

A clay−metal complex multilayer film was prepared by the Langmuir−Blodgett technique. A monolayer of an amphiphilic ruthenium(II) complex, [Ru(phen)2(dC18bpy)](ClO4)2 (phen = 1,10-phenanthroline, dC18bpy = 4,4‘-dioctadecyl-2,2‘-bipyridyl), was formed on an aqueous suspension of hectorite clay (Li-HT). The monolayer acted as a template for adsorption of a clay particle. A hybrid monolayer of a clay and a metal complex was transferred onto a hydrophilic glass plate to form a Z-type multilayer film. X-ray diffraction, UV−visible and FT-IR absorption spectra, and Brewster angle and atomic force microscopic (AFM) measurements confirmed the formation of an ordered film of [Ru(phen)2(dC18bpy)]2+/hectorite with the layer thickness of 5.4 nm.

Electrochemical scanning tunneling microscopy (STM) observations have been performed on a highly ordered pyrolytic graphite (HOPG) electrode modified with a cast film of hydrotalcite (HT) crystal ([Mg6Al2(OH)16]3/4CO3·1/2Cl·2H2O). The electrode was in contact with an aqueous solution of 5 mM Na3[Fe(CN)6] and 0.1 M Na2SO4 at 600 mV (vs Ag/AgCl). The STM image of the electrode showed a two-dimensional lattice with a = 1.40 ± 0.04 nm, b = 1.85 ± 0.04 nm, and α = 63 ± 3°. One bright spot in the image was present at every 3.4 [Mg6Al2(OH)16]2+ units, leading to the conclusion that the spot represented a [Fe(CN)6]3- ion adsorbed on a crystal surface. At 81 mV (vs Ag/AgCl), the STM image exhibited a two-dimensional lattice with a = 1.74 ± 0.04 nm, b = 1.83 ± 0.04 nm and α = 60 ± 3°. This was ascribed to the lattice made by a mixture of [Fe(CN)6]3- and [Fe(CN)6]4- on a HT surface. At −200 mV (vs Ag/AgCl), the STM image showed a two-dimensional lattice with a = 1.94 ± 0.04 nm, b = 1.90 ± 0.04 nm and α = 60 ± 3°, wh...

Atomic force microscopy (AFM) and scanningtunnel microscopy (STM) observations have been performed on the surfaces of a hydrotalcite (HT) crystal ([Mg 6 Al 2 (OH) 16 ](CO 3 ) 1/2 .Cl.2H 2 O) and HT crystals ion-exchanged with [Fe(CN) 6 ] 3- and [Fe(CN) 6 ] 4- (denoted by HT-[Fe(CN) 6 ] 3- and HT-[Fe(CN) 6 ] 4- , respectively). The AFM image of a HT crystal surface in contact with an aqueous solution of 0.1 M Na 2 SO 4 shows two-dimensional periodicity with the unit lattice of a = 0.31 ± 0.02 nm, b = 0.31 ± 0.02 nm, and α = 58 ± 3°. This corresponds to the lattice made by the external hydroxyl groups on a basal plane. No ion-exchanged anion was observed by the AFM method, indicating that an external anion is so weakly bound to a surface that it is removed under the scanning operation of an AFM tip. The STM image of the same crystal under air shows a two-dimensional lattice with a = 0.75 ± 0.04 nm, b = 1.10 ± 0.03 nm, and α = 70 ± 3°. One bright spot in the image exists at every 1.1 [Mg 6 Al 2 (OH) 16 ] 2+ unit, leading to the conclusion that the spot represents a chloride ion adsorbed on a surface. The STM image of the same crystal at less negative bias voltage exhibits a different two-dimensional lattice with a = 0.62 ± 0.03 nm, b = 0.62 ± 0.03 nm, and α = 65 ± 3°. This is ascribed to the lattice made by the aluminum atoms at the octahedral sites inside a layer. The STM images of HT-[Fe(CN) 6 ] 3- and HT-[Fe(CN) 6 ] 4- crystals in contact with an aqueous solution of 0.1 M Na 2 SO 4 show the two-dimensional lattices of a = 1.43 ± 0.06 nm, b = 1.86 ± 0.06 nm, and α = 90 ± 4° and a = 2.20 ± 0.06 nm, b = 2.20 ± 0.06 nm, and α = 75 ± 3°, respectively. These are ascribed to the molecular layers of [Fe(CN) 6 ] 3- and [Fe(CN) 6 ] 4- on a surface, respectively. The causes for the ordered molecular adsorption are discussed.

A 2:1 smectite-type clay containing thiol groups on a basal plane was synthesized by reacting nickel chloride with (3-mercaptopropyl)trimethoxysilane in an alkaline methanol/water solvent. The material (denoted as an HS-Ni layer) was revealed to be self-assembled on a gold surface. The process was confirmed by the mass increase of a gold electrode with a quartz crystal microbalance (QCM) when the electrode was immersed in a chloroform suspension of an HS-Ni layer. The nanoscale images of a gold surface modified with an HS-Ni layer were obtained with an atomic force microscope (AFM). The surface was covered with a single layer of the platelets of about 30 nm in diameter and 1.6 nm in thickness. When the cyclic voltammogram was measured on an electrode modified with such a layer, the reversible redox peaks were observed in the potential range 0−300 mV (vs SCE). The peaks were ascribed to the reduction-oxidation of nickel(II)/nickel(I) couple. From the Coulometric measurements, the fraction of the electroact...

