X-ray Crystallographic Observation of Chiral Transformations within a Metal–Peptide Pore

Porous metal complexes enable single-crystal X-ray crystallographic observation of included guests or reaction intermediates through simple soaking with the guests/substrates. Previous studies on this technique have often encountered difficulties in the observation of chiral structures because the host frameworks had no chirality. We synthesized a new metal–peptide porous complex through a folding-and-assembly strategy and utilized the chiral pore for trapping chiral guests. Chiral alcohols and ketones were successfully included within the pore. Crystallographic analyses clearly revealed not only their chemical structures but also chiral transformation events within the pore such as fixed conformations or an unstable hemiacetal formation.     

Reporting of quantitative oxygen mapping in EPR imaging

Oxygen maps derived from electron paramagnetic resonance spectral-spatial imaging (EPRI) are based upon the relaxivity of molecular oxygen with paramagnetic spin probes. This technique can be combined with MRI to facilitate mapping of pO(2) values in specific anatomic locations with high precision. The co-registration procedure, which matches the physical and digital dimensions of EPR and MR images, may present the pO(2) map at the higher MRI resolution, exaggerating the spatial resolution of oxygen, making it difficult to precisely distinguish hypoxic regions from normoxic regions. The latter distinction is critical in monitoring the treatment of cancer by radiation and chemotherapy, since it is well-established that hypoxic regions are three or four times more resistant to treatment compared to normoxic regions. The aim of this article is to describe pO(2) maps based on the intrinsic resolution of EPRI. A spectral parameter that affects the intrinsic spatial resolution of EPRI is the full width at half maximum (FWHM) height of the gradient-free EPR absorption line in frequency-encoded imaging. In single point imaging too, the transverse relaxation times (T(2)(?)) limit the resolution since the signal decays by exp(-t(p)/T(2)(?)) where the delay time after excitation pulse, t(p), is related to the resolution. Although the spin densities of two point objects may be resolved at this separation, it is inadequate to evaluate quantitative changes of pO(2) levels since the linewidths are proportionately affected by pO(2). A spatial separation of at least twice this resolution is necessary to correctly identify a change in pO(2) level. In addition, the pO(2) values are blurred by uncertainties arising from spectral dimensions. Blurring due to noise and low resolution modulates the pO(2) levels at the boundaries of hypoxic and normoxic regions resulting in higher apparent pO(2) levels in hypoxic regions. Therefore, specification of intrinsic resolution and pO(2) uncertainties are necessary to interpret digitally processed pO(2) illustrations.     

Amphoteric poly(vinyl alcohol) gel as a force generator: Observation of microporous gel formation with cryo-SEM

Amphoteric PVA hydrogels were made from mixed aqueous solutions of poly(acrylic acid), poly(allylamine) hydrochloride and poly(vinyl alcohol) by repetitive freezing and thawing. The hydrogen bond induced gelation produced an elastic and tough microporous hydrogel which generated tension as high as 0.3MPa corresponding to the solvent exchange from water to acetone. In this paper we show the microscopic structure of hydrogels determined by means of cryo-SEM technique and X-ray analysis.     

Reaction mechanism for target-like products from197Au target bombarded with12C ions of energies above 100 MeV/u

Target-like products, that is,^191–200Au,^185–200Pt, and^183–195Ir, from¹⁹⁷Au target bombarded with¹²C ions at the energies of 180, 230, and 400 MeV/u were measured by using off-line gamma-ray spectrometry combined with chemical separation procedures. Spallation systematics by Rudstam reproduces well the measured cross sections for formation of platinum and iridium isotopes. It was found that the cross sections of gold nuclides increase with increase of the incident energy in the range studied and they are enhanced if compared with the reported proton-induced reaction of gold at a similar incident energy. It is suggested that the electromagnetic dissociation process plays a role for production of such gold nuclides.     

