In situ surface-enhanced infrared absorption spectroscopy for the analysis of the adsorption and desorption process of Au nanoparticles on the SiO2/Si surface

The adsorption and desorption of Au nanoparticles (AuNP) in colloidal D2O suspension on the (3-aminopropyl)triethoxysilane treated SiO2/Si surface was investigated by in situ attenuated total reflection surface enhanced infrared absorption (ATR-SEIRA) spectroscopy with a liquid flow cell. With increasing surface density of AuNP, the absorption of the vibrational modes of D2O and of the citrate molecules covering the AuNP increases due to SEIRA. Repulsive electrostatic Coulomb forces between the AuNP lead to the saturation of the AuNP surface density at submonolayer coverage. We show that the adsorption kinetics can be investigated by monitoring in situ the molecular vibrational modes of D2O and the citrate molecules. Furthermore, we clarify that the adsorption process can be described very well by a diffusion-limited first-order Langmuir kinetics model. When exposing a saturated AuNP submonolayer to 2-aminoethanethiol (AET)/D2O solution, the AuNP are removed from the surface and the IR absorption of the D2O vibrational modes become weaker again. Taking into account the time dependencies of the OD and the CH peaks, we propose a microscopic model where the AET molecules quickly adsorb on the AuNP by replacing most of the precovering citrate molecules exposed to the AET solution. As this takes place, the AuNP agglomerate-as we could detect with scanning electron microscopy-and are finally removed from the surface.     

Surface design for precise control of spatial growth of a mesostructured inorganic/organic film on a large-scale area

A microfabrication technique is presented to fabricate a mesostructured inorganic/organic composite film, i.e., silica/cetyltrimethylammonium chloride (CTAC) film, with near-perfect site-selectivity on a large surface area based on a spatially regulated growth method. To precisely regulate the site-selective growth of this mesocomposite film at the solid/liquid interface, we designed a novel microtemplate consisting of a "dual-component" self-assembled monolayer (SAM) with alternating hydrophobic trifluorocarbon (CF3) and cationic amino (NH2) groups. First, (heptadecafluoro-1,1,2,2-tetrahydrodecyl)trimethoxysilane (FAS)-SAM was formed onto Si substrate covered with native oxide (SiO2/Si) from vapor phase. The substrate was then photolithographically micropatterned using 172 nm vacuum UV light. Finally, the micropatterned FAS-SAM was immersed in a solution of 1 vol % (aminoethylaminomethyl)phenethyltrimethoxysilane (AEAMPS) in absolute toluene. Due to these treatments, a dual-SAM microtemplate with CF3- and NH2-terminated surfaces was fabricated, as evidenced by lateral force microscopy, ellipsometry, and X-ray photoelectron spectroscopy. Using this template, the microfabrication of a mesocomposite film was demonstrated. As a control, the micropatterned hydrophobic FAS-SAM template (composed of CF3- and OH-terminated surfaces) was also treated under the same conditions. Optical microscopy and atomic force microscopy confirmed that the formation of the continuous mesocomposite film proceeded only on the FAS-SAM-covered regions, while the AEAMPS-SAM-covered regions remained free of deposits. This shielding effect also remained constant regardless of the pattern's geometry, i.e., the interval distance between the FAS-SAM-covered areas in the pattern. Through this approach, we were able to obtain well-defined 5-, 10-, and 20-mum wide mesocomposite microlines over the entire 10 x 10 mm2 area with high area-selectivity. On the other hand, when the SiO2 regions were not terminated with the cationic NH2 groups, cluster formation proceeded not only on the hydrophobic CF3 regions but also on the SiO2 regions, particularly with an increase in the pattern interval distance, resulting in lower final pattern resolution.     

Three-dimensional porous coordination polymer functionalized with amide groups based on tridentate ligand: selective sorption and catalysis

To create a functionalized porous compound, amide group is used in porous framework to produce attractive interactions with guest molecules. To avoid hydrogen-bond formation between these amide groups our strategy was to build a three-dimensional (3D) coordination network using a tridentate amide ligand as the three-connector part. From Cd(NO3)2.4H2O and a three-connector ligand with amide groups a 3D porous coordination polymer (PCP) based on octahedral Cd(II) centers, {[Cd(4-btapa)2(NO3)2].6H2O.2DMF}n (1a), was obtained (4-btapa = 1,3,5-benzene tricarboxylic acid tris[N-(4-pyridyl)amide]). The amide groups, which act as guest interaction sites, occur on the surfaces of channels with dimensions of 4.7 x 7.3 A2. X-ray powder diffraction measurements showed that the desolvated compound (1b) selectively includes guests with a concurrent flexible structural (amorphous-to-crystalline) transformation. The highly ordered amide groups in the channels play an important role in the interaction with the guest molecules, which was confirmed by thermogravimetric analysis, adsorption/desorption measurements, and X-ray crystallography. We also performed a Knoevenagel condensation reaction catalyzed by 1a to demonstrate its selective heterogeneous base catalytic properties, which depend on the sizes of the reactants. The solid catalyst 1a maintains its crystalline framework after the reaction and is easily recycled.     

