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71.
In order to make the lab-on-a-chip concept a reality, it is desirable to have an integrated component capable of pumping fluids through microchannels. We have developed novel, electrically actuated micropumps and have integrated them with microfluidic systems. These devices utilize the build-up of electrolysis gases to achieve pressure-driven pumping, only require small voltages (approximately 10 V), and have approximate dimensions of 5 cm x 3 cm x 2 cm. Furthermore, these micropumps are composed of relatively inexpensive materials, and the reversible sealability of their poly(dimethylsiloxane) body to different microfluidic arrays enables repeated uses of the same pump. Under an applied potential of 10 V, three different micropumps had average flow rates of 8-13 microL min(-1) for water being pumped through five different 2 cm-long, 5500 microm(2) cross-sectional-area channels in poly(methyl methacrylate), in approximate agreement with predicted pump rates. We have also evaluated pump operation at the lower applied potential of 8 V and observed an average flow rate of 6.1 microL min(-1) for a pump-channel system. The current micropump design is capable of sustaining pumping pressures in the range of 300 kPa. The various advantages of these micropumps make them well suited for use in lab-on-a-chip analysis techniques. 相似文献
72.
Ann M. Schmiedekamp Anthony Ginnetti Brian Piccione Kevin Cannon M. Dominic Ryan 《International journal of quantum chemistry》2007,107(6):1415-1429
Octahedral, six‐coordinate Co2+ can exist in two spin states: S = 3/2 and S = 1/2. The difference in energy between high spin (S = 3/2) and low spin (S = 1/2) is dependent on both the ligand mix and coordination stereochemistry. B3LYP calculations on combinations of neutral imidazole, NH3, and H2O ligands show that low‐spin isomers are stabilized by axial H2O ligands and in structures that also include trans pairs of equatorial NH3 and protonated imidazole ligands, spin crossover structures are predicted from spin state energy differences. Occupied Co d orbitals from the DFT calculations provide a means of estimating effective ligand strength for homoleptic and mixed ligand combinations. These calculations suggest that in a labile biological system, a spin crossover environment can be created. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 相似文献
73.
The accuracy, precision, and reproducibility of a rapid method for determination of fluoride in wine, using a fluoride selective ion electrode, were established by a collaborative study involving 12 laboratories, 5 in Europe and 7 in the United States. The laboratories assayed 6 Youden pairs of fluoride-fortified, red and white wine samples with fluoride concentrations ranging from 0.2 to 3.0 mg/L. The relative standard deviations of repeatability ranged from 1.94 to 4.88%; relative standard deviations of reproducibility ranged from 4.15 to 18.40%. HORRAT values ranged from 0.30 to 0.97. The average recovery was 99.97%. Based on the statistical results of this collaborative study, the Study Director recommends that this method be adopted First Action. 相似文献
74.
Hybrid density functional calculations have been carried out using cluster models of the H/Si(100)-2 x 1 surface to investigate the mechanistic details of the initial surface reactions occurring in the atomic layer deposition of hafnium and zirconium oxides (HfO2 and ZrO2). Reaction pathways involving the metal precursors ZrCl4, Zr(CH3)4, HfCl4, and Hf(CH3)4 have been examined. Pathways leading to the formation of a Zr-Si or Hf-Si linkage show a significant sensitivity to the identity of the leaving group, with chloride loss reactions being both kinetically and thermodynamically less favorable than reactions leading to the loss of a methyl group. The energetics of the Zr(CH3)4 and Hf(CH3)4 reactions are similar with an overall exothermicity of 0.3-0.4 eV and a classical barrier height of 1.1-1.2 eV. For the reaction between H2O and the H/Si(100)-2 x 1 surface, the activation energy and overall reaction enthalpy are 1.6 and -0.8 eV, respectively. Due to contamination, trace amounts of H2O may be encountered by metal precursors, leading to the formation of minor species that can lead to unanticipated side-reaction pathways. Such gas-phase reactions between the halogenated and alkylated metal precursors and H2O are exothermic with small or no reaction barriers, allowing for the possibility of metal precursor hydroxylation before the H/Si surface is encountered. Of the contaminant surface reaction pathways, the most kinetically favorable corresponds to the surface -OH deposition. Interestingly, for the hydroxylated metal precursors, a unique reaction pathway resulting in the direct formation of Si-O-Zr and Si-O-Hf linkages has been identified and found to be the most thermodynamically stable pathway available, being exothermic by approximately 1.0 eV. 相似文献
75.
