Masahiro Taniguchi

Atomic force microscopic studies on the structure of bovine femoral cortical bone at the collagen fibril-mineral level.

The structure of cortical bone at the collagen-mineral level was investigated by means of atomic force microscopy. Surfaces of the specimens treated with collagenase and ethylenediaminetetraacetic acid (EDTA) were examined. Images of blob-like objects observed in intact specimen became clearly outlined after collagenase treatment; the sizes of the blob decreased, suggesting that each blob had been fragmented by the collagenase treatment. Following EDTA treatment of an intact specimen, an image of thread-like objects appeared; the thread was partly constructed by trains of blobs and the other parts of the threads had a periodic pattern along its longer axis. The period was almost equal to the collagen D-period of the Hodge–Petruska model, indicating that the threads are collagen fibrils and that the blobs are related to the mineral phase in bone. It was concluded that minerals were deposited on and along collagen fibrils. A decorated collagen fibril model for the spatial relationship between mineral and collagen fibril was proposed. According to our model, the mineral inside the collagen fibril is about one forth of the extrafibrillar mineral.

First observation of in-plane X-ray diffraction arising from a single layered inorganic compound film by a grazing incidence X-ray diffraction system with a conventional laboratory X-ray source

Abstract Grazing incidence angle in-plane X-ray diffraction (in-plane XRD) was applied to characterization of an organic–inorganic hybrid Langmuir–Blodgett (LB) film in a laboratory scale. The hybrid LB film consisted of octadecyl ammonium cation and sodium montmorillonite layers at Si(1xa00xa00) wafer. The in-plane XRD measurements of the hybrid LB film gave one diffraction peak at 20.0° (0.44 nm), which we assigned to the (1xa01xa00) and (0xa02xa00) reflections of montmorillonite. This was the first example of the in-plane diffraction from a single layered montmorillonite, presenting a clear evidence for the parallel orientation of the (0xa00xa01) plane with respect to a film surface.

Clay column chromatography for optical resolution: selectivities of Λ-[Ru(phen)3]2+ and Λ-[Ru(bpy)3]2+ laponite columns towards 1,1′-binaphthol

Abstract 1,1′-Binaphthol was resolved chromatographically on a column packed with Λ-[Ru(phen) 3 ] 2+ and Λ-[Ru(bpy) 3 ] 2+ laponite columns when the compound was eluted with methanol solvent. The elution order of 1,1′-binaphthol enantiomers was R → S and S → R for the [Ru(phen) 3 ] 2+ and Λ-[Ru(bpy) 3 ] 2+ columns, respectively. From the temperature dependence of the retention time for each enantiomer, the difference of enthalpy of adsorption between the R- and S- enantiomers, − ΔH R − (− ΔH S ), was obtained to be −2.7 and 5.3 kcal/mol for the Λ-[Ru(phen) 3 ] 2+ and Λ-[Ru(bpy) 3 ] 2+ columns, respectively. The adsorption structures of 1,1′-binaphthol enantiomers were studied by the X-ray diffraction analyses of the powder samples of clay-Ru(II) complex-1,1′-binaphthol adducts. The stability of the binding of 1,1′-binaphthol was examined by the theoretical simulations based on the Monte Carlo method.

Underpotential deposition of zinc ions on Au(111) in phosphate solution (pH 4.6): kinetic and STM studies

Abstract In phosphate solution at pH 4.6, in situ STM images on Au(111) were different in the potential regions where the Au(111) interface is taken to be free from phosphate adsorption and where the upd Zn is formed. In the former region, the observed STM image was Au(111)(1×1), and in the upd region, the image was taken to be (√3×√3)R30°. As the phosphate is expected to adsorb on upd Zn by oxidative reaction, it is suggested that the latter image is due to the adsorbed phosphate species formed on upd Zn at Au(111) by upd induced adsorption.

Electrochemical behavior of hexa-ammineruthenium(III) cations in clay-modified electrodes prepared by the Langmuir-Blodgett method

The thin film of an ion-exchanged adduct of a clay and tetra-n-decylammonium cations ((n-decyl)4N+) was formed at an air|water interface. A clay-modified electrode was prepared by depositing the film onto a glassy carbon substrate with the Langmuir-Blodgett method. When the electrode was soaked in an aqueous solution of hexa-ammineruthenium(III) chloride ([Ru(NH3)6]Cl3), (n-decyl)4N+ cations were replaced with [Ru(NH3)6]3+ ions. The electrochemical behavior of [Ru(NH3)6]3+ in the ultra-thin film was studied by measuring the cyclic voltammetry and coulometry on the clay-modified electrode. The atomic force microscope images of a saponite film deposited on a microglass plate and saponite-(n-decyl)4N+ transferred on a microgalss plate were compared.

