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101.
Bacterial adhesion to epithelial cells is a key step in infections, allowing subsequent colonization, invasion and internalization of pathogens into tissues. Anti-adhesive agents are therefore potential prophylactic tools against bacterial infections. The range of anti-adhesive compounds is largely confined to carbohydrate analogues. Tannins are generously recognized as potent antimicrobials, but little data exist on their anti-adherence potency. Using a model for mucosal pathogenesis with labeled group A-streptococci (GAS) and human laryngeal HEp-2 cells, a series of flavan-3-ols (epicatechin, epigallocatechin, epigallocatechin-3-O-gallate) and highly purified and chemically characterized proanthocyanidin samples including procyanidins based on epicatechin, catechin or 'mixed' constituent flavanyl units, prodelphinidins made up of (epi)gallocatechin monomeric unts as well as oligomers possessing A-type units in their molecules was evaluated for anti-adhesive effects. Reduced microbial adherence was observed exclusively for prodelphinidins, suggesting that pyrogallol-type elements, i.e., (epi)gallocatechin units are important structural features. This is the first report on structure-activity relationships regarding the anti-adhesive potency of proanthocyanidins. In addition, the structures of the first chemically defined proanthocyanidins from Pelargonium sidoides are disclosed. 相似文献
102.
A new method for the analysis of three ecological insecticides, namely azadyrachtin, spinosad (sum of spinosyn A and spinosyn
D) and rotenone, in produce and soil samples is presented. Investigated compounds are one of the most significant insecticides
authorized for organic farming crop protection in many countries. Extraction of the pesticides from plant and soil matrices
was performed by using a modified quick, easy, cheap, effective, rugged, and safe (QuEChERS) method. The method entailed a
single extraction of the investigated compounds with acidified acetonitrile followed by a dispersive solid-phase extraction
cleanup step prior to the final determination by reverse-phase ultra-performance liquid chromatography/tandem quadrupole mass
spectrometry (UPLC-MS/MS). Validation studies were carried out on cabbage, tomato and soil samples. Recoveries of the spiked
samples were in the range between 67% and 108%, depending on the matrix and the spiking level. Relative standard deviations
for all matrix–compound combinations did not exceed 12%. The limits of quantification were ≤0.01 mg kg−1 in all cases, except for azadirachtin. The developed method was applied to the analysis of real samples originating from
organic farming production. 相似文献
103.
A reversed-phase high-performance liquid chromatography method with gradient elution was developed for the determination of the caffeic, p-coumaric, and ferulic acids in propolis concentrates. Solid-phase extraction on an RP18 column was applied for preliminary purification, and chromatographic separation was performed on 100 RP18e Lichrospher column of particle size 5 microm. The mobile phase was obtained by mixing in appropriate ratios 0.03 mM NaH2PO4, acidified with H3PO4 up to pH = 3.0, with acetonitrile to obtain a gradient in the elution process. Spectrophotometric detection was conducted at 320 nm. Under the established conditions, the method featured high sensitivity, good precision, and comparability of results, as proven by method validation and statistical analysis of the obtained results. The limits of detection were 0.315, 0.325, and 0.695 microg/mL for caffeic, p-coumaric, and ferulic acids, respectively. The corresponding recovery values were 98.14, 101.05, and 99.42% and the linearity ranges from 1.31 to 99.18 microg/mL, 1.52 to 119.16 microg/mL, and 2.42 to 184.14 microg/mL. The precision of the method was expresed by relative standard deviation values that did not exceed 3%. It was also shown that the propolis concentrates under examination had similar antibacterial activity against Staphylococcus aureus ranging from 119.8 to 124.3 microg/mL, contrary to model mixtures that showed no antibacterial activity. 相似文献
104.
Aneta Dudek 《Discrete Applied Mathematics》2006,154(9):1372-1379
A graph G is said to be hamiltonian path saturated (HPS for short), if G has no hamiltonian path but any addition of a new edge in G creates a hamiltonian path in G. It is known that an HPS graph of order n has size at most and, for n?6, the only HPS graph of order n and size is Kn-1∪K1. Denote by sat(n,HP) the minimum size of an HPS graph of order n. We prove that sat(n,HP)?⌊(3n-1)/2⌋-2. Using some properties of Isaacs’ snarks we give, for every n?54, an HPS graph Gn of order n and size ⌊(3n-1)/2⌋. This proves sat(n,HP)?⌊(3n-1)/2⌋ for n?54. We also consider m-path cover saturated graphs and Pm-saturated graphs with small size. 相似文献
105.
We consider the Kantorovich and the Durrmeyer type modifications of the generalized Favard operators and we prove some direct
approximation theorems for functions f such that w
σ
f ∈ L
p
(R), where 1 ≤ p ≤ ∞ and w
σ
(x) = exp(−σx
2), σ > 0. 相似文献
106.
Izabella Jastrzębska Aneta Dobrogowska Ewa Lutostańska Jacek W. Morzycki 《Tetrahedron》2010,66(27-28):5024-5029
Direct dehydrogenation of spirostane sapogenins with benzeneseleninic anhydride/iodoxybenzene afforded the Δ22 derivatives in low yields. The reactions catalyzed by BF3/Et2O produced the 23-oxo-sapogenins in addition to their 22-oxo-23-spiro-isomers. The reactions of sapogenins with benzeneseleninic anhydride carried out in the presence of TiCl4 afforded products chlorinated at C23. 相似文献
107.
The adsorption of urea on a polycrystalline copper electrode from 0.01 M NaClO4 solution has been studied by impedance spectroscopy and radiometric method. The dependence of the surface concentration of urea on the electrode potential and the bulk concentration was determined. From radiometric data, it follows that the adsorption of urea on the copper electrode takes place in the entire range of studied potentials where no faradaic processes occur. In this range, the process of adsorption is practically reversible with respect to the potential and the bulk concentration of urea. The experimental data were described by the Langmuir and the virial isotherms and the Gibbs energy of adsorption were calculated. The data of the urea adsorption on different electrodes have been compared and the role of the kind of the metal on the adsorption process was discussed. 相似文献
108.
109.
Modeling toxicity by using supervised kohonen neural networks 总被引:2,自引:0,他引:2
Mazzatorta P Vracko M Jezierska A Benfenati E 《Journal of chemical information and computer sciences》2003,43(2):485-492
Counterprogation neural network is shown to be a powerful and suitable tool for the investigation of toxicity. This study mined a data set of 568 chemicals. Two hundred eighty-two objects were used as the training set and 286 as the test set. The final model developed presents high performances on the data set R(2) = 0.83 (R(2) = 0.97 on the training set, R(2) = 0.59 on the test set). This technique distinguishes itself also for the ability to give to the expert two-dimensional maps suitable for the study of the distribution/clustering of the data and the identification of outliers. 相似文献
110.
T. Kowalska 《Chromatographia》1990,30(5-6):298-300
Summary We apply our new retention model introduced elsewhere to the studies of intermolecular interactions between the solute and
the remaining components of a normal-phase HPLC system using a binary mobile phase consisting of an alcohol and a hydrocarbon.
This can be achieved through the analysis of the regressional parameters A, B, and C appearing in the relationship of solute
retardation (RF) vs. mobile phase composition. Negative values of these parameters indicate a greater affinity of the solute to the stationary
phase than to a given mobile phase moiety, whereas positive values have a reverse meaning. According to the absolute values
of A, B, and C solute groups can be arranged according to the affinity toward a given mobile phase moiety, which is a detailed
and important information regarding their separation, the stationary phase and with each individual constituent of the mobile
phase. 相似文献