Biosurfaces

The enzyme catalysed epoxidation of alpha-olefins like 1-octene with oxygen to the optically active epoxide provides an interesting example of a four-phase system (de Bont et al., 1983). The hold-up of the organic phase may be 2-4 % and the presence of biosurface active agents leads to the creation of a large liquid-liquid interfacial area the liquid droplet size becomes smaller than the gas-liquid diffusion film thickness. 

As suggested before, the role of the interphasial double layer is insignificant in many transport processes that are involved with the supply of components from the bulk of the medium towards the biosurface. The thickness of the electric double layer is so small compared with that of the diffusion layer 8 that the very local deformation of the concentration profiles does not really alter the flux. Hence, in most analyses of diffusive mass transport one does not find any electric double layer terms. For the kinetics of the interphasial processes, this is completely different. Rate constants for chemical reactions or permeation steps are usually heavily dependent on the local conditions. Like in electrochemical processes, two elements are of great importance the local electric field which affects rates of transfer of charged species (the actual potential comes into play in the case of redox reactions), and the local activities... 

If the rate constants for interconversion between M and ML are infinitesimally small (on the effective timescale of the experimental conditions), the complex does not contribute significantly to the supply of metal to the biosurface. The equilibrium equation (50) behaves as if frozen. In a biouptake process, the complex ML then does not contribute to the supply of metal towards the biosurface, and all the expressions given in Section 2 apply, with the only noteworthy point that the value of c"M to be used differs from the total metal concentration. In this case, the complexed metal is not bioavailable on the timescale considered, as metal in the complex species is absent from any process affecting the uptake. 

E. H. Hellen, R. M. Fulbright, and D. Axelrod, Total internal reflection fluorescence Theory and applications at biosurfaces, in Spectroscopic Membrane Probes (L. M. Loew, ed.), Vol. II, pp. 47-49, CRC Press, Boca Raton, Florida (1988). 

The remote release of encapsulated materials is desired for bioapplications in order to minimize drug toxicity, to control the properties of biosurfaces and interfaces, and to study intracellular processes [132], Remote release can be more convenient for a patient because external stimuli like a magnetic field, light, and ultrasound are... 

Ellipsometry is useful in examining the behavior of enzymes on electrodes. Another excellent tool is the atomic force microsope (Section 7.5.18). Eppel (1993) used AFM to examine the absorption of a glycoprotein on some biosurfaces (AFM does not need conduction electrons to function), and was able to measure its elliptical cross section in the absorbed state. It was possible to map changes in the charge density of the protein (which plays a role in thrombus formation in arterial blockage) upon absorption by the change in the height of various parts of the molecule. This is an excellent example of the detail in which absorbed species can be examined. 

Something has been learned so far about electron transfer from a metal to simple ions in solution (normal electrochemistry, Chapter 7), from metals to biomolecules in solution, and from promoter-modified metals to biomolecules in solution. The next step is to examine electron transfer from a biosurface to a simple redox species dissolved in an ambient solution. 

The gain in absolute surface that is generated by the various etching techniques is shown in the side views of the silica structures in Figure 6. The three pictures in Figure 6 (a-c) show an absolute increase in surface area, accessible as an active biosurface for protein analysis. 

Electro-Of ical Reflection Methods for Studying Bioactive Substances at Electrode-Solution Interfaces—An Approach to Biosurface Behavior... 

Bio- and electrochemists have come to give increasing attention to the interface between a charged surface and aqueous electrolyte solution in recent years. Many bioactive substances are known to be localized at particular points on biosurfaces where they perform various functions in vivo. The complex formation of an enzyme and its substrate, the specific binding of an antigen and its antibody, and the attachment of a neurotransmitter at a site on a biomembrane are typical cases of specific interaction on biosurfaces. 

Such substances may initially be attracted to biosurfaces mainly through electrostatic interactions and then sometimes become closely linked to specific sites in a particular orientation or conformation state. Such attachment may be essential to the expression of their biological... 

Electrode surfaces can thus be expected to resemble biosurfaces with respect to charged surfaces in contact with electrolyte solutions. A study of the electrochemical behavior of bioactive substances should provide useful information regarding biosurface behavior. 

In this chapter the techniques and experimental procedures of the specular reflection method are discussed in detail. Its application to the study of the adsorption of various biologically important substances to electrode surfaces is presented, and an attempt is made to elucidate the biosurface behavior of these substances. 

These substances are known to localize at the particular sites of biosurfaces in their respective states in vivo and exert their functions through their own processes. Taking possible analogies between adsorp-... 

This chapter discussed the application of the electro-optical reflection method in the in situ observation of the adsorption and desorption of bioactive substances at an electrode surface acting as a simple model of charged sites at a biosurface. This method should find extensive application in various bioelectrochemical fields as a potent means of surface analysis. Electrode surfaces, though much simpler than biosurfaces, still provide data reflecting actual occurrences at biosurfaces in some respects. Electro-optical studies on the behavior of bioactive substances at electrode surfaces should provide some indication of how such substances behave at biosurfaces. 

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