Equivalent electric circuit analyses of ionic thermocurrent in sodium-doped CaF2 crystals

The characteristics of high-temperature ionic thermocurrent (HT ITC) in CaF₂ doped with different sodium concentrations were studied by the Teflon-insulated electrode ITC method. It was shown that, with increasing sodium concentration, the HT ITC band moved toward a Na⁺-F_V dipole band with a peak at 162 K. The results of analyses of the HT ITC spectra using an equivalent electric circuit proved that the activation energy of space charge migration related to HT ITC was also strongly dependent on the doped sodium concentrations if varied from 0.94 to 0.46 eV with increasing sodium concentration in our ITC study. In addition, the broadening of the Na⁺-F_V dipole band was observed in 3 nominal mole% NaF-doped CaF₂, which was accompanied by a considerable decrease of the activation energy from 0.46 to 0.29 eV without showing marked temperature shifts of the peak ITC bands.     

The homotopy groups of the at the prime 3

In this paper, we try to compute the homotopy groups of the -localized Toda-Smith spectrum at the prime 3 by using the Adams-Novikov spectral sequence, and have almost done so. This computation involves non-trivial differentials and of the Adams-Novikov spectral sequence, different from the case . We also determine the homotopy groups of some -localized finite spectra relating to . We further show some of the non-trivial differentials on elements relating so-called -elements in the Adams-Novikov spectral sequence for .

     

Chemoselective preparation of ketones by the grignard reaction of N-acylpyrazoles

N-Acylpyrazoles afford chemoselectively the corresponding ketones in good yields by the use of equimolar amounts of Grignard reagent. In the case of an optically active N-acylpyrazole, optical asymmetry was retained in comparable optical yield. Ketone formation by the Grignard reactions can be regarded as an important functionalization in a synthetic loop using pyrazoles as the auxiliary compound.     

Ionization energies and hydrogen-bond strength of the water clusters

The first vertical ionization energies of the water clusters (H₂O)_n for n = 1–8 have been evaluated from ab initio SCF MO calculations. The values obtained for n = 5 and 8 are in reasonable agreement with the experimental values of ice. The stability of the clusters is examined in terms of the hydrogen-bond strength per bond (B_h).     

WAVELENGTH DEPENDENCE OF THE FORMATION OF SINGLE-STRAND BREAKS AND BASE CHANGES IN DNA BY THE ULTRAVIOLET RADIATION ABOVE 150 nm

The wavelength dependence of the formation of two types of DNA damage, single-strand breaks and base changes, was investigated in the UV region from 150 nm to 254 nm using superhelical closed circular (form I) colicin El DNA with synchrotron radiation. Single-strand breaks were measured by agarose gel electrophoresis as a direct conversion of form I DNA to form II DNA (open circular). Base damages were defined as sensitive sites to a crude extract of endonuclease from Micrococcus luteus. They also were estimated using the same conversion, from form I to form II after the DNA was treated with endonuclease. The fluence-effect relationship could be fitted by a simple exponential function for both types of damage. Action spectra were constructed based on the reciprocal of the 37% fluence. The action spectrum for strand breaks increased rather monotonically over three decades from 254 nm to 150 nm in a logarithmic scale, while that for base damages showed a breaking point at 190 nm, being relatively flat above 190 nm. The characteristics of the action spectra are compared with the absorption spectra of the DNA and its main chain moiety calculated on the basis of data on calf thymus DNA and synthetic polynucleotides. Our main conclusions are (1) that the majority of single-strand breaks were induced by the absorption of photon in the sugar-phosphate group in the vacuum-UV region and (2) that the base changes were induced equally well by absorption in the vacuum-UV and in the far-UV region.     

The Effect of Cold Stress on UVB Injury in Mouse Skin and Cultured Keratinocytes

Abstract— The effect of cold stress on skin damage caused by UVB irradiation was investigated both in vivo and in vitro. Ear skin of mice that had been exposed to cold stress at 0°C for 20 min and at 5°C for 24 h was exposed to UVB radiation. Sunburn cell production was less in mice exposed to the lower temperature. In addition, the effect of cold stress on the survival rate of UVB-irradiated rat keratinocytes was examined in a cytotoxicity test, with the results showing that keratinocytes exposed to cold stress of 0°C had a higher survival rate than control cells. To pursue a promising clue for explaining the result, we examined metallothionein (MT) production in rat keratinocytes that had been exposed to cold stress at 0°C. Microfluorometric quantification showed a positive correlation between the time course and the intensity of immunofluorescence for MT, indicating that the molecule is inducible by exposure to cold stress in our experimental system. These results suggest that epidermal cells that have been exposed to cold stress maintain a higher resistance to UV radiation than nonexposed controls in vivo and in vitro , and that MT with radical-scavenging activity might contribute, at least in part, to photoprotection against UVB-induced oxidative damage in mammalian skin.     

