Electro-osmotic pumping and ion-concentration polarization based on conical nanopores.

A numerical investigation is performed into the characteristics of an electro-osmotic pump consisting of a negatively charged conical nanopore. It is shown that the dependence of the flow rectification effect on the bias direction is the reverse of that of the ion current rectification effect. Moreover, the nozzle mode (i.e., the bias is applied from the base side of the nanopore to the tip side) has a higher flow rate compared to the diffuser mode (i.e., the bias is applied from the tip side of the nanopore to the base side). The results showed that the ion-concentration polarization effect occurred inside the conical nanopore, resulting in surface conduction dominating in the ionic current. The ions inside the nanopore are depleted and enriched under the nozzle mode and the diffuser mode, respectively. As a result, the electro-osmotic pump yields a greater pumping pressure, flow rate, and energy conversion efficiency when operating in the nozzle mode. In addition, we also investigated the flow rate rectification behavior for the conical nanopore. The best flow rate rectification factor in this work is 2.06 for an electrolyte concentration of 10(-3) M.

Analysis of traveling-wave electro-osmotic pumping with double-sided electrode arrays.

In this paper, a series of numerical simulations was performed to investigate the pumping performance of electro-osmotic micropumps containing electrode arrays patterned on the upper and lower sides of a microchannel. The simulations have been analyzed with a linear electro-osmotic model based upon the Debye-Hückel theory of the double layer. The potential drop across the diffuse layer is assumed to be less than 25 mV (k(B)T/e), and there is a linear response between the surface charge and the voltage drop across the double layer. The double layer is not resolved but is lumped into effective parameters that are imported from the Debye-Hückel and Stern layers. We examined the effects of the relative positioning of the electrodes in the opposing arrays (i.e., symmetrical or staggered), and the phase lag and the angular frequency of the alternating current (ac) signals applied to the electrodes within the two arrays. A critical height of the microchannel was observed, below which the interactions of the applied electrical potentials on the walls became significant. The optimum pumping effect was obtained when the electrode arrays were symmetrical to one another around the centerline of the channel and were activated by ac potentials with a 0° phase shift. The corresponding angular frequency of the maximum pumping velocity for different phase shifts of the applied ac signals was also determined. Overall, the simulation results presented in this paper provide a useful insight into the optimal design parameters and operating conditions for micropumps containing two arrays of microelectrodes on the microchannel walls.

A new amide from the stems of Cinnamomum reticulatum Hay.

Cinnaretamine, a new amide, has been isolated from Cinnamomum reticulatum Hay (Lauraceae), together with six known compounds, N-trans-feruloylmethoxytyramine, N-cis-feruloylmethoxytyramine, (+)-syringaresinol, p-hydroxybenzoic acid, syringic acid and vanillic acid. The structure of cinnaretamine was determined on the basis of spectroscopic analysis.

A novel normonoterpenoid from the stems of Cinnamomum reticulatum Hay.

Reticuone (1), a novel Cinnamomum normonoterpenoid, has been isolated from Cinnamomum reticulatum Hay (Lauraceae), and its structure was determined on the basis of spectroscopic analysis.

Isolation of new esters from the stems of Cinnamomum reticulatum Hay.

The stems of Cinnamomum reticulatum Hay (Lauraceae) were extracted with hexane and chloroform successively. A series of new esters, including a mixture of 4-hydroxy-3-methoxyphenethyl derivatives, along with two butanolides, isoobtusilactone A and obtusilactone A, two amides, N-trans-feruloylmethoxytyramine and N-cis-feruloyl-methoxytyramine, three benzenoids, p-hydroxybenzoic acid, syringic acid and vanillic acid, one lignan, (+)-syringaresinol and one steroid, beta-sitostenone, were isolated. The structures of the new esters were elucidated by chemical and physical evidence.