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331.
There is no experimental proof documented in the literature for the existence of any beryllium peroxide compound. All recent pertinent preparative attempts described in this work, using a range of beryllium salts with various peroxides as reagents under mild conditions, were equally unsuccessful. (1)H and (9)Be NMR investigations of aqueous solutions containing beryllium salts and hydrogen peroxide in a broad pH range also gave no definite evidence for the presence of peroxoberyllates as components of the manifold equilibria in such solutions. Quantum chemical calculations have therefore been carried out to delineate the energetics and structures of various beryllium peroxide model compounds. Standard Hartree-Fock and density functional methods were employed at various levels of sophistication. The series of prototypes considered consists of [BeOH](+), Be(OH)(2), Be(OH)(OOH), Be(OOH)(2), [Be(O(2))(2)](2-), [BeO(2)(OH(2))(2)], and [Be(2)(O(2))(2)(OH(2))(4)] (all in the gas phase). Surprisingly, the triatomic cation [BeOH](+) has been found to have a linear structure. All the Be-O(peroxide) bonds are found to be rather long, suggesting weaker bonding compared to the Be-O bonds in aquo, hydroxo, or oxo complexes. Hydrogen peroxide or anions derived therefrom are therefore not able to compete successfully with water (hydroxide anions) in aqueous solution. In the mononuclear beryllium peroxide molecules, the peroxide groups form chelating units at tetrahedrally 4-coordinate metal atoms. The binuclear compound [Be(2)(O(2))(2)(OH(2))(4)] has a puckered six-membered-ring structure, close to the standard chair conformation. A significant lengthening of the O-O bonds upon coordination to the Be(2+) centers has been calculated, but it is unlikely that the polarization of the peroxide group by the high positive charge density at Be(2+) is significant to cause an intrinsic instability of beryllium peroxides. All structures represent distinct local minima on the potential energy surface and are predicted to be (meta)stable species in nonaqueous media. The field of aluminum peroxides is a similar gray area on the map of metal and metalloid peroxides and is reminiscent of the well-established "diagonal-relation" of Be and Al in the periodic table of the elements.  相似文献   
332.
Summary We study a superconvergence phenomenon which can be obtained when solving a 2nd order elliptic problem by the usual linear elements. The averaged gradient is a piecewise linear continuous vector field, the value of which at any nodal point is an average of gradients of linear elements on triangles incident with this nodal point. The convergence rate of the averaged gradient to an exact gradient in theL 2-norm can locally be higher even by one than that of the original piecewise constant discrete gradient.  相似文献   
333.
A new infrared spectroscopic method suitable for determining total fatty alcohol and fatty acid ester concentrations in industrial oils has been developed. Oil samples were diluted with toluene (1:3 w/w), the toxicity and volatility of which are relatively low compared with more commonly used IR solvents, like carbon tetrachloride or carbon disulfide. Mixture standards were prepared from dodecanol, tetradecanol, octadecanol, methyl stearate and methyl palmitate. Some analytical and statistical tests were performed on the developed method. The recoveries and the repeatability of the method proved to be sufficient for the quantitative determination of fatty alcohol and fatty acid ester additives in industrial oils. Reproducibility testing in another laboratory also produced satisfactory results. The developed method also proved to be relatively quick and simple. This method was developed to satisfy industry’s need to determine the concentrations of these oil additives, and it has already been applied successfully in machinery oil analysis.  相似文献   
334.
The interest in dry powder inhalers (DPIs) has recently increasedbecause the problems associated with the propellants used in pressurized metered-dose inhalers (PMDIs) will be avoided. Cyclodextrins (CDs) may be used as excipients in inhalation powders;e.g., in order to increase the solubility, stability and absorption of an inhaled drug. In thepresent study, the effect of complexation of budesonide with -CD on its pulmonary deposition wasstudied in vitro. In the presence of -CD, the aqueous solubility of budesonidefollowed BS-type phase-solubility behaviour. A precipitationcomplexation method was used to prepare the solid budenoside/-CD complexes. The pulmonary in vitrodeposition of budenoside was evaluated after inhalation of plain budesonide and budenoside/-CDcomplexes (lactose carrier used in both formulations) by using the ``Andersen' cascadeimpactor. The novel Taifun® was used as the DPI. The respirable fractionsof the emitted budesonide dose (initially and after the storage in 40 °C, RH 75%) werecomparable for both plain budesonide and budesonide/-CD complexes. The present studyindicates that a drug/CD-complex can be used in inhalation powderswithout lowering the pulmonary deposition of the drug.  相似文献   
335.