Charge mosaic membrane with a microstructure of poly(styrene-b-4-vinylpyridine)

Well defined AB and BAB type poly[styrene(ST)-b-4-vinylpyridine(4VP)]s were prepared by anionic living polymerization in tetrahydrofuran (THF) at ?78°C. Casting AB and BAB type poly(ST-b-4VP)s with a composition of about 50 mol% PST from 1,1,2-trichloroethane (TCE) produced specimens with lamellar microdomain structures. Quaternization of P4VP and sulfonation of PST domains (lamellar and spherical structures), accompanied by each domain fixing, were carried out under various reaction conditions. The piezodialysis of the prepared charge mosaic membrane with its lamellar microdomain structure was measured from a sodium chloride (NaCl) aqueous solution. The results are discussed in some detail.     

Cyclodextrin-modified monolithic columns for resolving dansyl amino acid enantiomers and positional isomers by capillary electrochromatography

We describe beta- and gamma-cyclodextrins (beta- and gamma-CD)-modified monolithic columns prepared by sol-gel process and chemical modifications. The monolithic silica column was fabricated inside a fused-silica capillary with 100 microm inner diameter by sol-gel process. The monolithic silica matrix was chemically modified chiral selectors of beta- or gamma-CDs with a spacer of 3-glycidoxypropyltrimethoxysilane by on-column reactions. Gamma-CD-modified monolithic column has successfully been applied for the separation of dansyl amino acid enantiomers. Beta-CD-modified monolithic column has been used for the separation of the positional isomers of o-, m-, and p-cresols and the enantioseparation of racemates of benzoin and several dansyl amino acids by capillary electrochromatography, respectively. For the separation of neutral positional isomers, a positive electric field was applied. However, for the separation of negatively charged analytes, a negative electric field was applied at the inlet of column. The separation efficiency of 5.0 x 10(4) theoretical plates/m for dansyl-L-threonine was obtained at electric field strength of -300 V/cm in the mobile phase of 50 mM 2-(N-morpholino)ethanesulfonic acid (MES)-Tris/methanol (70/30) buffer at pH 7.0. L-enantiomers were eluted as the first peak. Scanning electron micrograph showed that monolithic columns have the morphology of continuous skeleton and large through-pores.     

Electrical conductivities of potassium ferrites doped with divalent metal oxide

The electronic and ionic conduction in three kinds of potassium ferrites with β-alumina structure was studied. Undoped ferrite, K₂O·6Fe₂O₃, prepared by sintering at 1400°C after prefiring a mixture of potassium carbonate and ferric oxide, was a mixed conductor with about 1% ionic conduction and predominantly electronic conduction. The nickel- or zinc-doped potassium ferrite showed decreasing conductivity in the range of a single phase as the content of dopant increased. Variations of the electronic conduction in the doped potassium ferrites were assigned to changes of ferrous ion concentration accompanied by structural changes in the spinel-like blocks. Potassium ion conductivities of the three sorts of samples were estimated from the total conductivities and the transport numbers obtained by dc-polarization technique and electrolysis method. The decreases of the ionic conductivities were explained by narrowing of the alkali-oxygen slot caused by doping.     

Importance of specific hydrogen-bond donor-acceptor interactions for the key carbocycle-forming reaction catalyzed by 2-deoxy-scyllo-inosose synthase in the biosynthesis of 2-deoxystreptamine-containing aminocyclitol antibiotics

A crucial enzyme in the biosynthesis of the 2-deoxystreptamine aglycon of clinically important aminocyclitol antibiotics is 2-deoxy-scyllo-inosose synthase (DOIS), which converts ubiquitous D-glucose 6-phosphate (G-6-P) into the specific carbocycle 2-deoxy-scyllo-inosose. Among all the oxygenated carbons of the substrate, C-1, -4, -5, and -6 are directly involved in the chemical transformation. To get insight into the roles of C-2 and C-3 hydroxy groups, 2-deoxy-2-fluoro-, 3-deoxy-3-fluoro-, 2-amino-2-deoxy-, and 3-amino-3-deoxy-D-glucose 6-phosphates (2-F-G-6-P, 3-F-G-6-P, 2-NH(2)-G-6-P, and 3-NH(2)-G-6-P, respectively) were subjected to the DOIS reaction as probe, since a fluorine substituent generally acts as a hydrogen-bond acceptor, and an ammonium functionality derived physiologically from an amino group as a hydrogen-bond donor. Among those tested, 2-F-G-6-P and 3-NH(2)-G-6-P were used as substrates by DOIS and were converted into the corresponding deoxyfluoro- and aminodeoxy-scyllo-inososes, respectively. In contrast, 3-F-G-6-P and 2-NH(2)-G-6-P were inactive in the cyclization reaction. Clearly, DOIS recognizes the G-6-P substrate through specific hydrogen-bonding interactions, i.e., through a hydrogen-donating group for C-2 and an accepting group for C-3 of the substrate. Modeling of DOIS based on the structure of evolutionary-related dehydroquinate synthase is also described.