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991.
Two HPLC/MS/MS methods, one for determination of neomycin sulfate and the other for determination of oxytetracycline hydrochloride in the presence of their impurities, were developed and validated. Separations were achieved with gradient elution on a C18 column. All components were ionized by positive-ion electrospray and detected by multiple reaction monitoring. Calibration curves were linear, with correlation coefficients >0.99. Precision of the methods was confirmed by RSD values of 0.34 and 0.71% for neomycin and oxytetracycline, respectively. Recovery values of 101.5 and 101.0%, respectively, indicated adequate accuracy. Analysis time for neomycin was 24 min, with the retention time of the main compound at 10.1 min; for oxytetracycline, the analysis time was 18 min, with the main peak at 9.95 min. Longer retention times than expected were a consequence of the necessity of chromatographic separation of isomers with the same ion transition. All impurities defined in the pharmacopoeias were determined and their identities confirmed. The methods were tested for QC of veterinary dosage forms (commercial powders and injections containing these antibiotics). 相似文献
992.
Gröger K Baretić D Piantanida I Marjanović M Kralj M Grabar M Tomić S Schmuck C 《Organic & biomolecular chemistry》2011,9(1):198-209
Two novel guanidiniocarbonyl pyrrole-pyrene conjugates 3 and 4 as spectroscopic probes for ds-polynucleotides were synthesized and their interaction with different ds-DNAs/RNAs studied. Compared to a previously reported first set of conjugates (1 and 2) the significant extension and increased rigidity of the central part of the structure resulted in a switch of DNA binding mode from intercalative (previously studied derivatives 1 and 2 with a nonbinding and flexible linker) to minor groove binding of the two novel guanidiniocarbonyl-pyrrole-pyrene conjugates 3 and 4. These two compounds interact strongly with ds-DNAs, but only weakly with ds-RNA. The newly incorporated heterocyclic moieties within the central part of the structure of 3 and 4 were able to control by steric and hydrogen-bonding effects the alignment of the molecules within various, structurally different forms of DNA minor grooves, whereby even small differences in the position of the attached pyrene within the groove were reflected in different fluorimetric responses. In addition, 3 and 4 revealed intriguing in vitro selectivity among various human tumour cell lines. 相似文献
993.
994.
The histone deacetylase (HDAC) inhibitor suberoylanilide hydroxamic acid (SAHA) was used to turn on the biosynthesis of EGM-556, a new cyclodepsipeptide of hybrid biosynthetic origin, isolated from the Floridian marine sediment-derived fungus Microascus sp. The absolute configurations of three chiral centers were determined by Marfey's derivatization. EGM-556 represents one of the few examples in which silent biosynthetic genes, encoding a new secondary metabolite, were activated by means of epigenetic manipulation of the fungal metabolome. 相似文献
995.
Nanoparticles serve as fundamental building blocks for nanobiotechnology, especially in several applications in the development of novel (bio)sensing systems. Nanoparticles can be used for modification of the surfaces of (bio)sensing transducers or as optical or electroactive labels to improve different aspects of performance, for example sensitivity, detection limit, multidetection capability, and response stability. Nanoparticles can be integrated into the transducer materials on an individual basis or inside other matrices to ensure the immobilization of recognition biomolecules and/or receptors which are the principal components of the (bio)sensing systems. Incorporation of nanoparticles into optical and electrochemical (bio)sensing systems, including their use in microfluidic based systems has the advantages of enabling the design of robust, easy to use, portable, and cost-effective devices. 相似文献
996.
Hanć A Komorowicz I Iskra M Majewski W Barałkiewicz D 《Analytical and bioanalytical chemistry》2011,399(9):3221-3231
The study was aimed to evaluate the influence of the vascular disease, atherosclerotic obliterans (AO), on the location and
concentration of elements in the arterial wall and serum. Use of a modern method for studying element’s concentration and
distribution in samples of clinical material, i.e. laser ablation inductively coupled plasma mass spectrometry, is presented.
Elements are not equally distributed between the inner (intima) and the outer (media + adventitia) layer of the arterial wall.
Among the studied elements, calcium was found to have an unquestionable role in the calcification of the wall. Increased concentration
of calcium found in the inner part of the atherosclerotic arterial wall and in the plaque, as compared to the control arterial
wall samples, demonstrates the unquestionable role of this element in the calcification of the wall observed in AO. Applied
chemometric methods were useful for demonstrating the differences in the element’s concentration in blood serum and the arterial
wall samples between AO and the control group. 相似文献
997.
We consider the heat equation in a straight strip, subject to a combination of Dirichlet and Neumann boundary conditions. We show that a switch of the respective boundary conditions leads to an improvement of the decay rate of the heat semigroup of the order of t−1/2. The proof employs similarity variables that lead to a non-autonomous parabolic equation in a thin strip contracting to the real line, that can be analysed on weighted Sobolev spaces in which the operators under consideration have discrete spectra. A careful analysis of its asymptotic behaviour shows that an added Dirichlet boundary condition emerges asymptotically at the switching point, breaking the real line in two half-lines, which leads asymptotically to the 1/2 gain on the spectral lower bound, and the t−1/2 gain on the decay rate in the original physical variables.This result is an adaptation to the case of strips with twisted boundary conditions of previous results by the authors on geometrically twisted Dirichlet tubes. 相似文献
998.
In a series of papers, Green’s relations on the additive and multiplicative reducts of a semiring proved to be a very useful
tool in the study of semirings. However, in the vast majority of cases, Green’s relations are not congruences, and we show
that in such cases it is much more convenient to use the congruence openings of Green’s relations, instead of the Green’s
relations themselves. By means of these congruence openings we define and study several very interesting operators on the
lattices of varieties of semirings and additively idempotent semirings, and, in particular, we establish order embeddings
of the lattice of varieties of additively idempotent semirings into the direct products of the lattices of open (resp. closed)
varieties with respect to two opening (resp. closure) operators on this lattice that we introduced. 相似文献
999.
In this paper, we define the new generalized difference sequence spaces [V, λ, F, p, q]0(Δ
v
m
), [V, λ, F, p, q]1(Δ
v
m
) and [V, λ, F, p, q]∞(Δ
v
m
). We also study some inclusion relations between these spaces. 相似文献
1000.
Vladimir Pavlović 《Acta Mathematica Hungarica》2011,131(3):295-306
We identify continuous real-valued functions on a Tychonoff space X with their (closed) graphs thus allowing for C(X) to naturally inherit the lower Vietoris topology from the ambient hyperspace. We then calculate a bitopological version of tightness using the weak Lindelöf numbers of finite powers of X. We also characterize bitopological versions of countable fan and strong fan tightness of the point-open topology with respect to the lower Vietoris topology on C(X) in terms of suitable covering properties of the powers X n formulated using the language of S 1 and S fin selection principles. 相似文献