Banks CE Kruusma J Moore RR Tomcík P Peters J Davis J Komorsky-Lovrić S Compton RG 《Talanta》2005,65(2):423-429
Three different electroanalytical techniques for the detection of manganese in marine sediments are evaluated. The anodic stripping voltammetry of manganese at an in situ bismuth-film-modified boron-doped diamond electrode and cathodic stripping voltammetry at a carbon paste electrode are shown to lack the required sensitivity and reproducibility whereas cathodic stripping voltammetry at a bare boron-doped diamond electrode is shown to be reliable and selective with a limit of detection, from applying a 60 s accumulation period of 7.4 × 10−7 M and a sensitivity of 0.24 A M−1. The method was used to evaluate the manganese content of marine sediments taken from Šibenik, Croatia. 相似文献
76.
Donna F. Kusewitt Cindy L. Budge Mary M. Anderson Sharon L. Ryan Ronald D. Ley 《Photochemistry and photobiology》1993,58(3):450-454
Abstract— Thc frequency of spontaneous and ultraviolet radiation (UVR)-induced mutation at the hprt locus was determined in control and denV-transfected, repair-proficient murine fibroblasts. Control cells removed an average of 25% of pyrimidine dimers induced by exposure to 150 J/m2 UVR from an FS40 sunlamp within 24 h; under the same conditions of induction and repair, denV-transfected cells removed an average of 71% of pyrimidine dimers. Control cells were somewhat more resistant than denV-transfected cells to killing by UVR. The average frequency of spontancous mutation at the hprt locus for control and denV-transfected cells was 3 and 15 6-thioguanine (6-TG)-resistant colonies per 106 surviving cells, respectively; there was no statistically significant difference between control and dcnV-transfected cells. However, after exposure to 75 or 150 J/m2 UVR, denV-transfected cells had a significantly lower frequency of mutation to 6-TG resistance. After exposure to a fluence of 75 J/m2 , the average frequency of UVR-induced mutation at the hprt locus was 166 mutant colonies per loh surviving cells for control cells and 92 mutant colonies for denV-transfectcd cells; after 150 J/m2 , control cells had 205 6-TG-resistant colonies per 106 cells, while dmV-transfected cclls had 61 mutant colonies. These results demonstrate that UVR-induced pyrimidine dimers are mutagenic photoproducts in mammalian cells. 相似文献
77.
Secondary structure motifs in nucleic acid probes generally impair intended hybridization reactions and so efforts to predict and avoid such structures are commonly employed in probe design schemes. Another key facet of probe design that has received much less attention, however, is that secondary structure at targeted probe binding site regions may also impair hybridization. Thus, evaluation of both probe and target site secondary structures together should improve hybridization prediction and design effectiveness. Several challenges confound this goal, including imperfect empirical rules and parameters underlying predictions and the fact that folding algorithms scale poorly with respect to sequence length. Here, we attempt to quantify the consequences of target site structure on predicted hybridization using sequences sampled from the human genome. We also provide a methodology for choosing a reasonable “window size” around target sites that is as small as possible without compromising folding algorithm prediction accuracy. 相似文献
78.
Da Re RE Kuehl CJ Brown MG Rocha RC Bauer ED John KD Morris DE Shreve AP Sarrao JL 《Inorganic chemistry》2003,42(18):5551-5559
The novel charge-transfer ground state found in alpha,alpha'-diimine adducts of ytterbocene (C(5)Me(5))(2)Yb(L) [L = 2,2'-bipyridine (bpy) and 1,10-phenanthroline (phen)] in which an electron is spontaneously transferred from the f(14) metal center into the lowest unoccupied (pi*) molecular orbital (LUMO) of the diimine ligand to give an f(13)-L(*)(-) ground-state electronic configuration has been characterized by cyclic voltammetry, UV-vis-near-IR electronic absorption, and resonance Raman spectroscopies. The voltammetric data demonstrate that the diimine ligand LUMO is stabilized and the metal f orbital is destabilized by approximately 1.0 V each upon complexation for both bpy and phen adducts. The separation between the ligand-based oxidation wave (L(0/-)) and the metal-based reduction wave (Yb(3+/2+)) in the ytterbocene adducts is 0.79 V for both bpy and phen complexes. The UV-vis-near-IR absorption spectroscopic data for both the neutral adducts and the one-electron-oxidized complexes are consistent with those reported recently, but previously unreported bands in the near-IR have been recorded and assigned to ligand (pi*)-to-metal (f orbital) charge-transfer (LMCT) transitions. These optical electronic excited states are the converse of the ground-state charge-transfer process (e.g., f(13)-L(*-) <--> f(14)-L(0)). These new bands occur at approximately 5000 cm(-1) in both adducts, consistent with predictions from electrochemical data, and the spacings of the resolved vibronic bands in these transitions are consistent with the removal of an electron from the ligand pi* orbital. The unusually large intensity observed in the f --> f intraconfiguration transitions for the neutral phenanthroline adduct is discussed in terms of an intensity-borrowing mechanism involving the low-energy LMCT states. Raman vibrational data clearly reveal resonance enhancement for excitation into the low-lying pi* --> pi* ligand-localized excited states, and comparison of the vibrational energies with those reported for alkali-metal-reduced diimine ligands confirms that the ligands in the adducts are reduced radical anions. Differences in the resonance enhancement pattern for the modes in the bipyridine adduct with excitation into different pi* --> pi* levels illustrate the different nodal structures that exist in the various low-lying pi* orbitals. 相似文献
79.
