This paper describes a model of the motion of superparamagnetic beads in a microfluidic channel under the influence of a weak magnetic field produced by an electric current passing through a coplanar metal wire. The model based on the conventional expression for the magnetic force experienced by a superparamagnetic bead (suspended in a biologically relevant medium) and the parameters provided by the manufacturer failed to match the experimental data. To fit the data to the model, it was necessary to modify the conventional expression for the force to account for the non-zero initial magnetization of the beads, and to use the initial magnetization and the magnetic susceptibility of the beads as adjustable parameters. The best-fit value of susceptibility deviated significantly from the value provided by the manufacturer, but was in good agreement with the value computed using the magnetization curves measured independently for the beads from the same vial as those used in the experiment. The results of this study will be useful to researchers who need an accurate prediction of the behavior of superparamagnetic beads in aqueous suspensions under the influence of weak magnetic fields. The derivation of the force on a magnetic bead due to a magnetic field also identifies the correct treatment to use for this interaction, and resolves discrepancies present throughout the literature. 相似文献
A model for studying polar-pi interactions between arenes spaced at van der Waals distances is developed on the basis of peri-diarylbiphenylenes. A set of 1,8-diarylbiphenylenes is synthesized comprising two Hammett series, one with reference to mesityl ring interactions and the other with reference to pentafluorophenyl ring interactions. X-Ray crystal structures of several derivatives are determined. Barriers to rotation of the probe aryl ring are derived from dynamic NMR data and show a trend for the mesityl reference series (DeltaG(not equal) vs. sigma(0)). The model is also used as a test for comparison of modern density functional methods, including B3LYP, M06-2X and BMK functionals; dispersive effects are seen to be an important factor in the proper theoretical treatment of arene interactions. 相似文献
Dynamic gearing of molecular spur gears, the most common type of mechanical gear, is elucidated. Molecular design and conformational analysis show that derivatives of 4,4-bis(triptycen-9-ylethynyl)bibenzimidazole represent suitable constructs to investigate gearing behavior of collateral triptycene (Tp) groups. To test this design, DFT calculations (B97-D/Def2-TZVP) were employed and the results suggest that these molecules undergo geared rotation preferentially to gear slippage. Synthesis of derivatives was carried out, providing a series of molecular spur gears, including the first desymmetrized spur gear molecules, which were subsequently subjected to stereochemical analysis. 相似文献
The use of small molecules that can promote neuronal growth represents a promising approach to regenerative science. Along these lines we have developed separate short or modular syntheses of the natural products caryolanemagnolol and clovanemagnolol, small molecules previously shown to promote neuronal growth and induce choline acetyltransferase activity. The postulated biosynthetic pathways, potentially leading to the assembly of these molecules in nature, have guided the laboratory syntheses, allowing the preparation of both natural products in as few as two steps. With synthetic access to the compounds as single enantiomers we have examined clovanemagnolol's ability to promote the growth of embryonic hippocampal and cortical neurons. Clovanemagnolol has been shown to be a potent neurotrophic agent, promoting neuronal growth at concentrations of 10 nM. 相似文献
Pentapodal ω-functional derivatives of corannulene have been synthesized from sym-pentachlorocorannulene by iron-catalyzed aryl-alkyl cross coupling reactions. Click chemistry gives access to pentapods with bioconjugate appendages. 相似文献
A recent in situ infrared study on the selective hydrogenation of C5 dienes and monoenes over a Pd/Al(2)O(3) catalyst only reported incomplete vibrational assignments for some of the reagents, intermediates, and products encountered in that study. This work uses a combination of infrared absorption spectroscopy, Raman, and inelastic neutron scattering to characterize the vibrational spectra of pentane, 1-pentene, cis- and trans-2-pentene, cis- and trans-1,3-pentadiene, 1,4-pentadiene, cyclopentane, and cyclopentene. Ab initio calculations of the potential energy surface, geometry, and vibrational transition energies were performed and simulations of the vibrational spectra compared to the experimental data. Complete vibrational assignments for the majority of the molecules are presented. The potential for using gas-phase infrared measurements for studying heterogeneously catalyzed gas-phase reactions is also briefly considered. 相似文献
Cycloaromatization of a peri diyne with an external alkyne provides a general route to indeno-fused polynuclear aromatics. Fluoranthenes 9 (or 13) are easily accessible in good to excellent yields (75-99%; 18 examples) from the reaction of symmetric (or asymmetric) diynes 4 and alkynes 5 (or norbornadiene) in the presence of Wilkinson's catalyst. This formal [(2+2)+2] cycloaddition can also be applied to generate various indenocorannulenes 28 from 2,3-diethynylcorannulene derivatives 27 and alkynes 5. The indenocorannulenes 28 exist in a static bowl form at room temperature with bowl-to-bowl inversion barriers higher than 24 kcal/mol. This barrier renders the rate of inversion slow enough at room temperature to establish a class of chiral, bowl-shaped stereoiomers containing no tetrahedrally ligated atoms. The crystal structure of 28g provides insight into the bowl-shaped geometry of these compounds. This new synthetic method occurs under neutral conditions and tolerates various functional groups (e.g., alkyl, aryl, alcohols, and esters). 相似文献
Like penguins on ice , buckybowl molecules move closer together when cooled on a copper surface (see model of a corannulene molecule adsorbed on Cu(111)). Upon heating, the molecules spread out into the original crystal phase again. The lower density at room temperature can be explained by the increase in entropy owing to the excitation of bowl vibrations at the surface.