Erroneous results in earlier INDO spin density calculations for hydroaromatic radicals containing ortho disubstituted benzene rings are shown to be due to the wrong order of the e2u near degenerate π molecular orbitals of the benzene ring after the extended Hückel initialization. Agreement with experiment is obtained by interchanging these orbitals.  相似文献   
336.
A home-made temperature control unit has been developed for a commercial capillary electrophoresis apparatus, the Waters Quanta 4000. The effect of the unit on the absolute migration times and peak areas of nine β-blockers is described. It was found that this homemade temperature control unit considerably (≥ 100 %) improved the repeatability of the separation.  相似文献   
337.
Straka M  Pyykkö P 《Inorganic chemistry》2003,42(25):8241-8249
High-energy nitrogen-rich pentazolides of groups 6 and 13-16 are studied theoretically. Many of them have experimentally known azide analogues. Our highest nitrogen-to-element ratio of 40:1 is achieved in the systems [M(N5)8](2-) (M=Cr, Mo, W). The thermodynamic and kinetic stability of the studied systems grows with the negative charge on the system and is highest for tetra-pentazolides and hexa-pentazolides of B, Al, and Si. Systems such as B(N5)4- or Si(N5)6(2-) are examples of the most stable candidates for these new species. N(N5)2- is a candidate for a new all-nitrogen system. Neutral and positive systems were less stable. Pentazole derivatives of "dinuclear" C2Hn and N2Hn systems were investigated and were found to be of comparable stability as their "mononuclear" analogues. Pentazole derivatives of benzene, the C6H(6-n)(N5)n (n=2, 3, 6) systems, have a similar stability as the experimentally known phenylpentazole. A borazine analogue, N3B3H3(N5)3 is predicted to be one of the most stable systems of this family.  相似文献   
338.
A novel simple and mild technique to entrap glucose isomerase activeA. missouriensis cells within α-cellulose beads has been developed. Regenerated α-cellulose beads were shown by SEM to be highly loaded with microbial cells. Kinetics, high operational stability, reactor performance, and low cost of carrier showed the entrapped cell preparation to be suitable for continuous isomerization of 45% glucose solution. This paper was presented at the 4th Enzyme Engineering Conference, Bad Neuenahr, Germany. Sponsored by the Engineering Foundation, New York, New York.  相似文献   
339.
In earlier hydroformylation studies modification of the rhodium catalyst with o-methyl-substituted or o-ethyl-substituted phosphane ligands have increased regioselectivity to branched aldehydes. The promising results achieved created a need for further studies. Hence, a wider group of o-substituted arylphosphane ligands, e.g. (2-cyclohexylphenyl)diphenylphosphane, (2-isopropylphenyl)diphenylphosphane, (2-methylnaphthyl)diphenylphosphane, (2,5-dimethylphenyl)diphenylphosphane and (2-phenylphenyl)diphenylphosphane were synthesized and tested in rhodium-catalyzed hydroformylation to support the previous findings. Characterization of the ligands was made by NMR spectroscopy (1H, 31P{1H}, 13C{1H}, HSQC, COSY-90 and COLOC). Additional parameters for evaluation of the stereoelectronic properties of the ligands were provided by quantum mechanical calculations and by synthesizing Rh(acac)(CO)(PR3) complexes. In the rhodium-catalyzed hydroformylation of propene and 1-hexene the ligands increased the formation of branched aldehydes compared to triphenylphosphane. Additionally the increasing size of the o-alkyl-substituent was found to effect favorably to the iso-selectivity.  相似文献   
340.
The ligninolytic enzyme system ofPhanerochaete chrysosporiun is able to decolorize several recalcitrant dyes. Three lignin peroxidase isoenzymes, LiP 3.85, LiP 4.15, and LiP 4.65, were purified by preparative isoelectric focusing from the carbon-limited culture medium ofP. chrysosporium. Based on amino terminal sequences, the purified isoenzymes correspond to the isoenzymes H8, H6, and H2, respectively, from theN-limited culture. The purified isoenzymes were used for decolorization of an azo dye, Crocein Orange G (COG). According to the kinetic data obtained, the oxidation of COG by lignin peroxidase appeared to follow Michaelis-Menten kinetics. Kinetic parameters for each isoenzyme were determined. The inactivating effect of ascending H2O2 concentrations on COG oxidation is shown to be exponential within the used concentration range. The best degree of decolorization of 100 μM COG was obtained when the H2O2 concentration was 150 μM. This was also the lowest H2O2 concentration for maximal decolorization of 100 μM COG, regardless of the amount of lignin peroxidase used in the reaction.  相似文献   
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