Anthracene array-type porous coordination polymer with host-guest charge transfer interactions in excited states

Confinement of electron donor guests affords an efficient, photo-induced charge transfer (CT) with the anthracene moieties of a porous coordination polymer.     

Total synthesis and biological evaluation of pacidamycin D and its 3'-hydroxy analogue

Full details of the total synthesis of pacidamycin D (4) and its 3'-hydroxy analogue 32 are described. The chemically labile Z-oxyacyl enamide moiety is the most challenging chemical structure found in uridylpeptide natural products. Key elements of our approach to the synthesis of 4 include the efficient and stereocontrolled construction of the Z-oxyvinyl halides 6 and 7 and their copper-catalyzed cross-coupling with the tetrapeptide carboxamide 5, a thermally unstable compound containing a number of potentially reactive functional groups. This synthetic route also allowed us to easily prepare 3'-hydroxy analogue 32. The assemblage by cross-coupling of the Z-oxyvinyl halide 6 and the carboxamide 5 at a late stage of the synthesis provided ready access to a range of uridylpeptide antibiotics and their analogues, despite their inherent labile nature with potential epimerization, simply by altering the tetrapeptide moiety.     

Mode change in the self-motion of a benzoquinone disk coupled with a NADPH system

The self-motion of a benzoquinone (BQ) disk on NADPH was investigated as the coupling of an autonomous motor and an enzyme reaction. In the absence of the enzyme reaction, features of motion changed depending on the concentration of NADPH, that is, continuous motion→ intermittent oscillatory motion→ no motion. When the reverse reaction from NADP(+) to NADPH was introduced into the system with the addition of an enzyme reaction, continuous motion changed to intermittent oscillatory motion with small amplitude. The mechanism of this mode change is discussed in relation to the surface tension as a driving force and the time course of UV spectra as a window to the progress of the reaction. Characteristic features of the mode change were qualitatively reproduced by a numerical calculation.     

Diastereoselective addition of allyltitanocenes to cyclic enones

The reaction of allyltitanocenes with five- to seven-membered cyclic enones proceeded with good to high diastereoselectivity depending on the ring size of enones. The stereochemistry of the major isomers produced by the reaction of cinnamyltitanocene was opposite to that of crotyltitanocene.     

Synthetic studies on chartelline C: stereoselective construction of the core skeleton

What a core-ker! The title synthesis was achieved using a route featuring an intramolecular Mitsunobu reaction of a nosyl amide, stereoselective construction of the β-lactam, and formation of an enamide moiety by selenoxide elimination. The stereochemistry of the alkylation for the formation of the β-lactam was controlled by a secondary hydroxy group on the ten-membered ring. SEM=2-(trimethylsilyl)ethoxymethyl; TBS=tert-butyldimethylsilyl.     

19F NMR characterization of the thermodynamics and dynamics of the acid-alkaline transition in a reconstituted sperm whale metmyoglobin

A 19F NMR study on the acid-alkaline transition in sperm whale myoglobin reconstituted with a perfluoromethyl heme, 13,17-bis(2-carboxylatoethyl)-3,8-diethyl-2,12,18-trimethyl-7-trifluoromethylporphyrinatoiron(III), demonstrated that the thermodynamics of the transition is predominantly controlled by the stability of acidic form.     

Gas-Phase Alkylation of Pyridine and Phenol with Alcohols Over Halide Clusters of Group 5–7 Transition Metals as Solid Acid Catalysts

Pyridine is allowed to react with methanol under a hydrogen stream in the presence of (H₃O)₂[(W₆Cl₈)Cl₆]·6H₂O supported on silica gel. When the temperature is raised above 200 °C, the catalytic activity of the cluster appears. Methylation of pyridine proceeds yielding 2-methylpyridine in 61% selectivity at 400 °C. The corresponding hexanuclear chloride clusters of niobium, molybdenum, and tantalum also catalyze the reaction. Ethanol affords the corresponding 2-ethylpyridine. When phenol is allowed to react with methanol in the presence of (H₃O)₂[(Mo₆Cl₈)Cl₆]·6H₂O supported on silica gel in the same manner, selective O-methylation proceeds yielding anisole in 57% selectivity at 150–200 °C. Above 250 °C, C-methylation predominates and provides o-cresol with 67% selectivity at 300 °C. The corresponding clusters of niobium, tantalum, and tungsten also catalyze the reaction. Ethanol and 1-propanol afford the corresponding 2-alkylphenols. Alkyl cations produced over weak Brønsted acid sites (H ₀ ≈ +1.3) developed on the clusters are assumed as intermediates for both reactions.