The monolayer behavior and formation of Langmuir−Blodgett (LB) films were compared between the vinyl monomers of silver(II) tetraphenylporphyrin (AgTPP) and their polymers. In both cases, eicosanoic acid was mixed at [eicosanoic acid]/[AgTPP unit] = 1.5 ratio to reduce the aggregation of the porphyrins. From the isotherms of the monolayers at an air−water interface, the porphyrin moieties in the monomers occupied a larger area than those in the polymers. It indicated that the porphyrin groups were more compact in the polymers because they were attached to a polymer chain. Applying the electron spin resonance and polarized UV−vis absorption spectroscopies for the LB films deposited on a hydrophobic glass plate, the orientation of the AgTPP moieties was estimated. As a result, three orientations of porphyrin planes existed in the monomer films: the angle between the film normal and the transition dipole (or the porphyrin plane), φ, was 90° for one orientation and 39−59° for the other two orientations. Two ...

A chiral amphiphilic ruthenium(III) complex, [Ru(acac)2(C12-acac)] (acac = 2,4-pentanedionato, C12-acac = 3-dodecyl-2,4-pentanedionato), has been synthesized. The complex was resolved into pure optical isomers by being eluted with methanol on a column packed with an ion-exchange adduct of Δ-[Ru(phen) 3 ] 2+ (phen = 1,10-phenanthroline) and a synthetic hectorite clay. The surface pressure-molecular area (π-A) curves of the pure enantiomer and the racemic mixture were obtained in the temperature range 10-30 °C. The π-A curve of the pure enantiomer was little affected by the change of temperature, while that of the racemic mixture was displaced toward the larger molecular area with the increase of temperature. The pure enantiomer was concluded to form a more packed monolayer than the racemic mixture. When the monolayer of either the A- or A-enantiomer was formed on a subphase containing Δ-[Ru(phen) 3 ]Cl 2 , the molecular area ofthe monolayer was expanded due to the binding of Δ-[Ru(phen) 3 ] 2+ in a stereoselective way. The AFM images of the chiral and racemic monolayers deposited on mica at 20 mN m -1 showed that the chiral molecules formed an oblique lattice (a = 0.59 nm, b = 0.55 nm, and φ = 63 °C), while the racemic mixture exhibited no two-dimensional surface order.

The adsorption behaviors of tris(1,10-phenanthroline)metal(II) ([M(phen)3]2) by saponite clay have been simulated by the Monte Carlo method. A two-dimensional sheet of linked [SiO4]4- and [AlO4]5- tetrahedra is used for the model tetrahedral sheet of a saponite clay. The thermal distributions of the configurations are obtained using the Metropolis algorithm at 300 K for the systems which have racemic or enantiomeric metal complex molecules intercalated between two sheets. For adsorption within the cation exchange capacity (CEC), the interlayer distance at the thermal equilibrium is obtained to be 10.5 A for both the racemic and enantiomeric chelates. For adsorption over the CEC, the interlayer distance is 18.5 and 20.7 A for the racemic and enantiomeric chelates in the presence of SO42- anions, respectively. The racemic mixture with SO42- has a mean binding energy 31.1 kJ/mol lower than that of the pure enantiomer. In both cases, the adsorbed molecules form a bimolecular layer with the anions at the middl...

Stereochemical effects on monolayer formations have been studied at an air−water interface for the racemic mixture and enantiomer of [Ru(dpp)3](ClO4)2 (dpp = 4.7-diphenyl-1,10-phenanthroline). Stearic acid (SA) was added to reduce the cohesive interaction of the Ru(II) complexes. The ratio of SA to Ru(II) complex, [SA]/[Ru], was varied from 0 to 4. At [SA]/[Ru] = 0 and 1, the “lift-off” area per molecule at which the surface pressure increased from zero was smaller for the racemic mixture than for the enantiomer. The results indicated that the racemic mixture of the Ru(II) complex formed a more compact monolayer than the enantiomer. There was no difference observed in the surface pressure−molecular area (π−A) curves at [SA]/[Ru] larger than 3. The monolayer was transferred onto a hydrophobic glass or silicon wafer substrate as a Langmuir−Blodgett (LB) film of Y-type. At [SA]/[Ru(II)] = 1, the d(001) spacing of the film was determined by X-ray diffraction measurements, leading to d(001) = 50.4 and 37.8 A f...

A thin film was formed by spreading a chloroform dispersion of a hydrophobic clay−organic complex at an air−water interface. The clay−organic complexes were prepared by reacting synthetic saponite ...

