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131.
Sitafloxacin (STFX) hydrate is a non-stoichiometric hydrate. The hydration state of STFX hydrate varies non-stoichiometrically depending on the relative humidity and temperature, though X-ray powder diffraction (XRPD) of STFX hydrate was not affected by storing at low and high relative humidities. The detailed properties of crystalline water of STFX hydrate were estimated in terms of hygroscopicity, thermal analysis combined with X-ray powder diffractometry, crystallography and density functional theory (DFT) calculation. STFX hydrate changed the water contents continuously and reversibly from an equivalent amount of dihydrate through that of sesquihydrate depending on the relative humidity at 25°C. Thermal analysis and X-ray powder diffraction (XRPD) simultaneous measurement also revealed that STFX hydrate dehydrated into a hydrated state equivalent to monohydrate by heating up to 100°C, whereas XRPD patterns were slightly affected. This indicated that the crystal structure of STFX hydrate was retained at the dehydration level of monohydrate. Single-crystal X-ray structural analysis showed that two STFX molecules and four water molecule sites were contained in an asymmetric unit. STFX molecules formed a channel structure where water molecules were included. At the partially dehydrated state, at least two of four water molecules were considered to be disordered in occupancy and/or coordinates. Insight into the crystal structure of STFX hydrate stored at low and high relative humidities and geometry of the hydrogen bond were helpful to estimate the origin of non-stoichiometric hydration of STFX hydrate. 相似文献
132.
We investigate volume phase transition in gels immersed in mixture solvents, on the basis of a three-component Flory-Rehner theory. When the selectivity of the minority solvent component to the polymer network is strong, the gel tends to shrink with an increasing concentration of the additive, regardless of whether it is good or poor. This behavior originates from the difference of the additive concentration between inside and outside the gel. We also found the gap of the gel volume at the transition point can be controlled by adding the strongly selective solutes. By dissolving a strongly poor additive, for instance, the discontinuous volume phase transition can be extinguished. Furthermore, we observed that another volume phase transition occurs far from the original transition point. These behaviors can be well explained by a simplified theory neglecting the nonlinearity of the additive concentration. 相似文献
133.
S Kagaya M Saiki Z A Malek Y Araki K Hasegawa 《Fresenius' Journal of Analytical Chemistry》2001,371(3):391-393
The usefulness of coprecipitation with lanthanum phosphate for separation and preconcentration of some heavy metals has been investigated. Although lanthanum phosphate coprecipitates iron(III) and lead quantitatively at pH 2.3, iron(II) can barely be collected at this pH. This coprecipitation technique was applicable to the separation and preconcentration of iron(III) before inductively coupled plasma atomic-emission spectrometric (ICP-AES) determination; the recoveries of iron(III) and iron(II) from spiked water samples were 103-105% and 0.2-0.7%, respectively. The coprecipitation was also useful for separation of 20 microg lead from 100 mL of an aqueous solution that also contained 1-100 mg iron. Coprecipitation of iron was substantially suppressed by addition of ascorbic acid, which enabled recovery of 97-103% of lead added to the solution, bringing the recovery to within 1.6-5.0% of the relative standard deviations. Lanthanum phosphate can also coprecipitate cadmium and indium quantitatively, although chromium(III), cobalt, and nickel and large amounts of sodium, potassium, magnesium, and calcium are barely coprecipitated at pH approximately/= 3. 相似文献
134.
A determination method for lead in waste water and effluent was studied using flame atomic absorption spectrometry after
preconcentration of lead by the rapid coprecipitation technique with gallium phosphate. Lead ranging from 0.5 to 50 μg was
quantitatively coprecipitated with gallium phosphate from 100–150 mL sample solution (pH ∼5). The presence of gallium phosphate
did not affect the atomic absorbance of lead. Since the concentration of gallium in the final sample solution is also measurable
by flame atomic absorption spectrometry at 250.0 nm without further dilution, the rapid coprecipitation technique, which does
not require complete collection of the precipitate, becomes possible using a known amount of gallium and measuring the concentrations
of both lead and gallium in the final sample solution by flame atomic absorption spectrometry. The 32 diverse ions tested
gave no significant interferences in the lead determination. The method proposed here is rapid and has good reproducibility.
Received: 16 August 1999 / Revised: 6 October 1999 / Accepted: 14 October 1999 相似文献
135.
Native and three selectively methylated β-cyclodextrin (β-CD)-bonded stationary phases without an unreacted spacer arm for liquid chromatography were prepared, where heptakis(2-O-methyl)-β-CD, heptakis(3-O-methyl)-β-CD and heptakis(2,3-di-O-methyl)-β-CD were used as the methylated β-CDs. The enantiomer separation abilities of the resulting β-CD stationary phases for 12 pairs of dansylamino acid enantiomers and six pairs of N-3,5-dinitrobenzoyl amino acid methyl esters as model solutes were investigated. The effects of pH and methanol content of the mobile phase on the retention and resolution were examined to optimize the mobile phase conditions. The optimum resolution for the dansylamino acids was achieved using a mobile phase consisting of 1.0% triethylammonium acetate buffer (pH 5.0)–methanol (v/v 4/6) on the β-CD stationary phase. Heptakis(3-O-methyl)- and heptakis(2,3-di-O-methyl)-β-CD-bonded stationary phases showed little enantiomer separation abilities for the dansylamino acids. The heptakis(2-O-methyl)-β-CD-bonded stationary phase exhibited no enantioselectivities for those solutes.
For the N-3,5-dinitrobenzoyl amino acid methyl esters, the optimum resolution was achieved using a mobile phase consisting of 1.0% triethylammonium acetate buffer (pH 5.0)–methanol (v/v 9/1) on a heptakis(2-O-methyl)-β-CD stationary phase. The heptakis(2,3-di-O-methyl)-β-CD-bonded stationary phases exhibited no enantioselectivities for the N-3,5-dinitrobenzoyl amino acid methyl esters. β-CD and heptakis(3-O-methyl)-β-CD-bonded stationary phases had no enantiomer separation abilities for those solutes except for the N-3,5-dinitrobenzoyl phenylalanine methyl ester. 相似文献
136.
137.
138.
Yasuo Butsugan Akihiko Yamashita Shuki Araki 《Journal of organometallic chemistry》1985,287(1):103-108
The reaction of dipotassium tetracarbonylferrate with various allylic phosphates and halides gives 1,3-dienetricarbonyliron complexes. The formation of the complexes is highly stereoselective depending on the geometry of the allylic compounds used. 相似文献
139.
The aromatic character of the meso-ionic sesquifulvalene (2) is demonstrated by six electrophilic substitution reactions on the cyclopentadienide ring. 相似文献
140.
Samarium(II)-induced coupling of acid chlorides with allylic halides gave diallylated tertiary alcohols. Monoallylated allylic ketones could not be obtained. 相似文献