共查询到20条相似文献,搜索用时 10 毫秒
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Bradley B. Schneider Erkinjon G. Nazarov Thomas R. Covey 《International Journal for Ion Mobility Spectrometry》2012,15(3):141-150
Differential mobility spectrometry (DMS) can be used as a pre-filter to improve selectivity prior to mass spectral analysis, because it provides an additional mobility based separation to mass analysis. Ions within a differential mobility spectrometer are separated based upon differences in mobility behavior, which are manifested by applying a strong high frequency asymmetric RF waveform. Currently it is well documented that DMS separation power (peak capacity), can be substantially augmented by adding chemical modifiers to the transport gas. This process is generally referred to as the dynamic cluster/decluster model, and it occurs due to gas phase processes when analyte ions are clustered with modifier molecules in the lower field portion of the RF pulses and declustered during the higher field portion of the waveform. Previous publications have demonstrated that the planar electrode geometry is key to realizing improved performance of DMS sensors with high concentrations of chemical modifiers. The clustering modifier is provided with sufficient concentration to reach conditions where separation peak capacity can be substantially augmented (typically around 1.5?%). The present paper expands on these previous findings by mapping out the behavior of structurally similar compounds, including structural isomers, with a series of different transport gas modifiers, including isopropanol, methanol, acetonitrile, acetone, and ethylacetate. The results highlight the importance of analyte/modifier interactions, demonstrating the variability that can be achieved when different modifiers are used. 相似文献
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Three structural variants of azo substituted achiral bent-core compounds are reported. Here, the effect of symmetrical and non-symmetrical arms at 1,3-positions of the central phenyl ring on the mesogenic properties of the resulting bent-core azo compounds is studied. The structures of all the compounds synthesised are confirmed by the organic spectroscopic methods. The liquid crystalline properties are investigated using polarising optical microscopy, differential scanning calorimetry and X-ray diffraction studies. It was found that the non-symmetrical molecules are more conducive to mesomorphism than the symmetrical ones. We observed B1 (Colr), B2 (SmCAPA) and B7 mesophases in these compounds. The B7 mesophase was found to have a modulated layer structure. Interestingly, a reversible field-induced transition from the B7-like structure to the racemic SmCAPF was also observed. We also report the photo-induced studies in the B7 mesophase and make a comparison of these results with those obtained in a B2 mesophase. From our studies, we observed that these effects are more profound in the case of B7 mesophase when compared to the B2 mesophase in such systems. 相似文献
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Xue Dong William Tiznado Yu-qian Liu Luis Leyva-Parra Xin-bo Liu Sudip Pan Gabriel Merino Zhong-hua Cui 《Angewandte Chemie (International ed. in English)》2023,62(31):e202304997
Planar boron clusters have often been regarded as “π-analogous” to aromatic arenes because of their similar delocalized π-bonding. However, unlike arenes such as C5H5− and C6H6, boron clusters have not previously shown the ability to form sandwich complexes. In this study, we present the first sandwich complex involving beryllium and boron, B7Be6B7. The global minimum of this combination adopts a unique architecture having a D6h geometry, featuring an unprecedented monocyclic Be6 ring sandwiched between two quasi-planar B7 motifs. The thermochemical and kinetic stability of B7Be6B7 can be attributed to strong electrostatic and covalent interactions between the fragments. Chemical bonding analysis shows that B7Be6B7 can be considered as a [B7]3−[Be6]6+[B7]3− complex. Moreover, there is a significant electron delocalization within this cluster, supported by the local diatropic contributions of the B7 and Be6 fragments. 相似文献
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We have investigated the shape, size, and motility of a minimal model of an adherent biological cell using the Monte Carlo method. The cell is modeled as a two dimensional ring polymer on the square lattice enclosing continuously polymerizing and depolymerizing actin networks. Our lattice model is an approximate representation of a real cell at a resolution of one actin molecule, 5 nm. The polymerization kinetics for the actin network are controlled by appropriate reaction probabilities which correspond to the correct experimental reaction rates. Using the simulation data we establish various scaling laws relating the size of the model cell to the concentration of polymerized and unpolymerized actin molecules and the length of the enclosing membrane. The computed drift velocities, which characterize the motility of the cell, exhibit a maximum at a certain fraction of polymerized actin which agrees with physiological fractions observed in experiments. The appearance of the maximum is related to the competition between the polymerization-induced protrusion of the membrane and the concomitant suppression of membrane fluctuations. 相似文献
