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1.
A new series of BINOL-based macrocycles with two phenolic protons have been synthesized via oxidative coupling reaction using CuCl(OH)-TMEDA.  相似文献   
2.
The reaction of titanium isopropoxide with a Schiff base ligand containing an isobutenyl linker leads to double stranded dinuclear titanium(IV)-Schiff base complexes through self-assembly with concomitant formation of intramolecular mu-oxo bridges upon hydrolysis.  相似文献   
3.
A simple, sensitive and rapid solid-phase spectrophotometric procedure was developed for the determination of traces of phenol with 4-aminoantipyrine as a reagent (AAP-SPS), and the optimal experimental conditions were established. This method was performed by sorption and direct absorbance measurements of the product phenol-AAP sorbed on the anion-exchanger Dowex 1-X4 (0.2 g) at 495 nm (absorption maximum) and 700 nm (non-absorption wavelength). The sensitivity offered by the AAP-SPS procedure was higher by a factor of 40 compared with the respective conventional spectrophotometric method. Metrological characteristics were established using a prevalidation strategy. The AAP-SPS procedure is characterized by a linear calibration function in the working range of 0.05–0.50 μmol, low standard deviation of procedure (±0.012), low limit of determination (0.021 μmol), and favorable random (±0.85 to ±11.27%) and systematic deviations (−4.55 to +11.50%). Moreover, the accuracy of the system investigated by the recovery test is acceptable (99–102%). Favorable working and performance characteristics make the new SPS method ideal for phenol monitoring in pharmaceutical preparations as well as other matrices.  相似文献   
4.
Guinea pig skin becomes more pigmented following exposure to UV rays. This melanization was accompanied by enhanced intensity of tyrosinase-staining and increased number of tyrosinase-positive melanocytes (MELty+), with resultant enhancement of melanin synthesis. To clarify the regulatory mechanism for melanization following UV irradiation, organ-cultured guinea pig skins have been used to examine their melanogenic responses to exogenous stimulation. This organ culture system responded well to UV irradiation, by increasing melanogenic activity. Also, in this system, phospholipases (PL), arachidonic acid, interleukin-1α and melanocytestimulating hormone, but not endothelin-1 or phosphatidylinositol-specific PLC (PI-PLC), stimulated melanogenesis to various extents as indicated by the number of MELty+ and morphological changes. Among them, the PLA2 and PLD were found to have a potent stimulatory property for melanocytes. They might affect melanocytes directly or indirectly through an effect on keratinocytes. These results suggest that PLA2 and PLD play a key role in epidermal hyperpigmentation after UV irradiation or inflammation.  相似文献   
5.
Paramagnetic NMR and optical studies of the oxidized forms of mesophile Pseudomonas aeruginosa cytochrome c(551) and its quintuple mutant (F7A/V13M/F34Y/E43Y/V78I), and thermophile Hydrogenobacter thermophilus cytochrome c(552) demonstrated that the amino acid side chain packings in the protein interior influence the coordination bond between the heme iron and the axial methionine in the proteins. The strength of heme axial coordinations was found to correlate with the overall protein thermostability.  相似文献   
6.
Novel diiron complexes with an Fe2(mu-OMe)2 core were studied as models of the active site of nonheme iron-containing enzymes. X-ray crystal structures of the complexes showed the existence of two types of ligand folding-parallel and twisted-both of which have four virtually equivalent phenolato groups sticking out from the Fe2O2 rhombic plane. Cyclic voltammetry measurements revealed two or more distinct redox waves in a region of relatively high potential, in addition to known Fe(II)/Fe(III) redox waves in a region of lower potential. These new peaks were assigned to the high-valence state of iron atoms, that is, Fe(III)Fe(IV) and Fe(IV)Fe(IV), resonating with the phenoxyl radical(s). The split width of the redox waves ranged from 0.14 to 0.20 eV, which may be a measure of the electronic interaction of the phenolate groups through the Fe2(mu-OMe)2 core.  相似文献   
7.
A mixed-valence state of the cation radical tetrathiafulvalene dimer, [(TTF)2]+*, is generated by the electrochemical oxidation of a stacked TTF dimer accommodated within an organic-pillared coordination cage. This mixed-valence species is remarkably stable (t1/2 = approximately 1 day at room temperature in aqueous solution under air) and clearly characterized by cyclic voltammogram and electronic absorption spectroscopy.  相似文献   
8.
Combination of cyanocobalamin (VB12) and ascorbic acid (VC) has been widely seen in pharmaceutical products and dietary supplements. However, VB12 has been reported that its behavior in stability in aqueous solution is quite different when VC is mixed. In the present study, we examined the stabilities of these vitamins in acetate buffer (pH 4.8) using high performance liquid chromatography. Degradation of VB12 was not observed in the absence of VC in the buffer. However, when VC was mixed in the VB12 solution, VB12 concentrations decreased in accordance with VC degradation. VB12 and VC degradations were inhibited by adding sodium halides to acetate buffer at pH 4.8. These stabilization effects were also observed in the range from pH 3.5 to 5.3 and by adding potassium, magnesium, and calcium halides. Furthermore, our data demonstrated that increases in the halide anion concentrations and atomic number (Cl-相似文献   
9.
We have studied three-dimensional (3D) structures and growth processes of 14H-type long-period stacking order (LPSO) formed in Mg97Zn1Gd2 cast alloys by single tilt-axis electron tomography (ET) using high-angle annular dark-field scanning transmission electron microscopy. Evolution of the solute-enriched stacking faults (SFs) and the 14H LPSO by ageing were visualised in 3D with a high spatial resolution in multi-scale fields of views from a few nanometres to ~10 μm. Lateral growth of the solute-enriched SFs and the LPSO in the (0?0?0?1)Mg plane is notable compared to the out-of-plane growth in the [0?0?0?1]Mg direction. The 14H LPSO grows at the cost of decomposition of the (Mg, Zn)3Gd-type precipitates, and accompany a change of in-plane edge angles from 30 to 60°. We have updated the Time–Temperature–Transformation diagram for precipitation in Mg97Zn1Gd2 alloys: starting temperatures of both solute-enriched SFs and LPSO formation shifted to a shorter time side than those in the previous diagram.  相似文献   
10.
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