This study reports an optimized headspace-solid phase microextraction (HS-SPME) method for the determination of methoxypyrazines in wine. Analysis was performed by using comprehensive two-dimensional gas chromatography with novel detection capabilities, including nitrogen phosphorus detection (GC x GC-NPD) and time-of-flight mass spectrometry (GC x GC-TOFMS). In the latter, stable isotope dilution was performed for the quantitation of 2-methoxy-3-(2-methylpropyl) pyrazine (IBMP), using labelled 2-(2H3)methoxy-3-(2-methylpropyl)pyrazine (d3-IBMP) as the internal standard, and resolution of the two analogues was facilitated using the deconvolution capabilities of the TOFMS. This research represents the first report of HS-SPME with isotope dilution and GC x GC-TOFMS (GC x GC-IDTOFMS). Analysis by GC x GC-NPD enabled detection limits of 0.5 ng/L for the quantitation of IBMP, which was superior to that obtained using GC x GC-IDTOFMS (1.95 ng/L). Nevertheless, both methods were adequately sensitive for real wine analysis, yielding highly comparable IBMP concentrations of 26.1 and 27.8 ng/L, respectively, from a Sauvignon blanc wine. The complexity of the real wine headspace was simplified as a result of selective detection using GC x GC-NPD and, in the case of GC x GC-IDTOFMS, the use of extracted ion chromatograms (EICs). 相似文献
80.
Ahmed Qasem Hamza Assaggaf Domenico Montesano Zineb Khalil Samiah Hamad Al-Mijalli Aicha EL Baaboua Nasreddine El Omari Naoual El Menyiy Saad Bakrim Ryan A. Sheikh Mohammed Merae Alshahrani Ahmed Abdullah Al Awadh Gokhan Zengin Abdelhakim Bouyahya Hanae Naceiri Mrabti 《Molecules (Basel, Switzerland)》2022,27(18)
This exploratory investigation aimed to determine the chemical composition and evaluate some biological properties, such as antioxidant, anti-inflammatory, antidiabetic, and antimicrobial activities, of Matricaria chamomilla L. essential oils (EOs). EOs of M. chamomilla were obtained by hydrodistillation and phytochemical screening was performed by gas chromatography–mass spectrophotometry (GC-MS). The antimicrobial activities were tested against different pathogenic strains of microorganisms by using disc diffusion assay, the minimum inhibitory concentration (MIC), and minimum bactericidal concentration (MBC) methods. The antidiabetic activity was performed in vitro using the enzyme inhibition test. The antioxidant activity of EOs was tested using the free radical scavenging ability (DPPH method), ferrous ion chelating (FIC) ability, and β-carotene bleaching assay. The anti-inflammatory effects were tested in vivo using the carrageenan-induced paw edema method and in vitro using the inhibition of the lipoxygenase test. The analysis of the phytochemical composition by GC-MS revealed that camphor (16.42%) was the major compound of EOs, followed by 3-carene (9.95%), β-myrcene (8.01%), and chamazulene (6.54%). MCEO, honey, and their mixture exhibited antioxidant activity against the DPPH assay (IC50 ranging from 533.89 ± 15.05 µg/mL to 1945.38 ± 12.71 µg/mL). The mixture exhibited the best radical scavenging activity, with an IC50 of 533.89 ± 15.05 µg/mL. As antidiabetic effect, EO presented the best values against α-glucosidase (265.57 ± 0.03 μg/mL) and α-amylase (121.44 ± 0.05 μg/mL). The EOs and honey mixture at a dose of 100 mg/kg exhibited a high anti-inflammatory effect, with 63.75% edema inhibition after 3 h. The impact of EOs on the studied species showed an excellent antimicrobial (Staphylococcus aureus ATCC 29213 (22.97 ± 0.16 mm)), antifungal (Aspergillus niger (18.13 ± 0.18 mm)) and anti-yeast (Candida albicans (21.07 ± 0.24 mm) effect against all the tested strains. The results obtained indicate that the EOs of M. chamomilla could be a potential drug target against diabetes, inflammation and microbial infections; however, further investigations to assess their bioactive molecules individually and in combination are greatly required. 相似文献