Stereochemistry and mechanism of catalytic hydrogenation of substituted cyclohexanones

Substituted alkylcyclohexanones were hydrogenated over several transition metal catalysts. The hydrogenation with freshly prepared Raney Ni gave predominantly the axial alcohols but catalyst to which sodium hydroxide was added or aged catalyst increased the stereoselectivity. In contrast to the PtO₂ hydrogenation in which the equatorial alcohols were favoured, more axial alcohols were obtained than the equatorial counterparts on Pt-black. On Pd catalyst the isomeric ratios of the cyclohexanols changed as the reaction progressed. This may be due to a decrease in the amount of hydrogen available caused by the strong adsorption of ketones on the catalyst. Rh catalyst gave more of the axial alcohols than any other catalyst used in the present study.     

Reactions of 1,2-dimethoxytetramethyldisilane with styrenes: Formation of a new type of silacyclopentanes having phenyl substituents on ring carbons

The reaction of 1,2-dimethoxytetramethyldisilane with styrene and α-methylstyrene in the presence of NaOMe catalyst in tetrahydrofuran (THF) gave the new silacyclopentanes 1,1-dimethyl-2,4-diphenyl-1-silacyclopentane (IIIa) and 1,1,2,4-tetramethyl-2,4-diphenyl-1-silacyclopentane (IIIb), respectively. These silacyclopentanes were found to exist as cis-trans mixtures. The use of sodium metal in place of NaOMe afforded similar results. Reactions of a polysilane mixture, MeO-(SiMe₂)_nOMe (n ≧ 3), with the styrenes also gave similar results. In some cases, polysilacycloalkanes such as 1,2,3-trisilacyclopentanes (IV) and 1,2,3,4-tetrasilacyclohexanes (V) were obtained as by-products. A mechanism for the formation of the silacyclopentanes and polysilacycloalkanes is presented. It was found that electron impact decomposition of silacyclopentanes IIIa and IIIb, trisilacycloalkane IV and tetrasilacycloalkane V gave molecular ions corresponding to the silacyclopropane, cyclotrisilane and cyclotetrasilane systems.     

XPS for in situ observation of an Ag electrode on a solid electrolyte used as oxygen sensor

The Ag electrode surface of a solid electrolyte in its working state has been studied by X-ray photoelectron spectroscopy. The nature of the AgO system on the electrode is dependent on the temperature. There are three types of AgO systems at 400°C. Type 1 with an O is binding energy of 532.6 eV only appeared at 325°C. However, when the temperature was raised to 400°C, types II and III (with BEs 531.1 and 529.2 eV) appeared. These O is signals are discussed in detail.     

Studies on hypolipidemic agents. IV. 3-[4-(Phenylthio)benzoyl]propionic acid derivatives

2-Acetylthio-3-benzoylpropionic acid derivatives having two benzene rings or condensed-ring moieties were prepared, and tested for hypolipidemic activity in normal rats. Some of these compounds were active. 2-Acetylthio-3-[4-(phenylthio)benzoyl]propionic acid (10) and its derivatives seemed to have the most potent hypocholesterolemic activities. Compound 10 showed strong activity, especially in cholesterol-fed rats.     

Analysis of210Po in marine samples

A method for determining²¹⁰Po in marine samples by wet dissolution, deposition onto silver disc and counting by -spectrometry is described. Recovery of polonium was obtained with²⁰⁸Po tracer.²¹⁰Po levels in fish from the Brazilian coast and sediments from Antarctic region were determined. Levels in fish ranged from 0.5 to 5.3 Bq·kg^–1 wet and for sediments, mean values of 10 mBq·kg^–1 were obtained.     

Progradation of the Changjiang River delta since the mid-Holocene

Subaqueous deltaic deposits with approximately 30 radiocarbon ages show that the Changjiang River delta was strongly affected by tides and that the delta progradation rate after 2 kaBP was almost double the rate before 2 kaBP. This change in the progradation rate correlates well with the active extension of the subaerial delta plain shown by previous work. Widespread human activities, such as farming, deforestation, and dike construction, probably resulted in an increase in sediment discharge to the river-mouth area.