Donnan Electric Potential Dependence of Intraparticle Diffusion of Malachite Green in Single Cation Exchange Resin Particles: A Laser Trapping-Microspectroscopy Study

Abstract

A laser trapping-microspectroscopy technique combined with excitation energy transfer from a fluorescent cationic dye (Rhodamine B, RB + ) to a non-fluorescent cationic dye (Malachite Green, MG + ) was employed to study pH effects on the diffusion coefficients of MG + (D(MG + )) in single cation-exchange resin microparticles with the diameters of 16 μm. When RB + -pre-adsorbed resin particles were soaked in an aqueous MG + solution, the RB + fluorescence was quenched gradually with the soaking time. The time course of the quenching efficiency of RB + by MG + was then used to evaluate the D(MG + ) value in the particle. The D(MG + ) value increased from 1.1 × 10 -11 to 4.3 × 10 -11 cm 2 ·s -1 on going the solution pH value from 9 to 4. The results were explained reasonably by a Donnan electric potential model.

Unveiling the Modulating Role of Extracellular pH in Permeation and Accumulation of Small Molecules in Subcellular Compartments of Gram-negative Escherichia coli using Nonlinear Spectroscopy

“…Our next target was to resolve the other anomaly between pH 7 and 9, where in spite of k OM remaining nearly constant, k IM increased exponentially. Though this effect can be misinterpreted easily as the effect of MG + to MGOH conversion having p K a value 6.9, we already showed that, in the range pH 7–9, only less than 10% conversion takes place during the SHG experiment (Table S1). Therefore, any changes in membrane permeability due to formation of neutral MGOH will hardly contribute to the increase of k IM of MG + .…”

“…This factor is very important for our investigation, since different charge states may have different extent of adsorptions on cell membrane surfaces and therefore may yield different amplitude of SHG signals. Our probe molecule MG exists as MGH 2+ , MG + , and MGOH between pH 3 and 9 . Concentrations of these charge states ideally should be calculable from the p K a values of MG (p K a 1 ≈ 1 and p K a 2 = 6.9, Figure S5).…”

Determination of Malachite Green in Aquaculture Water by Adsorptive Stripping Voltammetry

“…At pH values greater than 6.9 (Cuong et al 2012) malachite green is chemically reduced to its carbinol form which can undergo a 2e -oxidation to give malachite green and a hydroxyl ion. The carbinol form is more non-polar in nature and hence would explain the reactant adsorptive behaviour seen in our investigation.…”