The emergence and prevalence of
multi-drug-resistant bacterial strains increase the potential for outbreaks of incurable infections. The discovery of novel antibiotics and pharmacological preparations requires the identification of novel bioactive small molecules. A specific, sensitive, and reliable quantification method using high-performance liquid chromatography (HPLC) with UV detection was developed for the determination of total persipeptides (A and B), which are cyclic pentapeptides found in the fermentation broth of Streptomyces zagrosensis UTMC 1154 that exhibit bioactivity against methicillin-resistant Staphylococcus aureus (MRSA). A simple liquid–liquid extraction (LLE) method using butanol was employed to extract persipeptides from the fermentation broth prior to HPLC analysis. The chromatographic separation of persipeptides and the internal standard, virginiamycin, was achieved with a gradient of acetonitrile and water on a C18 reversed-phase analytical column in a 25-min analytical run utilizing a flow rate of 0.8 mL min−1 and detection at 210 nm. The whole assay was validated, and the method presented a linear response range with a regression coefficient of determination R2 of 0.9996 for the quantification of persipeptides in the concentration range of 3.9–250.0 µg mL−1, as well as extraction recoveries ranging from 54.78 ± 9.83 % to 56.45 ± 16.33 %. The bias and the precision of the proposed method were <10 %. The detection and quantification limits for the persipeptides were 27 and 83 µg L−1, respectively.
The complexation reaction between Tl+, Ag+ and Pb2+ cations with 2,6-di(furyl-2yl)-4-(4-methoxy phenyl)pyridine as a new synthesis ligand in acetonitrile (ACN)–H2O and methanol (MeOH)–H2O binary solutions has been studied at different temperatures using conductometric method. The conductometric data show that the stoichiometry of the complexes is 1: 1 [M: L] and the stability constant of complexes changes with the binary solutions identity. Also, the structure of the resulting 1: 1 complexes was optimized using the LanL2dz basis set at the B3LYP level of theory using GAUSSIAN03 software. The results show that the change of logKf for (DFMP.Pb)2+ and (DFMP.Ag)+ complexes with the mole ratio of acetonitrile and for (DFMP.Ag)+ and (DFMP.Tl)+ complexes with the mole ratio of methanol have a linear behavior, while the change of logKf of (DFMP.Tl)+complex in ACN–H2O binary solutions (with a minimum in XACN = 0.5) and (DFMP.Ag)+ complex in MeOH–H2O binary solutions (with a minimum in XMeOH = 0.75) show a non-linear behavior. The selectivity order of DFMP ligand for these cations in mol % CAN = 25 and 75 obtain Tl+ > Pb2+ > Ag+ but in mol % CAN = 50, the selectivity order observe Pb2+ > Tl+ > Ag+. Also, this selectivity sequence of DFMP in MeOH–H2O (mol % MeOH = 75 and 100) and (mol % MeOH = 50) is obtained Pb2+ > Ag+ and Tl+ > Ag+ > Pb2+ respectively. The values of thermodynamic parameters show that these values are influenced by the nature and the composition of binary solution. In all cases, the resulting complexes are enthalpy stabilized and entropy destabilized. The TΔSC° versus ΔHC° plot of all obtained thermodynamic data shows a fairly good linear correlation which indicates the existence of enthalpy-entropy compensation in the complexation reactions. 相似文献
Schottky barrier diodes have been integrated into on-chip rectangular waveguides. Two novel techniques have been developed to fabricate diodes with posts suitable for integration into waveguides. One technique produces diodes with anode diameters of the order of microns with post heights from 90 to 125 microns and the second technique produces sub-micron anodes with post heights around 20 microns. A method has been developed to incorporate these structures into a rectangular waveguide and provide a top contact onto the anode which could be used as an I.F. output in a mixer circuit. Devices have been fabricated and D.C. characterized. 相似文献
We study one of the simplest covariant modified-gravity models based on the Dvali-Gabadadze-Porrati (DGP) brane cosmology,
a self-accelerating universe. In this model gravitational leakage into extra dimensions is responsible of late-time acceleration.
We mainly focus on the effects of the model parameters on the geometry and the age of universe. Also we investigate the evolution
of matter density perturbations in the modified gravity model, and obtain an analytical expression for the growth index, f. We show that increasing
leads to less growth of the density contrast δ, and also decreases the growth index. We give a fitting formula for the growth index at the present time and indicate that
dominant term in this expression verifies the well-known approximation relation f≃Ωmγ. As the observational test, the new Supernova Type Ia (SNIa) Gold sample and Supernova Legacy Survey (SNLS) data, size of
baryonic acoustic peak from Sloan Digital Sky Survey (SDSS), the position of the acoustic peak from the CMB observations and
the Cluster Baryon Gas Mass Fraction (gas) are used to constrain the parameters of the DGP model. We also combine previous
results with large scale structure formation (LSS) from the 2dFGRS survey. Finally to check the consistency of the DGP model,
we compare the age of old cosmological objects with age of universe in this model. 相似文献
ZnO nanoparticles, 10–20 nm in size, were synthesized by heat treatment in air at 500 °C for 5 h., using [N,N′-bis(salicylaldehydo) ethylene diamine]zinc(II), i.e., Zn(salen), as precursor, which was obtained by a solvent-free solid–solid reaction. Heat-treated products were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and transmission electron microscopy. Room temperature photoluminescence spectra of ZnO nanostructures are dominated by green emission attributed to oxygen vacancy related donor–acceptor transition. 相似文献
Stroke lesion-volume estimates derived from calculated water apparent diffusion coefficient (ADC) maps provide a quantitative surrogate end-point for investigating the efficacy of drug treatment or studying the temporal evolution of cerebral ischemia. Methodology is described for estimating ischemic lesion volumes in a rat model of permanent middle cerebral artery occlusion (MCAO) based on absolute and percent-reduction threshold values of the water ADC at 3 h post-MCAO. Volume estimates derived from average ADC (ADC(av)) maps were compared with those derived from post-mortem histological sections. Optimum ADC thresholds were established as those that provided the best correlation and one-to-one correspondence between ADC- and histologically derived lesion-volume estimates. At 3 h post-MCAO, an absolute-ADC(av) threshold of 47 x 10(-5) mm(2)/s (corresponding to a 33% reduction in ADC(av) based on a contralateral hemisphere comparison) provided the most accurate estimate of percent hemispheric lesion volume (%HLV). Experimental and data analysis issues for improving and validating the usefulness of DWI as a surrogate endpoint for the quantification of ischemic lesion volume are discussed. 相似文献
The inflation of a graph is obtained from by replacing every vertex of degree by a clique and each edge by an edge between two vertices of the corresponding cliques and of in such a way that the edges of which come from the edges of form a matching of . A set of vertices in a graph is a total dominating set, abbreviated TDS, of if every vertex of is adjacent to a vertex in . The minimum cardinality of a TDS of is the total domination number of . In this paper, we investigate total domination in inflated graphs. We provide an upper bound on the total domination number of an inflated graph in terms of its order and matching number. We show that if is a connected graph of order , then , and we characterize the graphs achieving equality in this bound. Further, if we restrict the minimum degree of to be at least , then we show that , with equality if and only if has a perfect matching. If we increase the minimum degree requirement of to be at least , then we show , with equality if and only if every minimum TDS of is a perfect total dominating set of , where a perfect total dominating set is a TDS with the property that every vertex is adjacent to precisely one vertex of the set. 相似文献