Electrochemical and in situ STM studies of anomalous phosphate adsorption induced on Zn UPD at Au(111) in the presence of halide ions in aqueous phosphate solutions

Abstract Underpotential deposition (UPD) of Zn2+ at Au(1xa01xa01) was studied in the phosphate solutions with and without halide ions (Cl−, Br−, and I−) by cyclic voltammetry and in situ STM for the evaluation of the anion adsorption induced on the Zn UPD. The order of the strength of anion adsorption induced on Zn UPD was found to be different from the order of specific adsorption strength of I−>Br−>Cl−>PO43−⩾SO42− at an Au substrate electrode. This anomalous tendency of anion adsorption induced on UPD Zn at Au seems to be identical with the cases of sulfate and phosphate adsorption induced on UPD Zn at a Pt electrode in the presence of chloride, being confirmed by radiotracer method. Such anomalous phosphate adsorption induced on Zn UPD was found to take place at Au(1xa01xa01) not only in the presence of chloride or bromide, but also even in the presence of iodide in the phosphate solution. The in situ STM images of Zn UPD were observed at Au(1xa01xa01) in the phosphate solution with iodide ions. At −200 mV (saturated calomel electrode; SCE) where the iodide adsorbs at substrate Au(1xa01xa01), the STM image was c (p× 3 R30°) , and in the Zn UPD region, the STM image became ( 3 × 3 )R30° . The latter image is discussed to be assigned to the image in the absence of iodide, i.e., that the adsorbed anions induced at Zn UPD are phosphate species even in the solution containing iodide ions.

Mass transport on an anionic clay-modified electrode as studied by a quartz crystal microbalance

Abstract A quartz crystal microbalance (QCM) has been used to investigate mass transfer coupled with electron transfer through a hydrotalcite clay film. The electrode was prepared by casting an aqueous suspension of hydrotalcite (denoted as Mg–Al–HT) or hydrotalcite ion-exchanged with [Fe(CN) 6 ] 3− (denoted as Mg–Al–HT–[Fe(CN) 6 ]) 3− . Adsorption studies using QCM and UV-visible spectroscopic measurements revealed that [Fe(CN) 6 ] 3− was incorporated as an ion-paired species with a counter cation. The adsorbed species on an electrode in contact with a 0.1 M NaCl solution was identified as a divalent ion-pair (Na[Fe(CN) 6 ] 2− ) while the adsorbed species in contact with a 0.1 M Na 2 SO 4 or Na 2 CO 3 solution was a monovalent ion-triplet (Na 2 [Fe(CN) 6 ] − ). Electrochemical QCM measurements on an electrode modified with Mg–Al–HT–[Fe(CN) 6 ] 3− revealed that one Na[Fe(CN) 6 ] 2− or Na 2 [Fe(CN) 6 ] − ion was leached from a film when one or two [Fe(CN) 6 ] 3− ions were reduced, respectively. The leaching of these anions took place in order to compensate the excess negative charge generated in a film.

STM observation of molecular chirality and alignment on solid surface.

Abstract Two-dimensional adlayer of a helically shaped aromatic compound, hexathia[11]heterohelicene ([11]TH), which consists of fused five benzene rings and six thiophene rings, was prepared on Au(1xa01xa01), Au(1xa01xa00) and polycrystalline gold under UHV condition. LEED and STM were used for characterization of alignment, ordering and chirality of [11]TH on these Au substrates. A [11]TH monolayer on Au(1xa01xa01) showed the presence of an adlayer lattice with six-fold symmetry, while [11]TH on Au(1xa01xa00) did align along 〈1 1 0〉 direction, and [11]TH adsorbed on a step bunching area formed chiral sensitive arrays, being one-dimensionally aligned chains. These observations are discussed in terms of stereoselective interaction among [11]TH’s, which is strongly affected by the surface structure of a substrate.

Molecular chirality on a solid surface : thiaheterohelicene monolayer on gold imaged by STM

Abstract Imaging of molecule–molecule recognition of chirality on a solid surface was attempted using scanning tunneling spectrocopy (STM) under ultra-high vacuum (UHV) conditions. The target molecule in this work, thiaheterohelicene ([11]TH), is a fused product which consists of five benzene rings and six thiophene rings. It has a helical chirality which can be compared to a spring washer. A racemic mixture of [11]TH was vaporized to prepare an adsorbed layer onto an Au(111)/mica substrate under UHV conditions. Images were obtained with molecular resolution on wide terrace areas and faceted narrow steps. The images obtained in the terrace areas show that the right handed and the left handed isomers were randomly adsorbed on the surface with little interaction. On the other hand, the images obtained in the steps showed that molecules of the same chirality formed a tightly packed row. The high resolution STM image obtained for [11]TH enabled us to distinguish not only the domain structures but also the domain compositions caused by the structural difference of the substrate.

Electrochemical STM observation of [Fe(CN)6]3− ions adsorbed on a hydrotalcite crystal surface

Abstract The electrochemical STM method has been applied to a hydrotalcite clay-modified electrode with the aim of obtaining evidence for the formation of a surface layer of the [Fe(CN) 6 ] 3−/4− couple. As a result, ordered surface layers of [Fe(CN) 6 ] 3−/4− ions on a hydrotalcite-modified electrode have been observed with an in-situ electrochemical STM instrument: the initial lattice of [Fe(CN) 6 ] 3− with a =1.40±0.04 nm, b =1.85±0.04 nm and α =63±3° changed to an expanded lattice of [Fe(CN) 6 ] 4− with a =1.94±0.04 nm, b =1.90±0.04 nm and α =60±3° due to the electrochemical reduction.