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Capillary electrophoresis of biomolecules
Electrocatalysis is key to the development of several important energy and biosensing applications. In this regard, the crystalline phase-dependent electrocatalytic activity of materials has been extensively studied for reactions such as hydrogen evolution, oxygen reduction, etc. But such comprehensive studies for evaluating the phase-dependence of electrochemical biosensing have not been undertaken. Herein, three crystalline phases (α-, β-, and γ-) of iron oxyhydroxide (FeOOH) have been synthesized and characterized by spectroscopic and microscopy techniques. Electrochemical studies revealed their high sensitivity and selectivity towards dopamine (DA) detection. Amongst the three electrocatalysts, β-FeOOH shows the highest sensitivity (337.15 μA mM-1 cm-2) and the lowest detection limit (0.56 μM). The enhanced electrocatalytic activity of β-FeOOH, as compared to that of α- and γ-FeOOH, was attributed to its higher active site percentage and facile electrode kinetics. Furthermore, theoretical studies probed into the DA-FeOOH interactions by evaluating the charge transfer characteristics and hydrogen adsorption energies of the three phases to support the experimental findings.
There is a lack of information about association between nonionic polymers and weak electrolyte type anionic surfactants, therefore the complexation between polyvinylpyrrolidone (PVP) and sodium dodecanoate (SD) is investigated by capillary electrophoresis for the first time, in assistance with conductometry, tensiometry and calcium stability. The experimental results show that values of critical aggregation concentration (cac) and polymer saturation point (psp) of the system determined by several methods are consistent with each other. It is firstly found that the PVP–SD complex is actually PVP–SD pseudo-polyanions with different charge densities corresponding to different pH levels. It is also found that H-bonding and counterion bridging between PVP and bound SD micelles play important roles in the self-assembling of the PVP–SD pseudo-polyanions, and the pH-dependent capillary electrophoresis behavior of the pseudo-polyanions is ascribed to sodium bridging being replaced by H-bonding at lower pH.
Accordance with the previously supposed polyelectrolyte-like behaviour of neutral polymer-anionic surfactant complexes, direct evidence for the formation of the pseudo-polyanions in polyvinylpyrrolidone (PVP)-sodium dodecylsulfate (SDS) solution is put forward in this paper by capillary electrophoresis (CE) experiments in assistance with capillary viscosimetry and conductometry. The contradictory phenomena of the absolute value of relative electrophoretic mobility (_re_) increasing while the ionization degree (_α_) decreasing with the increasing specific clusterization [_Г_] in aqueous PVP-SDS solution are explained by the finding that the PVP-SDS complex is eventually a family of PVP-SDS pseudo-polyanions with different charge densities. And it is found countercations playing an important role in the formation of the PVP-SDS pseudo-polyanions in virtue of bridge effect.
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