Polarized ITIES

Protein tertiary structure is also influenced by the environment In water a globu lar protein usually adopts a shape that places its hydrophobic groups toward the interior with Its polar groups on the surface where they are solvated by water molecules About 65% of the mass of most cells is water and the proteins present m cells are said to be m their native state—the tertiary structure m which they express their biological activ ity When the tertiary structure of a protein is disrupted by adding substances that cause the protein chain to unfold the protein becomes denatured and loses most if not all of Its activity Evidence that supports the view that the tertiary structure is dictated by the primary structure includes experiments m which proteins are denatured and allowed to stand whereupon they are observed to spontaneously readopt their native state confer matron with full recovery of biological activity... 

An interface between two immiscible electrolyte solutions (ITIES) is formed between two liqnid solvents of a low mutual miscibility (typically, <1% by weight), each containing an electrolyte. One of these solvents is usually water and the other one is a polar organic solvent of a moderate or high relative dielectric constant (permittivity). The latter requirement is a condition for at least partial dissociation of dissolved electrolyte(s) into ions, which thus can ensure the electric conductivity of the liquid phase. A list of the solvents commonly used in electrochemical measurements at ITIES is given in Table 32.1. 

A well-defined polarization of an ITIES can be accomplished by means of a four-electrode system with two couples of current-supplying (counter) and potentialmeasuring (reference) electrodes, which are connected to phases (w) and (o) in the... 

FIGURE 32.2 Scheme of a four-electrode system for polarization measurements at an ITIES comprising a potentiostat (POT), two reference electrodes connected to the cell by means of Luggin capillaries (REl, RE2), and two counter electrodes (CEl, CE2). The planar ITIES is formed at the edge of a round hole in a glass barrier between the spaces for the aqueous (water) and the organic (org) phases. 

Irradiation of an ITIES by visible or UV light can give rise to a photocurrent, which is associated with the transfer of an ion or electron in its excited state. Alternatively, the photocurrent can be due to transfer of an ionic product of the photochemical reaction occurring in the solution bulk. Polarization measurements of the photoinduced charge transfer thus extend the range of experimental approaches to... 

In this chapter, we describe some of the more widely used and successful kinetic techniques involving controlled hydrodynamics. We briefly discuss the nature of mass transport associated with each method, and assess the attributes and drawbacks. While the application of hydrodynamic methods to liquid liquid interfaces has largely involved the study of spontaneous processes, several of these methods can be used to investigate electrochemical processes at polarized ITIES we consider these applications when appropriate. We aim to provide an historical overview of the field, but since some of the older techniques have been reviewed extensively [2,3,13], we emphasize the most recent developments and applications. 

The electrolyte dropping electrode [63] method, introduced in 1976, and subsequently used in conjunction with the four-electrode potentiostat [64], is a hydrodynamic technique, offering controlled convective transport. In essence, this approach is identical to the dropping mercury electrode [65] however, the drop consists of a flowing electrolyte liquid phase which forms a polarized ITIES with an immiscible continuous (receptor) phase. In... 

The electrolyte dropping electrode has found particular application in the study of ion transfer at the polarized ITIES, with an emphasis on analysis. A range of species have been detected amperometrically by measuring the transport-limited current ... 

Eqs. (15), (17), and (21) can be used to define other observable quantities, such as relative surface excess concentrations of ions, which also comprise the contributions from the free ionic and ion-pair surface excesses, e.g., for the ideally polarized ITIES,... 

Koryta et al. [48] first stressed the relevance of adsorbed phospholipid monolayers at the ITIES for clarification of biological membrane phenomena. Girault and Schiffrin [49] first attempted to characterize quantitatively the monolayers of phosphatidylcholine and phos-phatidylethanolamine at the ideally polarized water-1,2-dichloroethane interface with electrocapillary measurements. The results obtained indicate the importance of the surface pH in the ionization of the amino group of phosphatidylethanolamine. Kakiuchi et al. [50] used the video-image method to study the conditions for obtaining electrocapillary curves of the dilauroylphosphatidylcholine monolayer formed on the ideally polarized water-nitrobenzene interface. This phospholipid was found to lower markedly the surface tension by forming a stable monolayer when the interface was polarized so that the aqueous phase had a negative potential with respect to the nitrobenzene phase [50,51] (cf. Fig. 5). 

When the ITIES is polarized with a potential difference 0, there is a separation of electrical charge across it. According to the Gouy-Chapman theory, the charges in the aqueous and organic diffuse layers are related to the potential drops and A0 in the respective layers by the equations... 

The electrical double layer has also been investigated at the interface between two immiscible electrolyte solutions and at the solid electrolyte-electrolyte solution interface. Under certain conditions, the interface between two immiscible electrolyte solutions (ITIES) has the properties of an ideally polarized interphase. The dissolved electrolyte must have the following properties ... 

Figure 2.1. Polarization of synchrotron radiation in a hypothetic non-relativistic case. In real ity the toroidal radiation pattern is degenerated to a narrow forwar... 

Iti wave mechanics yt(r, 0, wave-function is yi(r, 0, y) is to be found in u small volume dx centred at the point whose polar coordinates arc (r, 0,9 ). To make the total probability unity we must have... 

Fig. 9.2. The electrolytic cell for polarization of a stationary ITIES REi, RE2 - reference electrodes CEi, CE2 - auxilliary electrodes ...

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