Partial stripping of Ag atoms from silver bilayer on a Au(111) surface accompanied with the reductive desorption of hexanethiol SAM

The interfacial structures of Ag bilayer prepared by underpotential deposition on Au(111) (Ag(2ML)/Au(111)) were determined by ex situ scanning tunneling microscopy and in situ surface X-ray scattering measurements before and after oxidative adsorption and after reductive desorption of a self-assembled monolayer (SAM) of hexanethiol (C₆SH) in alkaline ethanol solution. While no structural change was observed after oxidative formation of C₆SH SAM on the Ag(2ML)/Au(111) in an ethanol solution containing 20 mM KOH and 0.1 mM C₆SH, some of the Ag atoms in the bilayer were stripped when the SAM was reductively desorbed. Dedicated to Professor J. O’M. Bockris on the occasion of his 85th birthday.     

Humidity-sensitive electrical conductivity of a Langmuir-Blodgett film of titania nanosheets: surface modification as induced by light irradiation under humid conditions

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.     

Metabolism of tomato steroidal glycosides in humans

Pregnane glycosides have been isolated in small amounts, along with the major components furostanol and spirostanol glycosides, from Dioscoreaceae, Taccaceae, and Solanaceae, suggesting that pregnane glycosides might be biosynthesized from furostanol and spirostanol glycosides. Recently, commercial natural foods composed of diosgenin have been used for the treatment of diseases such as osteoporosis and premenstrual syndrome in women. It is anticipated that diosgenin would be metabolized into a type of steroidal hormone, for instance progesterone, however, this metabolism has not been confirmed. Therefore, we have examined the metabolites in the urine of subjects who ingested tomatoes, which contain a considerable amount of the steroidal glycoside esculeoside A. The occurrence of steroidal hormones in the metabolites has been recognized. It has been proven that when a steroidal glycoside is administered, it is partly metabolized into a type of steroidal hormone exhibiting various physiological activities.     

Synthesis of tetrasubstituted and functionalized enol ethers by E-selective olefination of esters with ynolates

We have developed the E-selective olefination of ester carbonyls to afford tetrasubstituted, functionalized olefins and the C-S insertion of thiol esters to give beta-keto thiol esters via ynolates.     

Thermal hysteresis and thickness dependence of the molecular orientation of poly(di-n-hexylsilane) in the film state

Molecular orientation of poly(di-n-hexylsilane) adsorbed on poly(vinyl alcohol) film has been studied by making use of the stretching technique. Dichroic ratio, Rd, strongly depended on the thickness of poly(di-n-hexylsilane) thin film and the highest value ca. 19 was observed at the film thickness of 110 +/- 30 nm. The thermal hysteresis of the molecular orientation was observed in the heating-cooling cycles. By studying the fluorescence spectrum it was confirmed that a portion of the poly(di-n-hexylsilane) molecules were in transoid conformation even at 320 K, although most of poly(di-n-hexylsilane) molecules were in disordered conformation (conformation D). This poly(di-n-hexylsilane) in transoid conformation is formed in the stretching process and may play a role of crystallization nucleus to induce the whole orientation of the poly(di-n-hexylsilane) in the film state.     

Homogeneous DNA-detection based on the non-enzymatic reactions promoted by target DNA.

Much effort has focused on methods for detecting various genetic differences in individuals, including single nucleotide polymorphisms (SNPs). SNP can be characterized as a substitution, insertion, or deletion at a single base position on a DNA strand. There is expected to be on average one SNP for every 1000 bases of the human genome, and some variations located in genes are suspected to alter both the protein structure and the expression level. Therefore, highly sensitive techniques with a simple procedure would be desirable for a high-throughput screening of millions of SNPs widely dispersed throughout the human genome. In this short review, we consider recently reported unique techniques for genotyping in a homogeneous solution, and organize them in terms of the chemical and physical processes accelerated on DNA.     

The aminomethylation of electron-rich aromatics with an N-silyl-N,O-acetal catalyzed by a metal triflate-TMSCl system: facile synthesis of aromatic primary amines, 1-aryl-trichloroethylamines

The copper(II) triflate- and hafnium(IV) triflate-catalyzed aminomethylation of indole (2) with an N-silyl-N,O-acetal 1 containing a trichloromethyl group provides the primary amine derivative (3a) in modest yield. When 1 equiv of trimethylchlorosilane (TMSCl) was added to the reaction mixture, the reaction proceeded smoothly, and the yield of 3a was dramatically improved (>90%). The use of this catalytic system permitted the introduction of an aminomethyl group onto indoles 2a-h bearing a variety of functional groups, which appears to deactivate the Lewis acid, in 52-92% yields. Hf(OTf)4-doped TMSCl catalyzed the successful aminomethylation of various electron-rich aromatic compounds 4a-j to produce 1-aryl-trichloroethylamine derivatives 5a-j.     

Validation study of a method for assaying DE-310, a macromolecular carrier conjugate containing an anti-tumor camptothecin derivative, and the free drug in tumor tissue by high performance liquid chromatography/atmospheric pressure chemical ionization tandem mass spectrometry

DE-310 is a macromolecular carrier conjugate containing an anti-tumor camptothecin derivative, DX-8951, which is conjugated to a water-soluble polymer via a peptide spacer. Assay methods have been developed for the determination of a polymer-bonded DX-8951 conjugate, DX-8951, and Glycyl-DX-8951 concentrations in murine Meth A tumor tissue. Free DX-8951 and Glycyl-DX-8951 were extracted from tumor tissue homogenates by protein precipitation and analyzed by LC/MS/MS (method I). Conjugated DX-8951 was isolated by solid-phase extraction after digestion with a thermolysin. The productive phenylalanyl-glycyl-DX-8951 was analyzed by LC/MS/MS (method II). The lower limits of quantitation of DX-8951, Glycyl-DX-8951, and conjugated DX-8951 were 1.36, 1.34 and 73.7 ng/g (as DX-8951 equivalent). These two methods showed satisfactory sensitivity, precision and accuracy. To study the pharmacokinetics of DE-310, it would be of great help to assay the polymer-bonded DX-8951 and its released drugs in tumor tissue.     

Sassafrins A-D, new antimicrobial azaphilones from the fungus Creosphaeria sassafras

Four new azaphilones named sassafrins A-D (1-4) were isolated from the methanol extract of the stromata of the fungus Creosphaeria sassafras (Xylariaceae, Ascomycetes). Their structures were elucidated by 2D NMR, HR-MS, IR, UV and CD spectroscopy. Sassafrin D (4) possesses a novel skeleton and its biosynthetic pathway is also discussed. In addition, all compounds showed broad-spectrum antimicrobial activity. Their apparently unique occurrence in C. sassafras supports the status of this fungus as a member of a distinct genus within the Xylariaceae, coinciding with molecular and morphological traits.