Potential modulated fluorescence

Potential-modulated fluorescence spectroscopy at liquid/liquid interfaces between immiscible liquids has been reported and a cell design has been provided [78], The dependence of the adsorption of the free, bare or the water-soluble porphyrins at the polarized water/l,2-dichloroethane interface has been studied [79], Observed spectral differences suggest a solvation structure at the interface that is different from that inside the bulk of the respective solution phases. For further studies with related porphyrins at the same interface, see [79]. Details of the transfer mechanism of the rose bengal dianion across the water/l,2-dichloroethane interface have been elucidated [80],... 

Periodic perturbations of the potential across the Hquid/liquid boundary induce a modulation of the concentration of species located in the interfacial region. By collecting the spectroscopic signals at the same frequency as that of the potential perturbation, employing phase-sensitive detection, the interfacial sensitivity of the measurements is tremendously enhanced, as the contribution from species in the bulk of the electrolyte solutions can be effectively neglected. Based on this principle, Fermfn and co-workers introduced potential-modulated reflectance (PMR) and potential-modulated fluorescence (PMF) to study a variety of processes including ion transfer [22], electron transfer [20], and the specific adsorption of ionic species [15]. 

The potential dependence of the ZnTPPC coverage illustrates the typical trend observed for other anionic metalloporphyrin and chlorins as those shown in Figure 11.4. For instance, studies based on potential modulated fluorescence and capacitance curves have shown that ZnTPPS speciflcally adsorbs at the... 

Nagatani, H., D.J. Fermin, and H.H. Girault (2001). A kinetic model for adsorption and transfer of ionic species at polarized liquid/liquid interfaces as studied by potential modulated fluorescence spectroscopy. J. Phys. Chem. B 105, 9463-9473. 

In this chapter, electrochemical properties of ET proteins at electrode interfaces studied by spectroelectrochem-ical techniques are described. In situ spectroelectrochemical techniques at well-defined electrode surfaces are sufficiently selective and sensitive to distinguish not only steady state structures and oxidation states of adsorbed species but also dynamics of reactants, products, and intermediates at electrode surfaces on a monolayer level. The spectroelectrochemical techniques used in studies of ET proteins include IR reflection-absorption, potential-modulated UV-vis reflectance (electroreflectance), surface-enhanced Raman scattering (SERS) and surface plasmon resonance, total internal reflection fluorescence, (TIRE) and absorbance linear dichroism spectroscopies. 

From experiments on planar bilayer membranes (BLM), it was known that lipid bilayers were not able to withstand an increase in the applied voltage above a threshold value. A conductive state followed by a rupture was observed for values of the order of 200 mV. Electropulsation induces a transmembrane potential modulation, bringing a similar membrane instability. Indeed experiments on pure lipid vesicles showed that upon the field pulse the lipid bilayer could become leaky. This was observed on line by the associated increase in conductance of a salt-filled vesicle suspension [26]. But larger molecules could leak out and be directly detected outside the vesicles as observed with radiolabelled sucrose [27] or fluorescent dyes [28]. A very fast detection of the induction of membrane leakage is obtained by electrical conductance and light scattering... 

Nagatani, H., R. A. Iglesias, D. J. Fermin, P. F. Brevet, and H. H. Girault, Adsorption behavior of charged zinc porphyrins at the water/l,2-dichloroethane interface studied by potential modulated fluorescence spectroscopy, J Phys Chem B, Vol. 104, (2000) p. 6869. 

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