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排序方式: 共有71条查询结果,搜索用时 15 毫秒
1.
Most of the novel highly potent drugs, developed on the basis of modern molecular medicine, taking into account cell surface recognition techniques, show poor water solubility. A chemical modification of the drug substance enhancing the solubility often decreases the pharmacological activity. Thus, as an alternative an increase of the solubility can be obtained by the reduction of the size of the drug particles. Unfortunately, it is often difficult to obtain micro or nanosized drug particles by classical or more advanced crystallization using supercritical gases or by milling techniques. In addition, nanosized particles are often not physically stable and need to be stabilized in an appropriate matrix. Thus, it may be of interest to manufacture directly nanosized drug particles stabilized in an inert hydrophilic matrix, i.e. nanostructured and nanocomposite systems. Solid solutions and solid dispersions represent nanostructured and nanocomposite systems. In this context, the use of the vacuum-fluidized-bed technique for the spray-drying of a low water soluble drug cosolubilized with a hydrophilic excipient in a polar organic solvent is discussed. In order to avoid the use of organic solvents, a special spray-freeze-drying technique working at atmospheric pressure is presented. This process is very suitable for temperature and otherwise sensitive drugs such as pharmaproteins. 相似文献
2.
Sanchez-sanz M; Blyth MG 《The Quarterly Journal of Mechanics and Applied Mathematics》2007,60(2):125-138
Unsteady, axisymmetric stagnation flow about a circular cylinderis examined when the far-field flow is a periodic function oftime with a fixed time average and an oscillatory part of prescribedamplitude and frequency. Solutions are computed for arbitraryvalues of the Reynolds number, quantifying the effects of surfacecurvature, and a frequency parameter based on the period ofthe far-field flow. It is found that solutions remain regularand periodic provided that the far-field amplitude lies belowa critical value. Above this value, solutions terminate in afinite-time singularity. The blow-up time is delayed by increasingthe curvature of the surface. These results are corroboratedby asymptotic predictions valid in the limits of small and largeamplitude and frequency. For large Reynolds number, the problemreduces to the two-dimensional stagnation-point flow againsta plane wall studied by previous authors. 相似文献
3.
Leuenberger M Nyfeler P Moret HP Sturm P Indermuhle A Schwander J 《Rapid communications in mass spectrometry : RCM》2000,14(16):1552-1557
A new technique for measuring CO(2) concentration in air samples, based on mass spectrometry, is described as an alternative to the common gas chromatographic method. Using a dual inlet isotope ratio mass spectrometer (IRMS), the ratio of the abundances of the m/z peaks 44 and 28 is determined. The precision of measurements (standard deviation <3 ppmv) is generally as good as the analysis with gas chromatography for small air samples (<1 ml STP of air). A major advantage of this new method is the possibility of parallel elemental and isotopic measurements of many air components. The technique is further improved by new wide mass range mass spectrometers allowing simultaneous intensity measurements of several m/z values between 28 and 44, resulting in an uncertainty of <0.5 ppm. The precision is somewhat limited by the production of N(2)O and NO(2) from N(2) and O(2) in the ion source, which accounts for about half of the signal strength at m/z 44. Copyright 2000 John Wiley & Sons, Ltd. 相似文献
4.
The configurational isomers of astaxanthin (3,3′-dihydroxy-β,β-carotene-4,4′-dione) from the flesh of salmon (Salmo salar and Oncorhynchus) caught at different places in Europe and Canada were isolated and analyzed as (?)-camphanic acid diesters by means of HPLC. The biological variation in the composition of the configurational isomers in seven fish was surprisingly similar: 78 to 85% of (3S, 3′S)-astaxanthin, 12 to 17% (3R, 3′R)-astaxanthin and 2 to 6% meso-astaxanthin. 相似文献
5.
Iida K Todo H Okamoto H Danjo K Leuenberger H 《Chemical & pharmaceutical bulletin》2005,53(4):431-434
An attempt was made to produce carrier particles for dry powder inhalation with lactose carrier particles surface-coated using a Wurster fluidized bed. The lactose carrier particles were coated with lactose aqueous solution containing hydroxypropyl methyl cellulose (HPMC) as a binder using a Wurster coating apparatus. Drug/carrier powder mixtures were prepared consisting of micronized salbutamol sulfate and lactose carriers under various particle surface conditions. These powder mixtures were aerosolized by a Jethaler((R)), and the in vitro deposition properties of salbutamol sulfate were evaluated by a twin impinger. The in vitro inhalation properties of the powder mixture prepared using the coated lactose carrier differed significantly compared with those of the powder mixture prepared using the uncoated lactose carrier, indicating improvements in in vitro inhalation properties of sulbutamol sulfate. In vitro inhalation properties increased with the surface coating time. This surface coating system would thus be valuable for increasing the in vitro inhalation properties of dry powder inhalation with lactose carrier particles. 相似文献
6.