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The effects of flow type on aptamer capture in differential mobility cytometry cell separations 总被引:1,自引:0,他引:1
In this work, differential mobility cytometry (DMC) was used to monitor cell separation based on aptamer recognition for target cells. In this device, open-tubular capillaries coated with Sgc8 aptamers were used as affinity chromatography columns for separation. After cells were injected into the columns, oscillating flow was generated to allow for long-term cell adhesion studies. This process was monitored by optical microscopy, and differential imaging was used to analyze the cells as they adhered to the affinity surface. We investigated the capture time, capture efficiency, purity of target and control cells, as well as the reusability of the affinity columns. Capture time for both CCRF-CEM cells and Jurkat T cells was 0.4 ± 0.2 s, which demonstrated the high separation affinity between aptamers and target cells. The capture efficiency for CCRF-CEM cells was 95% and purity was 99% in a cell mixture. With the advantage of both high cell capture efficiency and purity, DMC combined with aptamer-based separation emerges as a powerful tool for rare cell enrichment. In addition, aptamer-based DMC channels were found to be more robust than antibody based channels with respect to reuse of the separation device. 相似文献
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A p-benzenedithiolate (BDT) molecule covalently bonded between two gold electrodes has become one of the model systems utilized for investigating molecular transport junctions. The plethora of papers published on the BDT system has led to varying conclusions with respect to both the mechanism and the magnitude of transport. Conductance variations have been attributed to difficulty in calculating charge transfer to the molecule, inability to locate the Fermi energy accurately, geometric dispersion, and stochastic switching. Here we compare results obtained using two transport codes, TRANSIESTA-C and HUCKEL-IV, to show that upon Au-S bond lengthening, the calculated low bias conductance initially increases by up to a factor of 30. This increase in highest occupied molecular orbital (HOMO) mediated conductance is attributed to charging of the terminal sulfur atom and a corresponding decrease in the energy gap between the Fermi level and the HOMO. Addition of a single Au atom to each terminal of the extended BDT molecule is shown to add four molecular states near the Fermi energy, which may explain the varying results reported in the literature. 相似文献
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M. Brufani W. Keller-Schierlein W. Lffler I. Mansperger H. Zhner 《Helvetica chimica acta》1968,51(6):1293-1304
The known antibiotic Venturicidin A and two new antifungal compounds, Venturicidin B and Botrycidin, have been isolated from a strain of Streptomyces aureofaciens DUGGAR . Venturicidin B gave on methanolysis the methyl glycoside of 2-deoxy-D -rhamnose, Venturicidin A the corresponding 3-O-carbamate. 相似文献
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Tuleshova A Badretdinov D Kukushkin A Khuznetsova S 《Bioelectrochemistry (Amsterdam, Netherlands)》2002,56(1-2):203-205
We have obtained the theoretical dependences of stromal metabolite steady-state concentrations on external inorganic phosphate (P(i)) concentration. For this purpose, the theoretical model of photosynthesis, earlier described in [Ann. Appl. Biol. 138 (2001) 117], was modified to account for the regulation of starch formation by 3-phosphoglycerate (PGA) to P(i) ratio. When the rate constant of starch synthesis is taken to be independent on PGA/P(i) ratio, the steady-state concentrations of Calvin cycle metabolites and starch were found to change insignificantly as external P(i) concentration increases in wide range. However, as external P(i) range exceeds a critical value, the steady-state concentrations of all metabolites change abruptly. If the rate constant of starch synthesis depends on PGA/P(i) ratio, the steady-state concentrations of stromal metabolites change qualitatively in the same way with the increase of external P(i). However, no abrupt changes of metabolite and starch steady-state levels at high concentration of P(i) are observed. These results testify that the control of starch synthesis by PGA/P(i) ratio makes the photosynthetic system more stable in wide range of external P(i) concentrations. 相似文献
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Arntsen C Lopata K Wall MR Bartell L Neuhauser D 《The Journal of chemical physics》2011,134(8):084101
Modulation of plasmon transport between silver nanoparticles by a yellow fluorophore, tartrazine, is studied theoretically. The system is studied by combining a finite-difference time-domain Maxwell treatment of the electric field and the plasmons with a time-dependent parameterized method number 3 simulation of the tartrazine, resulting in an effective Maxwell∕Schro?dinger (i.e., classical∕quantum) method. The modeled system has three linearly arranged small silver nanoparticles with a radius of 2 nm and a center-to-center separation of 4 nm; the molecule is centered between the second and third nanoparticles. We initiate an x-polarized current on the first nanoparticle and monitor the transmission through the system. The molecule rotates much of the x-polarized current into the y-direction and greatly reduces the overall transmission of x-polarized current. 相似文献
