Fourier-transform infrared spectroscopy and non-isothermal methods—chemiluminometry, differential scanning calorimetry, and differential thermogravimetry—were used to characterize potential structural changes of thiol-modified hyaluronans. Degradative conditions tested via rotational viscometry were first initiated applying oxidative Weissberger’s system in a reaction system under aerobic conditions. Several low-molecular-weight thiol compounds—cysteamine, l-cysteine, and N-acetyl-l-cysteine—were subsequently tested for their potential antioxidative effects against hyaluronan degradation. It was shown that different final values of dynamic viscosity of hyaluronan solutions were dependent on the thiol structure and its initial concentration. An idea has been put forward that together with the reduction of the hyaluronan molecular weight, which is a consequence of fragmentation, the degradation products might contain associated or even cross-linked structures. In the case of N-acetyl-l-cysteine application, the carbonaceous residue evidenced by differential thermogravimetry was increased when compared to that of intact hyaluronan. 相似文献
A new method for the determination of trace glyphosate (GLYP), non-selective pesticide, by CZE with online ITP pre-treatment of drinking waters on a column-coupling (CC) chip has been developed. CC chip was equipped with two injection channels of 0.9 and 9.9 μL volumes, two separation channels of 9.3 μL total volume and a pair of conductivity detectors. A very effective ITP sample clean-up performed in the first channel at low pH (3.2) was introduced for quick CZE resolution and detection of GLYP carried out at higher pH (6.1) in the second channel on the CC chip. The LOD for GLYP was estimated at 2.5 μg/L (15 nmol/L) using a 9.9 |mL volume of the injection channel. ITP-CZE analyses of model and real samples have provided very favorable intra-day (0.1-1.2% RSD) and inter-day (2.9% RSD) repeatabilities of the migration time for GLYP while 0.2-6.9% RSD values were typical for the peak area data. Recoveries of GLYP in spiked drinking water varied in the range of 99-109%. A minimum pre-treatment of drinking water (degassing and dilution) and a short analysis time (ca. 10 min) were distinctive features of ITP-CZE determinations of GLYP on the CC chip with high sample volume loaded, as well. 相似文献
In this study, forty-seven plant species belonging to seven families were analysed by GC and GC-MS for the contents of pharmacologically effective quinones: dithymoquinone (DTQ), thymohydroquinone (THQ), and thymoquinone (TQ). The results showed that detectable amounts (??1 mg kg?1) of at least one of these compounds have been found in three species of both Monarda (M. didyma, M. media, and M. menthifolia) and Thymus (T. pulegioides, T. serpyllum, and T. vulgaris) genera, two Satureja (S. hortensis and S. montana) species, and in single representatives of Eupatorium (E. cannabinum), Juniperus (J. communis), and Nigella (N. sativa) genera. The maximum contents of THQ and TQ were found in M. media aerial parts and M. didyma inflorescences (2674 and 3564 mg kg?1 of dried weight, respectively) in amounts significantly exceeding their maximum contents in N. sativa seeds (THQ = 530 mg kg?1 and TQ = 1881 mg kg?1), which are generally considered as the main natural source of both of these compounds. As a conclusion, M. didyma (bergamot) and M. media (purple bergamot) can be recommended as new prospective natural sources of THQ and TQ for pharmaceutical or food industries. 相似文献
In this paper we study the set of x ∈ [0, 1] for which the inequality |x − xn| < zn holds for infinitely many n = 1, 2, .... Here xn ∈ [0, 1) and zn s> 0, zn → 0, are sequences. In the first part of the paper we summarize known results. In the second part, using the theory of distribution
functions of sequences, we find the asymptotic density of n for which |x − xn| < zn, where x is a discontinuity point of some distribution function of xn. Generally, we also prove, for an arbitrary sequence xn, that there exists zn such that the density of n = 1, 2, ..., xn → x, is the same as the density of n = 1, 2, ..., |x − xn| < zn, for x ∈ [0, 1]. Finally we prove, using the longest gap dn in the finite sequence x1, x2, ..., xn, that if dn ≤ zn for all n, zn → 0, and zn is non-increasing, then |x − xn| < zn holds for infinitely many n and for almost all x ∈ [0, 1]. 相似文献
The most active form of sulfur in biomolecules is the thiol group, present in a number of biologically active compounds. Here we present a comprehensive study of thiol analysis using flow injection analysis/HPLC with electrochemical detection. The effect of different potentials of working electrodes, of organic solvent contents in the mobile phase, and of isocratic and gradient elution on simultaneous determination of thiol compounds (cysteine, cystine, N-acetylcysteine, homocysteine, reduced and oxidised glutathione, desglycinephytochelatin, and phytochelatins) are described and discussed. These thiol compounds were well separated and detected under optimised HPLC-electrochemical detection conditions (mobile phase: 80 mM trifluoroacetic acid and methanol with a gradient profile starting at 97:3 (TFA:methanol), kept constant for the first 8 min, then decreasing to 85:15 during one minute, kept constant for 8 min, and finally increasing linearly up to 97:3 from 17 to 18 min; the flow rate was 0.8 mL/min, column and detector temperature 25 degrees C, and the electrode potential 900 mV). We were able to determine tens of femtomoles (3 S/N) of the thiols per injection (5 microL), except for phytochelatin5 whose detection limit was 2.1 pmole. This technique was consequently used for simultaneous determination of compounds of interest in biological samples (maize tissue and human blood serum). 相似文献
If G is a connected graph of order n ⩾ 1, then by a hamiltonian coloring of G we mean a mapping c of V (G) into the set of all positive integers such that |c(x) − c(y)| ⩾ n − 1 − DG(x, y) (where DG(x, y) denotes the length of a longest x − y path in G) for all distinct x, y ∈ V (G). Let G be a connected graph. By the hamiltonian chromatic number of G we mean
, where the minimum is taken over all hamiltonian colorings c of G.