Iida K Hayakawa Y Okamoto H Danjo K Leuenberger H 《Chemical & pharmaceutical bulletin》2001,49(10):1326-1330
The effects of the flow and packing properties of a drug/carrier powder mixture on emission of drug adhering to the carrier from capsules and inhalation devices were investigated. Model powder mixtures were designed consisting of lactose carriers with different particle shapes were prepared by surface treatment and micronized salbutamol sulfate. These powder mixtures were aerosolized by a Spinhaler, and in vitro deposition properties of salbutamol sulfate were evaluated by a twin impinger. The flow properties of the mixed powders were evaluated by the Carr's flowability index (FI) and Hausner's ratio (HR). The packing properties of the mixed powders were determined employing the tapping method. Compared with the powder mixed with the untreated lactose carrier, the FI, HR, and the constant K in Kawakita's equation of the powder mixture prepared using the surface-treated lactose carrier were significantly different, showing that the flow and packing properties of the drug/carrier powder mixture were improved. Using this surface-treated system, the handling of the powder mixture when packing into capsules is improved, which is desirable for handling dry powder inhalants. The fraction (%) of drug emitted from capsules and devices (EM) and the FI of the powder mixture were correlated. As the flow properties improved, the outflow of the powder mixture from capsules and devices became easier, and emission of drug adhering on the carrier from capsules and devices improved. Improvement of the inhalation process, such as the drug particles emitted from the inhalation system, is valuable for increasing inhalation properties of dry powder inhalation. 相似文献
7.
S -nitrosothiols have many biological activities and may act as nitric oxide (NO) carriers and donors, prolonging NO half-life in vivo. In spite of their great potential as therapeutic agents, most S -nitrosothiols are too unstable to isolate. We have shown that the S -nitroso adduct of N -acetylcysteine (SNAC) can be synthesized directly in aqueous and polyethylene glycol (PEG) 400 matrix by using a reactive gaseous (NO/O2 ) mixture. Spectral monitoring of the S–N bond cleavage showed that SNAC, synthesized by this method, is relatively stable in nonbuf-fered aqueous solution at 25°C in the dark and that its stability is greatly increased in PEG matrix, resulting in a 28-fold decrease in its initial rate of thermal decomposition. Irradiation with UV light (λ= 333 nm) accelerated the rate of decomposition of SNAC to NO in both matrices, indicating that SNAC may find use for the photogeneration of NO. The quantum yield for SNAC decomposition decreased from 0.65 ± 0.15 in aqueous solution to 0.047 ± 0.005 in PEG 400 matrix. This increased stability in PEG matrix was assigned to a cage effect promoted by the PEG microenvironment that increases the rate of geminated radical pair recombination in the homolytic S–N bond cleavage process. This effect allowed for the storage of SNAC in PEG at −20°C in the dark for more than 10 weeks with negligible decomposition. Such stabilization may represent a viable option for the synthesis, storage and handling of S -nitrosothiol solutions for biomedical applications. 相似文献
8.
We propose a teleportation scheme that relies only on single-photon measurements and Faraday rotation, for teleportation of many-qubit entangled states stored in the electron spins of a quantum dot system. The interaction between a photon and the two electron spins, via Faraday rotation in microcavities, establishes Greenberger-Horne-Zeilinger entanglement in the spin-photon-spin system. The appropriate single-qubit measurements, and the communication of two classical bits, produce teleportation. This scheme provides the essential link between spintronic and photonic quantum information devices by permitting quantum information to be exchanged between them. 相似文献
9.
A new fast high-precision on-line technique is described for the determination of hydrogen isotope ratios of water by continuous-flow mass spectrometry. For the first time H(2)/H(2)O-equilibration using a platinum catalyst has been used in a fully continuous process. A significant reduction in the H(2)/H(2)O-equilibration time is achieved by a complete vaporization of the water and by increasing the exchange temperature to 100 degrees C. The analysis time is only approximately 5 min/sample which includes equilibration and processing. Measurement precision and accuracy are better than 1 per thousand and sample consumption is only approximately 5 microL. This new technique allows the measurement of a wide range of aqueous samples either in a semi-continuous way (discrete samples are injected one after another) or in a fully continuous way. This allows us, for the first time, to make continuous measurements of ice cores. 相似文献
10.
M. Münzenberg T. Neisius F. Leuenberger W. Felsch S. Pizzini A. Fontaine G. Krill S. Pascarelli 《Applied Physics A: Materials Science & Processing》2001,73(6):717-721
For rare-earth (RE)-hydrides (REHx), a metal-to-insulator transition is observed if the hydrogen concentration is increased
from the dihydride (x=2) towards the trihydride (x=3). This transition provides an object for studies of the magnetic interface
polarization in layered ferromagnet/insulator structures. For different samples with a fixed Fe and varied LaHx sublayer thickness tLaHx ([15 ? Fe/t? LaHx]xn), the H concentration x in the LaHx sublayer is gradually increased in the experiment. Starting from the as prepared dihydride REH2-δ, the modification of the magnetic polarization of the La-5d states at the Fe/Lax interface is studied across the transition by magnetic circular dichroism measurements at the La-L2 and L3 edges. The experiments reveal an induced magnetic polarization of the La-5d hole states on a length scale of 9 ? that is
independent of the altered electronic structure of the La-5d states.
Received: 23 May 2001 / Accepted: 4 July 2001 / Published online: 5 October 2001 相似文献