Original Vinca Derivatives: From P-Glycoprotein Substrates to P-Glycoprotein Inhibitors.

The first example of vinca derivatives 16-18 able to modulate P-glycoprotein (Pgp) efflux activity is reported. They were elaborated in two steps from vinorelbine 3 (VLN) by a modification of the velbenamine moiety. These compounds were able to decrease efficiently Pgp mediated influx and efflux of rhodamine-123 (Rho) and to restore the cytotoxicity of vinorelbine 3 (VLN) and doxorubicin (Dox) on K562R (dox-resistant) cell lines.

Effect of Surface Adsorption on Temporal and Spatial Broadening in Micro Free Flow Electrophoresis.

Analyte adsorption onto surfaces presents a challenge for many separations, often becoming a significant source of peak broadening and asymmetry. We have shown that surface adsorption has no effect on peak position or spatial broadening in micro free flow electrophoresis (µFFE) separations. Surface adsorption does affect the time it takes an analyte to travel through the µFFE separation channel and therefore contributes to temporal broadening. These results were confirmed using µFFE separations of fluorescein, rhodamine 110, and rhodamine 123 in a low ionic strength buffer to promote surface adsorption. Peak widths and asymmetries were measured in both the temporal and spatial dimensions. Under these conditions rhodamine 123 exhibited significant interactions with the separation channel surface, causing increased peak broadening and asymmetry in the temporal dimension. Broadening or asymmetry in the spatial dimension was not significantly different than that of fluorescein, which did not interact with the capillary surface. The effect of strong surface interactions was assessed using µFFE separations of Chromeo P503 labeled myoglobin and cytochrome c. Myoglobin and cytochrome c were well resolved and gave rise to symmetrical peaks in the spatial dimension even under conditions where permanent adsorption onto the separation channel surface occurred.

Using electrophoretic exclusion to manipulate small molecules and particles on a microdevice.

Electrophoretic exclusion, a novel separations technique that differentiates species in bulk solution using the opposing forces of electrophoretic velocity and hydrodynamic flow, has been adapted to a microscale device. Proof-of-principle experiments indicate that the device was able to exclude small particles (1 µm polystyrene microspheres) and fluorescent dye molecules (rhodamine 123) from the entrance of a channel. Additionally, differentiation of the rhodamine 123 and polystyrene spheres was demonstrated. The current studies focus on the direct observation of the electrophoretic exclusion behavior on a microchip.

Parallel separation of multiple samples with negative pressure sample injection on a 3-D microfluidic array chip.

A simple and powerful microfluidic array chip-based electrophoresis system, which is composed of a 3-D microfluidic array chip, a microvacuum pump-based negative pressure sampling device, a high-voltage supply and an LIF detector, was developed. The 3-D microfluidic array chip was fabricated with three glass plates, in which a common sample waste bus (SW(bus)) was etched in the bottom layer plate to avoid intersecting with the separation channel array. The negative pressure sampling device consists of a microvacuum air pump, a buffer vessel, a 3-way electromagnet valve, and a vacuum gauge. In the sample loading step, all the six samples and buffer solutions were drawn from their reservoirs across the injection intersections through the SW(bus) toward the common sample waste reservoir (SW(T)) by negative pressure. Only 0.5 s was required to obtain six pinched sample plugs at the channel crossings. By switching the three-way electromagnetic valve to release the vacuum in the reservoir SW(T), six sample plugs were simultaneously injected into the separation channels by EOF and electrophoretic separation was activated. Parallel separations of different analytes are presented on the 3-D array chip by using the newly developed sampling device.

Optimizing band width and resolution in micro-free flow electrophoresis.

The broadening mechanisms for micro-free flow electrophoresis (micro-FFE) have been investigated using a van Deemter analysis. Separation power, the product of electric field and residence time, is presented as a parameter for predicting the position of sample streams and for comparing separations under different conditions. Band broadening in micro-FFE is governed by diffusion at lower linear velocities and a migration distance-dependent mechanism at higher linear velocities. At higher linear velocities, the parabolic flow profile is elongated, generating a distribution of analyte residence times in the separation channel. This distribution of residence times gives rise to a distribution of migration distances in the lateral direction since analytes spend different amounts of time in the electric field. Equations were derived to predict the effect of electric field and buffer flow rate on broadening. Experimental data were collected to determine whether the derived equations were useful in explaining broadening caused by diffusion and hydrodynamic flow at different linear velocities and electric fields. Overall there was an excellent correlation between the predicted and experimentally observed values allowing linear velocity and electric field to be optimized. Suppression of electroosmotic flow is proposed as a means of reducing micro-FFE band broadening due to hydrodynamic effects and maximizing resolution and peak capacity.

Field amplified sample stacking coupled with chip-based capillary electrophoresis using negative pressure sample injection technique.

A multi-T microchip for integrated field amplified sample stacking (FASS) with CE separation to increase the chip-based capillary electrophoresis (chip-based CE) sensitivity was developed. Volumetrically defined large sample plug was formed in one step within 5s by the negative pressure in headspace of the two sealed sample waste reservoirs produced using a syringe pump equipped with a 3-way valve. Stacking and separation can proceed only by switching the 3-way valve to release the vacuum in headspace of the two sample waste reservoirs. This approach considerably simplified the operations and the equipments for FASS in chip-based CE systems. Migration time precisions of 3.3% and 1.3% RSD for rhodamine123 (Rh123) and fluorescien sodium salt (Flu) in the separation of a mixture of Flu and Rh123 were obtained for nine consecutive determinations with peak height precisions of 4.8% and 3.4% RSD, respectively. Compared with the chip-based CE on the cross microchip, the sensitivity for analysis of FlTC, FITC-labeled valine (Val) and Alanine (Ala) increased 55-, 41- and 43-fold, respectively.