Microheterogeneous Deposits

Let us consider the case of a set of crystals of a microporous material deposited on the surface of a metallic electrode. 

In the above equation, D, Dy, D, represent the charge diffusion coefficients along the X, y, and z directions. This formulation assumes that both electrons and ions are exchanged simultaneously and that no charge separation effects occur. The above diffusion coefficients will depend, in general, on the orientation of the particles of microporous material. 

FIGURE 2.6 Coordinate system for the idealized representation of a particle of a microporous material containing redox-active centers deposited on an electrode in contact with a suitable electrolyte. 

FIGURE 2.7 SQWV for microparticulate deposit of PY ion attached to zeolite Y deposited on paraffin-impregnated graphite electrode in contact with 0.10 M Et NClO /MeCN. Potential step increment, 4 mV square-wave amplitude, 25 mV frequency. 5 Hz. 

In this equation, A represents the number of crystals, p is the length of the three-phase junction (i.e., the perimeter of the electrode/crystal interface), and Ax, Az denote the size of the discrete boxes in which the crystal is divided for numerical simulation procedures. 

---

It is well known that experimental CVs for species in solution phase frequently diverge from theoretical ones for -electron reversible couples. The divergence can be caused by a variety of factors deviations from reversibility, occurrence of coupled chemical reactions and/or surface effects, and resistive and capacitive effects (Nicholson and Shain, 1964 Nicholson, 1965a). These last effects will be briefly treated here because of their potential significance when microheterogenous deposits or more or less homogeneous coatings of microporous materials cover the electrode surface. 

FIGURE 1.8 CV for a PIGE modified with a microheterogeneous deposit of zeolite Y. Potential scan rate, 50 mV/sec. 

MODELING ELECTROCATALYSIS AT MICROHETEROGENEOUS DEPOSITS OF POROUS MATERIALS THE STEADY-STATE APPROACH... 

ApoSAA, normally a trace component of plasma, is an acute-phase plasma protein, that is, one that is elevated in a variety of disease states (R18). Its identification is interesting. A small protein of 76 residues, now called protein AA, was identified during the study of the proteins present in extracellular amyloid deposits in the type of amyloidosis particularly associated with inflammation (B24, H36, Lll, S38), Antibodies to protein AA reacted with two AA-related proteins in plasma, one of approximate Mr 180,000 (SAA) and the other found in HDL of Mr 14,000-15,000 or 12,000 (apoSAA) (A19, B25, B26, L12, L15). The N-terminal 76-amino-acid portion of apoSAA is identical to that of amyloid protein AA (E8). Human apoSAA has now been sequenced and has been shown to consist of 104 amino acid residues (B27). Further studies in man have demonstrated microheterogeneity in apoSAA (B18, B19, M30) and Benditt et al. describe specific amino acid substitutions (B27, P6). Shore et al. have described a second similar threonine-poor apolipoprotein, apparently a dimer of Mr 40,000... 

---