Monte Carlo simulations are used to compare the binding states of tris(1,10-phenanthroline)metal(II) ((M(phen) 3 ] 2+ ) and tris(2,2'-bipyridyl)metal(II) ([M(bpy) 3 ] 2+ ) bound to a clay. A pair of [M(phen) 3 ] 2+ or [M(bpy) 3 ] 2+ complexes is placed on the model surface of a silicate sheet. The surface is composed of linked [SiO 4 ] 4- and [AlO 4 ] 5- tetrahedra

Monte Carlo simulations are used to investigate the intercalation structures of a metal complex within a smectite clay. The investigated model system [M(phen) 3 ] 2+ (phen=1,10-phenanthroline) intercalated between two linked [SiO 4 ] 4- and [AlO 4 ] 5- tetrahedra sheets

The adsorption of tris(1,10-phenanthroline)metal(II) ([M(phen) 3 ] 2+ ) by a clay is studied with Monte Carlo simulations. A two-dimensional sheet of linked [SiO 4 ] 4- and [AlO 4 ] 5- tetrahedra is used for the model tetrahedral sheet of a clay. The thermal distributions of the configurations are obtained using a Metropolis algorithm at 300 K

The binding structures of enantiomeric and racemic [M(phen) 3 ] 2+ (M=Ru, Fe; phen=1,10-phenanthroline) complexes with sodium montmorillonite were studied by means of X-ray diffraction and electric dichroism measurements. The electron density curves along the c axis of a clay layer were determined for the powder samples of clay-chelate adducts. At maximum adsorption, the enantiomeric and racemic chelates formed the single-molecular and double-molecular layers in the interlayer spaces, respectively

An apparatus for measuring stopped-flow electric dichroism is constructed. The instrument enables one to measure electric dichroism as a function of time after two solutions are mixed within 6 ms. The adsorption of enantiomeric or racemic [Ru(phen) 3 ] 2+ (phen=1,10-phenanthroline) by colloidally dispersed montmorillonite is studied with this instrument. As a result, it is confirmed that the adsorption of racemic [Ru(phen) 3 ] 2+ occurs by way of two successive paths: first the chelate binds with a clay rapidly within the cation-exchange capacity (CEC) and then it is adsorbed slowly in excess over the CEC

The adsorption of N-alkylated acridine orange derivatives (AO-C{sub n}; n = the number of carbon atoms in an alkyl group) by colloidally dispersed zirconium phosphate (ZrP) was studied by spectrophotometry and electric dichroism. An AO-C{sub n} cation was bound to ZrP by releasing a proton in the phosphate group of ZrP. The electronic spectrum of bound AO-C{sub n} showed that the dye cations formed an aggregate on the polymer. The reduced linear dichroism of a bound dye molecule, {rho}, was determined as a function of n: {rho} = 1.3-1.0 for n = 0-2, while {rho} = {minus}0.3 to {minus}0.4 for n = 3-9.

The helical twisting power of a chiral ruthenium complex Delta-[Ru(acac)2L], in which L (mesogenic ligand) and acac denote 5,5'-(4-octylphenyloxycarbonyl)-2,2'-bipyridyl and acetylacetonate, respectively, was determined to be betaM = -71 and -1.8 x 102 mum-1 in room-temperature nematics ZLI-1132 and MBBA, respectively.

Etudes, a l'aide de mesures de spectres electroniques, de dichroisme electrique et de dichroisme circulaire, de l'adsorption d'un complexe metallique, optiquement actif sur une particule colloidale de montmorillonite sous forme Na. Le compose d'addition de l'argile avec le Λ-tris-(phenanthroline-1,10) ruthenium(II), (Λ-Ru(phen) 3 2+ ) admet l'adsorption de Δ-M(phen) 3 2+ , (M=Ru, Fe, Ni), mais pas celle de Λ-M(phen) 3 2+ en exces par rapport a la capacite d'echange de cations. Par suite d'une telle adsorption stereospecifique, les melanges racemiques des complexes metalliques labiles, tels que Co(phen) 3 2+ et Fe(phen) 3 2+ sont antiracemises en presence de Λ-Ru(phen) 3 2+ -montmorillonite (ou Δ-Ni(phen) 3 2+ -montmorillonite). Lorsqu'une molecule achirale, comme le cation Orange d'acridine est adsorbe sur Δ-Ni(phen) 3 2+ -montmorillonite, il y a induction d'activite optique dans le spectre electronique de l'adsorbat

The oxidations by Ce(IV) ion of the cations of acridine orange (AOH/sup +/) and its n-alkyl derivatives (AO/sup +/-(CH/sub 2/)NH) have been studied in water and in the reversed micellar system of cetylpyridinium chloride (CYPCL)/water/chloroform. The length of a substituting alkyl chain (N) is varied from methyl to octadecyl groups. In both media, the oxidation is found to proceed via a 2-step mechanism. In water, the bimolecular rate constants, k1 and k2, do not vary very much with the change of N. In the reversed micellar system, the first-order rate constant of step 1, k1, has a sharp maximum at N = 1. In contrast to this, the first-order rate constant of step 2, k2, is little dependent on N. The remarkably high rate of the initial step for AO/sup +/-CH/sub 3/ is rationalized in terms of its favorable orientation at the boundary between the micellar water phase and the surfactant layer. 21 references.