The main result of this paper can be formulated as follows: Let G be a connected graph of order n ⩾ 3. Assume that there exists a subgraph F of G such that F is a hamiltonian-connected graph of order i, where 2 ⩽ i ⩽ 1/2 (n+1). Then hc(G) ⩽ (n−2)2+1−2(i−1)(i−2). 相似文献
The development of a mechanically stable, functionally graded Ti-doped a-C:H interface layer in combination with a functional a-C:H coating requires a reduction of the brittle phases which induce generally problems in the transitions from Ti to TiC/a-C:H. The core objective of this study was to develop an optimum interlayer between the substrate and the functional top layer for biomedical applications, namely for tooth implants. Since the interlayer may be exposed to the sliding process, in the case of local failure of the top layer it has to fulfil the same criteria: biocompatibility, high wear resistance and low friction.The functional Ti-C:H layers with thickness in the range 2.5–3.5 μm were deposited by a magnetron sputtering/PECVD hybrid process by sputtering a Ti-target in a C2H2 + Ar atmosphere in dc discharge regime. The sets of coating samples were prepared by varying the C and H concentrations controlled by the C2H2 flow during the deposition process. The tribological properties were evaluated on a pin-on-disc tribometer at room temperature (RT) and at 100 °C using 440C balls with a diameter of 6 mm. The tests at 100 °C were performed to investigate the effect of the sterilization temperature on the tribological properties and the coating lifetime as well. The tribological performance was examined with respect to the friction coefficient, the wear rates of the coating and the counter-parts and the analysis of the wear debris. The Ti/C ratio decreased almost linearly from 4.5 to 0.1 with increasing C2H2 flow; the hydrogen content showed a minimum of 5 at.% at C2H2 flow of 30 sccm, while for lower flows it was about 10 at.%. The coatings could be divided into three groups based on the C2H2 flow: (i) 10–15 sccm, exhibiting severe abrasive damage during the sliding tests, (ii) 20–45 sccm, showing the highest hardness and friction values, and (iii) 52–60 sccm, with moderate hardness and minimal values of the friction coefficient and the wear rate. 相似文献
Hot‐wired electrodes : Thin metallic wires (d=25 μm) are covered with a 3 μm layer of single‐walled carbon nanotubes (SWCNTs; see image) by electrophoresis from a suspension containing excess ionic surfactant. A pure SWCNT surface is achieved by heating the electrode in air. Strong differences between covered and bare metallic electrodes occur with in situ heating during electrochemical experiments.
The vertices of the odd-distance graph are the points of the plane ℝ2. Two points are connected by an edge if their Euclidean distance is an odd integer. We prove that the chromatic number of
this graph is at least five. We also prove that the odd-distance graph in ℝ2 is countably choosable, while such a graph in ℝ3 is not.
The research of J. Maňuch was supported in part by MITACS (Mathematics of Information Technology and Complex Systems).
The research of M. Rosenfeld was supported in part by the Chancellor Research Grant and the Institute of Technology, UWT.
The research of S. Shelah was supported by the United States-Israel Binational Science Foundation (Grant no. 2002323), and
by NSF grant No. NSF-DMS 0600940. No. 923 on Shelah’s publication list.
The research of L. Stacho was supported in part by NSERC (Natural Science and Engineering Research Council of Canada) grant. 相似文献