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Kenichi Takeuchi Toshikazu Kitagawa Akihiko Ueda Yoshihide Senzaki Kunio Okamoto 《Tetrahedron》1985,41(23):5455-5463
7-Cyano-7-methylcycloheptatrienes containing one t-butyl group on the 1-position () or two t-butyl groups on the 1- and 3-, 1- and 4-, or 1- and 5-positions (, , or , respectively) were synthesized and their cyclo- heptatriene (CHT)-norcaradiene (NCD) equilibria measured by variable-temperature 1H NMR for CS2-CD2Cl2 solutions. The 1H NMR chemical shifts of the 7-methyl group indicate that these compounds are composed of essentially one CHT and one NCD tautomer with an endo geometry of the methyl group. The introduction of a t-butyl group at the 1-position of 7-cyano-7-methylcycloheptatriene () markedly shifts the equilibrium to the NCD side and the addition of the second t-butyl group further favors the NCD form, with the NCD populations for , , , and at 25 °C 70.9, 96.5, 92.3, and 99.3%, respectively. An application of molecular mechanics (MMPI) calculations to various t-butylated CHT-NCD systems suggests that the t-butyl groups sterically destabilize the CHT form more than the NCD form, bringing about increased NCD populations. 相似文献
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We produced the B7Au2- mixed cluster and studied its electronic structure and chemical bonding using photoelectron spectroscopy and ab initio calculations. The photoelectron spectra of B7Au2- were observed to be relatively simple with vibrational resolution, in contrast to the complicated spectra observed for pure B7-, which had contributions from three isomers (Alexandrova et al. J. Phys. Chem. A 2004, 108, 3509). Theoretical calculations show that B7Au2- possesses an extremely stable planar structure, identical to that of B7H2-, demonstrating that Au mimics H in its bonding to boron, analogous to the Au-Si bonding. The ground-state structure of B7Au2- (B7H2-) can be viewed as adding two Au (H) atoms to the terminal B atoms of a higher-lying planar isomer of B7-. The bonding and stability in the planar B7Au2- (B7H2-) clusters are elucidated on the basis of the strong covalent B-Au (H) bonding and the concepts of aromaticity/antiaromaticity in these systems. 相似文献
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Given the success of the polaron model based on solvation in accounting for the width of a hole polaron on an all-adenine (A) sequence on DNA, we extend the calculations to other sequences. We find excellent agreement with the free energy differences measured by Lewis et al. (J. Am. Chem. Soc. 2000, 122, 12037-12038) between a guanine (G) cation and a pair of bases, GG, or a triple of bases, GGG, in all cases surrounded by As, by treating AGGA and AGGGA as solvated polarons. There is additional support for hole polaron formation in DNA from experiments in which oxidative damage due to injected holes is investigated in sequences involving Gs and As. Theory and comparison with transport measurements on repeated sequences involving multiple thymines (Ts) or combinations such as ATs or GCs, where C is cytosine, led to the suggestion that the basic sequences in these cases must be polarons whose wave functions have substantial amplitudes on both chains in a duplex. The size of an electron polaron in DNA is predicted to be similar to that of a hole polaron, approximately 4 or 5 bases. Although experiments have shown that polaron hopping is the dominant mode of charge transport in DNA with repeated sequences such as AGGA, further investigations, particularly of temperature dependence of site energies and transfer integrals, are needed to determine to what extent hole transport takes place by polaron hopping for arbitrary DNA sequences. 相似文献
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Nitric oxide, nitrite and nitrate are released by activated macrophages in an immune response. We showed here that nitrite influenced cell growth and antibody production in mouse lipopolysaccharide (LPS)-stimulated splenic B cells and B cell hybridomas. The addition of 10(-7) and 10(-6) M nitrite enhanced deoxyribonucleic acid (DNA) synthesis of LPS-stimulated splenic B cells. However, DNA synthesis and antibody production in the case of total spleen cells stimulated with LPS were suppressed by nitrite in a dose dependent-manner. These phenomena were also observed in a similar experiment involving mouse B cell hybridomas. Antibody production of all B cell hybridomas was significantly suppressed by the addition of nitrite. This suppressing effect could not be explained by changes in viable cell yields. This data suggests that the antibody production and cell proliferation of B cells may be influenced by nitrite from activated macrophages in the immune response. 相似文献
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《Radiation Physics and Chemistry》2007,76(8-9):1531-1534
Effects induced by high-dose irradiation on manganese- and silver-doped Li2B4O7 (lithium tetraborate, LTB) single crystals were monitored by photoluminescence and optical absorption spectroscopy. High-dose (1.0×103 and 1.2×104 Gy) irradiation of the samples was performed using high-energy, short-time (4 MeV, 2.6 μs) electron pulses of a linear electron accelerator. Changes in the oxidation states of dopants were revealed. Recharging of manganese Mn2+→Mn3+ and Ag+→Ag0 were observed. Ionization process Mn2+→Mn3++e− and creation of Ag0-nanoparticles are supposed. 相似文献